# DBT JRF 2022 — Question 58

Exam: DBT JRF 2022 · Section: B · Topic: Immunology › MHC Restriction & T-Cell Recognition · Difficulty: Medium

## Question

T-cell clones in an individual recognize peptides only when bound and displayed by that individual's MHC molecules on the surface of antigen presenting cells. This process is known as:

## Options

- **A.** MHC selection
- **B.** MHC restriction
- **C.** MHC interaction
- **D.** MHC display

## Answer

Option B

## Explanation

MHC restriction of T cells: MHC (Major Histocompatibility Complex) restriction means that T lymphocytes can only recognise foreign antigens when presented by SELF-MHC molecules on the surface of antigen-presenting cells (APCs): • CD8+ cytotoxic T cells: recognise peptides presented by MHC class I (on all nucleated cells). • CD4+ T helper cells: recognise peptides presented by MHC class II (on professional APCs: dendritic cells, macrophages, B cells). This restriction is established during T cell development in the THYMUS: • Positive selection: T cells that can recognise SELF-MHC (regardless of peptide) survive. • Negative selection: T cells that bind self-MHC+self-peptide too strongly are eliminated (prevents autoimmunity). Significance: MHC restriction ensures that T cells only respond to foreign antigens presented by cells of the same individual, not in isolation. Answer: T cells recognise foreign peptides only when presented by self-MHC molecules.

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