IL-33 and Its Receptor ST2 after Inhaled Allergen Challenge in Allergic Asthmatics.

BACKGROUND: Previous murine models have demonstrated interleukin (IL)-33 to be an important mediator of type-2 inflammation and to promote airway hyperresponsiveness in allergic asthma. A number of inflammatory cells produce IL-33 and eosinophils express ST2 mRNA. The relationship between IL-33 and eosinophils in allergic asthma, however, remains unclear. OBJECTIVE: The aim of this work was to evaluate in vitro the effect of allergen inhalation on IL-33 levels and expression of its receptor (ST2L) on eosinophils in allergic asthmatics, and the effect of IL-33 stimulation on eosinophil activity. METHODS: Plasma and sputum IL-33, soluble ST2 (sST2) levels, and ST2L expression on eosinophils were measured in 10 healthy controls and 10 allergic asthmatics. Asthmatics underwent allergen and diluent inhalation challenges. Blood and sputum samples were collected to measure IL-33, sST2, and ST2L eosinophil expression before and 24 h after allergen inhalation. Purified blood eosinophils from allergic asthmatics were incubated overnight with IL-33 to assess ST2 and intracellular IL-5 expression. RESULTS: Baseline levels of IL-33 in sputum and sST2 in plasma and sputum were similar in allergic asthmatics compared to healthy controls. In addition, there was no difference in blood or sputum eosinophil ST2L expression in healthy controls versus allergic asthmatics. Eosinophil ST2L expression was significantly increased 24 h postallergen inhalation in allergic asthmatics. In vitro stimulation of human eosinophils with IL-33 and LPS significantly increased eosinophil ST2L expression and IL-33 stimulation increased intracellular IL-5 expression, which was attenuated by treatment with sST2 and ST2 blockade. CONCLUSION AND CLINICAL RELEVANCE: In mild asthmatics, there was a significant upregulation of ST2 surface expression on eosinophils from blood and sputum following allergen inhalation challenge. In vitro, IL-33 stimulation of eosinophils increases both ST2 membrane expression and IL-5 production. These results support a role for IL-33 in causing allergen-induced eosinophilia. Blockade of IL-33 and ST2 signaling may present a novel therapeutic avenue for asthma treatment.

IL-25 and IL-33 induce Type 2 inflammation in basophils from subjects with allergic asthma.

BACKGROUND: The alarmin cytokines IL-25 and IL-33 are key promoters of type 2 inflammation. Basophils respond to alarmin cytokines, however the relationship of these cytokines with basophil activation and recruitment in human studies of allergic asthma has not been well characterized. This study investigated the effect of IL-25 and IL-33 on basophils in a model of allergic asthma. METHODS: 10 mild allergic asthmatics underwent allergen and diluent inhalation challenges. Bone marrow aspirates were collected at pre-challenge and 24 h (h) post challenge. Peripheral blood and sputum samples were collected at pre-challenge, 7 h, and 24 h post-challenge to measure basophil expression of IL-17RB, ST2, and intracellular IL-25. Freshly isolated peripheral blood basophils from allergic donors were incubated overnight with IL-25 and IL-33, or sputum supernatant collected post-allergen to assess pro-inflammatory effects of mediators released in the airways. RESULTS: There were increased percentage of basophils expressing IL-17RB, ST2, and intracellular IL-25 collected from bone marrow, peripheral blood, and sputum after allergen inhalation challenge. In vitro stimulation with IL-25 and IL-33 increased the percentage of basophils expressing intracellular type 2 cytokines and surface activation markers, and primed eotaxin-induced migratory potential of basophils, which was mediated directly through IL-17RB and ST2, respectively. Stimulation of basophils with sputum supernatants collected post-allergen challenge up-regulated the percentage of basophils expressing markers of activation and intracellular type 2 cytokines, which was reversed following blockade of the common ß chain (ßc). CONCLUSIONS: Our findings indicate that the alarmin cytokines IL-33 and IL-25 increase basophil activation and migratory potential, and may pose as a novel therapeutic targets for the treatment of allergic asthma.

Thymic stromal lymphopoietin activation of basophils in patients with allergic asthma is IL-3 dependent.

BACKGROUND: Thymic stromal lymphopoietin (TSLP) released after antigenic stimulation of allergic asthmatic airways is a key initiator of type 2 inflammation. Basophils are important effectors of allergic inflammation in the airways. Murine basophils have been shown to respond to TSLP independently of IL-3 by increasing functional thymic stromal lymphopoietin receptor (TSLPR) expression. OBJECTIVE: The purpose of this study was to investigate the effect of TSLP stimulation on human basophil function. METHODS: Ten patients with mild allergic asthma underwent diluent and allergen inhalation challenges. Peripheral blood and sputum samples were collected at baseline and 7 and 24 hours after challenge, and bone marrow samples were collected at baseline and 24 hours after challenge to measure basophil TSLPR expression. In vitro experiments were conducted on purified human basophils to measure the effect of TSLP on degranulation, expression of activation markers and TH2 cytokines, and eotaxin-induced shape change. RESULTS: Allergen inhalation increased basophil numbers in the airways and significantly upregulated the expression of activation markers, TH2 intracellular cytokines, and receptors for TSLP, IL-3, and eotaxin in blood, bone marrow, and sputum basophils. In vitro stimulation with TSLP primed basophil migration to eotaxin and induced rapid and sustained basophil activation mediated directly through TSLPR and indirectly through an IL-3-mediated basophil autocrine loop. Basophils responded to TSLP at a similar magnitude and potency as the well-described basophil-activating stimuli IL-3 and anti-IgE. CONCLUSION: Our findings indicate that basophil activation during early- and late-phase responses to inhaled allergen might be driven at least in part by TSLP.