Acsbg1 maintains intestinal immune homeostasis and controls inflammation by regulating ST2+ Tregs.

The immune balance in mucosal tissues depends on a delicate interplay between inflammatory T helper 17 (Th17) cells and immunosuppressive regulatory T cells (Tregs). But what happens when this balance is disturbed? In this study, we uncovered a critical role for Acyl-CoA synthetase bubblegum family member 1 (Acsbg1) in shaping Th17 and Treg dynamics. Using Acsbg1-deficient mice, we show that while its absence does not disrupt homeostasis under steady-state conditions, it significantly alters Treg populations, particularly in gut-associated tissues. Under high-fat diet-induced metabolic stress, Acsbg1-deficient mice display mild metabolic changes but maintain systemic immune and metabolic function, indicating that Acsbg1 is dispensable for metabolic adaptation in vivo. However, upon infection with Citrobacter rodentium, these mice exhibit excessive Th1/Th17-driven inflammation and impaired resolution, accompanied by a strong reduction in IL-10-producing and ST2+ Treg subsets. The impact is even more striking in an adoptive transfer colitis model, where Acsbg1-deficient Tregs fail to control inflammation, resulting in severe colitis and tissue damage. Our findings identify Acsbg1 as a key regulator of ST2+ Treg function and a central player in mucosal immune homeostasis, highlighting its potential as a therapeutic target for inflammatory bowel disease and colorectal cancer.