Potential therapeutic effect of dimethyl fumarate on Treg/Th17 cell imbalance in biliary atresia

The imbalance between Tregs and proinflammatory Th17 cells in children with biliary atresia (BA) causes immune damage to cholangiocytes. Dimethyl fumarate (DMF), an immunomodulatory drug, regulates the Treg/Th17 balance in diseases like multiple sclerosis (MS). This study explores DMF's effect on Treg/Th17 balance in BA and its potential mechanism. The differential gene expression profiles in liver of BA and choledochal cyst (CC) patients were analyzed by single-cell RNA sequencing (scRNA-seq). Treg and Th17 cell frequencies in BA hilar lymph nodes (LNs) were determined by flow cytometry. CD3⁺ T cells were isolated from BA hilar LNs and treated with DMF in vitro to observe their differentiation. The effects of DMF were evaluated on BA mouse model, and enzyme-linked immunosorbent assay to measure biochemical markers and cytokine profiles. The Treg/Th17 ratio in the liver was determined by flow cytometry. Nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream antioxidant genes solute carrier family 7 member 1 (Slc7a11), heme oxygenase - 1 (Hmox1) was validated by q-PCR and Western blot. ScRNA-seq showed CD4⁺ T cells in BA liver were enriched in antioxidant pathways. The Treg/Th17 ratio in BA hilar LNs was significantly reduced compared to CC. In vitro, DMF promoted Treg differentiation and inhibited Th17 differentiation. In vivo, the Treg/Th17 ratio increased in the liver of the DMF 40 mg/kg group. In the 40 mg/kg DMF group, interleukin-17 A (IL-17 A) expression decreased as seen in pathological staining. DMF increased Nrf2, Hmox1, Slc7a11 mRNA and protein levels in DMF 40 mg/kg group. There is a Treg/Th17 imbalance in BA patients' hilar LNs, which DMF can restore in vitro. DMF improves the survival rate of BA mice and corrects the Treg/Th17 imbalance, possibly via the Nrf2/antioxidant response elements (ARE) pathway.