Exam II Study Guide PDF

# Exam II Study Guide ## 1. Define cytokine. Generic term for soluble polypeptides produced by various cells, generally in response to infection or another antigen. Cytokines are involved in the innate and adaptive immune response and is the primary mechanism of cell-cell communication with immune...

# Exam II Study Guide ## 1. Define cytokine. Generic term for soluble polypeptides produced by various cells, generally in response to infection or another antigen. Cytokines are involved in the innate and adaptive immune response and is the primary mechanism of cell-cell communication with immune system. ## 2. List the characteristics common to most cytokines. - Tightly regulated expression - Cytokine may act locally or systemically (autocrine, paracrine, or endocrine) - May be pleiotropic (one cytokine can act on multiple cells with multiple functions) or redundant (more than one cytokine with the same function) - Actions of different cytokines may be synergistic or antagonistic - Cytokines exert action on cells through cell-surface receptors - Cells possess variety of mechanisms that down-regulate cytokine-mediated activation - Not pre-formed or stored, rapidly secreted after being made - Short half-life - Ultimately results in transcription and translation of new proteins ## 3. Summarize the six cytokine classes with their associated function in the immune system: - **Interleukins:** communication between WBCS - **Interferons:** broad pro-inflammatory cytokine - **Tumor necrosis factor:** mediates immune response to bacteria - **Colony-stimulating factors:** mediates survival and differentiation of immune precursor cells - **Transforming growth factors:** inhibits proliferation and activation of WBCs - **Chemokines:** regulates migration of WBCs ## 4. Correctly identify the functions of the cytokines including: - **Pleiotropic:** one cytokine can act on multiple cells and have multiple functions - **Redundant:** two or more cytokines can have the same function - **Synergistic:** the combined action of multiple cytokines is greater than the sum of actions of a single cytokine - **Antagonistic:** the action of one cytokine can have the opposite effect on the action of another or can downregulate its action ## 5. Summarize the cytokines important to: ### a. innate immunity - Major cell source: macrophages - Primary function in the immune system: mediate inflammation - Cellular target and biological effects: ### b. adaptive immunity - Major cell source: T cells - Primary function in the immune system: regulate lymphocyte proliferation and differentiation and activate effector cells - Cellular target and biological effects: ### c. hematopoiesis - Major cell source: BM stromal cells, fibroblasts, etc. - Primary function in the immune system: promote development of mature leukocytes from myeloid and lymphoid progenitor cells - Cellular target and biological effects: ## 6. List the three roles of Th1 cells in the | Cytokine | Cellular Target | Biologic Effect | |---|---|---| | IL-2 | T cells | Proliferation and survival | | | NK cells | Proliferation and activation | | | B cells | Proliferation and Ab production | | IFN-g | B cells | Differentiation to TH1 class | | | T cells | Isotype-switching to IgG | | TNF-b | Neutrophils | Recruitment and activation of phagocytosis | ## 7. List the four roles of Th2 cells in the | Cytoki ne | Cellular Target | Biologic Effect | |---|---|---| | IL-4 | T cells | TH2 differentiation | | | B cells | Isotype-switching to IgE | | | Macrophages | Inhibition of phagocytosis | | | Eosinophils | Increased proliferation and activation | | IL-5 | B cells | Isotype-switching to IgA | | IL-10 | Macrophages | Inhibition of activation | | | T cells | Inhibition of activation | | TGF-b | B cells | Isotype-switching to IgA | | | Macrophages | Inhibition of activation | ## 8. Describe the 5 classes of cytokine and chemokine receptors ### a. Immunoglobulin-Like Receptor Family IL-1, IL-18 - **Extracellular domain** - At least one immunoglobulin-like domain - **Transmembrane domain** - Single pass through cellular membrane - Composed mainly of hydrophobic residues - **Intracellular domain** - Toll/IL-1 receptor (TIR) motif that binds to IL-1 receptor associated kinase (IRAK) - IRAKs phosphorylate ІкВ - ІкВ dissociates from NF-kB - NF-kB translocates to nucleus and mediates transcription ### b. Type I Cytokine Receptor Family ☐ IL-2, IL-5 - **Dimeric or trimeric receptors** - One cytokine-binding sub-unit - One or two signaling sub-units - **Extracellular domain** - At least one domain with two conserved cysteine residue pairs - Membrane proximal WSXWS motif - **Transmembrane domain** - Similar to immunoglobulin-like receptor family (Single pass through cellular membrane Composed mainly of hydrophobic residues) - **Intracellular domain** ### c. Type II Cytokine Receptor Family IFN-a, IL-10 - **Dimeric receptors** - One cytokine-binding sub-unit - One signaling sub-unit - **Extracellular domain** - At least one domain with two conserved cysteine residue pairs - **Transmembrane domain** - Similar to type I cytokine receptor family (Single pass through cellular membrane Composed mainly of hydrophobic residues) - **Intracellular domain** ### d. TNF Receptor Family TNF-a, TNF-b - **Receptor structure** - Trimeric receptor - **Extra-cellular domain** - Cysteine-rich cytokine binding domain - Similar in structure to type I and type II cytokine receptors - (At least one domain with two conserved cysteine residue pairs) - **Intra-cellular domain** - “Death domains" in cytoplasmic tail bind to TNF receptor-associated death domains (TRADDs) - TRADDs form complex with TNF-receptor associated factors (TRAFs) - TRAFs initiate signaling through 2 pathways (MAP kinase pathway and NF-kB pathway) ### e. G-Protein Coupled Receptor Family - Chemokines - **Extra-cellular and transmembrane domains** - Single polypeptide that spans the cellular membrane seven times (4 extra-cellular loops, 3 intra-cellular loops) - Extra-cellular loops form chemokine-binding domains - **Intra-cellular domain** - Signaling mediated through G proteins - G proteins exist bound to GDP - Binding of chemokine to receptor initiates change in structure of G protein (G protein exchanges GTP for GDP) - GTP-bound form of G-protein initiates various signaling cascades ## 9. List the unique structural features and signaling mechanisms associated with the cytokine receptor families. ## 10. Compare and contrast a normal immune reaction and a hypersensitivity reaction. - **Normal immune reaction:** protects host against invading organisms - **Hypersensitivity reaction:** a pathogenic immune response resulting in damage to host tissue, caused by either an uncontrolled immune response or one against inappropriate antigens ## 11. Describe the 4 types of hypersensitivity reactions ### a. Type I - Immediate hypersensitivity - Dependent on IgE and mast cells ### b. Type II - Antibody-mediated hypersensitivity - Dependent IgM and IgG antibodies ### c. Type III - Immune complex-mediated hypersensitivity - Dependent on immune complexed between antigens and IgG or IgM ### d. Type IV: - T cell-mediated hypersensitivity - Dependent on CD4+ and CD8+ T cells ## 12. Compare and contrast IgE and mast cells. - **IgE:** - Least abundant Ig (20ng/mL) - Shortest half-life of any Ig (2 days) - Not present free in circulation (bound to receptors) - **Mast cells:** - Express high-affinity receptors for IgE - Reide in most tissues (skin and GI tract) - Contain many granules holding inflammatory mediators ## 13. List and describe the phases of type I hypersensitivity reactions - **Sensitization phase:** production of IgE in response to specific antigen - **Activation phase:** initiation of mast cell activation upon re-exposure to antigen - **Effector phase:** generation of inflammatory molecules ## 14. List the biological effects of Type I hypersensitivity. - Triggered by exposure to specific allergens (e.g., pollen, dust mites, food, insect stings). The response involves the production of IgE antibodies that sensitize mast cells and basophils - Mast cell degranulation releases histamine and other pro-inflammatory mediators - Inflammation - Edema and swelling - Redness - Smooth muscle contraction (broncho and GI) - Anaphylaxis - Tissue damage and chronic inflammation ## 15. List the pathologic mechanisms involved in each of the hypersensitivity reactions. - **Type I:** Immediate, IgE and mast cells - **Type II:** Antibody-mediated (IgG and IgM) - **Type III:** Immune complex-mediated hypersensitivity (antigens and IgG or IgM) - **Type IV:** T cell-mediated (CD4+ and CD8+) hypersensitivity ## 16. List diseases associated with Type I hypersensitivity. - Common manifestation of allergic disease (dermatitis, eczema, gastrointestinal, rhinitis) - Allergic march (progression of allergic disease in children) - Children < 1 year: development of atopic dermatitis (eczema) - Children 1-4 years: continuation or slight decrease in atopic dermatitis, development of GI symptoms - Children 4-15 years: decrease in dermatitis and GI symptoms, development of allergic rhinitis and asthma ## 17. Define anaphylaxis. Acute, often life-threatening, systemic allergic response induced be exposure to specific allergen. Generally accompanied release of inflammatory mediators and mast cells. ## 18. List clinical symptoms of anaphylaxis - Pruritus - Edema (skin and airway) - Bronchospasm - Tachycardia/arrhythmia - Hypotension - Nausea/vomiting ## 19. Identify diagnostic criteria for allergic disease - Compatible clinical history (correlation of clinical symptoms and allergen exposure) - Identification of allergen-specific IgE (in vivo skin testing or in vitro IgE assay) - Demonstration that exposure to allergen results in clinical disease (food challenge or inhalant challenge) ## 20. List and identify classes of allergens - Inhalants - Foods - Drugs - Insects - Occupational ## 21. List and identify the different laboratory testing - Total immunoglobulin E - Allergen-specific IgE (inhalant allergy, food allergy, venom allergy, drug allergy) - Inflammatory mediators (histamine, tryptase) ## 22. Diagram FEIA testing. ## 23. Discuss the clinical utility of in vitro total IgE testing. - Most common method - Sandwich immunoassay between two anti-IgE antibodies - Diagnosis of allergic disease (doesn't rule it out) - Determination of proper dosage of anti-IgE therapy - Diagnosis of allergenic bronchopulmonary aspergillosis - Diagnosis of hyper IgE syndrome ## 24. Identify testing for allergen-specific IgE. - Allergen-specific measures IgE antibodies that bind to specific antigens (inhalant allergy, food allergy, venom allergy, drug allergy) - Two approaches - In vivo: skin testing - In vitro: allergen-specific IgE by immunoassay ## 25. Explain the clinical utility of specific IgE testing. - Comparison of skin testing and in vitro testing - Both identify sensitized individual - In vitro testing has superior quantitative ability compared to skin testing - Provide evidence for diagnosis of allergic disease - Define probability that exposure to allergen will result in clinical allergic response - Related to quantitation of allergen-specific IgE - Identify clinically-relevant IgE - Optimize treatment strategy - Allergen avoidance - Immunotherapy ## 26. Compare and contrast tryptase and histamine testing. - **Tryptase:** - Protease responsible for protein degradation and tissue damage - Released from activated mast cells - Generally only measured in serum or plasma, long half-life about 2 hours - **Histamine:** - Responsible for vascular permeability - Released from activated mast cells - May be measured in plasma or urine (histamine or N-methylhistamine), short half-life about 30 mins ## 27. Identify disease states associated with each of the hypersensitivity reactions. ### Type I: - Allergic rhinitis (hay fever) - Asthma - Atopic dermatitis (eczema) - Food allergies - Anaphylaxis ### Type II: - AIHA - Goodpasture syndrome - Graves' disease - Rheumatic fever ### Type III: - SLE - Rheumatoid arthritis - Post-strep glomerulonephritis - Serum sickness ### Type IV: - Contact dermatitis - Tuberculosis - Graft-versus-Host Disease (GVHD) - Multiple sclerosis (MS) ## 28. Define: ### a. central tolerance - Tolerance derived during early stages of lymphocyte development - Occurs in primary lymphoid organs - Purpose: educate immature lymphocytes ### b. peripheral tolerance - Tolerance induced in mature lymphocytes - Occurs in secondary lymphoid organs and in periphery - Purpose: prevent activation of autoreactive lymphocytes that escape central tolerance ### c. autoimmune disease - Chronic inflammatory disorder caused by reaction of immne system againt autoantigen (antigen derived from self protein) ## 29. Explain: ### a. normal immune response - Elimination of pathogens or foreign substances without damage to self-tissues ### b. autoimmune response - An abnormal immune response where the immune system mistakenly attacks the body's own cells or tissues, leading to disease - System fails to see self-antigens as self and generates autoantibodies - Chronic inflammation and tissue damage: the immune system continuously attacks healthy cells, causing tissue destruction and inflammation ## 30. Describe: ### a. Type II hypersensitivity reactions - Soluble antibody mediated (IgG and IgM) ### b. Type III hypersensitivity reactions - Immune-complex mediated (IgG and IgM) ### c. Type IV hypersensitivity reactions - T-cell mediated (CD4+ and CD8+) ## 31. Explain complement, ADCC and functional antibody for Type II hypersensitivity reaction. - **Type II hypersensitivity reaction:** Antibody (IgG or IgM)-mediated mechanisms responsible for tissue damage - **Complement:** cells are lysed by complement due to antibody binding target cell, promoting phagocytosis through opsonization - **ADCC:** antibody-dependent cell-mediated cytotoxicity, antibody binds to antigen on cell surface, Fc receptors on NK cells recognize the antibody causing it to activate, degranulate, and kill the cell - **Functional antibodies:** antibodies bind antigen on cell surface and are antagonistic (block receptor function, e.g. Myasthenia gravis) or agonistic (stimulate receptor activity, e.g. grave's disease) ## 32. Identify the hypersensitivity reaction associated with the various autoimmune diseases: - **Type 1:** immediate, IgE - **Type 2:** antibody - **Type 3:** immune complex - **Type 4:** T cell ### a. transfusion reaction - **Type 2** - Antibody-mediated, complement activation, RBC lysis due to ABO incompatibility ### b. hemolytic disease of the newborn - **Type 2** - IgG (can cross placenta) antibodies against Rh+ fetal RBCs, complement activation, opsonization, and phagocytosis ### c. myasthenia gravis - **Type 2** - Antagonistic antibodies against acetylcholine receptors, impair neuromuscular transmission ### d. grave's disease - **Type 2** - Agonistic antibodies against thyroid-stimulating hormone receptor, overstimulation of thyroid hormone production ### e. systemic lupus erythematosus - **Type 3** - Immune complexes form and deposit in tissues, activating complement and causing inflammation - **Type 3** ### f. polyarteritis nodosa - **Type 3** - Immune complex-mediated vasculitis affecting medium-sized arteries ### g. type I diabetes - **Type 4** - T-cell mediated destruction of insulin-producing beta cells in the pancreas ## 33. Explain immune complexes with Type III hypersensitivity reactions. - Immune complex = antigen + antibody (IgG or IgM) - Complexes deposit in tissues (kidneys, joints, and blood vessels) causing complement activation, inflammation, and tissue damage ## 34. List the two stages in a Type IV hypersensitivity reaction - **Sensitization stage:** (generate antigen-specific TH1 cells) - **Elicitation stage:** (antigens activate TH1 cells and inflammatory response) ## 35. Describe laboratory tests used for the detection of autoantibodies: ### a. qualitative methods - Passive gel diffusion (single or double/Ouchterlony) - Immunoelectrophoresis ### b. quantitative methods - Gel-based methods (radial immunodiffusion, electroimmunoassay) - Precipitation/nephelometry - Labeled immunochemical assays ## 36. Match the clinical disease with the autoantibodies. - **Systemic lupus erythematosus** - Anti-nuclear antibody (ANA) - Anti-dsDNA antibody - **Rheumatoid arthritis** - Rheumatoid factor - Anti-CCP antibody - **Anti-phospholipid syndrome** - Anti-cardiolipin antibody - **Celiac disease** - Anti-TTG antibody - Anti-deamidated gliadin antibody - **Autoimmune hepatitis** - Anti-smooth muscle antibody - Anti-LKM-1 antibody - **Vasculitis** - Anti-neutrophil cytoplasmic antibody ## 37. Identify the diagnostic criteria for SLE - Photosensitivity and/or rash - Oral ulcers - Arthritis - Serositis - Renal disease - Neurologic disorder - Hematologic abnormalities - Seropositivity (ANA, Anti-dsDNA Ab, Anti-Sm Ab) ## 38. Define anti-nuclear antibodies (ANAs). - Antibodies that target nucler components of the cell (DNA, histones, etc.) that are typically released during cellular damage/apoptosis - Diagnostic markers: produce a variety of nuclear and cytoplasmic staining patterns on fixed cellular substrates as hallmarks of various autoimmune diseases ## 39. List the methodologies for autoimmunity laboratory testing - Immunofluorescence assay (IFA) - Enzyme immunoassay (EIA) - Bead-based assay (multiplex) ## 40. Match the IFA result with the target antigens. - Diffuse or homogeneous: dsDNA, histones - Peripheral or rim: dsDNA - Speckled: SS-A, SS-B, U1-RNP - Nucleolar: RNA polymerase, Scl-70 - Centromere: Centromere ## 41. Compare and contrast the advantages and disadvantages of IFA. ### Advantages: - Semi-quantitative (titer) - Identification of staining patterns suggest certain autoimmune disorder - Broad antigen specificity ### Disadvantages: - Labr intensive - Subject to interpretation (both titer and staining pattern), not amenable to automation ## 42. State the general characteristics of EIA (AKA ELISA) - Plate-based batch format - Extracted or purified antigen instead of tissue/cells - Detects bound antibody using enzyme and colorimetric reaction ## 43. Describe bead-based multiplex assays. - Detect antibodies to multiple antigens in one tube (separate results for each specificity) - Polystyrene beads with unique fluorescent signals, covalent antigen coupling to beads, flow-cytometry for bead suspension and detection - Beads pass through lasers, detecting signals: one from bead and one from detection antibody - Compare to standard curve ## 44. List the where the two fluorescent signals come from in the bead-based multiplex assay - Polystyrene bead: each set of beads has a unique fluorescent signal and corresponds to a different antigen - Labeled detection antibody: binds complex on bead if sample has the antibody, compare to standard curve to determine concentration ## 45. Identify and describe the characteristics of the five primary hepatitis viruses. | Virus | Source of Virus | Route of Transmission | Chronic Infection | Prevention | |---|---|---|---|---| | HAV | feces | fecal-oral | no | pre/post exposure immunization | | HBV | blood/blood-derived body fluids | percutaneosus permucosal | yes | pre/post exposure immunization | | HCV | blood/blood-derived body fluids | percutaneous permucosal | yes | blood donor screening; risk behavior modification | | HDV | blood/blood-derived body fluids | percutaneous permucosal | yes | pre/post exposure immunization risk behavior modification | | HEV | feces | fecal-oral | no | ensure safe drinking water | ## 46. List the viruses that may secondarily involve the liver as part of a systemic infection - Epstein Barr Virus (EBV) - Cytomegalovirus (CMV) - Rubella - Varicella-zoster virus (VZV) - Herpes Simplex virus (HSV) ## 47. List the hepatitis viruses that are RNA viruses - Hepatitis A virus (HAV) - Hepatitis C virus (HCV) - Hepatitis D virus (HDV) - Hepatitis E virus (HEV) ## 48. List the hepatitis viruses that are DNA viruses - Hepatitis B virus (HBV) ## 49. Compare: ### - Etiology - Fecal-oral: HAV, HEV - Blood/body fluids/mucosal: HBV, HCV, HDV - Contaminated food/water ### - Epidemiology - All ages - Worldwide (highest in developing countries, 90%) ### - Signs and symptoms - incubation period - 15-45 days (mean = 25 days) - prevention of the various types of hepatitis and HIV - Avoid endemic regions and infected people ## 50. List the confirmatory serologic testing for hepatitis A - Elevated serum ALT and AST levels - Serologic tests (anti-HAV IgM and/or IgG) ## 51. List the methods for serologic testing for hepatitis A. - Anti-HAV IgM - Qualitative - ΕIA, CIA - Acute hepatitis A - Anti-HAV Total (IgM + IgG) - Qualitative - ΕIA, CIA - Past or recovered hepatitis A - Immunity to hepatitis A (past infection or vaccination) - Anti-HAV IgG - Qualitative - CIA ## 52. Discuss the outcome for hepatitis A. - Usually acute and self-limited - Fulminant hepatitis and death: 0.1% - Relapse in 1-4mo is rare - No chronic or carrier state ## 53. Identify hepatitis B virus virologic nomenclature - HBV: Dane (complete) particle, infectious - HBsAg: surface antigen - HBcAg: core antigen (hepatocytes only) - HBeAg: 'e' antigen, in core of virus, measures infectivity - Anti-HBs: antibody to surface antigen (HBsAg); protective - Anti-HBc: antibody to core antigen (HBcAg); not protective - Anti-HBe: antibody to ‘e' antigen (HBeAg); not protective ## 54. Match the hepatitis B serologic test with the type of infection - HBsAg: acute infection, chronic carrier - Anti-HBs: recent and past infection - Anti-HBc IgM: acute infection - Anti-HBc Total: acute and previous infection - HBeAg: chronic carrier w/ viral replication - Anti-HBe: chronic carrier w/o viral replication ## 55. Explain the clinical picture for the diagnosis of hepatitis B. - Mode of infection: IV injection, blood transfusion, intercourse, childbirth - Incubation: 60-90 days on average - Jaundice - 1% acute case-fatality - Chronic infection more common <5 years - Mortality from chronic liver disease: 15-25% ## 56. Discuss how to prevent hepatitis B. - Avoid needlestick and sharp injuries - Screen blood donors for HBsAg - Avoiding contact with blood or body secretions of acute HBV or chronic carriers - Vaccination ## 57. Identify the clinical features for hepatitis C - Acute illness (jaundice): mild (~25%) - Incubation: average 6-7 weeks - Low case fatality rate - Chronic infection: 60-80% - Chronic hepatitis: 10-70% (most symptomatic) - Cirrhosis: <5-20% - Mortality from Chronic Liver Disease: 1 - 5% ## 58. Compare and contrast the modes of transmission for hepatitis C. - **Parenteral route:** injection (IV drug use) or infusion (blood transfusion) - **Non-parenteral route:** sporadic acute hepatitis, sexual contact ## 59. Name the method for confirmatory serologic hepatitis C testing. - HCV PCR - HCV RNA+ in acute and chronic HCV - HCV RNA- in resolved HCV infection ## 60. Describe the epidemiology for delta hepatitis. - Always requires HBV carrier for transmission, propagation, and disease - Prevalence: 1% of chronic HBV carriers - Same risk as HBV: IV drug use, hemophiliacs, homosexual males, transfusion recipients - Incubation period: 6-8wk ## 61. List the modes of transmission for delta hepatitis - Parenteral exposure: IV drug use, blood transfusion - Mucous membrane exposures - Sexual exposures ## 62. Name the epidemiologic features of hepatitis E - Transmission: contaminated food/water, fecal-oral - Geography: developing countries, travelers to these places, organ transplant recipients, hog farmers - Age groups: all ages, especially 15-39 ## 63. Identify the clinical features of hepatitis E - Incubation period: average 40 days - Case-fatality rate: 1%-3% overall, 15-25% in pregnant women - Illness severity: asymptomatic in 50%, severity increased with age - Chronic sequelae: none identified, no known carrier state, complete/lifelong immunity ## 64. List the FDA-mandated testing for screening in U.S. blood donors - HBsAg - HBc Total Ab - HCV Ab - HIV-1 + group O Ab (HIV-1 NAT) - CMV total Ab (only for WBC + products) - Syphilis - ZIKA PCR - WNV RNA - Chagas - Babesia ## 65. List the screening serologic test for HIV infection. - ΕΙΑ or CIA: - HIV-1 Antibody (Ab) - HIV-1 p24 Antigen (Ag) - HIV-2 Antibody (Ab) - HIV-1 / HIV-2 Antibody (Ab) - HIV-1 / HIV-2 + "O" Antibody (Ab) - HIV-1 Antibody (Ab) - HIV-1 Ab + HIV-2 Ab - Lateral Flow Immunochromatography (rapid test): - HIV-1 + HIV-2 Ab + HIV p24 Antigen (Ag) - Membrane immunoconcentration: - HIV-1 Ab - HIV-2 Ab - HIV-1 + HIV-2 Ab ## 66. List the confirmatory serologic test for HIV infection. - Western Blot - HIV-1 RNA qualitative PCR - HIV Proviral DNA PCR - Immunofluorescence Assay ## 67. List causes of indeterminate HIV-1 WB results - Nonspecific reactions - Acute HIV-1 infection - Hypergammaglobulinemia - Cross-reactive antibody (alloantibodies of pregnancy, HTLV-I/-II) - HIV-2 infection - Autoimmune diseases (SLE) ## 68. Diagram the principle of lateral flow devices. - Sample applied to the sample pad - Conjugate pad contains labeled antibodies/antigens - Sample flows across the membrane - Test line captures the target analyte, forming a visible signal if present - Control line confirms the test is valid - Absorbent pad absorbs excess liquid ## 69. List the clinical applications of rapid HIV antibody tests - Occupational exposure - Laboring women w/o prenatal HIV serologic testing - High-risk patients in ED - Public health and STD clinics - Resource-limited healthcare settings ## 70. Explain what primary immunodeficiencies (PIDs) are. - Defects of the immune system - Generally inherited, can be sporadic - Increased susceptibility to infections ## 71. List the broad classification of PIDs - B cell (humoral) defects - T cell (cellular) defects - Phagocytic (PMN and monocytic) defects - Complement (opsonic) defects ## 72. List the causes of secondary (acquired) immunodeficiencies such as: - Hematologic lymphoproliferative disorders - Other systemic processes and metabolic disorders - Viral infection - Surgical procedures and trauma - Premature/newborn - Hereditary and metabolic diseases - Immunosuppressive agents/drugs - Infectious diseases - Alcoholic cirrhosis - Immunosuppressive agents - Prednisone - Radiation - Anti-convulsants - Immunosuppressive drugs ## 74. Discuss the distribution and prevalence of PIDs. - Antibody deficiencies: 65% - Combined cellular and antibody deficiencies: 15% - Phagocytic deficiencies: 10% - Complement deficiencies: 5% - Cellular deficiencies: 5% ## 75. Describe the role of laboratory testing in the PIDs. - Accurate and early diagnosis (lifesaving in children) - Establishes whether recurrent infections are secondary to PID or not - Identification of specific genetic defect allows for early diagnosis and evaluation for associated sequelae - Allows genetic counseling for family members who may be affected ## 76. Define the genetic defects and general characteristics associated with examples of humoral, cellular, phagocytic, and complement deficiencies: ### a. XLA (X-linked agammaglobulinemia) - B cell deficiency (reduced to absent) - Defect in B cell development in the bond marrow due to defective Btk (Bruton's tyrosine kinase) - Profouond hypogammaglobulinemia - X linked - Recurrent sinopulmonary infections ### b. CVID (Common Variable Immunodeficiency) - B cell deficiency - Most common PID in adults - Broad and heterogenous clinical presentation (difficult to diagnose) - Only 10-25% of patients demonstrate familial inheritance ### c. Selective IgA Deficiency - B cell deficiency (due to an intrinsic B-cell defect or due to the presence of anti-IgA antibodies) - Serum IgA < 7mg/dL - Pathophysiology is heterogenous - Transient: due to medications - Deletions in IgA1 or A2 genes - Clinical presentation: - Increased frequency of GI disease - Increased lielihood of intestinal parasites - Antibodies to food proteins (10-fold increase in celiac disease) - Recurrent sinopulmonary infections - Autoimmune diseases ### d. IgG Subclass Deficiency - B cell deficiency - Total IgG is usually normal (or close), the deficiency is in a particular IgG subclass - Doesn't include IgG1 deficiency (70% of IgG) because when this is low, total IgG will be - Up to 20% of population can have 1+ IgG subclass deficiencies - Mostly asymptomatic - Recurrent URI (otitis, sinusitis, bronchitis) - IgG2 deficiency: most common in children and males, impaired polysaccharide responsiveness (IPR) - IgG3 deficiency: more common in adults, usually associated with another subclass deficiency - IgG4 deficiency: most common, respiratory infections, also seen in WAS, AT, CMC ### e. Selective IgM Deficiency - B cell deficiency - Associated with infection - Very rare - IgM levels < 10-15 mg/dL in children and <20-30 mg/dL in adults - Poor Ab response to vaccine antigens - May be asymptomatic or severe bacterial infections - T cell immunity is normal, and B cells are normal and express surface IgM (serum IgM is deficient) ### f. DiGeorge Syndrome - T cell deficiency - 22q11.2 deletion - CATCH 22 syndrome: Cardiac defects, abnormal facial features, thymic hypoplasia, cleft palate, hypocalcemia associated with 22q11.2 deletion ### g. Chronic Mucocutaneous Candidiasis - T cell deficiency: defective T-cell responses to Candida antigen - Persistent or recurrent infections of skin, nails, mucous membranes by Candida (esp C. albicans) - Seven clinical CMC subgroups - APECED/APS1 – Autoimmune polyendocrinopathy – candidiasis-ectodermal dysplasia, autosomal recessive (AR) disease due to mutations in the AIRE gene. - Susceptible to other diseases and infections ### h. Wiskott-Aldrich Syndrome - Combined B and T cell abnormalities - X-linked - Characteristics: reduced platelets, eczema, recurrent infections, and increased risk of autoimmunity and lymphoid malignancies - Defect in WASP gene ### i. Ataxia-Telangiectasia - Combined B and T cell deficiency - Autosomal recessive - progressive cerebellar neurodegeneration, immunodeficiency, cutaneous anomalies (including telangiectasia), radiation sensitivity, premature aging, predisposition to malignancies - Lymphopenia - Defect in ATM gene - Increased serum a-fetoprotein (AFP) in children > 8 mo - Immunological defects are very variable and can affect humoral and cellular immunity ### j. Hereditary Angioedema - Complement deficiency (dysfunctional C1 esterase inhibitor) - Causes uncontrolled C1, C2, C4 in kallikrein pathway → produces many vasoactive peptides - Causes increased vascular permeability → edema - Treat with recombinant C1 esterase inhibitor - Diagnosis: clinical features and test C1INH levels ### k. Chronic Granulomatous Disease - Phagocyte deficiency (defect of oxidative metabolism) - NADPH defect impairs respiratory burst and superoxide generation - Four genes involved, gp91phox or CYBB gene most common (70% of cases) - Diagnosis: measure superoxide production (NBT reduction, DHR oxidation) - Common bacterial/fungal infections: lung, skin, liver, lymph nodes; osteomyelitis, gingivitis, perianal abscesses. - Exuberant granulomas and dysregulated inflammatory responses ### l. Chediak-Higashi Syndrome - Phagocyte deficiency - Rare (autosomal recessive) and life-threatening - Mutations in LYST gene - Enlarged cytoplasmic granules seen in all granulocytes - Symptoms: - Oculocutaneous albinism - Frequent pyogenic infections - Neurological abnormalities - Late lymphoma-like accelerated phase of disease - Immunological abnormalities - Neutropenia - Deficient neutrophil chemotaxis - Impaired NK cell cytotoxicity ### m. Hyper-IgE Syndrome (Job's Syndrome) - Recurrent infections (staph) - Coarse facial features, skeletal abnormalities - Very high levels of serum IgE - Eosinophilia - Decreased memory T cells - STAT3 gene mutations: AD form and sporadic HIES - Tyk2 mutations produce similar condition ## 77. Describe the laboratory methods used to evaluate the following PIDS ### a. XLA - Btk protein expression on monocytes by flow cytometry - Btk genotyping ### b. DiGeorge syndrome - < 500 CD3+ T-cells cells/uL and 2/3 of the following - Conotruncal cardiac defect - Hypocalcemia of >3 weeks duration - Chromosome 22q11.2 deletion - OR: <1500 CD3+ T-cells cells/uL and 22q11.2 deletion - OR: <1500 CD3+ T-cells cells/uL and one of the following - Cardiac defect - Hypocalcemia of >3 weeks duration - Facial dysmorphism or palatal abnormalities ### c. CGD - Genetic testing: gp91phox or CYBB gene - Nitroblue Tetrazolium (NBT) Reduction Test - Dihydrorhodamine (DHR) 123 Oxidation Test - Flow cytometry - ELISA - Assessing the functional and genetic aspects of the NADPH oxidase complex ### d. SCID - TREC assay - Ig level assessment - Genetic testing: IL2RG (X-linked), ADA, RAG1, RAG2, JAKЗ - T-cell proliferation assay ##