Plays a key role in secretory granule-dependent cell death, and in defense against virus-infected or neoplastic cells. Plays an important role in killing other cells that are recognized as non-self by the immune system, e.g. in transplant rejection or some forms of autoimmune disease. Can insert into the membrane of target cells in its calcium-bound form, oligomerize and form large pores. Promotes cytolysis and apoptosis of target cells by facilitating the uptake of cytotoxic granzymes. Monomer, as sobluble protein. Homooligomer. Oligomerization is required for pore formation. Repressed by contact with target cells. Belongs to the complement C6/C7/C8/C9 family. Note: This description may include information from UniProtKB.