Expanded but dysfunctional regulatory T cells in treatment-naïve autoimmune hepatitis

Autoimmune hepatitis (AIH) is a chronic inflammatory liver disease characterized by immune-mediated hepatocellular injury. Regulatory T cells (Tregs) are crucial for maintaining immune tolerance, but their role in AIH remains unclear. This study aimed to evaluate the phenotype, function, and tissue distribution of Tregs in AIH and examine their potential association with immune dysregulation.

Peripheral blood and liver samples were collected from 57 biopsy-confirmed AIH patients. Single-cell RNA sequencing was performed on peripheral blood mononuclear cells (PBMCs) from one individual per group (healthy control, before treatment, and flare after steroid discontinuation). Flow cytometry (PBMCs n = 45; livers n = 37) and immunohistochemistry (IHC, n = 33) assessed Treg frequency and phenotype. Treg suppressive function was evaluated using co-culture assays with effector T cells (Teffs) isolated from PBMCs (n = 25).

IHC revealed marked immune cell infiltration in AIH liver tissues, and FOXP3 + cell counts correlated positively with serum AST levels (p = 0.0096) and portal-peripheral activity severity (p < 0.05). Single-cell RNA sequencing showed expansion of distinct Tregs and transcriptional changes, including IL-7R upregulation suggesting functional instability. Flow cytometry confirmed significantly increased total and activated Tregs in AIH liver samples (both p < 0.0001). However, co-culture assays demonstrated that Tregs from AIH patients had markedly reduced suppressive capacity compared to healthy controls (p < 0.0001).

Despite their expansion in liver tissue, Tregs in AIH exhibit impaired suppressive function, indicating functional instability contributes to immune dysregulation in AIH.