Allergic asthma occurs as a consequence of inappropriate immunologic inflammation to allergens and characterized by Th2 adaptive immune response. Recent studies indicated that interleukin (IL)-25, a member of the IL-17 cytokine family, had been implicated in inducing Th2 cell-dependent inflammation in airway epithelium and IL-25-deficient mice exhibit impaired Th2 immunity responses; however, how these cytokines influence innate immune responses remains poorly understood. In this study, we used ovalbumin (OVA) sensitization and challenge to induce the murine asthmatic model and confirmed by histological analysis of lung tissues and serum levels of total and OVA-specific immunoglobulin (Ig)-E. The expression of IL-25 was detected by quantitative real-time PCR and immunohistochemistry, respectively, and the dendritic cells (DCs) activation was detected by levels of CD80 and CD86 in bronchoalveolar lavage fluid (BALF) by flow cytometry. The mice sensitized and challenged with OVA showed high expression of IL-25 in both mRNA and protein levels in lungs. We detected the expression of CD80 and CD86 in BALF was also increased. A tight correlation between IL-25 mRNA and other Th2 cells producing cytokines such as IL-4, IL-5, and IL-13 in BALF was identified. Furthermore, when the asthmatic mice were treated with inhaled corticosteroids, the inflammatory cells infiltration and the inflammatory cytokines secretion were significantly decreased. In this study, we show that IL-25 promoted the accumulation of co-stimulatory molecules of CD80 and CD86 on DCs and then induced the differentiation of prime naive CD4+ T cells to become proinflammatory Th2 cells and promoted Th2 cytokine responses in OVA-induced airway inflammation. The ability of IL-25 to promote the activation and differentiation of DCs population was identified as a link between the IL-17 cytokine family and the innate immune response and suggested a previously unrecognized innate immune pathway that promotes Th2 cytokine responses in asthmatic airway inflammation. Inhaled corticosteroids might be capable of inhibiting the promotion of IL-25 and present a promising strategy for the treatment of asthma
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The authors thank Dr. Rutao Cui for supplying the IL25 antibody and Rong Wang (Key Laboratory of Cardiovascular Remodeling and Function Research of Chinese Ministry of Education and Public Health, Shandong University Qilu Hospital) for their excellent technical assistance. This work was supported by the Science and Technology Foundation of Shandong Province (2012GGB14068), the Natural and Science Foundation of Shandong Province (ZR2011HM020) and The National Natural Science Foundation of China (81270072). We also thank Dr. Xiaotian Chang (Medical Research Center of Qianfoshan Hospital, Shandong University) and Margaret Mysz, PhD (Loyola University, Chicago, USA), for revising the manuscript.
Conflict of interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
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