Clinical trials support a central role for TSLP in driving airway inflammation and asthma exacerbations, while ongoing trials blocking IL-33 and IL-25 will help to define their respective role in asthma.
O<sub>3</sub> induced significant BAL fluid neutrophilia and eosinophilia and increased AHR and expression of IL6 and IL25 mRNA in the airway epithelium together with increased BAL fluid group 2 innate lymphoid cell (ILC2s), CD1c<sup>+</sup> myeloid dendritic cell, and CD4<sup>+</sup> T-cell counts and diminished surfactant protein D expression.
(2) After in-vitro stimulation with house dust mite (HDM) antigen, the levels of IL-4 and IL-17E in culture supernatants of PBMCs from allergic children (AS group, AR group and ASR group) were significantly enhanced.
IL-25 played an important role in these models of asthma because IL-25 receptor-deficient mice did not develop disease after sensitization and challenge with allergen.
We investigated the time course of ILC2 accumulation in different tissues in murine models of asthma induced by a serial per-nasal challenge with ovalbumin (OVA), house dust mice (HDM), IL-25 and IL-33 and explored the potential roles of ILC2-attracting chemokines in this phenomenon.
The high expression of the IL-25 and IL-33 receptors on the basophil membrane of patients with severe asthma indicates an overstimulation of basophils by these cytokines in severe asthma.
Stimulation with IL-33 alone induced a significantly greater quantity of IL-13 by Lineage-cells from mugwort-allergic asthmatic compared with that from HDM-allergic asthmatics, whereas IL-25 induced a significantly greater amount of IL-5 by the Lineage-cells from mugwort-allergic asthmatic compared with that from HDM-allergic asthmatics.
The FeNO levels were significantly correlated with the peripheral blood eosinophil counts (r = 0.430, p = 0.001) and serum IL-25 concentrations (r = 0.338, p = 0.009) in patients with asthma.
The concentrations of IL-33 and TSLP, but not IL-25, correlated inversely with the lung function (forced expiratory volume in the first second) of asthmatics (IL-33: <i>r</i> = -0.488, <i>p</i> < 0.0001; TSLP: <i>r</i> = -0.565, <i>p</i> < 0.0001) independently of corticosteroid therapy.
We previously found that IL-25-circulating fibrocyte axis was significantly upregulated in patients with asthma, which may greatly contribute to asthmatic airway inflammation and remodeling.
Dexamethasone and budesonide groups exhibited significant protein and mRNA reductions in IL-25, as compared with the asthma group after excitation (P<0.05), whereas these two groups significantly increased levels compared with the normal group after excitation (P<0.05).
Compared with that in asthma models, SIT administration decreased (1) airway hyper-responsiveness; (2) the production of cytokines, including IL-4, IL-5, IL-13, and IL-25, as well as serum HDM-specific IgE and IgG1, as shown by ELISA; and (3) lipid oxidative species, such as reactive oxidative species (ROS) and malondialdehyde (MDA), in the lung tissue.
PM2.5 can enhance the Der p1 antigen-induced HBEC innate immune response through the expression of IL-25, IL-33 and TSLP, which may exacerbate the occurrence rate of bronchial asthma.
Further work is required to develop human monoclonal antibodies (hMabs) directed against IL-25 and IL-33 or their receptors, to help understand their role in the initiation and/or persistence of asthma.
Emerging data now suggest that epithelial cell-derived cytokines such as thymic stromal lymphopoietin (TSLP), IL-33, and IL-25 may drive the progression from atopic dermatitis to asthma and food allergy.
Whether the blockade of PI3K signalling directly inhibits the asthma relevant pathogenetic changes induced by IL-25 in an in vivo condition is still unclear.
Recent studies clearly show that not only Th2 cytokines but also other T cell-related cytokines such as IL-17A and IL-22 as well as epithelial cell cytokines such as IL-25, IL-33, and thymic stromal lymphopoietin (TSLP) are involved in the pathogenesis of asthma.
The function of IL-25 in allergic diseases such as asthma has been well established, and now also is extended to diseases such as inflammatory bowel disease and cancer.