FAK forms a complex with Csk and Lck in human T cells. A, Activated CD4 T cells were stimulated by anti-CD3 and anti-CD4 cross-linking for various times. The TCR/CD4 complex was then immunoprecipitated, and the expression of FAK, Csk, and Lck was analyzed by immunoblotting. Data is representative of three independent experiments. B, Control or Fak-deficient Jurkat T cells were stimulated for various times with anti-CD3. Csk was immunoprecipitated and its association with Lck was assessed by immunoblotting. Data is representative of three experiments.