IL-2 activation induces CD38 triggering function. Cells from 2 normal donors were cultured with 200 U/mL IL-2 for the indicated times and tested for the ability to lyse P815 target cells in the presence of medium alone (no Ab), anti-CD38, or anti-CD16 MoAbs. Lytic units were calculated from the E:T ratio giving 25% (donor 1) or 20% (donor 2) lysis (lytic units = 100/E:T). Asterisks indicate that lysis was less than 25% and 20% for donors 1 and 2, respectively, at all E:T. This experiment has been repeated 4 times with similar results. CD38-directed lysis appeared in different donors as early as 16 hours and as late as 4 days.