Effector Th cell development in the absence of Vav1. Naive CD4⁺ T cells from wild-type and Vav1^–/– mice were primed by stimulation with anti-CD3/CD28– coated tissue culture plates under Th1, Th2, or neutral conditions. After 7 days, the cells were washed, counted, and restimulated with plate-bound anti-CD3/CD28 antibodies. (A-B) Cytokine-producing cells were enumerated by ICCS after 8 hours of stimulation. (C) Levels of IFN-γ or IL-4 in 48-hour stimulated culture supernatants were quantified by ELISA. The data shown are representative of 5 independent experiments. Data are expressed as the mean value of triplicate determinations ± standard error (SE). (D) T cells primed under Th2-inducing conditions in the absence or presence of a neutralizing anti–IFN-γ antibody were restimulated in anti-CD3/CD28 antibodies– coated tissue culture plates, and IL-4⁺ versus IFN-γ⁺ cells were enumerated by ICCS.