Researchers have identified that when a virus enters the body a naturally occurring protein sets off an immune response that disrupts the virus from entering the body's cells. The finding, published in the journal Cell Host & Microbe, was carried out by researchers at the Keck School of Medicine of the University of Southern California (USC), and could be the key to developing future therapies against viral infections.

The lead researcher of the study, Jae U. Jung, said:

"Previous studies have shown that our bodies are already equipped to block viruses such as Ebola, influenza, West Nile, and SARS. The antiviral effector IFITM3 disrupts intracellular cholesterol homeostasis to block viral entry."

He explained that when a virus enters the human body the immune system is stimulated by interferon, which produces hundreds of proteins, such as the IFITM3. IFITM3, in particular, is responsible for disrupting the communication between two other proteins which increase cholesterol levels in the cells, preventing the viruses from being able to enter.

He noted that the increase in cholesterol is exclusively in the endosome compartment of the cells and does not have any effect on cholesterol levels in the bloodstream.

It was already known that the protein interferon has properties that can inhibit and prevent the spread of viruses. However, little was known about how it works.

They identified that interferon-inducible transmembrane protein 3 (IFITM3) is able to disrupt communication between two other proteins (VAPA and OSBP) which transport and regulate the cholesterol that many viruses need to survive.

Jung and his team carried out the study to see how the immune system is able to recognize viruses and block entry. In previous research, Jung and his team were able to identify the specific protein that sets off the alarm signal in the immune system.

They found that the rise in cholesterol only occured in the endosome compartment in the cell membrane.

Jung said:

"The membrane is usually very flexible. With an increase in cholesterol it becomes rigid, and doesn't allow viruses to pass through the endosome compartment into cytosol, the fluid portion inside cells. We were surprised to find that changing the balance of cholesterol concentration affects viral entry."

He concluded that in the future they "will be to identify a therapeutic molecule that activates the expression and function of the IFITM3 protein, which potentially can be used to create an anti-viral therapy. It could target the endosome compartment in order to control, combat, or prevent the spread of viral infection."

As a biotechnological product based on a protein the body naturally produces to fight infections, interferon is already being used to suppress viruses in patients infected with both HIV and hepatitis.

Written by Joseph Nordqvist