Cell-mediated immunity — Which T lymphocytes recognize and kill infected or foreign cells?

Introduction:
Cell-mediated immunity eliminates infected or altered self cells through specialized effector T cells. This question checks your understanding of terminology describing the cytolytic T-cell subset.

Given Data / Assumptions:

• Focus is on T-cell types involved in direct killing.
• Standard immunology nomenclature.
• Effector mechanisms include perforin/granzyme and Fas–FasL pathways.

Concept / Approach:
Cytotoxic T lymphocytes (CD8+) are commonly called killer T cells. They recognize peptides presented by MHC I on target cells and induce apoptosis to clear intracellular pathogens or malignant cells.

Step-by-Step Solution:

Verification / Alternative check:
Experimental assays (e.g., chromium release, flow cytometric killing assays) demonstrate specific lysis mediated by CD8+ CTLs against peptide-pulsed targets.

Why Other Options Are Wrong:

• None of the above: contradicts standard definitions.
• Memory B lymphocytes: mediate humoral memory, not cytolysis.

Common Pitfalls:
Confusing CTLs (CD8+) with NK cells (innate-like cytotoxicity) or with helper T cells (CD4+).

Final Answer:
both (a) and (b).