Study On The Role Of Regulatory T Cells In A Mice Model Of Traumatic Brain Injury

Objective:The aim of this research is to preliminarily investigate the role of regulatory T cell in Traumatic Brain Injury(TBI),by observing the changes of regulatory T cell and its impact on the recovery of neurological function afterTBI.Methods:In this experiment,the clean healthy adult male C57B1/6 mice(n=184)were divided into four groups according to the random number table:group 1(control group,n=46),group2(sham group,n=46),group3(TBI group,n=46),and group4(TBI+CD25 antibody group,n=46).Subsequently,the mice traumatic brain injury model was established using the fluid pressure device;the behavioral function and the pathological changes in brain were identified by modified neurological severity score and H.E staining,respectively.Firstly,fluorescence-activated cell sorting(FACS)and immunohistochemical staining were used to measure the changes of regulatory T cell in spleen and brain tissue on dayl,day3,day5,day7 and dayl4 of brain trauma in each group(n=30).Secondly,the differences of cognitive function in each group(n=10)were examined using the Morris water maze 7 days after the modeling.Thirdly,the blood-brain barrier penetration were determined by Evans blue(n=6)on day3.Finally,the immunohistochemical and TUNEL staining were applied to detect the MPO+ neutrophils and apoptotic cells in brain tissue.Results:The injured mice brain tissue of each group showed typical pathological changes after brain trauma;there was no difference in modified neurological severity score 12 hours after injury.However,the differences gradually emerged following the recovery of the injury.The level of regulatory T cell in spleen tissue of group3 started to decrease on day3 after brain trauma(P<0.05),and descended to the valley bottom on day5(P<0.05);subsequently,it increased gradually,but did not regain to the normal level.Interestingly,the regulatory T cell in brain tissue were able to be detected on day3(P<0.05),and its level reached the peak value(P<0.05)on day5.Then the amount of it reduced but remaining expression.Nevertheless,few levels of regulatory T cell were observed in both brain and spleen of group 4.Additionally,Group3 and group4 had significantly longer escape latency than group2(P<0.05);the escape latency of group4 were even longer than that of group 3(P<0.05).There were no differences in the swimming speed of all groups(P>0.05).In comparison with group3,group4 had more serious damage of blood-brain barrier and higher penetration of Evans Blue(P<0.05).MPO+ eutrophils presented in the injured brain tissue and necrotic tissue 3 day after brain trauma;but the apoptotic cells were mainly distributed in the penumbra Compared with group3,a higher amount of MPO+neutrophils and apoptotic cells exhibited in group 4(P<0.05).The mice of group 1 and group2 had no difference in the detection of targets and no EB leakage.In the meanwhile,MPO+ eutrophils and apoptotic cells also stayed at the normal levels.Conclusion:Regulatory T cell probably infiltrates the damage blood-brain barrier into the brain parenchyma to influence the development of brain trauma.It might relieve the damage of blood-brain barrier and reduce the death of neuron cell by inhibiting the infiltration of inflammatory cell.Generally,regulatory T cell plays a possibly important role in the prognosis of neurological function after traumatic brain injury.