Mechanism of tannic acid against Micropterus salmoides rhabdovirus（MSRV）

【Objective】 To investigate the potential mechanisms of tannic acid（TA） in the life cycle of Micropterus salmoides rhabdovirus（MSRV） infection in cells, which could provide theoretical basis for the development of efficient and safe anti-MSRV drugs for aquaculture. 【Method】 Using the fathead minnow muscle cell line（FHM） as a model, the toxicity of TA was assessed through optical microscopic observation, CCK-8 assay and immunofluorescence staining to determine its safe working concentration. Subsequently, crystal violet staining was employed to evaluate the inhibitory effect of TA on MSRV, while real-time fluorescence quantitative PCR was used to detect the in vitro anti-MSRV activity of TA against MSRV and investigate its mechanisms, including the effects of TA on MSRV particle, the adsorption of host cell surfaces by MSRV, the invasion in cells of MSRV, and the intracellular replication of MSRV. 【Result】 Based on optical microscopic observation and CCK-8 assay, the safe working concentration of TA on FHM cells was 0.0125 mg/mL. After incubation with 0.0125 mg/mL TA for 36 h, the cytoskeleton structure of FHM cells remained intact, and no abnormal phenomena such as nuclear membrane shrinkage or chromatin condensation were observed. When co-incubating cells with MSRV and TA at the concentrations of 0.0125, 0.00625 and 0.003125 mg/mL, it was found that the presence of TA reduced the cytopathic effect of MSRV infection in FHM cells. At the same time, the relative expression level of MSRV N gene in FHM cells treated with TA was extremely significantly lower than that in the MSRV infected group without TA treatment（P＜0.01, the same below）. The relative expression of the MSRV N gene and viral titer in the FHM cells infected with MSRV which treated with TA was significantly lower compared to MSRV-infected cells without TA treatment, that was, TA can directly acted on MSRV particles, thereby reducing their infectivity. When the FHM cells were treated with TA during the adsorption, invasion and replication stages of MSRV-infection, the relative expression level of MSRV N gene in cells was significantly lower than that in MSRV-infected cells untreated with TA, that was, TA exerted its antiviral effect by interfering with the adsorption, invasion and replication during the process of MSRV infection. 【Conclusion】 TA has a good antiviral effect on MSRV infection, it can directly act on MSRV particles and has inhibitory effects on the adsorption, invasion and replication stages of MSRV, indicating that TA has the potential to be developed into an efficient and safe anti-MSRV fishery drug.