CD8 surface antigen is a co-receptor characteristic of which T-cell subsets in human immunology?

Introduction / Context:
CD8 is a co-receptor that binds MHC class I and is central to cytotoxic T-cell function. Historically, “suppressor T cells” were also linked to CD8 expression in older literature, while modern terminology distinguishes CD8+ cytotoxic T lymphocytes and CD4+ regulatory T cells. The question reflects the legacy phrasing often seen on exams.

Given Data / Assumptions:

• We are using classical exam conventions where suppressor T cells are grouped with CD8 positivity.
• CD8 pairs with the TCR to recognize peptide–MHC class I.

Concept / Approach:
CD8 engagement stabilizes TCR–peptide–MHC I interactions and recruits signaling molecules. Most CD8+ cells are cytotoxic effectors or memory cells. Historical “Ts” (suppressor) were usually CD8+, although modern regulatory T cells (Treg) are primarily CD4+ CD25+ FoxP3+.

Step-by-Step Solution:

Verification / Alternative check:
Flow cytometry profiles show CD3+CD8+ for Tc cells. Older immunology texts list CD8 as a marker for cytotoxic/suppressor populations; contemporary Treg are CD4+ FoxP3+.

Why Other Options Are Wrong:

• Only cytotoxic: ignores the legacy suppressor designation used in some question banks.
• Only suppressor: incomplete.
• None or B/NK: incorrect; CD8 is T-lineage specific (with rare exceptions such as some NK subsets expressing CD8 alpha, but not as classical T-cell CD8αβ co-receptor).

Common Pitfalls:

• Mixing modern Treg (CD4+FoxP3+) with old “suppressor” terminology.

Final Answer:
Both cytotoxic (Tc) and suppressor subsets (historical term)