A gene that helps make Ebola so deadly to humans has a counterpart in the bat genome worldwide. It is thought bats are using it to regulate their immune systems, perhaps to prevent excessive responses to mild infections.
Bats need a powerful and sophisticated immune system to cope with their high metabolism and the potential for infection when roosting in enormous colonies. Some bats have apparently responded by turning a potentially deadly enemy into a friend, incorporating a viral protein into one of their defense mechanisms.
Animals, plants, and even fungi have been found to have integrated genes from RNA viruses into their own genome using a host reverse transcriptase – a type of enzyme that uses an RNA template to produce DNA. When this happens, the product is called a non-retroviral integrated RNA viral sequence (NIRV). These NIRVs have been identified in many sorts of living things, legacies of long-gone wars between viruses and hosts.
"NIRVs serve as a viral fossil record, providing evidence of historical viral interactions with a host and allowing for the study of the timescale and evolution of the virus-host interaction," said Dr Megan Edwards. "But relatively little is known about the biological significance of these genetic elements." Basler and Edwards, both of Georgia State University, are authors of a Cell Reports paper comparing a specific set of NIRVs from 16 different Myotis bat species with viral counterparts.
Known as viral proteins 35 (VP35s) these NIRVs aren't restricted to Myotis (mouse-eared) bats. Rodents, tarsiers, and even tammar wallabies have them. Nevertheless, VP35s occur in all Myotis species, where they bear a strong resemblance to an Ebola protein.
Previous research has shown the Ebola and Marburg viruses use the VP35 gene to stop human or animal immune systems from fighting back. Versions of Ebola that lack VP35s are rendered harmless by the immune response.
Basler and Edwards noted these VP35s have been in the bat genome for 18 million years, so they must be doing something useful, a theory confirmed by their independent adoption by other mammals. The paper shows the bat version is much weakened, but still appears to disrupt some, but not all immune system responses.
Despite all the products claiming to boost your immune system, an excessive immune response can be dangerous, leading to auto-immune diseases, something the bats may be using the proteins to avoid. Alternatively, Basler acknowledged; “It’s also possible that it does other things we don’t yet understand.”
Bats are known Marburg transmitters and suspected of doing the same with Ebola.