Q.36 Match the immune tolerance mechanisms in Group I with their respective
outcomes in Group II.
Group I                                                                            Group II
P. Anergy                                                           1. Elimination of activated T–cells after antigen clearance
Q. Activation–induced cell death                  2. Inhibition of auto–reactive T–cells at periphery
R. Receptor editing                                          3. Unresponsiveness to antigens due to lack of co–stimulatory molecules
S. Regulatory T–cells                                        4. Elimination of auto–reactive B–cells
(A) P–3, Q–1, R–4, S–2
(B) P–4, Q–3, R–1, S–2
(C) P–3, Q–4, R–2, S–1
(D) P–3, Q–2, R–4, S–1

Correct Answer: (A) P-3, Q-1, R-4, S-2

Anergy induces T-cell unresponsiveness when antigens lack co-stimulatory signals, activation-induced cell death (AICD) eliminates activated T-cells post-antigen clearance to prevent excess responses, receptor editing alters B-cell receptors to eliminate autoreactivity, and regulatory T-cells suppress peripheral autoreactive T-cells.

Mechanism Definitions

Anergy (P) renders T-cells unresponsive to antigens due to missing co-stimulation like CD28-B7 interaction, a key peripheral tolerance step. Activation-induced cell death (Q) triggers Fas-FasL apoptosis in expanded T-cells after pathogen clearance, contracting the response. Receptor editing (R) in bone marrow changes BCRs of autoreactive B-cells via RAG recombinases, promoting self-tolerance. Regulatory T-cells (S) inhibit autoreactive T-cells peripherally via IL-10, TGF-β, and contact suppression.

Option Analysis

• (A) P-3, Q-1, R-4, S-2: Matches perfectly—Anergy to lack of co-stimulation (3), AICD to T-cell elimination post-clearance (1), receptor editing to B-cell elimination (4, via editing failure leading to apoptosis), Tregs to peripheral inhibition (2).

• (B) P-4, Q-3, R-1, S-2: Incorrect—P (anergy) mismatches B-cell elimination (4); Q (AICD) mismatches co-stimulation lack (3); R mismatches T-cell clearance (1).

• (C) P-3, Q-4, R-2, S-1: Wrong—Q (AICD) not B-cell specific (4); R (editing) not peripheral T-inhibition (2); S not clearance-linked (1).

• (D) P-3, Q-2, R-4, S-1: Flawed—Q mismatches peripheral inhibition (2); S mismatches T-cell elimination (1).

Immune tolerance mechanisms prevent autoimmunity through processes like anergy, activation-induced cell death, receptor editing, and regulatory T-cells. This guide matches Group I mechanisms to Group II outcomes for competitive exams like GATE Biotechnology or IIT JAM, explaining P-3 (anergy to unresponsiveness sans co-stimulation), Q-1 (AICD for post-clearance T-cell elimination), R-4 (receptor editing eliminates autoreactive B-cells), and S-2 (Tregs inhibit peripheral autoreactive T-cells). Understanding these ensures self-tolerance in central (thymus/bone marrow) and peripheral immunity.

Central Tolerance Basics

Central tolerance deletes self-reactive cells early: receptor editing reshapes immature B-cell BCRs; failures trigger apoptosis (outcome 4). T-cells undergo negative selection via AIRE-driven self-antigen presentation.

Peripheral Tolerance Strategies

Anergy occurs when mature T-cells meet antigen without co-stimulation (outcome 3), blocking activation. Regulatory T-cells (FoxP3+ CD4+) suppress effectors at periphery via cytokines (outcome 2). AICD curbs responses post-infection by Fas-mediated death (outcome 1).