B cells: programmers of CD4 T cell responses.

B cells are once again gaining prominence as important programmers of CD4 T cell responses. With widespread use of B cell depletion therapy in the clinic, proving effective in treating diseases previously considered T cell-mediated, the time is right for a re-appraisal of the B cell. Though typically considered weak, Th2 driving APC, it is now clear that they are necessary for a robust and long-lived CD4 T cell response in many settings. The sphere of B cell influence extends well beyond that of simply antibody production; antigen presentation, cytokine secretion, costimulation and development of lymphoid tissue architecture are all critical aspects of B cell immunobiology, the absence of which has serious impacts for T cell priming and memory. The aim of this review is to look at non-antibody mediated B cell function and to ask how, where and when do B cells influence the CD4 T cell response?