IL‐1β promotes IL‐17A production of ILC3s to aggravate neutrophilic airway inflammation in mice

Abstract IL‐17A‐producing group 3 innate lymphoid cells (ILC3s) have been found to participate in the development of various phenotypes of asthma, however, little is known about how ILC3s mediate neutrophilic airway inflammation. Elevated IL‐1β has been reported in neutrophilic asthma (NA) and IL‐1β receptor is highly expressed on lung ILC3s. Therefore, we hypothesize that IL‐1β aggravates neutrophilic airway inflammation via provoking IL‐17A‐producing ILC3s. We sought to determine the pathological roles of the IL‐1β‐ILC3‐IL‐17A axis in neutrophilic airway inflammation. Lung ILC subsets were measured in eosinophilic asthma (ovalbumin [OVA]/Alum) and NA (OVA/lipopolysaccharides [LPS]) murine models. Rag2 −/− (lacking adaptive immunity), RORc −/− (lacking transcription factor RORγt), Rag2 −/− RORc −/− (lacking adaptive immunity and ILC3s), and ILCs depletion mice were used to verify the roles of ILC3s in neutrophilic airway inflammation by measurement of CXCL‐1, IL‐17A, IL‐22 and neutrophil counts in bronchoalveolar lavage fluid (BALF), detection of Muc5ac in lung tissues, and quantification of IL‐17A‐producing ILC3s after treatment of anti‐IL‐17A or recombinant IL‐1β (rIL‐1β) and its monoclonal antibody. NLRP3, Caspase 1 and their induction of IL‐1β were detected in lung tissues of OVA/LPS‐induced mice. The OVA/LPS model was characterized by an enrichment of airway neutrophilia, lung RORγt + ILC3s and Th17 cytokines (IL‐17A and IL‐22) and neutrophilic chemokine C‐X‐C motif (chemokine) ligand 1 (CXCL‐1), compared to the phenotypic features of airway eosinophilia, GATA3 + ILC2s and type‐2 cytokines in OVA/Alum model. The concentration of CXCL‐1 and neutrophil counts in BALF were decreased by anti‐IL‐17A. RORγt deficiency led to a decrease in IL‐17A and CXCL‐1 levels and neutrophil counts in BALF. ILC depletion in Rag2 −/− mice ameliorated OVA/LPS‐induced IL‐17A, IL‐22, CXCL‐1 and airway neutrophil counts. IL‐17A‐producing ILCs and BALF neutrophil counts were significantly lower in Rag2 −/− RORc −/− mice than those in Rag2 −/− mice. IL‐1β was highly expressed in BALF and bronchial epithelial cells (BECs) in OVA/LPS model, and administration of rIL‐1β substantially aggravated airway inflammation and promoted upregulation of RORγt + and IL‐17A‐producing lung ILC3s, which were reversed by anti‐IL‐1β. NLRP3 and Caspase 1 expressions were enhanced by OVA/LPS, and their inhibitors abolished the OVA/LPS‐induced IL‐1β in BECs. ILC3s play a pathogenic role in the pathogenesis of NA, which is triggered by IL‐1β via promoting IL‐17A production of lung ILC3s.