Single‐Particle Tracking of Hepatitis B Virus‐like Vesicle Entry into Cells

Abstract HBsAg, the surface antigen of the hepatitis B virus (HBV), is used as a model to study the mechanisms and dynamics of a single‐enveloped virus infecting living cells by imaging and tracking at the single‐particle level. By monitoring the fluorescent indicator of HBsAg particles, it is found that HBsAg enters cells via a caveolin‐mediated endocytic pathway. Tracking of individual HBsAg particles in living cells reveals the anomalously actin‐dependent but not microtubule‐dependent motility of the internalized HBsAg particle. The motility of HBsAg particles in living cells is also analyzed quantitatively. These results may settle the long‐lasting debate of whether HBV directly breaks the plasma membrane barrier or relies on endocytosis to deliver its genome into the cell, and how the virus moves in the cell.