The influence of cytomegalovirus (CMV) infection on the HLA expression on cultured biliary epithelial cells (BEC) was investigated. CMV-infection augmented expression of HLA class I but not of HLA class II. CMV reduced the IFN-gamma-mediated induction of the de novo expression of HLA class II while the stimulated expression of HLA class I was not impaired. Autologous but not allogeneic PBL responded to CMV-infected BEC. This response resulted in upregulation of HLA class I on BEC which was significantly higher compared with the expression on infected BEC alone or on uninfected BEC cocultured with autologous PBL. The results suggest that CMV modulates the immunogenic potential of BEC, which is important for the HLA and CMV-mediated pathomechanisms in vivo.