Different innate neutrophil responses in controlled and uncontrolled asthma

Introduction: Respiratory viruses are a major cause of asthma exacerbations. Neutrophilic inflammation occurs during infections and is associated with difficult to treat asthma. The role of neutrophils in viral infections and whether neutrophil dysfunction contributes to exacerbation pathogenesis remains unclear. Aim: We aimed to investigate neutrophil immune responses in controlled (CA) and uncontrolled asthma (UnCA). We hypothesised that neutrophils from UnCA but not CA have impaired immune responses. Methods: Peripheral blood neutrophils from patients with CA (ACQ0.75) (n=7) or nonasthmatics (NA) (n=9) were stimulated with bacterial (LPS (1μg/ml), fMLP (100nM)) and viral surrogates( imiquimod (3μg/ml), R848 (1.5μg/ml), poly I:C (10μg/ml)) or rhinovirus (RV)16 (multiplicity of infection 1). Cell free supernatant was collected after 1h for measurement of neutrophil elastase (NE) by a colourimetric activity assay and matrix metalloproteinase (MMP)-9 by zymography or after 24h for CXCL8 release by ELISA. Results: fMLP stimulated neutrophils from UnCA but not CA had a 70% reduction in CXCL8 compared to NA. fMLP induced MMP9 release was also impaired by 50% in UnCA and 30% in CA compared to NA. Enhanced NE release (double) occurred constitutively and with fMLP stimulation in neutrophils from CA compared to NA. Interestingly, RV16 induced CXCL8 and R848 induced MMP-9 in CA and UnCA but not NA neutrophils. UnCA and CA responded similarly to other stimuli. Conclusion: Impaired innate responses in neutrophils from UnCA occurred only with the bacterial toxin fMLP, this might allow certain bacteria to colonise the airways and contribute to an altered lung microbiome in UnCA.