V183G perforin has normal function but the C279Y substitution results in loss of perforin function. (A) Western immunoblot shows the relative expression of the wild-type, V183G, and C279Y perforins in transiently transfected FACS-sorted RBL cells. (B-C) ⁵¹Cr-release cytotoxicity assays using transfected RBL cells and Jurkat target cells at the E/T ratios indicated and comparing the putative perforin mutation V183G (B) and C279Y perforin (C) with WT perforin. Data shown are mean ± SD.