Immunology and the Immune System Practice Test

CD8 cytotoxic T cells specialize in destroying cells that harbor intracellular pathogens or have become abnormal. They patrol nearly all body cells for peptides presented on MHC class I molecules. When a CD8 T cell recognizes its specific antigen on an infected or transformed cell, it becomes activated (with help from co-stimulation and cytokines) and differentiates into a cytotoxic lymphocyte. It kills the target by releasing perforin to form pores in the cell membrane and granzymes to enter and trigger apoptosis; Fas-FasL interactions can also initiate cell death. This mechanism clears infected or malignant cells from the body while keeping the pathogens contained inside the dying cells. This role is distinct from antibody production by B cells and from phagocytosis by macrophages or neutrophils, which are separate parts of the immune response.