Spontaneous and induced NK/LAK activity against P815 tumor targets. NK cells from wild-type (A and D), gld/gld (B and E), and perforin KO (C and F) mice were tested for cytotoxicity against NK-resistant P815 tumor targets as described in Fig 1. In (D), (E), and (F), in vitro IL-2–activated LAK cells were used as effectors and cytotoxicity was performed in the presense of medium, concanamycin A (100 nmol/L), or anti-Fas MoAbs (2 μg/mL). The symbols used in (B) are common to (A) and (C). Also, symbols shown in (E) are similar to those used in (D) and (F).