IL-25 Promotes Th2 Immunity Responses in Asthmatic Mice via Nuocytes Activation.

Background: Interleukin-25 (IL-25) is a potent activator of type-2 immune responses, and is responsible for airway inflammation in asthma. Previous reports have shown that IL-25 expressed hyper-reactivity in an experimental mouse-model of asthma. In addition, the production of IL-13/IL-5 promoted by nuocytes induced airway inflammation. Thus, it has been questioned whether blocking IL-25 against its receptor IL-17BR could inhibit the expression of IL-13 and IL-5 via nuocytes, and further protect against inflammation in ovalbumin (OVA) induced mouse-model of asthma.

Methods: In this study, in order to investigate the correlation among IL-25, IL-5, IL-13 and nuocyte activities, we used OVA-sensitization and -challenging to induce the mouse model of asthma. The murine asthmatic model was validated by histology. The expressions of IL-5, IL-13 and IL-25 were detected by ELISA, quantitative real-time PCR, and western blotting of the lung tissue. Nuocyte activation was identified by the levels of ICOS (clone C398.4A) and T1/ST2 (cloneDJ8) (acting as nuocytes surface markers) in the bronchoalveolar lavage fluid (BALF). This, in turn, was done by means of flow cytometry. The expressions of IL-25, IL-5 and IL-13 in our murine model were detected in the BALF.

Results: The mice sensitized and challenged with OVA showed a high expression of IL-25 in both the mRNA and protein levels in lungs. The expressions of ICOS and T1/ST2 in BALF were increased. A significant correlation between IL-25 mRNA, protein, and other Th2-cell producing cytokines (such as IL-5 and IL-13) moreover were identified. Furthermore, when the asthmatic mice were treated with anti-IL-25, both the inflammatory cells' infiltration and the inflammatory cytokines' secretion were significantly decreased. The present findings indicate that IL-25 might be involved in a series of asthmatic immune responses, playing an important role in the increase of nuocytes, and that its activation is necessary in maintaining Th2 central memory and sustaining asthmatic inflammation.

Conclusion: This study showed that IL-25 promoted the accumulation of ICOS and T1/ST2 on nuocytes, further induced the pro-inflammatory Th2 cells, and promoted Th2 cytokine responses in OVA-induced airway inflammation.