Effect of IL-18 on DC2 differentiation. (A) Proliferation. Pre-DC2s were cultured with indicated agents for 3 days and subsequently pulsed with ³H-thymidine for 19 hours. IL-18 significantly inhibited proliferation of pre-DC2s expanded with IL-3 (n = 3). (B) Cell count. Pre-DC2s (initially 250 000 cells) were cultured with indicated cytokines and counted at the given time points (n = 2). Error bars indicated SEM.