Immunology (Hypersensitivity, Transplant, Immunodeficiency, Antibody-Antigen) MCQs

Microbiology · 103 free questions with answers & explanations.

1. A 6-year-old child develops generalized urticaria, bronchospasm, and hypotension within minutes of a penicillin injection. Which immunoglobulin class is primarily responsible for this reaction?
2. Goodpasture's syndrome involves autoantibodies directed against the alpha-3 chain of type IV collagen in the glomerular basement membrane. Immunofluorescence of renal biopsy shows a linear pattern of IgG deposition. This is an example of which type of hypersensitivity?
3. A patient with recurrent sino-pulmonary infections and absent serum immunoglobulins has normal T lymphocyte numbers but no B cells in peripheral blood. Which gene is mutated in this condition?
4. A transplanted kidney is rejected within minutes on the operating table. Biopsy shows fibrinoid necrosis of vessel walls and intravascular thrombosis. What is the mechanism of this rejection?
5. A farmer presents with erythema and induration at the site of a tuberculin (Mantoux) test 48-72 hours after injection. This delayed-type hypersensitivity reaction is mediated by:
6. A 24-year-old woman with systemic lupus erythematosus has elevated serum levels of anti-dsDNA antibodies. The renal biopsy shows granular deposits along the glomerular basement membrane on immunofluorescence. The tissue damage in this scenario is primarily mediated by which mechanism of hypersensitivity?
7. In the mixed lymphocyte reaction (MLR) used to assess HLA matching for transplantation, the ONE-WAY MLR is performed by irradiating stimulator cells. What is the specific purpose of irradiating the stimulator lymphocytes?
8. A child presents with recurrent pyogenic infections, absent lymph nodes and tonsils, markedly reduced serum immunoglobulin levels, and near-absent B cells on flow cytometry. Bone marrow shows normal pro-B cells but no pre-B cells onward. The defective enzyme/protein most likely responsible is:
9. The avidity of an antibody differs from its affinity in which of the following ways?
10. A renal transplant recipient develops acute graft rejection on day 10 post-transplant. Biopsy shows lymphocytic infiltration of tubules and interstitium. Which cytokine is the primary driver of this CD4+ T-cell-mediated allograft destruction?
11. A patient receiving a kidney transplant develops acute antibody-mediated rejection within 1 week despite negative pre-transplant crossmatch. Biopsy shows C4d deposition in peritubular capillaries. The primary effector mechanism responsible for this injury is:
12. In the germinal center reaction, which molecular event is responsible for generating antibodies with higher affinity for antigen during B-cell maturation?
13. A child with recurrent sinopulmonary infections is found to have absent tonsils, no palpable lymph nodes, and serum IgG <100 mg/dL with absent IgA and IgM. Peripheral blood lymphocytes show no CD19+ cells. Which gene mutation is most likely?
14. The Arthus reaction is an example of Type III hypersensitivity. The complement split product that is MOST responsible for neutrophil chemotaxis to the site of immune complex deposition is:
15. A 35-year-old woman develops fever, joint pain, and a butterfly rash. ANA is positive with anti-dsDNA antibodies. The mechanism by which anti-dsDNA antibodies evade peripheral tolerance and cause renal damage involves:
16. A 25-year-old patient with X-linked agammaglobulinemia (Bruton's disease) is evaluated for susceptibility to infections. Which of the following immunological findings would best distinguish this condition from common variable immunodeficiency (CVID)?
17. In the ABO blood group system, the Bombay phenotype (Oh) lacks both A and B antigens as well as H antigen. Which of the following statements correctly describes the serological consequence of this phenotype?
18. A kidney transplant recipient develops gradual graft dysfunction with proteinuria 3 years post-transplant. Biopsy shows 'double contour' appearance of glomerular basement membranes and C4d deposits in peritubular capillaries. What is the predominant mechanism of rejection?
19. A 5-year-old boy presents with recurrent catalase-positive bacterial infections (Staphylococcus, Aspergillus, Klebsiella) since infancy. NBT (nitroblue tetrazolium) test is negative. The underlying defect is in which specific pathway?
20. During affinity maturation in germinal centres, B cells undergo somatic hypermutation of their variable region genes. Which enzyme is primarily responsible for initiating this process?
21. A researcher investigates affinity maturation of B cells within germinal centers. Which enzyme is primarily responsible for introducing somatic hypermutation into the variable regions of immunoglobulin genes?
22. A patient with recurrent pyogenic infections is found to have normal B and T cell counts but markedly reduced serum complement CH50. Specific analysis shows absent classical pathway activity but intact alternative pathway. Which complement component deficiency best explains this pattern?
23. In transplant immunology, which HLA matching criterion is MOST critical for preventing hyperacute rejection in kidney transplantation?
24. A 6-year-old boy has recurrent Pneumocystis jirovecii pneumonia, oral candidiasis, and failure to thrive since infancy. Flow cytometry shows absent CD3+ T cells but normal B cell counts with very low immunoglobulins. The most likely molecular defect is:
25. The Arthus reaction is a localized immune complex-mediated phenomenon. Which complement-derived mediator is MOST directly responsible for the neutrophil infiltration seen in this reaction?
26. A 28-year-old man with X-linked agammaglobulinemia presents with recurrent sinopulmonary infections. Flow cytometry of peripheral blood shows absent mature B cells. The molecular defect responsible for the arrest in B-cell development at the pro-B cell to pre-B cell transition is a mutation in:
27. In a kidney transplant recipient, the classic biopsy finding of endarteritis with mononuclear cell infiltration in the vessel wall is most characteristic of which type of rejection?
28. Which complement pathway activation product directly cleaves C3 without involving C1q, MBL, or antibody?
29. A 6-year-old boy has recurrent Neisseria infections and a CH50 that is essentially zero; classical and alternative pathway components are individually normal. The most likely deficiency is:
30. The somatic hypermutation mechanism that generates antibody diversity after antigen exposure occurs in germinal centres of secondary lymphoid organs and is driven by which enzyme?
31. A 28-year-old woman with systemic lupus erythematosus has elevated anti-dsDNA antibody titres and low complement levels. Kidney biopsy shows subendothelial immune deposits and wire-loop lesions. Which complement pathway is PRIMARILY activated by immune complexes deposited in glomeruli?
32. CD4+ T-helper cell subsets are distinguished by their cytokine profiles. A patient with disseminated Mycobacterium avium infection is found to have a specific deficiency of the cytokine essential for macrophage activation and granuloma formation. Which Th subset is deficient in its function?
33. A laboratory measures antibody affinity maturation in germinal centres. The process that selects B cells with progressively higher affinity antibodies after somatic hypermutation involves competition for which limiting resource?
34. A 4-year-old boy has recurrent pyogenic infections since birth, with absent lymph nodes and tonsils. Flow cytometry shows absence of all B cells (CD19–) but normal T cells. Serum immunoglobulins are undetectable. This presentation is consistent with a defect at which developmental stage?
35. In MHC class I antigen presentation, peptides derived from cytosolic proteins are transported into the endoplasmic reticulum via a specific transporter for loading onto MHC I molecules. What is the name of this transporter?
36. A 7-year-old boy presents with recurrent pyogenic infections since infancy, with persistent lymphopenia (CD3+ T-cells <200/µL), absent thymic shadow on X-ray, and undetectable serum immunoglobulins. Maternal lymphocytes are present in circulation. Which enzyme deficiency most commonly underlies this presentation?
37. In the Arthus reaction (Type III hypersensitivity), which complement components are MOST critically responsible for neutrophil recruitment and subsequent tissue damage at the site of immune complex deposition?
38. A renal transplant patient develops acute rejection 10 days post-transplant with rising creatinine, fever and graft tenderness. Biopsy shows lymphocytic infiltration of the tubules and interstitium. What is the primary immunological mechanism?
39. Which characteristic best distinguishes IgA1 from IgA2 structurally, and which is the predominant form in secretions such as colostrum and saliva?
40. A 25-year-old man has recurrent sinopulmonary infections, low serum IgG/IgA/IgM, absent B cells in peripheral blood but normal T-cell counts. He is found to have a mutation in Bruton's tyrosine kinase (BTK). Which serology pattern is expected for his vaccination history?
41. A 6-year-old boy with recurrent sinopulmonary infections is found to have normal B-cell counts but absent serum immunoglobulins of all isotypes. His T-cell count and function are normal. Genetic testing reveals a mutation causing inability to signal downstream of the pre-B cell receptor. Which kinase is most likely deficient?
42. In HLA typing for renal transplantation, the mixed lymphocyte reaction (MLR) tests specifically for compatibility at which HLA locus?
43. A young woman with recurrent Neisseria meningitidis infections despite vaccination is evaluated for complement deficiency. Her CH50 is zero. Which component is most likely deficient if the AP50 (alternative pathway haemolysis) is also zero?
44. Which immunoglobulin isotype is predominantly produced during a primary immune response and is the best indicator of acute or recent infection in serology?
45. A bone marrow transplant recipient develops graft-versus-host disease (GVHD) 30 days post-transplant. This reaction is best classified as which type of immunological response?
46. A patient with recurrent bacterial and fungal infections has absent T cells but normal B cell counts. Genetic analysis reveals a mutation affecting the common gamma chain (γc) of cytokine receptors. This mutation affects signaling through which interleukins?
47. A 28-year-old woman with SLE develops hemolytic anemia after a viral upper respiratory infection. Direct Coombs test is positive. Complement levels (C3, C4) are low. The hemolysis in this scenario is best explained by which mechanism?
48. In HLA typing for renal transplantation, a patient receives a kidney that is matched for HLA-A, B but mismatched for one HLA-DR locus. Within 6 months, the graft is lost to an irreversible cellular rejection episode. The T cell population primarily responsible for recognizing the mismatched HLA-DR on donor antigen-presenting cells by DIRECT allorecognition is:
49. A 3-year-old boy has recurrent sinopulmonary infections starting at 6 months of age. Serum immunoglobulin levels are: IgG 80 mg/dL (normal 600–1600), IgA undetectable, IgM undetectable. Flow cytometry shows absence of CD19+ B cells. Bruton's tyrosine kinase (BTK) gene sequencing reveals a nonsense mutation. Which immunization should be specifically AVOIDED in this child?
50. Idiotype-anti-idiotype network theory was proposed to explain immune regulation. In this context, the idiotype refers to:
51. A 6-year-old boy is evaluated for recurrent bacterial infections since infancy. Flow cytometry shows absent B cells but normal T cells and NK cells. Serum immunoglobulins are markedly reduced. BTK gene mutation is confirmed. Which of the following best describes the immunological mechanism?
52. A 28-year-old receives a renal transplant. Biopsy on day 3 shows neutrophilic infiltration of vessel walls with fibrinoid necrosis, and pre-formed donor-specific HLA antibodies are detected. What type of rejection is this?
53. Serum protein electrophoresis of a patient with recurrent sinopulmonary infections shows normal IgM but markedly reduced IgG and IgA. Peripheral blood B cells are normal in number. CD40L expression on T cells is normal. What is the most likely diagnosis?
54. In the Arthus reaction, a farmer develops erythema and induration at the site of repeated subcutaneous antigen injection after 4–8 hours. The primary mediators are:
55. An HIV-positive patient with CD4 count 45 cells/μL is started on ART. Two weeks later he develops worsening cervical lymphadenopathy and fever. Prior to ART, a positive tuberculin skin test was noted but IGRA was not done. What phenomenon best explains this deterioration?
56. A 28-year-old woman with systemic lupus erythematosus has serum tested for anti-dsDNA antibodies by Crithidia luciliae immunofluorescence. The kinetoplast of this organism fluoresces brilliantly. What is the significance of this finding compared with a standard ELISA for anti-dsDNA?
57. During HLA typing for renal transplantation, a prospective recipient has a positive cross-match with the donor's T-lymphocytes using complement-dependent cytotoxicity (CDC). The same serum gives a negative B-cell cross-match. What is the most appropriate next step?
58. An infant presents at 6 months with severe bacterial infections (Streptococcus pneumoniae sepsis twice) but normal T-cell counts and normal delayed hypersensitivity skin tests. Flow cytometry shows absent B-cells; serum IgG is 120 mg/dL (normal >600). Bone marrow shows arrest at pro-B stage. The most likely molecular defect is in:
59. The mechanism by which a Type III hypersensitivity reaction causes glomerulonephritis in post-streptococcal disease involves:
60. A 6-year-old boy presents with recurrent sinopulmonary infections since infancy. Serum immunoglobulins show markedly reduced IgG, IgA, and IgM. Flow cytometry reveals absence of CD19+ B cells but normal CD3+ T cell counts. Genetic testing confirms a mutation in Bruton tyrosine kinase (BTK). Which of the following best describes the underlying mechanism of his susceptibility to encapsulated bacterial infections?
61. A renal transplant recipient on tacrolimus and mycophenolate develops a rising serum creatinine on day 8 post-transplant. Biopsy shows dense mononuclear cell infiltration of tubular epithelium with tubulitis. Panel reactive antibody (PRA) was 12% pre-transplant. Which type of rejection is this?
62. During investigation of a hypersensitivity reaction, intradermal injection of an antigen produces induration and erythema peaking at 48-72 hours. Histological examination of the reaction site shows predominantly CD4+ T lymphocytes and activated macrophages without significant eosinophils. This pattern is most consistent with which Coombs and Gell classification?
63. A 22-year-old woman is found to have selective IgA deficiency (serum IgA <7 mg/dL) on routine screening before blood donation. She is asymptomatic. She later receives a blood transfusion and develops severe anaphylaxis. What is the most likely immunological mechanism?
64. A laboratory measures antibody affinity maturation during a secondary immune response. Which of the following molecular processes in germinal centres is primarily responsible for generating antibodies with progressively higher affinity for antigen?
65. A 6-year-old child develops recurrent sino-pulmonary infections caused by encapsulated bacteria. IgG, IgA and IgM levels are all markedly reduced, and circulating B-lymphocytes are absent on flow cytometry. The underlying molecular defect most likely involves which gene product?
66. In a graft-versus-host disease (GVHD) scenario following allogeneic bone marrow transplantation, the primary effector mechanism of acute GVHD is mediated by:
67. A patient with selective IgA deficiency who requires a blood transfusion is at risk of anaphylaxis. This reaction is mediated by:
68. A 25-year-old presents with recurrent Neisseria infections (meningococcemia twice, disseminated gonococcal infection once). The most likely immunological defect is:
69. The prozone phenomenon in syphilis serology occurs because:
70. A 28-year-old woman with SLE has persistent low C3 and C4 levels with recurrent infections by encapsulated bacteria. Which complement pathway deficiency best explains this combined clinical and serological pattern?
71. In a cross-match assay prior to renal transplantation, the recipient's serum is incubated with donor lymphocytes and complement is added. Cell lysis is observed. This positive cross-match indicates the presence of which type of pre-formed antibody?
72. A 7-month-old boy presents with recurrent pyogenic infections. Immunoglobulin levels show absent IgG, IgA, and IgM. Flow cytometry reveals mature CD4+ and CD8+ T cells are present, but B cells are completely absent. The most likely diagnosis is:
73. In the Western blot confirmatory test for HIV, a result is interpreted as 'indeterminate' when:
74. A patient receives a skin graft from a sibling who is HLA-haploidentical. The graft is rejected at 12 days. Which immunological mechanism is primarily responsible?
75. A 28-year-old woman with SLE has serum complement levels C3 and C4 both markedly reduced. Which pathway of complement activation is predominantly responsible for this pattern of consumption?
76. A 5-year-old boy presents with recurrent Staphylococcal skin abscesses, elevated IgE (>2000 IU/mL), eczema, and coarse facies. Neutrophil count is normal. Which functional defect underlies this condition?
77. Post-renal transplant, a recipient develops acute rejection on day 5. Biopsy shows dense CD8+ T-cell infiltrate and tubulitis. HLA crossmatch was negative pre-transplant. What is the most likely mechanism?
78. A technician runs an ELISA for HIV antibody detection. The OD reading of the patient sample is 2.8 times the cut-off value. The positive predictive value of this test in a low-prevalence population is MOST dependent on which parameter?
79. A 35-year-old woman with common variable immunodeficiency (CVID) is found to have absent B cells and very low all immunoglobulin classes. She has recurrent sino-pulmonary infections and Giardia lamblia diarrhoea. What is the expected T-cell status?
80. A 14-year-old boy presents with recurrent skin abscesses caused by Staphylococcus aureus and Serratia marcescens. He has elevated IgG, normal lymphocyte counts and normal complement levels. His nitroblue tetrazolium (NBT) test shows 2% positive cells (normal >95%). Which of the following best explains the defect in this patient?
81. In the direct antiglobulin test (DAT/Coombs), a positive result is obtained when anti-human globulin reagent causes agglutination of washed red cells. Which of the following clinical scenarios would most specifically give a positive DAT with polyspecific AHG, positive with anti-IgG, but NEGATIVE with anti-C3d?
82. A 28-year-old woman with lupus nephritis is found on serological testing to have low C3, low C4, normal CH50 activity, and markedly elevated anti-dsDNA titres. Which component of the complement pathway is most likely being consumed preferentially in this patient?
83. HLA matching for allograft success is most important for which type of organ transplantation?
84. A neonate develops severe bacterial infections and requires granulocyte transfusions for survival. Laboratory evaluation shows absence of all lymphocyte subsets and markedly reduced serum immunoglobulins. Adenosine deaminase (ADA) activity is 5% of normal. What is the most likely mode of inheritance of this condition?
85. A 6-month-old infant develops recurrent bacterial infections, absent lymph nodes on examination, and laboratory findings show very low or absent B cells but normal T cell numbers and T cell function. Immunoglobulin levels are undetectable. This presentation is most consistent with:
86. Antibody-dependent cellular cytotoxicity (ADCC) is primarily mediated by which cell type and through which receptor?
87. In Coombs test (antiglobulin test) interpretation, a positive direct Coombs test (DCT) with negative indirect Coombs test (ICT) indicates:
88. A patient received a kidney transplant 10 days ago. Renal biopsy shows neutrophilic infiltration of glomeruli and capillary walls with complement deposition (C4d positive on peritubular capillaries). This histological pattern is characteristic of:
89. The prozone phenomenon in serological testing refers to a false-negative result caused by:
90. A 3-year-old boy has recurrent pyogenic infections (Staph aureus, Streptococcal) since infancy. Absolute lymphocyte count is normal. IgG and IgA are severely reduced, IgM is elevated (1200 mg/dL). CD19+ B cells are present in normal numbers. What is the most likely diagnosis?
91. A renal transplant recipient on tacrolimus + mycophenolate mofetil develops acute rejection at 10 days post-transplant. Renal biopsy shows diffuse interstitial infiltrate of CD4+ and CD8+ lymphocytes with tubulitis. What type of hypersensitivity reaction is this?
92. In complement cascade, C3b deposition on bacteria promotes opsonisation. In which primary immunodeficiency disease is there a specific defect in C3b opsonisation leading to recurrent pyogenic infections?
93. In the ELISA test, the principle involves antigen-antibody interaction detected through an enzyme-linked secondary antibody. In a competitive ELISA, if the patient sample contains a HIGH concentration of the target antigen, the absorbance reading will be:
94. A patient with systemic lupus erythematosus (SLE) has recurrent thromboses and recurrent foetal loss. Serological tests show prolonged APTT (not corrected by mixing study), anti-cardiolipin antibodies (IgG, high titre), and positive lupus anticoagulant. What mechanism underlies the thrombotic tendency in this patient?
95. Chronic rejection of a renal allograft is primarily mediated by:
96. A child with recurrent sino-pulmonary infections from age 6 months, normal lymphocyte count, normal IgM, but very low IgG, IgA, and IgE. B cells are present in normal numbers. Flow cytometry of B cells shows poor surface IgM expression but no CD40L defect. The MOST likely diagnosis is:
97. In the context of complement activation, which pathway is activated by mannose-binding lectin (MBL) binding to microbial carbohydrate patterns?
98. Which type of hypersensitivity reaction underlies the Arthus reaction and serum sickness?
99. The classical pathway of complement is activated by immune complexes. What is the correct sequence of events from C1q binding to opsonisation?
100. A 3-year-old girl has recurrent bacterial infections, normal B and T lymphocyte counts, normal serum immunoglobulins, but neutrophils fail to kill ingested bacteria. DHR (dihydrorhodamine flow cytometry) test shows absent fluorescence shift after PMA stimulation. Nitroblue tetrazolium (NBT) test is negative. What is the diagnosis and the underlying enzyme defect?
101. What is the mechanism by which regulatory T cells (Tregs, CD4+CD25+FoxP3+) suppress immune responses, and which cytokines do they predominantly secrete?
102. Toll-like receptor 4 (TLR-4) recognises which bacterial component as its primary ligand?
103. The recombinant subunit hepatitis B vaccine contains which viral antigen as its immunogen?