Imatinib inhibits signal transduction through TCR. Jurkat T cells were stimulated with 12F6 (100 ng/mL) or OKT3 (mouse ascites 1:250) for 5 minutes in the presence or absence of imatinib. (A) Whole-cell lysates were analyzed by Western blotting for tyrosine phosphorylation (PTyr). To control for protein loading, the antiphosphotyrosine antibody was inactivated and the membrane was reprobed with ZAP70 antibody. (B) ZAP70 was immunoprecipitated from 500 μg whole-cell lysate. Immunoblotting was performed with anti-ZAP70 or antiphosphotyrosine antibodies. (C) Whole-cell lysates were analyzed for LAT activation by immunoblotting for phosphorylated LAT (Tyr 171 and Tyr 191) and for total LAT as indicated.