Effect And Mechanism Of Dipotassium Glycyrrhizinate Against Infectious Bursal Disease

Objective:Modeling the Infectious bursal disease (IBD); Probing into the efficacy of Prevention and treatment of Dipotassium Glycyrrhizinate (DG) to Infectious bursal disease and antiviral machnism in vivo.Method:The chickens without maternal antibody were infected with a Infectious bursal disease Virus (IBDV) stain BC6/85to establish animal model of IBD. The establishment was assessed via observations of clinical symptom and detection of specific virus gene. Dividing24-day old200chicks, healthy and IBDV unvaccinated, into8groups,25chicks each, which nominated as A, B, C, D, E, F, G and H, A as control group (normal), B as negative group (IBDV Model), C and D as positive group (Ribavirin and Astragalus polysaccharides), E, F, G, H as experimental group (DG Medium dosage prevent group and DG high/Medium/low dosage therapy group). At28-day old, all the chicks were inoculated by Intraocular and Intranasal method with0.2mL IBDV BC6/85diluent (PBS dilution as1:100) except group A which only given0.2mL PBS. E (DG prevent group,40mg/kg/d) begins at25-day old by water imbibing. C (Ribavirin treatment group,26mg/kg/d)、 F (DG treatment group,20mg/kg/d)、 G (DG treatment group,40mg/kg/d)、 H (DG treatment group,80mg/kg/d) begins at31-day old by water imbibing. D (APS treatment group,10mg/kg/d) begins at31-day old by Intramuscular injection. The blood samples were collected at27,30,37,44-day old, to assay contents of IFN-y and IFN-β in the serum via ELISA, peripheral T lymphocytes proliferation status via MTT, CD4+/CD8+T lymphocyte Ratio via Flow cytometric analysis. Examine every chick’s immune organs exponents, and the VP1gene of IBDV and TLR3mRNA gene of chickens expression in the bursal tissue by Real-time PCR.Results:1. IBDV BC6/85strain infected the28-day old chicken, then this test indicated Infectious bursal disease models were established successfully through observing chicks’clinical symptoms and the result of PCR at post-infection10days.2. At27-day old, DG Medium dosage prevent group could improve markedly(P<0.01); At the10d and17d post infection, Fabricius index of the groups of infection were lower than control group(P<0.01), and virus group was the lowest. Ribavirin treatment group was the highest at the10d after infection (P<0.01).3. At10d post infection, spleen index of DG high treatment dosage group was the highest. At17d post infection, the spleen index of virus group was lowest than other infectious groups (P<0.05),and DG Medium dosage prevent group was the highest. 4. DG Medium dosage prevent group could improve thymus index significantly (P<0.05), then down-regulation without DG prevent. Ribavirin treatment group was the best among the treatment groups, but also down-regulation after stopping treatment(P<0.05). APS and DG Medium dosage treatment group were the most stable and always higher than virus group.5. Before infection, DG Medium dosage prevent group could improve IBDV antibody level significantly (P<0.01). After infection, DG could improve the antibody level higher than virus group (P<0.05), better than Ribavirin and APS treatment group.6. DG Medium dosage prevent group, Ribavirin treatment group and APS treatment group could improve IFN-β significantly, and DG Medium dosage prevent group was better at10d after infection, but Ribavirin and APS treatment group were more stable.7. APS treatment group could improve contents of IFN-y, then Ribavirin treatment group, and then DG high dosage treatment. DG treatment group were dose-dependent.8. DG high dosage treatment, Ribavirin treatment group and APS treatment group could improve T lymphocyte proliferation markedly at10d and17d post infection, and were higher than virus group (P<0.05).9. Each drug group could improve CD4+/CD8+T lymphocyte Ratio. At27,30,37-day old, DG Medium dosage prevent group was the best, then DG low dosage treatment and DG high dosage treatment, and they were all better than Ribavirin and APS treatment group.10. Each drug group were lower than virus group on virus contents(P<0.05), and DG high dosage treatment group was the best, then DG Medium dosage prevent group, and then DG Medium dosage treatment group, and all were better than Ribavirin treatment group.11. After IBDV infection, the express of TLR3was up-regulation, except DG high dosage treatment group, others all promoted the express, and DG Medium dosage prevent group was the best.Conclusion:1. DG, RV and APS could improve the clinical symptoms and immune organs index of infection groups, recduce damage of immune organs and promote development of immune organs to improve immunity ability;2. DG, RV and APS can improve IBDV-Ab, T lymphocytes proliferation, CD4+/CD8+T lymphocyte Ratio and IFN-γ markedly to enhance humoral immunology and cellular immune status of infection groups; DG high dosage therapy group (80mg/d/kg) got the best promoting effect to the first three factors, and DG prevent group (40mg/d/kg) got the highest express level of IFN-γ.3. DG, RV and APS can make the express of TLR3in the bursa Fabricius and IFN-P in the peripheral blood up-regulation Obviously to improve the innate immune response. DG prevent group (40mg/d/kg) had the best effect. 4. All DG groups, except DG low dosage therapy group, could inhibit the replication of the virus in the bursal tissue through reducing the express of VP1gene of IBDV markedly. DG high dosage therapy group (80mg/d/kg) and DG prevent group (40mg/d/kg) had the more significant inhibitory effect.