The Role Of ChTLR4 And Its Signaling Pathway In Chicken With LPS-induced Acute Respiratory Tract Injury

Toll-like receptors (TLRs) are pattern recognition receptors, highly conserved in evolution of innate immune system, that recognise a wide range of pathogen- associated molecular patterns (PAMPs), then trigger innate immunity and regulate function of adaptive immune response. TLRs mainly located at the membrane of macrophages, neutrophils, and dendritic cells that represent a primary line of defence against invading pathogens in the body. To date, at least 13 members of TLRs have been identified in mammals.Not only trigger TLRs the innate immune response, control the intensity and duration of inflammatory response, but also TLRs represent up-regulat the surface costimulatory molecules of the antigen-presenting cell, which promote the mature of DC and start the antigen-specific immune response. So TLRs are bridging the innate immune and adaptive immune response.excessive or insufficient activation of TLRs would lead to dysfunction and disease in the body. Further research of TLRs Signalling pathways has important theoretical and application value.The first TLR member to be discovered was TLR4, and its fanction was relatively well to understand.TLR4 was major activated by lipopolysaccharide (LPS) of gram-negative bacteria, and final NF-κB was activated through TLR-mediated a series of intracellular signal transduction process. The activion NF-κB induces a variety of inflammation gene transcription.TLR4 can cause inflammatory factors cascade, leading to severe inflammation of the pathological process. LPS can cause many diseases for instance animal intestinal endotoxemia, endotoxin shock, disseminated intravascular coagulation and acute respiratory distress. The research for the role of TLR4 in the process of LPS recognition and Signalling pathways were great significance for the prevention and treatment measures, new drugs discovery and effectively prevention uncontrolled inflammation induced by LPS.So far, 10 members of chicken TLRs (chTLRs) were found. chTLR4,chTLR5 and chTLR7 have the same highly conserved region with mammals. chTLR4 has 64% similarity with human TLR4.and 41% similarity with other human TLR family members. Birds have a lower affinity and vary greatly difference of the genome compared to mammals, the research of chTLR4 and its signal pathway in LPS-induced injury had its-own special academic value.In this study, the acute chicken respiratory tract injury was induced by intratracheal instillation with LPS. TLR4mRNA and NF-κBmRNA expression level changes in chicken trachea and lungs tissue were determined by the Real-time PCR , NF-κB and IL-1βprotein concentration in the lung were determined by ELISA, at the gene and protein level study the role chTLR4 and its signal pathway in LPS-induced acute respiratory injury. The results showed that: TLR4mRNA expression levels of the trachea and lung tissue in chickens from treatment group began to increase at 6h after LPS stimulation, were significantly higher than those in the control group at 24h. The expression level of NF-κBmRNA in lung tissue were significantly higher than those in the control group (p <0.05). At 6h,NF-KBp65 content in lung nuclear protein was significantly different compared with the control group (p<0.05), and increased significantly (p <0.01) at 24h. IL-1βlevels in lung at 6h were significant difference compared with the control group (p <0.01), and reached the peak at 24h. IL-1βlevels in serum while reached maximum at 24h, as compared with the control group significant difference (p <0.05), but the concentration was always lower than the content of the lungs.In summary, these results indicated that chTLR4 and its signal pathway involved LPS-induced acute injury in the chicken respiratory tract. After LPS administration, chTLR4mRAN expression increased in order to improve the capability of LPS recognition. Increased NF-κBp65 content in Nucleoprotein of lung showed that NF-κB has been activated and transferred to the nucleus playing a role. IL-1βsecretion increases in the lung showed that the innate immune response had been stimulated.