The control effects of FLT3 signaling-dependent pulmonary conventional dendritic cells on the initiation of acute lung inflammation response to lipopolysaccharide induced acute lung injury in mice

Abstract

Objective To clarify the role of FLT3 signaling-dependent pulmonary conventional dendritic cells (cDCs) in the pathogenesis of lipopolysaccharide (LPS)-induced acute lung injury (ALI), and as well as the modulation effects of cDCs in vivo on the inflammatory responses to acute lung injury. Methods Thirty C57BL/6 male mice were divided into normal control group, LPS group, FLT3L pretreatment group, lestaurtinib, (a high efficient and specific blocker in FLT3 signal pathway) pretreatment group and vehicle (DMSD) control group. FLT3L and lestaurtinib were administrated subcutaneously for 5 days. Murine model of ALI was subsequently established by intra-tracheal application of LPS and lung specimens were harvested 6 h or 24 h later. The accumulation and maturation of pulmonary cDCs were assessed by flow cytometry. IL-6 and TNF-α were quantified to evaluate lung inflammation. Lung injury was estimated by lung wet weight/body weight ratio (LWW/BW) and histopathological assessment. Lung myeloperoxidase (MPO) activity was measured to evaluate neutrophil infiltration. Transcription factors T-bet/GATA-3 mRNA ratio was determined to estimate balance of Th1/Th2 response. IFN-γ and IL-4 were quantified to evaluate Th1-specific and Th2-specific cytokine production respectively. Results The accumulation and maturation of pulmonary cDCs peaked at 6h after LPS challenge. FLT3L pretreatment significantly stimulated the accumulation and maturation of pulmonary cDCs (P<0.05), leading to markedly deterioration of LWW/BW and lung histopathological changes. Meanwhile lung MPO activity and T-bet/GATA-3 mRNA ratio were elevated (P<0.05). Furthermore, the production of IL-6, TNF-α and IFN-γ was markedly increased by FLT3L pretreatment (P<0.05). In contrast, lestaurtinib pretreatment markedly inhibited the accumulation and maturation of pulmonary cDCs (P<0.05), leading to significant improvement of LWW/BW and lung histopathological changes. Meanwhile lung MPO activity and T-bet/GATA-3 mRNA ratio were decreased (P<0.05). Furthermore lestaurtinib efficiently suppressed the production of IL-6, TNF-α and IFN-γ(P<0.05). Conclusion This study thus demonstrated that FLT3 signaling-dependent pulmonary cDCs could control the initiation of acute lung inflammation response to LPS-induced ALI through the regulation of neutrophil infiltration and balance of Th1/Th2 response. Key words: Acute lung injury; Conventional dendritic cells; FLT3 signaling; Inflammation; Neutrophils infiltration; T-helper-cell response; Pathogenesis