- The intracellular granzyme B inhibitor, proteinase inhibitor 9, is up-regulated during accessory cell maturation and effector cell degranulation, and its overexpression enhances CTL potency. Hirst, C.E., Buzza, M.S., Bird, C.H., Warren, H.S., Cameron, P.U., Zhang, M., Ashton-Rickardt, P.G., Bird, P.I. J. Immunol. (2003)