Primary biliary cholangitis (PBC) is a classic
autoimmune disease due to the loss of tolerance to
self-antigens.
Bile acids (BA) reportedly play a major role in biliary
inflammation and/or in the modulation of dysregulated immune responses in PBC. Several murine models have indicated that molecular mimicry plays a role in autoimmune
cholangitis; however, they have all been limited by the relative failure to develop hepatic
fibrosis. We hypothesized that species-specific differences in the BA composition between mice and humans were the primary reason for this limited pathology. Here, we aimed to study the impact of human-like hydrophobic BA composition on the development of autoimmune
cholangitis and hepatic
fibrosis. We took advantage of a unique construct, Cyp2c70/Cyp2a12 double knockout (DKO) mice, which have human-like BA composition, and immunized them with a well-defined mimic of the major mitochondrial
autoantigen of PBC, namely
2-octynoic acid (2OA). 2OA-treated DKO mice were significantly exacerbated portal
inflammation and bile duct damage with increased Th1
cytokines/
chemokines at 8 weeks post-initial immunization. Most importantly, there was clear progression of hepatic
fibrosis and increased expression of hepatic
fibrosis-related genes. Interestingly, these mice demonstrated increased serum BA concentrations and decreased biliary BA concentrations; hepatic BA levels did not increase because of the upregulation of transporters responsible for the basolateral efflux of BA. Furthermore,
cholangitis and hepatic
fibrosis were more advanced at 24 weeks post-initial immunization. These results indicate that both the loss of tolerance and the effect of hydrophobic BA are essential for the progression of PBC.