This work was supported by a Perpetual IMPACT Grant (IPAP201601422) and Novo Nordisk Foundation Biomedical Project Grant (NNF17OC0028990). YZ also acknowledges the receipt of an Australian Postgraduate Award from the University of Sydney. We would like to thank Mr. Pat Pisansarakit and Ms. Morgan Jones for assistance with the monocyte isolation and tissue culture.

The HMDM were isolated from human buffy coat preparations supplied by the blood bank with ethics approval from the Sydney Local Health District.
1. HMDM Culture
<ol>
	<li>Isolate the monocytes from buffy coat preparations prepared from the peripheral blood of healthy human donors using a commercially available preparation to isolate lymphocytes, followed by countercurrent centrifugal elutriation19,20.</li>
	<li>Confirm the presence of monocytes by cytospinning and staining with modified Giemsa stain for monocyte characterization19.</li>
	<li>Under sterile conditions, adjust the density of monocytes to 1 x 106 cells/mL using RPMI-1640 media without serum. Add 1 mL of this cell suspension to each well of a 12 well tissue culture plate. Culture in a cell incubator at 37 &#176;C in the presence of 5% CO2 for 2 h to promote adherence to the tissue culture plate.</li>
	<li>Under sterile conditions, remove the cell media and replace with complete RPMI-1640 culture media containing 10% (v/v) pooled human serum and 20 mM L-glutamine.</li>
	<li>Culture the cells at 37 &#176;C in the presence of 5% CO2 in a cell incubator for 8 days, changing the media every 2 days.</li>
</ol>
2. Polarization of HMDM
<ol>
	<li>Under sterile conditions, prepare the M1 priming media by adding interferon &#947; (IFN&#947;; 20 ng/mL) and lipopolysaccharide (LPS; 1 &#956;g/mL) to the complete RPMI-1640 culture media. Prepare the M2 priming media by adding interleukin 4 (IL-4; 20 ng/mL) to the complete RPMI-1640 culture media.</li>
	<li>Under sterile conditions, aspirate media from the tissue culture plate wells that contain the HMDM, which have been seeded and cultured as described in section 1.</li>
	<li>Carefully wash the wells containing the cells 3x with sterile PBS (pre-warmed to 37 &#176;C), using 1 mL aliquots of PBS.</li>
	<li>Add 1 mL of either the M1 or M2 priming media to each well containing the HMDM (whichever is appropriate for the experiment).</li>
	<li>Incubate the cells for 48 h at 37 &#176;C in the presence of 5% CO2 in a cell incubator.</li>
</ol>
3. Stimulation of HMDM to induce MET Release
<ol>
	<li>Under sterile conditions, prepare the culture media containing different stimulators of MET release (whichever is appropriate for the experiment) to the complete RPMI-1640 media: PMA (25 nM), human recombinant TNF&#945; (25 ng/mL), or human recombinant IL-8 (50 ng/mL).</li>
	<li>For experiments with HOCl stimulation, prepare HOCl (200 &#956;M) in HBSS (pre-warmed to 37 &#176;C), immediately before the addition to the cells. Ensure that the HOCl is not prepared in complete cell media. 
	NOTE: The concentration of the stock solution of HOCl is quantified by measuring the UV absorbance of the solution at 292 nm and pH = 116 and using an extinction coefficient of 350 M-1cm-1 21.</li>
	<li>After the polarization treatment described in section 2, aspirate the cell media from each well and carefully wash the cells 3x with 1 mL aliquots of either: sterile PBS (for PMA, TNF&#945; and IL-8) or HBSS (for HOCl), which have been pre-warmed to 37 &#176;C.</li>
	<li>For experiments with PMA, TNF&#945;, or IL-8: add 1 mL of the complete media containing PMA, TNF&#945;, or IL-8 after removing the PBS in the final washing step.</li>
	<li>For experiments with TNF&#945;, incubate the cells for 6 h at 37 &#176;C in the presence of 5% CO2 in a cell incubator. For experiments with PMA and IL-8, incubate the cells for 24 h at 37 &#176;C in the presence of 5% CO2 in a cell incubator.</li>
	<li>For experiments with HOCl, add 1 mL of HOCl in HBSS after removing the HBSS in the final washing step. Then, incubate the cells for 15 min at 37 &#176;C in the presence of 5% CO2 in a cell incubator.
	<ol>
		<li>Carefully aspirate the cell supernatant and wash the cells 3x with 1 mL aliquots of HBSS as described in step 3.3.</li>
		<li>After removing the HBSS from the final wash step, add 1 mL of complete RPMI-1640 culture media. Then, incubate the cells for 24 h at 37 &#176;C in the presence of 5% CO2 in a cell incubator.</li>
	</ol>
	</li>
</ol>
4. Visualization of MET in Live Cell Culture
<ol>
	<li>Prepare SYTOX green dye in HBSS at a concentration of 40 &#956;M.</li>
	<li>At the end of treatments described in section 3 to induce MET release, directly add 25 &#956;L of 40 &#956;M of the dye to each well containing HMDM.</li>
	<li>Incubate cells at room temperature (RT) for 5 min in the dark.</li>
	<li>Place the HMDM in tissue culture wells on the microscope stage of an inverted fluorescent microscope for imaging.</li>
	<li>Microscope procedures
	<ol>
		<li>Turn on a broad-spectrum fluorescent light source, brightfield light source, and inverted microscope installed with a high-resolution color digital camera (see Table of Materials).</li>
		<li>Rotate the filter wheel to the &#8220;number 2&#8221; position for green fluorescence (excitation = 504 nm, emission = 523 nm) for imaging of the green stained samples contained within the tissue culture wells.</li>
		<li>Using the 5x objective, focus the image with the coarse focus, then the fine focus knobs on the microscope, until the image appears sharp, clear, and focused when viewed through the microscope eyepiece.</li>
		<li>Switch the microscope to the camera mode.</li>
		<li>Start the associated software.</li>
		<li>Select the Capture tab on the software.</li>
		<li>Click the Play button to preview the image and adjust the fine focus knob on the microscope until the image appears sharp, clear, and focused in the software preview window.</li>
		<li>Click the Capture button. 
		NOTE: The captured image will automatically be displayed in the accompanying software.</li>
		<li>Within the software, click File | Save as the required image file type.</li>
		<li>On the microscope, rotate the filter wheel to the &#8220;number 5&#8221; position for brightfield imaging and repeat steps 4.5.2&#8211;4.5.9 to obtain the corresponding brightfield image.</li>
		<li>Repeat the steps 4.5.2&#8211;4.5.10 as necessary for subsequent image acquisition.</li>
	</ol>
	</li>
</ol>

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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=Cytokines+induced+neutrophil+extracellular+traps+formation:+implication+for+the+inflammatory+disease+condition.">Cytokines induced neutrophil extracellular traps formation: implication for the inflammatory disease condition.</a> PLoS One. 7 (10), 48111 (2012).</li><li>Rayner, B. 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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+reduces+vascular+damage+and+modulates+innate+immune+responses+in+murine+models+of+atherosclerosis.">Peptidylarginine deiminase inhibition reduces vascular damage and modulates innate immune responses in murine models of atherosclerosis.</a> Circulation Research. 114 (6), 947-956 (2014).</li><li>Megens, R. 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R., 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+traps+derived+from+macrophages,+mast+cells,+eosinophils+and+neutrophils+are+generated+in+a+time-dependent+manner+during+atherothrombosis.">Extracellular traps derived from macrophages, mast cells, eosinophils and neutrophils are generated in a time-dependent manner during atherothrombosis.</a> Journal of Pathology. 247 (4), 505-512 (2019).</li><li>Okubo, 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=Macrophage+extracellular+trap+formation+promoted+by+platelet+activation+is+a+key+mediator+of+rhabdomyolysis-induced+acute+kidney+injury.">Macrophage extracellular trap formation promoted by platelet activation is a key mediator of rhabdomyolysis-induced acute kidney injury.</a> Nature Medicine. 24 (2), 232-238 (2018).</li><li>Boeltz, 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=To+NET+or+not+to+NET:current+opinions+and+state+of+the+science+regarding+the+formation+of+neutrophil+extracellular+traps.">To NET or not to NET:current opinions and state of the science regarding the formation of neutrophil extracellular traps.</a> Cell Death and Differentiation. 26 (3), 395-408 (2019).</li><li>Doster, R. S., Rogers, L. M., Gaddy, J. A., Aronoff, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Macrophage+Extracellular+Traps:+A+Scoping+Review.">Macrophage Extracellular Traps: A Scoping Review.</a> Journal of Innate Immunology. 10 (1), 3-13 (2018).</li><li>Daigneault, M., Preston, J. A., Marriott, H. M., Whyte, M. K., Dockrell, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+identification+of+markers+of+macrophage+differentiation+in+PMA-stimulated+THP-1+cells+and+monocyte-derived+macrophages.">The identification of markers of macrophage differentiation in PMA-stimulated THP-1 cells and monocyte-derived macrophages.</a> PLoS One. 5 (1), 8668 (2010).</li><li>Mestas, J., Hughes, C. 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T., Jessup, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+macrophage-mediated+oxidation+of+low-density+lipoprotein+is+delayed+and+independant+of+superoxide+production.">Human macrophage-mediated oxidation of low-density lipoprotein is delayed and independant of superoxide production.</a> Biochemical Journal. 301, 421-428 (1994).</li><li>Morris, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+acid+ionization+constant+of+HOCl+from+5+&#176;C+to+35+&#176;C.">The acid ionization constant of HOCl from 5 &#176;C to 35 &#176;C.</a> Journal of Phyical Chemistry. 70, 3798-3805 (1966).</li><li>Pan, G. J., Rayner, B. S., Zhang, Y., van Reyk, D. M., Hawkins, C. 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The authors have nothing to disclose.

The generation and visualization of MET formation using M1 differentiated HMDMs represents a new in vitro model that may be useful for investigating the potential pathological role of these macrophage structures, particularly under chronic inflammatory conditions. It provides a robust protocol for the stimulation of primary human macrophages to release METs, which can also be utilized in related studies with human monocyte or murine macrophage cell lines. The successful implementation of this protocol for the stimulation...

The release of ETs from neutrophils was first identified as an innate immune response triggered by bacterial infection1. They consist of a DNA backbone to which various granule proteins with anti-bacterial properties are bound, including neutrophil elastase and myeloperoxidase2. The primary role of neutrophil ETs (NETs) is to capture pathogens and facilitate their elimination3. However, in addition to the protective role of ETs in immune defense, an increasing number of studies have also discovered a role in disease pathogenesis, particularly during the development of inflammation-driven diseases (i.e., rheumatoid arthritis and atherosclerosis4). The release of ETs can be triggered by various pro-inflammatory cytokines including interleukin 8 (IL-8) and tumor necrosis factor alpha (TNF&#945;)5,6, and the localized accumulation of ETs can increase tissue damage and evoke a pro-inflammatory response7. For example, ETs have been implicated as playing a causal role in the development of atherosclerosis8, promoting thrombosis9, and predicting cardiovascular risk10.
It is now recognized that in addition to neutrophils, other immune cells (i.e., mast cells, eosinophils, and macrophages) can also release ETs on exposure to the microbial or pro- inflammatory stimulation11,12. This may be particularly significant in the case of macrophages, considering their key role in the development, regulation, and resolution of chronic inflammatory diseases. Therefore, it is important to gain a greater understanding of the potential relationship between ET release from macrophages and inflammation-related disease development. Recent studies have shown the presence of METs and NETs in intact human atherosclerotic plaques and organized thrombi13. Similarly, METs have been implicated in driving kidney injury through the regulation of inflammatory responses14. However, in contrast to neutrophils, there are limited data on the mechanisms of MET formation from macrophages. Recent studies using human in vitro models of MET formation show some differences in the pathways involved in each cell type (i.e., regarding the absence of histone citrullination with macrophages)6. However, some have shown that NET release can also occur in the absence of histone citrullination15.
The overall goal of this protocol is to provide a simple and direct method to assess MET release in a clinically relevant macrophage model. There are a number of different in vitro macrophage cell models that have been used to study METs (i.e., the THP-1 human monocyte cell line and various murine macrophage cell lines)16. There are some limitations associated with these models. For example, the differentiation of THP-1 monocytes to macrophages usually requires a priming step, such as the addition of phorbol myristate acetate (PMA), which itself activates protein kinase C (PKC)-dependent pathways. This process is known to trigger ET release4 and results in a low basal MET release from THP-1 cells. Other studies have highlighted some differences in bioactivity and inflammatory responses mounted by macrophages in vivo compared to PMA-treated THP-1 cells17.
Similarly, the behavior and inflammatory responses of different murine macrophage-like cell lines do not completely represent the response spectrum of primary human macrophages18. Therefore, for the purpose of investigating macrophage ET formation in the clinical setting, primary human monocyte-derived macrophages (HMDMs) are believed to be a more relevant model rather than monocytic or murine macrophage-like cell lines.
ET release from M1 polarized HMDMs has been demonstrated following exposure of these cells to a number of different inflammatory stimuli, including the myeloperoxidase-derived oxidant hypochlorous acid (HOCl), PMA, TNF&#945;, and IL-86. Described here is a protocol to polarize HMDMs to the M1 phenotype and visualize subsequent MET release upon exposure to these inflammatory stimuli. PMA is used as a stimulus of MET release to facilitate comparisons to previous studies that have used neutrophils. Importantly, HOCl, IL-8, and TNF&#945; are also used to stimulate MET release, which are believed to be better models of the inflammatory environment in vivo. The microscopic method for visualization of ET release involves staining the extracellular DNA in live cell cultures using SYTOX green, an impermeable fluorescent green nucleic acid stain that has been successfully applied in previous neutrophil studies. This method allows for rapid and qualitative assessment of ET release, but it is not appropriate as a stand-alone method for the quantification of ET release extent. Alternative methodology should be used if quantification is required to compare the extent of ET release resulting from different treatment conditions or interventions.

<table>
	<tbody>
		<tr>
			<td>120Q broad spectrum fluorescent light source</td>
			<td>EXFO Photonic Solutions, Toronto, Canada</td>
			<td></td>
			<td>x-cite series</td>
		</tr>
		<tr>
			<td>Corning CellBIND Multiple Well Plate (12 wells)</td>
			<td>Sigma-Aldrich</td>
			<td>CLS3336</td>
			<td>For cell culture</td>
		</tr>
		<tr>
			<td>Differential Quik Stain Kit (Modified Giemsa)</td>
			<td>Polysciences Inc.</td>
			<td>24606</td>
			<td>Characterisation of monocytes</td>
		</tr>
		<tr>
			<td>Hanks balanced salt solution (HBSS)</td>
			<td>Thermo-Fisher</td>
			<td>14025050</td>
			<td>For washing steps and HOCl treatment</td>
		</tr>
		<tr>
			<td>Hypochlorous acid (HOCl)</td>
			<td>Sigma-Aldrich</td>
			<td>320331</td>
			<td>For MET stimulation</td>
		</tr>
		<tr>
			<td>Interferon gamma</td>
			<td>Thermo-Fisher</td>
			<td>PMC4031</td>
			<td>For M1 priming</td>
		</tr>
		<tr>
			<td>Interleukin 4</td>
			<td>Integrated Sciences</td>
			<td>rhil-4</td>
			<td>For M2 priming</td>
		</tr>
		<tr>
			<td>Interleukin 8</td>
			<td>Miltenyl Biotec</td>
			<td>130-093-943</td>
			<td>For MET stimulation</td>
		</tr>
		<tr>
			<td>L-Glutamine</td>
			<td>Sigma-Aldrich</td>
			<td>59202C</td>
			<td>Added to culture media</td>
		</tr>
		<tr>
			<td>Lipopolysaccharide</td>
			<td>Integrated Sciences</td>
			<td>tlrl-eblps</td>
			<td>For M1 priming</td>
		</tr>
		<tr>
			<td>Lymphoprep</td>
			<td>Axis-Shield PoC AS</td>
			<td>1114544</td>
			<td>For isolation of monocytes</td>
		</tr>
		<tr>
			<td>Olympus IX71 inverted microscope</td>
			<td>Olympus, Tokyo, Japan</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Phorbol 12- myristate 13-acetate (PMA)</td>
			<td>Sigma-Aldrich</td>
			<td>P8139</td>
			<td>For MET stimulation</td>
		</tr>
		<tr>
			<td>Phosphate buffered saline (PBS)</td>
			<td>Sigma-Aldrich</td>
			<td>D5652</td>
			<td>For washing steps</td>
		</tr>
		<tr>
			<td>RPMI-1640 media</td>
			<td>Sigma-Aldrich</td>
			<td>R8758</td>
			<td>For cell culture</td>
		</tr>
		<tr>
			<td>SYTOX green</td>
			<td>Life Technologies</td>
			<td>S7020</td>
			<td>For MET visulaization</td>
		</tr>
		<tr>
			<td>TH4-200 brightfield light source</td>
			<td>Olympus, Tokyo, Japan</td>
			<td></td>
			<td>x-cite series</td>
		</tr>
		<tr>
			<td>Tumor necrosis factor alpha</td>
			<td>Lonza</td>
			<td>300-01A-50</td>
			<td>For MET stimulation</td>
		</tr>
	</tbody>
</table>

in vitro stimulation and visualization of extracellular trap release in differentiated human monocyte-derived macrophages

The release of extracellular traps (ETs) by neutrophils has been identified as a contributing factor to the development of diseases related to chronic inflammation. Neutrophil ETs (NETs) consist of a mesh of DNA, histone proteins, and various granule proteins (i.e., myeloperoxidase, elastase, and cathepsin G). Other immune cells, including macrophages, can also produce ETs; however, to what extent this occurs in vivo and whether macrophage extracellular traps (METs) play a role in pathological mechanisms has not been examined in detail. To better understand the role of METs in inflammatory pathologies, a protocol was developed for visualizing MET release from primary human macrophages in vitro, which can also be exploited in immunofluorescence experiments. This allows further characterization of these structures and their comparison to ETs released from neutrophils. Human monocyte-derived macrophages (HMDM) produce METs upon exposure to different inflammatory stimuli following differentiation to the M1 pro-inflammatory phenotype. The release of METs can be visualized by microscopy using a green fluorescent nucleic acid stain that is impermeant to live cells (e.g., SYTOX green). Use of freshly isolated primary macrophages, such as HMDM, is advantageous in modeling in vivo inflammatory events that are relevant to potential clinical applications. This protocol can also be used to study MET release from human monocyte cell lines (e.g., THP-1) following differentiation into macrophages with phorbol myristate acetate or other macrophage cell lines (e.g., the murine macrophage-like J774A.1 cells).

Brightfield images showing the morphological changes of HMDM in response to stimuli for cell differentiation are shown in Figure 1. M1 polarized macrophages from experiments with HMDM exposed to IFN&#947; and LPS showed an elongated and spindle-like cell shape, as indicated by the black arrows in Figure 1 (middle panel). For comparison, the morphology of the M2 polarized macrophages after exposure of HMDM to IL-4 for 48 h were typically round and flat, as indica...

Watch this Scientific Journal Video about In Vitro Stimulation and Visualization of Extracellular Trap Release in Differentiated Human Monocyte-derived Macrophages at JoVE.com

In Vitro Stimulation and Visualization of Extracellular Trap Release in Differentiated Human Monocyte-derived Macrophages

Presented here is a protocol to detect macrophage extracellular trap (MET) production in live cell culture using microscopy and fluorescence staining. This protocol can be further extended to examine specific MET protein markers by immunofluorescence staining.

The release of extracellular traps (ETs) by neutrophils has been identified as a contributing factor to the development of diseases related to chronic ...

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Research

JoVE Journal

Immunology and Infection

9.5K Views.  Heart Research Institute. Presented here is a protocol to detect macrophage extracellular trap (MET) production in live cell culture using microscopy and fluorescence staining. This protocol can be further extended to examine specific MET protein markers by immunofluorescence staining.

Video: In Vitro Stimulation and Visualization of Extracellular Trap Release in Differentiated Human Monocyte-derived Macrophages

An In vitro Co-infection Model to Study Plasmodium falciparum-HIV-1 Interactions in Human Primary Monocyte-derived Immune Cells

Plasmodium falciparum, the causative agent of the deadliest form of malaria, and human immunodeficiency virus type-1 (HIV-1) are among the most important health problems worldwide, being responsible for a total of 4 million deaths annually1. Due to their extensive overlap in developing regions, especially Sub-Saharan Africa, co-infections with malaria and HIV-1 are common, but the interplay between the two diseases is poorly understood. Epidemiological reports have suggested that malarial infection transiently enhances HIV-1 replication and increases HIV-1 viral load in co-infected individuals2,3. Because this viremia stays high for several weeks after treatment with antimalarials, this phenomenon could have an impact on disease progression and transmission.
The cellular immunological mechanisms behind these observations have been studied only scarcely. The few in vitro studies investigating the impact of malaria on HIV-1 have demonstrated that exposure to soluble malarial antigens can increase HIV-1 infection and reactivation in immune cells. However, these studies used whole cell extracts of P. falciparum schizont stage parasites and peripheral blood mononuclear cells (PBMC), making it hard to decipher which malarial component(s) was responsible for the observed effects and what the target host cells were4,5. Recent work has demonstrated that exposure of immature monocyte-derived dendritic cells to the malarial pigment hemozoin increased their ability to transfer HIV-1 to CD4+ T cells6,7, but that it decreased HIV-1 infection of macrophages8. To shed light on this complex process, a systematic analysis of the interactions between the malaria parasite and HIV-1 in different relevant human primary cell populations is critically needed.
Several techniques for investigating the impact of HIV-1 on the phagocytosis of micro-organisms and the effect of such pathogens on HIV-1 replication have been described. We here present a method to investigate the effects of P. falciparum-infected erythrocytes on the replication of HIV-1 in human primary monocyte-derived macrophages. The impact of parasite exposure on HIV-1 transcriptional/translational events is monitored by using single cycle pseudotyped viruses in which a luciferase reporter gene has replaced the Env gene while the effect on the quantity of virus released by the infected macrophages is determined by measuring the HIV-1 capsid protein p24 by ELISA in cell supernatants.

An In vitro Co-infection Model to Study Plasmodium falciparum-HIV-1 Interactions in Human Primary Monocyte-derived Immune Cells

We have developed an in vitro malaria-HIV-1 co-infection model to study the impact of Plasmodium falciparum on the HIV-1 replicative cycle in human primary monocyte-derived macrophages. This versatile system can easily be adapted to other primary cell types susceptible to HIV-1 infection.

Plasmodium falciparum, the causative agent  of the deadliest form of malaria, and human immunodeficiency virus type-1 (HIV-1) are among the most important ...

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 ...

Culture of Macrophage Colony-stimulating Factor Differentiated Human Monocyte-derived Macrophages

A protocol is presented for cell culture of macrophage colony-stimulating factor (M-CSF) differentiated human monocyte-derived macrophages. For initiation of experiments, fresh or frozen monocytes are cultured in flasks for 1 week with M-CSF to induce their differentiation into macrophages. Then, the macrophages can be harvested and seeded into culture wells at required cell densities for carrying out experiments. The use of defined numbers of macrophages rather than defined numbers of monocytes to initiate macrophage cultures for experiments yields macrophage cultures in which the desired cell density can be more consistently attained. Use of cryopreserved monocytes reduces dependency on donor availability and produces more homogeneous macrophage cultures.

A protocol is presented for cell culture of macrophage colony-stimulating factor (M-CSF) differentiated human monocyte-derived macrophages. The protocol utilizes cryopreservation of monocytes coupled with their bulk differentiation into macrophages. Then harvested macrophages can then be seeded into culture wells at required cell densities for carrying out experiments.

A protocol is presented for cell culture of macrophage colony-stimulating factor (M-CSF) differentiated human monocyte-derived macrophages. For initiation ...

A Simple Fluorescence Assay for Quantification of Canine Neutrophil Extracellular Trap Release

Neutrophil extracellular traps are networks of DNA, histones and neutrophil proteins released in response to infectious and inflammatory stimuli. Although a component of the innate immune response, NETs are implicated in a range of disease processes including autoimmunity and thrombosis. This protocol describes a simple method for canine neutrophil isolation and quantification of NETs using a microplate fluorescence assay. Blood is collected using conventional venipuncture techniques. Neutrophils are isolated using dextran sedimentation and a density gradient using conditions optimized for dog blood. After allowing time for attachment to the wells of a 96 well plate, neutrophils are treated with NET-inducing agonists such as phorbol-12-myristate-13-acetate or platelet activating factor. DNA release is measured by the fluorescence of a cell-impermeable nucleic acid dye. This assay is a simple, inexpensive method for quantifying NET release, but NET formation rather than other causes of cell death must be confirmed with alternative methods.

Neutrophil extracellular traps (NETs) are networks of DNA, histones and neutrophil proteins. Although a component of the innate immune response, NETs are implicated in autoimmunity and thrombosis. This protocol describes a simple method for canine neutrophil isolation and quantification of NETs using a microplate fluorescence assay.

Neutrophil extracellular traps are networks of DNA, histones and neutrophil proteins released in response to infectious and inflammatory stimuli. Although ...

Generation of Human Monocyte-derived Dendritic Cells from Whole Blood

Dendritic cells (DCs) recognize foreign structures of different pathogens, such as viruses, bacteria, and fungi, via a variety of pattern recognition receptors (PRRs) expressed on their cell surface and thereby activate and regulate immunity. 
The major function of DCs is the induction of adaptive immunity in the lymph nodes by presenting antigens via MHC I and MHC II molecules to na&#239;ve T lymphocytes. Therefore, DCs have to migrate from the periphery to the lymph nodes after the recognition of pathogens at the sites of infection. For in vitro experiments or DC vaccination strategies, monocyte-derived DCs are routinely used. These cells show similarities in physiology, morphology, and function to conventional myeloid dendritic cells. They are generated by interleukin 4 (IL-4) and granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulation of monocytes isolated from healthy donors. Here, we demonstrate how monocytes are isolated and stimulated from anti-coagulated human blood after peripheral blood mononuclear cell (PBMC) enrichment by density gradient centrifugation. Human monocytes are differentiated into immature DCs and are ready for experimental procedures in a non-clinical setting after 5 days of incubation.

Here, we demonstrate how monocytes are isolated by magnetic bead separation from peripheral blood mononuclear cells after density gradient centrifugation of human anti-coagulated blood. Following incubation for 5 days, human monocytes are differentiated into immature dendritic cells and are ready for experimental procedures in a non-clinical setting.

Dendritic cells (DCs) recognize foreign structures of different pathogens, such as viruses, bacteria, and fungi, via a variety of pattern recognition ...

Analysis of Microglia and Monocyte-derived Macrophages from the Central Nervous System by Flow Cytometry

Numerous studies have demonstrated the role of immune cells, in particular macrophages, in central nervous system (CNS) pathologies. There are two main macrophage populations in the CNS: (i) the microglia, which are the resident macrophages of the CNS and are derived from yolk sac progenitors during embryogenesis, and (ii) the monocyte-derived macrophages (MDM), which can infiltrate the CNS during disease and are derived from bone marrow progenitors. The roles of each macrophage subpopulation differ depending on the pathology being studied. Furthermore, there is no consensus on the histological markers or the distinguishing criteria used for these macrophage subpopulations. However, the analysis of the expression profiles of the CD11b and CD45 markers by flow cytometry allows us to distinguish the microglia (CD11b+CD45med) from the MDM (CD11b+CD45high). In this protocol, we show that the density gradient centrifugation and the flow cytometry analysis can be used to characterize these CNS macrophage subpopulations, and to study several markers of interest expressed by these cells as we recently published. Thus, this technique can further our understanding of the role of macrophages in mouse models of neurological diseases and can also be used to evaluate drug effects on these cells.

This protocol provides an analysis of the macrophage subpopulations in the adult mouse central nervous system by flow cytometry and is helpful for the study of multiple markers expressed by these cells.

Numerous studies have demonstrated the role of immune cells, in particular macrophages, in central nervous system (CNS) pathologies. There are two main ...

Isolation of Salmonella typhimurium-containing Phagosomes from Macrophages

Salmonella typhimurium is a facultative intracellular bacterium that causes gastroenteritis in humans. After invasion of the lamina propria, S. typhimurium bacteria are quickly detected and phagocytized by macrophages, and contained in vesicles known as phagosomes in order to be degraded. Isolation of S. typhimurium-containing phagosomes have been widely used to study how S. typhimurium infection alters the process of phagosome maturation to prevent bacterial degradation. Classically, the isolation of bacteria-containing phagosomes has been performed by sucrose gradient centrifugation. However, this process is time-consuming, and requires specialized equipment and a certain degree of dexterity. Described here is a simple and quick method for the isolation of S. typhimurium-containing phagosomes from macrophages by coating the bacteria with biotin-streptavidin-conjugated magnetic beads. Phagosomes obtained by this method can be suspended in any buffer of choice, allowing the utilization of isolated phagosomes for a broad range of assays, such as protein, metabolite, and lipid analysis. In summary, this method for the isolation of S. typhimurium-containing phagosomes is specific, efficient, rapid, requires minimum equipment, and is more versatile than the classical method of isolation by sucrose gradient-ultracentrifugation.

Isolation of Salmonella typhimurium-containing Phagosomes from Macrophages

We describe here a simple and quick method for the isolation of Salmonella typhimurium-containing phagosomes from macrophages by coating the bacteria with biotin and streptavidin.

Salmonella typhimurium is a facultative intracellular bacterium that causes gastroenteritis in humans. After invasion of the lamina propria, S. ...

Isolation and In Vitro Culture of Murine and Human Alveolar Macrophages

Alveolar macrophages are terminally differentiated, lung-resident macrophages of prenatal origin. Alveolar macrophages are unique in their long life and their important role in lung development and function, as well as their lung-localized responses to infection and inflammation. To date, no unified method for identification, isolation, and handling of alveolar macrophages from humans and mice exists. Such a method is needed for studies on these important innate immune cells in various experimental settings. The method described here, which can be easily adopted by any laboratory, is a simplified approach to harvesting alveolar macrophages from bronchoalveolar lavage fluid or from lung tissue and maintaining them in vitro. Because alveolar macrophages primarily occur as adherent cells in the alveoli, the focus of this method is on dislodging them prior to harvest and identification. The lung is a highly vascularized organ, and various cell types of myeloid and lymphoid origin inhabit, interact, and are influenced by the lung microenvironment. By using the set of surface markers described here, researchers can easily and unambiguously distinguish alveolar macrophages from other leukocytes, and purify them for downstream applications. The culture method developed herein supports both human and mouse alveolar macrophages for in vitro growth, and is compatible with cellular and molecular studies.

Isolation and In Vitro Culture of Murine and Human Alveolar Macrophages

This communication describes methodologies for isolation and culture of alveolar macrophages from humans and murine models for experimental purposes.

Alveolar macrophages are terminally differentiated, lung-resident macrophages of prenatal origin. Alveolar macrophages are unique in their long life and ...

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 ...

Quantification of Monocyte Chemotactic Activity In Vivo and Characterization of Blood Monocyte Derived Macrophages

Tissue homeostasis and repair are critically dependent on the recruitment of monocyte-derived macrophages. Both under- and over-recruitment of monocyte-derived macrophages can impair wound healing. We showed that high fat and high sugar diets promote monocyte priming and dysfunction, converting healthy blood monocytes into a hyper chemotactic phenotype poised to differentiate into macrophages with dysregulated activation profiles and impaired phenotypic plasticity. The over-recruitment of monocyte-derived macrophages and recruitment of macrophages with dysregulated activation profiles is believed to be a major contributor to the development of chronic inflammatory diseases associated with metabolic disorders, including atherosclerosis and obesity. The goal of this protocol is to quantify the chemotactic activity of blood monocytes as a biomarker for monocyte priming and dysfunction and to characterize the macrophage phenotype blood monocytes are poised to differentiate into in these mouse models. Using single cell Western blot analysis, we show that after 24 h 33%of cells recruited into MCP-1-loaded basement membrane-derived gel plugs injected into mice are monocytes and macrophages; 58% after day 3. However, on day 5, monocyte and macrophage numbers were significantly decreased. Finally, we show that this assays also allows for the isolation of live macrophages from the surgically retrieved basement membrane-derived gel plugs, which can then be subjected to subsequent characterization by single cell Western blot analysis.

Here we present a protocol to quantify the chemotactic activity of blood monocytes in mouse models, to assess the effects of nutritional, pharmacological and genetic interventions on blood monocyte and to characterize the blood monocytes derived macrophages in mouse models using monocyte-chemoattractant protein-1 (MCP-1)-loaded basement membrane-derived gel plugs.