The acquisition of CD44DL requires IL-2 activation and transcription. LD-PBL were incubated for 3 days in the presence or absence of 100 U/mL IL-2 with or without 10 ng/mL actinomycin D, washed, and tested for the ability to lyse TNP-MC1 target cells at an effector:target ratio of 25:1. CD44DL, lysis measured in the presence of anti-CD44(Fab) × anti-DNP (Fab) bsAb; ADCC, lysis measured in the presence of intact rabbit anti-DNP Ab. Similar results were obtained at other effector:target ratios and in two of two other experiments. Data represent the means and standard errors of triplicate samples from a single experiment. (□) Resting; (▪) IL-2 activated.