Scientists discover why bats survive deadly viruses without getting sick

It is a mystery that has puzzled scientists for years. How can the world's only winged mammals carry viruses that cause severe disease while rarely becoming seriously ill themselves?

Now researchers at Tulane University, with collaborators at Stanford University and the Centers for Disease Control, may have found a reason.

In a study published in Science Advances, the research team found that the world's largest family of bats has two distinct copies of the genes that produce antibodies, the specialized proteins that help the immune system recognize and fight infections. Every other known mammal has only one such set. The discovery opens new avenues for understanding the evolution of immunity and how animals respond to disease.

We've never seen anything like this in a mammal before. This completely changes our understanding of how mammalian immune systems can be organized and raises exciting new questions about why bats have been so evolutionarily successful and how they respond to viruses."

Hannah Frank, associate professor of ecology and evolutionary biology, Tulane University School of Science and Engineering and corresponding author of the study

The discovery was made in vesper bats, which includes more than 500 species found on every continent except Antarctica. Their remarkable evolutionary success has long intrigued scientists, and this newly discovered antibody system may offer one explanation.

Antibodies are Y-shaped proteins made of two heavy protein chains and two light protein chains. In humans and every other known mammal, those heavy chains are built from a single set of genes. Frank and her collaborators discovered that vesper bats instead possess two separate heavy-chain gene systems, giving them an entirely new way to generate antibody diversity. 

While researchers have traditionally focused on bats' innate immune systems, Frank said this study highlights the importance of looking more closely at their adaptive immune system- the part responsible for producing antibodies.

"We think this discovery is an important piece of the puzzle," Frank said. "It doesn't fully explain why bats are such effective viral reservoirs, but it reveals a level of immune variety we didn't know existed and gives us an entirely new direction to explore."

Bats are critical pollinators, seed dispersers and natural pest controllers but also serve as natural hosts for many viruses, Frank said. Understanding how they coexist with those viruses without becoming ill may eventually help scientists better understand immune responses across species and improve strategies for preventing disease spillover.

"We've learned an enormous amount about immunity by studying humans and laboratory mice," Frank said. "But the natural world is far more varied than that. Every time we study a species that has evolved differently, we have the opportunity to discover something entirely new."