Introduction/Rationale: Regulatory T cells (Tregs) are essential mediators of immune tolerance, yet the ability to distinguish highly suppressive antigen specific subsets remain elusive. Here we identify a distinct subset of Tregs characterized by high expression of the surface protein GARP and demonstrate that these cells possess superior regulatory functions in the context of demyelinating autoimmunity. In experimental autoimmune encephalomyelitis (EAE) GARPHi Tregs exhibit enhanced suppressive capacity in vivo as demonstrated by Treg transfer assays. These cells show significantly increased trogocytosis acquiring higher levels of MHCII from antigen presenting cells compared to their GARPLo counter parts. This heightened ability to capture MHCII correlates with enrichment of antigen specific Tregs in the GARPHi population suggesting that GARPHi cells are more effectively positioned to engage with cognate antigen and exert regulatory control. Consistent with this GARPHi Tregs display elevated expression of the TCR strength of signal marker Nur77 following disease and upon MOG restimulation. Moreover, GARPHi Tregs are distinguished by increased F-actin and actin nucleation factor WASP, which are associated with enhanced immune synapse formation and mechanotransduction. Together these findings reveal that GARPHi Tregs integrate stronger TCR signaling coupled with cytoskeletal remodeling to support efficient antigen engagement and suppressive function. This work establishes GARP as a potent marker of an antigen enriched Treg subset and provides new insights into how antigen specific Tregs mediate suppression.
