Ultrastructural demonstration of hepatitis B virus production in a mouse model produced by hydrodynamic transfection

A mouse model of hepatitis B virus (HBV) infection produced by hydrodynamic injection of HBV DNA has been recently established. However, the ultrastructural demonstration of HBV particles in this mouse model has not as yet been reported. In our study, plasmid DNA containing wild-type HBV DNA was rapidly injected into 8-week-old female SCID mice via the tail vein. Serum levels of HBsAg were measured by ELISA kit. Intrahepatic HBV protein expression was detected by immunohistochemistry of HBcAg. Ultrastructural study of the serum samples was performed by transmission electron microscopy and immunogold electron microscopy. Serum HBsAg and intrahepatic HBcAg were detected in HBV DNA-injected mice for at least 14 days. Spherical and filamentous particles 22 nm in diameter and double-shelled Dane-like particles 42 nm in diameter were detected in the sera of mice. The ultrastructural features of these particles were identical to HBV particles observed in serum from chronic hepatitis B patients. These particles were confirmed to be HBV particles by immunogold electron microscopy. We conclude that our present HBV mouse model using hydrodynamic transfection of HBV DNA is appropriate for production of HBV virions including Dane particles. This mouse model may be useful for screening in vivo the efficacy of antiviral drugs.