Introduction Antimicrobial peptides act to defend the host from microbial action and colonisation. Patients with COPD and neutrophilic inflammation experience bacterial colonisation more frequently than other COPD phenotypes. Here we assess the levels of five antimicrobial peptides in peripheral blood and sputum in relation to their inflammatory phenotype. We hypothesise that patients with neutrophilic inflammation have lower antimicrobial peptide levels than other COPD inflammatory phenotypes and that the presence of non-typeable haemophilus influenzae (NTHi) is associated with low antimicrobial peptide levels.
Method Plasma and sputum supernatants from 8 healthy donors, 18 COPD patients and 10 non-eosinophilic asthmatics were tested for SLPI, osteopontin, lysozyme, elafin and beta defensin-1 by ELISA. Patients were stratified into eosinophilic and neutrophilic groups with a 3% sputum eosinophil cut-off. NTHi was measured in sputum plugs by qPCR of the Omp P6 gene.
Results Levels of antimicrobial peptides in plasma and sputum showed no difference between those with eosinophilic and neutrophilic COPD. Between disease groups, beta defensin-1 levels are higher in plasma of COPD patients (median: 10.92 ng/ml (IQR: 4.137–18.09)) than healthy individuals (median: 3.665 ng/ml (IQR: 2.59–4.549), p=0.0033) and non-eosinophilic asthmatics (median: 4.984 ng/ml IQR: 3.334–7.208), p=0.0442) (figure 1). No antimicrobial peptide correlated with NTHi levels in the sputum plug.
Conclusions Similar levels of SLPI, osteopontin, lysozyme, elafin and beta defensin-1 in sputum and plasma between COPD phenotypes suggests that defence against pathogens by these antimicrobial peptides is not lacking in differential inflammatory COPD phenotypes. The role antimicrobial peptides play in NTHi colonisation remains to be determined.
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