Abstract: Objective To investigate the changes in Th17/Treg immune balance and fraction of exhaled nitric oxide (FeNO) level in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD) before and after treatment and their effect on prognosis. 
Methods A total of 126 patients with AECOPD were selected, and forced expiratory volume in one second (FEV1), the percentage of predicted value of FEV1(FEV1%), forced vital capacity (FVC), the percentage of predicted value of FVC (FVC%), and FEV1/FVC were measured by pulmonary function detector. FeNO levels were detected using nitric oxide analyzer, and the scores were assessed using systemic inflammaton response syndrome (SIRS) scores. Serum T help 17cells (Th17) and Tregulatory cells (Treg) were detected using flow cytometry. The changes in pulmonary function index, FeNO level, SIRS score and Th17/Treg level before and after treatment were compared. 
Results At 3 months after treatment, the levels of FEV1%, FEV1/FVC, Th17 and Th17/Treg in AECOPD patients were significantly higher than those before treatment, while FeNO, serum Treg level and SIRS score were significantly lower than those before treatment (P＜0.05). Of 126 AECOPD patients, 94 (74.60%) survived and 32 (25.40%) died at 3 months after treatment. The levels of FEV1%, FEV1/FVC and Treg in survival group were significantly higher than those in death group, while the scores of FeNO, Th17, Th17/Treg and SIRS in survival group were significantly lower than those in death group (P＜0.05). Multivariate Logistic regression analysis showed that FEV1%, FEV1/FVC and Treg were the risk factors for prognosis of AECOPD patients before treatment (P＜0.05), where as FeNO, Th17, Th17/Treg and SIRS scores were protective factors for the prognosis of AECOPD patients (P＜0.05). 
Conclusion After treatment, the pulmonary function of patients with AECOPD is improved, while Th17/Treg and FeNO are decreased. Pulmonary function, Th17/Treg immune balance and FeNO level are of great significance for the efficacy evaluation and prognosis judgment of patients with AECOPD.

Key words: pulmonary disease, chronic obstructive, Th17 cells, T lymphocytes, regulatory