The expression of Tyk2 in DCs is required for in vivo priming of Th1 cells. DO11.10⁺ CD4⁺ T cells (1 × 10⁶ cells/mouse) were injected intraperitoneally into recipient BALB/c mice. Two days later, OVA323–339–pulsed WT or Tyk2^−/− CD11c⁺ DCs (3.5 × 10⁵ cells/mouse) were injected into footpad of the recipient mice. Five days later, popliteal lymph node cells were harvested from the recipient mice and cultured with OVA323–339–pulsed WT CD11c⁺ DCs at the indicated ratios for 96 hours. The amounts of IL-4 and IFN-γ in the supernatants were measured by ELISA. Data are means (± SD) from 4 independent experiments. *P < .05.