title: Anti-Ig-mediated proliferation of human B cells in the absence of protein kinase C.
abstract: Cross-linking of surface Ig has been shown to stimulate phosphatidylinositol hydrolysis in murine B cells, leading to increases in [Ca2+]i and activation of protein kinase C (PKC). Preliminary evidence suggests that a similar activation mechanism occurs in human B cells. We wished to examine whether anti-Ig antibody-stimulated human B cell proliferation is as dependent upon the presence of PKC as is anti-Ig-mediated murine B cell proliferation. Using highly purified, small, dense peripheral-blood B lymphocytes from healthy adult donors, we confirmed that PMA, a direct activator of PKC, is a potent mitogen for human B cells that synergizes with anti-mu antibody. Furthermore, we demonstrated that PMA treatment abolishes detectable cellular stores of immunoreactive PKC. However, after such depletion of cellular PKC, anti-mu antibody is still capable of delivering a proliferative signal to human B cells. It is unlikely that this signal occurs solely on the basis of increases in [Ca2+]i, because the calcium ionophore A23187 does not induce a proliferative response in PMA-treated B cells similar in magnitude to that seen with anti-mu. Additionally, the finding that pretreatment of B cells with PMA ablates the ability of anti-Ig antibody to mobilize intracellular and extracellular calcium also suggests that the ability of PMA to enhance anti-Ig mediated stimulation does not depend on elevations of [Ca2+]i induced by anti-Ig. Together, these observations suggest that anti-Ig signaling of human B cells may occur via other pathways in addition to the phosphatidylinositol system of calcium influx and PKC activation.
mesh_terms: D000328:Adult; D000888:Antibodies, Anti-Idiotypic / Q000502:physiology*; D001402:B-Lymphocytes / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology* / Q000502:physiology; D008213:Lymphocyte Activation / Q000187:drug effects; D010716:Phosphatidylinositols / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000888:Antibodies, Anti-Idiotypic; D007075:Immunoglobulin M; D010716:Phosphatidylinositols; C044203:anti-IgM; D000001:Calcimycin; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium