Normal induction but attenuated progression of germinal center responses in BAFF and BAFF-R signaling-deficient mice.

The factors regulating germinal center (GC) B cell fate are poorly understood. Recent studies have defined a crucial role for the B cell-activating factor belonging to TNF family (BAFF; also called BLyS) in promoting primary B cell survival and development. A role for this cytokine in antigen-driven B cell responses has been suggested but current data in this regard are limited. A BAFF receptor expressed by B cells (BAFF-R/BR3) is defective in A/WySnJ mice which exhibit a phenotype similar to BAFF-deficient (BAFF-/-) animals. Here, we show that although GC responses can be efficiently induced in both A/WySnJ and BAFF-/- mice, these responses are not sustained. In BAFF-/- mice, this response is rapidly attenuated and accompanied by perturbed follicular dendritic cell development and immune complex trapping. In contrast, analysis of the A/WySnJ GC response revealed a B cell autonomous proliferative defect associated with reduced or undetectable Ki67 nuclear proliferation antigen expression by GC B cells at all stages of the response. These data demonstrate a multifaceted role for the BAFF pathway in regulating GC progression.