The C5a/C5aR1 axis controls the development of experimental allergic asthma independent of LysM-expressing pulmonary immune cells

Abstract

C5a regulates the development of maladaptive immune responses in allergic asthma mainly through the activation of C5a receptor 1 (C5aR1). Yet, the cell types and the mechanisms underlying this regulation are ill-defined. Recently, we described increased C5aR1 expression in lung tissue eosinophils but decreased expression in airway and pulmonary macrophages as well as in pulmonary CD11b+ conventional dendritic cells (cDCs) and monocyte-derived DCs (moDCs) during the allergic effector phase using a floxed green fluorescent protein (GFP)-C5aR1 knock-in mouse. Here, we determined the role of C5aR1 signaling in neutrophils, moDCs and macrophages for the pulmonary recruitment of such cells and the importance of C5aR1-mediated activation of LysM-expressing cells for the development of allergic asthma. We used LysM-C5aR1 KO mice with a specific deletion of C5aR1 in LysMCre-expressing cells and confirmed the specific deletion of C5aR1 in neutrophils, macrophages and moDCs in the airways and/or the lung tissue. We found that alveolar macrophage numbers were significantly increased in LysM-C5aR1 KO mice. Induction of ovalbumin (OVA)-driven experimental allergic asthma in GFP-C5aR1fl/fl and LysM-C5aR1 KO mice resulted in strong but similar airway resistance, mucus production and Th2/Th17 cytokine production. In contrast, the number of airway but not of pulmonary neutrophils was lower in LysM-C5aR1 KO as compared with GFP-C5aR1fl/fl mice. The recruitment of macrophages, cDCs, moDCs, T cells and type 2 innate lymphoid cells was not altered in LysM-C5aR1 KO mice. Our findings demonstrate that C5aR1 is critical for steady state control of alveolar macrophage numbers and the transition of neutrophils from the lung into the airways in OVA-driven allergic asthma. However, C5aR1 activation of LysM-expressing cells plays a surprisingly minor role in the recruitment and activation of such cells and the development of the allergic phenotype in OVA-driven experimental allergic asthma.

Short‐term high‐fat diet feeding protects from the development of experimental allergic asthma in mice

“…Anaesthetized mice were prepared and mechanically ventilated using a FlexiVent (SciReq) system, aerosolized with different concentrations of acetyl‐β‐methyl‐choline (methacholine, Sigma‐Aldrich), and the airway resistance was measured as described previously …”

“…Lung histological staining, detection and quantification of mucus cell content were done as described previously, either with haematoxylin and eosin (H&E) or with periodic acid‐Schiff (PAS) to evaluate inflammatory influx in the tissue and mucus production, respectively. For the latter, the mucus positiveness of all the airways was evaluated by light microscopic observation and the percentages of PAS‐positive airways were established to quantify mucus production as described …”

“…For the latter, the mucus positiveness of all the airways was evaluated by light microscopic observation and the percentages of PAS-positive airways were established to quantify mucus production as described. 16,17…”

“…The right lung lobes and the visceral adipose tissue (VAT) were harvested and digested using Liberase TL and DNase I as described previously. 16,17 Cell numbers were assessed by manual enumeration, and cell suspensions were analysed by flow cytometry using specific gating strategies (Figure S1C-F). To determine in vivo T-cell polarization, lung cell suspensions were adjusted to 1 × 10 6 cells/ mL and rested overnight.…”

Allergen-Induced C5a/C5aR1 Axis Activation in Pulmonary CD11b+ cDCs Promotes Pulmonary Tolerance through Downregulation of CD40

“…administered to the throat in a total volume of 50 µL. Twenty-four hours after HDM/OVA exposure, the mice were euthanized, and the lungs were harvested for further analysis as described [20,21].…”