Hepatitis B Virus and Hepatitis D Virus Entry, Species Specificity, and Tissue Tropism

Entry of hepatitis B (HBV) and hepatitis D viruses (HDV) into a host cell represents the initial step of infection. This process requires multiple steps, including the low-affinity attachment of the virus to the cell surface, followed by high-affinity attachment to specific receptor(s), and subsequent endocytosis-mediated internalization. Within the viral envelope, the preS1 region is involved in receptor binding. Recently, sodium taurocholate cotransporting polypeptide (NTCP) has been identified as an entry receptor of HBV and HDV by affinity purification using a preS1 peptide. NTCP is mainly or exclusively expressed in the liver, and this membrane protein is at least one of the factors determining the narrow species specificity and hepatotropism of HBVand HDV. However, there are likely other factors that mediate the species and tissue tropism of HBV. This review summarizes the current understanding of the mechanisms of HBV/HDV entry.