Biomarkers play a central role in detecting chronic inflammatory diseases before irreversible tissue damage occurs. These measurable, ideally disease-specific, indicators can be detected in the organism even before the onset of symptoms. For example, neutrophil elastase (NE), a serine protease secreted by activated neutrophils and essential for the innate immune response to pathogen infections, already serves as a biomarker for certain chronic inflammatory diseases of the respiratory and digestive tracts. In these cases, the activity of secreted, i.e. “free” NE, which is released during chronic inflammatory processes and damages tissues due to proteolytic activity, has been determined so far. In previous work, we have shown that NE also occurs membrane-bound on the surface of activated neutrophils in the airways of chronic inflammatory lung diseases such as cystic fibrosis. There, membrane-bound NE is already catalytically active long before the activity of free NE can be detected and it is involved in airway damage.1,2 The results of these studies suggest that determining the activity of membrane-bound NE could also enable earlier diagnosis of other chronic inflammatory diseases and facilitate personalized therapy.
The aim of this translational research project is to investigate the role of membrane-bound NE activity on neutrophils circulating in the blood of healthy subjects and patients with chronic inflammatory (autoimmune) diseases in childhood and thus establish a method for early disease detection. For this purpose, a reporter molecule based on Förster resonance energy transfer (FRET) technology we developed is used.3 This allows the detection of NE activity on the surface of living, freshly isolated cells ex vivo using flow cytometry. In addition to state of the artcytometry and cell biology technologies, this experimental MD thesis also applies basic molecular biology laboratory work and microscopy and correlates experimental data with clinical patient data on disease progression.