Genome-wide identification of the interferon complex establishes IFNf in Cypriniformes

Type I interferons (IFNs) are pleiotropic cytokines widely recognized for their roles in the innate immunity of vertebrates, from fish to mammals. Previously, seven type I IFNs were identified in the order of Cypriniformes, the largest group of freshwater fish. Using whole genome analysis, we have identified the IFNf from this order, expanding the number of type I IFNs in this order to eight. IFNf exhibited conserved synteny across 25 Cypriniformes genomes and phylogenetically predated the divergence of group 1 and group 2 type I IFNs. Despite low sequence identity at both the nucleotide and protein levels, IFNf retained a conserved gene structure and three-dimensional conformation essential for its function. Expression analysis revealed drastic upregulation of IFNf in grass carp upon infection with hemorrhagic virus (GCRV-II), with the highest level of activation among all the eight IFNs. Additionally, four chemically synthesized α-helix peptides derived from both grass carp and zebrafish IFNfs acted as antimicrobial peptides (AMPs), displaying direct inhibitory activity against a variety of microorganisms. Thus, this study establishes IFNf as an important component of the immune system in Cypriniformes.