Granzyme B is a cysteine protease found in the cytoplasmic granules of cytolytic T lymphocytes (CTL) and natural killer (NK) cells. Granzyme B is required for the induction of target cell lysis, which occurs as part of cell mediated immune responses, and can activate apoptosis in target cells by both caspase dependent and caspase independent mechanisms. Proteolytic cleavage of substrates by Granzyme B takes place primarily after aspartic acid residues. Recombinant Mouse.