IFN-gamma-related gene (IFN-γrel) exert its antibacterial effects through IRF1 in humpback grouper (Cromileptes...

In mammals, interferon-gamma (IFN-γ) represents the only member of the type II interferon family; however, teleost fish possess an additional subtype known as ifn-gamma-related gene (ifn-γrel). While IFN-γrel has been shown to exert antiviral effects through activation of downstream signaling pathways, its roles and underlying mechanisms in antibacterial immunity remain poorly understood in teleosts. In this study, an IFN-γrel homolog (Caifn-γrel) was identified and characterized in the humpback grouper (Cromileptes altivelis). The open reading frame (ORF) of Caifn-γrel spans 564 bp, encoding a 187-amino acid protein, with the first 21 residues predicted to be a signal peptide. Sequence analysis revealed 83.66% identity between CaIFN-γrel and its counterpart from Epinephelus coioides. Phylogenetic analysis further confirmed close evolutionary relationships, with CaIFN-γrel clustering together with E. coioides IFN-γrel. Constitutive expression of Caifn-γrel was detected in all examined tissues, with particularly high levels observed in blood, intestine, gill, and liver. Upon Vibrio harveyi challenge, Caifn-γrel transcript levels were significantly upregulated. Recombinant CaIFN-γrel (rCaIFN-γrel) enhanced macrophage phagocytic activity, induced STAT1 phosphorylation, and promoted the expression of key cytokine genes. Moreover, CaIFN-γrel was found to activate downstream gene expression via the transcription factor CaIRF1. Functional studies demonstrated that overexpression of CaIFN-γrel suppressed V. harveyi replication in vivo, whereas knockdown of CaIFN-γrel increased host susceptibility to bacterial infection. Collectively, these findings provide new insights into the functional versatility and immunological significance of IFN-γrel in teleost fish.