The Histopathological,Viral Distribution And The Dynamic Changes Of TLR3 And IRF7 Expression Of Chickens Infected With Sub-genotype Ⅶh NDV

Newcastle disease virus(NDV)is one of the most important pathogens in the poultry industry.In recent years,Ⅶh NDV,a novel sub-genotype of NDV has spread widely in chicken flocks in Southeast Asia,South Africa and other regions.In order to explore the pathogenesis of sub-genotype Ⅶh NDV GXC110083 strain and the role of TLR3 and IRF7 in NDV infection,in this study,we used the NDV GXC110083 strain and Chinese standard virulent NDV strain F48E8 to infect the 42-day-old SPF chickens respectively.The clinical signs of infected chickens were observed and the spleen,thymus,bursa of fabricius,kidneys,pancreas,and duodenum of the chicken in each group at 1,2 and 4 days post inoculation(DPI)were collected and used to analyze the distribution and dynamic changes of viral antigen of NDV,TLR3 and IRF7 protein in various tissues and organs with immunohistochemistry(IHC),histopathology and image analysis techniques.The results are as follows:(1)Histopathological changes of tissues and organs after infection with NDVBoth GXC110083 and F48E8 strains could cause obvious disease within 2 days and rapid death within 4 days with typical clinical symptomthe s and autopsy lesions in infected chickens.The histopathological results showed that spleen,thymus,bursa of Fabricius,kidneys,pancreas,duodenum of the chickens infected with GXC110083 and F48E8 strain showed serious histopathological damage.On the first day after infection,histopathological lesions of varying degrees of manifestation began to appear in the spleen,thymus,bursa,kidneys and duodenum of the GXC110083 infected group,with immune organ tissue lymphopenia,tubular epithelial cells degeneration and necrosis,and intestinal mucosal epithelial necrosis and loss.With the development of the course of the disease,more severe tissue injury of each organ was observed,and the most severe damage was observed at 4DPI.Then all of the tissues showed different degrees of necrosis,and lymphatic follicles of bursa were severely depleted.Meanwhile,a lot of inflammatory exudates were observed in necroses tissue of the spleen,thymus,and duodenum.And the tissue damage of F48E8 infected group was also very severe;the degree of lesion of the spleen,pancreas,and bursa of F48E8 infected group was more severe compared to the GXC110083 infected group(2)The distribution and the dynamic changes of the virus after NDV infectionThe IHC results showed that viral antigens in the spleen,thymus,bursa of Fabricius,kidney,pancreas,and duodenum were detected in both infected groups at 1DPI.The viral antigens are mainly found in the cytoplasm of lymphocytes,reticular cells and various epithelial cells.At 1DPI,the highest level of the virus was found in the duodenum,bursa and kidneys of GXC110083 infected group,and the lowest level of virus was found in the pancreas.At 2DPI,the viral level of GXC110083 in kidneys and bursa of Fabricius showed a downward trend,while the viral level in the other tissues showed a significant upward trend.The viral level differences were found to besignificant compared to 1DPI(P<0.01).At 4DPI,the level of virus in kidney tissue increased significantly,and those in other tissues decreased.However,at 1DPI,the highest levels of virus in duodenum,spleen and kidney of F48E8 infected group was detected,and the lowest level of virus was found in the pancreas.At 2DPI,the viral level showed a significant up,ward trend in the spleen,and it remained the same level in the bursa,thymus and pancreas,however,the levels of virus significantly were decreased in kidney,duodenum.At 4DPI,the levels of virus were significantly increased in bursa,kidney and duodenum,while they were significantly decreased in Thymus,spleen and pancreas.(3)The dynamic changes of TLR3 expression of the NDV infected SPF chickenThe IHC results show that the expressions of TLR3 were detected in spleen,thymus,bursa of fabricius,kidney,pancreas,and duodenum in chickens.At 1DPI,2DPI and 4DPI,the expression of TLR3 in spleen and kidney of GXC110083 infected group was up-regulated,and the expression of TLR3 in spleen,thymus,bursa and kidney of F48E8 infected group were all up-regulated.The differences at the level of TLR3 expression of NDV infected groups were significant compared to the control group(P<0.01).The expression of TLR3 in thymus of GXC110083 infected group was up-regulated at 2DPI and 4DPI,the expression of TLR3 in bursa of GXC110083 infected group was up-regulated at 1DPI and 4DPI,the expression of TLR3 in pancreas and duodenum of GXC110083 infected group was up-regulated at 1DPI and 2DPI.The differences at the level of TLR3 expression of NDV infected groups were also significant compared to the control group(P<0.01).The expression of TLR3 in pancreas of F48E8 infected group was up-regulated at 2DPI and 4DPI,the expression of TLR3 in duodenum of F48E8 infected group was up-regulated at 1DPI.The TLR3 expression levels of both infected groups up-regulated significantly compared to control group(P<0.01).(4)The dynamic changes of IRF7 expression of the NDV infected SPF chickenThe IHC results show that the expressions of IRF7 were detected in spleen,thymus,bursa of fabricius,kidney,pancreas,and duodenum in chickens.At 1DPI,2DPI and 4DPI,the expression of IRF7 in thymus,bursa of fabricius,kidney,pancreas,and duodenum of GXC110083 infected group was up-regulated,the expression of IRF7 in spleen,thymus,bursa of fabricius,pancreas,and duodenum of F48E8 infected group was up-regulated.The IRF7 expression levels of both infected groups up-regulated significantly compared to control group(P<0.01).The expression of IRF7 in spleen of GXC110083 infected group was up-regulated at 1DPI and 2DPI,the expression of IRF7 in spleen of F48E8 infected group was up-regulated at 2DPI and 4DPI.The differences at the level of IRF7 expression of NDV infected groups were significant compared to the control group(P<0.01).In summary,the present study demonstrated that both sub-genotype Ⅶh NDV GXC110083 strain and F48E8 strain could cause serious damage to the internal organs of SPF chickens.The ND viruses were widely distributed in spleen,thymus,bursa,kidney,pancreas and duodenum of both virus strains infected chickens at 1DPI and proliferated rapidly,therefore the tissues and organs were damaged.The expression levels of TLR3 and IRF7 proteins in various tissues and organs were significantly increased,indicating that TLR3 and IRF7 are involved in the process of SPF chickens against GXC110083 and F48E8 virus infection.