Dexamethasone inhibited type 2 cytokine production by blood ILC2s. IL-7 and TSLP abrogated this inhibition and induced steroid resistance of ILC2s in a MEK- and STAT5-dependent manner. BAL fluid ILC2s from asthmatic patients with increased TSLP levels were steroid resistant, which was reversed by clinically available inhibitors of MEK and STAT5.

Background The mechanism of Th2/Th17-predominant and Th2/Th17-low asthma is unknown. Objective To study the immune mechanism of Th2/Th17-predominant and Th2/Th17-low asthma. Methods In a previously reported cohort of 60 asthmatic patients, 16 patients were immunophenotyped with Th2/Th17-predominant asthma and 22 patients with Th2/Th17-low asthma. We examined BAL leukocytes, cytokines, mediators, and epithelial cell function for these asthma subgroups. Results Th2/Th17-predominant asthma had elevated IL1β, IL6, IL23, C3a and serum amyloid A (SAA) in BAL, and correlated with IL1β and C3a. Th2/Th17 cells expressed higher levels of the IL1 receptor and p-p38 MAPK. Anakinra, an IL1 receptor antagonist protein, inhibited BAL Th2/Th17 cells. Th2/Th17-low asthma had two distinct subgroups—neutrophilic asthma (45%) and pauci-inflammatory asthma (55%). This contrasted with Th2/Th17-predominant and Th2-predominant asthma, which had neutrophilic asthma in 6% and 0% of patients, respectively. BAL neutrophils strongly correlated with BAL myeloperoxidase, IL8, IL1α, IL6, G-CSF, and GM-CSF.. Sixty percent of the patients with neutrophilic asthma had a pathogenic microorganism in BAL culture, which suggested a subclinical infection. Conclusion We uncovered a critical role for the IL1β pathway in Th2/Th17-predminant asthma. A subgroup of Th2/Th17-low patients had neutrophilic asthma and elevated BAL IL1α, IL6, IL8, G-CSF, and GM-CSF. IL1α was directly involved in IL8 production and likely contributed to neutrophilic asthma. Sixty percent of neutrophilic patients had a subclinical infection.

Genetic deletion of the IL-33 receptor paradoxically increases TSLP production, which stimulates the emergence of IL-9 and IL-13 ILC2s and mast cells and leads to development of chronic experimental asthma. An anti-TSLP antibody abrogates all pathologic features of asthma in this model.

Background Despite the progress in diagnosis and management of asthma, many patients have poorly controlled or refractory asthma. The mechanism of this refractory asthma is not well understood. Objective Explore the relationship between neutrophils and other biomarkers of refractory asthma. Method Sixty subjects with refractory asthma (RA), 30 with non-refractory asthma (NRA) and 20 healthy subjects were enrolled. We performed a comprehensive characterization of these study subjects, which included laboratory and pulmonary function studies, chest CT, and bronchoscopy with bronchoalveolar lavage. We analyzed BAL and serum for a total of 244 biomolecules by multiplex assay and correlated them with the clinical and other laboratory parameters. Results RA was significantly different from NRA with regard to pulmonary function indices, bronchial basement membrane thickness, and BAL neutrophils and lymphocytes but not eosinophils. BAL neutrophils negatively and positively correlated with the forced vital capacity and age, respectively. Of the 244 biomolecules studied, 52 and 14 biomolecules from BAL and serum, respectively, were significantly different among the study groups. Thirteen of these 52 molecules correlated with BAL neutrophils. BAL from 40% of RA patients was positive for a pathogenic microbe. Infection-negative neutrophilic RA was associated with an increase in select biomarkers of inflammation in the serum suggesting the presence of systemic inflammation. Conclusions RA was associated with increased number of neutrophils and proneutrophilic biomolecules in the airways. Subclinical infection was present in 40% of RA patients, which likely contributed to neutrophilic inflammation. A subgroup of non-infected neutrophilic RA was associated with systemic inflammation.

Repetitive exposure of Rag1−/− mice to the Alternaria allergen extract generated a form of memory that elicited an asthma-like response upon a subthreshold recall challenge 3–15 wk later. This memory was associated with lung ICOS+ST2+ ILC2s. Genetic, pharmacologic, and antibody-mediated inhibition and adoptive transfer established an essential role for ILC2s in memory-driven asthma. ATAC-seq demonstrated a distinct epigenetic landscape of memory ILC2s and identified Bach2 and AP1 (JunD and Fosl2) motifs as major drivers of altered gene accessibility. scRNA-seq, gene knockout, and signaling studies suggest that repetitive allergenic stress induces a gene repression program involving Nr4a2, Zeb1, Bach2, and JunD and a preparedness program involving Fhl2, FosB, Stat6, Srebf2, and MPP7 in memory ILC2s. A mutually regulated balance between these two programs establishes and maintains memory. The preparedness program (e.g., Fhl2) can be activated with a subthreshold cognate stimulation, which down-regulates repressors and activates effector pathways to elicit the memory-driven phenotype.