Antigen-independent regulation of cytoplasmic calcium in B cells with a 12-kDa B-cell growth factor and anti-CD19

Abstract

Increases in cytoplasmic free calcium ([Ca2+](i)) can be induced in resting B cells either by a low molecular weight (12-kDa) B-cell growth factor (LMW-BCGF) or by crosslinking the B-cell antigen CD19 with monoclonal antibody (mAb). LMW-BCGF causes a slow [Ca2+](i) increase in peripheral blood and tonsillar B cells but has no effect on [Ca2+](i) in resting T cells. B-cell [Ca2+](i) responses mediated by anti-surface immunoglobulin (sIg) or anti-CD19 are potentiated by LMW-BCGF, but anti-sIg and anti-CD19 do not show additive [Ca2+](i) responses. LMW-BCGF- and anti-CD19-induced [Ca2+](i) signals are similar to the sIgM or sIgD-mediated signals in that they are inhibited by prior treatment with phorbol 12-myristate 13-acetate. However, LMW-BCGF- and CD19-mediated signals do not depend on the expression of sIg, since they were also observed on sIgB-cell precursor acute lymphoblastic leukemia (ALL) cells. Both anti-CD19 and LMW-BCGF stimulated in vitro colony formation by ALL cells and showed additive effects when used together. [Ca2+](i) responses to LMW-BCGF or CD19 crosslinking were also evident on certain pre-B-cell and lymphoma B-cell lines.