Identification of a novel receptor for B lymphocyte stimulator that is mutated in a mouse strain with severe B cell deficiency

BLyS (also called BAFF, TALL-1, THANK, and zTNF4), a TNF superfamily member, binds two receptors, TACI and BCMA, and regulates humoral immune responses 1-7]. These two receptors also bind APRIL 7-10], another TNF superfamily member. The results from TACI(-/-) and BCMA(-/-) mice suggest the existence of additional receptor(s) for BLyS. The TACI knockout gives the paradoxical result of B cells being hyperresponsive, suggesting an inhibitory role for this receptor 11, 12], while BCMA null mice have no discernable phenotype 13]. Here we report the identification of a third BLyS receptor (BR3; BLyS receptor 3). This receptor is unique in that, in contrast to TACI and BCMA, BR3 only binds BLyS. Treatment of antigen-challenged mice with BR3-Fc inhibited antibody production, indicating an essential role for BLyS, but not APRIL, in this response. A critical role for BR3 in B cell ontogeny is underscored by our data showing that the BR3 gene had been inactivated by a discrete, approximately 4.7 kb gene insertion event that disrupted the 3' end of the BR3 gene in A/WySnJ mice, which lack peripheral B cells.