CD271 restrains the B1b cell antibody response in a T cell dependent manner

Co-signaling molecules modulate T cell function and are essential to control the duration and amplitude of immune responses. These molecules belong to the immunoglobulin and tumor necrosis factor receptor (TNFR) superfamilies and have been extensively studied; however, the immunomodulatory role of several family members remains unknown. We show that CD271 (also known as p75 or NGFR), a TNFR superfamily member, is highly expressed on peritoneal B1 B cells, but not on conventional (B2) B cells at steady state. CD271 expression by B cells specifically restrains the response to T cell-independent type 2 antigens (TI-2). B1 cell-expressed CD271 maintains peritoneal CD4+ T cell quiescence, and augmented antibody responses to TI-2 antigens in CD271-deficient mice are dependent on CD4+ T cells. This increase in antibody production correlates with improved bacterial neutralization in vitro and survival after bacterial challenge in vivo. Further, our results suggest that CD271 can directly inhibit mouse and human T cell activity to the same extent as PD-L1, a known, negative regulator of T cell function. These results establish CD271 as a co-inhibitory molecule that could be targeted to improve the efficacy of vaccines against pathogenic encapsulated bacteria and to broadly modulate the T cell response in therapeutic contexts. eTOC summaryLebel et al. identify an unexpected role for CD271, a neurotrophin receptor, in directly inhibiting T cell function. B1 cell-expressed CD271 maintains CD4+ T cell quiescence; in the absence of CD271, T cells bolster antibody production to T-independent antigens, enhancing the response to encapsulated bacteria.