NIBV Mediated TLR4/TLR7 Signaling Axis On Renal Inflammation

Kidney is the main target organ of Nephropathogenic infectious bronchitis virus（NIBV）,but the mechanism of renal inflammation caused by NIBV is not clear.The purpose of this study was to investigate the correlation between TLR4/TLR7signaling axis and renal inflammation caused by NIBV,and to clarify the mechanism of TLR4/TLR7 signaling pathway and renal inflammation after host infection with NIBV.Hy-Line brown laying hens were randomly divided into two groups—the control group（Con,100）and the disease group（Dis,200）.At 28 days of age,eye drops and nose drops(the SX9 strain was administered according to the median embryo lethal dose 10^-5/0.2 m L)were used for each chicken in the Dis group.The samples were collected at 1dpi,5dpi,11dpi,18dpi and 28dpi.Renal tissue was collected for pathological section and ultrastructural observation,and TLR4,TLR7,Myd88,TRAF6,IRF7,NF-κB P65,NF-κB P50,IL-6,IL-8,IKKα,IKKβ,TNF-αand IFNγm RNA level and partial protein level were detected;the expression and distribution of TLR4,NF-κB P65 and IFNγwere analyzed qualitatively and quantitatively by immunofluorescence.The experimental results are as follows:1.Compared with the control group,the renal histopathological observation in the challenge group showed that there were a large number of inflammatory cell infiltration,red blood cell aggregation or obstruction inside and outside the renal corpuscles and renal tubules,the renal tubular structure was destroyed and the renal corpuscles were shrunk.Under electron microscope,multiple virus particles were observed in the kidney tissue of the virus attack group,which were coronal,and there was light transmission in the particles.The renal cell structure was seriously damaged,the nucleus was pyknotic and the nuclear membrane was not clear;Mitochondria appeared edema,cristae structure was fuzzy,broken and arranged disorderly;The golgi apparatus structure is fuzzy.2.Compared with the control group,the challenge group:The m RNA level of TLR4,TLR7,Myd88,TRAF6,IRF7,NF-κB P65,NF-κB P50,IL-6,IL-8,IKKα,IKKβ,TNF-α,IFNγincreased significantly at multiple time points;TLR4,NF-κB P50,IL-6,IL-8,IFNγProtein levels increased significantly at multiple time points,but the level of NF-κB P65 protein was opposite to its m RNA level,showing a downward trend.3.The immunofluorescence intensity of TLR4 was significantly higher than that of the control group at 1dpi,5dpi and 18dpi,and significantly lower than that of the control group at 11dpi,which was consistent with the trend of WB results.The immunofluorescence intensity of NF-κB P65 was lower than that of the control group at 1dpi and 5dpi,mainly located in the cytoplasm;the immunofluorescence intensity of NF-κB P65 from 11dpi to 28dpi was stronger than that of 1dpi and 5dpi,mainly distributed in the nucleus.The immunofluorescence intensity of IFNγwas lower than that of the control group at 5dpi,and higher than that of the control group at 11dpi to28dpi.Conclusion:Infection with the NIBV SX9 strain activates the TLR4/TLR7signaling axis in renal tissue,activates the nuclear transcription factors IRF7 and NF-κB,induces the production of proinflammatory cytokines,causes an inflammatory response and leads to kidney damage.