Peripheral blood mononuclear cells are possible extrahepatic replication sites for hepatitis C virus.

Background/Aims: Hepatitis C virus is a major causative agent of chronic liver disease and hepatocellular carcinoma and is considered to be a hepatotropic virus. It remains controversial whether hepatitis C virus exists in peripheral blood mononuclear cells and replicates there. In order to resolve this issue, we performed nested RT-PCR (reverse transcription polymerase chain reaction) and RT-PCR in situ hybridization in peripheral blood mononuclear cells of patients with chronic hepatitis C. Methodology: We collected peripheral blood mononuclear cells from patients with chronic hepatitis C, extracted total RNA from the samples, and performed nested RT-PCR to detect hepatitis C virus RNA in the peripheral blood mononuclear cells lysates. We also fixed peripheral blood mononuclear cells of the patients in 4% paraformaldehyde and performed RT-PCR in situ hybridization with a digoxigenin-labeled RNA probe to detect hepatitis C virus RNA in the cells. Results: Using these methods, we detected both positive- and negative-stranded hepatitis C virus RNA in peripheral blood mononuclear cells of hepatitis C patients. To determine in which cell population of peripheral blood mononuclear cells hepatitis C virus is present, we performed PCR in situ hybridication after incubation with fluorescent latex microbeads which could be phagocytozed by monocytes. We obtained positive signals of the replicative hepatitis C virus genome not only in lymphocytes but also in monocytes. Conclusions: RT-PCR in situ hybridization with a nonradioactive probe was found to be useful for in situ detection of hepatitis C virus RNA. Our findings suggest that peripheral blood mononuclear cells may be extrahepatic replication sites for hepatitis C virus.