Functional characterization of interferon-induced protein 44-like in Amphiprion clarkii: Expression profiles, immunomodulatory activity, and antiviral function.

Interferon-induced protein 44-like (IFI44L) is an interferon-stimulated gene (ISG) that plays a critical role in antiviral defense by modulating host innate immune responses. In this study, IFI44L homolog (AcIFI44L) was identified and functionally characterized in yellowtail clownfish (Amphiprion clarkii). The AcIFI44L gene is 1350 base pairs long and encodes a polypeptide of 449 amino acids containing two conserved domains: TLDc and MMR_HSR1. AcIFI44L transcripts were abundant in peripheral blood cells, followed by spleen and gills, and were strongly upregulated in response to viral and bacterial immune stimuli. AcIFI44L overexpression in fathead minnow cells markedly inhibited viral hemorrhagic septicemia virus (VHSV) proliferation, as evidenced by decreased viral transcript abundance, reduced viral titers, and concomitant modulation of key antiviral genes, indicating a robust antiviral effect. Flow cytometry revealed that AcIFI44L overexpression reduced VHSV-induced cytopathic effects and improved cell survival. Furthermore, AcIFI44L enhanced NF-κB-dependent luciferase activity and increased NFκB1 (p50) and RELA (p65) transcript levels, consistent with potentiation of NF-κB signaling in teleost cells. Together, these findings define a species-specific antiviral role for IFI44L in fish and highlight its potential as a therapeutic target for viral diseases in aquaculture species.