Scientists have long been intrigued by a question surrounding bats: How can these flying mammals carry viruses capable of causing serious illness while at the same time rarely becoming seriously ill?
Researchers at Tulane University, working with collaborators at Stanford University and the Centers for Disease Control and Prevention, may now have identified part of the answer.
A study published in Scientific advances discovered that the world’s largest family of bats carries two different copies of the genes involved in antibody production. These specialized proteins help the immune system identify and fight infections. All other known mammals have only one such set of genes.
The finding offers scientists a new way to think about how immune systems evolved and how different animals respond to diseases.
“We’ve never seen anything like this in a mammal before,” said Hannah Frank, associate professor of ecology and evolutionary biology in the College of Science and Engineering at Tulane University and corresponding author of the study. “This completely changes our understanding of how mammalian immune systems can be organized and raises interesting new questions about why bats have been so evolutionarily successful and how they respond to viruses.”
A unique antibody system in Vesper bats
The discovery was made in vesper bats, a group that includes more than 500 species that live on every continent except Antarctica. Scientists have long been interested in the extraordinary evolutionary success of these bats, and their unusual antibody system may provide part of the explanation.
Antibodies are Y-shaped proteins made up of two heavy protein chains and two light protein chains. In humans and all other known mammals, heavy chains are produced using a single set of genes.
Frank and his colleagues discovered that vesper bats are different. They have two separate heavy chain genetic systems, potentially giving them another way to create a wider variety of antibodies.
Researchers studying bat immunity have traditionally paid more attention to the innate immune system. Frank said the new findings show why the adaptive immune system (the part responsible for producing antibodies) also deserves closer study.
“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 a whole new direction to explore.”
Why immunity to bats is important
Bats play important ecological roles as pollinators, seed dispersers, and natural pest controllers. At the same time, they are natural hosts for many viruses, Frank said.
Learning how bats can live alongside such viruses without getting sick could eventually help researchers better understand immune responses in other species. That knowledge can also help improve strategies to reduce the risk of disease spread.
“We’ve learned a ton about immunity by studying humans and laboratory mice,” Frank said. “But the natural world is much more varied than that. Every time we study a species that has evolved differently, we have the opportunity to discover something completely new.”