Subtopic: Fundamentals of Cell structure and signaling
Question Statement:
Which one of the following mechanisms is used by human pathogens to evade host immune
responses?
Options:
(A) Somatic hypermutation
(B) Antibody production
(C) Antigenic variation
(D) Complement activation
Official Answer Key:
C
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2017 Q.07)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Topic**: Immunology & Medical Microbiology (Pathogen Immune Evasion Strategies)
**2. Detailed Step-by-Step Analysis**:
- To persist within hosts despite robust adaptive immune responses, successful pathogens employ sophisticated immune evasion strategies.
- **Antigenic variation** is the primary mechanism whereby a pathogen systematically alters its surface proteins, antigens, or epitopes over time:
- Examples include the Variant Surface Glycoproteins (VSG) of *Trypanosoma brucei*, the PilE/PilS pilin recombination in *Neisseria gonorrhoeae*, and antigenic drift/shift in Influenza virus.
- When the host mounts high-affinity neutralizing antibodies against the dominant surface antigen, a minority subpopulation expressing an altered variant antigen escapes immune clearance, multiplies, and causes relapsing infection waves.
- **Option-by-Option Evaluation**:
- **Option (A) [INCORRECT]**: Somatic hypermutation is a host immune mechanism occurring in germinal center B cells to increase antibody affinity, not a pathogen evasion strategy.
- **Option (B) [INCORRECT]**: Antibody production is an effector function of the host humoral immune system.
- **Option (C) [CORRECT]**: Antigenic variation allows pathogens to alter surface epitopes and evade pre-existing neutralizing antibodies and cytotoxic T-cell responses.
- **Option (D) [INCORRECT]**: Complement activation is a host innate defense pathway that lyses pathogens and recruits phagocytes.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **C**
- **Scoring Criteria**: +1.0 Mark (Negative marking: -0.33 marks).
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