Role of cytotoxic T cells (CD8+) in adaptive immunity?

• A. They recognize and kill infected or abnormal host cells presenting antigen on MHC class I.
• B. They produce antibodies.
• C. They present antigens to B cells.
• D. They differentiate into plasma cells.

Answer: (A)

Cytotoxic CD8+ T cells are the cellular immune effectors that identify and destroy cells showing abnormal or foreign peptides on MHC class I. When a nucleated cell presents a viral or aberrant peptide on MHC I, the CD8+ T cell recognizes it and, after activation, delivers killer signals—perforin creates pores and granzymes enter to induce the target cell to undergo apoptosis. This directly eliminates infected or transformed cells and prevents pathogen spread from within.

Producing antibodies is the job of B cells that become plasma cells, not CD8+ T cells. Antigen presentation to B cells is typically done by antigen-presenting cells like dendritic cells, macrophages, or B cells themselves, usually involving MHC II, and CD8+ T cells do not differentiate into plasma cells.