Exosomes Exploit the Virus Entry Machinery and Pathway To Transmit Alpha Interferon-Induced Antiviral Activity.

Alpha interferon (IFN-α) induces the transfer of resistance to hepatitis B virus (HBV) from liver nonparenchymal cells (LNPCs) to hepatocytes via exosomes. However, little is known about the entry machinery and pathway involved in the transmission of IFN-α-induced antiviral activity. In this study, we found that macrophage exosomes uniquely depend on T cell immunoglobulin and mucin receptor 1 (TIM-1), a hepatitis A virus (HAV) receptor, to enter hepatocytes for delivering IFN-α-induced anti-HBV activity. Moreover, two primary endocytic routes for virus infection, clathrin-mediated endocytosis (CME) and macropinocytosis, collaborate to permit exosome entry and anti-HBV activity transfer. Subsequently, lysobisphosphatidic acid (LBPA), an anionic lipid closely related to endosome penetration of virus, facilitates membrane fusion of exosomes in late endosomes/multivesicular bodies (LEs/MVBs) and the accompanying exosomal cargo uncoating. Together, our findings provide comprehensive insights into the transmission route of macrophage exosomes to efficiently deliver IFN-α-induced antiviral substances and highlight the similarities between the entry mechanisms of exosomes and virus. Our previous study showed that LNPC-derived exosomes could transmit IFN-α-induced antiviral activity to HBV replicating hepatocytes, but the concrete transmission mechanisms, which include exosome entry and exosomal cargo release, remain unclear. In this study, we found that virus entry machinery and pathway were also applied to exosome-mediated cell-to-cell antiviral activity transfer. Macrophage-derived exosomes distinctively exploit hepatitis A virus receptor for access to hepatocytes. Later, CME and macropinocytosis are utilized by exosomes, followed by exosome-endosome fusion for efficient transfer of IFN-α-induced anti-HBV activity. We believe that understanding the cellular entry pathway of exosomes will be beneficial to designing exosomes as efficient vehicles for antiviral therapy.