Rapamycin Attenuates Acute Lung Injury Induced By Lps Through Inhibition Of Th17 Cell Proliferation In Mice

Background and Objective: ALI/ARDS is an acute and progressive hypoxic respiratory failure syndrome caused by various pathogenic factors leading to the injury of alveolar epithelial cells and vascular endothelial cells. It is a critical illness in the Department of Respiration, the mortality rate always maintains high level. A large number of inflammatory mediators release and neutrophil activation mediated different degrees of lung injury is considered to be the central link in the pathogenesis of lung disease. However, a number of clinical trials with anti-inflammatory therapy did not receive the expected results to improve outcomes of patients with ALI/ARDS. Under the physiological condition, the neutrophils mainly exist in the bone marrow, and the half-life is short. The recruitment and activation of neutrophils in the lung tissue of ALI/ARDS are required continuous drive of chemokines or proinflammatory factors. Immune response as the body’s first line of defense against injury triggered earlier than inflammation reacted. Th17 cells as effector cells of the adaptive immune response, through the secretion of IL-17 cytokines to recruit and activate the neutrophils. Th17 cells mediated immune responses may be initial motive force and key links during the ALI / ARDS occurrence and development. According to this, this study intends to explore the activation characteristics of Th17 cells in ALI/ARDS to find a new entry point for the treatment of ALI/ARDS.Methods: 1. Collected peripheral blood samples and clinical data of ARDS patients were, and measured the plasma levels of IL-17 and IL-22 of each group during different time points. 2. To identify the activation characteristics of Th17 cells, wild type mice and IL-17-/- mice were used to establish the ALI animal model. Observe and compare the pathological changes of lung tissue and the inflammatory factors expression of BALF in two kinds of mice model at different time points during ALI development. 3. The ALI animal model intervened with the m TORC1 inhibitor rapamycin or its upstream inhibitor wortmannin in wild type mice. The regulation mechanism of Th17 cells was examined by detecting the expression of nuclear transcription factors and related proteins.Results: 1. IL-17 and IL-22 levels were elevated in ARDS patients, and high levels were maintained in nonsurvivors after 7 days of treatment.2. The MPO level and number of neutrophils in IL-17-/- BALF were both decreased, the degree of lung inflammation attenuated significantly. 3. The proliferation of induced Th17 cells occurred on D2 of ALI murine model. IL-17 increased significantly since 6h after LPS challenged, and continued high expression. The expression of IL-22 was much higher than IL-17 thanks to positive feedback loop forming with STAT3. 4. Rapamycin has a protective effect on acute lung injury in mice. In vitro and in vivo experiments showed that this protective effect was not achieved by enhancing the proliferation of Treg cells which owns the effect of anti- inflammation. 5. Inhibition of Th17 cell differentiation and its mediated immune response is the possible mechanism for the protective effect of rapamycin on ALI mice. The inflammation attenuated and outcomes improved. 6. The mechanism of rapamycin inhibiting Th17 cell differentiation may be: up-regulated SOCS3 to inhibit STAT3 phosphorylation and promotes the expression of Gfi1 to prevent ROR gamma t nuclear translocation through PI3K/AKT-m TORC1-S6K1 pathway.Conclusions: 1. Th17 linear cytokines unregulated in ARDS patients. Th17 cells in the ALI animal model differentiated and proliferated. These results reveal that the Th17 cell mediated immune response is involved in the pathogenesis of ALI/ARDS.2. The protective effect of rapamycin on ALI mice is mediated by a weakened Th17 cell mediated pro-inflammatory response, rather than enhanced Treg cell mediated anti-inflammatory response. 3. The mechanisms for regulation the differention of Th17 cells by rapamycin involved in regulating the expression of the transcription factor STAT3 and RORγT through inhibitors SOCS3 and Gfi1 via m TORC1-S6K1 pathway.