Clinical Implications of Basic Science Discoveries: Janus Resurrected—Two Faces of B Cell and Plasma Cell Biology

B cells play a complex role in the immune response. In addition to giving rise to plasma cells (PCs) and promoting T cell responses via antigen presentation, they perform immunoregulatory functions. This knowledge has created concerns regarding nonspecific B cell depletional therapy because of the potential to paradoxically augment immune responses. Recent studies now indicate that PCs have immune functions beyond immunoglobulin synthesis. Evidence for a new role for PCs as potent regulatory cells (via IL‐10 and IL‐35 production) is discussed including the implications for PC‐targeted therapies currently being developed for clinical transplantation. In this new feature, the authors discuss the recent article “IL‐35‐producing B cells are critical regulators of immunity during autoimmune and infectious diseases” (Nature 2014; 507: 366–370) and its implications for transplantation.