Tyrosine phosphorylation of CD33.

U937 cells were treated with (lanes 1 and 2) or without (lane 3) the phosphatase inhibitor pervanadate, lysed in Triton X-100 lysis buffer, and immunoprecipitated with anti-CD33 (lanes 2 and 3) or control antibody (IgG, lane 1). Immunoprecipitates were blotted with anti-phosphotyrosine (upper panel). Parallel blots were immunoblotted with anti-CD33 (lower panel).