Unconventional IFNω -like genes dominate the type I IFN locus and the constitutive antiviral responses in bats

Bats are the natural reservoir hosts of some viruses, some of which may spillover to humans and cause global-scale pandemics. Different to humans, bats may coexist with high pathogenic viruses without showing symptoms of diseases. As one of the most important first defenses, bat type I interferon (IFN-Is) were thought to play a role during this virus coexistence and thus were studied in recent years. However, there are arguments that whether bats have a contracted genome locus or constitutive expressed IFNs, mainly due to species-specific findings. We hypothesized that because of the lacking of pan-bat analysis, the common characters for bat IFN-Is have not been revealed yet. Here, we characterized the IFN-I locus for 9 Yangochiroptera bats and 3 Yinpterochiroptera based on the their high quality bat genomes. We also compared the basal expression for 6 bats and compared the antiviral, anti-proliferative activity and thermo-stability of a representative Rhinolophus bat IFNs. We found a dominance of unconventional IFNω -like responses in the IFN-I system, which is unique to bats. In contrast to IFNa -dominated IFN-I loci in the majority of other mammals, bats generally have shorter IFN-I loci with more unconventional IFNω -like genes ( IFNω or related IFNaω ), but with less or even no IFNa genes. In addition, bats generally have constitutively expressed IFNs, the highest expressed of which is more likely an IFNω -like gene. Likewise, the highly expressed IFNω-like protein also demonstrated the best antiviral activity, anti-proliferative activity or thermo-stability, as shown in a representative Rhinolophus bat species. Overall, we revealed pan-bat unique characteristics in IFN-I system, which provide insights into our understanding of the innate immunity that contribute to a special coexistence between bats and viruses.