Low-level signaling generated by FcgammaRIIB-B cell receptor co-ligation establishes a state of global B cell receptor nonresponsiveness.

In addition to the stimulatory, antigen-specific B cell receptor (BCR), B lymphocytes also express multiple inhibitory receptors, including Fc gamma receptor type IIB (FcgammaRIIB). Moreover, many laboratories have demonstrated that co-ligation of BCR molecules to inhibitory FcgammaRIIB molecules with high concentrations (10-15 microg/ml) of ligand results in altered BCR signaling. However, there are no reports on the effect of low concentrations of ligand on BCR-FcgammaRIIB co-ligation and subsequent signaling. This knowledge will be critical for optimizing the in vivo use of such reagents. Accordingly, the effect of low ligand concentration on the level of BCR-FcgammaRIIB co-ligation and subsequent BCR signaling was analyzed. The results demonstrate that co-ligation of BCR and FcgammaRIIB molecules at low concentrations (0.5-1.5 microg/ml) of cross-linking reagent, establishes a condition that prevents the B cell from responding to subsequent stimulation, even when the initial exposure to cross-linking reagent fails to generate a calcium flux. Moreover, analysis of the effect of BCR-FcgammaRIIB co-ligation in cells expressing a nonsignaling competent BCR suggest that FcgammaRIIB-mediated inhibition of BCR signaling requires co-ligation of FcgammaRIIB with signaling competent BCR molecules. These results suggest that in vivo treatments with low levels of BCR-FcgammaRIIB cross-linking reagent can induce BCR-FcgammaRIIB co-ligation and establish a condition of B cell nonresponsiveness.