Cytokine-producing B cells as regulators of pathogenic and protective immune responses.

B lymphocytes play a unique role in immunity through the production of antibodies. In addition, they can secrete various arrays of cytokines classically associated with innate or adaptive immune cells. During the last 10 years, it has become apparent that secretion of cytokines by B cells can play decisive roles in immunity. For instance, B cells can act both as regulators and drivers of autoimmune pathogenesis through production of cytokines, such as interleukin-10 or interleukin-6, respectively. Similarly, B cells can either inhibit or stimulate antimicrobial immunity through secretion of interleukin-10 or interleukin-2, respectively. Despite the fact that other cell types can produce the same factors, B cells are often a non-redundant source of these cytokines, a feature possibly attributable to the fact that B cells generally reside in microenvironments different from T cells in secondary lymphoid organs and inflamed tissues. This review discusses examples that illustrate the diversity of functions B cells can perform through the production of cytokines, highlighting the importance of this aspect of B cell biology in health and disease.