CD38 ligation induces ZAP-70 tyrosine phosphorylation. (A) CLL cells were purified from patients with CLL and ligated with the indicated Ab for 5 minutes at 37°C. Lysates were immunoprecipitated (IP) using an antiphosphotyrosine mAb, followed by Western blot (WB) with an anti–ZAP-70 reagent. The arrows indicate the relevant band; molecular weights are shown on the right. Ctrl indicates control total lysate of BJAB–ZAP-70–transfected cells; NT, not treated; H chain; heavy chain of the precipitating Ab. Vertical line has been inserted to indicate a repositioned gel lane. (B) BJAB–ZAP-70–transfected cells and control BJAB-mock were treated as in panel A. Top panel shows the results of the Western blot with an anti–c-myc mAb, which is confirmed in the bottom panel using an anti–ZAP-70 reagent. No tyrosine phosphorylation of ZAP-70 is observed in the mock-transfected cells. Ctrl indicates control total lysate of BJAB–ZAP-70⁺ or mock-transfected cells.