Why don't bats die from the lethal viruses they carry? A new DNA study uncovers a second genetic system hidden inside their blood not seen in mammals before

Bats have long puzzled scientists for a simple reason: they can carry viruses that cause serious disease in other animals, yet the bats themselves often show little sign of illness.

Now, researchers have uncovered an unusual feature of the bat immune system that may help explain part of that mystery.

A team from Tulane University, Stanford University and the U.S. Centers for Disease Control and Prevention has found that vesper bats possess two distinct sets of genes involved in producing antibodies. That arrangement has not previously been documented in any other mammal.


The finding, published in Science Advances, gives researchers a new direction for understanding bat immunity and raises questions about how these animals evolved such an unusual relationship with infectious diseases.

Bats appear to have an immune system unlike other mammals

Vesper bats are not a small or isolated group. The family contains more than 500 species and is found across much of the world, with bats living on every continent except Antarctica.

Their ability to survive in environments where viruses circulate has attracted considerable scientific attention.

Researchers have traditionally focused heavily on bats' innate immune responses — the body's rapid first line of defence against invading pathogens. The new study points toward another part of the immune system that may be equally important: the adaptive immune response.

This is the system that learns to recognise specific threats and produces antibodies capable of targeting them.

The researchers found that vesper bats possess an unexpected genetic arrangement within this antibody-producing machinery.

The genetic discovery surprised researchers

In most mammals, including humans, antibody heavy chains are produced from a single set of genes.

Vesper bats appear to have two.

Antibodies are specialised proteins that help the immune system recognise foreign substances such as viruses and bacteria. Their familiar Y-shaped structure is made from heavy and light protein chains.

The heavy-chain component is particularly important because genetic rearrangements allow the immune system to generate a huge variety of antibodies capable of recognising different threats.

Having two distinct heavy-chain gene systems could potentially give vesper bats additional flexibility in generating antibodies.

Exactly how that extra genetic architecture functions, however, remains an open question.

Why bats are so interesting to virus researchers

Bats occupy a unique position in infectious disease research.

They are natural hosts for a wide range of viruses, including pathogens that can cause severe disease when they infect other mammals. Yet bats frequently coexist with these infections without developing the same level of illness seen in other species.

Scientists have therefore been trying to understand what makes their immune response different.

The answer is unlikely to be a single biological trick.

Instead, bat immunity appears to involve several unusual characteristics that have evolved alongside the animals' long evolutionary history and their demanding lifestyle as flying mammals.

The newly identified antibody system adds another possible piece to that puzzle.

The discovery does not explain everything about bat viruses

Researchers caution that the unusual antibody genes do not, by themselves, solve the mystery of why bats can tolerate so many viruses.

There is still much to learn about how the two gene systems operate, whether they produce different types of antibodies and how those antibodies respond during actual infections.

The finding is best viewed as a new starting point rather than a complete explanation.

For scientists, that may be precisely what makes it valuable.

A previously unknown feature of the mammalian immune system creates an opportunity to investigate questions that could not have been asked before.

Scientists are looking beyond humans and mice

Much of what is known about mammalian immunity comes from studying humans and laboratory animals such as mice.

Those studies have provided an enormous amount of information about how the immune system works. But they represent only a small portion of the biological diversity found across mammals.

Bats offer a particularly interesting comparison because their evolutionary path has produced several traits that are unusual among mammals.

Studying those differences can reveal alternative ways an immune system can be organised and regulated.

The vesper bat discovery is therefore important beyond bats themselves. It demonstrates that fundamental features of mammalian biology may be more diverse than scientists previously realised.

Could this help scientists understand future disease outbreaks?

Understanding how bats tolerate viruses could eventually improve scientists' understanding of infectious diseases and the conditions under which pathogens move between species.

That does not mean a new treatment or vaccine is immediately on the horizon.

The research is still focused on basic biology: determining how the bat immune system is built and why it evolved in this particular way.

But such knowledge can become important when scientists study disease spillover, the process by which a pathogen moves from its natural host into another species.

The better researchers understand how bats and their viruses coexist, the better they may understand the biological factors that influence these events.

More than 500 bat species could hold more clues

The study focused on vesper bats, one of the largest and most diverse bat families.

With hundreds of species spread across different environments, bats provide researchers with an unusually broad opportunity to investigate how immune systems evolve.

The next question is whether the newly identified genetic arrangement is shared across the wider group and how it varies between species.

Scientists could also investigate whether similar immune adaptations exist elsewhere in the bat family tree.

Such comparisons may reveal whether the unusual antibody system developed once in a common ancestor or emerged through different evolutionary pathways.

A new chapter in the study of bat immunity

The discovery changes the way scientists think about one of the most intriguing aspects of bat biology.

Bats are not simply animals that happen to carry viruses without becoming sick. Their immune systems have evolved in distinctive ways, and researchers are only beginning to uncover how those systems work.

Finding two separate antibody heavy-chain gene systems in vesper bats suggests that the diversity of mammalian immunity is greater than previously known.

For now, the discovery raises more questions than it answers.

But that is often how major advances in biology begin — with an unexpected feature that forces scientists to reconsider what they thought they already knew.