Th9 cells producing interleukin (IL) 9 are novel subset of CD4+ T helper cells, which might contribute to airway inflammation in asthma. Moreover, the effect of IL-9 on eosinophils is still not fully understood. Study aim was to evaluate peripheral blood Th9 cells and eosinophil apoptosis in allergic asthma patients.

Eighteen patients with allergic asthma and fourteen patients with allergic rhinitis were examined. Control group included sixteen healthy subjects. Allergic asthma and rhinitis patients did not use corticosteroids and antihistamines at least for 1 week. Peripheral blood eosinophils and CD4⁺ cells were isolated by high density gradient centrifugation and magnetic separation. Th9 cells and apoptotic eosinophils were estimated by flow cytometer. Serum IL-9 and IL-5 concentration were determined by ELISA.

Peripheral blood Th9 cells percentage was increased in allergic asthma group compared with allergic rhinitis and control group (0.74% ± 0.32% vs. 0.19% ± 0.10% and 0.15% ± 0.08%, respectively, P < 0.05). The same tendency was observed for IL-9 (P < 0.01). Percentage of peripheral blood apoptotic eosinophils was decreased in allergic asthma and allergic rhinitis groups compared with control group (P < 0.05). IL-9 concentration correlated with percentage of Th9 cells (r = 0.64, P < 0.05) and negatively with percentage of apoptotic eosinophils in allergic asthma group (r = −0.58, P < 0.05). Negative correlation was found between apoptotic eosinophils count and IL-5 concentration in allergic asthma group (r = −0.76, P < 0.05).

Patients with allergic asthma demonstrate increased peripheral blood Th9 cells count and serum IL-9, while eosinophil apoptosis is inversely related to IL-9 concentration.