Primary bile acid shapes peripheral immunity in inflammatory bowel disease-associated primary sclerosing cholangitis.

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease often associated with underlying inflammatory bowel disease (IBD). This study investigates how PSC predisposes individuals to altered inflammatory immune responses compared with IBD alone. A case-control study was conducted with a cohort of 75 patients, including 16 with PSC (14 with concomitant IBD), 39 with IBD alone, and 20 controls. Serum bile acid profile, proteomic analysis, and immune-related gene expression in the colon tissue were examined. Colonic tissue from PSC patients exhibited up-regulation of immune regulation and inflammatory signaling mRNA markers, including LGR5, IL-8, CCL2, COX2, TWIST1, and SNAIL. Additionally, PSC patients displayed a distinct proinflammatory serum proteomic signature and moderate elevation of some bile acids, such as glycochenodeoxycholic acid (GCDCA). Co-incubation of human-derived monocytes with GCDCA partially replicated the inflammatory profile observed in PSC. These findings suggest that circulating bile acids modulate the peripheral immune system proinflammatory response, contributing to the unique PSC phenotype.