The Change Of TLR4 Signal Pathway On Inflammatory Response In Chick Induced By O₈₈ Escherichia Coli

TLR4 that is regarded as pattern recognition receptor（PAMPs）is a vital part of innate immune system.It can activating expression of inflammation gene in signaling pathway by specifically recognize LPS in cytoderm of G-bacteria,and induce inflammation response to anti infection of bacteria.Escherichia coli is one of the main pathogenic bacteria that endanger poultry.This article aim to research the change of expression level of TLR4 and inflammation factor in bacteria infection of poultry by O₈₈ E.coli.This article use 10 day ages chick as model,to research clinical symptoms and ocular lesions by H-E stain,Western Blot and QRT-PCR in O₈₈ E.coli infection.And the change of construction in tissues of heart,liver,spleen and bursa of Fabricius.Meanwhile,the expression of inflammation gene,pyroptsis gene and related molecular in TLR4 signaling pathway were measure.The result are as follows:Serous fibrinous pericarditis and hepatic retrograde hepatitis were observed in O₈₈ E.coli infected chick.Detection of serum AST enzyme activity showed that the level of serum AST increased gradually with the increase of infection time compared with that of the control group,indicating that O₈₈ E.coli infection would lead to heart and liver damage in chicks.Expression of IL-1β、TNF-α in heart,liver,spleen and bursa of Fabricius were detected.It showed that expression of IL-1β、TNF-α were increased after infection of O₈₈ E.coli.The expression of IL-1β increased 6 times in liver in 8 hour post infection,and expression of TNF-α increased 5 times.However,expression of IL-1β、TNF-α were decreased in liver in 24 and 72 hour post infection,rise to level of control group in the last.It indicating that O₈₈ E.coli can induce expression of inflammation gene.It shows a dynamic change from rising to falling.Detection level of TLR4 protein showed that a time-dependent increase in heart,liver,spleen and bursa of Fabricius.The expression of NF-κB m RNA shows a dynamic change from rising to falling.The expression of NF-κB increased 3 times in liver in 8 hour post infection,and decreased in 24,72 and 120 hour post infection.Expression of My D88 m RNA shows a dynamic change from rising to falling.The expression of TRIF significantly increase 8 hour post infection,and it showed that a time-dependent decrease in 24,72 and 120 hour post infection.It suggests that O₈₈ E.coli activates the TLR4 signaling pathway through the My D88 pathway to regulate occurrence and development of inflammation response.The expression level of caspase-1 in the heart and liver was detected,and it was found that a significantly increased in 8 hour post infection,while the expression level of caspase-1 was decreased in 24 and 72 hour post infection.It shows a dynamic change from rising to falling,suggesting that cell pyroptsis induced by caspase-1 may be involved in the inflammatory response mediated by the TLR4 signaling pathway.In this study,the change of expression level caused by O₈₈ E.coli was explained from the perspective of innate immunity,providing a basis for the prevention and treatment of this serotype escherichia coli in chickens.