This project was supported by grants from the German Ministry for Education and Research (FKZ 82DZL004A1 to M.A.M) and the German Research Foundation (SFB-TR84TP B08 to M.A.M). Work described in this manuscript was supported by the German Center of Lung Research (DZL) and the EMBL Heidelberg through a PhD fellowship for M.G. We thank J. Schatterny, S. Butz and H. Scheuermann for expert technical assistance.

<ol>
	<li>Korkmaz, B., Moreau, T., Gauthier, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophil+elastase,+proteinase+3+and+cathepsin+G:+Physicochemical+properties,+activity+and+physiopathological+functions.">Neutrophil elastase, proteinase 3 and cathepsin G: Physicochemical properties, activity and physiopathological functions.</a> Biochimie. 90 (2), 227-242 (2008).</li><li>Sheshachalam, A., Srivastava, N., Mitchell, T., Lacy, P., Eitzen, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Granule+Protein+Processing+and+Regulated+Secretion+in+Neutrophils.">Granule Protein Processing and Regulated Secretion in Neutrophils.</a> Frontiers in Immunology. 5, 448 (2014).</li><li>Pham, C. T. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophil+serine+proteases:+Specific+regulators+of+inflammation.">Neutrophil serine proteases: Specific regulators of inflammation.</a> Nature Reviews Immunology. 6 (7), 541-550 (2006).</li><li>Gehrig, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lack+of+neutrophil+elastase+reduces+inflammation,+mucus+hypersecretion,+and+emphysema,+but+not+mucus+obstruction,+in+mice+with+cystic+fibrosislike+lung+disease.">Lack of neutrophil elastase reduces inflammation, mucus hypersecretion, and emphysema, but not mucus obstruction, in mice with cystic fibrosislike lung disease.</a> American Journal of Respiratory and Critical Care Medicine. 189 (9), 1082-1092 (2014).</li><li>McKelvey, M. C., Weldon, S., McAuley, D. F., Mall, M. A., Taggart, C. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Targeting+proteases+in+cystic+fibrosis+lung+disease+paradigms,+progress,+and+potential.">Targeting proteases in cystic fibrosis lung disease paradigms, progress, and potential.</a> American Journal of Respiratory and Critical Care Medicine. 201 (2), 141-147 (2020).</li><li>Clancy, D. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extracellular+Neutrophil+Proteases+Are+Efficient+Regulators+of+IL-1,+IL-33,+and+IL-36+Cytokine+Activity+but+Poor+Effectors+of+Microbial+Killing.">Extracellular Neutrophil Proteases Are Efficient Regulators of IL-1, IL-33, and IL-36 Cytokine Activity but Poor Effectors of Microbial Killing.</a> Cell Reports. 22 (11), 2937-2950 (2018).</li><li>Giacalone, V. D., Margaroli, C., Mall, M. A., Tirouvanziam, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophil+adaptations+upon+recruitment+to+the+lung:+New+concepts+and+implications+for+homeostasis+and+disease.">Neutrophil adaptations upon recruitment to the lung: New concepts and implications for homeostasis and disease.</a> International Journal of Molecular Sciences. 21 (3), 1-21 (2020).</li><li>Sly, P. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Risk+Factors+for+Bronchiectasis+in+Children+with+Cystic+Fibrosis.">Risk Factors for Bronchiectasis in Children with Cystic Fibrosis.</a> New England Journal of Medicine. 368 (21), 1963-1970 (2013).</li><li>Owen, C. A., Campbell, M. A., Sannes, P. L., Boukedes, S. S., Campbell, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+surface-bound+elastase+and+cathepsin+G+on+human+neutrophils:+A+novel,+non-oxidative+mechanism+by+which+neutrophils+focus+and+preserve+catalytic+activity+of+serine+proteinases.">Cell surface-bound elastase and cathepsin G on human neutrophils: A novel, non-oxidative mechanism by which neutrophils focus and preserve catalytic activity of serine proteinases.</a> Journal of Cell Biology. 131 (3), 775-789 (1995).</li><li>Brinkmann, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophil+Extracellular+Traps+Kill+Bacteria.">Neutrophil Extracellular Traps Kill Bacteria.</a> Science. 303 (5663), 1532-1535 (2004).</li><li>Margaroli, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elastase+Exocytosis+by+Airway+Neutrophils+Associates+with+Early+Lung+Damage+in+Cystic+Fibrosis+Children.">Elastase Exocytosis by Airway Neutrophils Associates with Early Lung Damage in Cystic Fibrosis Children.</a> American Journal of Respiratory and Critical Care Medicine. , (2018).</li><li>Owen, C., Campbell, M. A., Sannes, P. L., Boukedes, S. S., Carolina, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+surface-bound+elastase+and+cathepsin+G+on+human+neutrophils:+a+novel,+non-oxidative+mechanism+by+which+neutrophils+focus+and+preserve+catalytic+activity+of+serine+proteinases.">Cell surface-bound elastase and cathepsin G on human neutrophils: a novel, non-oxidative mechanism by which neutrophils focus and preserve catalytic activity of serine proteinases.</a> The Journal of cell biology. 131 (3), 775-789 (1995).</li><li>Garland, M., Yim, J. J., Bogyo, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Bright+Future+for+Precision+Medicine:+Advances+in+Fluorescent+Chemical+Probe+Design+and+Their+Clinical+Application.">A Bright Future for Precision Medicine: Advances in Fluorescent Chemical Probe Design and Their Clinical Application.</a> Cell chemical biology. 23 (1), 122-136 (2016).</li><li>Gehrig, S., Mall, M. A., Schultz, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatially+resolved+monitoring+of+neutrophil+elastase+activity+with+ratiometric+fluorescent+reporters.">Spatially resolved monitoring of neutrophil elastase activity with ratiometric fluorescent reporters.</a> Angewandte Chemie - International Edition. 51 (25), 6258-6261 (2012).</li><li>Guerra, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cathepsin+G+Activity+as+a+New+Marker+for+Detecting+Airway+Inflammation+by+Microscopy+and+Flow+Cytometry.">Cathepsin G Activity as a New Marker for Detecting Airway Inflammation by Microscopy and Flow Cytometry.</a> ACS Central Science. 5 (3), 539-548 (2019).</li><li>Hu, H. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+imaging+of+mouse+tumors+by+a+lipidated+cathepsin+S+substrate.">In vivo imaging of mouse tumors by a lipidated cathepsin S substrate.</a> Angewandte Chemie - International Edition. 53 (29), 7669-7673 (2014).</li><li>Korkmaz, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measuring+elastase,+proteinase+3+and+cathepsin+G+activities+at+the+surface+of+human+neutrophils+with+fluorescence+resonance+energy+transfer+substrates.">Measuring elastase, proteinase 3 and cathepsin G activities at the surface of human neutrophils with fluorescence resonance energy transfer substrates.</a> Nature Protocols. 3 (6), 991-1000 (2008).</li><li>Craven, T. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Super-silent+FRET+Sensor+Enables+Live+Cell+Imaging+and+Flow+Cytometric+Stratification+of+Intracellular+Serine+Protease+Activity+in+Neutrophils.">Super-silent FRET Sensor Enables Live Cell Imaging and Flow Cytometric Stratification of Intracellular Serine Protease Activity in Neutrophils.</a> Scientific Reports. 8 (1), 13490 (2018).</li><li>Mu, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+small-molecule+fret+reporter+for+the+real-time+visualization+of+cell-surface+proteolytic+enzyme+functions.">A small-molecule fret reporter for the real-time visualization of cell-surface proteolytic enzyme functions.</a> Angewandte Chemie - International Edition. 53 (52), 14357-14362 (2014).</li><li>Hagner, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+method+for+rapid+and+dynamic+quantification+of+elastase+activity+on+sputum+neutrophils+from+patients+with+cystic+fibrosis+using+flow+cytometry.">New method for rapid and dynamic quantification of elastase activity on sputum neutrophils from patients with cystic fibrosis using flow cytometry.</a> European Respiratory Journal. 55 (4), 1902355 (2020).</li><li>Dittrich, A. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elastase+activity+on+sputum+neutrophils+correlates+with+severity+of+lung+disease+in+cystic+fibrosis.">Elastase activity on sputum neutrophils correlates with severity of lung disease in cystic fibrosis.</a> European Respiratory Journal. , 1701910 (2018).</li><li>Cobos-Correa, A., Trojanek, J. B., Diemer, S., Mall, M. A., Schultz, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membrane-bound+FRET+probe+visualizes+MMP12+activity+in+pulmonary+inflammation.">Membrane-bound FRET probe visualizes MMP12 activity in pulmonary inflammation.</a> Nature Chemical Biology. 5 (9), 628-630 (2009).</li><li>Hu, H. -. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=FRET-based+and+other+fluorescent+proteinase+probes.">FRET-based and other fluorescent proteinase probes.</a> Biotechnology Journal. 9 (2), 266-281 (2014).</li><li>Trojanek, J. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Airway+mucus+obstruction+triggers+macrophage+activation+and+matrix+metalloproteinase+12-dependent+emphysema.">Airway mucus obstruction triggers macrophage activation and matrix metalloproteinase 12-dependent emphysema.</a> American Journal of Respiratory Cell and Molecular Biology. 51 (5), 709-720 (2014).</li><li>Wagner, C. J., Schultz, C., Mall, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophil+elastase+and+matrix+metalloproteinase+12+in+cystic+fibrosis+lung+disease.">Neutrophil elastase and matrix metalloproteinase 12 in cystic fibrosis lung disease.</a> Molecular and Cellular Pediatrics. 3 (1), 25 (2016).</li><li>Gaggar, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+matrix+metalloproteinases+in+cystic+fibrosis+lung+disease.">The role of matrix metalloproteinases in cystic fibrosis lung disease.</a> The European respiratory journal. 38 (3), 721-727 (2011).</li><li>Guerra, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protease+FRET+Reporters+Targeting+Neutrophil+Extracellular+Traps.">Protease FRET Reporters Targeting Neutrophil Extracellular Traps.</a> Journal of the American Chemical Society. 142 (48), 20299-20305 (2020).</li><li>Middleton, P. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elexacaftor-Tezacaftor-Ivacaftor+for+Cystic+Fibrosis+with+a+Single+Phe508del+Allele.">Elexacaftor-Tezacaftor-Ivacaftor for Cystic Fibrosis with a Single Phe508del Allele.</a> New England Journal of Medicine. 381 (19), 1809-1819 (2019).</li></ol>

The authors declare no conflict of interests.

The reported protocols explain different approaches to quantify the activity of neutrophil elastase and cathepsin G in human sputum samples. Critical points for a successful enzyme activity measurement are the i) precise timing and standardization of the operative procedure and ii) the use of reliable negative and positive controls. If these conditions are met, the described methods are not limited to sputum but can also be easily adapted to the analysis of protease activity in blood, bronchoalveolar lavage fluids and tissue sections or homogenates.
Each of the three techniques has its strengths and limitations, which often complement each other. For example, flow cytometry allows for the rapid analysis of rare cell populations as well as cell phenotyping but lacks spatial resolution information, which can be achieved by microscopy. Instead, plate reader measurements permit for the parallel assessment of several samples or conditions in a high-throughput fashion. Since fresh sputum cells cannot be frozen and stored, the three methods require that samples must be processed rapidly after expectoration. This limits the flexibility or the throughput of the membrane-bound activity measurements. The development of a flow cytometry protocol that allows to fix cells after probe addition and enzymatic cleavage would open to the parallel measurement of a higher number of tubes. Moreover, particular attention should be paid to the handling and storage of the FRET probes. In fact, some aminoacids present in the peptide substrate, such as methionine, undergo oxidation which leads to decreased reporter sensitivity. To increase the reporter&#39;s shelf life (estimated of&#160;about three months at 20 &#176;C), they can be stored in small volume aliquots (1-2 &#181;L) under inert gas such as Nitrogen or Argon.
In CF and other chronic inflammatory lung diseases it is important to detect the inflammation as early as possible, and reliable biomarkers have the potential to achieve such a goal. The possibility to detect surface-bound NSPs activity, which has been shown to be harmful for the surrounding tissue, also in conditions when there is no or little free NE activity, adds another level of valuable information, which can be hardly achieved by means of other existing methods4,11.
The reporters can be used to study the link of membrane-bound associated NSP activity with severity and progression of lung disease, especially at its early-onset. The methods can be utilized to monitor treatment efficacy (e.g., anti-inflammatory treatments or highly effective CFTR modulators and potentiators28) and investigate the resulting dampening of neutrophil-driven inflammation. In addition, the protocols are based on non-invasive sample procedures which carry very low risk for the patient and, therefore, can be used on a very broad scale and open the doors to numerous exciting applications.

Neutrophil elastase (NE), cathepsin G (CG), proteinase 3 (PR3) and neutrophil serine protease 4 (NSP4) are the four neutrophil serine proteases (NSPs)1. They are stored, together with myeloperoxidase, within neutrophil primary or azurophilic granules. Due to their elevated proteolytic content, the secretion of primary granules is tightly regulated and neutrophils have to be sequentially challenged with priming and activating stimuli2.
Inside the phagolysosome, NSPs function as intracellular bactericidal agents3. When secreted, NSPs become strong mediators of inflammation: they cleave cytokines and surface receptors, activating parallel pro-inflammatory pathways3. Importantly, inflammatory conditions feature an uncontrolled NSPs secretion. For example, within inflamed airways, excessive NE activity causes mucus hypersecretion, goblet cells metaplasia, CFTR inactivation and extracellular matrix remodeling4,5. Cathepsin G participates in inflammation as well: it specifically cleaves and activates two components of the IL-1 family, IL-36&#945; and IL-36&#946;6. In concert with NE, CG cleaves protease-activated receptors on the airway epithelium and also activates TNF-&#945; and IL-1&#946;.
Endogenous anti-proteases such as alpha-1-antitrypsin, alpha-1-antichymotrypsin and the secretory leukocyte protease inhibitor regulate neutrophil elastase and cathepsin G activity5. However, over the course of lung disease progression, the continuous secretion of proteases exceeds stoichiometrically the anti-protease shield, leading to non-resolving neutrophilia in the airways, inflammation worsening and tissue damage5,7. Although NE concentration and activity in soluble fractions of patient airways has been shown to be a promising biomarker of disease severity8, NE and CG also associate to the neutrophil plasma membrane and to extracellular DNA via electrostatic interactions9,10 where they become less accessible to anti-proteases. Importantly, preclinical studies defined a scenario where cell surface-associated protease activity appears earlier and/or independently of its soluble counterpart4,11. In fact, to become detectable, free protease activity first needs to overwhelm the anti-protease shield. Instead, at the cell surface, membrane-bound protease activity remains at least partially intact due to the inaccessibility of large inhibitors to the cell plasma membrane12. Such complex protease behavior has important consequences on neutrophil-mediated inflammation onset and propagation, and therefore needs to be investigated with precise and informative tools.
Over the years, F&#246;rster resonance energy transfer (FRET)-based probes found numerous biomedical applications as tools that efficiently and rapidly assess a specific protease activity in human samples13. To function, protease reporters are composed of a recognition motif (i.e., a peptide), which is recognized by the target enzyme and rely on FRET, a physical process where, upon excitation, a donor fluorophore transfers energy to an acceptor molecule. The processing operated by the enzyme on the reporter, namely the cleavage of the recognition part, results in the acceptor to diffuse away from the donor: the enzyme activity is therefore measured as a time-dependent change in the donor over the acceptor fluorescence. Such read-out is self-normalizing and ratiometric, hence only marginally affected by environmental conditions such as pH and local probe concentration. NEmo-114 and sSAM15 are FRET probes that report specifically on NE and CG activity, respectively. However, such reporters do not localize specifically to any cellular compartment, therefore they are employed to monitor the protease activity present in human fluids. In order to monitor protease activity in a spatially localized fashion, we and others developed FRET probes that associate to subcellular components via molecular tags14,15,16,17,18,19. Such a synthetic strategy allowed the development of NEmo-2 and mSAM, two FRET probes equipped with lipid anchors that localize to the plasma membrane. These reporters fueled a deeper understanding of NE and CG proteases in cystic fibrosis and chronic obstructive pulmonary diseases14,15.
Here, detailed protocols are provided for the visualization and quantification of soluble and membrane-bound NE and CG activities in human sputum by means of NEmo and SAM series of FRET probes. To address diverse aspects of NSPs pathophysiology and provide an array of methods that can be employed according to the user-specific need, the analysis via fluorescence spectroscopy, fluorescence microscopy and flow cytometry are shown.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>100 &#181;m Nylon cell strainer</td>
			<td>Corning Inc.</td>
			<td>431752</td>
			<td></td>
		</tr>
		<tr>
			<td>2300 EnSpire (Multilabel Plate Reader)</td>
			<td>PerkinElmer</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>35x10mm Dish, Nunclon Delta</td>
			<td>Thermo Fisher Scientific</td>
			<td>150318</td>
			<td></td>
		</tr>
		<tr>
			<td>40 &#181;m Nylon cell strainer</td>
			<td>Corning Inc.</td>
			<td>431750</td>
			<td></td>
		</tr>
		<tr>
			<td>50 mL tubes</td>
			<td>Sarstedt</td>
			<td>10535253</td>
			<td></td>
		</tr>
		<tr>
			<td>7-AAD, viability dye</td>
			<td>Bio Legend</td>
			<td>420404</td>
			<td>5 &#181;L/100 &#181;L</td>
		</tr>
		<tr>
			<td>Balance</td>
			<td>OHAUS Instruments (Shanghai) Co., Ltd.</td>
			<td>PR124</td>
			<td></td>
		</tr>
		<tr>
			<td>BD Falcon Round-Bottom Tubes 5 mL</td>
			<td>BD Bioscience</td>
			<td>352054</td>
			<td></td>
		</tr>
		<tr>
			<td>BD LSRFortessa cell analyzer</td>
			<td>BD Bioscience</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>black flat bottom 96 well half area plate</td>
			<td>Corning Life Science</td>
			<td>3694</td>
			<td></td>
		</tr>
		<tr>
			<td>Cathepsin G</td>
			<td>Elastin Products Company</td>
			<td>SG623</td>
			<td></td>
		</tr>
		<tr>
			<td>Cathepsin G Inhibitor I</td>
			<td>Merck KGaA</td>
			<td>219372</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge 5418R</td>
			<td>Eppendorf AG</td>
			<td>EP5401000137</td>
			<td></td>
		</tr>
		<tr>
			<td>Combitips advanced 1.0 mL</td>
			<td>Eppendorf AG</td>
			<td>0030 089 430</td>
			<td></td>
		</tr>
		<tr>
			<td>cOmplete proteinase inhibitor</td>
			<td>Roche</td>
			<td>11697498001</td>
			<td></td>
		</tr>
		<tr>
			<td>Countig chambers improved Neubauer</td>
			<td>Glaswarenfabrik Karl Hecht GmbH &#38; Co KG</td>
			<td>40442</td>
			<td></td>
		</tr>
		<tr>
			<td>coverslips &#216; 25mm</td>
			<td>Thermo Fisher Scientific</td>
			<td>MENZCB00250RA003</td>
			<td></td>
		</tr>
		<tr>
			<td>Cytospin 4</td>
			<td>Thermo Fisher Scientific</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>DRAQ5 (nuclear stain)</td>
			<td>BioStatus Limited</td>
			<td>DR50050</td>
			<td>1:10000</td>
		</tr>
		<tr>
			<td>FACSDiva software, v8.0.1</td>
			<td>BD Bioscience</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>FcBlock</td>
			<td>BD Bioscience</td>
			<td>564219</td>
			<td></td>
		</tr>
		<tr>
			<td>Fiji (Fiji Is Just ImageJ)</td>
			<td>fiji.sc</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Flow Jo software, v10</td>
			<td>TreeStar</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>FluoQ Plugin, v3-97</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Heraeus Megafuge 16R</td>
			<td>Thermo Fisher Scientific</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Human Sputum Leucocyte Elastase</td>
			<td>Elastin Products Company</td>
			<td>SE563</td>
			<td></td>
		</tr>
		<tr>
			<td>Leica SP8 confocal microscope</td>
			<td>Leica Microsystems</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Mini Rock-Shaker</td>
			<td>PEQLAB Biotechnologie GmbH</td>
			<td>MR-1</td>
			<td></td>
		</tr>
		<tr>
			<td>mouse anti-human CD14, Pe-Cy7, clone M5E2</td>
			<td>BD Bioscience</td>
			<td>557742 Lot:8221983</td>
			<td>1:50</td>
		</tr>
		<tr>
			<td>mouse anti-human CD16, AF700, clone 3G8</td>
			<td>BD Bioscience</td>
			<td>557820 Lot:8208791</td>
			<td>1:50</td>
		</tr>
		<tr>
			<td>mouse anti-human CD45, APC-Cy7, clone 2D1</td>
			<td>BD Bioscience</td>
			<td>557833 Lot:8059688</td>
			<td>1:33</td>
		</tr>
		<tr>
			<td>mouse anti-human CD66b, PE/Dazzel 594, clone G10F5</td>
			<td>BioLegend</td>
			<td>305122 Lot:B241921</td>
			<td>1:50</td>
		</tr>
		<tr>
			<td>mSAM</td>
			<td>in house</td>
			<td></td>
			<td>2 mM</td>
		</tr>
		<tr>
			<td>Multipette plus</td>
			<td>Eppendorf AG</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NEmo-1</td>
			<td>SiChem</td>
			<td>SC-0200</td>
			<td>1 mM</td>
		</tr>
		<tr>
			<td>NEmo-2E</td>
			<td>SiChem</td>
			<td>SC-0201</td>
			<td>2 mM</td>
		</tr>
		<tr>
			<td>Pari Boy SX with an LC Sprint jet nebulizer</td>
			<td>Pari</td>
			<td>085G3001</td>
			<td></td>
		</tr>
		<tr>
			<td>phosphate buffered saline</td>
			<td>Gibco</td>
			<td>10010-015</td>
			<td></td>
		</tr>
		<tr>
			<td>ROTI Histokitt (mounting medium)</td>
			<td>Carl Roth GmbH + Co.KG</td>
			<td>6638.1</td>
			<td></td>
		</tr>
		<tr>
			<td>Salbutamol</td>
			<td>Teva GmbH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sivelestat</td>
			<td>Cayman Chemicals</td>
			<td>17779</td>
			<td></td>
		</tr>
		<tr>
			<td>Sputolysin</td>
			<td>Calbiochem</td>
			<td>560000-1SET</td>
			<td></td>
		</tr>
		<tr>
			<td>sSAM</td>
			<td>in house</td>
			<td></td>
			<td>2 mM</td>
		</tr>
		<tr>
			<td>SuperFrost Plus Adhesion slides</td>
			<td>Thermo Fisher Scientific</td>
			<td>10149870</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypan Blue solution</td>
			<td>Sigma-Aldrich</td>
			<td>T8154</td>
			<td></td>
		</tr>
	</tbody>
</table>

monitoring neutrophil elastase and cathepsin g activity in human sputum samples

Proteases are regulators of countless physiological processes and the precise investigation of their activities remains an intriguing biomedical challenge. Among the ~600 proteases encoded by the human genome, neutrophil serine proteases (NSPs) are thoroughly investigated for their involvement in the onset and progression of inflammatory conditions including respiratory diseases. Uniquely, secreted NSPs not only diffuse within extracellular fluids but also localize to plasma membranes. During neutrophil extracellular trap (NETs) formation, NSPs become an integral part of the secreted chromatin. Such complex behavior renders the understanding of NSPs pathophysiology a challenging task. Here, detailed protocols are shown to visualize, quantify and discriminate free and membrane-bound neutrophil elastase (NE) and cathepsin G (CG) activities in sputum samples. NE and CG are NSPs whose activities have pleiotropic roles in the pathogenesis of cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD): they promote tissue remodeling, regulate downstream immune responses and correlate with lung disease severity. The protocols show how to separate fluid and cellular fraction, as well as the isolation of neutrophils from human sputum for enzymatic activity quantification via small-molecule F&#246;rster resonance energy transfer-based (FRET) reporters. To gather specific insights into the relative role of NE and CG activities, a FRET readout can be measured by different technologies: i) in vitro plate reader measurements allow for high-throughput and bulk detection of protease activity; ii) confocal microscopy spatiotemporally resolves membrane-bound activity at the cell surface; iii) small-molecule FRET flow cytometry enables for the rapid evaluation of anti-inflammatory treatments via single-cell protease activity quantification and phenotyping. The implementation of such methods opens the doors to explore NSPs pathobiology and their potential as biomarkers of disease severity for CF and COPD. Given their standardization potential, their robust readout and simplicity of transfer, the described techniques are immediately shareable for implementation across research and diagnostic laboratories.

The results shown in Figure 1a illustrate a representative microscopy dataset. The nuclear signal is used to identify neutrophils by their characteristic segmented nuclei. The region of interest (ROI) is selected manually (dashed line in Figure 1a). The D/A ratio image is calculated by dividing the intensities of the donor channel by the intensities of the acceptor channel on a pixel-by-pixel basis. In the last step the average D/A ratio per cell (ROI) is calculated. In Figure 1b each dot represents the mean of one ROI (neutrophil). It is recommended to image and evaluate about 100 cells per condition.
A representative flow cytometry gating strategy is shown in Figure 2a. Such gating allows to discriminate and study sputum neutrophils. To avoid fluorescence spillover or compensation artifacts, it is recommended to dedicate a laser line (e.g., blue laser) to the FRET probe fluorescence detection. Flow cytometry fluorescence compensation should be performed for antibodies and not for the FRET probe. Figure 2b depicts the MFI distribution at 0 and 10 min after reporter addition. Each row in Figure 2c indicates the mean donor and acceptor MFIs values for 1000 sputum neutrophils. The D/A ratio is calculated by dividing the donor and acceptor MFIs. The time course in Figure 2c on the right side shows the progression of the measurement: after a rapid initial increase, the D/A ratio reaches a plateau, according to the activity of the membrane-bound enzyme.

Watch this Scientific Journal Video about Monitoring Neutrophil Elastase and Cathepsin G Activity in Human Sputum Samples at JoVE.com

Monitoring Neutrophil Elastase and Cathepsin G Activity in Human Sputum Samples

The protocols herein described provide a guide to visualize and quantify the activity of neutrophil proteases in human sputum. The applications of such analysis span from the evaluation of anti-inflammatory treatments, to biomarker validation, drug screening and large cohort clinical studies.

Proteases are regulators of countless physiological processes and the precise investigation of their activities remains an intriguing biomedical ...

monitoring-neutrophil-elastase-cathepsin-g-activity-human-sputum

Research

JoVE Journal

Immunology and Infection

15.3K Views.  German Center for Lung Research (DZL). The protocols herein described provide a guide to visualize and quantify the activity of neutrophil proteases in human sputum. The applications of such analysis span from the evaluation of anti-inflammatory treatments, to biomarker validation, drug screening and large cohort clinical studies.

Video: Monitoring Neutrophil Elastase and Cathepsin G Activity in Human Sputum Samples

Determining the Phagocytic Activity of Clinical Antibody Samples

Antibody-driven phagocytosis is induced via the engagement of Fc receptors on professional phagocytes, and can contribute to both clearance as well as pathology of disease. While the properties of the variable domains of antibodies have long been considered critical to in vivo function, the ability of antibodies to recruit innate immune cells via their Fc domains has become increasingly appreciated as a major factor in their efficacy, both in the setting of recombinant monoclonal antibody therapy, as well as in the course of natural infection or vaccination1-3.
Importantly, despite its nomenclature as a constant domain, the antibody Fc domain does not have constant function, and is strongly modulated by IgG subclass (IgG1-4) and glycosylation at Asparagine 2974-6. Thus, this method to study functional differences of antigen-specific antibodies in clinical samples will facilitate correlation of the phagocytic potential of antibodies to disease state, susceptibility to infection, progression, or clinical outcome.
Furthermore, this effector function is particularly important in light of the documented ability of antibodies to enhance infection by providing pathogens access into host cells via Fc receptor-driven phagocytosis7. Additionally, there is some evidence that phagocytic uptake of immune complexes can impact the Th1/Th2 polarization of the immune response8.
Here, we describe an assay designed to detect differences in antibody-induced phagocytosis, which may be caused by differential IgG subclass, glycan structure at Asn297, as well as the ability to form immune complexes of antigen-specific antibodies in a high-throughput fashion. To this end, 1 &mu;m fluorescent beads are coated with antigen, then incubated with clinical antibody samples, generating fluorescent antigen specific immune complexes. These antibody-opsonized beads are then incubated with a monocytic cell line expressing multiple Fc&gamma;Rs, including both inhibitory and activating. Assay output can include phagocytic activity, cytokine secretion, and patterns of Fc&gamma;Rs usage, and are determined in a standardized manner, making this a highly useful system for parsing differences in this antibody-dependent effector function in both infection and vaccine-mediated protection9.

We present a high-throughput flow cytometric assay to determine the phagocytic activity of antigen-specific antibodies from clinical samples, utilizing fluorescent antigen-coated beads and a monocytic cell line expressing multiple Fc receptors&#x2014;providing receptor usage and phagocytic activity determinations in a standardized and reproducible fashion for any antigen of interest.

Antibody-driven phagocytosis is induced via the engagement of Fc receptors on professional phagocytes, and can contribute to both clearance as well as ...

Saliva, Salivary Gland, and Hemolymph Collection from Ixodes scapularis Ticks

Ticks are found worldwide and afflict humans with many tick-borne illnesses. Ticks are vectors for pathogens that cause Lyme disease and tick-borne relapsing fever (Borrelia spp.), Rocky Mountain Spotted fever (Rickettsia rickettsii), ehrlichiosis (Ehrlichia chaffeensis and E. equi), anaplasmosis (Anaplasma phagocytophilum), encephalitis (tick-borne encephalitis virus), babesiosis (Babesia spp.), Colorado tick fever (Coltivirus), and tularemia (Francisella tularensis) 1-8. To be properly transmitted into the host these infectious agents differentially regulate gene expression, interact with tick proteins, and migrate through the tick 3,9-13. For example, the Lyme disease agent, Borrelia burgdorferi, adapts through differential gene expression to the feast and famine stages of the tick's enzootic cycle 14,15. Furthermore, as an Ixodes tick consumes a bloodmeal Borrelia replicate and migrate from the midgut into the hemocoel, where they travel to the salivary glands and are transmitted into the host with the expelled saliva 9,16-19.
As a tick feeds the host typically responds with a strong hemostatic and innate immune response 11,13,20-22. Despite these host responses, I. scapularis can feed for several days because tick saliva contains proteins that are immunomodulatory, lytic agents, anticoagulants, and fibrinolysins to aid the tick feeding 3,11,20,21,23. The immunomodulatory activities possessed by tick saliva or salivary gland extract (SGE) facilitate transmission, proliferation, and dissemination of numerous tick-borne pathogens 3,20,24-27. To further understand how tick-borne infectious agents cause disease it is essential to dissect actively feeding ticks and collect tick saliva. This video protocol demonstrates dissection techniques for the collection of hemolymph and the removal of salivary glands from actively feeding I. scapularis nymphs after 48 and 72 hours post mouse placement. We also demonstrate saliva collection from an adult female I. scapularis tick.

Saliva, Salivary Gland, and Hemolymph Collection from Ixodes scapularis Ticks

The collection of infected tick hemolymph, salivary glands, and saliva is important to study how tick-borne pathogens cause disease. In this protocol we demonstrate how to collect hemolymph and salivary glands from feeding Ixodes scapularis nymphs. We also demonstrate saliva collection from female I. scapularis adults.

Ticks are found worldwide and afflict humans with many tick-borne illnesses. Ticks are vectors for pathogens that cause Lyme disease and tick-borne ...

Quantitative In vitro Assay to Measure Neutrophil Adhesion to Activated Primary Human Microvascular Endothelial Cells under Static Conditions

The vascular endothelium plays an integral part in the inflammatory response. During the acute phase of inflammation, endothelial cells (ECs) are activated by host mediators or directly by conserved microbial components or host-derived danger molecules. Activated ECs express cytokines, chemokines and adhesion molecules that mobilize, activate and retain leukocytes at the site of infection or injury. Neutrophils are the first leukocytes to arrive, and adhere to the endothelium through a variety of adhesion molecules present on the surfaces of both cells. The main functions of neutrophils are to directly eliminate microbial threats, promote the recruitment of other leukocytes through the release of additional factors, and initiate wound repair. Therefore, their recruitment and attachment to the endothelium is a critical step in the initiation of the inflammatory response. In this report, we describe an in vitro neutrophil adhesion assay using calcein AM-labeled primary human neutrophils to quantitate the extent of microvascular endothelial cell activation under static conditions. This method has the additional advantage that the same samples quantitated by fluorescence spectrophotometry can also be visualized directly using fluorescence microscopy for a more qualitative assessment of neutrophil binding.

Quantitative In vitro Assay to Measure Neutrophil Adhesion to Activated Primary Human Microvascular Endothelial Cells under Static Conditions

Neutrophil adherence to the activated endothelium at sites of infection is an integral component of the host's inflammatory response. Described in this report is a neutrophil binding assay that allows for the in vitro quantitation of primary human neutrophil binding to endothelial cells activated by inflammatory mediators under static conditions.

The vascular  endothelium plays an integral part in the inflammatory response. During the  acute phase of inflammation, endothelial cells (ECs) are ...

Human Neutrophil Flow Chamber Adhesion Assay

Neutrophil firm adhesion to endothelial cells plays a critical role in inflammation in both health and disease. The process of neutrophil firm adhesion involves many different adhesion molecules including members of the &beta;2 integrin family and their counter-receptors of the ICAM family. Recently, naturally occurring genetic variants in both &beta;2 integrins and ICAMs are reported to be associated with autoimmune disease. Thus, the quantitative adhesive capacity of neutrophils from individuals with varying allelic forms of these adhesion molecules is important to study in relation to mechanisms underlying development of autoimmunity. Adhesion studies in flow chamber systems can create an environment with fluid shear stress similar to that observed in the blood vessel environment in vivo. Here, we present a method using a flow chamber assay system to study the quantitative adhesive properties of human peripheral blood neutrophils to human umbilical vein endothelial cell (HUVEC) and to purified ligand substrates. With this method, the neutrophil adhesive capacities from donors with different allelic variants in adhesion receptors can be assessed and compared. This method can also be modified to assess adhesion of other primary cell types or cell lines.

A method of quantitating neutrophil adhesion is reported. This method creates a dynamic flow environment similar to that encountered in a blood vessel. It allows the investigation of neutrophil adhesion to either purified adhesion molecules (ligand) or endothelial cell substrate (HUVEC) in a context similar to the in vivo environment with sheer stress.

Neutrophil firm adhesion to endothelial cells plays a critical role in inflammation in both health and disease. The process of neutrophil firm adhesion ...

Flow Cytometric Analysis of Natural Killer Cell Lytic Activity in Human Whole Blood

NK cell cytotoxicity is a widely used measure to determine the effect of outside intervention on NK cell function. However, the accuracy and reproducibility of this assay can be considered unstable, either because of user&#39;s errors or because of the sensitivity of NK cells to experimental manipulation. To eliminate these issues, a workflow that reduces them to a minimum was established and is presented here. To illustrate, we obtained blood samples, at various time points, from runners (n = 4) that were submitted to an intense bout of exercise. First, NK cells are simultaneously identified and isolated through CD56 tagging and magnetic-based sorting, directly from whole blood and from as little as one milliliter. The sorted NK cells are removed of any reagent or capping antibodies. They can be counted in order to establish an accurate NK cell count per milliliter of blood. Secondly, the sorted NK cells (effectors cells or E) can be mixed with 3,3&#39;-Diotadecyloxacarbocyanine Perchlorate (DiO) tagged K562 cells (target cells or T) at an assay-optimal 1:5 T:E ratio, and analyzed using an imaging flow-cytometer that allows for the visualization of each event and the elimination of any false positive or false negatives (such as doublets or effector cells). This workflow can be completed in about 4 h, and allows for very stable results even when working with human samples. When available, research teams can test several experimental interventions in human subjects, and compare measurements across several time points without compromising the data&#39;s integrity.

This work describes an advanced workflow for the accurate and fast determination of NK (Natural Killer) cell count and NK cell cytotoxicity in human blood samples.

NK cell cytotoxicity is a widely used measure to determine the effect of outside intervention on NK cell function. However, the accuracy and ...

In Vitro Differentiation Model of Human Normal Memory B Cells to Long-lived Plasma Cells

Plasma cells (PCs) secrete large amounts of antibodies and develop from B cells that have been activated. PCs are rare cells located in the bone marrow or mucosa and ensure humoral immunity. Due to their low frequency and location, the study of PCs is difficult in human. We reported a B to PC in vitro differentiation model using selected combinations of cytokines and activation molecules that allow to reproduce the sequential cell differentiation occurring in vivo. In this in vitro model, memory B cells (MBCs) will differentiate into pre-plasmablasts (prePBs), plasmablasts (PBs), early PCs and finally, into long-lived PCs, with a phenotype close to their counterparts in healthy individuals.&#160;We also built an open access bioinformatics tools to analyze the most prominent information from GEP data related to PC differentiation. These resources can be used to study human B to PC differentiation and in the current study, we investigated the gene expression regulation of epigenetic factors during human B to PC differentiation.

Using multi-step culture systems, we report an in vitro B cell to plasma cell differentiation model.

Plasma cells (PCs) secrete large amounts of antibodies and develop from B cells that have been activated. PCs are rare cells located in the bone marrow or ...

Measurement of Chitinase Activity in Biological Samples

Chitinases are the enzymes that cleave chitin. Even in the absence of chitin, mammalians have significant amounts of chitinases present in the body including at baseline. The precise role of chitinase is not known, however it was believed to play important role in digestion and host defense against chitin-containing food and pathogens, respectively. Recent work, including ours, has shown an important role of chitinase and chitinase-like proteins in host immunity and allergic diseases. Importantly, chitinase activities serve as important biomarkers of disease severity in a wide-range of diseases including type 2 inflammatory diseases such as asthma and pulmonary fibrosis. Similarly, patients with genetic disorders like Gaucher disease have significantly elevated chitinase levels, which not only correlate with disease severity but also serve as a reliable biomarker for therapeutic effectiveness. The protocol outlined here describes a simple, quick, and straightforward way to measure chitinase activity in BAL or serum samples of mice and can be widely adapted to human subjects and other model organisms due to the highly conserved nature of the enzymes.

Presented here is a simple method to measure chitinase activity in biological fluids such as bronchoalveolar lavage or serum.

Chitinases are the enzymes that cleave chitin. Even in the absence of chitin, mammalians have significant amounts of chitinases present in the body ...

Quantifying Myeloperoxidase-DNA and Neutrophil Elastase-DNA Complexes from Neutrophil Extracellular Traps by Using a Modified Sandwich ELISA

Certain stimuli, such as microorganisms, cause neutrophils to release neutrophil extracellular traps (NETs), which are basically web-like structures composed of DNA with granule proteins, such as myeloperoxidase (MPO) and neutrophil elastase (NE), and cytoplasmic and cytoskeletal proteins. Although interest in NETs has increased recently, no sensitive, reliable assay method is available for measuring NETs in clinical settings. This article describes a modified sandwich enzyme-linked immunosorbent assay to quantitatively measure two components of circulating NETs, MPO-DNA and NE-DNA complexes, which are specific components of NETs and are released into the extracellular space as breakdown products of NETs. The assay uses specific monoclonal antibodies for MPO or NE as the capture antibodies and a DNA-specific detection antibody. MPO or NE binds to one site of the capture antibody during the initial incubation of samples containing MPO-DNA or NE-DNA complexes. This assay shows good linearity and high inter-assay and intra-assay precision. We used it in 16 patients with COVID-19 with accompanying acute respiratory distress syndrome and found that the plasma concentrations of MPO-DNA and NE-DNA were significantly higher than in the plasma obtained from healthy controls. This detection assay is a reliable, highly sensitive, and useful method for investigating the characteristics of NETs in human plasma and culture supernatants.

We present a protocol for a modified sandwich enzyme-linked immunosorbent assay technique to quantitatively measure two components of neutrophil extracellular trap remnants, myeloperoxidase conjugated-DNA and neutrophil elastase conjugated-DNA complexes,derived from activated neutrophils.

Certain stimuli, such as microorganisms, cause neutrophils to release neutrophil extracellular traps (NETs), which are basically web-like structures ...

Staining and Imaging to Visualize Neutrophil Extracellular Traps

Immunofluorescence Imaging of Neutrophil Extracellular Traps in Human and Mouse Tissues

Neutrophil extracellular traps (NETs) are released by neutrophils as a response to bacterial infection or traumatic tissue damage but also play a role in autoimmune diseases and sterile inflammation. They are web-like structures composed of double-stranded DNA filaments, histones, and antimicrobial proteins. Once released, NETs can trap and kill extracellular pathogens in blood and tissue. Furthermore, NETs participate in homeostatic regulation by stimulating platelet adhesion and coagulation. However, the dysregulated production of NETs has also been associated with various diseases, including sepsis or autoimmune disorders, which makes them a promising target for therapeutic intervention. Apart from electron microscopy, visualizing NETs using immunofluorescence imaging is currently one of the only known methods to demonstrate NET interactions in tissue. Therefore, various staining methods to visualize NETs have been utilized. In the literature, different staining protocols are described, and we identified four key components showing high variability between protocols: (1) the types of antibodies used, (2) the usage of autofluorescence-reducing agents, (3) antigen retrieval methods, and (4) permeabilization. Therefore, in vitro immunofluorescence staining protocols were systemically adapted and improved in this work to make them applicable for different species (mouse, human) and tissues (skin, intestine, lung, liver, heart, spinal disc). After fixation and paraffin-embedding, 3 &#181;m thick sections were mounted onto slides. These samples were stained with primary antibodies for myeloperoxidase (MPO), citrullinated histone H3 (H3cit), and neutrophil elastase (NE) according to a modified staining protocol. The slides were stained with secondary antibodies and examined using a widefield fluorescence microscope. The results were analyzed according to an evaluation sheet, and differences were recorded semi-quantitatively.
Here, we present an optimized NET staining protocol suitable for different tissues. We used a novel primary antibody to stain for H3cit and reduced non-specific staining with an autofluorescence-reducing agent. Furthermore, we demonstrated that NET staining requires a constant high temperature and careful handling of samples.

Author Spotlight: Neutrophil Extracellular Traps Imaging in Human and Mouse Tissues 

Neutrophil extracellular traps (NETs) are associated with various diseases, and immunofluorescence is often used for their visualization. However, there are various staining protocols, and, in many cases, only one type of tissue is examined. Here, we establish a generally applicable protocol for staining NETs in mouse and human tissue.

Neutrophil extracellular traps (NETs) are released by neutrophils as a response to bacterial infection or traumatic tissue damage but also play a role in ...