Comparative analysis of mouse and human perforin in RBL cells. (A) The experiment shown is a representative ⁵¹Cr release assay of RBL cells transfected with wild-type murine (mPRF-WT) or human (hPRF-WT) perforin or homologous mutants, mPRF-A90V or hPRF-A91V (mean ± SD). The Western blot shows relative levels of expression of human and mouse perforin in RBL cells. (B) Relative half-lives of the wild-type and A91V mutant perforin expressed in RBL cells. Shown is mean ± SE of 3 independent experiments. Intracellular levels of perforin at time “0” (prior to adding cyclohexamide) were designated as 100%.