A Chronological Journey of Breg Subsets: Implications in Health and Disease

B cells play a multidimensional role in host immunity. Regulatory B (Breg) cells are a class of B lymphocytes with immunomodulatory properties that play an important role in maintaining immunological tolerance along with dampening harmful immune responses. Bregs suppress various immune pathologies through the production of interleukin (IL)-10, IL-35, and transforming growth factor-β (TGF-β). They act by inhibition of T helper 1 (Th1) and Th17 cells proliferation, suppression of dendritic cell (DC), differentiation and simultaneous enhancement of the expression and differentiation of fork head transcription factor P3-positive regulatory T cells (FoxP3+ Tregs). In this chapter, we discuss the induction, function, and phenotypes of the various Breg cell subsets defined in both mice and humans along with their proposed mechanism of action in various immune responses.