Abstract
B cells are differentiated to recognize antigen and respond by producing antibodies. These activities, governed by recognition of ancillary signals, defend the individual against microorganisms and the products of microorganisms and constitute the canonical function of B cells. Despite the unique differentiation (e.g. recombination and mutation of immunoglobulin gene segments) toward this canonical function, B cells can provide other, "non-canonical" functions, such as facilitating of lymphoid organogenesis and remodeling and fashioning T cell repertoires and modifying T cell responses. Some non-canonical functions are exerted by antibodies, but most are mediated by other products and/or direct actions of B cells. The diverse set of non-canonical functions makes the B cell as much as any cell a central organizer of innate and adaptive immunity. However, the diverse products and actions also confound efforts to weigh the importance of individual non-canonical B cell functions. Here we shall describe the non-canonical functions of B cells and offer our perspective on how those functions converge in the development and governance of immunity, particularly immunity to transplants, and hurdles to advancing understanding of B cell functions in transplantation.