The Lytic enzymes of cytotoxic lymphocytes seem to be contained within lysosome-like granules found in the cytoplasm. These granules contain perforin，a membrane pore-forming protein，and a family of serine proteases (granzymes). Granzyme B，a 32 kDa protein，is a serine Aspase associated with the granules of Natural Killer (NK) cells. Granzyme B seems to be able to elicit cell death，perhaps by activating an endogenous pathway of programmed cell death.
