Could Dracula have survived the bubonic plague? Considering that bats constantly host viruses without falling ill, he probably could’ve. While bats are feared for swooping low at night, drinking blood, and carrying diseases, they are also revered as outstanding creatures. Beyond being the world’s only winged mammal, they have a unique and highly effective immune system, which allows them to co-exist with some of the world’s deadliest viruses. Bats, a so-called reservoir species, naturally harbor certain viruses within their population, without mass sickness. These viruses can undergo zoonotic transformation, mutating in ways that allow them to jump from one species to another, in some cases from bats to humans. This spillover potential makes bats a point of interest in the immunology community.

Dr. Hannah Frank at Tulane University and the U.S. Centers for Disease Control and Prevention set out to answer this long-studied question: how do the immune systems of bats enable them to tolerate viruses? In the past, studies focused on the innate immunity of bats, which is a general response to disease that many organisms are capable of. Innate immunity is a first line of defense maintained by high body temperature, expulsion of pathogens, and native macrophages destroying foreign microbes.

The Tulane team took an untraditional approach, focusing on the bats’ adaptive immunity. Adaptive immunity is unique to vertebrates and relies on lymphocytes, a group of white blood cells, to target specific viruses. This is done through antibodies, which are proteins that sit on the surface of some lymphocytes to identify and bind with viral material called antigens. Once an antigen is bound, the immune system is primed for attack. Each antibody consists of a heavy chain and a light chain, and there can be many antibodies in one organism that each bind to their own antigen.

By digging into the genome of vesper bats, the scientists discovered that twenty six species of vesper bats contain two sets of genes that make antibody heavy chains. These genes are commonly referred to as "immunoglobulin genes,” and all other mammals have only one copy of them. These copies reside on separate chromosomes, and each has its own mechanisms for shaping antibodies. Scientists theorize that an ancestor gene was duplicated by chance, creating two identical copies that underwent their own evolutionary histories. One copy of the immunoglobulin genes has undergone purifying selection, meaning it only identifies a few antigens and binds strongly to them. For the other copy, the opposite happened. The second copy has undergone differentiating selection and binds with a large variety of antigens weakly. Ultimately, these two gene copies now play different functional roles for the bat immune system, both of which wield stakes on harmful invaders.

While it’s handy to have an extra copy lying around, scientists believe the duplication of the immunoglobulin genes is only a piece of the bat immunity puzzle, as it can’t fully explain why bats are so resistant to illness in the presence of viruses. For the vesper bat scientists, the answer is rarely neat and easy, so there’s still more research to be done. Discovering the immunity of bats can inspire new disease-fighting strategies and open the door to a new future in biotechnology. More directly, it can help prevent spillover of diseases from the bat population into humans. Understanding these strange, night-dwelling friends is the key to coexisting with them. The vesper bat is a pollinator, a pest exterminator, and a wonder of nature to anyone so fortunate to see them. Perhaps they can lend a wing in the future of human health, if the human race can learn to drop their pitchforks and pick up a lab notebook.