A 70 Kd (kilodalton) protein that is instrumental in the lysis of infected cells. A series of reactions occurs on the surface of a cell which results in the polymerization of certain monomers to form trans-membrane (i.e., through the membrane) pores 100 A (Angstroms) wide, which allows ions to rush into the cell (due to osmotic pressure) and thus burst (lyse) that cell, so the (formerly) internal pathogens can be attacked by the body’s immune system. Perforin is a protein that is akin to the C9 component of the complement.
One of a group of membrane-altering proteins released from natural killer cells and cytotoxic T cells that drill holes in cell membranes, causing affected cells to die. Perforins contribute to innate immune defenses against viruses and tumors.