granzyymes

Granzymes are a family of serine proteases found in the granules of cytotoxic lymphocytes, specifically cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. Their primary role is to induce apoptosis, or programmed cell death, in target cells. When a CTL or NK cell recognizes a target cell that needs to be eliminated, such as a virus-infected cell or a tumor cell, it degranulates, releasing its granular contents, including granzymes, into the immunological synapse formed between the two cells.

Once released, granzymes can enter the target cell through various mechanisms, often facilitated by other proteins like perforin. Inside the target cell, granzymes activate a cascade of caspases, which are a group of proteases that execute the apoptotic program. This leads to the systematic dismantling of the cell, including DNA fragmentation and the formation of apoptotic bodies, which are then cleared by phagocytes. Different granzymes exist, each with slightly different substrate specificities and roles in initiating the apoptotic pathway. They are crucial components of the adaptive and innate immune systems for maintaining tissue homeostasis and defending against pathogens and cancer.