| Objectives:Bronchial asthma is a chronic respiratory disease characterized by airway inflammation dominated by eosinophils infiltration.However,the hygiene hypothesis can not explain all the allergic asthma incidence and the house dust and endotoxin of Gram-negative bacteria have a controversial role in the asthmatics airway inflammation.Lipopolysaccharide(LPS),a cell wall component of Gram-negative bacteria,are ubiquitous in the environment.Recent studies demonstrate that the concentration of LPS has an effect on the balance of immune response.When presented with OVA containing low dose LPS,mice demonstrated Th2 immune response with a significant increases in cytokines IL-4,IL-5 and IL-13,a high dose of LPS in OVA resulted in a Thl associated response with an increase in IFN-γproduction,which indicated its ubiquitous role in supersensitivity response.Asthma is a complicated genetic disorder caused by interaction of the acquired and innate immune responses.Acquired immune responses to protein antigens could induce type 2 T lymphocyte-driven responses and result in atopic asthma.Recent studies demonstrated that endotoxin,LPS and air pollution-induced innate immunity induce asthma through Toll-like receptors(TLR).However,the definite mechanism of LPS-induced asthma is still not known.Here to evaluate the role of LPS in the inflammatory response of asthma.We used a mouse model of allergic asthma to identify the LPS-induced changes in the TLR4 signaling pathway.We used different doses of LPS to induce a mouse model of Th2 pulmonary inflammation by which to explore the distinct types of airway inflammatory responses.We investigated the effects of different doses of LPS in a mouse model of allergic asthma to define the molecular mechanism of LPS-induced asthma.Toll-like receptor 4(TLR4),a novel pattern-recognition molecule in antigen present cells(APC) such as alveolar macrophage(AM),could identify LPS and activate the immune cells.Although it is known that LPS signaling through TLR4 influence the development and severity of asthma,however,the definite mechanism by which LPS influences asthma pathogenesis via TLRs and the role of activated AM in allergic asthma is poorly understood.Here,we studied the effect of different doses of LPS in animal models of allergic asthma and the actvition of AM through TLR4 signaling pathway in the asthma pathology mechanism and furthermore identify the pathology mechanism of asthma.Methods:40 BALB/c mice were randomly divided into asthma group A using OVA to sensitize and challenge,experimental group B(0.1ug/ml LPS+OVA) experimental group C(100ug/ml LPS+OVA),and control group D with saline instead of OVA.The histopathology change of pulmonary tissues was observed by light microscope. Measuring the concentration of cytokine IL-4,IL-5,IL-13 and IFN-γin supematant of BALF by ELISA.The expression of TLR4 mRNA in AM was analyzed by quantitative real-time RT-PCR.The expression of CD40 protein in AM was analyzed by Flow Cyto Meter.Results:1.The Mice Asthma ModelStudies in the OVA-induced model had demonstrated that a subset of overreaction as a major feature of asthma successful model.When compared with mice in saline group,the mice of OVA group showed dysphoria,more activity,upper limb raise, urinary and fecal incontinence and so on.2.Patho-manifestation by HE in lung tissuesWhen compared with mice in saline group,the lung tissue from OVA treated mice (group A) showed wall thickening,inflammatory cells infiltration,subepithelial fibrosis,mucous metaplasia,and myocyte hyperplasia and hypertrophy.Besides,the lung tissue of group B and group C mice showed obvious alveolus hyperemia and neutrophil infiltration.However,we observed no obvious inflammation in saline group(group D).3.The concentration of IFN-γ,IL-4,IL-5andlL-13 in BALF The animals in group A developed eosinophilic inflammation with significant increased production IL-4,IL-5 and IL-13 compared with group D(P＜0.05).Besides, we also detected significant higher expression of cytokines IL-4,IL-5,IL-13(P＜0.05) while the IFN-γexpression showed no significant differences in BALF supernatants in group B(P＞0.05).As for mice in group C,the expression of cytokines IL-4,IL-5,IL-13 were significantly decreased and IFN-γexpression was increased(P＜0.05).4.Expression of TLR4mRNA in AMMice in group A developed the pattern of eosinophilic airway inflammation we had observed while the expression of TLR4mRNA in AM was equivalent to that of control group(P=0.136).TLR4mRNA in AM of mice in group B and C were both significantly high expressed compared with group A(P=3.26×10-6) with no difference was found between them(P=0.347).5.Expression of CD40 protein in AMMice in group A developed the pattern of eosinophilic airway inflammation we had observed while the expression of TLR4mRNA in AM was equivalent to that of control group(P=0.253).TLR4mRNA in AM of mice in group B and C were both significantly high expressed compared with group A(P=5.17×10-6) with no difference was found between them(P=0.171).Conclusions:1.TLR4 signaling pathway plays a vital role in asthma inflammatory reaction.2.LPS in low dose(0.1ug/ml) may aggratate airway inflammation of asthma mice by inducing high expression of TLR4mRNA in AM.3.AM,which is activated by TLR4 signaling pathway,is a key factor in the interaction of innate and acquired immunity in asthma pathology.
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