Viral miR-004-5p Hijacks Host Exosomes to Suppress TBK1-Mediated Antiviral Immunity During Koi Herpes Virus Infection.

Virus-infected cells release exosomes that transport viral and host molecules to recipient cells and modulate viral replication. However, the biological roles of exosomes derived from Koi Herpes Virus (KHV)-infected carp remain poorly characterized. In this work, we isolated serum exosomes from KHV-infected koi carp via differential centrifugation and validated their identity using transmission electron microscopy (TEM), nanoparticle flow analysis and Western blot. High-throughput sequencing was further applied to profile the molecular composition of these exosomes. We identified that KHV-encoded miR-004-5p is packaged into host serum exosomes. Functional assays revealed that exosomal miR-004-5p directly targets and downregulates host TANK-binding kinase 1 (TBK1). Reduced TBK1 expression subsequently suppresses the type I interferon (IFN-I) signaling pathway and promotes cellular autophagy, ultimately facilitating viral immune evasion. Moreover, miR-004-5p markedly impairs the host antiviral defense by modulating TBK1-mediated immune responses. Collectively, this study uncovers a novel immune regulatory mechanism mediated by exosome-carried viral miR-004-5p during KHV infection. Our results demonstrate that exosomes act as critical carriers for viral miRNAs and participate in host-virus interactions. These findings not only deepen the understanding of fish antiviral immunity, but also provide theoretical references and potential targets for the prevention and control of aquatic viral diseases.