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 (B), similar to regulatory T cells (T). B 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. B limit host defense against various pathogens. In addition, B contribute to increased levels of regulatory cytokines and leads to an induction of suppressive T, which exert broader suppressive functions against various pathogens. The high percentage of B is positively associated with viral and bacterial load and can contribute to poor vaccine responses. B 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, B afford protection against the hyper-inflammatory response in parasitic infections. Here we review the central role of B in many major bacterial and viral human infections, and provide an overview of the immunoregulatory mechanisms used by B.