Pretreatment of LPS-DCs and ssRNA-DCs with the p38 MAPK inhibitor SB203580 recovers the late IL-12p70 response but not a Th1-polarizing potential. For pretreatment, on day 0 (d0), monocytes cultured in GM-CSF and IL-4 to induce DC differentiation were treated for 30 min with 1 μM SB203580 (SB) or left untreated before medium, LPS, or ssRNA was added. For maturation stimulus, on day 5 (d5), DCs were stimulated with LPS for 24 h or left untreated. (A) Day 6 supernatants were tested for IL-12p70 by ELISAs. (B and C) DCs were cocultured with allogeneic carboxyfluorescein diacetate succinimidyl ester-labeled naive CD4 T cells. On day 6, T-cell proliferation (B) and intracellular IFN-γ accumulation (C) were determined by FACS analysis. In the proliferation assay (B), the frequency of responding autologous naive CD4 T cells was under 1.0% in all cases (not shown). Statistically significant differences (P < 0.05) between the control and a given test are indicated with an asterisk.