Granzyme B belongs to the family of granule serineproteases and is exclusively found in cytotoxic T cells ornatural killer cells. Both natural killer (NK) cells andcytolytic T lymphocytes (CTL) have the capacity to identify,attach to, and lyse particular target cells. By lysing cells thathave “nonself” antigens—typically peptides or proteins—on their surface as a result of intracellular pathogeninvasion, they are believed to protect their host. GranzymeB is essential for CTLs to quickly induce target cell deathduring the cell-mediated immune response. When used inconjunction with CD56, Granzyme B is a helpful marker forNK/T-cell lymphomas.