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Abstract

Cluster of differentiation 1 (CD1) is a family of four distinct nonpolymorphic major histocompatibility complex class I-like molecules that can present microbial nonpeptide lipid antigens to T cells. Among the CD1 gene family, CD1d is found in a wide range of tissues including the intestine and liver, and has been proposed to play an important role in mucosal immunity. Primary biliary cirrhosis (PBC) is an immune-mediated liver disease involving the intrahepatic small bile ducts, which also belong to the mucosal immune system. In this study, we studied the expression of CD1d in patients with PBC and compared the data with those of patients with hepatic sarcoidosis, primary sclerosing cholangitis (PSC), chronic viral hepatitis (CVH), and normal liver as controls. CD1d was found to be expressed in hepatocytes in all cases examined, and in epithelioid granuloma cells in 19 of 22 PBC livers and in 4 of 4 livers with hepatic sarcoidosis. In addition, CD1d was focally expressed on epithelial cells of the small bile ducts in approximately 50% of the PBC patients but in no controls. Such bile duct epithelial staining of CD1d was seen in early-stage PBC and virtually absent in late-stage PBC. Moreover, there was no evidence of expression of CD1d in large bile duct epithelial cells of PBC. The CD1d on biliary epithelial cells in PBC may be involved in the antigen presentation of microbial lipid antigen(s) to surrounding T cells. Alternatively, modified endogeneous lipidic compounds may share analogy with bacterial lipid antigens and explain CD1d expression, a possible epiphenomenon rather than a proof of bacterial involvement.