Perforin 1 is one of the major cytolytic proteins of cytolytic granules. It is known to be a crucial effector molecule in cytolytic T lymphocyte and natural killer cell-mediated cytotoxicity. This protein has structural and functional similarities to complement component C9. Like C9, this protein creates transmembrane tubules and is capable of lysing nonspecifically a variety of target cells. Defects in PRF1 are the cause of familial hemophagocytic lymphohistiocytosis type 2 (FHL2), a rare and lethal autosomal recessive disorder of early childhood，which is characterized by immune dysregulation with hypercytokinemia and defective natural killer cell function. Alternative splicing results in multiple transcript variants encoding the same protein.