Itk null CD4⁺ γδ T cells secrete IL-4 and induced B-cell class switch to IgE. (A) Sorted CD4⁺CD3⁺γδTCR⁺ cells and CD4⁻CD3⁺γδTCR⁺ cells from WT and Itk^−/− mice were stimulated with anti-γδTCR for 3 days. Supernatants were then analyzed for IL-4, IFN-γ, and IL-17. Data are representative of 3 independent experiments. Serum concentrations of IgE antibody in unimmunized mice. (B) Sera from the indicated mice were analyzed for IgE concentration. *P < .05. (C) Rag^−/− mice were reconstituted with different groups of B cells and T cells as indicated. Sera were analyzed for IgE 4 weeks after transfer.