IMMUNOLOGY

Detailed explanation-1: -Cytotoxic CD8 T cells carry out their killing function by releasing two types of preformed cytotoxic protein: the granzymes, which seem able to induce apoptosis in any type of target cell, and the pore-forming protein perforin, which punches holes in the target-cell membrane through which the granzymes can enter.

Detailed explanation-2: -Cytotoxic T cells and NK cells can use the release of perforin and granzymes from lytic granules and the surface expression of ligands for death receptors to kill virally infected or transformed cells (Figure 2).

Detailed explanation-3: -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-4: -Natural killer (NK) cells kill cancer cells by secreting perforins and granzymes. Upon contact with cancer cells, NK cells form immune synapses to deliver the lethal hit. Mature NK cells are differentiated from hematopoietic stem cells in the bone marrow.

Detailed explanation-5: -Once perforin has formed a pore in the cell membrane, granzymes may enter the target cell cytoplasm and cleave a number of substrates, leading to apoptosis via the intrinsic pathway: Granzyme B cleaves pro-caspases 3, 7 and 8, triggering apoptosis in the target cell.