PD-L1hi B cells are critical regulators of humoral immunity
Specific B-cell subsets can regulate T-cell immune responses, and are termed regulatory B cells (Breg). The majority of Breg cells described in mouse and man have been identified by IL-10 production and are known to suppress allergy and autoimmunity. However, Breg cell mediated immune suppression, independent of IL-10, also occurs. Here we show that Breg cells play a critical role in regulating humoral immunity mediated by CD4+CXCR5+PD-1+ follicular helper T cells, and can suppress inflammation in autoimmune disease through elevated expression of PD-L1. We have also identified that these B cells are resistant to αCD20 B-cell depletion. This work describes how Breg cells are critical in humoral homoeostasis and may have implications for the regulation of autoimmune diseases. Follicular helper T cells promote antibody production by B cells, and regulatory B cells, in turn, can restrain T cell activation. Here, Khan et al. show that PD-L1 plays a critical role in regulatory B cell function, curbing excessive immune responses by engaging the PD-1 receptor on follicular helper T cells.