In vitro and in vivo infectivity and pathogenicity of the lymphoid cell-derived woodchuck hepatitis virus

Woodchuck hepatitis virus (WHV) and human hepatitis B virus are closely rel ated, highly hepatotropic mammalian DNA viruses that also replicate in the lymphatic system. The infectivity and pathogenicity of hepadnaviruses propa gating in lymphoid cells are under debate. In this study, hepato- and lymph otropism of WHV produced by naturally infected lymphoid cells was examined in specifically established woodchuck hepatocyte and lymphoid cell cultures and coculture systems, and virus pathogenicity was tested in susceptible a nimals. Applying PCR-based assays discriminating between the total pool of WHV genomes and covalently closed circular DNA (cccDNA), combined with enzy matic elimination of extracellular viral sequences potentially associated w ith the cell surface, our study documents that virus replicating in woodchu ck lymphoid cells is infectious to homologous hepatocytes and lymphoid cell s in vitro. The productive replication of WHV from lymphoid cells in cultur ed hepatocytes was evidenced by the appearance of virus-specific DNA, cccDN A, and antigens, transmissibility of the virus through multiple passages in hepatocyte cultures, and the ability of the passaged virus to infect virus naive animals. The data also revealed that WHV from lymphoid cells can ini tiate classical acute viral hepatitis in susceptible animals, albeit small quantities (similar to 10(3) virions) caused immunovirologically undetectab le (occult) WHV infection that engaged the lymphatic system but not the liv er. Our results provide direct in vitro and in vivo evidence that lymphoid cells in the infected host support propagation of infectious hepadnavirus t hat has the potential to induce hepatitis. They also emphasize a principal role of the lymphatic system in the maintenance and dissemination of hepadn avirus infection, particularly when infection is induced by low virus doses .