A serum biomarker reflecting human neutrophil elastase degraded calprotectin is elevated in COPD and IPF

Background: Neutrophils play a crucial role in pathogenesis of chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). Upon activation, neutrophils can degranulate multiple protein species in an immune response, herein calprotectin (CP) and human neutrophil elastase (HNE). Thus, the decay-rate of circulating neutrophils is rapid. The aim of this study was to examine neutrophil activity in COPD and IPF in serum samples by quantifying the novel biomarker CPa9-HNE (specific neo-epitope fragment of HNE mediated CP degradation), which reflects neutrophil activity. Methods: A specific monoclonal antibody was raised towards a neoepitope of CP generated by HNE and a robust competitive ELISA (CPa9-HNE) was developed. Two patient cohorts were used to assess serum levels of CPa9-HNE: 1) A cohort of clinically stable COPD patients (n=68), where 25 of these came back for a four weeks follow-up visit. These were compared to a panel of healthy controls (n=36) and; 2) A cohort of IPF patients (n=16) as compared to a panel of healthy controls (n=10). Results: CPa9-HNE levels were significantly elevated in COPD patients (median 247.9 ng/mL) as compared with healthy controls (median 18.32 ng/mL), (pl0.0001, AUROC: 0.9996). At four weeks follow-up, the CPa9-HNE levels remained stable. Moreover, the CPa9-HNE was not dependent on age or sex. Serum CPa9-HNE was also significantly elevated in IPF patients (median 161.0 ng/mL) compared to healthy controls (median 26 ng/mL), (pl0.0001, AUROC: 0.9813). Conclusions: Systemically assessed CPa9-HNE was highly elevated in patients with COPD and IPF as compared to healthy controls, thus indicating that neutrophil activity may be evaluated utilizing this novel assay and that neutrophil activity is indeed elevated in IPF and COPD.