Oral administration of IFN-γrel elicits antiviral immunity and enhances protective efficacy against LMBV in largemouth bass (Micropterus salmoides).

Largemouth bass virus (LMBV) poses a severe threat to global aquaculture, yet effective antiviral strategies remain limited. This study characterized the antiviral properties of type II interferon IFN-γrel in largemouth bass and evaluated its prophylactic and therapeutic efficacy via oral delivery. The open reading frame (ORF) sequence of largemouth bass IFN-γrel (MsIFN-γrel) is 564 bp, encoding 188 amino acids, which includes an N-terminal signal peptide and a C-terminal IFN-γ signature motif; it lacks a nuclear localization signal. Our findings indicate that overexpressing of MsIFN-γrel reduces mRNA and protein levels of viral genes (MCP and DNMT), confirming its anti-LMBV activity in vitro. Oral delivery of Bacillus subtilis-expressed recombinant MsIFN-γrel protein upregulated the expression of IFN-γrel, Mx, and ISG15, enhancing serum antiviral activity in largemouth bass. Following LMBV challenge, prophylactic treatment yielded a relative percent survival (RPS) of 40.0% compared to the PBS group. MsIFN-γrel alleviated tissue damage in the spleen and liver, reduced pro-inflammatory gene expression (TNF-α and IL-8), and restricted LMBV replication. Compared to the PBS group, an increase in the dose of MsIFN-γrel led to an increase in RPS from 29.1% to 65.1%. Importantly, therapeutic administration of MsIFN-γrel after LMBV infection significantly improved survival outcomes, resulting in an RPS of 31.6% in largemouth bass. This treatment markedly suppressed LMBV replication in vivo, mitigated histopathological damage in spleen and liver tissues, and reduced the expression of pro-inflammatory genes (TNF-α and IL-8). Oral delivery offers distinct practical advantages for aquaculture applications due to its non-invasive nature and ease of implementation. Collectively, our results indicate that MsIFN-γrel exhibits robust anti-LMBV activity, and its oral administration serves as a convenient and efficient method for preventing and treating LMBV infection in largemouth bass aquaculture.