What bats are teaching us about immunity to viruses

Egyptian rousette bats (Rousettus aegyptiacus), photographed here in 2017 at Python Cave, Uganda, are a reservoir for Marburg virus. (Jonathan Towner, M.D., CDC)

Bats can host several viruses without ever developing symptoms—even Marburg and Ebola, both of which can be deadly to people. So what’s the secret to the bats’ immunity, and could it point to new therapies to fight lethal viruses?

Scientists from the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) are studying DNA from Egyptian fruit bats in the hopes of answering those questions. And they’ve developed a bat genome that’s helping them compare antiviral mechanisms in the animal with those of people.

Initial evidence suggests that bats have a natural ability to tolerate infection with Marburg virus. The research team tracked bat tolerance to a family of natural killer (NK) cell receptors. These receptors either activate or inhibit NK cells, which are immune cells that govern how the body responds to viral infections.

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Specifically, the Army researchers discovered that a diverse family of NK cell receptors create an outsized number of inhibitory signals in bats, allowing them to tolerate Marburg infection. The receptors, called MHC class I genes and type I interferons, are quite different from corresponding receptors in mice and nonhuman primates, they discovered. They reported their findings in the journal Cell.

"Further evaluation of these expanded sets of genes suggests that other key components of the immune system … in bats may have evolved toward a state of immune tolerance," said USAMRIID researcher Mariano Sanchez-Lockhart, Ph.D., in a statement.

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Marburg virus is a member of the filovirus family, which also includes Ebola. Marburg is passed from bats to people and causes severe hemorrhagic fever. The most recent outbreaks of Marburg, which is 50% fatal on average, were in Uganda, according to the Centers for Disease Control.

When a CDC investigator traveled to Uganda to investigate a fatality caused by the virus, he collected the Egyptian fruit bats that USAMRIID used to generate the genome they’re investigating for clues to filovirus protection. USAMRIID is working with scientists from the CDC and Boston University to conduct the research.

The next step for the team is to compare the bats’ antiviral responses to those of nonhuman primates, according to the statement. As the researchers gain a better understanding of viral protection in bats, they hope to find new targets for therapies directed against filovirus infections.