T cell antigen recognition in adaptive immunity Which statement best describes the requirements and properties of antigen recognition by T lymphocytes in vertebrates?

Introduction:
T lymphocytes recognize short peptide fragments derived from proteins, a process central to cell-mediated immunity. Unlike B cells, which bind native antigens via surface immunoglobulin, T cells engage peptide–MHC complexes using the T cell receptor (TCR). Understanding this distinction clarifies why protein denaturation usually does not impair T cell epitope recognition.

Given Data / Assumptions:

• T cells recognize peptides presented by MHC molecules on antigen-presenting cells.
• Peptides are generated after antigen processing (proteolysis).
• Denaturation disrupts conformational epitopes but not the primary amino acid sequence.
• TCR is not an antibody; it is a distinct receptor with MHC restriction.

Concept / Approach:

Because T cells recognize linear peptides bound to MHC, the native 3D conformation of a protein is not required. Denaturation may even facilitate processing. In contrast, B cell epitopes are often conformational and can be lost upon denaturation.

Step-by-Step Solution:

Verification / Alternative check:

Experimental systems show T cells responding to chemically denatured proteins after processing, whereas many B cell antibodies fail to bind denatured antigens because conformational epitopes collapse.

Why Other Options Are Wrong:

Option A: T cells use TCRs, not membrane antibodies (those are on B cells).

Option C: MHC is essential (MHC restriction); removing MHC abrogates TCR recognition.

Option D: Antigen exposure during thymic maturation leads to tolerance, not a requirement for later recognition.

Option E: Some lipids and polysaccharides can be presented via specialized pathways, but direct recognition without presentation is not the general rule for conventional αβ T cells.

Common Pitfalls:

Confusing B cell conformational epitopes with T cell linear peptide epitopes; assuming all antigen recognition mechanisms are identical across lymphocyte subsets.

Final Answer:

Denaturation of the antigen generally does not reduce T cell epitope recognition