(209) IL-17C–activated MAIT cells drive fibrosis in immune-mediated liver disease

Introduction/Rationale: Primary sclerosing cholangitis (PSC) is an immune-mediated chronic fibrotic liver disease with no effective medical therapies. We showed that bile duct epithelial cells, called cholangiocytes, express IL-17C, a cytokine that modulates immune responses. Mucosal-associated invariant T cells (MAITs) have been implicated in fibrosis, but their mechanistic role in PSC remains unknown. SPARC (secreted protein acidic and rich in cysteine) is an extracellular matrix protein whose role in hepatic fibrosis is unexplored.

Methods: Flow cytometry, RNAscope, ELISA, RNA sequencing, immunofluorescence, immunocytochemistry, spheroid culture.

Results: Flow cytometry of bile duct brushings from PSC patients (n=8) revealed that 41.32% of T cells were MAITs, indicating their proximity to cholangiocytes within the epithelial-immune niche. MAITs co-cultured with PSC patients-derived cholangiocytes showed increased activation than with normal human cholangiocytes (p=0.018, n=4). RNAscope on human livers identified increased IL17C expression in PSC cholangiocytes compared to controls (p=0.064, n=3), and IL-17C levels were elevated in PSC bile (p=0.035, n=25). Surprisingly, the receptor of IL-17C is enriched in MAITs in PSC (re-analysis of single cell-RNA seq, PMID: 33774059). Bulk RNA sequencing of IL-17C-treated peripheral blood MAITs revealed upregulation of T cell activation markers and pathways associated with hepatic fibrosis. Moreover, IL-17C-treated MAITs increased SPARC secretion (p=0.025, n=7), an effect attenuated by IL-17C blockade. Consistently, conditioned media from IL-17C–treated MAITs activated hepatic fibroblasts (HF), evidenced by increased PDGFRβ expression (p=0.048, n=6). SPARC directly promoted HF activation, marked by increased α-SMA (p=0.039, n=5). Co-culture of primary human HF, MAITs and cholangiocytes in the presence of IL-17C enhanced HF activation.

Conclusion: IL-17C drives MAITs toward a profibrogenic phenotype in PSC, promoting HF activation through SPARC.