Neutrophils are known to have an impact on the pathogenesis mechanism in different pulmonary diseases, since they are a crucial part of the innate immune system. When activated, neutrophils can degranulate proteins and proteases, herein calprotectin (CP) and human neutrophil elastase (HNE). The aim of this study was to examine neutrophil activity in different pulmonary diseases by quantifying HNE-mediated CP degradation in serum using the novel neoepitope biomarker CPa9-HNE. Methods: A specific monoclonal antibody was raised towards a neoepitope of CP produced by HNE-mediated cleavage and employed in a competitive ELISA (CPa9-HNE). Serum levels of CPa9-HNE were assessed in two cohorts: 1) clinically stable chronic obstructive pulmonary disease (COPD) (n=68), idiopathic pulmonary fibrosis (IPF) (n=16), and healthy controls (n=38); and 2) COPD (n=10), asthma (n=9), non-small cell lung cancer (NSCLC) (n=5), small cell lung cancer (SCLC) (n=11), and healthy controls (n=10). Results: In Cohort 1, serum CPa9-HNE levels were significantly elevated in patients with COPD (median 247.9 ] ng/mL, AUROC 0.9996, p<0.0001) and IPF (median 161.0 ] ng/mL, AUROC 0.9655, p<0.0001) as compared with healthy controls (median 22.96 ] ng/mL). In Cohort 2, serum CPa9-HNE levels were most significantly elevated in COPD (median 332.3 ] ng/mL) compared to the healthy controls (median 116.7 ng/mL, IQR 90.10-175.7 ng/mL, p=0.0015). Furthermore, SCLC patients had significantly elevated levels (median 218.2 [IQR 176.9-458.7] ng/mL, p=0.0166) as compared to the healthy controls, whereas the increase seen for NSCLC was borderline significant ] ng/mL, p=0.0502). Asthma patients (median 75.64 ] ng/mL) had CPa9-HNE levels comparable to the healthy controls in this cohort. Results from the SCLC patients indicated a difference in CPa9-HNE levels related to gender (six males, median 356.5 ] ng/mL; four females, median 151.1 ] ng/mL). However, this was not found in the other participants. Additionally, available data indicated that CPa9-HNE levels were not affected by age or BMI. Surprisingly, serum CPa9-HNE levels differed between the two groups of healthy controls. This may be due to differences in demographics. Conclusions: Systemically assessed CPa9-HNE levels were elevated in patients with COPD, IPF, and lung cancer, but not asthma, as compared to healthy controls. These results indicate that neutrophil activity may be easily evaluated using this novel serum biomarker and that neutrophil activity is elevated in COPD, IPF, and lung cancer.
