Mucosal-Associated Invariant T Cells Drive Bile Duct Inflammation

Mucosal-associated invariant T cells recognize microbial-derived vitamin B metabolites presented by MHC I-related molecules. Because bile from patients with chronic biliary inflammation contain mucosal-associated invariant T antigens, we investigated whether intrabiliary mucosal-associated invariant T antigen exposure activates mucosal-associated invariant T cells and induce pathogenic biliary inflammation.

Escherichia coli, phosphate-buffered saline, or the known mucosal-associated invariant T ligand 5-(2-oxopropylideneamino)-6-D-ribitylaminouracil were injected into bile ducts of mice with increased mucosal-associated invariant T cell frequencies (Mr1⁺ B6-MAIT^CAST and iVα19 Cα^-/- Tg). Mice were monitored clinically and liver tissue analyzed after 1 to 14 days. Portal inflammation was assessed histologically. The immunophenotype of lymphocytes was determined by flow cytometry, and serum liver enzymes were measured. Hepatic mucosal-associated invariant T cell transcriptional profiles were analyzed by single-nucleus RNA sequencing.

Intrabiliary injection of E coli in iVα19 Cα^-/- Tg mice caused cholangitis at day 2, elevated alanine aminotransferase, increased histologic grade of cholangitis, and portal accumulation of T-lymphocytes and macrophages. This coincided with marked hepatic mucosal-associated invariant T cell activation. Similar signs of experimental cholangitis were observed in mice containing 2% mucosal-associated invariant T cells (Mr1⁺ B6-MAIT^CAST). Selective activation with 5-(2-oxopropylideneamino)-6-D-ribitylaminouracil in iVα19 Cα^-/- Tg mice confirmed the mucosal-associated invariant T specificity of the inflammatory response. In Mr1⁺ B6-MAIT^CAST mice, the mucosal-associated invariant T cell frequency was too low to induce biliary inflammation. Single-nucleus RNA sequencing of mucosal-associated invariant T cells from 5-(2-oxopropylideneamino)-6-D-ribitylaminouracil-injected iVα19 Cα^-/- Tg mice demonstrated antigen-driven transcriptional reprogramming toward a mucosal-associated invariant T-17-skewed phenotype with enrichment of T cell receptor signaling pathways.

Mucosal-associated invariant T cells can drive pathogenic bile duct inflammation in vivo when locally exposed to antigens. These findings suggest that modulation of mucosal-associated invariant T-driven immune pathways may represent a therapeutic approach in inflammatory cholangiopathies.