A view to a kill: signals triggering cytotoxicity.

Tumor immunity requires the participation of lymphocyte effector cells that display powerful processes to destroy malignant cells. Natural killer (NK) cells and CTLs, once activated, use the same lytic processes for mediating target cell death. However, they are triggered through distinctly separate antigen receptors. NK cells are currently known to express at least three families of receptors unrelated to the T cell receptor, i.e., NKG2, KIR, and NCR, to mediate cytotoxicity. This review provides a view to a kill, bringing together a unifying concept for a common signal pathway that dictates lytic function. What emerges is a specific Syk/Zap70 --> PI3K --> Rac --> PAK --> MEK --> ERK signal cascade triggered by target cell recognition, which is responsible for mobilizing the lytic granules containing perforin and granzyme B toward the contacted target cell.