The Related Mechanism Of Myeloid-derived Suppressor Cells Proliferation In The Severely Injured Of Bone

Background:Polytrauma often induces inflammatory responses and immune dysfunction leading to infections and multiple organ failure.Immune dysfunction,frequently observed as T cell dysfunction,is central to the development of infections after trauma.Myeloid-derived suppressor cells(MDSCs)accumulate in the spleen and suppress T cell functions after polytrauma.The release of glucocorticoids(GCs)is activated by the Hypothalamic-Pituitary-Adrenal(HPA)axis following polytrauma and GCs have been shown to induce a monocyte subset which resembles MDSCs in vitro.In this study,we investigated the effect of GCs on MDSC expansion following polytrauma.Objective:To study the correlation between the release of glucocorticoids and the dynamic changes of MDSCs and the related mechanism by building a murine polytrauma model.Methods:thirty Sprague-Dawley rats were subjected to a polytrauma model.animals were sacrificed at 6h,24h and 72h,and their lung and blood were collected.ElISA was used to test the serum concentration of TNF-α,IL-1βand IL-6.Lung HE staining was performed and lung MPO were measured by the MPO assay kit.RT-PCR was used to test GRαand GRβmRNA expressions.Then Rats were divided into three groups as follows:the control group,the femur fracture(FFx)group,and the polytrauma(PT)group.Animals were sacrificed at 2,6,12,18,or 24 h postoperatively,and spleen was harvested for study.The MDSCs were identified by a flow cytometry and calculated.Lastly,Thirty-six Sprague-Dawley rats were subjected to a polytrauma model.Animals were sacrificed at 2,6,12,18,24 or 48h postoperatively,and their blood,spleen and bone marrow were collected for analysis.Dexamethasone was given to the naive rats(n=6).The rats then sacrificed 2 hours after the administration.The rats was received RU486 30 min before polytrauma(n=6)and sacrificed 2 hours postoperatively.The serum concentrations of corticosterone were measured using an ELISA kit.The MDSCs expansion was assessed by flow cytometry.The incorporation of[~3H]thymidine was used as a measure of T cell proliferation.Results:(1)At 6 hours,serum TNF-α,IL-1βand IL-6levels were markedly increased after polytrauma when compared with sham(P<0.05).MPO lung levels were significantly increased at 6h and 24h after polytrauma when compared with sham(P<0.05)and marked neutropil infiltrates,alveolar wall congestion,and disruption of the alveolar architecture were seen.GRαand GRβmRNA expressions were increased in lung after polytrauma.GRβmRNA expression were much higher.(2)The peak number of MDSCs in the PT group was about four times greater(P<0.001);and in the FFx group,about one and a half times more(P=0.003)than in the control group.The increased level of MDSCs returned to normal after 18 h in the PT group,and after 6h in the FFx group,post-surgery.(3)MDSCs were mobilized in the bone marrow,increased in the blood and accumulate in the spleen after polytrauma(P<0.05)which had a linear correlation with the release of glucocorticoids(P<0.05).MDSCs induced by polytrauma suppressed the T cell proliferation.Further,the application of dexamethasone in the naive rats enhanced the MDSC expansions while RU486 used before polytrauma attenuated MDSC expansions(P<0.05).Conclusion:(1)The animal model used in this study imitates the process of trauma pathophysiology.(2)Different kinds of trauma stress represent differences in the dynamic changes in MDSCs.The more severe the trauma is,the greater the MDSCs expansion is.(3)The release of GCs following polytrauma is involved in MDSC expansion which suppress T cell functions.