AIM2 deficiency in B cells ameliorates systemic lupus erythematosus by regulating Blimp-1-Bcl-6 axis-mediated B-cell differentiation

Absent in melanoma 2 (AIM2) has been reported to be a component of inflammasomes in innate immune cells. Surprisingly, AIM2 is expressed by B cells, and higher AIM2 expression is observed in the B cells from lupus patients. To date, the inflammasome-independent function of AIM2 in B cells remains unclear. Here, we report increased expression of AIM2 in human tonsil memory and germinal center (GC) B cells and in memory B cells and plasma cells from the circulation and skin lesions of lupus patients. Conditional knockout of AIM2 in B cells reduces the CD19(+) B-cell frequency in lymph nodes and spleens, and dampens KLH-induced IgG1-antibody production. In a pristane-induced mouse model of lupus, AIM2 deficiency in B cells attenuates lupus symptoms and reduces the frequency of GC B cells, T follicular helper (Tfh) cells, plasmablast cells, and plasma cells. Furthermore, the loss of AIM2 in human B cells leads to the increased expression of Blimp-1 and reduces the expression of Bcl-6. However, the silencing of Blimp-1 and Bcl-6 has no significant effect on AIM2 expression, indicating that AIM2 might be the upstream regulator for Blimp-1 and Bcl-6. In addition, IL-10 is found to upregulate AIM2 expression via DNA demethylation. Together, our findings reveal that AIM2 is highly expressed in the B cells of lupus patients and promotes B-cell differentiation by modulating the Bcl-6-Blimp-1 axis, providing a novel target for SLE treatment.