This research was founded by the German Research Society (BO5534). We thank Antonia Kiwitt, Moritz Lenz, Johanna Hagens, Dr. Annika Heuer, and PD Dr. Ingo K&#246;nigs for providing us with samples. Additionally, the authors thank the team of the UKE Microscopy Imaging Facility (Core facility, UKE Medical School) for support with the immunofluorescence microscopy.

This study included mouse tissues derived from experiments approved by the Hamburg State Administration for Animal Research, Beh&#246;rde f&#252;r Justiz und Verbraucherschutz, Hamburg, Germany (73/17, 100/17, 94/16, 109/2018, 63/16). The tissues used were mouse lung and colon from a septic model and burned skin. We used 8 week old male and female mice. The European Directive 2010/63/EU on the protection of animals used for scientific purposes was followed for all the experiments. The anonymized human samples included ti...

Staining and Imaging to Visualize Neutrophil Extracellular Traps

<ol>
	<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>Urban, C. F., 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+contain+calprotectin,+a+cytosolic+protein+complex+involved+in+host+defense+against+Candida+albicans.">Neutrophil extracellular traps contain calprotectin, a cytosolic protein complex involved in host defense against Candida albicans.</a> PLoS Pathogens. 5 (10), e1000639 (2009).</li><li>Abu Abed, U., Brinkmann, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunofluorescence+labelling+of+human+and+murine+neutrophil+extracellular+traps+in+paraffin-embedded+tissue.">Immunofluorescence labelling of human and murine neutrophil extracellular traps in paraffin-embedded tissue.</a> Journal of Visualized Experiments. (151), e60115 (2019).</li><li>Kawasaki, H., Iwamuro, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Potential+roles+of+histones+in+host+defense+as+antimicrobial+agents.">Potential roles of histones in host defense as antimicrobial agents.</a> Infectious Disorders - Drug Targets. 8 (3), 195-205 (2008).</li><li>Bianchi, M., Niemiec, M. J., Siler, U., Urban, C. F., Reichenbach, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Restoration+of+anti-Aspergillus+defense+by+neutrophil+extracellular+traps+in+human+chronic+granulomatous+disease+after+gene+therapy+is+calprotectin-dependent.">Restoration of anti-Aspergillus defense by neutrophil extracellular traps in human chronic granulomatous disease after gene therapy is calprotectin-dependent.</a> Journal of Allergy and Clinical Immunology. 127 (5), 1243-1252 (2011).</li><li>Hakkim, 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=Impairment+of+neutrophil+extracellular+trap+degradation+is+associated+with+lupus+nephritis.">Impairment of neutrophil extracellular trap degradation is associated with lupus nephritis.</a> Proceedings of the National Academy of Sciences of the United States of America. 107 (21), 9813-9818 (2010).</li><li>Papadaki, 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=Neutrophil+extracellular+traps+exacerbate+Th1-mediated+autoimmune+responses+in+rheumatoid+arthritis+by+promoting+DC+maturation.">Neutrophil extracellular traps exacerbate Th1-mediated autoimmune responses in rheumatoid arthritis by promoting DC maturation.</a> European Journal of Immunology. 46 (11), 2542-2554 (2016).</li><li>Toussaint, 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=Host+DNA+released+by+NETosis+promotes+rhinovirus-induced+type-2+allergic+asthma+exacerbation.">Host DNA released by NETosis promotes rhinovirus-induced type-2 allergic asthma exacerbation.</a> Nature Medicine. 23 (6), 681-691 (2017).</li><li>Fuchs, T. 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=Extracellular+DNA+traps+promote+thrombosis.">Extracellular DNA traps promote thrombosis.</a> Proceedings of the National Academy of Sciences of the United States of America. 107 (36), 15880-15885 (2010).</li><li>Park, 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=Cancer+cells+induce+metastasis-supporting+neutrophil+extracellular+DNA+traps.">Cancer cells induce metastasis-supporting neutrophil extracellular DNA traps.</a> Science Translational Medicine. 8 (361), (2016).</li><li>Warnatsch, A., Ioannou, M., Wang, Q., Papayannopoulos, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inflammation.+Neutrophil+extracellular+traps+license+macrophages+for+cytokine+production+in+atherosclerosis.">Inflammation. Neutrophil extracellular traps license macrophages for cytokine production in atherosclerosis.</a> Science. 349 (6245), 316-320 (2015).</li><li>Schauer, 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=Aggregated+neutrophil+extracellular+traps+limit+inflammation+by+degrading+cytokines+and+chemokines.">Aggregated neutrophil extracellular traps limit inflammation by degrading cytokines and chemokines.</a> Nature Medicine. 20 (5), 511-517 (2014).</li><li>Radermecker, C., Hego, A., Delvenne, P., Marichal, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+and+quantitation+of+neutrophil+extracellular+traps+in+human+tissue+sections.">Identification and quantitation of neutrophil extracellular traps in human tissue sections.</a> BioProtocol. 11 (18), e4159 (2021).</li><li>de Buhr, N., von K&#246;ckritz-Blickwede, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+neutrophil+extracellular+traps+become+visible.">How neutrophil extracellular traps become visible.</a> Journal of Immunology Research. 2016, 4604713 (2016).</li><li>Brinkmann, V., Abu Abed, U., Goosmann, C., Zychlinsky, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunodetection+of+NETs+in+paraffin-embedded+tissue.">Immunodetection of NETs in paraffin-embedded tissue.</a> Frontiers in Immunology. 7, 513 (2016).</li><li>Villanueva, E., 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=Netting+neutrophils+induce+endothelial+damage,+infiltrate+tissues,+and+expose+immunostimulatory+molecules+in+systemic+lupus+erythematosus.">Netting neutrophils induce endothelial damage, infiltrate tissues, and expose immunostimulatory molecules in systemic lupus erythematosus.</a> The Journal of Immunology. 187 (1), 538-552 (2011).</li><li>Santos, 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=NETs+detection+and+quantification+in+paraffin+embedded+samples+using+confocal+microscopy.">NETs detection and quantification in paraffin embedded samples using confocal microscopy.</a> Micron. 114, 1-7 (2018).</li><li>Savchenko, 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=Neutrophil+extracellular+traps+form+predominantly+during+the+organizing+stage+of+human+venous+thromboembolism+development.">Neutrophil extracellular traps form predominantly during the organizing stage of human venous thromboembolism development.</a> Journal of Thrombosis and Haemostasis. 12 (6), 860-870 (2014).</li><li>O'Sullivan, K. 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=Renal+participation+of+myeloperoxidase+in+antineutrophil+cytoplasmic+antibody+(ANCA)-associated+glomerulonephritis.">Renal participation of myeloperoxidase in antineutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis.</a> Kidney International. 88 (5), 1030-1046 (2015).</li><li>Barliya, T., 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=Possible+involvement+of+NETosis+in+inflammatory+processes+in+the+eye:+Evidence+from+a+small+cohort+of+patients.">Possible involvement of NETosis in inflammatory processes in the eye: Evidence from a small cohort of patients.</a> Molecular Vision. 23, 922-932 (2017).</li><li>Xu, 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=Overproduced+bone+marrow+neutrophils+in+collagen-induced+arthritis+are+primed+for+NETosis:+An+ignored+pathological+cell+involving+inflammatory+arthritis.">Overproduced bone marrow neutrophils in collagen-induced arthritis are primed for NETosis: An ignored pathological cell involving inflammatory arthritis.</a> Cell Proliferation. 53 (7), e12824 (2020).</li><li>Nonokawa, 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=Association+of+neutrophil+extracellular+traps+with+the+development+of+idiopathic+osteonecrosis+of+the+femoral+head.">Association of neutrophil extracellular traps with the development of idiopathic osteonecrosis of the femoral head.</a> American Journal of Pathology. 190 (11), 2282-2289 (2020).</li><li>Tucker, S. L., Sarr, D., Rada, B. <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+are+present+in+the+airways+of+ENaC-overexpressing+mice+with+cystic+fibrosis-like+lung+disease.">Neutrophil extracellular traps are present in the airways of ENaC-overexpressing mice with cystic fibrosis-like lung disease.</a> BMC Immunology. 22 (1), 7 (2021).</li><li>Knackstedt, S. L., 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+drive+inflammatory+pathogenesis+in+malaria.">Neutrophil extracellular traps drive inflammatory pathogenesis in malaria.</a> Science Immunology. 4 (40), (2019).</li><li>Nakazawa, 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=Histones+and+neutrophil+extracellular+traps+enhance+tubular+necrosis+and+remote+organ+injury+in+ischemic+AKI.">Histones and neutrophil extracellular traps enhance tubular necrosis and remote organ injury in ischemic AKI.</a> Journal of the American Society of Nephrology. 28 (6), 1753-1768 (2017).</li><li>Duler, L., Nguyen, N., Ontiveros, E., Li, R. H. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+neutrophil+extracellular+traps+in+paraffin-embedded+feline+arterial+thrombi+using+immunofluorescence+microscopy.">Identification of neutrophil extracellular traps in paraffin-embedded feline arterial thrombi using immunofluorescence microscopy.</a> Journal of Visualized Experiments. (157), e60834 (2020).</li><li>Stehr, A. 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=Neutrophil+extracellular+traps+drive+epithelial-mesenchymal+transition+of+human+colon+cancer.">Neutrophil extracellular traps drive epithelial-mesenchymal transition of human colon cancer.</a> Journal of Pathology. 256 (4), 455-467 (2022).</li><li>Th&#229;lin, 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=Quantification+of+citrullinated+histones:+Development+of+an+improved+assay+to+reliably+quantify+nucleosomal+H3Cit+in+human+plasma.">Quantification of citrullinated histones: Development of an improved assay to reliably quantify nucleosomal H3Cit in human plasma.</a> Journal of Thrombosis and Haemostasis. 18 (10), 2732-2743 (2020).</li><li>Yamashita, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heat-induced+antigen+retrieval:+Mechanisms+and+application+to+histochemistry.">Heat-induced antigen retrieval: Mechanisms and application to histochemistry.</a> Progress in Histochemistry and Cytochemistry. 41 (3), 141-200 (2007).</li><li>Jamur, M. C., Oliver, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Permeabilization+of+cell+membranes.">Permeabilization of cell membranes.</a> Methods in Molecular Biology. 588, 63-66 (2010).</li><li>Smyth, L., 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-vascular+interactions+drive+myeloperoxidase+accumulation+in+the+brain+in+Alzheimer's+disease.">Neutrophil-vascular interactions drive myeloperoxidase accumulation in the brain in Alzheimer's disease.</a> Acta Neuropathologica Communications. 10 (1), 38 (2022).</li><li>Whittington, N. C., Wray, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Suppression+of+red+blood+cell+autofluorescence+for+immunocytochemistry+on+fixed+embryonic+mouse+tissue.">Suppression of red blood cell autofluorescence for immunocytochemistry on fixed embryonic mouse tissue.</a> Current Protocols in Neuroscience. 81, 2-22 (2017).</li><li>Nazir, S., Charlesworth, R. P. G., Moens, P., Gerber, P. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+autofluorescence+quenching+techniques+on+formalin-fixed+chicken+tissues.">Evaluation of autofluorescence quenching techniques on formalin-fixed chicken tissues.</a> Journal of Immunological Methods. 496, 113097 (2021).</li><li>Schneider, 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=IVIG+regulates+the+survival+of+human+but+not+mouse+neutrophils.">IVIG regulates the survival of human but not mouse neutrophils.</a> Scientific Reports. 7 (1), 1296 (2017).</li><li>Risso, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Leukocyte+antimicrobial+peptides:+Multifunctional+effector+molecules+of+innate+immunity.">Leukocyte antimicrobial peptides: Multifunctional effector molecules of innate immunity.</a> Journal of Leukocyte Biology. 68 (6), 785-792 (2000).</li></ol>

In this work, we aimed to adapt and optimize the existing protocols for imaging NETs to more tissue types, beginning with the actual staining process. The first critical step for this method is the selection of the most suitable antibodies. For NE, we tried an NE antibody from a mouse host on human tissue, which showed no reliable staining compared to NE from a rabbit host. Furthermore, Th&#229;lin et al. proposed H3cit (R8) as a more specific antibody for extracellular staining. We compared this antibody with the widely...

An erratum was issued for:&#160;<a href="https://www.jove.com/t/65272">Immunofluorescence Imaging of Neutrophil Extracellular Traps in Human and Mouse Tissues</a>. The Authors section was updated from:
Lavinia Sch&#246;enfeld1 
Birgit Appl1 
Laia Pagerols-Raluy1 
Annika Heuer3 
Konrad Reinshagen1 
Michael Boettcher1,2 
1Department of Pediatric Surgery, University Medical Center Hamburg-Eppendorf, University of Hamburg 
2Department of Pediatric Surgery, University Medical Center Mannheim, University of Heidelberg 
3Division of Spine Surgery, Department of Trauma and Orthopedic Surgery, University Medical Center Hamburg-Eppendorf (UKE)
to:
Lavinia Schoenfeld1 
Birgit Appl1 
Laia Pagerols-Raluy1 
Annika Heuer3 
Konrad Reinshagen1 
Michael Boettcher1,2 
1Department of Pediatric Surgery, University Medical Center Hamburg-Eppendorf, University of Hamburg 
2Department of Pediatric Surgery, University Medical Center Mannheim, University of Heidelberg 
3Division of Spine Surgery, Department of Trauma and Orthopedic Surgery, University Medical Center Hamburg-Eppendorf (UKE)

An erratum was issued for:&#160;<a href="https://www.jove.com/t/65272">Immunofluorescence Imaging of Neutrophil Extracellular Traps in Human and Mouse Tissues</a>. The Authors section was updated.

Erratum: Immunofluorescence Imaging of Neutrophil Extracellular Traps in Human and Mouse Tissues

Neutrophil extracellular traps (NETs) were first visualized by Brinkmann et al. as a pathway of cellular death different from apoptosis and necrosis in 20041. In this pathway, neutrophils release their decondensed chromatin into the extracellular space to form large web-like structures covered in antimicrobial proteins that were formerly stored in the granules or cytosol. These antimicrobial proteins include neutrophil elastase (NE), myeloperoxidase (MPO), and citrullinated histone H3 (H3cit), which are commonly used for indirect immunofluorescence detection of NETs2. This method not only identifies the quantitative presence of these proteins; indeed, it has the advantage of specifically detecting NET-like structures. In the NETs, the mentioned proteins co-localize with extracellular DNA, which can be detected by an overlap of the fluorescence signals of each stained protein and the extracellular DNA. In contrast to the overlapping signals due to extracellular DNA and protein co-localization in NETs, intact neutrophils show no co-localization. Here, the NET components are usually stored separately in the granules, nuclei, and cytosol3.
Since their first discovery, it has been shown that NETs play a central role in numerous diseases, particularly those involving inflammation. NETs show antimicrobial functions during infection through trapping and killing extracellular pathogens in blood and tissue4,5. However, NETs have also been connected to autoimmune diseases and hyperinflammatory responses, like systemic lupus erythematosus, rheumatic arthritis, and allergic asthma6,7,8. NETs promote vaso-occlusion and inflammation in atherosclerosis, platelet adhesion, and are speculated to play a role in metastatic cancer9,10,11. Nevertheless, they are thought to have anti-inflammatory properties by reducing proinflammatory cytokine levels12. While NETs are gaining more interest in a broader field of research, a robust NET detection method is fundamental for future research.
Even though the visualization of NETs in different tissue using immunofluorescence imaging is complex and requires customization, apart from electron microscopy, it is currently one of the most renowned methods for visualizing the interactions between NETs and cells and is predominantly used in formalin-fixed paraffin-embedded tissues (FFPE)13,14. However, comparing NET imaging is difficult, as different laboratories use their own customized protocols. These protocols differ in their use of antibodies, antigen retrieval, or permeabilization method and are often optimized for a specific type of tissue3,13,15,16,17,18,19,20,21,22,23,24,25,26,27.
After Brinkmann et al. published the first methodic study using immunofluorescent visualization of NETs in FFPE tissue, we wanted to optimize this protocol for a wider variety of tissues and species15. Additionally, to establish a broadly applicable immunofluorescence protocol, we tested different modified protocols from studies that used immunofluorescence methods in FFPE tissue to detect NETs3,13,16,17,18,19,20,21,22,23,24,25,26,27. Furthermore, we tried a new H3cit antibody for more specific extracellular staining28. We hypothesize that by systematically adapting current staining protocols to different species and tissue, in vitro imaging can be improved, resulting in a better representation of the interaction between neutrophils and NETs both locally and systemically.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>&#160;&#160;</td>
			<td>&#160;&#160;</td>
			<td>&#160;&#160;</td>
			<td>Dilution</td>
		</tr>
		<tr>
			<td>Anti-Neutrophil Elastase antibody 100&#181;g</td>
			<td>abcam</td>
			<td>Ab 68672&#160;</td>
			<td>1:100</td>
		</tr>
		<tr>
			<td>Anti-Histone H3 (citrulline R2 + R8 + R17) antibody&#160; 100&#181;g</td>
			<td>abcam</td>
			<td>Ab 5103</td>
			<td>1:50</td>
		</tr>
		<tr>
			<td>Anti-Myeloperoxidase antibody [2C7] anti-human 100 &#181;g</td>
			<td>abcam</td>
			<td>Ab 25989</td>
			<td>1:50</td>
		</tr>
		<tr>
			<td>Anti-Myeloperoxidase antibody [2D4] anti-mouse 50 &#181;g</td>
			<td>abcam</td>
			<td>Ab 90810</td>
			<td>1:50</td>
		</tr>
		<tr>
			<td>Axiovision Microscopy Software&#160;</td>
			<td>Zeiss</td>
			<td>4.8.2.</td>
			<td></td>
		</tr>
		<tr>
			<td>Blocking solution with donkey serum (READY TO USE) 50ml</td>
			<td>GeneTex</td>
			<td>&#160;GTX30972</td>
			<td></td>
		</tr>
		<tr>
			<td>Coverslips</td>
			<td>Marienfeld</td>
			<td>0101202</td>
			<td></td>
		</tr>
		<tr>
			<td>Dako Target Retrieval Solution Citrate pH6 (x10)</td>
			<td>Dako</td>
			<td>S2369</td>
			<td></td>
		</tr>
		<tr>
			<td>DAPI 25 mg</td>
			<td>Roth</td>
			<td>6335.1</td>
			<td>1:25000</td>
		</tr>
		<tr>
			<td>DCS antibody dilution 500 mL</td>
			<td>DCS diagnostics</td>
			<td>DCS AL120R500</td>
			<td></td>
		</tr>
		<tr>
			<td>Donkey ant goat Cy3</td>
			<td>JacksonImmunoResearch</td>
			<td>705-165-147</td>
			<td>1:200</td>
		</tr>
		<tr>
			<td>Donkey anti rabbit AF647</td>
			<td>JacksonImmunoResearch</td>
			<td>711-605-152</td>
			<td>1:200</td>
		</tr>
		<tr>
			<td>Donkey anti rabbit Cy3</td>
			<td>JacksonImmunoResearch</td>
			<td>711-165-152</td>
			<td>1:200</td>
		</tr>
		<tr>
			<td>Fluoromount-G Mounting Medium</td>
			<td>Invitrogen</td>
			<td>00-4958-02</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass slide rack</td>
			<td>Roth</td>
			<td>H552.1</td>
			<td></td>
		</tr>
		<tr>
			<td>Human/Mouse MPO Antibody</td>
			<td>R&#38;D Systems</td>
			<td>AF 3667&#160;</td>
			<td>1:20</td>
		</tr>
		<tr>
			<td>Hydrophobic Pen</td>
			<td>KISKER</td>
			<td>MKP-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Isokontrolle Rabbit IgG Polyclonal 5mg</td>
			<td>abcam</td>
			<td>Ab 37415</td>
			<td>1:2000 and 1:250</td>
		</tr>
		<tr>
			<td>MaxBlock Autofluorescence Reducing Reagent Kit (RUO) 100 ml</td>
			<td>Maxvision</td>
			<td>MB-L</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscopy camera</td>
			<td>Zeiss</td>
			<td>AxioCamHR3</td>
			<td></td>
		</tr>
		<tr>
			<td>Microwave</td>
			<td>Bosch</td>
			<td>HMT84M421</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse IgG1 negative control</td>
			<td>Dako</td>
			<td>X0931 Aglient</td>
			<td>1:50 and 1:5</td>
		</tr>
		<tr>
			<td>Normal Goat IgG Control</td>
			<td>R&#38;D Systems</td>
			<td>AB-108-C&#160;</td>
			<td>1:100</td>
		</tr>
		<tr>
			<td>PBS Phosphate buffered saline (10x)</td>
			<td>Sigma-Aldrich</td>
			<td>P-3813</td>
			<td></td>
		</tr>
		<tr>
			<td>PMP staining jar</td>
			<td>Roth</td>
			<td>2292.2</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant Anti-Histone H3 (citrulline R8) antibody 100&#181;g</td>
			<td>abcam</td>
			<td>Ab 219406</td>
			<td>1:100</td>
		</tr>
		<tr>
			<td>Recombinant Rabbit IgG, monoclonal [EPR25A] - Isotype Control 200&#181;g</td>
			<td>abcam</td>
			<td>Ab 172730</td>
			<td>1:300</td>
		</tr>
		<tr>
			<td>ROTI Histol</td>
			<td>Roth</td>
			<td>&#160;6640</td>
			<td></td>
		</tr>
		<tr>
			<td>SuperFrost Plus slides</td>
			<td>R. Langenbrinck</td>
			<td>03-0060</td>
			<td></td>
		</tr>
		<tr>
			<td>TBS Tris buffered saline (x10)</td>
			<td>Sigma-Aldrich</td>
			<td>T1503</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma-Aldrich</td>
			<td>T8787</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween 20</td>
			<td>Sigma-Aldrich</td>
			<td>P9416</td>
			<td></td>
		</tr>
		<tr>
			<td>Water bath</td>
			<td>Memmert</td>
			<td>830476</td>
			<td></td>
		</tr>
		<tr>
			<td>Water bath rice cooker</td>
			<td>reishunger</td>
			<td>RCP-30</td>
			<td></td>
		</tr>
		<tr>
			<td>Wet chamber</td>
			<td>Weckert Labortechnik</td>
			<td>600016</td>
			<td></td>
		</tr>
		<tr>
			<td>Zeiss Widefield microscope</td>
			<td>Zeiss</td>
			<td>Axiovert 200M</td>
			<td></td>
		</tr>
	</tbody>
</table>

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 

Immunofluorescence Imaging of Neutrophil Extracellular Traps in Human and Mouse Tissues

Among antibody selection for tissue imaging, the fixation process poses a challenge by epitope masking. Therefore, customized retriever step is required to expose these antigens for antibody binding. Additionally, tissue inherent autofluorescence can cause difficulties through to a high background staining.However, the use of different approaches in the protocols in the literature hinders a standardized comparison between the images. Our study aims to address the demand for standardized procedures and assist the researcher in overcoming challenges during the imaging process. We established a versatile imaging protocol applicable to different tissues by comparing various different protocols.So our work provides guiding and troubleshooting tips from antibody usage to sample mounting, highlighting the potential pitfalls. Our findings advance research by introducing a new primary antibody for citrullinated hisone three, and an autofluorescent reducing agent to minimize background staining. Furthermore, for successful imaging, we emphasize the careful handling of samples and the importance of maintaining a constant high temperature for antigen retrieval.

Before starting our protocol optimization, we identified key steps for successful staining by searching PubMed for studies that used FFPE tissue for the immunostaining of NETs and compared their protocols. The most promising protocol differences were identified as the key steps for the protocol optimization, while steps that mostly corresponded to each other were not changed (Table 1).
Table 1: PubMed Research for FFPE immunostaining of NETs. This table shows ...

Watch this Scientific Journal Video about Neutrophil Extracellular Traps Imaging in Human and Mouse Tissues at JoVE.com

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 ...

immunofluorescence-imaging-neutrophil-extracellular-traps-human-mouse