Activation of ERK1/2 phosphorylation in sIgM-stimulated CLL B cells. (A) CLL samples were stimulated with anti-IgM for up to 60 minutes and ERK1/2 phosphorylation analyzed by flow cytometry. Graphs show the fold increase in ERK1/2 phosphorylation after stimulation with anti-IgM relative to untreated cells for 5 representative samples. (B) Correlation between the maximal percentage of cells showing increased intracellular Ca²⁺ and maximal fold induction of ERK1/2 phosphorylation after sIgM stimulation. Results of linear regression are shown (n = 37).