CROSS-LINKING OF FC-GAMMA RECEPTOR TO SURFACE-IMMUNOGLOBULIN ON B-CELLS PROVIDES AN INHIBITORY SIGNAL THAT CLOSES THE PLASMA-MEMBRANE CALCIUM-CHANNEL

Stimulation of B lymphocytes by the cross-linking of surface Ig (sIg) with an F(ab'), antibody fragment leads to the rapid activation of sev eral tyrosine kinases. This gives rise to the activation of phospholip ase C gamma (PLCgamma) and the generation of inositol phosphates. Thes e, in turn, lead to a prolonged elevation of intracellular Ca2+ ([Ca2]i) consisting of a rapid release of Ca2+ from intracellular stores an d a sustained influx of extracellular Ca2+. In contrast, co-cross-link ing sIg to Fcgamma receptor (FcgammaRII) with intact anti-sIg induces a much more transient increase in [Ca2+]i. Stimulation of the murine B cell lymphoma, A20, with F(ab')2 anti-sIgG leads to the production of high levels of IL-2, while co-cross-linking of sIgG with FcgammaRII b locks this response. In studies reported here, we show that co-cross-l inking of FcgammaRII with sIg prevents the influx of extracellular Ca2 + without significantly affecting the tyrosine phosphorylation of subs trates including PLCygamma1, PLCgamma2, and Syk or the mobilization of Ca2+ from intracellular stores. In cells that had been previously act ivated with F(ab')2 anti-IgG, co-cross-linking of slg to FcgammaRII ra pidly abrogated the influx of extracellular Ca2+ by closing the plasma membrane Ca2+ channel. Additionally, even 2-3 h after stimulation of the cells with F(ab')2 fragment, addition of intact anti-IgG to the ce lls, or removal of extracellular Ca2+, markedly inhibited (>90%) IL-2 production. These results indicate that co-cross-linking slg with Fcga mmaRII both prevented the opening of and actively closed the Ca2+ chan nel, and, through this mechanism, FcgammaRII was able to control produ ction of IL-2. Overall, since influx of extracellular Ca2+ has been fo und to be necessary for the proliferation and differentiation of B cel ls, FcgammaRII may play a critical role in controlling these responses by regulating the opening of the Ca2+ channel.