Which of the following pairings is correct?

• A. Cytotoxic T cells destroy host cells bearing foreign antigen
• B. Helper T cells suppress T cell and B cell activity
• C. Suppressor T cells secrete IL-2
• D. B cells present antigen to T cells

Answer: (A)

Cytotoxic T cells protect the body by destroying host cells that display foreign antigens, such as virus‑infected or transformed cells. They recognize peptide fragments presented on MHC class I molecules on nearly all nucleated cells and, once activated, induce apoptosis through mechanisms like perforin/granzyme release or Fas–FasL signaling. This is the direct, targeted way the cell‑mediated immune response eliminates intracellular threats.

Helper T cells, in contrast, coordinate and amplify the response by providing cytokine signals to other immune cells, rather than suppressing them. Suppressor (regulatory) T cells regulate the immune response and help maintain tolerance; they do not primarily secrete IL‑2, which is a growth factor produced by activated helper T cells to promote proliferation. B cells can present antigen to T cells via MHC class II, especially to helper T cells, but the most general and representative antigen‑presentation interaction that drives primary T cell activation is typically dendritic cells presenting to naive T cells.