Regulatory B cells: heterogeneity, immunosuppressive networks, and contributions to autoimmune pathogenesis.

B cells contribute to humoral immunity by producing antibodies, presenting antigens, and secreting cytokines. Traditionally, B cells have been viewed as predominantly pro-immunogenic effectors that promote adaptive immune responses. However, accumulating evidence has identified a distinct B cell subset with immunosuppressive properties, termed regulatory B cells (Bregs), which restrain pathogenic T-cell responses by secreting anti-inflammatory cytokines including interleukin-10 (IL-10), IL-35, and transforming growth factor β (TGF-β), and by expressing immunoregulatory surface molecules such as T cell immunoglobulin and mucin domain 1 (Tim-1), programmed cell death protein 1 (PD-1), and Fas ligand (FasL). Through these mechanisms, Bregs contribute to immune homeostasis and the maintenance of immune tolerance. Moreover, published studies have linked Bregs to the progression of autoimmune diseases, and substantial experimental data support quantitative and functional abnormalities of Bregs across multiple autoimmune conditions. In this review, we summarize current knowledge regarding the developmental origin, phenotypic features, and biological functions of Bregs, with emphasis on their roles in autoimmune diseases. A deeper understanding of Bregs in autoimmunity may provide a promising foundation for future immunotherapeutic strategies.