THE IMMUNEREGULATORY MECHANISMS OF AN ATTENUATED LMBV IN MICROPTERUS SALMOIDES BASED ON TRANSCRIPTOME ANALYSIS

This study aimed to investigate the immunoregulatory effects and mechanisms of an attenuated LMBV strain (LMBV-ZJDSS-F110) developed through serial passage, which exhibited strong immunoprotective properties in Micropterus salmoides. Immune responses were evaluated at the tissue and molecular levels following immunization by sampling liver, spleen, and head kidney tissues at days 1, 4, 7, and 28 post-vaccination. Histopathological analysis demonstrated the minimal tissue damage, with observable recovery by day 7 and nearly normal tissue structure by day 28, suggesting mild effects on fish tissues by the attenuated strain. Viral load assessments showed a significant reduction over time across all examined tissues, indicating effective viral clearance. To further elucidate the immune regulatory mechanisms, transcriptome analysis of head kidney samples was performed. Early in the immune response (days 1 and 4), 4979 and 6891 differentially expressed genes (DEGs) were predominantly enriched in innate immune pathways, such as cytokine-cytokine receptor interaction, cytoplasmic DNA sensing, and apoptosis pathways. This early upregulation of innate immunity likely facilitated a rapid antiviral response. During the mid-to-late immune phases (days 7 and 28), 1693 and 1758 DEGs were enriched in adaptive immune pathways, including T-cell receptor, B-cell receptor, Fc epsilon RI signaling, and Th1/Th2 cell differentiation pathways, indicating a transition from innate to adaptive immunity. Additionally, metabolic pathways involving cysteine and methionine metabolism and glutathione metabolism were enriched during the early immune phase, while glycolysis/gluconeogenesis pathways were more prominent during the mid-to-late phase. This metabolic shift may support immune cell activation and function throughout the immune response. The reliability of RNA-Seq data was verified using RT-qPCR, which showed consistent results, further confirming the accuracy of the data. The findings highlight the dynamic progression from innate to adaptive immunity and the essential role of metabolic pathways in supporting immune activity.