Elevated serum IgE, oral corticosteroid dependence and IL-17/22 expression in highly neutrophilic asthma

Abstract

Information on the clinical traits associated with bronchial neutrophilia in asthma is scant, preventing its recognition and adequate treatment. We aimed to assess the clinical, functional and biological features of neutrophilic asthma and identify possible predictors of bronchial neutrophilia.

The inflammatory phenotype of 70 mild-to-severe asthma patients was studied cross-sectionally based on the eosinophilic/neutrophilic counts in their bronchial lamina propria. Patients were classified as neutrophilic or non-neutrophilic. Neutrophilic asthma patients (neutrophil count cut-off: 47.17 neutrophils·mm⁻²; range: 47.17–198.11 neutrophils·mm⁻²; median: 94.34 neutrophils·mm⁻²) were further classified as high (≥94.34 neutrophils·mm⁻²) or intermediate (47.17– <94.34 neutrophils·mm⁻²). The effect of smoking ≥10 pack-years was also assessed.

Neutrophilic asthma patients (n=38; 36 mixed eosinophilic/neutrophilic) had greater disease severity, functional residual capacity, inhaled corticosteroid (ICS) dose and exacerbations, and lower forced vital capacity (FVC) % pred and forced expiratory volume in 1 s (FEV₁) reversibility than non-neutrophilic asthma patients (n=32; 28 eosinophilic and four paucigranulocytic). Neutrophilic asthma patients had similar eosinophil counts, increased bronchial CD8⁺, interleukin (IL)-17-F⁺ and IL-22⁺ cells, and decreased mast cells compared with non-neutrophilic asthma patients. FEV₁ and FVC reversibility were independent predictors of bronchial neutrophilia in our cohort. High neutrophilic patients (n=21) had increased serum IgE levels, sensitivity to perennial allergens, exacerbation rate, oral corticosteroid dependence, and CD4⁺ and IL-17F⁺ cells in their bronchial mucosa. Excluding smokers revealed increased IL-17A⁺ and IL-22⁺ cells in highly neutrophilic patients.

We provide new evidence linking the presence of high bronchial neutrophilia in asthma to an adaptive immune response associated with allergy (IgE) and IL-17/22 cytokine expression. High bronchial neutrophilia may discriminate a new endotype of asthma. Further research is warranted on the relationship between bronchoreversibility and bronchial neutrophilia.