Regulatory B cells: the new "it" cell.

Regulatory B cells (Breg) are a subpopulation of B cells that play a suppressive role in the immune system. The mechanism of how these immune cells perform their effects has been explored by experiments in mice and in humans. Intracellular staining for interleukin 10 continues to be a consistent and reproducible method of identifying Breg in mouse and human studies. The lack of Breg is associated with a worsening of several autoimmune diseases such as collagen-induced arthritis, systemic lupus erythematosus, and experimental autoimmune encephalomyelitis in murine studies. The purpose of this review is to provide a concise summary of the role of Breg in the immune system, including the most recently studied cell surface markers associated with Breg, and to describe the role of Breg in the etiology of several autoimmune diseases, the current understanding of Breg development, their role in the development of autoimmune diseases, and their role in inducing tolerance after transplantation.