Virtually all of the measurable cell-mediated cytotoxicity delivered by cytotoxic T
lymphocytes and natural killer cells comes from either the granule exocytosis pathway or the
Fas pathway. The granule exocytosis pathway utilizes perforin to traffic the granzymes to
appropriate locations in target cells, where they cleave critical substrates that initiate DNA
fragmentation and apoptosis; granzymes A and B induce death via alternate,
nonoverlapping pathways. The Fas/FasL system is responsible for activation-induced cell …