New insights into regulatory B cells biology in viral, bacterial, and parasitic infections

B lymphocytes are primarily well known for their contribution to immunity by antibody production, antigen presentation and, the production of cytokines. In recent years several studies demonstrated the existence of B cells with regulatory functions, which have been termed regulatory B cells (Bregs), similar to regulatory T cells (Tregs). Bregs are a subpopulation of B cells that have immunosuppressive effects via the production of regulatory cytokines including interleukin-10 (IL-10), transforming growth factor-β (TGF-β), and IL-35. Bregs limit host defense against various pathogens. In addition, Bregs contribute to increased levels of regulatory cytokines and leads to an induction of suppressive Tregs, which exert broader suppressive functions against various pathogens. The high percentage of Bregs is positively associated with viral and bacterial load and can contribute to poor vaccine responses. Bregs can also facilitate pathogen survival at an early stage of infection, and subsequently cause increased severity of disease by inhibiting pro-inflammatory cytokine production, macrophage activation, and inflammatory T cells activation such as Th1, Th17, and Th22. Also, Bregs afford protection against the hyper-inflammatory response in parasitic infections. Here we review the central role of Bregs in many major bacterial and viral human infections, and provide an overview of the immunoregulatory mechanisms used by Bregs.