IL-33-induced neutrophilic inflammation and NETosis underlie rhinovirus-triggered exacerbations of asthma.

Rhinovirus-induced neutrophil extracellular traps (NETs) contribute to acute asthma exacerbations; however, the molecular factors that trigger NETosis in this context remain ill-defined. Here, we sought to implicate a role for IL-33, an epithelial cell-derived alarmin rapidly released in response to infection. In mice with chronic experimental asthma (CEA), but not naïve controls, rhinovirus inoculation induced an early (1 day post infection; dpi) inflammatory response dominated by neutrophils, neutrophil-associated cytokines (IL-1α, IL-1ß, CXCL1), and NETosis, followed by a later, type-2 inflammatory phase (3-7 dpi), characterised by eosinophils, elevated IL-4 levels, and goblet cell hyperplasia. Notably, both phases were ablated by HpARI (Heligmosomoides polygyrus Alarmin Release Inhibitor), which blocks IL-33 release and signalling. Instillation of exogenous IL-33 recapitulated the rhinovirus-induced early phase, including the increased presence of NETs in the airway mucosa, in a PAD4-dependent manner. Ex vivo IL-33-stimulated neutrophils from mice with CEA, but not naïve mice, underwent NETosis and produced greater amounts of IL-1α/ß, IL-4, and IL-5. In nasal samples from rhinovirus-infected people with asthma, but not healthy controls, IL-33 levels correlated with neutrophil elastase and dsDNA. Our findings suggest that IL-33 blockade ameliorates the severity of an asthma exacerbation by attenuating neutrophil recruitment and the downstream generation of NETs.

Maternal diet modulates the infant microbiome and intestinal Flt3L necessary for dendritic cell development and immunity to respiratory infection.

Poor maternal diet during pregnancy is a risk factor for severe lower respiratory infections (sLRIs) in the offspring, but the underlying mechanisms remain elusive. Here, we demonstrate that in mice a maternal low-fiber diet (LFD) led to enhanced LRI severity in infants because of delayed plasmacytoid dendritic cell (pDC) recruitment and perturbation of regulatory T cell expansion in the lungs. LFD altered the composition of the maternal milk microbiome and assembling infant gut microbiome. These microbial changes reduced the secretion of the DC growth factor Flt3L by neonatal intestinal epithelial cells and impaired downstream pDC hematopoiesis. Therapy with a propionate-producing bacteria isolated from the milk of high-fiber diet-fed mothers, or supplementation with propionate, conferred protection against sLRI by restoring gut Flt3L expression and pDC hematopoiesis. Our findings identify a microbiome-dependent Flt3L axis in the gut that promotes pDC hematopoiesis in early life and confers disease resistance against sLRIs.

Targeting the P2Y13 Receptor Suppresses IL-33 and HMGB1 Release and Ameliorates Experimental Asthma.

Rationale: The alarmins IL-33 and HMGB1 (high mobility group box 1) contribute to type 2 inflammation and asthma pathogenesis. Objectives: To determine whether P2Y13-R (P2Y13 receptor), a purinergic GPCR (G protein-coupled receptor) and risk allele for asthma, regulates the release of IL-33 and HMGB1. Methods: Bronchial biopsy specimens were obtained from healthy subjects and subjects with asthma. Primary human airway epithelial cells (AECs), primary mouse AECs, or C57Bl/6 mice were inoculated with various aeroallergens or respiratory viruses, and the nuclear-to-cytoplasmic translocation and release of alarmins was measured by using immunohistochemistry and an ELISA. The role of P2Y13-R in AEC function and in the onset, progression, and exacerbation of experimental asthma was assessed by using pharmacological antagonists and mice with P2Y13-R gene deletion. Measurements and Main Results: Aeroallergen exposure induced the extracellular release of ADP and ATP, nucleotides that activate P2Y13-R. ATP, ADP, and aeroallergen (house dust mite, cockroach, or Alternaria antigen) or virus exposure induced the nuclear-to-cytoplasmic translocation and subsequent release of IL-33 and HMGB1, and this response was ablated by genetic deletion or pharmacological antagonism of P2Y13. In mice, prophylactic or therapeutic P2Y13-R blockade attenuated asthma onset and, critically, ablated the severity of a rhinovirus-associated exacerbation in a high-fidelity experimental model of chronic asthma. Moreover, P2Y13-R antagonism derepressed antiviral immunity, increasing IFN-λ production and decreasing viral copies in the lung. Conclusions: We identify P2Y13-R as a novel gatekeeper of the nuclear alarmins IL-33 and HMGB1 and demonstrate that the targeting of this GPCR via genetic deletion or treatment with a small-molecule antagonist protects against the onset and exacerbations of experimental asthma.