Normal expression and function of perforin with a serine substitution at residue 252. (A) The Western immunoblot shows the relative expression of D252S, D252N (as in human perforin), and D252E (as in flounder perforin) in transiently transfected RBL cells. (B) The line graph shows the lytic activity of D252S perforin (equivalent to N252S in humans) in the ⁵¹Cr-release cytotoxicity assay. (C) The bar charts compare the lytic capacity of perforin variants at position 252 grafted onto mouse perforin: D252E found in flounder (left) and D252N in human perforin (right). The data shown are mean ± SD and are representative of 3 independent experiments.