Q.92 The formation of antigen-antibody complex helps in disposing antigen through the following
pathways EXCEPT:
(A) Neutralizing the antigen by blocking its activity
(B) By directly hydrolyzing the antigen
(C) By promoting the precipitation of antigen
(D) By activating cell lysis pathway
Antibodies do not directly hydrolyze antigens; this is not a disposal mechanism of antigen-antibody complexes.
The correct answer is (B).
Antigen-Antibody Complex Disposal Pathways
Antigen-antibody (Ag-Ab) complexes trigger effector functions via Fc region: neutralization blocks pathogen binding sites; precipitation/agglutination forms lattices cleared by phagocytosis; complement activation (classical pathway) leads to C3b opsonization, MAC lysis. Hydrolysis requires enzymes (lysosomal hydrolases post-phagocytosis), not Ab catalysis.
Option Breakdown
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(A) Neutralizing by blocking activity: Correct mechanism—steric hindrance prevents viral attachment, toxin binding (e.g., IgG vs. tetanus toxin).
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(B) Directly hydrolyzing antigen: Incorrect—Abs lack catalytic domains for hydrolysis; they bind, don’t cleave peptide bonds. Disposal post-binding via phagocytes/complement.
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(C) Promoting precipitation: Correct—multivalent IgM/IgG lattice formation exceeds solubility, precipitates for Fc-receptor clearance.
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(D) Activating cell lysis pathway: Correct—C1q binds Fc → C3 convertase → MAC pores lyse bacteria/enveloped viruses.
Introduction to Antigen Antibody Complex Disposal Pathways
Antigen antibody complex disposal pathways include neutralization, precipitation, opsonization, complement lysis—but never direct hydrolysis by antibodies. GATE Life Sciences immunology PYQ Q.92 tests effector mechanisms: Abs bind/mark for clearance, don’t enzymatically degrade.
Key Mechanisms
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Neutralization (A): Blocks pathogen receptors (IgG vs. viruses).
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Precipitation (C): Lattice formation → phagocytosis.
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Lysis (D): C1q → MAC pore formation.
Why No Hydrolysis
Antibodies = Y-shaped glycoproteins with Fab (binding) + Fc (effector). No active site for catalysis—contrast catalytic Abs (rare, artificial). Hydrolysis occurs post-phagocytosis in lysosomes.
Comparison Table
| Option | Valid Pathway? | Mechanism |
|---|---|---|
| (A) Neutralization | ✅ Yes | Steric block |
| (B) Hydrolysis | ❌ No | Abs non-catalytic |
| (C) Precipitation | ✅ Yes | Lattice formation |
| (D) Cell lysis | ✅ Yes | Complement MAC |
GATE Tip
Antigen antibody complex disposal pathways = effector functions, not catalysis. Memorize: “Antibodies tag, don’t chop.” Answer: (B). Essential for XL immunology.
