Increased circulating IL-9-producing CD8+ T cells are associated with eosinophilia and high FeNO in allergic asthmatics

Allergic asthma is a chronic airway disorder mediated by Th2 cells. It has been shown that IL-9-producing CD8(+) cytotoxic T (Tc9) cells promote the subsequent onset of allergic airway inflammation in mice mediated by abnormal Th2 immunity. Whether Tc9 cells are associated with the immunopathogenesis of asthmatic patients remains unknown. In the present study, peripheral blood mononuclear cells (PBMCs) were separated by Ficoll-Hypaque gradient centrifugation from all subjects. The frequency of Tc9 cells was measured by flow cytometry. Serum IL-9 levels were assessed by enzyme-linked immunosorbent assay (ELISA). mRNA expression levels of IL-9, STAT6, and IRF4 in PBMCs from healthy controls and asthmatic patients were detected by reverse transcription-quantitative polymerase chain reaction. The results showed that the numbers of Tc9 cells in allergic asthmatics were significantly increased, compared with healthy controls (P<0.0001). Notably, IL-9 protein and mRNA levels were increased in allergic asthmatics and STAT6 and IRF4 mRNA levels were elevated, as compared with healthy controls. In addition, circulating numbers of Tc9 cells were positively correlated with blood eosinophil counts and fractioned exhaled nitric oxide (FeNO) levels in asthmatic patients. Moreover, the number of Tc9 cells and serum IL-9 levels in asthmatic patients were significantly decreased after treatment with glucocorticoids (P<0.05). These findings suggest that increased circulating Tc9 cells are associated with eosinophilia and high FeNO of allergic asthma, and that abnormal Tc9 immunity may contribute to the pathogenesis of allergic asthmatics.