IL-10-producing regulatory B cells (B10 cells) in autoimmune disease

B cell abnormalities contribute to the development and progress of autoimmune disease. Traditionally, the role of B cells in autoimmune disease was thought to be predominantly limited to the production of autoantibodies. Nevertheless, in addition to autoantibody production, B cells have other functions potentially relevant to autoimmunity. Such functions include antigen presentation to and activation of T cells, expression of co-stimulatory molecules and cytokine production. Recently, the ability of B cells to negatively regulate cellular immune responses and inflammation has been described and the concept of regulatory B cells has emerged. A variety of cytokines produced by regulatory B cell subsets have been reported, with IL-10 being the most studied. In this review, this specific IL-10-producing subset of regulatory B cells has been labeled B10 cells to highlight that the regulatory function of these rare B cells is mediated by IL-10, and to distinguish them from other B cell subsets that regulate immune responses through different mechanisms. B10 cells are a functionally defined subset currently identified only by their competency to produce and secrete IL-10 following appropriate stimulation. Although B10 cells share surface markers with other previously defined B cell subsets, currently there is no cell surface or intracellular phenotypic marker or set of markers unique to B10 cells. The recent discovery of an effective way to expand B10 cells ex vivo opens new horizons in the potential therapeutic applications of this rare B cell subset. This review highlights the current knowledge on B10 cells and discusses their potential as novel therapeutic agents in autoimmunity.