Co‐cross‐linking of surface immunoglobulin Fcγ receptors on B lymphocytes uncouples the antigen receptors from their associated G protein

摘要

AbstractCross‐linking of surface Ig receptors (sIg) by mitogenic forms of anti‐Ig antibodies (e.g.F(ab′)2fragments of rabbit anti‐Ig) causes the rapid, and prolonged breakdown of phosphatidylinositol 4,5‐bisphosphate. This response involves an unidentified guanine nucleotide regulatory protein (termed Gp), which couples sIg to the polyphosphoinositide‐specific phosphodiesterase. Intact (IgG) rabbit anti‐Ig antibodies, which co‐cross‐link sIg and Fcγ receptors on B cells, only induce short‐lived inositol phospholipid breakdown and abortive B cell activation. We show here that in permeabilized B cells intact anti‐Ig inhibits the reconstituted breakdown of inositol phospholipids given by a combination of F(ab′)2anti‐Ig and the non‐hydrolyzable GTP analogue guanosine‐5′‐O‐(3‐thiotriphosphate) (GTPγS), but not the basal stimulation of Gpinduced by GTPγS alone. These results therefore indicate that cocross‐linkage of sIg and Fcγ receptors on B cells uncouples the antigen receptors from the associated G protein, but does not affect coupling between Gpand the phosphodiesterase. These observations therefore provide further insight into the mechanisms whereby engaging Fc receptors on B cells, by antigen‐antibody complexes for example, cou