Name: methods to study lipid alterations in neutrophils and the subsequent formation of neutrophil extracellular traps
Uploaded: 2017-03-29T13:00:00
Description: Watch this Scientific Journal Video about Methods to Study Lipid Alterations in Neutrophils and the Subsequent Formation of Neutrophil Extracellular Traps at JoVE.com

This work was supported by a fellowship of the Akademie f&#252;r Tiergesundheit (AfT) and a fellowship from the PhD program, "Animal and Zoonotic Infections," of the University of Veterinary Medicine, Hannover, Germany, provided to Ariane Neumann.

The collection of the peripheral blood in this protocol was approved by the local human research ethics commission. All human subjects provided their written informed consent.
1. Isolation of Human Blood-derived Neutrophils by Density Gradient Centrifugation
<ol>
	<li>Isolation of human blood-derived neutrophils
	<ol>
		<li>Layer ~20 mL of blood onto 20 mL of sodium diatrizoate/dextran solution near a flame and without mixing.</li>
		<li>Centrifuge for 30 min at 470 x g with...

<ol>
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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=Statins+Enhance+Formation+of+Phagocyte+Extracellular+Traps.">Statins Enhance Formation of Phagocyte Extracellular Traps.</a> Cell Host Microbe. 8 (5), 445-454 (2010).</li><li>Simons, K., Vaz, W. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Model+systems,+lipid+rafts,+and+cell+membranes.">Model systems, lipid rafts, and cell membranes.</a> Annu Rev Biophys Biomol Struct. 33, 269-295 (2004).</li><li>Bligh, E. G., Dyer, W. 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N., Bragagnolo, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HPLC+separation+and+determination+of+12+cholesterol+oxidation+products+in+fish:+comparative+study+of+RI,+UV,+and+APCI-MS+detectors.">HPLC separation and determination of 12 cholesterol oxidation products in fish: comparative study of RI, UV, and APCI-MS detectors.</a> J Agric Food Chem. 54 (12), 4107-4113 (2006).</li><li>Hubicka, U., Krzek, J., Woltynska, H., Stachacz, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+identification+and+quantitative+determination+of+selected+aminoglycoside+antibiotics+by+thin-layer+chromatography+and+densitometry.">Simultaneous identification and quantitative determination of selected aminoglycoside antibiotics by thin-layer chromatography and densitometry.</a> J AOAC Int. 92 (4), 1068-1075 (2009).</li><li>Maalouf, K., 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+modified+lipid+composition+in+Fabry+disease+leads+to+an+intracellular+block+of+the+detergent-resistant+membrane-associated+dipeptidyl+peptidase+IV.">A modified lipid composition in Fabry disease leads to an intracellular block of the detergent-resistant membrane-associated dipeptidyl peptidase IV.</a> J Inherit Metab Dis. 33 (4), 445-449 (2010).</li><li>Correia, 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=Helicobacter+pylori's+cholesterol+uptake+impacts+resistance+to+docosahexaenoic+acid.">Helicobacter pylori's cholesterol uptake impacts resistance to docosahexaenoic acid.</a> Int J Med Microbiol. 304 (3-4), 314-320 (2014).</li><li>Gorudko, I. 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=Lectin-induced+activation+of+plasma+membrane+NADPH+oxidase+in+cholesterol-depleted+human+neutrophils.">Lectin-induced activation of plasma membrane NADPH oxidase in cholesterol-depleted human neutrophils.</a> Arch Biochem Biophys. 516 (2), 173-181 (2011).</li><li>Masoud, R., Bizouarn, T., Hou&#233;e-Levin, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cholesterol:+A+modulator+of+the+phagocyte+NADPH+oxidase+activity+-+A+cell-free+study.">Cholesterol: A modulator of the phagocyte NADPH oxidase activity - A cell-free study.</a> Redox Biol. 3, 16-24 (2014).</li><li>Knight, J. 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=Peptidylarginine+deiminase+inhibition+is+immunomodulatory+and+vasculoprotective+in+murine+lupus.">Peptidylarginine deiminase inhibition is immunomodulatory and vasculoprotective in murine lupus.</a> J Clin Invest. 123 (7), 2981-2993 (2013).</li><li>Reichel, 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=Harbour+seal+(Phoca+vitulina)+PMN+and+monocytes+release+extracellular+traps+to+capture+the+apicomplexan+parasite+Toxoplasma+gondii.">Harbour seal (Phoca vitulina) PMN and monocytes release extracellular traps to capture the apicomplexan parasite Toxoplasma gondii.</a> Dev Comp Immunol. 50 (2), 106-115 (2015).</li><li>Chuammitri, P., 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=Chicken+heterophil+extracellular+traps+(HETs):+novel+defense+mechanism+of+chicken+heterophils.">Chicken heterophil extracellular traps (HETs): novel defense mechanism of chicken heterophils.</a> Vet Immunol Immunopathol. 129, 126-131 (2009).</li><li>Palic, D., Ostojic, J., Andreasen, C. B., Roth, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fish+cast+NETs:+Neutrophil+extracellular+traps+are+released+from+fish+neutrophils.">Fish cast NETs: Neutrophil extracellular traps are released from fish neutrophils.</a> Dev Comp Immunol. 31 (8), 805-816 (2007).</li><li>Ng, T. H., Chang, S. H., Wu, M. H., Wang, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shrimp+hemocytes+release+extracellular+traps+that+kill+bacteria.">Shrimp hemocytes release extracellular traps that kill bacteria.</a> Dev Comp Immunol. 41 (4), 644-651 (2013).</li><li>Hawes, M. 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=Extracellular+DNA:+the+tip+of+root+defenses?.">Extracellular DNA: the tip of root defenses?.</a> Plant Sci. 180 (6), 741-745 (2011).</li><li>Brinkmann, V., 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=Neutrophil+extracellular+traps:+is+immunity+the+second+function+of+chromatin?.">Neutrophil extracellular traps: is immunity the second function of chromatin?.</a> J Cell Biol. 198 (5), 773-783 (2012).</li><li>Xu, 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=Lipid+raft-associated+&#946;-adducin+is+required+for+PSGL-1-mediated+neutrophil+rolling+on+P-selectin.">Lipid raft-associated &#946;-adducin is required for PSGL-1-mediated neutrophil rolling on P-selectin.</a> J Leukoc Biol. 97 (2), 297-306 (2015).</li><li>Ermert, 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=Mouse+neutrophil+extracellular+traps+in+microbial+infections.">Mouse neutrophil extracellular traps in microbial infections.</a> J Innate Immun. 1 (3), 181-193 (2009).</li><li>Metzler, K. 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The methods described here can be used to analyze specific lipids, such as cholesterol, by HPTLC or HPLC and to investigate the effects of pharmacological lipid alterations on the formation of NETs (see Neumann et al.15).
HPTLC is a relatively cost-effective and simple method to analyze a broad range of lipids in a large number of samples. This method has been used in many research areas, including antibiotic quantification25, lipid stor...

Lipids have been shown to play important roles in cell homeostasis, cell death, host-pathogen interactions, and cytokine release1. Over time, interest for and knowledge on the impact of lipids in host-pathogen interactions or inflammation have increased, and several publications confirm the central role of certain lipids, especially the steroid cholesterol, in cellular responses. Pharmacological treatment with statins, which are used as inhibitors of cholesterol biosynthesis by blocking 3-hydroxy-3-methylglutaryl-coenzym-A-reductase (HMG-CoA-reductase), can act as anti-inflammatory agents by lowering the serum levels of interleukin 6 and C-reactive protein2. Cholesterol- and glycosphingolipid-enriched structures can be used by several pathogens, such as bacteria and viruses, as a gateway into the host3,4,5,6. Sphingolipids (e.g., sphingomyelin) have been shown to be used by pathogens to promote their pathogenicity7. In macrophages, mycobacteria use cholesterol-enriched domains for entering cells; a depletion of cholesterol inhibits mycobacterial uptake8. Furthermore, infection of macrophages with Francisella tularensis, a zoonotic agent responsible for tularemia (also known as rabbit fever)9, led to an infection that was abolished when cholesterol was depleted from the membranes10. Similarly, the invasion of host cells by Escherichia coli via lipid-rich structures was demonstrated to be cholesterol-dependent4. Moreover, Salmonella typhimurium infection experiments of epithelial cells demonstrated that cholesterol is essential for pathogen entry into the cells11. Cholesterol depletion inhibited the uptake of Salmonella11. Furthermore, a recent study by Gilk et al. demonstrated that cholesterol plays an important role in the uptake of Coxiella burnetti12. Additionally, Tuong et al. found that 25-hydroxycholesterol plays a crucial role in phagocytosis by lipopolysaccharide (LPS)-stimulated macrophages13. Phagocytosis was reduced when macrophages were pharmacologically treated to deplete cholesterol14. Thus, cholesterol and other lipids seem to play an important role in infection and inflammation, since their depletion can reduce the risk of invasion from several pathogens10,11,12.
Recently, we were able to show that lipid alterations, especially the depletion of cholesterol from the cell, induce the formation of neutrophil extracellular traps (NETs) in human blood-derived neutrophils15. Since the discovery of NETs in 2004, they have been shown to play critical roles in bacterial entrapment, and thus in hindering the spread of infection16,17. NETs consist of a DNA backbone associated with histones, proteases, and antimicrobial peptides16. The release of the NETs by neutrophils can be induced by invading pathogens18,19 and chemical substances such as phorbol-myristate-acetate (PMA) or statins16,20. However, the detailed cellular mechanisms, and especially the role of lipids in this process, are still not entirely clear. The analysis of lipids can lead to a better understanding of the mechanisms involved in a wide variety of cellular processes and interactions, such as the release of NETs. Cholesterol and sphingomyelin are vital constituents of the cell membrane and lipid microdomains, where they add stability and facilitate the clustering of the proteins involved in protein trafficking and signaling events21. To investigate the mechanistic role of certain lipids, amphiphilic pharmacological agents, such as the cyclic oligosaccharide methyl-&#946;-cyclodextrin (M&#946;CD), can be used to alter the lipid composition of a cell and to reduce cholesterol in vitro15. Here, we present a method to use HPTLC to analyze the lipid composition of neutrophils in response to M&#946;CD. HPLC was used to confirm the level of cholesterol in the neutrophil population. Furthermore, we describe a method to visualize the formation of NETs by immunofluorescence microscopy in human blood-derived neutrophils in response to M&#946;CD.

<table>
	<tbody>
		<tr>
			<td>Neutrophil isolation, NET staining and quantification</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa Flour 633 goat anti-rabbit IgG</td>
			<td>Invitrogen</td>
			<td>A-21070</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-MPO&#945; antibody</td>
			<td>Dako</td>
			<td>A0398</td>
			<td></td>
		</tr>
		<tr>
			<td>BSA</td>
			<td>Sigma-Aldrich</td>
			<td>3912-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Marienfeld-Neubauer improved counting chamber</td>
			<td>Celeromics</td>
			<td>MF-0640010</td>
			<td></td>
		</tr>
		<tr>
			<td>Confocal microscope TCS SP5 AOBS with tandem scanner</td>
			<td>Leica</td>
			<td>DMI6000CS</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#180;s PBS 10X</td>
			<td>Sigma-Aldrich</td>
			<td>P5493-1L</td>
			<td>Dilute 1:10 in water for 1X working solution</td>
		</tr>
		<tr>
			<td>Dy Light 488 conjugated highly cross-absorbed</td>
			<td>Thermo Fisher Scientific</td>
			<td>35503</td>
			<td></td>
		</tr>
		<tr>
			<td>Excel</td>
			<td>Microsoft</td>
			<td>2010</td>
			<td></td>
		</tr>
		<tr>
			<td>DNA/Histone 1 antibody</td>
			<td>Millipore</td>
			<td>MAB3864</td>
			<td></td>
		</tr>
		<tr>
			<td>Image J</td>
			<td>NIH</td>
			<td>1.8</td>
			<td>http://imagej.nih.gov/ij/</td>
		</tr>
		<tr>
			<td>Light microscope</td>
			<td>VWR</td>
			<td>630-1554</td>
			<td></td>
		</tr>
		<tr>
			<td>Methyl-&#946;-cyclodextrin</td>
			<td>Sigma-Aldrich</td>
			<td>C4555-1G</td>
			<td></td>
		</tr>
		<tr>
			<td>PFA</td>
			<td>Carl Roth</td>
			<td>0335.3</td>
			<td>dissolve in water, heat up to 65 &#176;C and add 1N NaOH to clear solution</td>
		</tr>
		<tr>
			<td>PMA</td>
			<td>Sigma-Aldrich</td>
			<td>P8139-1MG</td>
			<td>Stock 16 &#181;M, dissolved in 1X PBS</td>
		</tr>
		<tr>
			<td>Poly-L-lysine</td>
			<td>Sigma-Aldrich</td>
			<td>P4707</td>
			<td></td>
		</tr>
		<tr>
			<td>Polymorphprep</td>
			<td>AXIS-SHIELD</td>
			<td>AN1114683</td>
			<td></td>
		</tr>
		<tr>
			<td>ProLong Gold antifade reagent with DAPI</td>
			<td>Invitrogen</td>
			<td>P7481</td>
			<td></td>
		</tr>
		<tr>
			<td>Quant-iT PicoGreen dsDNA Reagent</td>
			<td>Invitrogen</td>
			<td>P7581</td>
			<td></td>
		</tr>
		<tr>
			<td>RPMI1640</td>
			<td>PAA</td>
			<td>E 15-848</td>
			<td></td>
		</tr>
		<tr>
			<td>HBSS with CaCl and Mg</td>
			<td>Sigma</td>
			<td>H6648</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma-Aldrich</td>
			<td>T8787-50ml</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypanblue</td>
			<td>Invitrogen</td>
			<td>15250-061</td>
			<td>0.4% solution</td>
		</tr>
		<tr>
			<td>Water</td>
			<td>Carl Roth</td>
			<td>3255.1</td>
			<td>endotoxin-free</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number&#160;</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Lipid isolation and analysis</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1-propanol</td>
			<td>Sigma-Aldrich</td>
			<td>33538</td>
			<td></td>
		</tr>
		<tr>
			<td>10 &#181;l syringe</td>
			<td>Hamilton</td>
			<td>701 NR 10 &#181;l</td>
			<td></td>
		</tr>
		<tr>
			<td>Diethyl ether</td>
			<td>Sigma-Aldrich</td>
			<td>346136</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyl acetate</td>
			<td>Carl Roth</td>
			<td>7336.2</td>
			<td></td>
		</tr>
		<tr>
			<td>Canullla 26G</td>
			<td>Braun</td>
			<td>4657683</td>
			<td></td>
		</tr>
		<tr>
			<td>Copper(II)sulphatepentahydrate</td>
			<td>Merck</td>
			<td>1027805000</td>
			<td></td>
		</tr>
		<tr>
			<td>Chloroform</td>
			<td>Carl Roth</td>
			<td>7331.1</td>
			<td></td>
		</tr>
		<tr>
			<td>CP ATLAS software</td>
			<td>Lazarsoftware</td>
			<td>2.0</td>
			<td></td>
		</tr>
		<tr>
			<td>Chromolith HighResolution RP-18 endcapped 100-4.6 mm column</td>
			<td>Merck</td>
			<td>152022</td>
			<td></td>
		</tr>
		<tr>
			<td>High Performance Liquid Chromatograph Chromaster</td>
			<td>Hitachi</td>
			<td>HITA 892-0080-30Y</td>
			<td>Paramaters are dependent on individual HPLC machine</td>
		</tr>
		<tr>
			<td>HPLC UV Detector</td>
			<td>Hitachi</td>
			<td>5410</td>
			<td></td>
		</tr>
		<tr>
			<td>HPLC Column Oven</td>
			<td>Hitachi</td>
			<td>5310</td>
			<td></td>
		</tr>
		<tr>
			<td>HPLC Auto Sampler</td>
			<td>Hitachi</td>
			<td>5260</td>
			<td></td>
		</tr>
		<tr>
			<td>HPLC Pump</td>
			<td>Hitachi</td>
			<td>5160</td>
			<td></td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Carl Roth</td>
			<td>7342.1</td>
			<td></td>
		</tr>
		<tr>
			<td>n-Hexane</td>
			<td>Carl Roth</td>
			<td>7339.1</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphoric acid</td>
			<td>Sigma-Aldrich</td>
			<td>30417</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium chloride</td>
			<td>Merck</td>
			<td>49,361,000</td>
			<td></td>
		</tr>
		<tr>
			<td>Potters</td>
			<td>LAT Garbsen</td>
			<td>5 ml</td>
			<td></td>
		</tr>
		<tr>
			<td>SDS</td>
			<td>Carl Roth</td>
			<td>CN30.3</td>
			<td></td>
		</tr>
		<tr>
			<td>HPTLC silica gel 60</td>
			<td>Merck</td>
			<td>105553</td>
			<td></td>
		</tr>
		<tr>
			<td>Vacufuge plus basic device</td>
			<td>Eppendorf</td>
			<td>22820001</td>
			<td></td>
		</tr>
		<tr>
			<td>Corning Costar cell culture 48-well plate, flat bottom</td>
			<td>Sigma</td>
			<td>CLS3548</td>
			<td></td>
		</tr>
		<tr>
			<td>Coverslip</td>
			<td>Thermo Fisher Scientific</td>
			<td>1198882</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass slide</td>
			<td>Carl Roth</td>
			<td>1879</td>
			<td></td>
		</tr>
		<tr>
			<td>BD Tuberculin Syringe Only 1 ml</td>
			<td>BD Bioscience</td>
			<td>309659</td>
			<td></td>
		</tr>
	</tbody>
</table>

methods to study lipid alterations in neutrophils and the subsequent formation of neutrophil extracellular traps

Lipid analysis performed by high performance thin layer chromatography (HPTLC) is a relatively simple, cost-effective method of analyzing a broad range of lipids. The function of lipids (e.g., in host-pathogen interactions or host entry) has been reported to play a crucial role in cellular processes. Here, we show a method to determine lipid composition, with a focus on the cholesterol level of primary blood-derived neutrophils, by HPTLC in comparison to high performance liquid chromatography (HPLC). The aim was to investigate the role of lipid/cholesterol alterations in the formation of neutrophil extracellular traps (NETs). NET release is known as a host defense mechanism to prevent pathogens from spreading within the host. Therefore, blood-derived human neutrophils were treated with methyl-&#946;-cyclodextrin (M&#946;CD) to induce lipid alterations in the cells. Using HPTLC and HPLC, we have shown that M&#946;CD treatment of the cells leads to lipid alterations associated with a significant reduction in the cholesterol content of the cell. At the same time, M&#946;CD treatment of the neutrophils led to the formation of NETs, as shown by immunofluorescence microscopy. In summary, here we present a detailed method to study lipid alterations in neutrophils and the formation of NETs.

Human blood-derived neutrophils were isolated by density gradient centrifugation (Figure 2). To investigate the effect of lipid alterations on neutrophils, the cells were treated with 10 mM M&#946;CD, which depletes cholesterol from the cell. Subsequently, the lipids were isolated from the samples by Bligh and Dyer (Figure 1, left panel), as described by Brogden et al.23. The prepared lipid samples were loaded onto silica ...

Watch this Scientific Journal Video about Methods to Study Lipid Alterations in Neutrophils and the Subsequent Formation of Neutrophil Extracellular Traps at JoVE.com

Methods to Study Lipid Alterations in Neutrophils and the Subsequent Formation of Neutrophil Extracellular Traps

Lipids are known to play an important role in cellular functions. Here, we describe a method to determine the lipid composition of neutrophils, with emphasis on the cholesterol level, by using both HPTLC and HPLC to gain a better understanding of the underlying mechanisms of neutrophil extracellular trap formation.

Lipid analysis performed by high performance thin layer chromatography (HPTLC) is a relatively simple, cost-effective method of analyzing a broad range of ...

The overall goal of this method is to investigate changes in the lipid composition of neutrophils during the release of neutrophil extracellular traps by using thin layer chromatography and HPLC. This method can be used to gain more detailed information about the mechanisms that are involved in the formation of neutrophil extracellular traps, or shortly named, NET formation. The main advantage of this procedure is that it provides information on the role of lipids in the general function of neutrophils by utilizing an easy to follow protocol.The isolation of human blood-derived cells will be demonstrated by a former PhD student of our lab, Ariane Neumann. And she will be assisted by Friederike Reuner. The preparation of cells for lipid analysis will be demonstrated by Graham Brogden a post-doc in my laboratory and Diab Husein, a master student in the biochemistry program.To isolate human blood-derived neutrophils layer approximately 20 mL of blood onto 20 mL of sodium diatrizoate/dextran solution near a flame, without mixing. Centrifuge for 30 minutes at 470 times g without braking. It is critical not to mix the blood phase with the density grade in solution.After the centrifugation step plus mononuclear cells need to be carefully removed to avoid contamination or unspecific activation of cells. Remove the mononuclear cells and the yellowish plasma layer. Transfer the polymorphonuclear cell, or PMN phase, into a new 50 mL tube, and fill it up to 50 mL with 1X phosphate buffered saline.Centrifuge the sample for 10 minutes at 470 times g with braking. Then, remove the supernatant and re-suspend the pellet in 5 mL of sterile water for five seconds to lyse the erythrocytes. Immediately fill up the tube to 50 mL with 1X PBS and centrifuge the sample.Upon removing the supernatant, the pellet should be white. If it is still red, repeat these steps. Then re-suspend the pellet in 1000 microliters of Roswell Park Memorial Institute, or RPMI medium.Count the cell number using Trypan Blue staining and a hemocytometer under a light microscope. Prepare a cell suspension in RPMI at a concentration of two million cells per mL. Approximately 25 million neutrophils can be harvested from 20 mL of blood.To pharmacologically treat neutrophils for lipid analysis use 15 million of the prepared cells. Incubate the samples in the reaction tubes for two hours at 37 degrees Celsius and 5%carbon dioxide. Following centrifugation of the samples remove the supernatant, and re-suspend the cell pellet in 300 microliters of HBSS.After centrifuging the sample again using the same parameters, re-suspend the cell pellet in 1 mL of a 1:1 chloroform:methanol solution. Then homogenize the re-suspended pellet with a 26 gauge canula by pushing the sample in and out of a 1 mL syringe 10 times. To isolate the lipids from the human peripheral blood-derived neutrophils, take the prepared neutrophils and place them on ice.Pipette the neutrophils to a 15 mL screw-cap glass tube with a PTFE seal, and homogenize them by shaking for one minute. Then add 2 mL of methanol followed one minute later by 1 mL of chloroform. After shaking for another one minute, rotate the glass tubes at room temperature and 50 rpm for 30 minutes.Next, pellet the protein fraction by centrifuging the solution at 7 degrees celsius and 1, 952 times g for 10 minutes. Carefully decant the supernatant into a new 15 mL glass screw-cap tube, leaving the protein-containing pellet behind. Store the pellet at 20 degrees celsius for future quantification.Add 1 mL of chloroform and wait one minute. Then, add 1 mL of double distilled water and invert the glass screw-cap tube with the sample for 30 seconds. After centrifuging the sample as before, remove and discard the upper phase down to, but not including the cloudy layer.Dry the samples in a vacuum concentrator at 60 degrees celsius and store them at 20 degrees celsius until required. To begin, fill up to 5 mL of each solution in the corresponding glass chamber. Add any kind of filter paper to increase the running speed in each chamber.Pre-incubate a 20x10cm HPTLC silica gel 60 glass plate in the first running solution. Once the running solution reaches the top of the plate dry it for 10 minutes at 110 degrees celsius. Dissolve the lipid pellet, previously obtained after drying with a vacuum concentrator, in the desired volume of 1:1 chloroform:methanol solution, and incubate for 15 minutes at 37 degrees celsius to dissolve.Next use a ruler and a soft pencil to mark the loading spots for the desired number of samples plus at least one standard. Mark the running distance at approximately 4 cm for the first running solution and at approximately 6 cm for the second running solution. To load the samples, wash the 10 microliter syringe three times in 1:1 chloroform:methanol prior to loading each new sample.Load 10 microliters of each sample drop-wise trying to concentrate the sample on as small an area as possible. Place the plate vertically into the first chamber with running solution one. Ensure that the plate is parallel to the wall of the glass chamber to achieve a uniform migration speed.Take care that the plates are placed parallel to the back wall of the glass chambers and that the solvent fronts do not run too far to ensure that the lipids are efficiently separated. Once the solvent line has reached the first mark, remove the plate, dry it, and place it in the second solution. Repeat similar steps for the second and for the third running solutions.Leave the plate in the solution until the solvent front reaches the top of the plate. Then, remove the plate, and dry it at room temperature for one minute. Place the plate in the copper sulfate solution for seven seconds.After drying the plate thoroughly, bake it in an oven for seven minutes at 170 degrees celsius. Remove the plate from the oven and allow it to cool. To perform HPLC, attach the column to a guard cartridge on the instrument, and heat it to 32 degrees celsius.Use methanol as the mobile phase at a flow rate of 1 mL per minute and 65 bar. Set the UV detector to measure at 202 nanometers to quantify the amount of cholesterol in each sample. Wash the HPLC machine thoroughly prior to analyzing the samples and establish a cholesterol standard curve as described in the text protocol.Finally, re-suspend the samples in 500 microliters of 1:1 chloroform:methanol in amber colored 1.5 mL glass bottles with screw top red PTFE/white silicone lids before loading them on the HPLC instrument. Shown here is the lipid profile of neutrophils on an HPTLC plate. Lipids can be identified by comparing migration distances to the standard.Also shown is an HPLC chromatogram showing two large peaks. The first peak just before two minutes is chloroform. The second large peak at five minutes is cholesterol.Shown here are cholesterol standard curves determined by HPLC and by HPTLC. The standard curve obtained by HPLC is linear over a broader concentration range as compared to the HPTLC standard curve. After watching this video you should have a good understanding of how to isolate human blood-derived neutrophils and subsequently analyze their lipid composition.While attempting this procedure it is important to remember to wear nitrile gloves to protect your hands against hazardous chloroform:methanol exposure and also to work under a fume hood. Future experiments will provide further information about the mechanisms involved in NET formation and general neutrophil functions which are still not fully understood. Don't forget that working with primary human blood-derived cells requires ethical permission as well as appropriate safety precautions such as working in a respective bio-safety lab to avoid risk exposure to human pathogens.Finally the aim of our study is to find new therapeutic targets against an infection based on the innate immune system, and especially the lipid composition is very interesting for us since it will help us to understand why the neutrophil is acting antimicrobial against an infection.

methods-to-study-lipid-alterations-neutrophils-subsequent-formation

Research

JoVE Journal

Immunology and Infection

Neutrophil Extracellular Traps: How to Generate and Visualize Them

Neutrophil granulocytes are the most abundant group of leukocytes in the peripheral blood. As professional phagocytes, they engulf bacteria and kill them intracellularly when their antimicrobial granules fuse with the phagosome. We found that neutrophils have an additional way of killing microorganisms: upon activation, they release granule proteins and chromatin that together form extracellular fibers that bind pathogens. These novel structures, or Neutrophil Extracellular Traps (NETs), degrade virulence factors and kill bacteria1, fungi2 and parasites3. The structural backbone of NETs is DNA, and they are quickly degraded in the presence of DNases. Thus, bacteria expressing DNases are more virulent4. Using correlative microscopy combining TEM, SEM, immunofluorescence and live cell imaging techniques, we could show that upon stimulation, the nuclei of neutrophils lose their shape and the eu- and heterochromatin homogenize. Later, the nuclear envelope and the granule membranes disintegrate allowing the mixing of NET components. Finally, the NETs are released as the cell membrane breaks. This cell death program (NETosis) is distinct from apoptosis and necrosis and depends on the generation of Reactive Oxygen Species by NADPH oxidase5. 
Neutrophil extracellular traps are abundant at sites of acute inflammation. NETs appear to be a form of innate immune response that bind microorganisms, prevent them from spreading, and ensure a high local concentration of antimicrobial agents to degrade virulence factors and kill pathogens thus allowing neutrophils to fulfill their antimicrobial function even beyond their life span. There is increasing evidence, however, that NETs are also involved in diseases that range from auto-immune syndromes to infertility6.
We describe methods to isolate Neutrophil Granulocytes from peripheral human blood7 and stimulate them to form NETs. Also we include protocols to visualize the NETs in light and electron microscopy.

Neutrophil Extracellular Traps (NETs) are an important innate immune mechanism to fight pathogenic bacteria, fungi and parasites. Here we describe methods to isolate neutrophil granulocytes from human blood and to activate them to form NETs. We present preparation techniques to visualize NETs in light and electron microscopy.

Neutrophil granulocytes are the most abundant group of leukocytes in the peripheral blood. As professional phagocytes, they engulf bacteria and kill them ...

Simplified Human Neutrophil Extracellular Traps (NETs) Isolation and Handling

Neutrophil Extracellular Traps (NETs) have been recently identified as part of the neutrophil&#8217;s antimicrobial armamentarium. Apart from their role in fighting infections, recent research has demonstrated that they may be involved in many other disease processes, including cancer progression. Isolating purified NETs is a crucial element to allow the study of these functions.
In this video, we demonstrate a simplified method of cell free NET isolation from human whole blood using readily available reagents. Isolated NETs can then be used for immunofluorescence staining, blotting or various functional assays. This enables an assessment of their biologic properties in the absence of the potential confounding effects of neutrophils themselves.
A density gradient separation technique is employed to isolate neutrophils from healthy donor whole blood. Isolated neutrophils are then stimulated by phorbol 12-myristate 13-acetate (PMA) to induce NETosis. Activated neutrophils are then discarded, and a cell-free NET stock is obtained.
We then demonstrate how isolated NETs can be used in an adhesion assay with A549 human lung cancer cells. The NET stock is used to coat the wells of a 96 well cell culture plate O/N, and after ensuring an adequate NET monolayer formation on the bottom of the wells, CFSE labeled A549 cells are added. Adherent cells are quantified using a Nikon TE300 fluorescent microscope. In some wells, 1000U DNAse1 is added 10 min before counting to degrade NETs

Simplified Human Neutrophil Extracellular Traps NETs Isolation and Handling

In the following protocol, we describe a very simple way to isolate Neutrophil Extracellular traps (NETs) from human whole blood using readily available reagents. We then demonstrate how the isolated NETs can be used in an in vitro adhesion assay with cancer cells.

Neutrophil Extracellular Traps (NETs) have been recently identified as part of the neutrophil&#8217;s antimicrobial armamentarium. Apart from their role ...

High Throughput Measurement of Extracellular DNA Release and Quantitative NET Formation in Human Neutrophils In Vitro

Neutrophil granulocytes are the most abundant leukocytes in the human blood. Neutrophils are the first to arrive at the site of infection. Neutrophils developed several antimicrobial mechanisms including phagocytosis, degranulation and formation of neutrophil extracellular traps (NETs). NETs consist of a DNA scaffold decorated with histones and several granule markers including myeloperoxidase (MPO) and human neutrophil elastase (HNE). NET release is an active process involving characteristic morphological changes of neutrophils leading to expulsion of their DNA into the extracellular space. NETs are essential to fight microbes, but uncontrolled release of NETs has been associated with several disorders. To learn more about the clinical relevance and the mechanism of NET formation, there is a need to have reliable tools capable of NET quantitation. 
Here three methods are presented that can assess NET release from human neutrophils in vitro. The first one is a high throughput assay to measure extracellular DNA release from human neutrophils using a membrane impermeable DNA-binding dye. In addition, two other methods are described capable of quantitating NET formation by measuring levels of NET-specific MPO-DNA and HNE-DNA complexes. These microplate-based methods in combination provide great tools to efficiently study the mechanism and regulation of NET formation of human neutrophils.

High Throughput Measurement of Extracellular DNA Release and Quantitative NET Formation in Human Neutrophils In Vitro

High throughput assays are presented that in combination provide excellent tools to quantitate NET release from human neutrophils.

Neutrophil granulocytes are the most abundant leukocytes in the human blood. Neutrophils are the first to arrive at the site of infection. Neutrophils ...

In Vitro Canine Neutrophil Extracellular Trap Formation: Dynamic and Quantitative Analysis by Fluorescence Microscopy

In response to invading pathogens, neutrophils release neutrophil extracellular traps (NETs), which are extracellular networks of DNA decorated with histones and antimicrobial proteins. Excessive NET formation (NETosis) and citH3 release during sepsis is associated with multiple organ dysfunction and mortality in mice and humans but its implications in dogs are unknown. Herein, we describe a technique to isolate canine neutrophils from whole blood for observation and quantification of NETosis. Leukocyte-rich plasma, generated by dextran sedimentation, is separated by commercially available density gradient separation media and granulocytes collected for cell count and viability testing. To observe real-time NETosis in live neutrophils, cell permeant and cell impermeant fluorescent nucleic acid stains are added to neutrophils activated either by lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA). Changes in nuclear morphology and NET formation are observed over time by fluorescence microscopy. In vitro NETosis is further characterized by co-colocalization of cell-free DNA (cfDNA), myeloperoxidase (MPO) and citrullinated histone H3 (citH3) using a modified double-immunolabelling protocol. To objectively quantify NET formation and citH3 expression using fluorescence microscopy, NETs and citH3-positive cells are quantified in a blinded manner using available software. This technique is a specific assay to evaluate the in vitro capacity of canine neutrophils to undergo NETosis.

In Vitro Canine Neutrophil Extracellular Trap Formation: Dynamic and Quantitative Analysis by Fluorescence Microscopy

We describe methods to isolate canine neutrophils from whole blood and visualize NET formation in live neutrophils using fluorescence microscopy. Also described are protocols to quantify NET formation and citrullinated histone H3 (citH3) expression using immunofluorescence microscopy.

In response to invading pathogens, neutrophils release neutrophil extracellular traps (NETs), which are extracellular networks of DNA decorated with ...

Automated Image-Based Quantification of Neutrophil Extracellular Traps Using NETQUANT

Neutrophil extracellular traps (NETs) are web-like antimicrobial structures consisting of DNA and granule derived antimicrobial proteins. Immunofluorescence microscopy and image-based quantification methods remain important tools to quantitate neutrophil extracellular trap formation. However, there are key limitations to the immunofluorescence-based methods that are currently available for quantifying NETs. Manual methods of image-based NET quantification are often subjective, prone to error and tedious for users, especially non-experienced users. Also, presently available software options for quantification are either semi-automatic or require training prior to operation. Here, we demonstrate the implementation of an automated immunofluorescence-based image quantification method to evaluate NET formation called NETQUANT. The software is easy to use and has a user-friendly graphical user interface (GUI). It considers biologically relevant parameters such as an increase in the surface area and DNA:NET marker protein ratio, and nuclear deformation to define NET formation. Furthermore, this tool is built as a freely available app, and allows for single-cell resolution quantification and analysis.

Here, we present a protocol for generating neutrophil extracellular traps (NETs) and operating NETQUANT, a fully automatic software option for quantification of NETs in immunofluorescence images.

Neutrophil extracellular traps (NETs) are web-like antimicrobial structures consisting of DNA and granule derived antimicrobial proteins. ...

A High-throughput Assay to Assess and Quantify Neutrophil Extracellular Trap Formation

Neutrophil extracellular traps (NETs) are immunogenic extracellular DNA structures that can be released by neutrophils upon a wide variety of triggers. NETs have been demonstrated to serve as an important host defense mechanism that traps and kills microorganisms. On the other hand, they have been implicated in diverse systemic autoimmune diseases. NETs are immunogenic and toxic structures that contain a pool of relevant autoantigens including anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) and systemic lupus erythematosus (SLE). Different forms of NETs can be induced depending on the stimulus. The amount of NETs can be quantified using different techniques including measuring DNA release in supernatants, measuring DNA-complexed with NET-molecules like myeloperoxidase (MPO) or neutrophil elastase (NE), measuring the presence of citrullinated histones by fluorescence microscopy, or flow cytometric detection of NET-components which all have different features regarding their specificity, sensitivity, objectivity, and quantity. Here is a protocol to quantify ex vivo NET formation in a highly-sensitive, high-throughput manner by using three-dimensional immunofluorescence confocal microscopy. This protocol can be applied to address various research questions about NET formation and degradation in health and disease.

This protocol describes a highly sensitive and high throughput neutrophil extracellular trap (NET) assay for the semi-automated quantification of ex vivo NET formation by immunofluorescence three-dimensional confocal microscopy. This protocol can be used to evaluate NET formation and degradation after different stimuli and can be used to study potential NET-targeted therapies.

Neutrophil extracellular traps (NETs) are immunogenic extracellular DNA structures that can be released by neutrophils upon a wide variety of triggers. ...

Identification of Neutrophil Extracellular Traps in Paraffin-Embedded Feline Arterial Thrombi using Immunofluorescence Microscopy

Neutrophil extracellular traps (NETs), composed of cell-free DNA (cfDNA) and proteins like histones and neutrophil elastase (NE), are released by neutrophils in response to systemic inflammation or pathogens. Although NETs have previously been shown to augment clot formation and inhibit fibrinolysis in humans and dogs, the role of NETs in cats with cardiogenic arterial thromboembolism (CATE), a life-threatening complication secondary to hypertrophic cardiomyopathy, is unknown. A standardized method to identify and quantify NETs in cardiogenic arterial thrombi in cats will advance our understanding of their pathological role in CATE. Here, we describe a technique to identify NETs in formaldehyde-fixed and paraffin-embedded thrombi within the aortic bifurcation, extracted during necropsy. Following deparaffinization with xylene, aortic sections underwent indirect heat-induced antigen retrieval. Sections were then blocked, permeabilized, and ex vivo NETs were identified by colocalization of cell-free DNA (cfDNA), citrullinated histone H3 (citH3), and neutrophil elastase (NE) using immunofluorescence microscopy. To optimize the immunodetection of NETs in thrombi, autofluorescence of tissue elements was limited by using an autofluorescence quenching process prior to microscopy. This technique could be a useful tool to study NETs and thrombosis in other species and offers new insights into the pathophysiology of this complex condition.

We describe a method to identify neutrophil extracellular traps (NETs) in formaldehyde-fixed and paraffin-embedded feline cardiogenic arterial thrombi using heat-induced antigen retrieval and a double immunolabeling protocol.

Neutrophil extracellular traps (NETs), composed of cell-free DNA (cfDNA) and proteins like histones and neutrophil elastase (NE), are released by ...

Morphological and Compositional Analysis of Neutrophil Extracellular Traps Induced by Microbial and Chemical Stimuli

Neutrophils function as the first line of cellular defense in an innate immune response by employing diverse mechanisms, such as the formation of neutrophil extracellular traps (NETs). This study analyzes the morphological and compositional changes in NETs induced by microbial and chemical stimuli using standardized in vitro methodologies for NET induction and characterization with human cells. The procedures described here allow the analysis of NET morphology (lytic or non-lytic) and composition (DNA-protein structures and enzymatic activity), and the effect of soluble factors or cellular contact on such characteristics. Additionally, the techniques described here could be modified to evaluate the effect of exogenous soluble factors or cellular contact on NET composition.
The applied techniques include the purification of polymorphonuclear cells from human peripheral blood using a double density gradient (1.079-1.098 g/mL), guaranteeing optimal purity and viability (&#8805; 95%) as demonstrated by Wright's staining, trypan blue exclusion, and flow cytometry, including FSC versus SSC analysis and 7AAD staining. NET formation is induced with microbial (Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans) and chemical (phorbol myristate acetate, HOCl) stimuli, and the NETs are characterized by DNA-DAPI staining, immunostaining for the antimicrobial peptide cathelicidin (LL37), and quantification of enzymatic activity (neutrophil elastase, cathepsin G, and myeloperoxidase). The images are acquired through fluorescence microscopy and analyzed with ImageJ.

Presented here is a protocol for the induction and analysis of in vitro neutrophil extracellular traps (NETs). Quantification of DNA, cathelicidin (LL37), and enzyme activity yielded data that show the variability in the composition and morphology of NETs induced by microbial and chemical stimuli under similar controlled conditions.

Neutrophils function as the first line of cellular defense in an innate immune response by employing diverse mechanisms, such as the formation of ...

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 ...