Etiopathogenesis of primary sclerosing cholangitis.

The etiopathogenesis of primary sclerosing cholangitis (PSC) remains undefined. Immunopathogenetic mechanisms appear to be involved, based on human leukocyte antigen complex susceptibility associations, existence of multiple autoantibodies, and presence of inflammatory bowel disease in > 75% of patients. PSC may represent an autoimmune disease with atypical features or an immune-mediated inflammatory disease, similar to inflammatory bowel disease itself. Immunogenetic susceptibility is closely linked to ligands for innate immune cells and capacity for sustained production of proinflammatory cytokines. Immunopathogenesis involves a multistep process initiated by the activation of cholangiocyte by bacterial pathogen-associated molecular patterns (stimuli of innate immunity) and proinflammatory cytokines in conjunction with aberrant expression of gut-specific chemokines and endothelial cell adhesion molecules in the liver. After recruitment of gut-primed memory T cells into the portal tracts and peribiliary space, additional mechanisms produce focal, fibrous, obliterative lesions. Progressive periductal fibrosis, chronic inflammation, and ischemic atrophy of biliary epithelia result in ductopenia, cholestasis, and obstructive strictures, culminating in secondary biliary cirrhosis.