Type I IFNs, IFNc, IFNd1, IFNd2, IFNh, and type II IFNs, IFN-γ and IFN-γrel, and their possible receptors with the identification of two variants of IFNc and IFNh in turbot (Scophthalmus maximus).

Interferons (IFNs) play a critical role in innate and adaptive immune responses of vertebrates. In this study, type I and type II IFNs and their corresponding receptors were identified in turbot (Scophthalmus maximus), including IFNc-v1, IFNc-v2, IFNd1, IFNd2, IFNh-v1, IFNh-v2, IFN-γ, and IFN-γrel, as well as cytokine receptor family B (CRFB) 1-v1 and v2, CRFB2-v1 and v2, CRFB5, CRFB6, CRFB13 and CRFB17. Phylogenetic analysis revealed that these IFNs were clustered with homologous genes from teleost fish and were distributed in conserved synteny. Both type I and type II IFNs were constitutively expressed in head kidney, spleen, liver, heart, muscle, gill, intestine, and brain, and were significantly upregulated in head kidney, spleen, liver, gill, and intestine following poly(I:C) stimulation. Furthermore, recombinant type I and type II IFN proteins were shown to activate the expression of IFN-stimulated genes (ISGs) in SMI cells. Moreover, the potential receptors for IFNc-v1 and IFNc-v2 are CRFB2-v2 and CRFB5, while IFNd1, IFNd2, IFNh-v1 and IFNh-v2 induce ISGs mainly through CRFB1-v2 and CRFB5. IFN-γ can significantly upregulate ISGs when binding to CRFB6 or CRFB13, and IFN-γrel can be also functional when binding to CRFB17. These findings collectively enhance our understanding on the composition of IFN system in teleost, and should contribute further to immunological research of fish IFN system.