Effect and mechanism of allergen-specific immunotherapy on small airway dysfunction in children with asthma

Background: The purpose of this study was to investigate the effectiveness of allergen-specific immunotherapy (AIT) on small airway dysfunction (SAD) and the underlying mechanism with a special focus on basophils. Methods: Sixty-five children with mild to moderate asthma who were under regular inhaled corticosteroid (ICS) treatment for more than 1 year but whose FEF75 remained below 65% of the predicted value and had positive results for serum Der p or Der f were enrolled. Children with asthma underwent house dust mite (HDM) subcutaneous immunotherapy (SCIT) treatment for 1 year. Clinical symptoms and lung function were evaluated every 3 months during HDM SCIT treatment. Basophil activation test (BAT) was carried out before and after HDM SCIT treatment. RNA sequencing was performed in isolated basophils from peripheral blood after 6 months of HDM SCIT treatment, followed by GO term and KEGG pathway enrichment analysis between patients with and without HDM SCIT treatment. Results: HDM AIT treatment ameliorated clinical symptoms while concurrently improved lung function parameters, such as FEV1/FVC, FEF75, FEF50 and MMEF (p < .05). It is worth noting that FEF75 values showed a highly significant, gradual and persistent increase (from 49.55 +/- 1.27% at baseline to 71.89 +/- 2.64% after 1 year of therapy) and 22 of 35 patients no longer had SAD after 1 year of treatment. BAT results revealed that AIT treatment significantly reduced basophil activity to the inhalant allergen mixtures containing HDM in vitro challenge from baseline. GO term and KEGG pathway enrichment analysis of basophils revealed that downregulated genes were mainly involved in immune cell activation, antigen presentation, and Th2 cell differentiation. Conclusions: Our study demonstrated that HDM AIT not only improved SAD related lung function parameters, but also reduced basophil activity. RNA sequencing revealed the inhibition of phagocytosis and the phagosome pathway in basophils which may affect the polarization of Th2 cell differentiation after HDM AIT.