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Bats are the only mammals capable of flying alone and they represent 20% of existing mammal diversity. Furthermore, they are hosts from many emerging or reemerging viruses, notably several coronaviruses, including some that are highly pathogenic for other mammals, but without showing any signs of disease in bats. How these viruses and bats coexist is not yet totally understood. Existing proof suggests a specific role of the innate immune system, in particular the type I interferon response, a major component of antiviral immunity. Previous studies in bats showed that the components of the type I IFN pathway are activated in a constitutive manner on the transcriptional level.

In this study, we tested the hypothesis according to which the type I IFN response in bats is also activated in a constitutive manner on the protein level. For this, we used an ultrasensitive digital ELISA technique (Simoa), developed previously for humans and that we adapted to bat samples. We took prospective samples from four non-native chiropteran species living in French zoos. We identified a constitutive expression of the IFNα protein in the blood of healthy bats, at active physiological concentrations in man. The expression levels were different according to species but were not associated with age, sex or health status, suggesting a constitutive expression of the IFNα protein independent of disease.

These results confirm the unique IFN response in bats that could explain their capacity to coexist with multiple viruses without disease. These results could help manage potential zoonotic viral reservoirs and identify new antiviral strategies.