Phosphorylation of ERK in CLL cells. (A) Extracts from CLL cells purified from peripheral blood of 6 representative patients (of 51 tested) were analyzed for phosphorylation of ERK1/2 by Western blot with p-ERK1/2–specific antibody (top panel). Immunoblot was stripped and reblotted with ERK2-specific antibody (middle panel) or β-actin–specific antibody (bottom panel). (B) Extracts from unstimulated Daudi cells, anti-IgM–treated Daudi cells, and unstimulated MEC1 cells were analyzed by SDS-PAGE followed by immunoblot with p-ERK1/2 antibody (top panel), followed by stripping and reblotting of the immunoblots with ERK2-specific antibody (middle panel) or β-actin–specific antibody (botttom panel). (C) Densitometric analysis of p-ERK/ERK levels in CLL samples. The values of individual patients were calculated as percentage of the positive control (MEC1 cell line) and determined as the ratio of the OD of p-ERK and OD of total ERK.