Immunogenicity of biliary epithelial cells: study of the expression of B7 molecules.

Efficient antigen presentation requires the provision of a co-stimulatory signal, the best characterized of which is provided by the B7 molecules. It is unclear whether biliary epithelial cells expressing Class II major histocompatibility complex molecules can function as antigen presenting cells, although this has been suggested as an important mechanism in the initiation and/or perpetuation of some immune-mediated liver diseases, including primary biliary cirrhosis and liver allograft rejection. We have found that human intrahepatic biliary epithelial cells do not express B7-1 (CD80) or B7-2 in vitro, even after activation with high doses of interferon-gamma, tumour necrosis factor-alpha or phorbol myristate acetate, or in vivo. However, they express similar levels of class II major histocompatibility complex antigens to those expressed by professional antigen presenting cells (Epstein-Barr virus transformed B cells). It is therefore unlikely that biliary epithelial cells stimulate efficient primary T cell activation. It may be possible that these non co-stimulatory class II major histocompatibility complex positive cells play a role in modulating immune responses in the liver.