Background
A human betaretrovirus resembling the MMTV has been cloned from biliary epithelial cells and perihepatic lymph nodes of patients with primary biliary cirrhosis (PBC) [1]. The human betaretrovirus can trigger a PBC specific phenotype in vitro and antiviral therapy improves both biochemical and histological disease in patients with PBC. The human betaretrovirus can be detected in perihepatic lymph nodes in 75% of PBC patients by immunochemistry and RT-PCR [1]. Our goal was to provide proof that a human betaretrovirus infects patients by isolating the human betaretrovirus and detecting viral integration sites.