Immunology MCQs
Part 1 — Immunology MCQs (1–25)
1) Hallmark of adaptive immunity is:
A. Phagocytosis
B. Inflammation
C. Immunologic memory
D. Complement activation
Answer: C
- A: Innate mechanism, non-specific.
- B: Innate, early response.
- C: Correct—memory and specificity define adaptive immunity.
- D: Mostly innate (also helps adaptive), not the hallmark.
2) MHC class I presents peptides that are typically:
A. Exogenous, endosomal
B. Endogenous, cytosolic
C. Lipids from endosomes
D. Carbohydrates from lysosomes
Answer: B
- A: Describes MHC II pathway.
- B: Correct—proteasome→TAP→MHC I for CD8 T cells.
- C: CD1 presents lipids, not MHC I.
- D: Carbohydrates are generally T-independent antigens.
3) Classical pathway C3 convertase is:
A. C3bBb
B. C4b2a
C. C5b-9
D. MASP-2
Answer: B
- A: Alternative pathway C3 convertase.
- B: Correct—classical/lectin C3 convertase.
- C: Membrane attack complex (MAC), not C3 convertase.
- D: Enzyme in lectin pathway initiation, not the convertase.
4) Enzyme essential for class-switch recombination:
A. RAG1/2
B. AID (Activation-Induced cytidine Deaminase)
C. TdT
D. DNA ligase IV
Answer: B
- A: V(D)J recombination, not class switching.
- B: Correct—AID initiates CSR and SHM.
- C: Adds N-nucleotides during V(D)J, not CSR.
- D: DNA repair, supportive but not specific to CSR.
5) Positive selection of T cells occurs mainly in the:
A. Bone marrow
B. Thymic cortex
C. Thymic medulla
D. Spleen white pulp
Answer: B
- A: B cell development site.
- B: Correct—cortex tests TCR recognition of self-MHC.
- C: Medulla handles negative selection (AIRE).
- D: Secondary lymphoid organ, not selection site.
6) BCR can recognize antigens that are:
A. Only peptides presented on MHC
B. Soluble or native conformational epitopes
C. Only lipids on CD1
D. Only nucleic acids
Answer: B
- A: TCRs require MHC; BCRs don’t.
- B: Correct—BCR binds native proteins, carbs, lipids.
- C: CD1-restricted T cells, not BCR requirement.
- D: Too narrow; BCR is broader.
7) Hinge region of IgG provides:
A. Complement fixation site
B. Antigen-binding specificity
C. Flexibility between Fab arms
D. Fc receptor binding
Answer: C
- A: Mostly on Fc constant region, not hinge alone.
- B: Determined by variable regions.
- C: Correct—improves avidity/epitope reach.
- D: Fc portion (CH2/CH3) mediates FcR binding.
8) A key opsonin is:
A. IL-2
B. C3b
C. Histamine
D. IFN-α
Answer: B
- A: T cell growth factor, not opsonin.
- B: Correct—promotes phagocytosis via complement receptors.
- C: Vasoactive amine, not opsonin.
- D: Antiviral cytokine, not opsonin.
9) Type I hypersensitivity is mediated primarily by:
A. IgM
B. IgG
C. IgA
D. IgE
Answer: D
- A: Early immune response, not allergy.
- B: Type II/III commonly involve IgG.
- C: Mucosal immunity.
- D: Correct—IgE + mast cells cause anaphylaxis/allergy.
10) Superantigens activate T cells by:
A. Binding peptide groove of MHC I
B. Crosslinking MHC II and TCR Vβ region
C. Directly activating CD28
D. Blocking CTLA-4
Answer: B
- A: Not their mechanism.
- B: Correct—massive cytokine release (TSST-1, SPEs).
- C: Costimulation is involved, but not direct target.
- D: Not the mechanism of superantigen action.
11) NK cells kill targets that:
A. Express high MHC I
B. Present antigen via MHC II
C. Lack or have reduced MHC I (“missing self”)
D. Express high CD28
Answer: C
- A: Inhibitory signals prevent killing.
- B: NK cells are not MHC II-restricted.
- C: Correct—reduced MHC I removes inhibition.
- D: CD28 is a T cell molecule.
12) Live-attenuated vaccines typically induce:
A. Only humoral immunity
B. Strong humoral and cellular immunity
C. No memory response
D. Only innate immunity
Answer: B
- A: They induce both arms.
- B: Correct—robust CD8 and antibody responses.
- C: They create memory.
- D: Innate is engaged but not “only.”
13) Secondary immune response is characterized by:
A. Predominant IgM, low affinity
B. Predominant IgG/IgA/IgE with higher affinity
C. No memory B cells
D. Lack of class switching
Answer: B
- A: Primary response hallmark.
- B: Correct—class-switched, affinity-matured antibodies.
- C: Memory B cells drive it.
- D: Class switching is central here.
14) TLR4 primarily recognizes:
A. dsRNA
B. Unmethylated CpG DNA
C. Lipopolysaccharide (LPS)
D. Flagellin
Answer: C
- A: TLR3 ligand.
- B: TLR9 ligand.
- C: Correct—TLR4–MD2–CD14 detects LPS.
- D: TLR5 ligand.
15) Maternal IgG to fetus is an example of:
A. Active natural immunity
B. Passive natural immunity
C. Active artificial immunity
D. Passive artificial immunity
Answer: B
- A: Host makes its own antibodies.
- B: Correct—transplacental transfer.
- C: Vaccination-induced response.
- D: Injected antibodies (e.g., IVIG).
16) Cytokine that drives T cell proliferation:
A. IL-2
B. IL-4
C. IL-5
D. IL-10
Answer: A
- A: Correct—autocrine growth factor for T cells.
- B: TH2 differentiation & IgE class switch.
- C: Eosinophils/IgA support.
- D: Anti-inflammatory, regulatory.
17) AIRE gene defect causes failure of:
A. Positive selection
B. Central tolerance (negative selection in medulla)
C. Peripheral tolerance via Tregs
D. B cell somatic hypermutation
Answer: B
- A: Cortex process.
- B: Correct—APECED due to poor self-antigen display.
- C: FOXP3/Tregs handle peripheral tolerance.
- D: Dependent on AID, not AIRE.
18) V(D)J recombination requires:
A. AID
B. RAG1/2 endonucleases
C. HLA-DM
D. TAP1/2
Answer: B
- A: CSR/SHM, not V(D)J initiation.
- B: Correct—cleave RSS for recombination; deficiency → SCID.
- C: Loads peptides onto MHC II.
- D: Transports peptides to MHC I.
19) Deficiency of terminal complement (C5–C9) predisposes to:
A. Recurrent Staphylococcus aureus
B. Recurrent Neisseria infections
C. Severe viral infections
D. Mycobacterial disease
Answer: B
- A: Mainly opsonization/phagocyte issues.
- B: Correct—MAC needed vs Neisseria.
- C: Interferons/NK/T cells more relevant.
- D: IFN-γ/IL-12 axis defects predispose.
20) Common lymphoid progenitor gives rise to:
A. Neutrophils and eosinophils
B. B cells, T cells, NK cells
C. Erythrocytes and platelets
D. Dendritic cells only
Answer: B
- A: Myeloid lineage.
- B: Correct—lymphoid lineage products.
- C: Megakaryocyte/erythroid lineage.
- D: DCs can arise from both lineages; not “only.”
21) Antibody neutralization primarily:
A. Tags pathogens for phagocytosis
B. Activates complement directly
C. Blocks pathogen binding/toxin activity
D. Triggers ADCC
Answer: C
- A: Opsonization (IgG, C3b).
- B: Fc-dependent, but neutralization isn’t “activation.”
- C: Correct—prevents entry/toxin effects.
- D: FcγRIII on NK mediates ADCC, different mechanism.
22) MHC restriction of T cells results from:
A. Negative selection only
B. Positive selection in thymic cortex
C. Peripheral tolerance
D. Somatic hypermutation
Answer: B
- A: Removes strongly self-reactive cells.
- B: Correct—selects TCRs that recognize self-MHC.
- C: Occurs after thymus; not restriction.
- D: Happens in B cells, not T cells.
23) Exogenous antigen loading onto MHC II involves:
A. Proteasome and TAP
B. Invariant chain, CLIP, HLA-DM
C. Immunoproteasome only
D. Endoplasmic reticulum peptide loading to MHC II
Answer: B
- A: MHC I pathway.
- B: Correct—endosomal processing, CLIP exchange via HLA-DM.
- C: Variant of proteasome for MHC I, not II.
- D: MHC II loads in endosomes, not ER.
24) Monoclonal antibodies are commonly produced by:
A. ELISA
B. Flow cytometry
C. Hybridoma technology
D. Western blot
Answer: C
- A: Detection assay, not production.
- B: Sorting/analysis, not production method.
- C: Correct—B cell + myeloma fusion.
- D: Protein detection method.
25) Most potent professional APC for naïve T cell priming:
A. Neutrophil
B. Dendritic cell
C. B cell
D. Macrophage
Answer: B
- A: Not an APC for naïve T cells.
- B: Correct—key initiators in lymph nodes.
- C: Can present, but less potent for priming naïve T cells.
- D: Strong effectors, but DCs are superior primers.
Part 2 — Immunology MCQs (26–50)
26) Antigenic determinant recognized by an antibody is called:
A. Paratope
B. Epitope
C. Hapten
D. Idiotope
Answer: B
- A: The antigen-binding site of the antibody.
- B: Correct—specific site on antigen recognized by antibody.
- C: Small molecule, not immunogenic alone.
- D: Unique region in antibody variable domain.
27) The first antibody produced during primary immune response is:
A. IgA
B. IgM
C. IgE
D. IgG
Answer: B
- A: Mainly at mucosal sites.
- B: Correct—IgM is pentameric and produced first.
- C: In allergy and parasitic infections.
- D: IgG appears later after class switching.
28) Which T helper subset promotes cell-mediated immunity against intracellular pathogens?
A. TH1
B. TH2
C. TH17
D. Treg
Answer: A
- A: Correct—produces IFN-γ, activates macrophages and CD8 T cells.
- B: Supports humoral and allergic responses.
- C: Defends against fungi and extracellular bacteria.
- D: Regulates immune suppression.
29) Antigen cross-presentation refers to:
A. B cells presenting to T helper cells
B. Exogenous antigens presented on MHC I
C. Endogenous antigens presented on MHC II
D. NK cells presenting antigen
Answer: B
- A: Standard antigen presentation.
- B: Correct—allows dendritic cells to present exogenous proteins to CD8 T cells.
- C: Wrong direction of presentation.
- D: NK cells don’t present antigens.
30) The main function of IgA:
A. Complement activation
B. Opsonization
C. Mucosal immunity
D. Antibody-dependent cell-mediated cytotoxicity
Answer: C
- A: IgM and IgG are strong activators.
- B: Mainly IgG.
- C: Correct—IgA protects mucosal surfaces, neutralizes pathogens.
- D: ADCC is mediated by IgG.
31) Deficiency of adenosine deaminase (ADA) causes:
A. Chronic granulomatous disease
B. Severe combined immunodeficiency (SCID)
C. DiGeorge syndrome
D. Wiskott–Aldrich syndrome
Answer: B
- A: NADPH oxidase defect, recurrent infections.
- B: Correct—ADA deficiency leads to toxic buildup, blocks T and B cells.
- C: Thymic hypoplasia, defective T cells.
- D: Cytoskeletal defect, thrombocytopenia, eczema.
32) The process of increasing antibody affinity during immune response is called:
A. Class-switch recombination
B. Affinity maturation
C. Somatic recombination
D. Opsonization
Answer: B
- A: Isotype change, not affinity change.
- B: Correct—driven by somatic hypermutation and selection.
- C: Occurs early in lymphocyte development.
- D: Enhances phagocytosis but unrelated.
33) Immune privilege is observed in all of the following except:
A. Eye
B. Brain
C. Testis
D. Liver
Answer: D
- A: Correct site of immune privilege.
- B: CNS has partial immune privilege.
- C: Testes are immune privileged.
- D: Liver is immunoregulatory but not classically immune privileged.
34) Cytotoxic T cells kill target cells by:
A. Complement activation
B. Perforin and granzymes
C. Histamine release
D. Antibody neutralization
Answer: B
- A: Mediated by antibodies, not CTLs.
- B: Correct—perforin makes pores, granzymes trigger apoptosis.
- C: Mast cell function.
- D: Antibodies neutralize toxins, not CTL mechanism.
35) Which complement component forms the membrane attack complex (MAC)?
A. C1q
B. C3b
C. C5b-9
D. C2a
Answer: C
- A: Initiates classical pathway.
- B: Opsonin, not MAC.
- C: Correct—C5b with C6–C9 forms MAC.
- D: Part of C3 convertase, not MAC.
36) The receptor for IgG Fc fragment on phagocytes is:
A. FcεRI
B. FcαRI
C. FcγR
D. FcRn
Answer: C
- A: High-affinity IgE receptor.
- B: IgA receptor.
- C: Correct—FcγR binds IgG and promotes phagocytosis.
- D: Neonatal IgG receptor for placental transfer.
37) Major site of hematopoiesis in adults:
A. Liver
B. Spleen
C. Bone marrow
D. Thymus
Answer: C
- A: Fetal site.
- B: Filters blood, not major hematopoiesis.
- C: Correct—primary adult hematopoietic tissue.
- D: T cell maturation, not hematopoiesis.
38) Which cytokine promotes differentiation of TH17 cells?
A. IL-12
B. IL-6 + TGF-β
C. IL-4
D. IL-10
Answer: B
- A: Drives TH1.
- B: Correct—IL-6 + TGF-β promote TH17 differentiation.
- C: Drives TH2.
- D: Immunosuppressive cytokine.
39) Diapedesis of leukocytes is mediated by:
A. Selectins and integrins
B. TLRs
C. Antibodies
D. Complement only
Answer: A
- A: Correct—selectins mediate rolling, integrins mediate firm adhesion and transmigration.
- B: Recognize pathogens, not extravasation.
- C: Antibodies don’t mediate diapedesis.
- D: Complement is involved in chemotaxis, but adhesion requires selectins/integrins.
40) Which immunoglobulin crosses the placenta?
A. IgA
B. IgG
C. IgM
D. IgE
Answer: B
- A: Secreted at mucosal sites.
- B: Correct—IgG provides passive immunity to fetus.
- C: Too large to cross placenta.
- D: Involved in allergy, not placental transfer.
41) The main cytokine produced by regulatory T cells (Tregs) is:
A. IL-2
B. IL-4
C. IL-10
D. IL-12
Answer: C
- A: Growth factor for T cells.
- B: TH2 cytokine.
- C: Correct—Tregs produce IL-10 and TGF-β to suppress immunity.
- D: Produced by dendritic cells/macrophages for TH1.
42) Which lymphoid organ is the site of naïve T and B cell activation?
A. Bone marrow
B. Thymus
C. Lymph nodes
D. Liver
Answer: C
- A: B cell development.
- B: T cell maturation.
- C: Correct—antigen presentation activates naïve lymphocytes in secondary lymphoid organs.
- D: Not a primary immune activation site.
43) Somatic hypermutation occurs in:
A. Bone marrow
B. Germinal centers
C. Thymus cortex
D. Spleen red pulp
Answer: B
- A: B cell development, no SHM.
- B: Correct—germinal centers in lymph nodes and spleen.
- C: T cell selection.
- D: Red pulp filters RBCs, not SHM site.
44) Which antibody is most effective in activating the classical complement pathway?
A. IgA
B. IgD
C. IgG1
D. IgM
Answer: D
- A: Neutralizes at mucosal surfaces.
- B: Low levels on naïve B cells.
- C: IgG1 can activate complement but less effectively.
- D: Correct—pentameric IgM is most efficient.
45) The “respiratory burst” in neutrophils involves:
A. IL-1 secretion
B. ROS generation via NADPH oxidase
C. Antigen presentation
D. Histamine release
Answer: B
- A: Macrophages produce IL-1.
- B: Correct—NADPH oxidase produces superoxide, hydrogen peroxide.
- C: Dendritic cells/macrophages are better APCs.
- D: Basophils/mast cells release histamine.
46) Which interleukin is crucial for B cell growth and differentiation?
A. IL-1
B. IL-2
C. IL-4
D. IL-12
Answer: C
- A: Pro-inflammatory cytokine.
- B: T cell growth.
- C: Correct—IL-4 drives B cell activation, IgE/IgG1 class switching.
- D: Drives TH1 differentiation.
47) Anaphylatoxins include:
A. C1q, C2a
B. C3a, C4a, C5a
C. C3b, C5b
D. Factor B, Properdin
Answer: B
- A: Not anaphylatoxins.
- B: Correct—cause inflammation, histamine release.
- C: Opsonins, not anaphylatoxins.
- D: Alternative pathway proteins.
48) Which antibody is pentameric in serum?
A. IgA
B. IgE
C. IgM
D. IgG
Answer: C
- A: Secretory IgA is dimeric.
- B: Monomer, mediates allergy.
- C: Correct—IgM is pentameric, first responder.
- D: Monomeric in blood.
49) Antigen-presenting cells include all except:
A. B cells
B. Dendritic cells
C. Macrophages
D. Neutrophils
Answer: D
- A: Professional APC.
- B: Most potent APC.
- C: Present antigens effectively.
- D: Correct—neutrophils rarely present antigens.
50) Toll-like receptor 9 (TLR9) recognizes:
A. LPS
B. Flagellin
C. CpG DNA
D. dsRNA
Answer: C
- A: TLR4 ligand.
- B: TLR5 ligand.
- C: Correct—TLR9 detects unmethylated CpG motifs in bacterial/viral DNA.
- D: TLR3 ligand.
Part 3 — Immunology MCQs (51–75)
51) The genetic region encoding MHC molecules in humans is called:
A. BCR locus
B. HLA complex
C. TCR locus
D. CD cluster region
Answer: B
- A: Encodes immunoglobulins, not MHC.
- B: Correct—HLA (Human Leukocyte Antigen) complex on chromosome 6 encodes MHC.
- C: T cell receptor genes.
- D: CD designations are surface markers, not gene loci.
52) Which antibody predominates in secondary immune response?
A. IgM
B. IgD
C. IgG
D. IgE
Answer: C
- A: First in primary response.
- B: Mainly found on naïve B cells.
- C: Correct—IgG dominates due to class switching and memory.
- D: Seen in allergy, not typical secondary response.
53) The function of invariant chain (Ii) in MHC II pathway is to:
A. Transport peptides into ER
B. Block peptide binding groove of MHC II until endosome
C. Enhance cytotoxic T cell killing
D. Promote class switching
Answer: B
- A: TAP does this for MHC I.
- B: Correct—prevents premature peptide binding until MHC II reaches endosomes.
- C: Not related.
- D: Mediated by AID, not invariant chain.
54) Which cytokine induces class switching to IgE?
A. IL-2
B. IL-4
C. IL-10
D. IFN-γ
Answer: B
- A: T cell proliferation.
- B: Correct—IL-4 promotes IgE and IgG1 switching.
- C: Immunosuppressive, enhances IgG production.
- D: Favors IgG2a (in mice) and TH1 responses.
55) Antigen processing for MHC I presentation involves which transporter?
A. HLA-DM
B. TAP1/2
C. Invariant chain
D. Cathepsins
Answer: B
- A: Assists MHC II loading.
- B: Correct—TAP transports peptides into ER for MHC I.
- C: Blocks groove of MHC II.
- D: Proteases in endosomes for MHC II, not I.
56) Which cells mediate antibody-dependent cellular cytotoxicity (ADCC)?
A. NK cells
B. B cells
C. Neutrophils
D. Dendritic cells
Answer: A
- A: Correct—NK cells use FcγRIII to kill antibody-coated cells.
- B: Produce antibodies, not cytotoxic.
- C: Can phagocytose, but not main ADCC mediators.
- D: Antigen-presenting, not cytotoxic.
57) A primary lymphoid organ in humans is:
A. Lymph node
B. Thymus
C. Spleen
D. Tonsil
Answer: B
- A: Secondary lymphoid organ.
- B: Correct—T cell maturation site.
- C: Secondary lymphoid organ.
- D: Secondary lymphoid tissue.
58) Complement regulatory protein that prevents C9 polymerization (MAC formation) is:
A. Factor H
B. CD59 (Protectin)
C. C1 inhibitor
D. DAF (CD55)
Answer: B
- A: Regulates alternative pathway, prevents C3 convertase.
- B: Correct—CD59 blocks MAC formation.
- C: Inhibits C1r/s activation.
- D: Prevents formation of C3 convertases.
59) Which Ig is involved in type II hypersensitivity?
A. IgE
B. IgG and IgM
C. IgA
D. IgD
Answer: B
- A: Mediates type I hypersensitivity.
- B: Correct—antibodies bind cell-surface antigens causing cytotoxicity.
- C: Mucosal immunity, not hypersensitivity.
- D: Not involved in hypersensitivity.
60) Which immune cell is the main defense against helminths?
A. NK cells
B. Eosinophils
C. Neutrophils
D. Dendritic cells
Answer: B
- A: Kill virus-infected/tumor cells.
- B: Correct—release major basic protein and respond to IL-5.
- C: Phagocytes for bacteria.
- D: Antigen-presenting role.
61) Which molecule provides co-stimulation for T cell activation?
A. TCR–MHC interaction
B. CD28–B7 binding
C. IL-2 receptor binding
D. CTLA-4 binding
Answer: B
- A: First signal only.
- B: Correct—CD28 (T cell) with B7 (APC) provides second signal.
- C: Occurs after activation.
- D: Inhibitory receptor.
62) Which Ig class is present in highest concentration in serum?
A. IgM
B. IgG
C. IgA
D. IgE
Answer: B
- A: Large molecule but less abundant.
- B: Correct—IgG is most abundant in circulation (~75%).
- C: Secreted abundantly at mucosal sites.
- D: Very low in serum.
63) A cytokine storm is caused by excessive production of:
A. TNF-α, IL-1, IL-6
B. IL-2, IL-4, IL-5
C. IL-10, TGF-β
D. IFN-β, IL-12
Answer: A
- A: Correct—major pro-inflammatory cytokines drive storm.
- B: Promote adaptive responses but not storm.
- C: Regulatory cytokines, suppress storm.
- D: Antiviral cytokines, not cytokine storm.
64) Which immunoglobulin is primarily secreted in breast milk?
A. IgM
B. IgE
C. IgA
D. IgG
Answer: C
- A: First antibody, but not milk-specific.
- B: Allergy-related, not in breast milk.
- C: Correct—secretory IgA protects infant mucosa.
- D: Crosses placenta, not milk.
65) Which receptor family recognizes pathogen-associated molecular patterns (PAMPs)?
A. Fc receptors
B. T cell receptors
C. Toll-like receptors (TLRs)
D. B cell receptors
Answer: C
- A: Bind Fc of antibodies.
- B: Recognize peptides, not broad PAMPs.
- C: Correct—TLRs are pattern recognition receptors.
- D: Recognize specific antigens, not conserved patterns.
66) Which immunoglobulin is found as a dimer in secretions?
A. IgG
B. IgM
C. IgE
D. IgA
Answer: D
- A: Monomer.
- B: Pentamer in serum.
- C: Monomer.
- D: Correct—secretory IgA forms dimers with J chain.
67) The thymus-independent antigens are usually:
A. Proteins
B. Lipids
C. Polysaccharides
D. Nucleic acids
Answer: C
- A: Require T cell help.
- B: Rarely immunogenic alone.
- C: Correct—repetitive polysaccharides activate B cells without T help.
- D: Not typical TI antigens.
68) Which T cell marker is characteristic of cytotoxic T lymphocytes?
A. CD4
B. CD8
C. CD19
D. CD25
Answer: B
- A: Helper T cells.
- B: Correct—CD8+ T cells are cytotoxic.
- C: B cell marker.
- D: Activation marker, not lineage-specific.
69) The complement fragment most potent for chemotaxis is:
A. C3a
B. C4a
C. C5a
D. C1q
Answer: C
- A: Weak anaphylatoxin.
- B: Mild activity.
- C: Correct—C5a is strongest chemoattractant.
- D: Initiates complement, no chemotaxis.
70) Which cytokine is produced by virus-infected cells as first defense?
A. IL-4
B. IFN-α and IFN-β
C. IL-10
D. TNF-α
Answer: B
- A: Class switching factor.
- B: Correct—type I interferons induce antiviral state.
- C: Immunosuppressive, not antiviral.
- D: Pro-inflammatory but not primary antiviral.
71) The “missing self” hypothesis is related to:
A. T helper cell tolerance
B. NK cell recognition of low MHC I
C. Treg function
D. Complement regulation
Answer: B
- A: Not relevant.
- B: Correct—NK cells kill cells with low/absent MHC I.
- C: Regulatory suppression.
- D: Complement, unrelated.
72) Anergy in T cells occurs when:
A. TCR signal occurs without co-stimulation
B. BCR is crosslinked
C. Complement is activated
D. Cytokine storm develops
Answer: A
- A: Correct—lack of CD28–B7 leads to T cell inactivation.
- B: Activates B cells, not anergy.
- C: Complement activation is separate.
- D: Excess cytokines cause hyperactivation, not anergy.
73) Central tolerance in B cells occurs in:
A. Lymph nodes
B. Bone marrow
C. Spleen
D. Thymus
Answer: B
- A: Peripheral tolerance.
- B: Correct—autoreactive B cells deleted or edited in bone marrow.
- C: Secondary organ, peripheral tolerance.
- D: T cell tolerance site.
74) Which antibody is most effective at neutralizing viruses at mucosal surfaces?
A. IgG
B. IgA
C. IgM
D. IgE
Answer: B
- A: Effective systemically.
- B: Correct—secretory IgA prevents viral entry at mucosa.
- C: First responder but not specialized for mucosa.
- D: Allergy-related.
75) Graft rejection mediated by T cells is an example of:
A. Type I hypersensitivity
B. Type II hypersensitivity
C. Type III hypersensitivity
D. Type IV hypersensitivity
Answer: D
- A: IgE mediated.
- B: IgG/IgM against cells.
- C: Immune complex-mediated.
- D: Correct—delayed-type hypersensitivity (cell-mediated).
🧬 Immunology MCQs – Part 4 (Q76–100)
Q76. Which immunoglobulin can cross the placenta?
A) IgA
B) IgM
C) IgG ✅
D) IgE
Answer: C) IgG
Explanation: IgG is the only antibody class that crosses the placenta, providing passive immunity to the fetus.
Q77. The main function of IgE is:
A) Agglutination
B) Complement activation
C) Allergic response and defense against parasites ✅
D) Opsonization
Answer: C) Allergic response and defense against parasites
Explanation: IgE binds to allergens and triggers mast cell degranulation; also provides defense against helminths.
Q78. The first antibody produced during a primary immune response is:
A) IgA
B) IgM ✅
C) IgG
D) IgD
Answer: B) IgM
Explanation: IgM is the earliest antibody produced in response to infection due to its pentameric structure and efficiency.
Q79. Which cytokine is critical for T helper 1 (Th1) cell differentiation?
A) IL-4
B) IL-2
C) IFN-γ
D) IL-12 ✅
Answer: D) IL-12
Explanation: IL-12 drives naïve CD4+ T cells to differentiate into Th1 cells, which produce IFN-γ.
Q80. The antigen-binding site of an antibody is formed by:
A) Constant heavy chains
B) Constant light chains
C) Variable regions of heavy and light chains ✅
D) Fc region
Answer: C) Variable regions of heavy and light chains
Explanation: The Fab portion (variable regions of both chains) binds to specific antigens.
Q81. Which is a secondary lymphoid organ?
A) Thymus
B) Bone marrow
C) Spleen ✅
D) Liver
Answer: C) Spleen
Explanation: Spleen, lymph nodes, and MALT are secondary lymphoid organs where immune responses occur.
Q82. The complement membrane attack complex (MAC) consists of:
A) C1–C4
B) C5b–C9 ✅
C) C2–C3
D) C3b only
Answer: B) C5b–C9
Explanation: MAC is formed by complement proteins C5b, C6, C7, C8, and multiple C9 molecules, creating pores in membranes.
Q83. Which MHC molecule presents exogenous antigens?
A) MHC I
B) MHC II ✅
C) Both MHC I and II
D) CD8
Answer: B) MHC II
Explanation: MHC II presents extracellular (exogenous) antigens to CD4+ T helper cells.
Q84. Toll-like receptor 4 (TLR4) recognizes:
A) Peptidoglycan
B) Lipopolysaccharide (LPS) ✅
C) Flagellin
D) CpG DNA
Answer: B) Lipopolysaccharide (LPS)
Explanation: TLR4 is specific for LPS, a component of Gram-negative bacterial cell walls.
Q85. The primary lymphoid organ for B-cell maturation in humans is:
A) Bone marrow ✅
B) Thymus
C) Spleen
D) Peyer’s patches
Answer: A) Bone marrow
Explanation: In humans, B cells mature in the bone marrow, while in birds they mature in the bursa of Fabricius.
Q86. Anergy in T cells refers to:
A) Overactivation
B) Cell death
C) Unresponsiveness despite antigen recognition ✅
D) Autoimmunity
Answer: C) Unresponsiveness despite antigen recognition
Explanation: T cell anergy occurs when antigen recognition happens without costimulatory signals.
Q87. Which immunoglobulin is found in breast milk and provides mucosal immunity?
A) IgG
B) IgA ✅
C) IgM
D) IgE
Answer: B) IgA
Explanation: Secretory IgA in breast milk protects infants’ mucosal surfaces.
Q88. Which cytokine is key for B cell class switching to IgE?
A) IL-2
B) IL-4 ✅
C) IL-12
D) IFN-γ
Answer: B) IL-4
Explanation: IL-4 promotes class switching of B cells to IgE, important in allergy and parasitic responses.
Q89. The process of generating antibody diversity occurs through:
A) Allelic exclusion
B) Somatic recombination ✅
C) Apoptosis
D) Antigen presentation
Answer: B) Somatic recombination
Explanation: V(D)J recombination generates diverse antibody specificities during B cell development.
Q90. Which type of immunity is provided by vaccines?
A) Natural active
B) Artificial active ✅
C) Natural passive
D) Artificial passive
Answer: B) Artificial active
Explanation: Vaccines stimulate the immune system to develop active, long-term immunity.
Q91. Which complement pathway is antibody-dependent?
A) Alternative
B) Lectin
C) Classical ✅
D) Terminal
Answer: C) Classical
Explanation: The classical pathway is initiated when antibodies (IgG or IgM) bind to antigens.
Q92. In HIV infection, which immune cells are primarily destroyed?
A) CD8+ T cells
B) CD4+ T cells ✅
C) B cells
D) NK cells
Answer: B) CD4+ T cells
Explanation: HIV targets CD4+ T helper cells, leading to immunodeficiency.
Q93. Which is an example of Type II hypersensitivity?
A) Asthma
B) Hemolytic anemia ✅
C) Serum sickness
D) Tuberculin reaction
Answer: B) Hemolytic anemia
Explanation: Type II hypersensitivity involves antibody-mediated cytotoxicity, as in autoimmune hemolytic anemia.
Q94. Delayed-type hypersensitivity is mediated by:
A) IgE
B) IgM
C) T cells ✅
D) Complement
Answer: C) T cells
Explanation: Type IV hypersensitivity is T-cell mediated, occurring after 24–48 hours.
Q95. Which organ is crucial for T cell maturation?
A) Bone marrow
B) Thymus ✅
C) Liver
D) Spleen
Answer: B) Thymus
Explanation: Immature T cells mature in the thymus before entering circulation.
Q96. Which immunoglobulin exists as a pentamer?
A) IgG
B) IgA
C) IgM ✅
D) IgE
Answer: C) IgM
Explanation: IgM circulates as a pentamer, making it effective in agglutination and complement activation.
Q97. What is the role of regulatory T cells (Tregs)?
A) Stimulate B cell proliferation
B) Suppress immune responses ✅
C) Activate NK cells
D) Produce IgE
Answer: B) Suppress immune responses
Explanation: Tregs maintain tolerance and prevent autoimmunity by suppressing overactive responses.
Q98. Which complement fragment is a strong opsonin?
A) C3b ✅
B) C4a
C) C5a
D) C1q
Answer: A) C3b
Explanation: C3b coats pathogens, enhancing phagocytosis (opsonization).
Q99. Which molecule provides the “second signal” for T cell activation?
A) CD28-B7 interaction ✅
B) TCR-MHC binding
C) IL-2 receptor
D) CD40-CD40L interaction
Answer: A) CD28-B7 interaction
Explanation: Costimulatory interaction between CD28 (T cells) and B7 (APCs) provides the second signal for activation.
Q100. Which antibody is most abundant in serum?
A) IgA
B) IgM
C) IgG ✅
D) IgE
Answer: C) IgG
Explanation: IgG constitutes about 70–75% of serum immunoglobulins, providing systemic immunity.
Immunology mcqs for cbse students, icse immunology objective questions, neet immunology solved mcqs, cuet biology immunology practice, csir net immunology multiple choice, gate life sciences immunology questions, usmle step 1 immunology mcqs, plab immunology exam practice, amc medical exam immunology questions, sat biology immunology subject test, gre biology immunology mcqs, bmat imat immunology solved questions
