Immunity comes in small packages

A mechanism by which mice side-step viral strategies for evading destruction by the host immune system and establishing chronic infection is reported in a study published this week in Nature Immunology.

Zhenghong Yuan and colleagues looked at the potential role of exosomes-cell-derived vesicles-in controlling hepatitis virus in mice. Once released from cells, exosomes have important roles in intercellular communication but have been little studied in the context of immunity. The authors found that the presence of the hepatitis virus in the liver stimulated the release of exosomes from infection-resistant liver resident cells such as Kupffer cells and transmitted them to virus-susceptible liver cells. These exosomes contained a high concentration of diverse anti-viral molecules that the hepatocytes could then utilize to resist viral infection.

The authors believe that the sheer variety of anti-viral molecules present in the exosomes makes it difficult for viruses to evolve evasion mechanisms for each and every one, thus the transmission of a bolus of molecules by way of exosomes is an effective weapon in the arsenal of immunity.Yuan and colleagues also found that blocking exosomes increased hepatitis in mice, and therefore eliciting exosome release could be beneficial in certain treating some viral infections.