Cytotoxicity mediated by LAK cells activated in vivo with IL-2. Wild-type (A), gld/gld (B), or perforin KO (C) mice were injected with 10,000 U of IL-2 twice a day for 4 days and the LAK cells were tested for cytotoxicity against L1210 Fas⁻ and L1210 Fas⁺ tumor targets. Cytotoxicity was studied as described in Fig 1.