Granzyme B

Also: GZMB

Granzymes are exogenous serine proteinases released from cytoplasmic granules of cytotoxic lymphocytes (CTLs) and NK cells. The name “granzymes” is derived from: granules + enzymes. Upon binding of the CTL to a target cell, the contents of the granules are released in the intercellular space where perforin perforates the target cell membrane by forming transmembrane pores. Through these pores, granzymes enter the cytosol of the target cell to intiate the apoptotic pathway. Granzyme B has been called CTLA-1 (cytotoxic T lymphocyte-associated serine esterase 1) based on identification of mRNA in various cytotoxic T cells, but not observed in non-cytotoxic lymphoid cells. Granzyme B is crucial for the rapid induction of target cell death by apoptosis, induced by interaction with cytotoxic T cells. Granzyme B activates the intracellular cascade of caspases finally resulting in the killing of the target cells.