PCI-32765 potently inhibits anti-IgM stimulation of pBtk and pERK, calcium mobilization, early activation marker and anti-IgM induced cell proliferation in human primary B lymphocytes. (a) Inhibition of intracellular pBtk (Y551) and pERK1/2 staining in B cells following anti-IgM stimulation with flow cytometry methods. (b) Inhibition of calcium mobilization following B-cell antigen receptor (BCR) stimulation in primary B cells. (c) Inhibition of the early activation marker CD69 following BCR stimulation in primary B cells. (d) PCI-32765 inhibits B lymphocyte proliferation stimulated by anti-IgM but not phorbol myristate acetate. Anti-CD3/28 failed to stimulate purified human B lymphocytes (not shown).