Peripheral immature B cells: modulators of autoimmunity.

B cells play an essential role in humoral immunity by producing antigen-specific antibodies. However, B cells also participate in cellular immune responses by presenting antigens, providing costimulation, and producing cytokines to activate and expand effectors and memory T cell populations. Recent identification of antibody-independent functions of B cells has reawakened interest in the many roles of B cells in normal immune responses as well as in autoimmune diseases. B cells interact with other immunocompetent cells during a tightly regulated immune activation process, acting as both effector and regulator. If this balance between effector and regulatory B cell functions is disrupted, harmful effects of immune activation such as autoimmunity can occur. In this review, we will discuss the role of human peripheral immature B cells in normal immune responses as a modulator of autoimmunity. We will also discuss abnormalities of these cells in pathogenesis of systemic autoimmunity with particular focus on systemic lupus erythematosus pathogenesis.