Low-Level Signaling Generated by FcγRIIB-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 (FcγRIIB). Moreover, many laboratories have demonstrated that co-ligation of BCR molecules to inhibitory FcγRIIB molecules with high concentrations (10-15 µg/ml) of ligand results in altered BCR signaling. However, there are no reports on the effect of low concentrations of ligand on BCR-FcγRIIB 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-FcγRIIB co-ligation and subsequent BCR signaling was analyzed. The results demonstrate that co-ligation of BCR and FcγRIIB molecules at low concentrations (0.5-1.5 µg/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-FcγRIIB co-ligation in cells expressing a nonsignaling competent BCR suggest that FcγRIIB-mediated inhibition of BCR signaling requires co-ligation of FcγRIIB with signaling competent BCR molecules. These results suggest that in vivo treatments with low levels ofBCR-FcγRIIB cross-linking reagent can induce BCR-FcγRIIB co-ligation and establish a condition of B cell nonresponsiveness.