Subtopic: Fundamentals of Cell structure and signaling
Question Statement:
Which one of the following is NOT a principal component of innate immunity?
Options:
(A) Mucosal epithelia
(B) Dendritic cells
(C) Complement system
(D) Memory B-cells
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2018 Q.21)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Topic**: Immunology (Innate vs. Adaptive Immunity)
**2. Detailed Step-by-Step Analysis**:
- The immune system is bifurcated into innate immunity and adaptive (acquired) immunity:
- **Innate Immunity**: The first, non-specific line of defense present from birth. Its primary cellular and humoral components include:
- Physical and chemical barriers (epithelial cell layers, mucosal linings, antimicrobial peptides).
- Phagocytic cells (macrophages, neutrophils, dendritic cells).
- Natural killer (NK) cells.
- Humoral pattern recognition and cascade systems, notably the **complement system**.
- **Adaptive Immunity**: Characterized by antigen specificity, somatic gene rearrangements, clonal selection, and immunological memory. Its principal effectors are **B lymphocytes** (humoral immunity) and **T lymphocytes** (cell-mediated immunity).
- Therefore, **T lymphocytes** are the principal components of adaptive immunity, NOT innate immunity.
- **Option-by-Option Evaluation**:
- **Option (A) [INCORRECT]**: Mucosal epithelium is a fundamental physical and chemical barrier of innate immunity.
- **Option (B) [INCORRECT]**: Dendritic cells are key cellular components of innate immunity that act as antigen-presenting cells (APCs).
- **Option (C) [INCORRECT]**: Complement system is a major humoral effector arm of innate immunity.
- **Option (D) [CORRECT]**: T lymphocytes are antigen-specific cells belonging strictly to adaptive immunity.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **D**
- **Scoring Criteria**: +1.0 Mark (Negative marking: -0.33 marks).
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