Cytotoxic Lymphocytes

Killer lymphocytes provide powerful immune protection from cancer and infection by eliminating dangerous cells. Innate killer cells (principally natural killer cells) and innate-like T cells provide the first response. Antigen-specific immunity by cytotoxic T lymphocytes takes over about a week later and provides life-long immunity. When killer cells recognize a target cell, they mobilize cytotoxic granules filled with death-inducing pore-forming proteins (perforin, granulysin) and proteases (granzymes) to cause noninflammatory programmed death of the target cell. The pore-forming proteins deliver the granzymes into target cells and microbes, where they cleave multiple proteins to activate multifocal programs of cell death. Killer cells also control the immune response to infection by eliminating activated T cells once an infection has cleared using an alternate death pathway activated by death receptors on the target cell.