Neutrophil activity assessed using a novel serological marker of human neutrophil elastase degraded calprotectin is elevated in patients with COPD or IPF

Abstract

<b>Background:</b> Neutrophils are part of the first cellular response to acute inflammation prompting neutrophil extracellular traps (NETs) triggered by microorganisms and proinflammatory stimuli. Among others, NETs release calprotectin (CP) and human neutrophil elastase (HNE). The aim of this study was to develop a neoepitope-specific assay for HNE degraded CP to serologically assess neutrophil activity in patients with chronic obstructive pulmonary disease (COPD) or idiopathic pulmonary fibrosis (IPF). <b>Methods:</b> A neoepitope-specific monoclonal antibody was raised towards an HNE cleavage site in the calprotectin domain S100A9, which was used to develop a competitive ELISA (CPa9-HNE). Following validation, CPa9-HNE serum levels were evaluated in IPF (n=16), COPD (n=67), and healthy controls (n=39). <b>Results:</b> The CPa9-HNE assay was technically robust with high sensitivity, accuracy, and precision for quantification in serum. Serum CPa9-HNE levels were significantly elevated in patients with COPD (median 247.4 [IQR 179.2-334.7] ng/mL, p&lt;0.0001) or IPF (median 161.0 [IQR 82.86-238.5] ng/mL) compared to healthy controls (median 18.94 [IQR 18.32-32.29] ng/mL). ROC analysis showed almost complete separation of COPD (AUC 0.9996, p&lt;0.0001) and IPF (AUC 0.9679, p&lt;0.0001) from healthy controls. <b>Conclusions:</b> CPa9-HNE was shown to be a technically robust assay, which may be used as a serological marker of neutrophil activity. IPF and COPD patients had increased CPa9-HNE levels compared to healthy controls, indicating that a measure of neutrophil activity is a potential marker for identifying chronic lung disease with a neutrophilic component.