80 SEC TION II Biochemistry BIOCHEMISTRY—Metabolism Urea cycle Amino acid catabolism generates common Ordinarily, Careless Crappers Are Also metabolites (eg, pyruvate, acetyl-CoA), which Frivolous About Urination. serve as metabolic fuels. Excess nitrogen is converted to urea and excreted by the kidneys. CO2 + H2O HCO3– + NH3 N -acetylglutamate Carbamoyl 2 ATP Citrulline Aspartate (allosteric activator) phosphate 2 ADP + Pi lase Arg ATP synthetase I Urea Carbamoyl ininsyonstuhcectiansaetetranscaOrrbniathmiyneAMP + PPi phosphate Arginase rgini lnyoassueccinate NH3 NH2 Mitochondria Argininosuccinate CO2 CO Ornithine Aspartate NH2 Cytoplasm (liver) To kidney Urea A H2O Arginine Fumarate Transport of ammonia by alanine START Amino acids Muscle Alanine Alanine Liver (NH3) α-Ketoglutarate (NH3) (NH3) α-Ketoglutarate Glucose Glucose Cahill cycle Glutamate (NH3) Urea (NH3) FINISH α-Ketoacids Glutamate (NH3) Pyruvate Cori cycle Pyruvate Lactate Lactate Hyperammonemia Can be acquired (eg, liver disease) or hereditary Treatment: limit protein in diet. (eg, urea cycle enzyme deficiencies). Asterixis May be given to ammonia levels: Presents with flapping tremor (asterixis), slurring Lactulose to acidify GI tract and trap NH4+ of speech, somnolence, vomiting, cerebral for excretion. edema, blurring of vision. Antibiotics (eg, rifaximin) to NH3 changes relative amounts of α-ketoglutarate, glutamate, GABA, and ammoniagenic bacteria. glutamine. CNS toxicity mainly involves: GABAergic tone ( GABA) Benzoate, phenylacetate, or phenylbutyrate TCA cycle inhibition ( α-ketoglutarate) Cerebral edema (glutamine induced osmotic react with glycine or glutamine, forming shifts) products that are excreted renally. NH3 NH3 Glutamine ␣-ketoglutarate Glutamate B6 GABA
Biochemistry BIOCHEMISTRY—Metabolism SEC TION II 81 Ornithine Most common urea cycle disorder. X-linked recessive (vs other urea cycle enzyme deficiencies, transcarbamylase which are autosomal recessive). Interferes with the body’s ability to eliminate ammonia. Often deficien y evident in the first few days of life, but may present later. Excess carbamoyl phosphate is converted to orotic acid (part of the pyrimidine synthesis pathway). Findings: orotic acid in blood and urine, BUN, symptoms of hyperammonemia. No megaloblastic anemia (vs orotic aciduria). Amino acid derivatives Thyroxine Melanin Phenylalanine BH4 BH4 Dopa B6 Vitamin C SAM Tyrosine Dopamine NE Epi B2, B6 Niacin NAD+/NADP+ Melatonin Tryptophan BH4, B6 Heme Histidine Serotonin B6 Histamine Glycine B6 Porphyrin Glutamate B6 GABA B6 Glutathione Arginine Creatine Urea BH4 Nitric oxide BH4 = tetrahydrobiopterin Catecholamine synthesis/tyrosine catabolism Phenylalanine BH4 Phenylalanine PKU hydroxylase Homogentisic acid Tyrosine Alkaptonuria Homogentisate BH4 Tyrosine Albinism oxidase hydroxylase Tyrosinase Maleylacetoacetic acid DOPA Melanin (Dihydroxyphenylalanine) Fumarate B6 DOPA – Carbidopa decarboxylase Dopamine TCA cycle Vitamin C Dopamine β-hydroxylase Catechol-O-methyltransferase Norepinephrine Phenylethanolamine-N- Cortisol Normetanephrine SAM methyltransferase Monoamine Monoamine Catechol-O- oxidase oxidase methyltransferase Vanillylmandelic acid Epinephrine Metanephrine Homovanillic acid uploaded by medbooksvn
82 SEC TION II Biochemistry BIOCHEMISTRY—Metabolism Phenylketonuria Caused by phenylalanine hydroxylase (PAH). Autosomal recessive. Tyrosine becomes essential. phenylalanine Screening occurs 2–3 days after birth (normal at phenyl ketones in urine. birth because of maternal enzyme during fetal Tetrahydrobiopterin (BH4) deficiency—BH4 life). essential cofactor for PAH. BH4 deficiency Findings: intellectual disability, microcephaly, phenylalanine. Varying degrees of clinical seizures, hypopigmented skin, eczema, musty severity. Untreated patients typically die in body odor. infancy. Treatment: phenylalanine and tyrosine in diet (eg, soy products, chicken, fish, milk), Phenylalanine embryopathy— phenylalanine tetrahydrobiopterin supplementation. levels in pregnant patients with untreated Phenyl ketones—phenylacetate, phenyllactate, PKU can cause fetal growth restriction, and phenylpyruvate. microcephaly, intellectual disability, congenital Disorder of aromatic amino acid metabolism heart defects. Can be prevented with dietary musty body odor. measures. Patients with PKU must avoid the artificial sweetener aspartame, which contains phenylalanine. Dietary protein Phenyl ketones PKU Tyrosine Thyroxine Norepinephrine/epinephrine Aspartame Phenylalanine Dopamine Phenylalanine Melanin Endogenous hydroxylase protein Tetrahydrobiopterin BH₄ Dihydropteridine BH₂ deficiency reductase NAD+ NADH + H+ Maple syrup urine Blocked degradation of branched amino acids Autosomal recessive. disease (Isoleucine, leucine, valine) due to branched- Presentation: vomiting, poor feeding, urine Alkaptonuria chain α-ketoacid dehydrogenase (B1). Causes smells like maple syrup/burnt sugar. Causes A α-ketoacids in the blood, especially those of progressive neurological decline. leucine. I love Vermont maple syrup from maple trees (with B1ranches). Treatment: restriction of isoleucine, leucine, valine in diet, and thiamine supplementation. Congenital deficiency of homogentisate oxidase in the degradative pathway of tyrosine to fumarate pigment-forming homogentisic acid builds up in tissue. Autosomal recessive. Usually benign. Findings: bluish-black connective tissue, ear cartilage, and sclerae (ochronosis A ); urine turns black on prolonged exposure to air. May have debilitating arthralgias (homogentisic acid toxic to cartilage).
Biochemistry BIOCHEMISTRY—Metabolism SEC TION II 83 Homocystinuria Causes (all autosomal recessive): All forms result in excess homocysteine. Cystathionine synthase deficiency HOMOCYstinuria: Homocysteine in (treatment: methionine, cysteine, B6, urine, Osteoporosis, Marfanoid habitus, B12, and folate in diet) Ocular changes (downward and inward affinity of cystathionine synthase for lens subluxation), Cardiovascular effects pyridoxal phosphate (treatment: B6 and (thrombosis and atherosclerosis stroke cysteine in diet) and MI), kYphosis, intellectual disability, Methionine synthase (homocysteine hypopigmented skin. In homocystinuria, lens methyltransferase) deficiency (treatment: subluxes “down and in” (vs Marfan, “up and methionine in diet) fans out”). Methylenetetrahydrofolate reductase (MTHFR) deficiency (treatment: folate in diet) Methionine Cystathionine Methionine synthase Homocysteine synthase Cystathionine Cysteine Methyl B12 B6 B6 Serine Methyl folate + B12 Cystinuria Hereditary defect of renal PCT and intestinal Autosomal recessive. Common (1:7000). A amino acid transporter that prevents Cystinuria detected with urinary sodium- reabsorption of Cystine, Ornithine, Lysine, and Arginine (COLA). cyanide nitroprusside test and proton nuclear magnetic resonance spectroscopy of urine. Cystine is made of 2 cysteines connected by a disulfide bond. Excess cystine in the urine can lead to recurrent precipitation of hexagonal cystine stones A . Treatment: urinary alkalinization (eg, potassium citrate, acetazolamide) and chelating agents (eg, penicillamine) solubility of cystine stones; good hydration; diet low in methionine. Organic acidemias Most commonly present in infancy with poor feeding, vomiting, hypotonia, high anion gap metabolic acidosis, hepatomegaly, seizures. Organic acid accumulation: Propionic acidemia Inhibits gluconeogenesis fasting blood glucose levels, ketoacidosis high anion gap Methylmalonic metabolic acidosis acidemia Inhibits urea cycle hyperammonemia Deficiency of propionyl-CoA carboxylase Treatment: low-protein diet limited in propionyl-CoA, methylmalonic acid. substances that metabolize into propionyl- CoA: Valine, Odd-chain fatty acids, Deficiency of methylmalonyl-CoA mutase or Methionine, Isoleucine, Threonine vitamin B12. (VOMIT). Protein metabolism TCA cycle Valine Propionyl-CoA Methylmalonyl-CoA Odd-chain fatty acids Methionine Propionate Propionyl-CoA carboxylase Methylmalonyl-CoA mutase Succinyl-CoA Intermediates of citric Isoleucine acid cycle Threonine Biotin B12 uploaded by medbooksvn
84 SEC TION II Biochemistry BIOCHEMISTRY—Metabolism Glycogen regulation by insulin and glucagon/epinephrine Epinephrine Epinephrine Insulin (liver and muscle) (liver) (liver and muscle) Glucagon Receptor Receptor Protein kinase A Tyrosine (liver) − kinase Adceyncylalastee Endoplasmic dimer Glucagon reticulum Glycogen receptor receptor ATP Calcium synthase cAMP Calcium-calmodulin Protein kinase A in muscle during contraction Glycogen Glycogen phosphorylase kinase Glycogen − phosphorylase Glucose Protein phosphatase Glycogen Branches have α-(1,6) bonds; linear linkages have α-(1,4) bonds. Skeletal muscle Glycogen undergoes glycogenolysis glucose-1-phosphate glucose-6-phosphate, which is Hepatocytes rapidly metabolized during exercise. Glycogen is stored and undergoes glycogenolysis to maintain blood sugar at appropriate levels. Glycogen phosphorylase liberates glucose-1-phosphate residues off branched glycogen until 4 glucose units remain on a branch. Then 4-α-d-glucanotransferase (debranching enzyme ) moves 3 of the 4 glucose units from the branch to the linear linkage. Then α-1,6-glucosidase (debranching enzyme ) cleaves off the last residue, liberating a free glucose. Limit dextrin—2–4 residues remaining on a branch after glycogen phosphorylase has shortened it. Gluconeogenesis Glycolysis Lysosome only II Glycogen storage Glucose disease type I I Von Gierke disease Glucose-6-P II Pompe disease III Cori disease IV Anderson disease V McArdle disease Glycogen enzymes III Glucose-6-phosphatase Glucose-1-P UDP-glucose pyrophosphorylase Glycogen synthase UDP-glucose III Branching enzyme Glycogen phosphorylase IV Debranching enzyme Glycogen V Limit dextrin (4-α-D-glucanotransferase) Glycogenesis / glycogenolysis Debranching enzyme (α-1,6-glucosidase) α-1,4-glucosidase Note: A small amount of glycogen is degraded in lysosomes by α-1,4-glucosidase (acid maltase).
Biochemistry BIOCHEMISTRY—Metabolism SEC TION II 85 Glycogen storage At least 15 types have been identified, all Vice president can’t accept money. diseases resulting in abnormal glycogen metabolism Types I-V are autosomal recessive. and an accumulation of glycogen within cells. Andersen: Branching. DISEASE Periodic acid–Schiff stain identifies glycogen Cori: Debranching. (ABCD) and is useful in identifying these diseases. Von Gierke disease (type I) FINDINGS DEFICIENT ENZYME COMMENTS Pompe disease Severe fasting hypoglycemia, Glucose-6-phosphatase. Treatment: frequent oral (type II) Glycogen in liver and glucose/cornstarch; avoidance Cori disease kidneys, blood lactate, Lysosomal acid α-1,4- of fructose and galactose. (type III) triglycerides, uric acid glucosidase (acid maltase). (Gout), and hepatomegaly, Impaired gluconeogenesis and Andersen disease renomegaly. Liver does not Debranching enzymes glycogenolysis. (type IV) regulate blood glucose. (α-1,6-glucosidase and 4-α-d-glucanotransferase). Pompe trashes the pump (1st McArdle disease Cardiomyopathy, hypotonia, and 4th letter; heart, liver, (type V) exercise intolerance, enlarged Branching enzyme. and muscle). tongue, and systemic findings Neuromuscular form can lead to early death. Gluconeogenesis is intact. present at any age. Similar to von Gierke disease, Hypoglycemia occurs late in but milder symptoms and Skeletal muscle glycogen the disease. normal blood lactate levels. phosphorylase Can lead to cardiomyopathy. (myophosphorylase). Blood glucose levels typically Limit dextrin–like structures unaffected. accumulate in cytosol. Characterized by a flat venous lactate curve with normal McArdle = muscle. Most commonly presents rise in ammonia levels during with hepatosplenomegaly exercise. and failure to thrive in early infancy. Other findings include infantile cirrhosis, muscular weakness, hypotonia, cardiomyopathy early childhood death. glycogen in muscle, but muscle cannot break it down painful muscle cramps, myoglobinuria (red urine) with strenuous exercise, and arrhythmia from electrolyte abnormalities. Second-wind phenomenon noted during exercise due to muscular blood flow. uploaded by medbooksvn
86 SEC TION II Biochemistry BIOCHEMISTRY—Metabolism Lysosomal storage Lysosomal enzyme deficiency accumulation of abnormal metabolic products. incidence of diseases Tay-Sachs, Niemann-Pick, and some forms of Gaucher disease in Ashkenazi Jews. DISEASE FINDINGS DEFICIENT ENZYME ACCUMULATED SUBSTRATE INHERITANCE Sphingolipidoses Progressive neurodegeneration, Hexosaminidase A GM2 ganglioside. AR Tay-Sachs disease developmental delay, hyperreflexia, (“TAy-Sax”). A hyperacusis, “cherry-red” spot on macula A (lipid accumulation in α-galactosidase A. Ceramide XR Fabry disease ganglion cell layer), lysosomes with trihexoside B onion skin, no hepatosplenomegaly (globotriaosylce (vs Niemann-Pick). ramide). Metachromatic leukodystrophy Early: triad of episodic peripheral Arylsulfatase A. Cerebroside sulfate. AR Krabbe disease neuropathy, angiokeratomas B , hypohidrosis. G alactocerebrosi- Galactocerebroside, AR Gaucher disease dase (galactosylce- psychosine. AR Late: progressive renal failure, ramidase). Niemann-Pick disease cardiovascular disease. C Glucocerebrosidase Glucocerebroside. Central and peripheral demyelination (β-glucosidase); treat with ataxia, dementia. with recombinant glucocerebrosidase. Peripheral neuropathy, destruction of oligodendrocytes, developmental Sphingomyelinase. Sphingomyelin. AR delay, CN II atrophy, globoid cells. Most common. Hepatosplenomegaly, pancytopenia, osteoporosis, avascular necrosis of femur, bone crises, Gaucher cells (lipid-laden macrophages resembling crumpled tissue paper). Progressive neurodegeneration, hepatosplenomegaly, foam cells (lipid-laden macrophages) C , “cherry-red” spot on macula A . Mucopolysaccharidoses Hurler syndrome Developmental delay, hirsutism, α-l-iduronidase. Heparan sulfate, AR dermatan sulfate. skeletal anomalies, airway obstruction, Heparan sulfate, XR clouded cornea, hepatosplenomegaly. dermatan sulfate. Hunter syndrome Mild Hurler + aggressive behavior, no Iduronate-2 (two)- corneal clouding. sulfatase. GM2 Ceramide trihexoside Hunters see clearly (no corneal clouding) and GM3 aggressively aim for the X (X-linked recessive). Glucocerebroside Sulfatides Galactocerebroside Ceramide Sphingomyelin
Biochemistry BIOCHEMISTRY—Metabolism SEC TION II 87 Fatty acid metabolism Fatty acid synthesis requires transport of citrate from mitochondria to cytosol. Predominantly Synthesis Degradation occurs in liver, lactating mammary glands, and Fatty acid synthesis adipose tissue. (palmitate, a 16C FA) Fatty acid + CoA − Long-chain fatty acid (LCFA) degradation Malonyl-CoA requires carnitine-dependent transport into the Fatty acyl-CoA mitochondrial matrix. Insulin Acetyl-CoA synthetase Glucagon − carboxylase “Sytrate” = synthesis. CO2 (biotin) Fatty acyl-CoA Carnitine = carnage of fatty acids. Cytoplasm Carnitine Acetyl-CoA palmitoyl Systemic 1° carnitine deficiency—no cellular transferase I uptake of carnitine no transport of LCFAs ATP citrate into mitochondria toxic accumulation lyase of LCFAs in the cytosol. Causes weakness, hypotonia, hypoketotic hypoglycemia, dilated Mitochondrial Citrate Carnitine cardiomyopathy. membranes shuttle shuttle Medium-chain acyl-CoA dehydrogenase Mitochondrial deficiency— ability to break down fatty matrix acids into acetyl-CoA accumulation of fatty acyl carnitines in the blood with Citrate Fatty acyl-CoA hypoketotic hypoglycemia. Causes vomiting, β-oxidation lethargy, seizures, coma, liver dysfunction, (acyl-CoA hyperammonemia. Can lead to sudden death in infants or children. Treat by avoiding dehydrogenases) fasting. Acetyl-CoA Ketone TCA bodies cycle uploaded by medbooksvn
88 SEC TION II Biochemistry BIOCHEMISTRY—Metabolism Ketone bodies In the liver, fatty acids and amino acids Ketone bodies: acetone, (ketone) acetoacetate are metabolized to acetoacetate and (ketoacid), β-hydroxybutyrate (ketoacid). KETONE LEVELS β-hydroxybutyrate (to be used in muscle GLUCOSE LEVELS and brain). Breath smells like acetone (fruity odor). DEFICIENCY Urine test for ketones can detect acetoacetate, In prolonged starvation and diabetic ketoacidosis, oxaloacetate is depleted for but not β-hydroxybutyrate. gluconeogenesis. With chronic alcohol RBCs cannot utilize ketone bodies; they strictly overuse, high NADH state leads to accumulation of oxaloacetate (downregulated use glucose. Liver cells lack β ketoacyl-CoA TCA cycle), shunting it to malate. transferase cannot use ketone bodies as fuel. HMG-CoA lyase for ketone body production. Hyperammonemia Hypoketosis HMG-CoA reductase for cholesterol synthesis. Normal Ketosis Normal OTC (urea cycle) MCAD deficiency Methylmalonic acidemia, propionic acidemia Hepatocyte Blood Extrahepatic tissues (liver) Expired by lungs (eg, skeletal muscle) 2 Acetyl-CoA Fatty acids, amino acids Acetoacetyl-CoA Acetyl-CoA Acetone TCA cycle HMG-CoA Acetoacetate Acetoacetate Acetoacetate β-hydroxybutyrate β-hydroxybutyrate β-hydroxybutyrate Lipid metabolism Ketogenesis ATP Fasted vs fed state Adipocyte (fasted) Blood Adipocyte (fed) HSL Glucose TG Insulin TG Protein Epinephrine Glucose kinase A Glucagon DHAP cAMP FFA Glycerol HSL-P ATP FFA TG Glycerol 3-P Glycerol FFA LPL Apo CII
Biochemistry BIOCHEMISTRY—Metabolism SEC TION II 89 Metabolic fuel use 1g carb/protein = 4 kcal 1g alcohol = 7 kcal 100% 1g fatty acid = 9 kcal (# letters = # kcal) in % Maximal energy by source Stored ATP Stored energy (kJ)Creatine phosphate % Maximal energy by sourceAnaerobic metabolism Aerobic metabolism Overall performance 456 78 2 sec 10 sec 1 min 2 hr f starvation Duration of exercise Fasting and starvation Priorities are to supply sufficient glucose to the brain and RBCs and to preserve protein. Fed state (after a Glycolysis and aerobic respiration. Insulin stimulates storage of lipids, proteins, and meal) glycogen. Fasting (between Hepatic glycogenolysis (major); hepatic Glucagon and epinephrine stimulate use of fuel meals) gluconeogenesis, adipose release of FFA reserves. (minor). Starvation days 1–3 Blood glucose levels maintained by: Glycogen reserves depleted after day 1. Hepatic glycogenolysis RBCs lack mitochondria and therefore cannot Adipose release of FFA Muscle and liver, which shift fuel use from use ketone bodies. glucose to FFA Hepatic gluconeogenesis from peripheral 100% tissue lactate and alanine, and from 12 adipose tissue glycerol and propionyl- CoA (from odd-chain FFA—the only 10 Protein triacylglycerol component that contributes to gluconeogenesis) 8 Fat 6 4 Starvation after Adipose stores (ketone bodies become the main 2 day 3 source of energy for the brain). After these are Carbohydrate depleted, vital protein degradation accelerates, leading to organ failure and death. 0 012345678 Amount of excess stores determines survival Weeks of starvation time. uploaded by medbooksvn
90 SEC TION II Biochemistry BIOCHEMISTRY—Metabolism Lipid transport Thoracic duct Chylomicron enters lymphatics Subclavian vein Dietary fat HDL transfers apo CII and apoE and Chylomicron apo CII activates LPL cholesterol (impaired in type I familial dyslipidemia) Micelles Liver releases VLDL (overproduction in type IV familial dyslipidemia) Adipocyte VLDL apo CII activates LPL 6 IDL delivers TGs and cholesterol to the liver via apoE 7 Endocytosis of LDL (impaired in type II familial dyslipidemia) Lipids Chylomicron TG TG Intestinal cell TG FFA Lipoprotein lipase Systemic circulation Small intestine lumen Peripheral cell Apo TG Chol E B48 TG Adipocyte Chylomicron Hepatocyte TG Cholesterol TG TG Chylomicron Apo CII TG + TG FFA ApoE TGs HDL Chylomicron remnant Bile VLDL TG canaliculus LDL receptor Chol E Chol E TG Apo 7 VLDL B100 ApoE receptor TG LDL Chol E Chol E TG TG IDL Chol E 6 HDL Hepatic lipase
Biochemistry BIOCHEMISTRY—Metabolism SEC TION II 91 Key enzymes in lipid transport Cholesteryl ester Mediates transfer of cholesteryl esters to other lipoprotein particles. transfer protein Hepatic lipase Degrades TGs remaining in IDL and chylomicron remnants. Hormone-sensitive Degrades TGs stored in adipocytes. Promotes gluconeogenesis by releasing glycerol. lipase Lecithin-cholesterol Catalyzes esterification of 2⁄3 of plasma cholesterol (ie, required for HDL maturation). acyltransferase Lipoprotein lipase Degrades TGs in circulating chylomicrons and VLDL. Pancreatic lipase Degrades dietary TGs in small intestine. PCSK9 Degrades LDL receptor serum LDL. Inhibition LDL receptor recycling serum LDL. Liver Apo CII Transfer of cholesteryl LCAT Chol E CETP esters to Mature HDL VLDL, IDL, ApoE Nascent HDL LDL Small intestine Major apolipoproteins APOLIPOPROTEIN FUNCTION CHYLOMICRON CHYLOMICRON VLDL IDL LDL HDL ✓ REMNANT ✓✓ ✓ E Mediates remnant uptake ✓ AI (everything except LDL) ✓ ✓ ✓ ✓ CII Found only on alpha- ✓✓ B48 lipoproteins (HDL), activates ✓ LCAT B100 ✓ ✓✓ Lipoprotein lipase cofactor that catalyzes cleavage Mediates chylomicron secretion into lymphatics Only on particles originating from the intestines Binds LDL receptor Only on particles originating from the liver (I hope I live to Be 100) uploaded by medbooksvn
92 SEC TION II Biochemistry BIOCHEMISTRY—Metabolism Lipoprotein functions Lipoproteins are composed of varying proportions of proteins, cholesterol, TGs, and phospholipids. LDL and HDL carry the most cholesterol. Chylomicron VLDL Cholesterol is needed to maintain cell membrane integrity and synthesize bile acids, steroids, and IDL vitamin D. LDL Delivers dietary TGs to peripheral tissues. Delivers cholesterol to liver in the form of chylomicron HDL remnants, which are mostly depleted of their TGs. Secreted by intestinal epithelial cells. Delivers hepatic TGs to peripheral tissue. Secreted by liver. Delivers TGs and cholesterol to liver. Formed from degradation of VLDL. Delivers hepatic cholesterol to peripheral tissues. Formed by hepatic lipase modification of IDL in the liver and peripheral tissue. Taken up by target cells via receptor-mediated endocytosis. LDL is Lethal. Mediates reverse cholesterol transport from peripheral tissues to liver. Acts as a repository for apoC and apoE (which are needed for chylomicron and VLDL metabolism). Secreted from both liver and intestine. Alcohol synthesis. HDL is Healthy. Abetalipoproteinemia Autosomal recessive. Mutation in gene that encodes microsomal transfer protein (MTP). A Chylomicrons, VLDL, LDL absent. Deficiency in apo B48– and apo B100–containing lipoproteins. Affected infants present with severe fat malabsorption, steatorrhea, failure to thrive. Later manifestations include retinitis pigmentosa, spinocerebellar degeneration due to vitamin E deficiency, progressive ataxia, acanthocytosis. Intestinal biopsy shows lipid-laden enterocytes (arrow in A ). Treatment: restriction of long-chain fatty acids, large doses of oral vitamin E. Familial dyslipidemias INHERITANCE PATHOGENESIS BLOOD LEVEL CLINICAL TYPE AR Lipoprotein lipase or Chylomicrons, TG, Pancreatitis, apo CII deficiency cholesterol hepatosplenomegaly, and I—Hyper- eruptive/pruritic xanthomas chylomicronemia Absent or defective IIa: LDL, cholesterol (no risk for atherosclerosis). LDL receptors, or IIb: LDL, cholesterol, Creamy layer in supernatant. II—Hyper- AD defective apo B100 cholesterolemia VLDL Heterozygotes (1:500) have ApoE (defective in cholesterol ≈ 300 mg/dL; III—Dysbeta AR type thrEE) Chylomicrons, VLDL homozygotes (very rare) have lipoproteinemia AD cholesterol ≥ 700 mg/dL. Hepatic VLDL, TG IV—Hyper- overproduction of Accelerated atherosclerosis (may triglyceridemia VLDL have MI before age 20), tendon (Achilles) xanthomas, and corneal arcus. Premature atherosclerosis, tuberoeruptive and palmar xanthomas. Hypertriglyceridemia (> 1000 mg/dL) can cause acute pancreatitis. Related to insulin resistance.
HIGH-YIELD PRINCIPLES IN Immunology “I hate to disappoint you, but my rubber lips are immune to your charms.” ` Lymphoid Structures 94 —Batman & Robin ` Cellular Components 97 ` Immune Responses 102 “Imagine the action of a vaccine not just in terms of how it affects a ` Immunosuppressants 118 single body, but also in terms of how it affects the collective body of a community.” —Eula Biss “Some people are immune to good advice.” —Saul Goodman, Breaking Bad Learning the components of the immune system and their roles in host defense at the cellular level is essential for both the understanding of disease pathophysiology and clinical practice. Know the immune mechanisms of responses to vaccines. Both congenital and acquired immunodeficiencies are very testable. Cell surface markers are high yield for understanding immune cell interactions and for laboratory diagnosis. Know the roles and functions of major cytokines and chemokines. 93 uploaded by medbooksvn
94 SEC TION II Immunology Immunology—Lymphoid Structures ` IMMUNOLOGY—LYMPHOID STRUCTURES Immune system 1° organs: organs Bone marrow—immune cell production, B cell maturation Thymus—T cell maturation 2° organs: Spleen, lymph nodes, tonsils, Peyer patches Allow immune cells to interact with antigen Lymph node A 2° lymphoid organ that has many afferents, 1 or more efferents. Encapsulated, with trabeculae A . Functions are nonspecific filtration by macrophages, circulation of B and T cells, and immune Follicle response activation. Medulla Paracortex Located in outer cortex; site of B-cell localization and proliferation. 1° follicles are dense and quiescent. 2° follicles have pale central germinal centers and are active. Consists of medullary cords (closely packed lymphocytes and plasma cells) and medullary sinuses (contain reticular cells and macrophages). Medullary sinuses communicate with efferent lymphatics. Contains T cells. Region of cortex between follicles and medulla. Contains high endothelial venules through which T and B cells enter from blood. Underdeveloped in patients with DiGeorge syndrome. Paracortex enlarges in an extreme cellular immune response (eg, EBV and other viral infections paracortical hyperplasia lymphadenopathy). A A erent lymphatic Follicles 1º follicle Paracortex 2º follicle Cortex Germinal center Mantle zone Trabecula Medullary cords Capsule Vein Artery Postcapillary venule E erent lymphatic Medullary sinus Capillary supply
Immunology Immunology—Lymphoid Structures SEC TION II 95 Lymphatic drainage associations Lymph node cluster Area of body drained Associated pathology Palpable lymph node Submandibular, Oral cavity, anterior tongue, Malignancy of and metastasis to the Nonpalpable lymph node submental lower lip oral cavity Deep cervical Head, neck, oropharynx Upper respiratory tract infection Infectious mononucleosis Kawasaki disease Malignancy of head, neck, oropharynx Supraclavicular Right: right hemithorax Malignancies of thorax, abdomen, Left (Virchow node): left pelvis Mediastinal hemithorax, abdomen, pelvis Hilar Pulmonary TB (unilateral hilar) Axillary Trachea, esophagus Sarcoidosis (bilateral hilar) Lung cancer Lungs Granulomatous disease Upper limb, breast, skin above Mastitis umbilicus Metastasis (especially breast cancer) Epitrochlear Hand, forearm Secondary syphilis Celiac Liver, stomach, spleen, pancreas, Mesenteric lymphadenitis Superior mesenteric upper duodenum Inflammatory bowel disease Inferior mesenteric Celiac disease Lower duodenum, jejunum, ileum, colon to splenic flexure Colon from splenic flexure to upper rectum Periumbilical (Sister Mary Abdomen, pelvis Gastric cancer Joseph node) Para-aortic Pair of testes, ovaries, kidneys, Metastasis External iliac fallopian tubes, fundus of uterus Internal iliac Sexually transmitted infections Body of uterus, cervix, superior Medial foot/leg cellulitis Superficial inguinal bladder (superficial inguinal) Cervix, proximal vagina, corpus cavernosum, prostate, inferior bladder, lower rectum to anal canal (above pectinate line) Distal vagina, vulva, scrotum, urethra, anal canal (below pectinate line), skin below umbilicus (except popliteal area) Popliteal (“pop-lateral”) Dorsolateral foot, posterior calf Lateral foot/leg cellulitis Right lymphatic duct drains right side of body above diaphragm into junction of the right subclavian and internal jugular vein Thoracic duct drains below the diaphragm and left thorax and upper limb into junction of left subclavian and internal jugular veins (rupture of thoracic duct can cause chylothorax) uploaded by medbooksvn
96 SEC TION II Immunology Immunology—Lymphoid Structures Spleen Capsule Located in LUQ of abdomen, anterolateral Trabecula to left kidney, protected by 9th-11th ribs. White pulp (WBCs) Splenic dysfunction (eg, postsplenectomy, Follicle (B cells) Red pulp (RBCs) sickle cell disease autosplenectomy) IgM complement activation C3b Mantle zone Sinusoid opsonization susceptibility to encapsulated Germinal center Reticular fibrous organisms. Marginal zone framework Periarteriolar Postsplenectomy findings: lymphoid sheath Closed Howell-Jolly bodies (nuclear remnants) (T cells) circulation Target cells Open Thrombocytosis (loss of sequestration and Periarteriolar circulation removal) lymphatic sheath Lymphocytosis (loss of sequestration) Follicle Pulp vein Marginal zone Vaccinate patients undergoing splenectomy or Vein Artery with splenic dysfunction against encapsulated organisms (pneumococci, Hib, meningococci). Contains T cells. Located within white pulp. Contains B cells. Located within white pulp. Contains macrophages and specialized B cells. Site where antigen-presenting cells (APCs) capture blood-borne antigens for recognition by lymphocytes. Located between red pulp and white pulp. Thymus Located in the anterosuperior mediastinum. T cells = Thymus A Site of T-cell differentiation and maturation. B cells = Bone marrow Encapsulated. Thymus epithelium is derived Absent thymic shadow or hypoplastic thymus from third pharyngeal pouch (endoderm), whereas thymic lymphocytes are of seen in some immunodeficiencies (eg, SCID, mesodermal origin. Cortex is dense with DiGeorge syndrome). immature T cells; medulla is pale with mature T cells and Hassall corpuscles containing Thymoma—neoplasm of thymus. Associated epithelial reticular cells. with myasthenia gravis, superior vena cava syndrome, pure red cell aplasia, Good Normal neonatal thymus “sail-shaped” on syndrome. CXR (asterisks in A ), involutes by age 3 years.
Immunology Immunology—Cellular Components SEC TION II 97 ` IMMUNOLOGY—CELLULAR COMPONENTS Innate vs adaptive immunity Innate immunity Adaptive immunity T cells, B cells, circulating antibodies COMPONENTS Neutrophils, macrophages, monocytes, dendritic cells, natural killer (NK) cells Variation through V(D)J recombination during (lymphoid origin), complement, physical lymphocyte development epithelial barriers, secreted enzymes Highly specific, refined over time MECHANISM Germline encoded Develops over long periods; memory response is RESPONSE TO PATHOGENS Nonspecific faster and more robust Occurs rapidly (minutes to hours) Immunoglobulins, cytokines SECRETED PROTEINS No memory response KEY FEATURES IN PATHOGEN Memory cells: activated B and T cells; subsequent Lysozyme, complement, C-reactive protein exposure to a previously encountered antigen RECOGNITION (CRP), defensins, cytokines stronger, quicker immune response Toll-like receptors (TLRs): pattern recognition receptors that recognize pathogen-associated molecular patterns (PAMPs) and lead to activation of NF-κB. Examples of PAMPs: LPS (gram ⊝ bacteria), flagellin (bacteria), nucleic acids (viruses) Immune privilege Organs (eg, eye, brain, placenta, testes) and tissues where chemical or physical mechanisms limit immune responses to foreign antigens to avoid damage that would occur from inflammatory sequelae. Allograft rejection at these sites is less likely. uploaded by medbooksvn
98 SEC TION II Immunology Immunology—Cellular Components Major MHC encoded by HLA genes. Present antigen fragments to T cells and bind T-cell receptors histocompatibility (TCRs). complex I and II MHC I MHC II LOCI HLA-A, HLA-B, HLA-C HLA-DP, HLA-DQ, HLA-DR BINDING MHC I loci have 1 letter MHC II loci have 2 letters STRUCTURE EXPRESSION TCR and CD8 TCR and CD4 FUNCTION 1 long chain, 1 short chain 2 equal-length chains (2 α, 2 β) ANTIGEN LOADING All nucleated cells, APCs, platelets (except RBCs) APCs ASSOCIATED PROTEINS STRUCTURE Present endogenous antigens (eg, viral or Present exogenous antigens (eg, bacterial cytosolic proteins) to CD8+ cytotoxic T cells proteins) to CD4+ helper T cells Antigen peptides loaded onto MHC I in RER Antigen loaded following release of invariant after delivery via TAP (transporter associated chain in an acidified endosome with antigen processing) β2-microglobulin Invariant chain Endogenous antigen Exogenous antigen Endogenous antigen-binding groove Exogenous antigen binding groove α2 chain α1 chain α1 chain β1 chain Long chain α2 chain α3 chain Short chain Long chain Extracellular space Short chain Cell membrane β2−Microglobulin β2 chain Cytoplasm HLA subtypes associated with diseases HLA SUBTYPE DISEASE MNEMONIC B27 Psoriatic arthritis, Ankylosing spondylitis, PAIR IBD-associated arthritis, Reactive arthritis I ate (8) too (2) much gluten at Dairy Queen B57 Abacavir hypersensitivity DM type 1: HLA-3 and -4 (1 + 3 = 4) SL3 (SLE) DQ2/DQ8 Celiac disease There are 4 walls in 1 “rheum” (room) DR3 DM type 1, SLE, Graves disease, Hashimoto thyroiditis, Addison disease DR4 Rheumatoid arthritis, DM type 1, Addison disease
Immunology Immunology—Cellular Components SEC TION II 99 Functions of natural Lymphocyte member of innate immune system. killer cells Use perforin and granzymes to induce apoptosis of virally infected cells and tumor cells. Activity enhanced by IL-2, IL-12, IFN-α, and IFN-β. Induced to kill when exposed to a nonspecific activation signal on target cell and/or to an absence of an inhibitory signal such as MHC I on target cell surface. Also kills via antibody-dependent cell-mediated cytotoxicity (CD16 binds Fc region of bound IgG, activating the NK cell). Major functions of B and T cells B cells Humoral immunity. Recognize and present antigen—undergo somatic hypermutation to optimize antigen specificity. Produce antibody—differentiate into plasma cells to secrete specific immunoglobulins. Maintain immunologic memory—memory B cells persist and accelerate future response to antigen. T cells Cell-mediated immunity. CD4+ T cells help B cells make antibodies and produce cytokines to recruit phagocytes and activate other leukocytes. CD8+ T cells directly kill virus-infected and tumor cells via perforin and granzymes (similar to NK cells). Delayed cell-mediated hypersensitivity (type IV). Acute and chronic cellular organ rejection. Rule of 8: MHC II × CD4 = 8; MHC I × CD8 = 8. uploaded by medbooksvn
100 SEC TION II Immunology Immunology—Cellular Components Differentiation of T cells Thymus Lymph node Peripheral blood Medulla Bone marrow Cortex IFN-γ, IL-12 Th1 Secretes Function IL-4, IL-10 IFN-γ, IL-2 Activate macrophages and cytotoxic T cells CD8+ Cytotoxic IL-2, IL-4 Th2 IL-4, IL-5, IL-6, Activate eosinophils, CD4+ Helper IFN-γ IL-10, IL-13 IgE T cell CD4+ precursor CD8+ Positive selection TGF-β, IL-1, IL-6 Th17 IL-17, IL-21, Induce neutrophilic Negative selection IFN-γ, IL-4 IL-22 infiltration Macrophage- TGF-β, IL-2 Treg TGF-β, IL-10, Prevent autoimmunity lymphocyte IL-6 IL-35 (maintain tolerance) interaction Cytotoxic T cells selection selection Regulatory T cells Thymic cortex. Double-positive (CD4+/CD8+) T cells expressing TCRs capable of binding self- MHC on cortical epithelial cells survive. Thymic medulla. T cells expressing TCRs with high affinity for self antigens undergo apoptosis or become regulatory T cells. Tissue-restricted self-antigens are expressed in the thymus due to the action of autoimmune regulator (AIRE); deficiency leads to autoimmune polyendocrine syndrome-1 (Chronic mucocutaneous candidiasis, Hypoparathyroidism, Adrenal insufficiency, Recurrent Candida infections). “Without AIRE, your body will CHAR”. Th1 cells secrete IFN-γ, which enhances the ability of monocytes and macrophages to kill microbes they ingest. This function is also enhanced by interaction of T cell CD40L with CD40 on macrophages. Macrophages also activate lymphocytes via antigen presentation. Kill virus-infected, neoplastic, and donor graft cells by inducing apoptosis. Release cytotoxic granules containing preformed proteins (eg, perforin, granzyme B). Cytotoxic T cells have CD8, which binds to MHC I on virus-infected cells. Help maintain specific immune tolerance by suppressing CD4+ and CD8+ T-cell effector functions. Identified by expression of CD3, CD4, CD25, and FOXP3. Activated regulatory T cells (Tregs) produce anti-inflammatory cytokines (eg, IL-10, TGF-β). IPEX (Immune dysregulation, Polyendocrinopathy, Enteropathy, X-linked) syndrome— genetic deficiency of FOXP3 autoimmunity. Characterized by enteropathy, endocrinopathy, nail dystrophy, dermatitis, and/or other autoimmune dermatologic conditions. Associated with diabetes in male infants.
Immunology Immunology—Cellular Components SEC TION II 101 T- and B-cell activation APCs: B cells, dendritic cells, Langerhans cells, macrophages. T-cell activation Two signals are required for T-cell activation, B-cell activation, and class switching. B-cell activation and APC ingests and processes antigen, then Q class switching migrates to the draining lymph node. Antigen T-cell activation (signal 1): exogenous antigen is presented on MHC II and MHC II/I R T cell Naïve T cell recognized by TCR on Th (CD4+) cell. receptor Endogenous or cross-presented antigen is presented on MHC I to Tc (CD8+) cell. Antigen-presenting CD4/8 Proliferation and survival (signal 2): cell costimulatory signal via interaction of B7 protein (CD80/86) on dendritic cell and CD80/86 S CD28 T CD28 on naïve T cell. (B7) Activated Activated Th cell produces cytokines. Tc cell T cell actions able to recognize and kill virus-infected cell. Th-cell activation as above. Antigen R B-cell receptor–mediated endocytosis. Exogenous antigen is presented on MHC II T cell S MHC II B cell and recognized by TCR on Th cell. receptor CD40 receptor on B cell binds CD40 ligand Q receptor (CD40L) on Th cell. B cell Th cells secrete cytokines that determine Ig Activated CD4 class switching of B cells. CD4+ T cell B cells are activated and produce IgM. They undergo class switching and affinity CD40L CD40 maturation. T V U Activated B cell actions Cytokines uploaded by medbooksvn
102 SEC TION II Immunology Immunology—Immune Responses ` IMMUNOLOGY—IMMUNE RESPONSES Antibody structure Fab fragment consisting of light (L) and heavy (H) chains recognizes antigens. Fc region of and function IgM and IgG fixes complement. Heavy chain contributes to Fc and Fab regions. Light chain contributes only to Fab region. Antigen- VH Fab region Epitope Fab: binding site Fragment, antigen binding CH1 Heavy chain JHD Determines idiotype: unique antigen-binding VL pocket; only 1 antigenic specificity expressed Hypervraergiaiobnles CL SS Hinge CH1 JL per B cell C = Constant Light chain V = Variable SS SS CL Fc (5 C’s): L = Light SS Constant H = Heavy Carboxy terminal SS = Disulfide bond CH2 CH2 Complement Complement binding CH3 binding Carbohydrate side chains Fc region Confers (determines) isotype (IgM, IgD, etc) Macrophage CH3 binding Generation of antibody diversity (antigen independent) Neutralization Opsonization Complement 1. Random recombination of VJ (light-chain) activation or V(D)J (heavy-chain) genes by RAG1 and RAG2 Membrane 2. Random addition of nucleotides to attack complex DNA during recombination by terminal (MAC) deoxynucleotidyl transferase (TdT) 3. Random combination of heavy chains with C3b light chains Generation of antibody specificity (antigen dependent) 4. Somatic hypermutation and affinity maturation (variable region) 5. Isotype switching (constant region) Antibody prevents Antibody promotes Antibody activates bacterial adherence phagocytosis complement, enhancing opsonization and lysis
Immunology Immunology—Immune Responses SEC TION II 103 Immunoglobulin All isotypes can exist as monomers. Mature, naïve B cells prior to activation express IgM and IgD isotypes on their surfaces. They may differentiate in germinal centers of lymph nodes by isotype switching (gene rearrangement; induced by cytokines and CD40L) into plasma cells that secrete IgA, IgG, IgG or IgE. “For B cells, IgMom and IgDad mature to plasma cells as they AGE. IgG Affinity refers to the individual antibody-antigen interaction, while avidity describes the cumulative IgG binding strength of all antibody-antigen interactions in a multivalent molecule. IIIgggIgAGG A Main antibody in 2° response to an antigen. Most abundant isotype in serum. Fixes complement, opsonizes bacteria, neutralizes bacterial toxins and viruses. Only isotype that crosses the placenta IIggAG (provides infants with passive immunity that starts to wane after birth). “IgG Greets the Growing fetus.” Associated with warm autoimmune hemolytic anemia (“warm weather is Great!”). IgA J chain IgA Prevents attachment of bacteria and viruses to mucous membranes; does not fix complement. J chain Monomer (in circulation) or dimer (with J chain when secreted). Crosses epithelial cells by IIggMA J chain transcytosis. Produced in GI tract (eg, by Peyer patches) and protects against gut infections (eg, Giardia). Most produced antibody overall, but has lower serum concentrations. Released into IgIgMMJJJ ccchhhaaaiiinnn secretions (tears, saliva, mucus) and breast milk. Picks up secretory component from epithelial cells, which protects the Fc portion from luminal proteases. IgM JJJ ccchhhaaaiiinnn IgM First antibody to be produced during an immune response. Fixes complement. Antigen receptor on the surface of B cells. Monomer on B cell, pentamer with J chain when secreted. Pentamer IIggDM J chain enables avid binding to antigen while humoral response evolves. Associated with cold autoimmune hemolytic anemia. IgD Expressed on the surface of mature, naïve B cells. Normally, low levels are detectable in serum. IIIgggIgEDD D Binds mast cells and basophils; cross-links when exposed to allergen, mediating immediate (type I) IIggED hypersensitivity through release of inflammatory mediators such as histamine. Contributes to immunity to parasites by activating Eosinophils. IgE IIggIgEE E Antigen type and memory Thymus-independent Antigens lacking a peptide component (eg, lipopolysaccharides from gram ⊝ bacteria); cannot antigens be presented by MHC to T cells. Weakly immunogenic; vaccines often require boosters and adjuvants (eg, capsular polysaccharide subunit of Streptococcus pneumoniae PPSV23 vaccine). Thymus-dependent Antigens containing a protein component (eg, diphtheria toxoid). Class switching and immunologic antigens memory occur as a result of direct contact of B cells with Th cells. uploaded by medbooksvn
104 SEC TION II Immunology Immunology—Immune Responses Complement System of hepatically synthesized plasma proteins that play a role in innate immunity and ACTIVATION PATHWAYS inflammation. Membrane attack complex (MAC) defends against gram ⊝ bacteria. The CH50 test FUNCTIONS is used to screen for activation of the classical complement pathway. Classic—IgG or IgM mediated. General Motors makes classic cars. Alternative—microbe surface molecules. Lectin—mannose or other sugars on microbe surface. C3b—opsonization. C3b binds to lipopolysaccharides on bacteria. C3a, C4a, C5a—anaphylaxis. MAC complex is important for neutralizing C5a—neutrophil chemotaxis. C5b-9 (MAC)—cytolysis. Neisseria species. Deficiency results in recurrent infection. Get “Neis” (nice) Big MACs from 5-9 pm. Opsonins—C3b and IgG are the two 1° Opsonin (Greek) = to prepare for eating. opsonins in bacterial defense; enhance phagocytosis. C3b also helps clear immune complexes. Inhibitors—decay-accelerating factor (DAF, also called CD55) and C1 esterase inhibitor help prevent complement activation on self cells (eg, RBCs). D Bb C3 B Alternative C3b C3bBb C3bBb3b C3 (C3 convertase) (C5 convertase) Spontaneous and C3a microbial surfaces Amplifies generation of C3b Lectin C1-like C3b C5 C5a C6-C9 Lysis, Microbial surfaces complex C3a C4b2b3b cytotoxicity C4 C4b2b (C5 convertase) C5b MAC (eg, mannose) C4a (C3 convertase) (C5b-9) C4b Classic C1 C1 Antigen-antibody complexes C2 C*2b C3 C*2a *Historically, the larger fragment of C2 was called C2a but is now called C2b.
Immunology Immunology—Immune Responses SEC TION II 105 Complement disorders Complement protein deficiencies Early complement risk of severe, recurrent pyogenic sinus and respiratory tract infections. C3b used in clearance of deficiencies (C1–C4) antigen-antibody complexes risk of SLE (think SLEarly). Terminal complement susceptibility to recurrent Neisseria bacteremia. deficiencies (C5–C9) Complement regulatory protein deficiencies C1 esterase inhibitor Causes hereditary angioedema due to unregulated activation of kallikrein bradykinin. deficiency Characterized by C4 levels. ACE inhibitors are contraindicated (also bradykinin). Paroxysmal nocturnal A defect in the PIGA gene prevents the formation of glycosylphosphatidylinositol (GPI) anchors for hemoglobinuria complement inhibitors, such as decay-accelerating factor (DAF/CD55) and membrane inhibitor of reactive lysis (MIRL/CD59). Causes complement-mediated intravascular hemolysis A haptoglobin, dark urine A . Can cause atypical venous thrombosis (eg, Budd-Chiari syndrome; portal vein, cerebral, or dermal thrombosis). uploaded by medbooksvn
106 SEC TION II Immunology Immunology—Immune Responses Important cytokines Acute (IL-1, IL-6, TNF-α), then recruit (IL-8, IL-12). Secreted by macrophages Interleukin-1 Causes fever, acute inflammation. Activates “Hot T-bone stEAK”: Interleukin-6 endothelium to express adhesion molecules. IL-1: fever (hot). Induces chemokine secretion to recruit WBCs. IL-2: stimulates T cells. Also called osteoclast-activating factor. IL-3: stimulates bone marrow. IL-4: stimulates IgE production. Causes fever and stimulates production of acute- IL-5: stimulates IgA production. phase proteins. IL-6: stimulates aKute-phase protein production. Tumor necrosis Activates endothelium. Causes WBC Causes cachexia in malignancy. factor-α recruitment, vascular leak. Maintains granulomas in TB. IL-1, IL-6, TNF-α can mediate fever and sepsis. Interleukin-8 Major chemotactic factor for neutrophils. “Clean up on aisle 8.” Neutrophils are recruited by IL-8 to clear infections. Interleukin-12 Induces differentiation of T cells into Th1 cells. Facilitates granuloma formation in TB. Activates NK cells. Secreted by T cells Interleukin-2 Stimulates growth of helper, cytotoxic, and regulatory T cells, and NK cells. Interleukin-3 Supports growth and differentiation of bone marrow stem cells. Functions like GM-CSF. From Th1 cells Secreted by NK cells and T cells in response to Increases MHC expression and antigen Interferon-γ antigen or IL-12 from macrophages; stimulates presentation by all cells. macrophages to kill phagocytosed pathogens. Inhibits differentiation of Th2 cells. Activates macrophages to induce granuloma formation. Induces IgG isotype switching in B cells. From Th2 cells Induces differentiation of T cells into Th Ain’t too proud 2 BEG 4 help. Interleukin-4 (helper) 2 cells. Promotes growth of B cells. Interleukin-5 Enhances class switching to IgE and IgG. I have 5 BAEs. Interleukin-10 Promotes growth and differentiation of B cells. TGF-β and IL-10 both attenuate the immune Interleukin-13 Enhances class switching to IgA. Stimulates response. growth and differentiation of Eosinophils. Interleukin thirtEEn promotes IgE. Attenuates inflammatory response. Decreases expression of MHC class II and Th1 cytokines. Inhibits activated macrophages and dendritic cells. Also secreted by regulatory T cells. Promotes IgE production by B cells. Induces alternative macrophage activation.
Immunology Immunology—Immune Responses SEC TION II 107 Respiratory burst Also called oxidative burst. Involves the activation of the phagocyte NADPH oxidase complex (eg, in neutrophils, monocytes), which utilizes O2 as a substrate. Plays an important role in the immune response rapid release of reactive oxygen species (ROS). NADPH plays a role in both the creation and neutralization of ROS. Myeloperoxidase contains a blue-green, heme-containing pigment that gives sputum its color. NO Safe Microbe (NADPH Oxidase Superoxide dismutase Myeloperoxidase). NADPH oxidase Phagolysosome Q deficiency = chronic NADPH O2 granulomatous disease NADP+ Q R Superoxide dismutase O2- ∞ S Myeloperoxidase R Neutrophil cell membrane Catalase/glutathione T peroxidase H2O2 U Glutathione reductase H2O + O2 Cl – H2O2 H2O via bacterial GSSG V Glucose-6-phosphate S GSH T dehydrogenase G6PD catalase HOCl ∞ GSH/ Glutathione reduced/ Bacteria U NADPH GSSG oxidized from HMP shunt NADP+ 6-phosphogluconolactone HOCl ∞ Hypochlorite bleach O2- ∞ Superoxide Glucose-6-P V Phagocytes of patients with CGD can utilize H2O2 generated by invading organisms and convert it to ROS. Patients are at risk for infection by catalase ⊕ species (eg, S aureus, Aspergillus) capable of neutralizing their own H2O2, leaving phagocytes without ROS for fighting infections. Pyocyanin of P aeruginosa generates ROS to kill competing pathogens. Oxidative burst leads to release of lysosomal enzymes. Interferons IFN-α, IFN-β, IFN-γ. MECHANISM A part of innate host defense, interferons interfere with both RNA and DNA viruses. Cells infected with a virus synthesize these glycoproteins, which act on local cells, priming them CLINICAL USE for viral defense by downregulating protein synthesis to resist potential viral replication and by ADVERSE EFFECTS upregulating MHC expression to facilitate recognition of infected cells. Also play a major role in activating antitumor immunity. Chronic HBV, Kaposi sarcoma, hairy cell leukemia, condyloma acuminatum, renal cell carcinoma, malignant melanoma, multiple sclerosis, chronic granulomatous disease. Flulike symptoms, depression, neutropenia, myopathy, interferon-induced autoimmunity. uploaded by medbooksvn
108 SEC TION II Immunology Immunology—Immune Responses Cell surface proteins TCR (binds antigen-MHC complex), CD3 Must be 21 to drink at a Barr T cells (associated with TCR for signal transduction), CD28 (binds B7 on APC) Helper T cells Cytotoxic T cells CD4, CD40L, CXCR4/CCR5 (coreceptors for Regulatory T cells HIV) B cells CD8 NK cells Macrophages CD4, CD25 Hematopoietic Ig (binds antigen), CD19, CD20, CD21 stem cells (receptor for Epstein-Barr virus), CD40, MHC II, B7 (CD80/86) CD16 (binds Fc of IgG), CD56 (suggestive marker for NK cells) CD14 (receptor for PAMPs [eg, LPS]), CD40, CCR5, MHC II, B7, Fc and C3b receptors (enhanced phagocytosis) CD34 Anergy State during which a cell cannot become activated by exposure to its antigen. T and B cells become anergic when exposed to their antigen without costimulatory signal (signal 2). Another mechanism of self-tolerance. Passive vs active immunity Passive Active Exposure to exogenous antigens MEANS OF ACQUISITION Receiving preformed antibodies Slow Long-lasting protection (memory) ONSET Rapid Natural infection, vaccines, toxoid DURATION Short span of antibodies (half-life = 3 weeks) Combined passive and active immunizations can be given for hepatitis B or rabies exposure EXAMPLES IgA in breast milk, maternal IgG crossing placenta, antitoxin, humanized monoclonal antibody NOTES IVIG and other immune globulin preparations can be administered to provide temporary but specific passive immunity to a target pathogen.
Immunology Immunology—Immune Responses SEC TION II 109 Vaccination Induces an active immune response (humoral and/or cellular) to specific pathogens. VACCINE TYPE DESCRIPTION PROS/CONS EXAMPLES Live attenuated Microorganism rendered Pros: induces cellular and Adenovirus (nonattenuated, vaccine nonpathogenic but retains humoral responses. Induces given to military recruits), capacity for transient growth strong, often lifelong typhoid (Ty21a, oral), Killed or inactivated within inoculated host. MMR immunity. polio (Sabin), varicella vaccine and varicella vaccines can be (chickenpox), smallpox, given to people living with Cons: may revert to virulent BCG, yellow fever, influenza Subunit, recombinant, HIV without evidence of form. Contraindicated in (intranasal), MMR, rotavirus. polysaccharide, and immunity if CD4+ cell count pregnancy and patients with conjugate ≥ 200 cells/mm3. immunodeficiency. “Attention teachers! Please vaccinate small, Beautiful Toxoid young infants with MMR routinely!” mRNA Pathogen is inactivated by heat Pros: safer than live vaccines. Hepatitis A, Typhoid or chemicals. Maintaining Cons: weaker cell-mediated (Vi polysaccharide, epitope structure on surface intramuscular), Rabies, antigens is important for immune response; mainly Influenza (intramuscular), immune response. Mainly induces a humoral response. Polio (SalK). induces a humoral response. Booster shots usually needed. A TRIP could Kill you. All use specific antigens that Pros: targets specific epitopes HBV (antigen = HBsAg), best stimulate the immune of antigen; lower chance of HPV, acellular pertussis system. adverse reactions. (aP), Neisseria meningitidis (various strains), Streptococcus Cons: expensive; weaker pneumoniae (PPSV23 immune response. polysaccharide primarily T-cell–independent response; PCV13, PCV15, and PCV20 polysaccharide produces T-cell–dependent response), Haemophilus influenzae type b, herpes zoster. Denatured bacterial toxin with Pros: protects against the Clostridium tetani, an intact receptor binding bacterial toxins. Corynebacterium diphtheriae. site. Stimulates immune system to make antibodies Cons: antitoxin levels decrease without potential for causing with time, thus booster shots disease. may be needed. A lipid nanoparticle delivers Pros: high efficacy; induces SARS-CoV-2 mRNA, causing cells to cellular and humoral synthesize foreign protein (eg, immunity. Safe in pregnancy. spike protein of SARS-CoV-2). Cons: local and transient systemic (fatigue, headache, myalgia) reactions are common. Rare myocarditis, pericarditis particularly in young males. uploaded by medbooksvn
110 SEC TION II Immunology Immunology—Immune Responses Hypersensitivity types Four types (ABCD): Anaphylactic and Atopic (type I), AntiBody-mediated (type II), Immune Complex (type III), Delayed (cell-mediated, type IV). Types I, II, and III are all antibody-mediated. Type I Anaphylactic and atopic—two phases: First (type) and Fast (anaphylaxis). hypersensitivity Immediate (minutes): antigen crosslinks Test: skin test or blood test (ELISA) for allergen- preformed IgE on presensitized mast cells Allergen Allergen- immediate degranulation release of specific IgE. specific IgE histamine (a vasoactive amine), tryptase Example: (marker of mast cell activation), and Fc receptor leukotrienes. Anaphylaxis (eg, food, drug, or bee sting for IgE Late (hours): chemokines (attract allergies) inflammatory cells, eg, eosinophils) and other mediators from mast cells Allergic asthma inflammation and tissue damage. Degranulation Type II Antibodies bind to cell-surface antigens or Direct Coombs test—detects antibodies hypersensitivity extracellular matrix cellular destruction, attached directly to the RBC surface. inflammation, and cellular dysfunction. NK cell Indirect Coombs test—detects presence of unbound antibodies in the serum. Fc receptor Cellular destruction—cell is opsonized (coated) Examples: for IgG by antibodies, leading to either: Autoimmune hemolytic anemia (including Phagocytosis and/or activation of drug-induced form) Surface antigen complement system. Immune thrombocytopenia NK cell killing (antibody-dependent cellular Transfusion reactions Abnormal cell cytotoxicity). Hemolytic disease of the newborn Antibody-dependent cellular cytotoxicity Inflammation—binding of antibodies to cell Examples: surfaces activation of complement system Goodpasture syndrome and Fc receptor-mediated inflammation. Rheumatic fever Hyperacute transplant rejection Cellular dysfunction—antibodies bind to Examples: cell-surface receptors abnormal blockade or Myasthenia gravis activation of downstream process. Graves disease Pemphigus vulgaris
Immunology Immunology—Immune Responses SEC TION II 111 Hypersensitivity types (continued) Type III Immune complex—antigen-antibody (mostly In type III reaction, imagine an immune hypersensitivity IgG) complexes activate complement, which complex as 3 things stuck together: antigen- attracts neutrophils; neutrophils release antibody-complement. Neutrophils lysosomal enzymes. Examples: Can be associated with vasculitis and systemic SLE manifestations. Rheumatoid arthritis Reactive arthritis Enzymes from Serum sickness—the prototypic immune Polyarteritis nodosa neutrophils complex disease. Antibodies to foreign proteins Poststreptococcal glomerulonephritis damage are produced and 1–2 weeks later, antibody- IgA vasculitis endothelial cells antigen complexes form and deposit in tissues complement activation inflammation Fever, urticaria, arthralgia, proteinuria, and tissue damage ( serum C3, C4). lymphadenopathy occur 1–2 weeks after antigen exposure. Serum sickness–like reactions are associated with some drugs (may act as haptens, eg, penicillin, monoclonal antibodies) and infections (eg, hepatitis B). Type IV Arthus reaction—a local subacute immune Response does not involve antibodies (vs types I, hypersensitivity complex-mediated hypersensitivity reaction. II, and III). Intradermal injection of antigen into a Antigen- presensitized (has circulating IgG) individual Examples: presenting cell leads to immune complex formation in the Contact dermatitis (eg, poison ivy, nickel skin (eg, enhanced local reaction to a booster allergy) Antigen vaccination). Characterized by edema, Drug reaction with eosinophilia and fibrinoid necrosis, activation of complement. systemic symptoms (DRESS) Sensitized Graft-versus-host disease Th1 cell Two mechanisms, each involving T cells: Cytokines 1. Direct cell cytotoxicity: CD8+ cytotoxic T Tests: PPD for TB infection; patch test for cells kill targeted cells. contact dermatitis; Candida skin test for T cell 2. Inflammatory reaction: effector CD4+ immune function. T cells recognize antigen and release inflammation-inducing cytokines (shown 4T’s: T cells, Transplant rejections, TB skin in illustration). tests, Touching (contact dermatitis). Fourth (type) and last (delayed). Activated Delayed-type macrophage hypersensitivity uploaded by medbooksvn
112 SEC TION II Immunology Immunology—Immune Responses Immunologic blood transfusion reactions TYPE PATHOGENESIS TIMING CLINICAL PRESENTATION DONOR BLOOD HOST BLOOD Allergic/ Type I hypersensitivity Within minutes Allergies: urticaria, IgE anaphylactic reaction against plasma to 2–3 hr (due to pruritus (anti-IgA) reaction proteins in transfused release of preformed blood inflammatory Anaphylaxis: mediators in wheezing, Donor plasma proteins, Host mast cell IgA-deficient individuals degranulating mast hypotension, including IgA should receive blood cells) respiratory arrest, products without IgA shock Acute Type II hypersensitivity During transfusion Fever, hypotension, hemolytic reaction or within 24 hr tachypnea, transfusion (due to preformed tachycardia, reaction Typically causes antibodies) flank pain, intravascular hemolysis hemoglobinuria (ABO blood group Within 1–6 hr (due (intravascular), Donor RBC with A and/ Host anti-A, anti-B IgG, incompatibility) to preformed jaundice or B group antigens IgM cytokines) (extravascular) Febrile Cytokines created by nonhemolytic donor WBCs accumulate Fever, headaches, Donor WBC releases Host anti-HLA, anti- transfusion during storage of blood chills, flushing preformed cytokines leukocyte IgG reaction products More common in Transfusion- Reactions prevented by children related acute leukoreduction of blood lung injury products Within minutes to Respiratory distress, 6 hr noncardiogenic Delayed Two-hit mechanism: pulmonary edema hemolytic Neutrophils are Host transfusion neutrophils reaction sequestered and primed in pulmonary Donor antileukocyte vasculature due to antibody recipient risk factors Neutrophils are Onset over 24 hr Generally self limited activated by a product Usually presents and clinically silent (eg, antileukocyte antibodies) in the within 1–2 wk Mild fever, transfused blood and (due to slow hyperbilirubinemia release inflammatory destruction by mediators capillary reticuloendothelial permeability system) pulmonary edema Anamnestic response to a foreign antigen on donor RBCs (Rh [D] or other minor blood group antigens) previously encountered by recipient Typically causes extravascular hemolysis
Immunology Immunology—Immune Responses SEC TION II 113 Autoantibodies AUTOANTIBODY ASSOCIATED DISORDER Anti-postsynaptic ACh receptor Myasthenia gravis Anti-presynaptic voltage-gated Ca2+ channel Lambert-Eaton myasthenic syndrome Anti-β2 glycoprotein I Antiphospholipid syndrome Antinuclear (ANA) Nonspecific screening antibody, often associated Anticardiolipin, lupus anticoagulant with SLE Anti-dsDNA, anti-Smith SLE, antiphospholipid syndrome Antihistone SLE Anti-U1 RNP (ribonucleoprotein) Drug-induced lupus Rheumatoid factor (IgM antibody against IgG Mixed connective tissue disease Rheumatoid arthritis Fc region), anti-cyclic citrullinated peptide (anti-CCP, more specific) Sjögren syndrome Anti-Ro/SSA, anti-La/SSB Scleroderma (diffuse) Anti-Scl-70 (anti-DNA topoisomerase I) Limited scleroderma (CREST syndrome) Anticentromere Polymyositis, dermatomyositis Antisynthetase (eg, anti-Jo-1), anti-SRP, anti- helicase (anti-Mi-2) 1° biliary cholangitis Antimitochondrial Autoimmune hepatitis Anti-smooth muscle, anti-liver/kidney microsomal-1 Microscopic polyangiitis, eosinophilic Myeloperoxidase-antineutrophil cytoplasmic granulomatosis with polyangiitis, ulcerative antibody (MPO-ANCA)/perinuclear ANCA colitis, 1° sclerosing cholangitis (p-ANCA) PR3-ANCA/cytoplasmic ANCA (c-ANCA) Granulomatosis with polyangiitis Anti-phospholipase A2 receptor 1° membranous nephropathy Anti-hemidesmosome Bullous pemphigoid Anti-desmoglein (anti-desmosome) Pemphigus vulgaris Antithyroglobulin, antithyroid peroxidase Hashimoto thyroiditis (antimicrosomal) Anti-TSH receptor Graves disease IgA anti-endomysial, IgA anti-tissue Celiac disease transglutaminase, IgA and IgG deamidated gliadin peptide Type 1 diabetes mellitus Anti-glutamic acid decarboxylase, islet cell cytoplasmic antibodies Pernicious anemia Antiparietal cell, anti-intrinsic factor Goodpasture syndrome Anti-glomerular basement membrane uploaded by medbooksvn
114 SEC TION II Immunology Immunology—Immune Responses Immunodeficiencie DEFECT PRESENTATION FINDINGS DISEASE Defect in BTK, a tyrosine Recurrent bacterial and Absent B cells in peripheral kinase gene no B-cell enteroviral infections after 6 blood, Ig of all classes. B-cell disorders maturation; X-linked recessive months ( maternal IgG) X-linked (Bruton) ( in Boys) Absent/scanty lymph nodes agammaglobulinemia Majority Asymptomatic and tonsils (1° follicles Cause unknown Can see Airway and GI and germinal centers Selective IgA Most common 1° absent) live vaccines deficiency infections, Autoimmune contraindicated immunodeficiency disease, Atopy, Anaphylaxis to Common variable IgA in blood products IgA with normal IgG, IgM immunodeficiency Defect in B-cell differentiation. levels Cause unknown in most cases May present in childhood T-cell disorders but usually diagnosed after susceptibility to giardiasis Thymic aplasia 22q11 microdeletion; failure puberty Can cause false-negative celiac to develop 3rd and 4th IL-12 receptor pharyngeal pouches absent risk of autoimmune disease, disease test and false-positive deficiency thymus and parathyroids bronchiectasis, lymphoma, serum pregnancy test sinopulmonary infections plasma cells, Autosomal dominant DiGeorge syndrome—thymic, immunoglobulins hyper-IgE syndrome parathyroid, cardiac defects CATCH-22: Cardiac defects (Job syndrome) (conotruncal abnormalities T cells, PTH, Ca2+ Velocardiofacial syndrome— [eg, tetralogy of Fallot, truncus Thymic shadow absent on Chronic palate, facial, cardiac defects arteriosus]), Abnormal facies, mucocutaneous Thymic hypoplasia T-cell CXR candidiasis Th1 response; autosomal deficiency (recurrent viral/ recessive fungal infections), Cleft IFN-γ palate, Hypocalcemia 2° to Most common cause of Deficiency of Th17 cells due to parathyroid aplasia tetany STAT3 mutation impaired Mendelian susceptibility recruitment of neutrophils to Disseminated mycobacterial to mycobacterial diseases sites of infection and fungal infections; may (MSMD) present after administration of IgE T-cell dysfunction BCG vaccine eosinophils Impaired cell-mediated Learn the ABCDEF’s to get a Cold (noninflamed) Job STAT! immunity against Candida sp staphylococcal Abscesses, Classic form caused by defects retained Baby teeth, Coarse Absent in vitro T-cell facies, Dermatologic problems proliferation in response to in AIRE (eczema), IgE, bone Candida antigens Fractures from minor trauma Absent cutaneous reaction to Persistent noninvasive Candida Candida antigens albicans infections of skin and mucous membranes
Immunology Immunology—Immune Responses SEC TION II 115 Immunodeficiencie (continued) DISEASE DEFECT PRESENTATION FINDINGS B- and T-cell disorders T-cell receptor excision circles (TRECs) Severe combined Several types including Failure to thrive, chronic immunodeficiency defective IL-2R gamma diarrhea, thrush Part of newborn screening for chain (most common, SCID X-linked recessive); adenosine Recurrent viral, bacterial, deaminase deficiency fungal, and protozoal Absence of thymic shadow (autosomal recessive); infections (CXR), germinal centers RAG mutation VDJ (lymph node biopsy), and recombination defect T cells (flow cytometry) Ataxia-telangiectasia Defects in ATM gene failure Triad: cerebellar defects AFP A to detect DNA damage (Ataxia), spider Angiomas IgA, IgG, and IgE failure to halt progression (telangiectasia A ), IgA Lymphopenia, cerebellar of cell cycle mutations deficiency accumulate; autosomal atrophy recessive sensitivity to radiation (limit risk of lymphoma and x-ray exposure) leukemia Hyper-IgM syndrome Most commonly due to Severe pyogenic infections defective CD40L on Th cells early in life; opportunistic Normal or IgM class switching defect; infection with Pneumocystis, IgG, IgA, IgE X-linked recessive Cryptosporidium, CMV Failure to make germinal Wiskott-Aldrich Mutation in WAS gene; WATER: Wiskott-Aldrich: centers syndrome leukocytes and platelets Thrombocytopenia, Eczema, to normal IgG, IgM unable to reorganize actin Recurrent (pyogenic) IgE, IgA cytoskeleton defective infections Fewer and smaller platelets antigen presentation; X-linked recessive risk of autoimmune disease neutrophils in blood and malignancy Absence of neutrophils at Phagocyte dysfunction infection sites impaired wound healing Leukocyte adhesion Defect in LFA-1 integrin Late separation (>30 days) of deficiency (type 1) (CD18) protein on umbilical cord, absent pus, Giant granules ( B , arrows) in phagocytes; impaired dysfunctional neutrophils granulocytes and platelets migration and chemotaxis; recurrent skin and autosomal recessive mucosal bacterial infections Pancytopenia Mild coagulation defects Chédiak-Higashi Defect in lysosomal trafficking PLAIN: Progressive syndrome regulator gene (LYST) neurodegeneration, Lymphohistiocytosis, B Microtubule dysfunction in Albinism (partial), recurrent phagosome-lysosome fusion; pyogenic Infections, autosomal recessive peripheral Neuropathy Chronic Defect of NADPH oxidase susceptibility to catalase ⊕ Abnormal dihydrorhodamine granulomatous reactive oxygen organisms (flow cytometry) test ( green disease species (eg, superoxide) fluorescence) and respiratory burst in Recurrent infections and neutrophils; X-linked form granulomas Nitroblue tetrazolium dye most common reduction test (obsolete) fails to turn blue uploaded by medbooksvn
116 SEC TION II Immunology Immunology—Immune Responses Infections in immunodeficien y PATHOGEN T CELLS B CELLS GRANULOCYTES COMPLEMENT Bacteria Sepsis Encapsulated (Please Some Bacteria Encapsulated SHINE my SKiS): Produce No species with early Pseudomonas Serious granules: complement aeruginosa, Staphylococcus, deficiencies Streptococcus Burkholderia cepacia, pneumoniae, Pseudomonas Neisseria with late Haemophilus aeruginosa, Nocardia, complement (C5– Influenzae type b, Serratia C9) deficiencies Neisseria meningitidis, Escherichia coli, Salmonella, Klebsiella pneumoniae, group B Streptococcus Viruses CMV, EBV, JC Enteroviral N/A N/A virus, VZV, chronic encephalitis, infection with poliovirus respiratory/GI viruses (live vaccine contraindicated) Fungi/parasites Candida (local), PCP, GI giardiasis (no IgA) Candida (systemic), N/A Cryptococcus Aspergillus, Mucor Note: B-cell deficiencies tend to produce recurrent bacterial infections, whereas T-cell deficiencies produce more fungal and viral infections.
Immunology Immunology—Immune Responses SEC TION II 117 Transplant rejection ONSET PATHOGENESIS FEATURES TYPE OF REJECTION Within minutes Pre-existing recipient antibodies Widespread thrombosis of graft vessels Weeks to months react to donor antigen (type II (arrows within glomerulus A ) Hyperacute Months to years hypersensitivity reaction), activate ischemia and fibrinoid necrosis Acute complement Varies Graft must be removed Chronic Cellular: CD8+ T cells and/or CD4+ T cells activated against donor MHCs Vasculitis of graft vessels with dense Graft-versus-host (type IV hypersensitivity reaction) interstitial lymphocytic infiltrate B disease Humoral: similar to hyperacute, except Prevent/reverse with antibodies develop after transplant immunosuppressants (associated with C4d deposition) Dominated by arteriosclerosis C CD4+ T cells respond to recipient Recipient T cells react and secrete APCs presenting donor peptides, including allogeneic MHC cytokines proliferation of vascular smooth muscle, parenchymal Both cellular and humoral components atrophy, interstitial fibrosis (type II and IV hypersensitivity Organ-specific examples: reactions) Chronic allograft nephropathy Bronchiolitis obliterans Grafted immunocompetent Accelerated atherosclerosis (heart) T cells proliferate in the Vanishing bile duct syndrome immunocompromised host and reject host cells with “foreign” proteins Maculopapular rash, jaundice, severe organ dysfunction diarrhea, hepatosplenomegaly HLA mismatches (most importantly Usually in bone marrow and liver HLA-A, -B, and -DR antigens) the transplants (rich in lymphocytes) risk for GVHD Potentially beneficial in bone marrow Type IV hypersensitivity reaction transplant for leukemia (graft-versus- tumor effect) For patients who are immunocompromised, irradiate blood products prior to transfusion to prevent GVHD ABC uploaded by medbooksvn
118 SEC TION II Immunology Immunology—Immunosuppressants ` I MMUNOLOGY — I MMUNO S UPPRE S S ANT S Immunosuppressants Agents that block lymphocyte activation and proliferation. Reduce acute transplant rejection by suppressing cellular immunity (used as prophylaxis). Frequently combined to achieve greater efficacy with toxicity. Chronic suppression risk of infection and malignancy. CD4 Basiliximab – FKBP + FKBP + IL-2R Azathioprine CD3 TCR Tacrolimus Sirolimus (rapamycin) Mycophenolate 6–MP Cyclophilin + – Cyclosporine – – – – Calcineurin IMP PRPP dehydrogenase amidotransferase NFAT–P NFAT mTOR Glucocorticoids Proliferation Purine genes nucleotides T HELPER –– CELL DNA replication De novo purine NFAT NF–κB Inflammatory synthesis cytokine genes DRUG MECHANISM INDICATIONS TOXICITY NOTES Cyclosporine Calcineurin inhibitor; Psoriasis, rheumatoid Nephrotoxicity, Both calcineurin Tacrolimus (FK506) binds cyclophilin arthritis hypertension, inhibitors are hyperlipidemia, highly nephrotoxic, Sirolimus (Rapamycin) Blocks T-cell activation Immunosuppression neurotoxicity, gingival especially in higher by preventing IL-2 after solid organ hyperplasia, hirsutism doses or in patients Basiliximab transcription transplant with renal function Similar to cyclosporine, Calcineurin inhibitor; Kidney transplant risk of diabetes binds FK506 binding rejection prophylaxis and neurotoxicity; protein (FKBP) specifically no gingival hyperplasia or Blocks T-cell activation Sir Basil’s kidney hirsutism by preventing IL-2 transplant transcription “Pansirtopenia” Kidney “sir-vives.” (pancytopenia), Synergistic with mTOR inhibitor; binds insulin resistance, FKBP hyperlipidemia; cyclosporine not nephrotoxic Blocks T-cell Also used in drug- activation and B-cell differentiation by eluting stents preventing response to IL-2 Edema, hypertension, tremor Monoclonal antibody; blocks IL-2R
Immunology Immunology—Immunosuppressants SEC TION II 119 Immunosuppressants (continued) DRUG MECHANISM INDICATIONS TOXICITY NOTES Azathioprine Antimetabolite Rheumatoid arthritis, Pancytopenia 6-MP degraded by precursor of Crohn disease, xanthine oxidase; 6-mercaptopurine glomerulonephritis, toxicity by other autoimmune allopurinol Inhibits lymphocyte conditions proliferation by Pronounce “azathio- blocking nucleotide purine” synthesis Associated with Mycophenolate Reversibly inhibits Glucocorticoid-sparing GI upset, invasive CMV mofetil IMP dehydrogenase, agent in rheumatic pancytopenia, infection preventing purine disease hypertension synthesis of B and T Demargination cells Many autoimmune Less nephrotoxic and of WBCs causes and inflammatory neurotoxic artificial leukocytosis Glucocorticoids Inhibit NF-κB disorders, adrenal Suppress both B- and insufficiency, asthma, Cushing syndrome, Adrenal insufficiency CLL, non-Hodgkin osteoporosis, may develop if drug is T-cell function by lymphoma hyperglycemia, stopped abruptly after transcription of diabetes, amenorrhea, chronic use adrenocortical many cytokines atrophy, peptic ulcers, psychosis, cataracts, Induce T cell apoptosis avascular necrosis (femoral head) Recombinant cytokines and clinical uses CYTOKINE AGENT CLINICAL USES Bone marrow stimulation Anemias (especially in renal failure) Associated with risk of hypertension, Erythropoietin Epoetin alfa (EPO analog) thromboembolic events Colony stimulating Filgrastim (G-CSF), Sargramostim (GM-CSF) Leukopenia; recovery of granulocyte and factors Romiplostim (TPO analog), eltrombopag (think monocyte counts Thrombopoietin “elthrombopag.” TPO receptor agonist) Autoimmune thrombocytopenia Platelet stimulator Immunotherapy Aldesleukin Interleukin-2 IFN-α Renal cell carcinoma, metastatic melanoma Interferons Chronic hepatitis C (not preferred) and B, renal IFN-β IFN-γ cell carcinoma Multiple sclerosis Chronic granulomatous disease uploaded by medbooksvn
120 SEC TION II Immunology Immunology—Immunosuppressants Therapeutic antibodies AGENT TARGET CLINICAL USE NOTES Autoimmune disease therapy Adalimumab, Soluble TNF-α IBD, rheumatoid arthritis, Pretreatment screening certolizumab, ankylosing spondylitis, (TB, HBV, HCV, VZV, golimumab, psoriasis EBV, CMV) due to risk of infliximab reactivation Paroxysmal nocturnal Eculizumab Complement protein C5 hemoglobinuria Etanercept is a decoy IL-23 TNF-α receptor and not a Guselkumab IL-17A Psoriasis monoclonal antibody Ixekizumab, α4-integrin Psoriasis, psoriatic arthritis secukinumab Associated with risk of Natalizumab IL-12/IL-23 Multiple sclerosis, Crohn meningococcal infection α4-integrin disease Ustekinumab α4-integrin: WBC adhesion Vedolizumab Psoriasis, psoriatic arthritis Risk of PML in patients with IBD JC virus Gut-specific anti-integrin, preventing migration of leukocytes to the gastrointestinal tract Other applications RANKL Osteoporosis; inhibits osteoclast Denosumab helps make dense Denosumab maturation (mimics bones osteoprotegerin) Emicizumab Factor IXa and X Bispecific; mimics factor VIII Omalizumab IgE Hemophilia A Palivizumab—virus Palivizumab RSV F protein Refractory allergic asthma; prevents IgE binding to FcεRI RSV prophylaxis for high-risk infants
HIGH-YIELD PRINCIPLES IN Microbiology “That within one linear centimeter of your lower colon there lives and ` Basic Bacteriology 122 works more bacteria (about 100 billion) than all humans who have ever been born. Yet many people continue to assert that it is we who are in ` Clinical Bacteriology 132 charge of the world.” ` Mycology 149 —Neil deGrasse Tyson ` Parasitology 152 “What lies behind us and what lies ahead of us are tiny matters compared to what lies within us.” ` Virology 159 —Henry S. Haskins ` Systems 175 “Wise and humane management of the patient is the best safeguard ` Antimicrobials 184 against infection.” —Florence Nightingale “I sing and play the guitar, and I’m a walking, talking bacterial infection.” —Kurt Cobain Microbiology questions on the Step 1 exam often require two (or more) steps: Given a certain clinical presentation, you will first need to identify the most likely causative organism, and you will then need to provide an answer regarding some features of that organism or relevant antimicrobial agents. For example, a description of a child with fever and a petechial rash will be followed by a question that reads, “From what site does the responsible organism usually enter the blood?” This section therefore presents organisms in two major ways: in individual microbial “profiles” and in the context of the systems they infect and the clinical presentations they produce. You should become familiar with both formats. When reviewing the systems approach, remind yourself of the features of each microbe by returning to the individual profiles. Also be sure to memorize the laboratory characteristics that allow you to identify microbes. 121 uploaded by medbooksvn
122 SEC TION II Microbiology microbiology—Basic Bacteriology ` MICROBIOLOGY—BASIC BACTERIOLOGY Bacterial structures CHEMICAL COMPOSITION FUNCTION STRUCTURE Proteins Motility Glycoprotein Appendages Mediate adherence of bacteria to cell surface; Flagellum sex pilus forms during conjugation Pilus/fimbria Keratinlike coat; dipicolinic acid; peptidoglycan, Gram ⊕ only Specialized structures DNA Spore Survival: resist dehydration, heat, chemicals Cell envelope Discrete layer usually made of polysaccharides Protects against phagocytosis Capsule (and rarely proteins) Mediates adherence to surfaces, plays a role in Slime (S) layer Loose network of polysaccharides biofilm formation (eg, indwelling catheters) Outer membrane Outer leaflet: contains endotoxin (LPS/LOS) Gram ⊝ only Embedded proteins: porins and other outer Endotoxin: lipid A induces TNF and IL-1; Periplasm membrane proteins (OMPs) antigenic O polysaccharide component Cell wall Inner leaflet: phospholipids Most OMPs are antigenic Porins: transport across outer membrane Cytoplasmic Space between cytoplasmic membrane membrane and outer membrane in gram ⊝ bacteria Accumulates components exiting gram (peptidoglycan in middle) ⊝ cells, including hydrolytic enzymes (eg, β-lactamases) Peptidoglycan is a sugar backbone with peptide side chains cross-linked by transpeptidase Netlike structure gives rigid support, protects against osmotic pressure damage Phospholipid bilayer sac with embedded proteins (eg, penicillin-binding proteins Site of oxidative and transport enzymes; PBPs [PBPs]) and other enzymes involved in cell wall synthesis Lipoteichoic acids (gram positive) only extend Lipoteichoic acids induce TNF-α and IL-1 from membrane to exterior Cell envelope Common to both Unique to Flagellum gram ⊝ Unique to Pilus gram Capsule Endotoxin/LPS Outer Lipoteichoic acid Porin membrane Cell wall Wide periplasmic space Gram Peptidoglycan containing β-lactamase Cytoplasmic membrane Gram ⊝
Microbiology microbiology—Basic Bacteriology SEC TION II 123 Stains First-line lab test in bacterial identification. Bacteria with thick peptidoglycan layer retain crystal Gram stain violet dye (gram ⊕); bacteria with thin peptidoglycan layer turn red or pink (gram ⊝) with counterstain. Giemsa stain Periodic acid–Schiff These bugs do not Gram stain well (These Little Microbes May Unfortunately Lack Real Color stain But Are Everywhere): Ziehl-Neelsen stain (carbol fuchsin) Treponema, Leptospira Too thin to be visualized India ink stain Silver stain Mycobacteria Cell wall has high lipid content Fluorescent antibody stain Mycoplasma, Ureaplasma No cell wall A Legionella, Rickettsia, Chlamydia, Bartonella, Primarily intracellular; also, Chlamydia lack Anaplasma, Ehrlichia classic peptidoglycan because of muramic acid Chlamydia, Rickettsia, Trypanosomes A , Clumsy Rick Tripped on a Borrowed Borrelia, Helicobacter pylori, Plasmodium Helicopter Plastered in Gems Stains glycogen, mucopolysaccharides; used PaSs the sugar to diagnose Whipple disease (Tropheryma whipplei B ) Acid-fast bacteria (eg, Mycobacteria C , Auramine-rhodamine stain is more often used Nocardia; stains mycolic acid in cell wall); for screening (inexpensive, more sensitive) protozoa (eg, Cryptosporidium oocysts) Cryptococcus neoformans D ; mucicarmine can also be used to stain thick polysaccharide capsule red Helicobacter pylori, Legionella, Bartonella HeLiCoPters Are silver henselae, and fungi (eg, Coccidioides E , Pneumocystis jirovecii, Aspergillus fumigatus) Used to identify many bacteria, viruses, Example is FTA-ABS for syphilis Pneumocystis jirovecii, Giardia, and Cryptosporidium BCDE uploaded by medbooksvn
124 SEC TION II Microbiology microbiology—Basic Bacteriology Special culture requirements BUG MEDIA USED FOR ISOLATION MEDIA CONTENTS/OTHER H influenzae Chocolate agar Factors V (NAD+) and X (hematin) Selectively favors growth of Neisseria by N gonorrhoeae, Thayer-Martin agar N meningitidis inhibiting growth of gram ⊕ organisms with vancomycin, gram ⊝ organisms except B pertussis Bordet-Gengou agar (Bordet for Bordetella) Neisseria with trimethoprim and colistin, and Regan-Lowe medium fungi with nystatin C diphtheriae Tellurite agar, Löffler medium Very typically cultures Neisseria M tuberculosis Löwenstein-Jensen medium, Middlebrook Potato extract Charcoal, blood, and antibiotic M pneumoniae medium, rapid automated broth cultures Lactose-fermenting Eaton agar Requires cholesterol enterics MacConkey agar Fermentation produces acid, causing colonies to E coli Brucella, Francisella, Eosin–methylene blue (EMB) agar turn pink Legionella, Charcoal yeast extract agar buffered with Colonies with green metallic sheen Pasteurella The Ella siblings, Bruce, Francis, a cysteine and iron Fungi legionnaire, and a pasteur (pastor), built the Sabouraud agar Sistine (cysteine) chapel out of charcoal and iron “Sab’s a fun guy!”
Microbiology microbiology—Basic Bacteriology SEC TION II 125 Anaerobes Examples include Clostridium, Bacteroides, Anaerobes Can’t Breathe Fresh Air. Facultative anaerobes Fusobacterium, and Actinomyces israelii. They Anaerobes are normal microbiota in GI lack catalase and/or superoxide dismutase and are thus susceptible to oxidative damage. tract, typically pathogenic elsewhere. Generally foul smelling (short-chain fatty AminO2glycosides are ineffective against acids), are difficult to culture, and produce gas anaerobes because these antibiotics require O2 in tissue (CO2 and H2). to enter into bacterial cell. May use O2 as a terminal electron acceptor to Streptococci, staphylococci, and enteric gram ⊝ generate ATP, but can also use fermentation bacteria. and other O2-independent pathways. Intracellular bacteria Rickettsia, Chlamydia, Coxiella Stay inside (cells) when it is Really Chilly and Obligate intracellular Rely on host ATP Cold Facultative Salmonella, Neisseria, Brucella, Mycobacterium, Some Nasty Bugs May Live FacultativeLY intracellular Listeria, Francisella, Legionella, Yersinia pestis Encapsulated bacteria Examples are Pseudomonas aeruginosa, Please SHiNE my SKiS. A Streptococcus pneumoniae A , Haemophilus Are opsonized, and then cleared by spleen. influenzae type b, Neisseria meningitidis, Escherichia coli, Salmonella, Klebsiella Asplenics (No Spleen Here) have opsonizing pneumoniae, and group B Strep. Their ability and thus risk for severe infections; capsules serve as an antiphagocytic virulence need vaccines to protect against: factor. N meningitidis S pneumoniae Capsular polysaccharide +/– protein conjugate H influenzae can serve as an antigen in vaccines. A polysaccharide antigen alone cannot be presented to T cells; immunogenicity can be enhanced by conjugating capule antigens to a carrier protein. Urease-positive Proteus, Cryptococcus, H pylori, Ureaplasma, Pee CHUNKSS. organisms Nocardia, Klebsiella, S epidermidis, S saprophyticus. Urease hydrolyzes urea to release ammonia and CO2 pH. Predisposes to struvite (magnesium ammonium phosphate) stones, particularly Proteus. uploaded by medbooksvn
126 SEC TION II Microbiology microbiology—Basic Bacteriology Catalase-positive Catalase degrades H2O2 into H2O and bubbles of O2 A before it can be converted to microbicidal organisms products by the enzyme myeloperoxidase. People with chronic granulomatous disease (NADPH A oxidase deficiency) have recurrent infections with certain catalase ⊕ organisms. Big Catalase ⊕ organisms include Bordetella pertussis, Helicobacter pylori, Burkholderia cepacia, Nocardia, Pseudomonas, Listeria, Aspergillus, Candida, E coli, Serratia, Staphylococci. Cats Have BeeN to PLACESS. Pigment-producing Actinomyces israelii—yellow “sulfur” granules, Israel has yellow sand bacteria which are composed of filaments of bacteria Aureus (Latin) = gold S aureus—golden yellow pigment Aerugula is green P aeruginosa—blue-green pigment (pyocyanin Think red Sriracha hot sauce and pyoverdin) Serratia marcescens—red pigment In vivo biofilm S epidermidis Catheter and prosthetic device infections producing bacteria Viridans streptococci (S mutans, S sanguinis) P aeruginosa Dental plaques, infective endocarditis Nontypeable (unencapsulated) H influenzae Respiratory tree colonization in patients with cystic fibrosis, ventilator-associated pneumonia Contact lens–associated keratitis Otitis media
Microbiology microbiology—Basic Bacteriology SEC TION II 127 Spore-forming Some gram ⊕ bacteria can form spores when Examples: B anthracis (anthrax), B cereus (food bacteria nutrients are limited. Spores lack metabolic poisoning), C botulinum (botulism), C difficile activity and are highly resistant to heat (pseudomembranous colitis), C perfringens and chemicals. Core contains dipicolinic (gas gangrene), C tetani (tetanus). acid (responsible for heat resistance). Must autoclave to kill spores (as is done to surgical Autoclave to kill Bacillus and Clostridium equipment) by steaming at 121°C for 15 (ABC). minutes. Hydrogen peroxide and iodine-based agents are also sporicidal. Bacterial virulence These promote evasion of host immune response. factors Capsular Highly charged, hydrophilic structure. Acts as barrier to phagocytosis and complement-mediated lysis. Major determinant of virulence. polysaccharide Protein A Binds Fc region of IgG. Prevents opsonization and phagocytosis. Expressed by S aureus. IgA protease Enzyme that cleaves IgA, allowing bacteria to adhere to and colonize mucous membranes. Secreted M protein by S pneumoniae, H influenzae type b, and Neisseria (SHiN). Helps prevent phagocytosis. Expressed by group A streptococci. Sequence homology with human cardiac myosin (molecular mimicry); possibly underlies the autoimmune response seen in acute rheumatic fever. uploaded by medbooksvn
128 SEC TION II Microbiology microbiology—Basic Bacteriology Bacterial genetics Competent bacteria can bind and import short Degraded Recipient DNA Transformation pieces of environmental naked bacterial uncombined Donor DNA chromosomal DNA (from bacterial cell Conjugation lysis). The transfer and expression of newly DNA F+ × F– transferred genes is called transformation. A feature of many bacteria, especially Naked DNA Recipient cell Transformed cell Hfr × F– S pneumoniae, H influenzae type b, and Neisseria (SHiN). Transduction Generalized Adding deoxyribonuclease degrades naked DNA, preventing transformation. F+ plasmid contains genes required for sex pilus F+ plasmid contains Single strand of No transfer of and conjugation. Bacteria without this plasmid genes for sex pilus and Sex pilus forming congugal plasmid DNA chromosomal DNA are termed F–. Sex pilus on F+ bacterium contacts F− bacterium. A single strand conjugation bridge “mating bridge” transferred of plasmid DNA is transferred across the conjugal bridge (“mating bridge”). No transfer F+ plasmid contains Single strand of No transfer of of chromosomal DNA. genes for sex pilus and Sex pilus forming congugal plasmid DNA chromosomal DNA F+ plasmid can become incorporated into conjugation bridge “mating bridge” transferred F+ cell F+ cell bacterial chromosomal DNA, termed high- frequency recombination (Hfr) cell. Transfer F+ cell F– cell F+ cell F– cell F+ cell F– cell of leading part of plasmid and a few flanking chromosomal genes. High-frequency High-frequency recombination Leading portion of plasmid recombination may integrate some of those (Hfr) cell contains F+ plasmid transfers along with flanking bacterial genes. Recipient cell remains F– but F+ cinelclorpFo–rcaetelld into baFc+tceerilal l DNF–Ac.ell baFc+tceerilal l chFr–ocmelol some F+ cell F+ cell now may have new bacterial genes. Plasmid High-frequency recombination Leading portion of plasmid (Hfr) cell contains F+ plasmid transfers along with flanking incorporated into bacterial DNA. bacterial chromosome F+ cell F– cell Hfr cell F– cell Hfr cell F– cell Hfr cell Recombinant Plasmid F– cell F+ cell F– cell Hfr cell F– cell F– cell +F– ceblal ctFe+rciaelllDHNfrAce+ll Rpelacsommidbicnoapnyt bacterHiafrl DceNlAl F– cell F– cell + F+ cell + plasmid copy bacterial DNA bacterial DNA A “packaging” error. Lytic phage infects Lytic Cleavage of Bacterial DNA packaged bacterium, leading to cleavage of bacterial phage Bacteria bacterial DNA in phage capsids DNA. Parts of bacterial chromosomal DNA may become packaged in phage capsid. Phage infects another bacterium, transferring these genes. Release of new phage Infects other Genes transferred from lysed cell bacteria to new bacteria Phage particles Specialized An “excision” event. Lysogenic phage infects Lysogenic Viral DNA Viral DNA carry bacterial DNA bacterium; viral DNA incorporates into phage incorporates in Bacteria bacterial DNA Genes di erent from donor and recipient bacterial chromosome. When phage DNA is excised, flanking bacterial genes may be excised with it. DNA is packaged into phage capsid and can infect another bacterium. Genes for the following 5 bacterial toxins are encoded in a lysogenic phage (ABCD’S): Group A strep erythrogenic toxin, Botulinum toxin, Release of new phage Infects other Cholera toxin, Diphtheria toxin, Shiga toxin. from lysed cell bacteria
Microbiology microbiology—Basic Bacteriology SEC TION II 129 Bacterial genetics (continued) Transposition A “jumping” process involving a transposon Plasmid (specialized segment of DNA), which can copy and excise itself and then insert into the same DNA molecule or an unrelated DNA (eg, Integration of genes plasmid or chromosome). Critical in creating plasmids with multiple drug resistance and Transposon Bacterial DNA transfer across species lines (eg, Tn1546 with Target site vanA from Enterococcus to S aureus). Main features of exotoxins and endotoxins Exotoxins Endotoxins Outer cell membrane of most gram ⊝ bacteria SOURCE Certain species of gram ⊕ and gram ⊝ bacteria No Lipid A component of LPS (structural part of SECRETED FROM CELL Yes bacteria; released when lysed) CHEMISTRY Polypeptide Bacterial chromosome Low (fatal dose on the order of hundreds of LOCATION OF GENES Plasmid or bacteriophage TOXICITY High (fatal dose on the order of 1 µg) micrograms) Fever, shock (hypotension), DIC CLINICAL EFFECTS Various effects (see following pages) Induces TNF, IL-1, and IL-6 MODE OF ACTION Various modes (see following pages) Poorly antigenic ANTIGENICITY Induces high-titer antibodies called antitoxins No toxoids formed and no vaccine available VACCINES Toxoids used as vaccines Stable at 100°C for 1 hr HEAT STABILITY Destroyed rapidly at 60°C (except Meningococcemia; sepsis by gram ⊝ rods TYPICAL DISEASES staphylococcal enterotoxin and E coli heat- stable toxin) Endotoxin Tetanus, botulism, diphtheria, cholera Exotoxin Downstream TNF, IL-1, cellular reaction IL-6 Host cell uploaded by medbooksvn
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