p35^–/– and p40^–/– mice fail to generate Th1 immune responses. (a) Splenocytes from p35^–/–, p40^–/–, and WT mice were unstimulated (black bars) or were stimulated for 48 hours with IFN-γ and LPS (white bars). IL-12 p70 secretion was measured by ELISA. (b–d) p35^–/–, p40^–/–, and WT mice were immunized subcutaneously with KLH in CFA. After 5 days, recall responses of LN cells to either KLH (gray bars) or irrelevant ovalbumin (black bars) were measured by (b) [H]thymidine-uptake, (c) IL-2 ELISA, and (d) IFN-γ ELISA. Shown is a representative of at least two individual experiments.