Neutrophilic asthma: a distinct phenotype?

<b>Background:</b> Over the past years, the existence of a neutrophilic asthma phenotype has been subject of much debate. Bullone et al recently described a specific subgroup of asthma patients based on biopsy neutrophilia and concluded that those with high bronchial neutrophils had increased IgE, increased perennial allergies and IL-17 expression. The aim of this study was to identify key pathogenic pathways in neutrophilic asthma and to see whether sputum neutrophils are a predictor for bronchial neutrophilia. <b>Methods:</b> We used an existing cohort of 90 patients with asthma and the same neutrophil values (&gt; 47.17 neutrophils/mm2 for intermediate, &gt;94.34 neutrophils/mm2 for high neutrophils) as Bullone et al used. We tested for differences in lung function parameters (FEV1, FEV/FVC), cell counts in sputum and blood, phadiatop and IgE. For the gene expression and pathway analysis, R with DESeq2, biomaRt and clusterProfiler were used. <b>Results:</b> In the three groups separated on the values on biopsy neutrophilia, we did not find differences in pulmonary function parameters, allergy and sputum neutrophils. A regression model for bronchial neutrophilia with sputum neutrophils (p = 0.09), had an r2 of 0.052. Gene expression analysis revealed several immune pathways, partly related to IL-17 signalling. <b>Conclusions:</b> Asthma patients with bronchial neutrophilia do not have more severe disease and do not differ in clinical parameters associated with asthma. However, they do have a different gene expression profile associated with inflammatory pathways, indicating there could be specific endotype of neutrophilic asthma. Importantly, sputum neutrophilia is not a predictor for bronchial neutrophilia, which is essential information in studying this phenotype in asthma.