First in vitro and in vivo evaluation of recombinant IL-1β protein as a potential immunomodulator against viral infection in fish.

IL-1β is an important proinflammatory cytokine with multifaceted modulatory roles in immune responses. In fish, recombinant IL-1β has been employed in the control of bacterial diseases, while the antiviral mechanisms of IL-1β remain largely unknown, and the efficacy of recombinant IL-1β as an immunomodulator to prevent viral diseases is still not determined. This study evaluated the immunomodulatory effects of recombinant grass carp IL-1β against grass carp reovirus (GCRV) in vitro and in vivo. Firstly, the mature form (Ser-Lys) of grass carp IL-1β was identified, and its recombinant protein (designated as rgcIL-1β) was prepared through prokaryotic expression. Then, an in vitro evaluation model for rgcIL-1β activity was established in the CIK cells, with the appropriate concentration (600 ng/mL) and effect time (1 h). In vitro, rgcIL-1β could not only induce the production of proinflammatory cytokines such as IL-1β, IL-6, IL-8, and TNF-α but also a series of antiviral factors including IFN-1, IFN-2, IFN-γ, and ISG15. Mechanistically, transcriptome analysis and western blotting confirmed that rgcIL-1β activated multiple transcriptional factors, including NF-κB, IRF1, IRF3, and IRF8, and the signal pathways associated with inflammatory cytokines and antiviral factors expression. Expectedly, rgcIL-1β treatment significantly inhibited GCRV replication in vitro. In vivo administration of rgcIL-1β via intraperitoneal pre-injection significantly aroused an antiviral response to restrict GCRV replication and intense tissue inflammation in grass carp, demonstrating the immunomodulatory effects of rgcIL-1β. More importantly, rgcIL-1β administrated with 10 ng/g and 1 ng/g could improve the survival rate of grass carp during GCRV infection. This study represents the first time to comprehensively reveal the immunomodulatory and antiviral mechanisms of IL-1β in fish and may also pave the way for further developing recombinant IL-1β as an immunotherapy for the prevention and control of fish viral diseases.