ITAM signaling is required for T-cell priming in vivo. WT and DF mice were immunized in the footpad with OVA peptide in CFA, and 7 days later, the draining popliteal lymph nodes were harvested. Lymph node cells were restimulated in vitro with the indicated doses of OVA peptide (continuous peptide) and analyzed 1 day later for the frequency of antigen-specific T cells by ELISPOT (A) and 3 days later for proliferation by thymidine incorporation (B). Data shown are the mean ± SD of triplicate samples. At least 4 mice per group were analyzed; *P < .05, **P < .01.