Effect Of Seaweed Polysaccharide On Immune Function In SPF Chickens And Replication Of ALV-K

Avian leukemia subgroup K is a neoplastic disease of birds that has been severely affected by the global poultry industry due to the lack of vaccines and drugs to prevent and control it.Seaweed polysaccharide is a kind of multi-component mixture extracted from seaweed,which has anti-virus,anti-inflammatory,immunomodulatory and other biological activities.By studing the effect of seaalgae polysaccharide on immune function in SPF chickens and ALV-K replication,which laid a foundation for practical application in animal husbandry in the future.In this study,SPF chickens were fed seaweed polysaccharide and immunized with Newcastle disease vaccine.Weighed SPF chickens and measured its immune organ index.The antibody titer and the contents cytokines IL-2 and IFN-γin serum were detected by ELISA.The ratio of CD4⁺and CD8⁺T lymphocytes in chicken peripheral blood was analyzed by flow cytometry.He staining of tissue sections with paraffin wax was used to observe whether it had toxic side effects on immune organs.The effects of different concentrations of seaweed polysaccharides on the replication of ALV-K on CEF cells were detected by RT-PCR.Through measuring TCID₅₀to analyzed the influence on the titer of ALV-K.The expression levels of inflammatory factors in virus-infected cells were compared and analyzed to further explore the role of ALV-K replication at the molecular level.The results showed that there was no significant difference in body weight among all groups（P>0.05）,indicating that seaweed polysaccharide had no effect on promoting the growth of chickens.The indexes of immune organs in experimental groups were significantly increased（P<0.05）,which proved that polysaccharides from seaweed had immune-enhancing effects at the organ and tissue level.ELISA results showed that the experimental group chicken Newcastle disease in serum antibody titer,cytokine IL-2,IFN-γlevels were increased,at the same time,the data of flow cytometry measure according to experimental group chicken peripheral blood CD4⁺,CD8⁺T lymphocyte ratio varying degrees higher than the blank control group,and further from cellular level to justifying the seaweed polysaccharides has enhanced immune function.It was found that dietary seaweed polysaccharide had no side effects on the liver,spleen and bursa of Fabricius of chickens by tissue section observation,which verified its safety.By the effect of ALV-K on CEF cells,it was found that the relative expression of ALV-K decreased by69%when the final concentration of seaweed polysaccharides reached 200μg/m L,and by8%,26%and 55%when the final concentration of seaweed polysaccharides was 25μg/m L,50μg/m L and 100μg/m L,respectively,indicating that the inhibitory effect of ALV-K on CEF cells was dose-dependent.TCID₅₀ results showed that 200μg/m L seaweed polysaccharide could significantly reduce the titer of ALV-K（P<0.01）,which further verified that seaweed polysaccharide could inhibit the proliferation of ALV-K on CEF cells.RT-PCR results showed that the expression levels of pro-inflammatory factors ISG12-2,IL-1βand TNF-αwere significantly down-regulated,and the inhibition of IL-1βgene expression was the most significant,which was down-regulated 0.926 times,and the expression levels of ISG12-2 and TNF-αwere down-regulated 0.75 and 0.88 times,respectively.In conclusion,dietary supplementation of Seaalgae polysaccharides can significantly promote the development of spleen and bursal of Fadburi,increase serum NDV-Ab titer,IL-2,IFN-γlevels and peripheral blood CD4⁺,CD8⁺T lymphocyte ratio of chickens,and promote cellular and humoral immunity of chickens.Seaalgae polysaccharides could inhibit the replication of ALV-K and significantly down-regulate the expression of ISG12-2,IL-1βand TNF-αgenes in CEF cells.