TNFSF14 Regulates Th9 Differentiation and Hepatobiliary Inflammation in Primary Biliary Cholangitis

CD4 + T cells drive immune-mediated damage in primary biliary cholangitis (PBC), but their role in the intrahepatic inflammatory microenvironment remains unclear. This study aimed to elucidate the roles of TNF superfamily member 14 (TNFSF14) and Th9 in sustaining a progressive inflammatory microenvironment in PBC. Flow cytometry and immunofluorescence analyses were used to identify the immune cell populations that predominantly expressed TNFSF14. Flow cytometry were performed to evaluate the effect of TNFSF14 on Th9 cell differentiation. The pro-inflammatory mechanism of Th9 cells in biliary epithelial cells (BECs) via TNFSF14 was investigated by transcriptome sequencing and western blot analysis. 2OA-BSA+PolyI: C immunization and CD4⁺T-cell-specific Tnfsf14 conditional deletion were used to verify the effects of TNFSF14. TNFSF14 levels and Th9 cell frequencies were markedly elevated in the peripheral blood and liver tissues of the patients. The frequency of TNFSF14 + CD4 + T cells correlated with liver biochemical markers, and TNFSF14 enhanced Th9 cell differentiation via the NF-κB pathway. In BECs, TNFSF14 stimulation activated canonical and non-canonical NF-κB signaling in an HVEM/LTβR-dependent manner and increased IL-34 expression and secretion. Th9–BEC co-culture further supported a TNFSF14-dependent increase in IL-34 expression, accompanied by enhanced macrophage proliferation and chemotaxis. CD4⁺T-cell-specific Tnfsf14 deletion reduced Th9 cells and macrophage accumulation and attenuated cholangitis in mice immunized with 2OA-BSA+PolyI: C. TNFSF14-expressing Th9 cells may contribute to PBC-associated biliary inflammation by promoting Th9 differentiation and activating HVEM/LTβR–NF-κB signaling in BECs, thereby increasing IL-34 production and macrophage accumulation. This pathway warrants further investigation as a potential therapeutic target.