FIG. 3.
Proliferative responses and protein tyrosine phosphorylation of cellular proteins in APS−/− B cells. (A) Proliferation of splenic B cells induced by anti-IgM F(ab′)2, LPS, anti-IgM F(ab′)2 plus IL-4, and anti-CD40. Splenic B cells from +/+ (□) or −/− (⧫) mice were treated with the indicated stimuli, and proliferation was measured on day 3 by [3H]thymidine incorporation. The values are the mean counts per minute ± standard deviations of triplicate determinations. Representative results of three independent experiments are shown. (B) Phosphorylation of intracellular proteins induced by anti-IgM F(ab′)2 stimulation of splenic B cells from +/+ or −/− mice. Purified splenic B cells were stimulated with 30 μg of anti-IgM F(ab′)2 antibody/ml for the indicated times. The total cell lysates were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred to a polyvinylidene difluoride membrane. The membrane was probed with an anti-phosphotyrosine antibody, 4G10, and visualized by enhanced chemiluminescence.