How can bats harbor so many viruses without developing symptoms?

Bats are asymptomatic carriers of a multitude of viruses that are pathogenic to most other mammals. How has their immune system evolved to shield them from these pathogens? A team of scientists—the majority affiliated with the CNRS, Claude Bernard Lyon 1 University, and ENS de Lyon1 —has just published an article in Science Advances addressing that question. Part of the explanation may lie in the number of copies and diversification of the gene encoding the PKR enzyme, which is involved in the immune response to viruses. While most mammals possess a single copy of this gene, some bats have several copies, allowing them to diversify their antiviral repertoire and thus defend themselves from a wide range of viruses.  This has been made possible in bats by the accumulation of multiple copies of the PKR gene, each subjected to positive selection2  during the evolution of these animals. To reach this conclusion, the team of researchers adopted an interdisciplinary approach integrating genetics, evolution, molecular and cellular biology, virology, and field data. They delved into the evolutionary history of the PKR gene in various bat species and analysed, at the molecular level, the adaptations these animals acquired after facing epidemics in the ancient past. Their work contributes to our understanding of viral transmission between host species.

• 1In France, this research involved scientists from the Laboratoire de Biométrie et Biologie Évolutive (CNRS / VetAgro Sup / Claude Bernard Lyon 1 University) and the Centre International de Recherche en Infectiologie (CNRS / INSERM / Claude Bernard Lyon 1 University / ENS de Lyon), and was primarily funded by the Ecofect Laboratory of Excellence (LabEx) and the French National Research Agency (ANR).
• 2Positive selection is the evolutionary acquisition by species of genetic mutations that increase their chances of reproducing. Mutated genes are transmitted to following generations until they come to replace the previous forms.