Hepatitis A Virus Yields Clues About How Pathogens Survive in the Liver
Viruses infecting the liver cause thousands of cases of liver failure, cancer and death each year. Now, two such viruses, hepatitis A and hepatitis C, have been shown to attack the same part of the immune system, according to a paper published in the Proceedings of the National Academy of Sciences earlier this month. Stanley Lemon, a University of Texas microbiology professor, and his colleagues believe that destroying a protein called mitochondrial antiviral signalling (MAVS) may be a necessary step for viruses seeking to infect the liver.
This research is the first time that a clear link has been made between the ways in which hepatitis A and hepatitis C viruses survive within the liver. According to Lemon, "With 30,000-plus proteins in the cell, it's really remarkable that these two very different viruses have chosen to strike at the same one."
The MAVS protein lies on structures within liver cells called mitochondria. When MAVS detects an infecting virus, it triggers a cascade of signals which result in the release from the cell of interferon beta, a chemical which slows virus replication. It has long been known that hepatitis C protects itself from the immune response by destroying MAVS. Now, Lemon and his colleagues have shown that hepatitis A does exactly the same thing. If researchers were able to sustain this immune mechanism then this may later form the basis of a new vaccine or drug therapy.
Although both cause inflammation in the liver, hepatitis A and hepatitis C have previously been treated as two completely separate viruses. For example, hepatitis A is transmitted by consumption of faecal particles (perhaps due to not washing hands after using the bathroom) and can cause weeks of fever, nausea and abdominal pain. Hepatitis C, however, spreads by direct contact with infected blood and damages the liver over decades, often causing cirrhosis and liver cancer. Understanding how these viruses persist in the liver may ultimately aid the development of new treatments for viral hepatitis and similar infections of the liver.