[The mobilization effect of IL-25 on eosinophil progenitor cells in allergic asthma]

Objective: Eosinophil progenitor cells (EoP) play a critical role in allergic airway inflammation in asthma. Previous studies have revealed that the expression of IL-25 receptor subunits (IL-17RA and IL-17RB) are increased on eosinophils (Eos) from allergic asthmatics upon allergen inhalation but few study has explored the role of IL-25 on EoP. Thus, in this research we examined the possible role of IL-25 on EoP in allergic asthmatics challenged by allergen, as well as in animal models where we verified the changes of newly produced Eos after IL-25 knockout. Methods: Asthmatics (n=14, during 2017-2018) who developed allergen-induced early and late responses were enrolled in this study. Blood was collected at pre-and 24 h post-challenge. Surface expression of IL-17RA and IL-17RB were evaluated by flow cytometry on EoP. In vitro migration assay was used to examine migrational responses of EoP and hematopoietic cells (HPC) from these subjects. In animal models, mice were grouped according to whether IL-25 was knock-out and whether mice were sensitized and challenged by ovalbumin (OVA) into asthmatic, control, knockout asthmatic and knockout control groups. Lung tissues, bronchoalveolar lavage flow (BALF) and bone marrow tissues of these mice were collected in order to evaluate airway inflammation and amount of newly produced (Brdu positive) and mature Eos. Results: EoP expressing IL-17RB were significantly increased after allergen inhalation in allergic asthmatics [(514±138) vs. (1146±450)/10(6) cells, pre-and post-challenge, F=6.819, P=0.022]. Pre-exposure to IL-25 primed the migrational responsiveness of EoP to stromal cell-derived factor (SDF)1α [(39.0±10.1)% vs. (73.0±7.9)%, control and IL-25 exposure groups respectively, P=0.021, 95% CI 5.19%~58.45%]. In OVA sensitized mice, knockout of IL-25 significantly reduced Eos and newly produced Eos percentage in the BALF [Eos, (7.8±2.0)% vs. (3.1±0.6)%, asthmatic and knockout asthmatic group respectively, P=0.002, 95% CI-7.57% to -1.98%; Brdu positive Eos, (50.0±7.6)% vs. (8.6±4.3)%, asthmatic and knockout asthmatic group respectively, P=0.011, 95% CI-72.41% to -10.27%], and newly produced Eos were also reduced in the bone marrow [(70.8±6.1)% vs. (1.3±1.3)%, asthmatic and knockout asthmatic group respectively, P=0.000, 95% CI -94.88% to -44.18%]. Conclusion: These results suggest an important role of IL-25 in allergen-induced EoP migration, local differentiation and eosinophilia in the airways.