Ultrastructural Evidences of Hepatitis B Infection in Human Liver Biopsies Disclose Complex Assembly and Morphogenesis Pathways for Hepatitis B Virus

Abstract

Despite of recent advances on acknowledge of hepatitis B virus (HBV) structure and biology, little is known about the morphogenesis and release of virions. In this study, the ultrastructural analysis of HBV components in liver biopsies from chronically HBV-infected patients disclosed complex assembly and morphogenesis pathways for HBV. HBV core (HBcAg) and surface (HBsAg) antigens were specifically identified in all liver biopsies from HVB-infected patients. HBcAg containing core-like particles 24-28 nm in diameter were observed both in nucleus and cytoplasm of hepatocytes. Dane’s-like particles were detected either budding to or into the lumen of ER close to HBsAg containing tubular structures. Besides, Dane’s-like particles were detected in different vesicular compartments resembling multivesicular endosomes. Other kind of enveloped HBV-like particles similar to the previously described cobra-shaped and horn-shaped particles were also observed in hepatocytes. Some of these particles were connected to the vesicle membrane through a stalk 20-22 nm in diameter. On the other hand, spherical subviral particles (SVP) were frequently observed in cytoplasmic vesicles. Moreover, a minor proportion of enveloped HBV-like particles budding through the plasma membrane to the extracellular space and bile canaliculi were detected. Interestingly, Dane’s-like particles in the bile canaliculi and entering into ductular-like cells were shown. Strikingly, Dane’s-like particles close to tubular structures and specific immunolabeling for HBcAg both in cytoplasm and nuclei of stellate-like cells were detected. Remarkably, HVB-like particles appeared entering hepatocytes from large cytoplasmic processes of fibrocytes raising the interesting possibility of a cell to cell passage of HBV through direct transcellular migration.