Antibody to a novel 95-kDa surface glycoprotein on human B cells induces calcium mobilization and B cell activation.
These findings characterize a 95-kDa glycoprotein on the surface of B lymphocytes recognized by the mAb G28-8. This protein (designated Bgp95), previously classified as a CD39 molecule, is unique based on functional, cell distribution, and immunochemical criteria. Biochemical analyses revealed that Bgp95 is a 95-kDa glycoprotein with N-linked carbohydrate and is reduced to about 70-kDa after treatment with endoglycopeptidase F. In functional studies, stimulation by G28-8 mAb or its F(ab')2 fragments induced a G0 to G1 cell cycle transition and was synergistic with PMA, anti-mu, or anti-CDw40 in stimulating proliferation of resting B cells. G28-8 mAb also could induce increases of cytoplasmic free calcium concentration [Ca2+]i in a subpopulation of tonsillar or peripheral blood B cells. The G28-8 mAb alone induced a steady increase in [Ca2+]i detectable even 1 h after stimulation. Cross-linking the G28-8 mAb with a second mAb specific for murine kappa light chains induced a more rapid increase of [Ca2+]i which peaked at 10 to 20 min and then declined. At 1 h after stimulation, [Ca2+]i was higher in B cells stimulated with G28-8 alone than in B cells stimulated with G28-8 plus anti-kappa. The same conditions of cross-linking with the anti-kappa which increased the kinetics of the [Ca2+]i response decreased the proliferative response which otherwise followed co-incubation of the mAb with B cell growth factor or PMA. Thus, conditions leading to rapid but transient [Ca2+]i increase via Bgp95 may not be as effective at stimulating B cell proliferation as conditions favoring a slower prolonged [Ca2+]i response. Although the Bgp95 molecule is present on activated buoyant tonsillar B cells, mAb to Bgp95 did not trigger [Ca2+]i increases in these cells. These results suggest that the Bgp95 protein may function in early B cell activation and that its signal mechanisms are altered by the activation state of the cell.
Valentine
M A
MA
Department of Microbiology, University of Washington, Seattle 98195.
Clark
E A
EA
Shu
G L
GL
Norris
N A
NA
Ledbetter
J A
JA
D000911:Antibodies, Monoclonal / Q000502:physiology*; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002453:Cell Cycle; D003432:Cross-Linking Reagents; D006801:Humans; D015847:Interleukin-4; D007378:Interleukins / Q000276:immunology* / Q000302:isolation & purification; D007399:Interphase; D007700:Kinetics; D008213:Lymphocyte Activation; D008562:Membrane Glycoproteins / Q000276:immunology* / Q000302:isolation & purification; D008970:Molecular Weight; D014066:Palatine Tonsil / Q000166:cytology
D000911:Antibodies, Monoclonal; D003432:Cross-Linking Reagents; D007378:Interleukins; D008562:Membrane Glycoproteins; D015847:Interleukin-4; D002118:Calcium