Section 4: Bioprocess Engineering and Process Biotechnology
Bioreactor types, scale-up
Subtopic: Fundamentals of Bioreactor types, scale-up
Question Statement:
Which of the following statement(s) is/are CORRECT for antigen activated effector T cells?
P. CD4+ cells make contact with macrophages and stimulate their microbicidal activity
Q. CD4+ cells make contact with B cells and stimulate them to differentiate into plasma cells
R. CD8+ cells make contact with B cells and stimulate them to differentiate into plasma cells
S. CD8+ cells make contact with virus infected cells and kill them
Options:
(A) Q only
(B) Q and S only
(C) P, Q and S only
(D) P, Q, R and S
Official Answer Key:
C
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2016 Q.48)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (2 Marks)
- **Topic**: Immunology (Effector T Cell Functions: $CD4^+$ Helper vs. $CD8^+$ Cytotoxic T Cells)
**2. Detailed Step-by-Step Analysis**:
- Let us evaluate each statement describing effector T lymphocyte functions:
- **Statement P**: *CD4+ cells make contact with macrophages and stimulate their microbicidal activity.*
- **CORRECT**: Effector $T_H1$ ($CD4^+$) cells recognize bacterial peptides on macrophage MHC Class II and secrete IFN-$\gamma$ plus engage CD40-CD40L, activating macrophages to kill intra-vacuolar pathogens.
- **Statement Q**: *CD4+ cells make contact with B cells and stimulate them to differentiate into plasma cells.*
- **CORRECT**: T follicular helper ($T_{FH}$) and $T_H2$ ($CD4^+$) cells recognize peptide-MHC Class II on antigen-specific B cells and deliver CD40L and cytokines (IL-4, IL-21) to induce B-cell proliferation, class switching, and plasma cell differentiation.
- **Statement R**: *CD8+ cells make contact with B cells and stimulate them to differentiate into plasma cells.*
- **INCORRECT**: Helper stimulation of B cells is performed exclusively by **$CD4^+$ T cells**, not cytotoxic $CD8^+$ T cells.
- **Statement S**: *CD8+ cells make contact with virus infected cells and kill them.*
- **CORRECT**: Cytotoxic T lymphocytes (CTLs, $CD8^+$) recognize viral peptides on MHC Class I and trigger targeted apoptosis via perforin/granzyme secretion or FasL-Fas interactions.
- Therefore, statements **P, Q, and S only** are CORRECT.
- **Option-by-Option Evaluation**:
- **Option (A) [INCORRECT]**: Omits P and S.
- **Option (B) [INCORRECT]**: Omits P.
- **Option (C) [CORRECT]**: P, Q, and S accurately describe the canonical physiological roles of $CD4^+$ helper and $CD8^+$ cytotoxic effector T cells.
- **Option (D) [INCORRECT]**: Includes false statement R.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **C**
- **Scoring Criteria**: +2.0 Marks (Negative marking: -0.67 marks).
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