Why does he have invincible immunity? Scientists have made new research discoveries!

Bats are amazing creatures. Not only are they the only mammals that can fly continuously , they also have amazing immunity. Even if they are infected with viruses that are deadly to humans, such as Ebola, Marburg or rabies, they can still be safe and sound and rarely get sick. This mysterious phenomenon has always fascinated scientists.

Why do bats have this ability? And what can we humans learn from them? Let's start with the bats themselves.

A big family in the shadows

Carrying a deadly virus

When we talk about bats, we may easily think of "vampires" or the figure walking through the night of Gotham City. But when asked what bats look like, we may often only have a vague impression of "a mouse with wings"... This is probably because we don't have the opportunity to observe bats up close - after all, bats can fly, and most of them are nocturnal, which gives us the illusion that bats are "niche creatures".

Image from wiki

In fact, the bat family is quite large. So far, there are more than 1,400 known bat species. There are only more than 6,400 mammals in total. Bats alone account for more than one-fifth of mammals . And because they have wings, bats can be seen all over the world except in the Arctic, Antarctic and some remote and isolated islands.

Bats are often known as "blood suckers" because of their unattractive appearance and their nocturnal nature. However, there are very few bats that feed purely on blood. Most bat species can be divided into carnivorous and herbivorous. Carnivorous species prey on insects, and a few prey on fish, frogs and other vertebrates. Herbivorous bat species feed on nectar, pollen and fruit. Many bat species can kill a large number of pests such as mosquitoes, and some can help plants pollinate.

If we look at bats from the perspective of infectious disease risk, then bats have become living “petri dishes” – bats are known to carry at least 60 viruses and are natural hosts for a large number of zoonotic pathogens, including the dreaded rabies, but bats themselves rarely get sick from them. More importantly, these viruses have the opportunity to spread to other animals and even humans, and cross-infection between bats may lead to the emergence of new viruses that are more likely to break through our immune system.

What kind of "divine protection"

What makes bats immune to all poisons?

So the question is, why can bats carry so many viruses but remain fine themselves?

A widely circulated explanation is that bats need to fly, which raises their body temperature. This view seems to make sense, because "fever" is a common weapon of our immune system to resist the invasion of pathogens - an increase in body temperature can inhibit the reproduction of many pathogens in our body.

However, in the case of bats, although their body temperature is indeed higher when they fly, their large wings are densely covered with blood vessels, making them excellent heat dissipators, which makes it easy for heat to dissipate. This is why bats often wrap their wings around themselves like a "cloak" when they rest. In addition, since flying consumes a lot of energy, bats will also reduce their activities and enter a dormant state, at which time their body temperature may drop to the same level as the environment. In this case, won't the virus "take advantage of the opportunity to enter"? Moreover, many viruses are not that afraid of heat, and it is not very convincing to explain the "immunity to all poisons" of bats based solely on high body temperature.

Bats resting on a tree. Image from Wikipedia

Recently, the top academic journal Nature published an interesting paper, which put forward a very novel idea: bats' super immunity may be precisely because they can fly.

In this study, in order to better explain the secrets of bat immunity, a team led by Aaron Irving, a comparative immunologist at the Zhejiang University-University of Edinburgh Joint Institute, and Michael Hiller, an evolutionary geneticist at the Senckenberg Institute in Germany, used advanced sequencing and analysis technologies to obtain the genomes of 10 bat species. They then further compared the results with 10 previously completed bat genome data and the genomes of another 95 other mammals.

Comparison found that compared with other mammals, bats not only have more immune-related genes, but these genes themselves have also undergone some changes, helping them better identify pathogens, regulate inflammatory responses and respond to viral infections.

The ISG15 gene is a classic example, which exists in both bats and humans. The human ISG15 gene is like a double-edged sword. On the one hand, it helps fight viruses, but on the other hand, if the human body has a serious infection, it will cause an overly strong inflammatory response, which may be dangerous.

But bats have just the right mutations in their ISG15 gene — some changes that make bats more resistant to the virus, others that make them safer. This allows bats to effectively block the virus without triggering the excessive inflammation common in humans, the study authors said.

Hypothesis: Does flying depend on immunity?

When did bats acquire these immune "superpowers" during their long evolutionary journey? Looking back in time, researchers found that adaptive changes related to immune genes can be traced back to the common ancestor of bats that learned to fly. This result suggests that there may be some connection between bats' extraordinary immunity and their ability to fly.

Image from wiki

This conclusion seems puzzling at first glance: Do you need strong immunity to fly into the sky? Maybe it is true. Professor Owen believes that this may be because flying puts a great burden on the body of bats.

When flying, bats can maintain a heart rate of 1,000 beats per minute for a long time. Extreme metabolism produces a large amount of toxic byproducts such as reactive oxygen. In order to deal with these "metabolic wastes", bat ancestors evolved powerful immune regulation capabilities while evolving the ability to fly. Inadvertently, these immune capabilities allow them to better tolerate deadly viral infections.

Of course, there are still some unanswered questions in this study. For example, some molecular virologists pointed out that although this theory sounds reasonable, it is still only at the hypothesis stage and it is difficult to really confirm it. In addition, some of the current results still need further explanation. For example, although the different types of bats selected by the researchers have the same key changes in their ISG15 genes, there are still differences in the ability of these species to inhibit viruses. This shows that in some bat species, there are other immune functions that are also at work, which need to be further explored.

It is worth mentioning that the significance of this study is not limited to bats. Since most of the bat species selected by the researchers carry viruses that may be transmitted to humans, understanding the resistance of bats to viruses is not only expected to reduce the occurrence and spread of zoonotic diseases, but also may provide valuable insights for the treatment of human diseases , such as helping to develop new drugs or providing inspiration for regulating human immune responses. This will also be the future research direction of scientists.

References

[1]Bat genomes illuminate adaptations to viral tolerance and disease resistance, https://www.nature.com/articles/s41586-024-08471-0

[2]Viral tolerance enabled by a bat-specific genomic tweak, https://www.nature.com/articles/d41586-025-00081-8

[3]How flight helped bats become invincible to viruses, https://www.nature.com/articles/d41586-025-00268-z

[4]Wong S, Lau S, Woo P, Yuen KY. Bats as a continuing source of emerging infections in humans. Rev Med Virol. 2007 Mar-Apr;17(2):67-91. doi: 10.1002/rmv.520. PMID: 17042030; PMCID: PMC7169091.

[5] Microbes Everywhere

Planning and production

Author: Ye Shi Popular Science Writer

Review丨Huang Chengming, Professor of Hainan University

Hu Qiwen, Associate Professor, Department of Microbiology, School of Basic Medical Sciences, Army Medical University

Planning丨Xu Lai

Editor: Ding Zong

Proofread by Xu Lai and Lin Lin