Which statement correctly describes CD8 T cells and their effector function in antiviral immunity?

Introduction / Context:CD8+ cytotoxic T lymphocytes (CTLs) are key effectors against intracellular pathogens, especially viruses. They survey MHC class I–presented peptides and kill infected targets through focused, contact-dependent mechanisms that limit bystander damage.

Given Data / Assumptions:

• Effector mechanisms include perforin/granzyme exocytosis and Fas–FasL engagement.
• Antigen recognition is peptide–MHC I–restricted.

Concept / Approach:Upon TCR recognition of foreign peptide on MHC I, CTLs form an immunological synapse with the target cell and deliver lethal hits through granule exocytosis or death receptor signaling. They do not secrete antibodies; that is a B-cell function. Both CD4 and CD8 thymocytes undergo positive and negative selection during development.

Step-by-Step Solution:

Verification / Alternative check:Immunology references detail CTL killing kinetics, immunological synapse, and serial killing capacity of CD8+ T cells.

Why Other Options Are Wrong:

• Only virus-infected: Too narrow; any MHC I–presented foreign peptide (including tumor neoantigens) can be targeted.
• Same epitopes as B cells: B cells recognize native conformations; T cells recognize processed peptides on MHC.
• Thymic selection claim: Both lineages undergo positive and negative selection.
• Antibody secretion: A B-cell function, not CD8+ T-cell.

Common Pitfalls:

• Confusing humoral and cellular effectors.
• Overgeneralizing targets of CD8+ T cells.

Final Answer:CD8 T cells can kill individual virus-infected cells via contact-dependent cytotoxicity (perforin/granzyme or Fas–FasL pathways)