Deficiency of Act1, a critical modulator of B cell function, leads to development of Sjögren's syndrome

Abstract

CD40L and B lymphocyte‐activating factor (BAFF), members of the TNF superfamily, play critical roles in B cell survival and activation, and in the regulation of humoral immunity. We previously reported that the adaptor molecule Act1 functions as a negative regulator of CD40‐ and BAFF‐mediated B cell survival. Here we demonstrated that mice deficient in Act1 developed systemic autoimmune disease with histological and serological features of human Sjögren's syndrome (SS), in association with systemic lupus erythematosus‐like nephritis. Analyses of Act1^−/−CD40^−/− and Act1^−/−BAFF^−/− double‐deficient mice revealed that Act1 regulates different stages of the disease development through its impact on both CD40‐ and BAFF‐mediated pathways. We found that Act1 modulates the survival of autoreactive B cells mainly through its negative regulatory role in BAFF‐mediated cell survival, while the effect of Act1 on autoantibody production is likely through modulation of CD40‐mediated T cell‐dependent antibody response. The impact of Act1 on both BAFF and CD40 pathways establishes Act1‐deficient mice as a unique model to study distinct steps of autoimmunity and regulation of self tolerance.