Pulmonary neuroendocrine cells (PNECs) are rare airway epithelial cells whose function is poorly understood. Here we show that Ascl1-mutant mice that have no PNECs exhibit severely blunted mucosal type 2 response in models of allergic asthma. PNECs reside in close proximity to group 2 innate lymphoid cells (ILC2s) near airway branch points. PNECs act through calcitonin gene-related peptide (CGRP) to stimulate ILC2s and elicit downstream immune responses. In addition, PNECs act through the neurotransmitter γ-aminobutyric acid (GABA) to induce goblet cell hyperplasia. The instillation of a mixture of CGRP and GABA in Ascl1-mutant airways restores both immune and goblet cell responses. In accordance, lungs from human asthmatics show increased PNECs. These findings demonstrate that the PNEC-ILC2 neuroimmunological modules function at airway branch points to amplify allergic asthma responses.

Exaggerated airway constriction triggered by repeated exposure to allergen, also called hyperreactivity, is a hallmark of asthma. Whereas vagal sensory neurons are known to function in allergen-induced hyperreactivity^1-3, the identity of downstream nodes remains poorly understood. Here we mapped a full allergen circuit from the lung to the brainstem and back to the lung. Repeated exposure of mice to inhaled allergen activated the nuclei of solitary tract (nTS) neurons in a mast cell-, interleukin-4 (IL-4)- and vagal nerve-dependent manner. Single-nucleus RNA sequencing, followed by RNAscope assay at baseline and allergen challenges, showed that a Dbh⁺ nTS population is preferentially activated. Ablation or chemogenetic inactivation of Dbh⁺ nTS neurons blunted hyperreactivity whereas chemogenetic activation promoted it. Viral tracing indicated that Dbh⁺ nTS neurons project to the nucleus ambiguus (NA) and that NA neurons are necessary and sufficient to relay allergen signals to postganglionic neurons that directly drive airway constriction. Delivery of noradrenaline antagonists to the NA blunted hyperreactivity, suggesting noradrenaline as the transmitter between Dbh⁺ nTS and NA. Together, these findings provide molecular, anatomical and functional definitions of key nodes of a canonical allergen response circuit. This knowledge informs how neural modulation could be used to control allergen-induced airway hyperreactivity.

Although increased neuropeptides are often detected in lungs that exhibit respiratory distress, whether they contribute to the condition is unknown. Here, we show in a mouse model of neuroendocrine cell hyperplasia of infancy, a pediatric disease with increased pulmonary neuroendocrine cells (PNECs), excess PNEC-derived neuropeptides are responsible for pulmonary manifestations including hypoxemia. In mouse postnatal lung, prolonged signaling from elevated neuropeptides such as calcitonin gene-related peptide (CGRP) activate receptors enriched on endothelial cells, leading to reduced cellular junction gene expression, increased endothelium permeability, excess lung fluid, and hypoxemia. Excess fluid and hypoxemia were effectively attenuated by either prevention of PNEC formation, inactivation of CGRP gene, endothelium-specific inactivation of CGRP receptor gene, or treatment with CGRP receptor antagonist. Neuropeptides were increased in human lung diseases with excess fluid such as acute respiratory distress syndrome. Our findings suggest that restricting neuropeptide function may limit fluid and improve gas exchange in these conditions.