BAFF promotes follicular helper T cell development and germinal center formation through BR3 signal.

ABSTRACT

T follicular helper (Tfh) cells represent an important subset of CD4+ T cells that is crucial to the maturation and differentiation of B cells and the production of high-affinity antibodies. Since BAFF, a vital B cell survival factor, is also crucial to B cell maturation and differentiation, we assessed the effects of BAFF on Tfh cell development and function. We demonstrate that deficiency of BAFF, but not of APRIL, markedly inhibits Tfh cell development, germinal center (GC) formation, and antigen-specific antibody production. The promoting effect of BAFF on Tfh cell development is dependent on expression of BR3 on T cells, and its promoting effect on GC formation is dependent on expression of BR3 on both T cells and B cells. BAFF directly promotes expression of the Tfh cell-characteristic genes via NF-κB signaling. This effect does need BR3 expression. Thus, BAFF not only has direct effects on B cells, but it also has direct effects on Tfh cell differentiation via engagement of BR3 which collectively promote GC formation and production of high-affinity antibodies. This dual effect of BAFF on B cells and Tfh cells may help explain the clinical utility of BAFF antagonists in the management of certain autoimmune diseases.