Subtopic: Fundamentals of Cell structure and signaling
Question Statement:
Which of the following conditions promote the development of human autoimmune disorders?
P. Inability to eliminate self-reactive lymphocytes
Q. Generation of auto-antibodies
R. Ability to eliminate self-reactive T-cells
S. Induction of regulatory T-cells in the thymus
Options:
(A) P. R
(B) Q. S
(C) P, Q
(D) R. S
Official Answer Key:
C
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2017 Q.55)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (2 Marks)
- **Topic**: Immunology (Autoimmunity & Breakdown of Self-Tolerance)
**2. Detailed Step-by-Step Analysis**:
- **Autoimmune disorders** occur when the immune system breaks immunological self-tolerance and mounts destructive humoral or cell-mediated responses against host antigens:
- **Condition P**: *Inability to eliminate self-reactive lymphocytes.*
- **PROMOTES AUTOIMMUNITY**: Central tolerance (clonal deletion in bone marrow and thymus) eliminates immature B and T lymphocytes bearing high-affinity receptors for self-antigens. Failure of negative selection allows self-reactive clones to escape into the periphery, directly promoting autoimmunity.
- **Condition Q**: *Generation of auto-antibodies.*
- **PROMOTES AUTOIMMUNITY**: The synthesis of auto-antibodies by autoreactive B cells leads to immune complex deposition (e.g., in Systemic Lupus Erythematosus) or direct cytotoxic autoantibody destruction of host tissues (e.g., anti-AChR in Myasthenia Gravis, anti-TSHR in Graves' disease).
- **Condition R**: *Ability to eliminate self-reactive T-cells.*
- **PREVENTS AUTOIMMUNITY**: Eliminating autoreactive T cells is the hallmark of healthy central tolerance, protecting the host.
- **Condition S**: *Induction of regulatory T-cells ($T_{\text{reg}}$) in the thymus.*
- **PREVENTS AUTOIMMUNITY**: Thymic $T_{\text{reg}}$ cells ($CD4^+CD25^+\text{FoxP3}^+$) actively suppress autoreactive effector T cells in peripheral tissues, enforcing self-tolerance.
- Therefore, conditions **P and Q only** promote autoimmune pathology.
- **Option-by-Option Evaluation**:
- **Option (A) [INCORRECT]**: Condition R protects against autoimmunity.
- **Option (B) [INCORRECT]**: Condition S enforces peripheral tolerance and prevents autoimmunity.
- **Option (C) [CORRECT]**: Conditions P (failure to delete self-reactive clones) and Q (pathogenic autoantibody production) directly promote autoimmune disease.
- **Option (D) [INCORRECT]**: R and S both prevent autoimmunity.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **C**
- **Scoring Criteria**: +2.0 Marks (Negative marking: -0.67 marks).
Practice This in Real CBT Exam Interface
Test yourself with the official TCS-iON palette, virtual calculator, and immediate performance analytics.