A more recent study, however, strengthened the case for involvement of retroviruses in (immune-mediated) liver disease: Sera of 179 patients with diverse chronic liver diseases and 31 controls were tested for reverse transcriptase activity and presence of human betaretrovirus by polymerase chain reaction. Reverse transcriptase activity was detected in 73% of autoimmune hepatitis patients, 42% of PBC subjects, 35% of patients with viral hepatitis, 22% of liver patients without viral or autoimmune pathogenesis (non-alcoholic fatty liver disease and alcoholic liver disease), and 7% of control subjects. In polymerase chain reactions, 24% of PBC samples were positive for human betaretrovirus compared to 13% in autoimmune hepatitis, 5% in other liver diseases, and 3% in non-liver disease control subjects [154] . If these data can be confirmed, a retroviral compound in the pathogenesis of immunemediated and viral liver disease seems attractive, though not specific for PBC. Thus, despite some intriguing findings, the pathogenetic relevance of retroviruses in the development of PBC remains enigmatic.