Tyrosine phosphorylation of STAT3 through the chimeric receptors. Cells expressing various chimeric receptors were either stimulated (+) with hGM-CSF (10 ng/mL) for 10 minutes or left unstimulated (-). STAT3 was immunoprecipitated from cell lysates using anti-STAT3 antibodies and then probed with either antiphosphotyrosine antibodies (upper panel) or anti-STAT3 antibodies (lower panel). The immune complex was visualized by chemiluminescence.