Transcriptome analysis reveals the immune responses of leopard coral grouper to nervous necrosis virus infection

The leopard coral grouper (Plectropomus leopardus) is a key marine aquaculture species that is vulnerable to nervous necrosis virus infection during its larval stage. This infection often causes viral nervous necrosis disease, resulting in significant losses in aquaculture. The brain tissue serves as a target organ for viral invasion in fish, with vacuolization being the most prominent characteristic observed in susceptible individuals. In this study, a transcriptome analysis was conducted using brain tissues from naturally resistant and susceptible P. leopardus to investigate the defensive mechanisms against nervous necrosis virus infection. Histological observations revealed irregular vacuolization in the brains of fish infected with the nervous necrosis virus. Based on the differentially expressed genes, our study revealed a significant upregulation pathway of neuroactive ligand-receptor interaction, glutamatergic synapse, and GABAergic synapse in the resistant group, while COVID-19 infection pathway and NF-kappa B signaling pathway were primarily downregulated in the susceptible group. These findings suggest that neuroprotective and repair mechanisms may enhance resistance to viral infection while suppressing the immune response, thereby preventing hyperactive damage caused by inflammation. The expression profiles of key differentially expressed genes were validated using qRT-PCR. These genes include those related to the nervous system (grin2b, id4, mpz, sema6bb, dab1a, and nmda2d), cytokine interaction (ccr7), and antigen processing and presentation (hsp90aa1). Fluorescence in situ hybridization (FISH) demonstrated virus co-localization at both the tissue and cellular levels. These findings provide insights into the immune mechanism of leopard coral grouper, aiding in the prevention and treatment of nervous necrosis virus infection.