Comparison of spontaneous, poly I:C-, and IL-2–induced NK/LAK-cell activity in C57BL/6 wild-type, gld/gld, and perforin KO mice. NK/LAK cells from wild-type (A), gld/gld (B), and perforin KO (C) mice were tested for cytotoxicity against NK-sensitive YAC-1 tumor targets. The same symbols were used in (A), (B), and (C) to depict different types of cytotoxicity. The cytotoxicity was studied using ⁵¹Cr-release assay and the mean percent cytotoxicity ± SEM of triplicate culture were plotted.