Immunity, Vaccines, and Cancer Practice Test 2026 – Complete Exam Prep

CD8+ T cells are cytotoxic T lymphocytes that kill infected or transformed cells. They recognize peptides presented by MHC class I molecules on nearly all nucleated cells, with the CD8 co-receptor helping stabilize this interaction. When activated, they release perforin and granzymes to induce apoptosis in the target cell (and can also use death-receptor pathways like Fas). This direct killing role sets them apart from helper T cells (CD4+), which mainly coordinate other immune cells through cytokines; regulatory T cells, which suppress immune responses; and B cells, which produce antibodies.