Brain’s Defense System Against Viruses May Offer Clues as to What Goes Wrong in MS

The brain has a system for orchestrating a defense against viral infections, scientists report in a finding that may advance the understanding of disease processes in multiple sclerosis (MS).

The newly discovered system is run by brain immune cells called microglia, and researchers will now focus on understanding how these cells balance the ordered immune reactions so that a virus can be conquered without too much damage to the brain.

The study, “Sensing of HSV-1 by the cGAS–STING pathway in microglia orchestrates antiviral defence in the CNS,” was published in the journal Nature Communications.

Working with the Herpes simplex virus, which can cause encephalitis, researchers at Aarhus University in Denmark discovered that when microglia detect a virus in the brain, they turn on an “alarm system,” called cGAS/STING.

Although the cGAS/STING system is present in other brain cells, such as neurons and astrocytes, only microglia are capable of using it to coordinate a defense.

With the help of this communication system, they bring in reinforcements by calling for microglia from other brain parts to arrive, while signaling to neurons and other glial cells nearby that an intruder is present.

The same system is involved in calling proteins, involved in removing damaged and dead cells, to the site once the infection has been brought under control.

“We have identified and described a communication network that begins in the brain when the cGAS/STING alarm system is activated,” Line Reinert, an associate professor from the Department of Biomedicine at Aarhus University, and the study’s lead author, said in a press release.

“This new knowledge can potentially be utilized to prevent other types of diseases of the brain, where the same alarm system is either not activated or is activated too much,” added Reinert, referring to diseases such as MS, Alzheimer’s, or psychiatric disorders.

Researchers know that any immune process within the brain needs to be tightly controlled, since the brain can only take minute amounts of damage.

“If microglia are activated too much, they do not only suppress the virus, but also damage some of the brain tissue. We are now working to understand this,” said Søren Riis Paludan, a professor at the same department and senior author of the study.