Hepatitis B virus is lost – DocCheck

Although the hepatitis B virus is well known, it still hides some mysteries. Now scientists have identified a previously unknown way for HBV particles to escape from cells.

Hepatitis B is one of the most common infectious diseases. It is caused by the hepatitis B virus (HBV), which can cause both acute and chronic hepatitis. An estimated 300 million people worldwide suffer from chronic hepatitis B infection, which is associated with an increased risk of developing liver cirrhosis or hepatocellular carcinoma.

Around 900,000 people worldwide die from HBV infection every year. In fact, serological evidence suggests that more than two billion people are estimated to have past or current HBV infection. HBV is transmitted mainly through blood, but also through other body fluids such as saliva, tears, semen or vaginal secretions.

A new transport pathway for hepatitis B virus has been identified

Although safe and effective vaccines have been approved, HBV remains a major public health concern, as many countries with a high epidemic burden either lack effective vaccination strategies or lack a vaccine. Moreover, complete cure of chronic infection remains a medical challenge.

Much is now known about the life cycle of HBV. But it is not yet fully understood, for example, what mechanisms allow the virus to leave the cell it needs to reproduce like all viruses to infect other cells. Various studies have shown that some viruses are found in exosomes. Small bubbles are released from the cell into the environment and serve for cellular communication and transport of molecules.

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A research team from the Paul Ehrlich Institute, led by Professor Eberhard Hildt, Head of the Virology Department, investigated whether hepatitis B viruses also use exosomes to transport them out of cells. It is not known yet. To this end, the research group isolated exosomes from the cell culture supernatant of HBV-producing human liver cells and found both typical exosomal markers and hepatitis B virus markers. These exosomal fractions were separated from the fractions containing free virions to verify whether the hepatitis B virus was actually present in exosomes. Intact HBV virions could be gradually released from exosomes using detergents that solubilize the exosome membrane.

Different viruses, same release path

The researchers further observed that laboratory-induced inhibition of exosome morphogenesis impairs the release of exosome-packaged HBV. In addition, electron micrographs confirmed the presence of intact virions in the examined exosomes. In addition, the research group detected the HBV surface protein LHB (hepatitis B virus large surface antigen) on the surface of the exosomes. This allows hepatitis B viruses encapsulated in exosomes to infect susceptible cells. However, uptake of exosomal hepatitis B viruses has also been observed—albeit at a low efficiency—in cells that are not usually very susceptible to HBV infection.

Current research data suggest that a portion of intact HBV virions may be released as exosomes. This reveals a previously undescribed release pathway for hepatitis B viruses. Although hepatitis B, C and E viruses are completely different viruses, they all use this pathway to exit cells.

High safety of blood products in Germany

Like some other infectious agents, the hepatitis B virus is transmitted through blood. Due to the high safety standards for the collection and processing of blood and blood products in Germany, the risk of transmission has been extremely reduced in recent decades, and in 2020 no case of HBV transmission by blood transfusion has been confirmed.

This text is based on a Press Release from the Paul Ehrlich Institute – Federal Institute for Vaccines and Biomedical Sciences. We have an original publication for you here and referenced in the text.

Image source: Pablo Garcia Saldaña, splash

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