IC reduces T-cell cytokine production and contact hypersensitivity responses in vivo. WT B6 mice were given one oral dose of IC (30 mg/kg) 30 minutes before being administered anti-CD3 or ConA intravenously. Cytokine concentrations in the serum 1.5 hours after injection were measured: (A) IL-2, (B) IL-4, (C) IL-17, (D) IFN-γ, and (E) TNF-α. (F-G) WT and p110δ^D910A mice were sensitized on the abdomen with TNCB and then rechallenged with TNCB on one ear 6 days (F; primary response) or 6 and 30 days (G; secondary response) later. Mice were dosed twice orally with 30 mg/kg IC or MCL alone on the day of the final rechallenge, and the change in ear thickness was measured 24 hours later. The effect of p110δ genetic or pharmacologic inactivation was compared with WT mice receiving MCL only, and P values were calculated using 1-way analysis of variance with Bonferroni posttest. *.01 < P < .05; **.001 < P < .01; ***P < .001. Data are representative of 3 experiments for primary responses and 1 experiment for secondary responses.