Background A close association between obesity and asthma has been described. The nature of this association remains elusive, especially with respect to allergic asthma. Controversial findings exist regarding the impact of short‐term high‐fat diet (HFD) feeding on the development of allergic asthma. Objective To delineate the impact of short‐term HFD feeding on the development of experimental allergic asthma. Methods Female C57BL/6JRJ mice were fed with a short‐term HFD or chow diet (CD) for 12 weeks. Allergic asthma was induced by intraperitoneal OVA/alum sensitization followed by repeated OVA airway challenges. We determined airway hyperresponsiveness (AHR) and pulmonary inflammation by histologic and flow cytometric analysis of immune cells. Furthermore, we assessed the impact of HFD on dendritic cell (DC)‐mediated activation of T cells. Results Female mice showed a mild increase in body weight accompanied by mild metabolic alterations. Upon OVA challenge, CD‐fed mice developed strong AHR and airway inflammation, which were markedly reduced in HFD‐fed mice. Mucus production was similar in both treatment groups. OVA‐induced increases in DC and CD4+ T‐cell recruitment to the lungs were significantly attenuated in HFD‐fed mice. MHC‐II expression and CD40 expression in pulmonary CD11b+ DCs were markedly lower in HFD‐fed compared to CD‐fed mice, which was associated in vivo with a decreased T helper (Th) 1/17 differentiation and Treg formation without impacting Th2 differentiation. Conclusions/clinical relevance These findings suggest that short‐term HFD feeding attenuates the development of AHR, airway inflammation, pulmonary DC recruitment and MHC‐II/CD40 expression leading to diminished Th1/17 but unchanged Th2 differentiation. Thus, short‐term HFD feeding and associated metabolic alterations may have protective effects in allergic asthma development.

BackgroundAsthma is a heterogeneous syndrome substantiating the urgent requirement for endotype-specific biomarkers. Dysbalance of fibrosis and fibrolysis in asthmatic lung tissue leads to reduced levels of the inflammation-protective collagen 4 (COL4A3).ObjectiveTo delineate the degradation of COL4A3 in allergic airway inflammation and evaluate the resultant product as a biomarker for anti-IgE therapy response.MethodsThe serological COL4A3 degradation marker C4Ma3 (Nordic Bioscience, Denmark) and serum cytokines were measured in the ALLIANCE cohort (pediatric cases/controls: 134/35; adult cases/controls: 149/31). Exacerbation of allergic airway disease in mice was induced by sensitising to OVA, challenge with OVA aerosol and instillation of poly(cytidylic-inosinic). Fulacimstat (chymase inhibitor, Bayer) was used to determine the role of mast cell chymase in COL4A3 degradation. Patients with cystic fibrosis (CF, n=14) and CF with allergic broncho-pulmonary aspergillosis (ABPA, n=9) as well as severe allergic, uncontrolled asthmatics (n=19) were tested for COL4A3 degradation. Omalizumab (anti-IgE) treatment was assessed by the Asthma Control Test.ResultsSerum levels of C4Ma3 were increased in asthma in adults and children alike and linked to a more severe, exacerbating allergic asthma phenotype. In an experimental asthma mouse model, C4Ma3 was dependent on mast cell chymase. Serum C4Ma3 was significantly elevated in CF plus ABPA and at baseline predicted the success of the anti-IgE therapy in allergic, uncontrolled asthmatics (diagnostic odds ratio 31.5).ConclusionC4Ma3 level depend on lung mast cell chymase and are increased in a severe, exacerbating allergic asthma phenotype. C4Ma3 may serve as a novel biomarker to predict anti-IgE therapy response.

Background Pulmonary eosinophils comprise at least two distinct populations of resident eosinophils (rEOS) and inflammatory eosinophils (iEOS), the latter recruited in response to pulmonary inflammation. Here, we determined the impact of complement activation on rEOS and iEOS trafficking and function in two models of pulmonary inflammation. Methods BALB/c wild‐type and C5ar1−/− mice were exposed to different allergens or IL‐33. Eosinophil populations in the airways, lung, or mediastinal lymph nodes (mLN) were characterized by FACS or immunohistochemistry. rEOS and iEOS functions were determined in vivo and in vitro. Results HDM and IL‐33 exposure induced a strong accumulation of iEOS but not rEOS in the airways, lungs, and mLNs. rEOS and iEOS expressed C3/C5 and C5aR1, which were significantly higher in iEOS. Initial pulmonary trafficking of iEOS was markedly reduced in C5ar1−/− mice and associated with less IL‐5 production from ILC2 cells. Functionally, adoptively transferred pulmonary iEOS from WT but not from C5ar1−/− mice‐induced airway hyperresponsiveness (AHR), which was associated with significantly reduced C5ar1−/− iEOS degranulation. Pulmonary iEOS but not rEOS were frequently associated with T cells in lung tissue. After HDM or IL‐33 exposure, iEOS but not rEOS were found in mLNs, which were significantly reduced in C5ar1−/− mice. C5ar1−/− iEOS expressed less costimulatory molecules, associated with a decreased potency to drive antigen‐specific T cell proliferation and differentiation into memory T cells. Conclusions We uncovered novel roles for C5aR1 in iEOS trafficking and activation, which affects key aspects of allergic inflammation such as AHR, ILC2, and T cell activation.

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