Background:Immune disorder is an important feature of patients with out-of-hospital cardiac arrest (OHCA) after the ret of spontaneous circulation (ROSC).We investigated the expression of circulatory T helper type (Th) 1,Th2,and Thl7 cells to explore the early immune alteration in OHCA patients after ROSC.Methods:During July-September 2016 and March-September 2017,65 consecutive OHCA patients with ROSC＞ 12 h and 30 healthy individuals were enrolled in this study.Clinical and 28-day survival data were collected.Peripheral blood samples were analyzed to evaluate the expression of Thl/Th2/Th 17 cells by flow cytometry from OHCA patients after ROSC on days 1 and 3 and from healthy individuals.Results:Compared with healthy individuals,T lymphocyte counts and Th l cell counts decreased on days 1 and 3 after ROSC (1464 [1198,2152] vs.779 [481,1140] vs.58l [324,1118]/μl,x2 =30.342,P ＜ 0.001;154 [90,246] vs.39 [19,78] vs.24 [12,53]/μl,x2 =42.880,P ＜ 0.001),and Th2 and Th 17 cell counts decreased on day 3 (17.0 [10.8,24.0] vs.9.0 [3.0,15.5]/μl,Z =3.228,P =0.001;4.7 [2.7,9.1] vs.2.7 [1.0,6.5]/μl,Z =-2.294,P =0.022).No change in CD4+/CD3+ lymphocyte ratio was seen on day 1 or day 3 (57.9 [49.4,63.0] vs.55.4 [46.5,66.5] vs.55.4 [50.2,67.0]％,x2 =0.171,P =0.918).Th1/CD4+ lymphocyte ratio decreased on days 1 and 3 (19.0 [14.0,24.9] vs.9.3 [4.6,13.9] vs.9.5 [4.9,13.6]％,x2 =25.754,P ＜ 0.001),and Th2/CD4+ lymphocyte ratio increased on day 1 and decreased on day 3 (1.9 [1.2,2.5] vs.2.5 [1.6,4.0] vs.1.9 [1.6,3.8]％,x2 =6.913,P =0.032).Thl/Th2 cell ratio also decreased on both days (9.4 [7.3,13.5] vs.3.1 [1.9,5.6] vs.4.2 [2.8,5.9],x2 =44.262,P ＜ 0.001).Despite an upward trend in the median of Th 17/CD4+ lymphocyte ratio in OHCA patients,there was no significant difference compared with healthy individuals (0.9 [0.4,1.2] vs.0.7 [0.4,1.2] vs.0.6 [0.3,1.0]％,x2=2.620,P =0.270).The dynamic expression of Th1/Th2/Th17 cells on days 1 and 3 were simultaneously analyzed in 28/53 OHCA patients who survived ＞3 days;patients were divided into survivors (n =1 0) and nonsurvivors (n 18) based on 28-day survival.No significant differences in Th 1/Th2/Th 17 cell counts,ratios in CD4+ lymphocytes,and Th 1/Th2 cell ratio were seen between survivors and nonsurvivors on both days (all P ＞ 0.05).There was no difference over time in both survivors and nonsurvivors (all P ＞ 0.05).Conclusion:Downregulated T lymphocyte counts,including Th 1/Th2/Th 17 subsets and Th 1/Th2 cell ratio imbalance,occur in the early period after ROSC,that may be involved in immune dysfunction in OHCA patients.