Abstract： Objective To detect the Th1 and Th2 cell percentage in pleural effusion mononuclear cells (PEMCs) stimulated by early secretory antigenic target protein-6 (ESAT-6)/culture filtrate protein-10 (CFP-10) fusion protein (E/C) with flow cytometry (FCM),and therefore to explore the local antigen specific Th1 and Th2 response and its diagnostic value in tuberculous pleuritis.Methods Forty patients with tuberculous pleural effusion and 30 patients with malignant pleural effusion were included in this study from Sep.2008 to Mar.2009.PEMCs were isolated and cryopreserved.After resuscitation,the cells were cultured with E/C (simultaneously with positive control and negative control),and antigen-specific Th1 and Th2 cells were detected with intracellular cytokine staining of FCM.Normal distribution data using t test,abnormal distribution data using Wilcoxon test.Results In the TB group,the medians (quartile range) of Th1 cells and Th1/Th2 ratio among PEMCs stimulated by ESAT-6/CFP-10 fusion protein were 3.06％(1.59％-6.92％) and 17 (7.38-35.53),significantly higher than those of the negative control [0.38％(0.02％-1.80％) and 3.59 (0.49-25.09)],the differences being statistically significant (Z =-5.345 and 3.314,P ＜0.01).The percentage of Th2 cells [(0.22 ±0.19) ％] was also increased compared with that of the negative control [(0.10 ± 0.08) ％],the difference being statistically significant (t =4.108,P＜0.01).In the malignant effusion group,the medians (quartile range) of Th1 percentage and Th1/Th2 ratio were 0.12％ (0.05％-0.39％) and 1.05 (0.25-2.52),which were significantly different as compared with those of the TB group (Z =-6.624 and-5.536,P ＜ 0.01).The Th2 percentage in the 2 groups were (0.22 ±0.19)％ and (0.15 ±0.02)％,respectively (t =1.954,P ＞0.05).The receiver operating characteristic curve indicated that the area under the curve (AUC),sensitivity,and specificity were 0.937,85.4％,and 90.6％ respectively for Th1 to diagnose tuberculous pleurisy.For Th1/Th2,the AUC,sensitivity,and specificity were 0.883,81.5％,and 90.6％respectively.Conclusions The feature of ESAT-6/CFP-10 fusion protein-specific Th1 and Th2 response in tuberculous pleurisy was a mixed reaction of Thl and Th2 with Th1 predominance.Th1 percentage and Th1/Th2 ratio could be diagnostic indexes for identifying tuberculous from malignant pleural effusions.