Leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1) is differentially expressed during human B cell differentiation and inhibits B cell receptor-mediated signaling.

Leukocyte-associated Ig-like receptor-1 (LAIR-1) belongs to the growing family of immunoreceptor tyrosine-based inhibitory motif-bearing receptors and is expressed on the majority of peripheral mononuclear cells, including NK cells, T cells, B cells, monocytes, and dendritic cells. In this study, we investigated the distribution and the capacity of LAIR-1 to function as an inhibitory receptor on human B cells. LAIR-1 is expressed from early on during B cell differentiation, but is absent on approximately half of the memory B cells, and all germinal center B cells, plasmablasts, and terminally differentiated plasma cells. In vitro stimulation of naive B cells via the B cell receptor (BCR) or CD40, triggering proliferation and differentiation into Ig-producing plasma cells, is accompanied by loss of LAIR-1 expression. We previously reported that LAIR-1 can function as an inhibitory receptor on NK cells and T cells. Here, we demonstrate that it can also function as a negative regulator of BCR-mediated signaling, since simultaneous cross-linking of LAIR-1 and the BCR reduces the increase of intracellular Ca(2+) evoked by BCR ligation. Taken together, this suggests that the inhibitory mechanism of LAIR-1 is functional in multiple components of the hematopoietic system.