A cytotoxic T cell carries the CD8 marker. Which MHC class does that marker bind?
AMHC class I
BMHC class II
CMHC class III
DMHC class IV
Answer & Solution
Correct answer: A. MHC class I
1. T cells leaving the thymus are single positives, expressing either CD4 or CD8 but never both.
2. CD4 and CD8 are adhesion molecules that hold the T cell against the antigen-presenting cell by binding the MHC molecule itself.
3. CD4-bearing T cells bind class II MHC and are associated with helper functions.
4. CD8-bearing T cells bind class I MHC and are associated with cytotoxicity, so a cytotoxic T cell reads class I.
5. Class II is the trap here, since it belongs to the helper and regulatory side, and only class I and class II take part in antigen presentation.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 21 "The Lymphatic and Immune System", section 21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types_
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