Identification and functional characterization of type II interferon receptors (CRFB6, CRFB13 and CRFB17) in Japanese...

In mammals, IFN-γ acts as a critical cytokine that triggers intracellular signaling by binding to specific IFNGR1 and IFNGR2 receptors. Unlike mammals, teleosts possess two members of type II IFN genes (IFN-γ and IFN-γrel), two IFNGR1 paralogs (CRFB13 and CRFB17) and a single IFNGR2 homolog (CRFB6). Despite the identification of type II IFN receptors in multiple fish species, the molecular features, expression profiles and signaling-associated function remain limited. In this study, three type II interferon receptor genes, AjCRFB6, AjCRFB13 and AjCRFB17 were identified in Japanese eel, Anguilla japonica. All three receptors possess typical conserved structural domains of class II cytokine receptors. Phylogenetic analysis assigned them to respective teleost CRFB subfamilies. These three genes displayed broad tissue expression, with predominant abundance in immune-related spleen, trunk kidney and liver tissues. Following Poly(I:C) stimulation, AjCRFB6 and AjCRFB13 generally showed significant upregulation from 6 hpi in the liver, trunk kidney and spleen, maintaining elevated expression at most subsequent time points, while AjCRFB17 exhibited a distinct expression pattern from AjCRFB6 and AjCRFB13, with a generally downregulated or unchanged expression trend across most tested time points. It was revealed that AjIFN-γ initiates downstream ISGs transcription and STAT1 phosphorylation through AjCRFB6+AjCRFB13 or AjCRFB6+AjCRFB13+AjCRFB17, whereas all AjCRFB17-containing complexes confer responsiveness to AjIFN-γrel. Furthermore, co-immunoprecipitation assays revealed that AjSTAT1 specifically interacts with AjCRFB13 and AjCRFB17, but not with AjCRFB6. These results provide a reference for further exploring the potential roles of type II IFN receptors in teleost immunity and signaling.