Background: Asthma is a heterogeneous disease of the airways that involves several types of granulocytic inflammation. Recently, we have shown that the activation status of myeloid cells regulated by TNFAIP3/A20 is a crucial determinant of eosinophilic or neutrophilic airway inflammation. However, whether neutrophilic inflammation observed in this model is dependent on IL-17 remains unknown. Objective: In this study, we investigated whether IL-17RA-signalling is essential for eosinophilic or neutrophilic inflammation in house dust mite (HDM)-driven airway inflammation. Methods: Tnfaip3fl/flxLyz2+/cre (Tnfaip3LysM-KO) mice were crossed to Il17raKO mice, generating Tnfaip3LysMIl17raKO mice and subjected to an HDM-driven airway inflammation model. Results: Both eosinophilic and neutrophilic inflammation observed in HDM-exposed WT and Tnfaip3LysM-KO mice respectively were unaltered in the absence of IL-17RA. Production of IL-5, IL-13 and IFN-γ by CD4+ T cells was similar between WT, Tnfaip3LysM-KO and Il17raKO mice, whereas mucus-producing cells in Tnfaip3LysM-KOIl17raKO mice were reduced compared to controls. Strikingly, spontaneous accumulation of pulmonary Th1, Th17 and γδ-17 T cells was observed in Tnfaip3LysM-KOIl17raKO mice, but not in the other genotypes. Th17 cell-associated cytokines such as GM-CSF and IL-22 were increased in the lungs of HDM-exposed Tnfaip3LysM-KOIl17raKO mice, compared to IL-17RA-sufficient controls. Moreover, neutrophilic chemo-attractants CXCL1, CXCL2, CXCL12 and Th17-promoting cytokines IL-1β and IL-6 were unaltered between Tnfaip3LysM-KO and Tnfaip3LysM-KOIl17raKO mice. Conclusion and Clinical Relevance: These findings show that neutrophilic airway inflammation induced by activated TNFAIP3/A20-deficient myeloid cells can develop in the absence of IL-17RA-signalling. Neutrophilic inflammation is likely maintained by similar quantities of pro-inflammatory cytokines IL-1β and IL-6 that can, independently of IL-17-signalling, induce the expression of neutrophil chemo-attractants.

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Clinical and Experimental Allergy
Department of Pulmonology

Vroman, H., Das, T., Bergen, I., van Hulst, J.A.C. (Jennifer A. C.), Ahmadi, F. (Fatemeh), van Loo, G., … Kool, M. (2018). House dust mite-driven neutrophilic airway inflammation in mice with TNFAIP3-deficient myeloid cells is IL-17-independent. Clinical and Experimental Allergy. doi:10.1111/cea.13262