Interactions between exogenous IL-12 and OX40 costimulation at priming. Cells were primed with anti-CD3 and CD32/B7.1 L cells alone (□) or in the presence of anti-OX40 (315; ▧) or control mouse IgG2a (▧) together with the indicated concentrations of IL-12. Primed cells were examined for cytokine production. Shown are the mean ± SEM of five experiments. IL-12 significantly inhibits (P < .05) the enhancing effect of OX40 costimulation on IL-5 and IL-13, but not on IL-4 production.