AP BIOLOGY

Detailed explanation-1: -Cytotoxic T cells kill target cells bearing specific antigen while sparing neighboring uninfected cells. All the cells in a tissue are susceptible to lysis by the cytotoxic proteins of armed effector CD8 T cells, but only infected cells are killed.

Detailed explanation-2: -Natural killer (NK) cells target and kill aberrant cells, such as virally infected and tumorigenic cells. Killing is mediated by cytotoxic molecules which are stored within secretory lysosomes, a specialized exocytic organelle found in NK cells.

Detailed explanation-3: -Perforin plays an important role in cytotoxic activity of NK and cytotoxic CD8 T cells [3]. Both NK and CD8 cells use the same mechanisms to destroy target cells; however, activation pathways differ.

Detailed explanation-4: -CTLs kill target cells directly by inducing apoptosis. They release preformed perforins at the target cell surface to generate transmembrane pores in the target cell, through which a second set of proteins and granzymes gain entry into the cytosol to initiate an apoptotic series of events.

Detailed explanation-5: -Cytokine Secretion The first method cytotoxic T cells use to fight infection is the secretion of cytokines. Cytokines are substances that activate other cells. Cytotoxic T cells release two cytokines in particular, TNF-alpha and IFN-gamma, which facilitate the activation of macrophages.