Innate immunity in the pathogenesis of cholangiopathy: a recent update

Biliary innate immunity is involved in the pathogenesis of cholangiopathies in patients with various biliary diseases. Biliary epithelial cells possess an innate immune system consisting of the Toll-like receptor (TLR) family and recognize pathogen-associated molecular patterns (PAMPs). Recently, regulatory mechanisms by intracellular negative regulators including peroxisome proliferator-activated receptor-γ and micro-RNA have been clarified. In primary biliary cirrhosis (PBC) and primary sclerosing cholangitis, dysregulated biliary innate immunity, namely hyper-responsiveness to PAMPs, is associated with the histopathogenesis of cholangiopathy. Moreover, biliary epithelial cells produce monocyte chemotactic protein-1 (MCP-1/CCL2) as a result of the innate immune response and bile ductules play a role in hepatic fibrosis caused by hepatic stellate cells (HSCs). Also, biliary innate immune responses induce the production of two chemokines, fractalkine and macrophage inflammatory protein-3α (MIP-3α), causing the migration of inflammatory cells and a population of antigen-presenting cell found in epithelium, Langerhans cell, and involve chronic cholangitis associated with biliary epithelium-specific innate and acquired immunity in PBC.