IFN-γ and its receptor: the roles of antiviral and antibacterial immunity in black rockfish Sebastes schlegelii.

Type II interferon (IFN-γ) plays a central role in immune regulation in teleosts, but the signaling mechanisms mediated by its receptor subunits in teleosts remain unclear. This study investigated the immune regulatory network of Sebastes schlegelii (S. schlegelii) IFN-γ (SsIFN-γ) and the molecular functional characteristics of its receptor chains, SsIFNGR1 and SsIFNGR2. Transcriptome analysis of spleen after stimulation with recombinant SsIFN-γ protein revealed 5402 differentially expressed genes, which were mainly concentrated in antigen processing and presentation, cytokine-cytokine receptor interactions, IL-17 signaling and apoptosis pathways. The sequence analysis indicated that both SsIFNGR1 (419 aa) and SsIFNGR2 (287 aa) possess conserved fibronectin type III (FN III) domains, signal peptides and transmembrane regions. Both receptors are widely expressed in tissues, with the highest expression levels in gills/intestine (SsIFNGR1) and spleen/gills (SsIFNGR2). Meanwhile, the mRNA expression of SsIFNGR1 and SsIFNGR2 were significantly upregulated following stimulation by bacteria, virus, poly(I:C), or rSsIFN-γ. Co-localization and co-immunoprecipitation experiments demonstrated that SsIFN-γ could interacts with SsIFNGR1 and SsIFNGR2. SsIFNGR1 and SsIFNGR2 enhance the expression of rSsIFN-γ-induced antiviral effector molecules (ISG15, Viperin, Mx) and signaling components (STAT1, SOCS1). In EPC cells, two receptors significantly enhance SsIFN-γ-mediated inhibition of carp spring viremia virus replication. In vivo, SsIFNGR1 and SsIFNGR2 alleviated intestinal pathological damage caused by Edwardsiella piscicida, accompanied by significant upregulation of pro-inflammatory cytokines, antimicrobial peptides (Hepcidin-1, TFPI-1) and JAK-STAT pathway genes. These findings characterize the IFN-γ signaling mechanism in teleosts and highlight the synergistic roles of these receptors in antiviral and antibacterial defenses, providing new insights for disease prevention and control in aquaculture.