B lymphocyte receptors and polyphosphoinositide degradation

Summary Resting B lymphocytes can be activated and induced to proliferate by antibodies against their antigen receptors (anti-Ig). We demonstrate an early increase in the level of [3H]inositol trisphosphate in [ 3 H]inositol-labeled murine B cells, which suggests breakdown of phosphatidylinositol bisphosphate by phospholipase C. In line with this, the level of [ 3 H]1,2-diacylglycerol was also elevated after incubation of [ 3 H]arachidonic-acid-labeled B cells with anti-Ig. Anti-Ig also caused a rapid increase in the level of cytosolic Ca 2+ in B cells. In contrast, two other polyclonal B cell activators, lipopolysaccharide and phorbol myristate acetate, failed to induce any of these effects. Our results suggest that anti-Ig may induce B cell growth via phosphoinositide degradation and Ca 2+ . mobilization, and that phorbol myristate acetate, and possibly lipopolysaccharide, bypass these initial events.