The authors acknowledge the following funding agencies: FAPDF, CNPq, CAPES, UnB, FINEP, and FINATEC.

All experiments strictly followed the ethical guidelines set by the institutional review board at the University of Brasilia (process 13364819.0.0000.5558), and samples were identified by codes to ensure donor anonymity. The cells were obtained from normal healthy male donors aged 18-35 years, who signed the informed consent and met the following eligibility criteria: non-smokers/vapers, no chronic health conditions, and no history of inflammatory conditions in the last 14 days.
1. Blood collection
<ol>
	<li>Aseptically place 0.3 mL of 5,000 IU/mL heparin (see Table of Materials) in a sterile 20 mL syringe to heparinize it.</li>
	<li>Apply a venous tourniquet about 4 in above the puncture site and identify the median cubital or cephalic vein for venipuncture. 
	NOTE: Ensure that the total tourniquet time does not exceed 1 min.</li>
	<li>Clean the puncture site with 70% alcohol and perform the venipuncture.</li>
	<li>Gently invert the syringe three or four times after collecting the blood to mix the blood and heparin properly.</li>
</ol>
2. Neutrophil isolation
NOTE: Polymorphonuclear leukocytes (PMNs) are isolated through density gradient centrifugation followed by hypotonic lysis of the remaining red blood cells (RBC), as previously described11 with some changes. This method is not mandatory to perform the screening assays, and can be replaced as long as the chosen method results in a viability of &#62;97%, priming or activation of &#60;3% of the PMNs, and yields enough cells for all assays, replicates, and conditions. Performing these steps under aseptic conditions and using endotoxin-free solutions are mandatory to avoid cell activation.
<ol>
	<li>Make 12 mL dilutions of 60% and 70% separation media (commercially available; see Table of Materials) in 50 mL conical tubes.</li>
	<li>Prepare the gradient from bottom to top by adding 4 mL at a time of the 60% dilution over the 70% dilution, using a 5 mL pipette. Do this gently to prevent mixing the interface.</li>
	<li>Carefully layer 12 mL of heparinized blood on top of the density gradient. Centrifuge at 200 x g for 15 min at room temperature. 
	NOTE: From this step onward, until PMN activation, all the reagents and tubes used must be kept in a cooler filled with ice.</li>
	<li>Discard the plasma/mononuclear cell layer, then gently transfer the layer above the erythrocyte pellet into two 15 mL conical tubes with approximately 7.5 mL in each. Make up the tube volume with Hank&#39;s balanced salt solution (HBSS; see Table of Materials).</li>
	<li>Centrifuge at 300 x g for 5 min at 19 &#176;C.</li>
	<li>Wash the cell pellet with HBSS.
	<ol>
		<li>Discard the supernatant by pouring the tube and gently resuspend the pellet in 7 mL of HBSS.</li>
		<li>Centrifuge at 300 x g for 5 min at 19 &#176;C to remove all the separation media.</li>
	</ol>
	</li>
	<li>Perform hypotonic lysis of the remaining RBCs.
	<ol>
		<li>Discard the supernatant and combine the pellets in a single tube.</li>
		<li>Resuspend the RBC/PMN pellet in 3 mL of sterile H2O and add 3 mL of HBSS (2x) within 25 s to restore the osmolarity. Then, centrifuge at 300 x g for 5 min at 19 &#176;C.</li>
		<li>Repeat steps 2.8.1 and 2.8.2 for a white, erythrocyte-free pellet. 
		NOTE: The supernatant must be removed as soon as possible to minimize the contact of neutrophils&#160;with RBC breakdown products. Alternatively, the second hypotonic lysis can be replaced by gently resuspending the residual RBC layer and removing all the supernatant, as the remaining RBCs will sediment above the PMN pellet.</li>
	</ol>
	</li>
	<li>Discard the supernatant by pouring the tube, gently resuspend the PMNs in the remaining buffer, and transfer them to an ice-cold microtube. 
	NOTE: Ensure to annotate the volume while transferring the resuspended cells with a micropipette.</li>
	<li>Transfer 3 x 1 &#181;L of the cell suspension to a clean glass slide (three wells of 1 &#181;L each) and stain with fast panoptic (see Table of Materials) for morphology and purity evaluation12.
	<ol>
		<li>To stain with fast panoptic, immerse the slide five times in panoptic fixative n&#176; 1, six times in eosin n&#176; 2, and twice in hematoxylin&#160; n&#176; 3, with each immersion lasting 1 s.</li>
		<li>Gently wash the glass slide with distilled water.</li>
		<li>Allow to drain and air-dry.</li>
	</ol>
	</li>
	<li>Observe under a microscope and count 300 random cells in each well, thus differentiating the neutrophils from other granulocytes.</li>
	<li>Transfer 1 &#181;L of the cell suspension to 49 &#181;L of 0.2% trypan blue dye13&#160;and count the cells using a Neubauer chamber, distinguishing between dead and viable cells.</li>
	<li>Adjust the cell concentration to 6,667 cells/&#181;L using a solution of 50% autologous plasma and 50% HBSS supplemented with calcium and magnesium. Divide the 6,667 cells/&#181;L suspension evenly among the microtubes corresponding to the conditions to be tested, including the negative control. 
	&#8203;NOTE: Any cell concentration similar to the circulating neutrophils in the model organism can be used, but it is important to use the same cell concentration in all experiments for reproducibility.</li>
</ol>
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/65329/65329fig01.jpg" /> 
Figure 1: The neutrophil isolation protocol. Two concentrations of the separation media (percoll) (A) are stacked (B), then the blood is layered on top of the separation gradient (C). After centrifugation, the PMN is in the central layer (D), which is divided into two 15 mL tubes (E). The cell suspension is washed twice in HBSS and centrifuged (G-I) to remove the media, then the cells are resuspended, and residual RBCs are submitted to two rounds of hypotonic lysis (J-M). <a href="https://www.jove.com/files/ftp_upload/65329/65329fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
3. Preparation for neutrophil activation
<ol>
	<li>In 1.5 mL microtubes, prepare an activation system for each condition so that the final cell concentration is 6,600 cells/&#181;L. For instance, to test the effects of 100 nM fMLP (N-formyl-methionyl-leucyl-phenylalanine; see Table of Materials), add 5 &#181;L of 10 &#181;M fMLP to 495 &#181;L of the 6,667 cell/&#181;L suspension. For the negative (unstimulated) control, add HBSS containing Ca2+ and Mg2+. 
	NOTE: To demonstrate this methodology, the following final concentrations of the stimuli were used: 100 nM fMLP, 16 &#181;M of fallaxin, a naturally occurring antimicrobial peptide14, and 100 nM PMA (phorbol 12-myristate 13-acetate) (see Table of Materials).</li>
	<li>Incubate at 37 &#176;C without rotation. 
	&#8203;NOTE: All aliquots for functional assays are taken from this cell suspension, hereafter referred to as the activation system.</li>
</ol>
4. Nitrotetrazolium blue chloride (NBT) assay for evaluating ROS production
<ol>
	<li>Preparation of NBT working solution: For each experimental condition, prepare an NBT (see Table of Materials) working solution of 6 mM using the following steps:
	<ol>
		<li>Dissolve 0.0005 g of NBT in 10 &#181;L of dimethyl sulfoxide (DMSO) and vortex for at least 15 min.</li>
		<li>Add 90 &#181;L of HBSS Ca2+Mg2+ and vortex up to 2 min. 
		NOTE: All steps involving NBT must be performed in the dark.</li>
	</ol>
	</li>
	<li>Perform NBT slide test.
	<ol>
		<li>After 20 min of cell activation, gently mix the cell suspension and carefully transfer 2 &#181;L of PMN to a clean glass slide. Incubate for 20 min in a humidified chamber at 37 &#176;C. 
		NOTE: Do not spread the cell suspension too much over the slide; otherwise it may dry out before incubation.</li>
		<li>Add 1 &#181;L of the NBT working solution over the cells and further incubate for 20 min protected from light.</li>
		<li>Dry the slide with hot air and fix it with a drop of methanol in each well for 1 min. Stain with 0.03% safranin (see Table of Materials) for 1 min.</li>
		<li>Gently wash the glass slide with distilled water.</li>
		<li>Allow the slide to air-dry and observe under a microscope.</li>
		<li>Count 100 random cells in each well, differentiating neutrophils with and without formazan deposits.</li>
	</ol>
	</li>
	<li>Perform NBT spectrophotometry assay.
	<ol>
		<li>After 40 min of cell activation, gently mix the cell suspension and transfer 90 &#181;L of PMNs from the activation system to a clean microtube. Then, carefully add 20 &#181;L of the 6 mM NBT solution. Incubate in the dark for 20 min at 37 &#176;C.</li>
		<li>Add 100 &#181;L of 10% Sodium dodecyl sulfate (SDS; see Table of Materials) and vortex.</li>
		<li>Sonicate using a tip-sonicator at an amplitude of 60%, five cycles of 15 s each with 15 s intervals. Centrifuge at 12,000 x g for 5 min.</li>
		<li>Transfer 60 &#181;L of the supernatant to a clear-bottom 96-well plate and measure the absorbance of the formazan product at 570 nm.</li>
	</ol>
	</li>
</ol>
5. Phagocytosis assay
<ol>
	<li>Prepare a 33,000 yeasts/&#181;L suspension for each condition, as described below:
	<ol>
		<li>Add approximately 0.75 mg of dry yeast (Saccharomyces cerevisiae; see Table of Materials) to 200 &#181;L of HBSS Ca2+Mg2+ and incubate in a thermomixer at 100 &#176;C with 500 rpm for at least 15 min.</li>
		<li>Homogenize the mixture by vortexing and transfer 5 &#181;L of yeast suspension to 45 &#181;L of 0.2% trypan blue dye. Count the yeasts using a Neubauer chamber.</li>
		<li>Adjust the concentration of the initial suspension to 33,000 yeast cells/&#181;L using HBSS Ca2+Mg2+. Keep the suspension on ice until use.</li>
	</ol>
	</li>
	<li>After 20 min of cell activation, gently mix the cell suspension and transfer 5 &#181;L of the activation system to 5 &#181;L of the 33,000 yeast/&#181;L Saccharomyces cerevisiae suspension in a new sterile microtube. 
	NOTE: The neutrophil to yeast ratio is 1:5 (PMN:yeast).</li>
	<li>Immediately transfer 6 &#181;L of the PMN/yeast suspension into three wells of a clean glass slide (2 &#181;L each) and incubate the slide in a humidified chamber for 40 min. 
	NOTE: Do not spread the cell suspension too much over the slide; otherwise, it may dry out before incubation.</li>
	<li>Dry the slide under hot air and stain with fast panoptic, as described in step 2.9 above. 
	NOTE: The third step of the fast panoptic staining is critical to the microscopy analysis of the slide. Staining the slide for &#8805;3 s at this step can render it unfit for analysis, since it will be difficult to differentiate yeast from neutrophil nuclear lobes.</li>
	<li>Observe the slides under the microscope, counting 100 random neutrophils of each well and discriminating between PMNs positive and negative for phagocytosis. 
	NOTE: At least one yeast particle within or in direct contact with the PMN cellular membrane indicates a PMN positive for phagocytosis. If interested in the yeast/neutrophil ratio, count the number of yeast particles engulfed as well.</li>
</ol>
6. Real-time PMN chemotaxis assay
NOTE: The migration assay is performed similarly to the protocol described previoulsy15, with the following adaptations:
<ol>
	<li>Prepare the chemotactic gradient by adding 160 &#181;L of chemoattractant (e.g., fMLP, IL-8, C5, or LTB4; see Table of Materials) to the lower chamber of an impedance-based real time cell analyzer (RTCA) plate. For negative controls and blanks, add 160 &#181;L of HBSS Ca2+Mg2+.</li>
	<li>Attach the upper chamber and add 25 &#181;L of HBSS Ca2+Mg2+. Incubate at room temperature for at least 1 h to form the chemotactic gradient.</li>
	<li>After 60 min of cell activation, gently mix the cell suspension and place 60 &#181;L of cell suspension in the upper chamber. Add 60 &#181;L of HBSS Ca2+Mg2+ to the blank.</li>
	<li>Place the RTCA plate and program the RTCA software to measure the cell index (CI) every 60 s for 2 h. 
	&#8203;NOTE: The RTCA plates can be washed for reuse as previously described16. In summary, wash the RTCA chambers and electrodes with phosphate-buferred saline (PBS) three times, then with type I ultrapure water twice. Incubate the lower and upper chamber with 0.25% trypsin 0.53 mM ethylenediaminetetraacetic acid (EDTA) for 40 min. Wash with ultrapure water three times.</li>
</ol>
7. NET suggestive assay
<ol>
	<li>After 10 min of cell activation, gently mix the cell suspension and transfer 4 &#181;L of the PMNs from each activation system under evaluation, divided into two wells of a clean glass slide. Incubate in a humidified chamber at 37 &#176;C for 30 min.</li>
	<li>Add 1 &#181;L of DNAse I to one of the wells and incubate for 20 min at 37 &#176;C (in a wet chamber).</li>
	<li>Dry the slide and stain with fast panoptic, as previously described in step 2.9&#160;of the &#34;neutrophil isolation&#34; section.</li>
	<li>Evaluate the slides under a microscope. 
	NOTE: Look for any indication of NET release, characterized by the presence of web-like structures. Once identified, confirm if the DNAse I treatment was capable of removing such structures. This assay is suggestive of NET formation, as additional tests are required to confirm their presence.</li>
</ol>

Neutrophil Functional Assays for Screening Different Signaling Pathways

The authors declare no conflict of interest.

Neutrophils are highly dynamic and responsive cells that are short-lived and cannot yet be cryopreserved19, making investigations into their biology challenging. Therefore, it is essential to follow careful steps to obtain viable, enriched, and resting neutrophils11,20. This study employed a density-based isolation technique that emphasizes gentle and minimal manipulation, as well as the use of low temperatures until the activation step. A...

Neutrophils are the most abundant innate immune cells in human blood and are known to play a major part in infection and inflammation, being the first responders to arrive at the site of tissue damage1. In recent years, there has been a growing recognition of the crucial role that neutrophils play in a variety of diseases and in supporting homeostasis2. Neutrophils not only have tightly regulated signaling themselves, but also participate in the regulation of other components of the immune system3,4,5. Therefore, investigating neutrophils and their many unusual cellular functions, such as chemotaxis, reverse migration6, phagocytosis7, respiratory burst8, and the release of neutrophil extracellular traps (NETs)7, is imperative in numerous research contexts where it is necessary to assess the potential neutrophil functional, morphological, or molecular changes triggered by specific conditions under analysis.
Freshly isolated neutrophils are terminally differentiated, short-lived, highly dynamic, and easily activated9. However, an efficient storage method that does not affect the neutrophil responses has not yet been achieved, making it challenging to perform multiple assays that must be uninterrupted. Furthermore, previously described functional analyses10,11, based on assays that require cytometry and/or fluorescent staining, may not be a viable choice when a broad and initial evaluation of the neutrophil is needed.
To address these issues, this protocol describes a set of tests that can be carried out following a single isolation process, including the evaluation of cell viability, reactive oxygen species (ROS) production, real-time migration, and phagocytosis of Saccharomyces cerevisiae, whose results can be used to reason in-depth follow-up studies. This procedure, named NeutroFun Screen, was designed to encompass the leading effector activities, except degranulation, and can be completed in an average time of 4 h, including 1 h of activation. Additionally, the remaining cells can be used for more detailed approaches like omics studies. The advantage of this method lies in its balance between speed, comprehensiveness, cost, and accuracy.
Furthermore, there is a way to easily observe a preliminary suggestion of NETs, without specific markers, but enough to indicate if further efforts in that direction would be worthwhile. The diversity of functions tested aims to combine common points among tests, reducing the analysis time and expenses. The main goal of this method is to provide a balanced, functional analysis regarding speed, comprehensiveness, cost, and accuracy that allows for an overview of the neutrophil&#39;s response, making it a useful initial step in investigating the effects of novel stimuli on normal density neutrophils.

<table><tbody><tr><td>CIM-Plate 16</td><td>Agilent&amp;nbsp;</td><td>5665825001</td><td></td></tr><tr><td>CLARIOstar Plate Reader&amp;nbsp;</td><td>BMG LABTECH</td><td></td><td>US Patent Number 9,733,124&lt;br/&gt; Product details: MARS Data Analysis Software</td></tr><tr><td>Dimethyl sulfoxide</td><td>Din&amp;acirc;mica</td><td>1582</td><td></td></tr><tr><td>DNAse I</td><td>Sigma - Aldrich</td><td>DN 25</td><td></td></tr><tr><td>Ethylenediaminetetraacetic acid disodium salt dihydrate</td><td>Sigma - Aldrich</td><td>E5134</td><td></td></tr><tr><td>Fast panoptic stain</td><td>Laborclin</td><td>620529</td><td></td></tr><tr><td>Glass slide</td><td>Exacta</td><td>7102</td><td></td></tr><tr><td>Hank&amp;rsquo;s Balanced Salt Solution with calcium, with magnesium, without phenol red.</td><td>Sigma - Aldrich</td><td>55037C</td><td></td></tr><tr><td>Hank&amp;rsquo;s Balanced Salt Solution without calcium chloride, magnesium sulfate and sodium bicarbonate.</td><td>Sigma - Aldrich</td><td>H4641</td><td></td></tr><tr><td>Heparin</td><td>Blau</td><td>&amp;nbsp;7896014655229</td><td></td></tr><tr><td>Laminar flow cabinet</td><td>Veco</td><td>VLFS-12</td><td></td></tr><tr><td>Microscope</td><td>Zeiss</td><td>415501-0101-002</td><td>Product details: Primostar 1</td></tr><tr><td>Mixing Block</td><td>BIOER</td><td>MB-102</td><td></td></tr><tr><td>Neubauer improved bright-lined</td><td>New Optik</td><td>1110000</td><td></td></tr><tr><td>N-formyl-methionyl-leucyl-phenylalanine</td><td>Sigma - Aldrich</td><td>F3506</td><td></td></tr><tr><td>Nitroblue tetrazolium</td><td>Neon</td><td>CAS 298-83-9</td><td></td></tr><tr><td>Percoll</td><td>Cytiva</td><td>17089101</td><td>separation media</td></tr><tr><td>Phorbol 12-myristate 13-acetate</td><td>Sigma - Aldrich</td><td>P8139</td><td></td></tr><tr><td>Phosphate buffered saline tablet</td><td>Sigma - Aldrich</td><td>P4417</td><td></td></tr><tr><td>ROTOFIX 32 A</td><td>Hettich</td><td>1206</td><td></td></tr><tr><td>Saccharomyces cerevisiae</td><td>Fleischmann</td><td></td><td></td></tr><tr><td>Safranin</td><td>Sigma - Aldrich</td><td>50240</td><td></td></tr><tr><td>Sodium dodecyl sulfate</td><td>Cytiva</td><td>17-1313-01</td><td></td></tr><tr><td>Sonicator</td><td>Qsonica</td><td>Q125</td><td></td></tr><tr><td>Trypan blue solution</td><td>Vetec</td><td>C.I. 23850</td><td></td></tr><tr><td>Vortex Genie 2</td><td>Scientific Industries, Inc.</td><td>0K-0500-902</td><td></td></tr><tr><td>xCELLigence Real-Time Cell Analysis (RTCA) DP (dual purpose)</td><td>Agilent&amp;nbsp;</td><td>380601050</td><td>Product details: RTCA system composed of detection hardware, cell plates and software</td></tr></tbody></table>

a set of screening techniques for a quick overview of the neutrophil function

Neutrophils are known as one of the first lines of defense in the innate immune response and can perform many particular cellular functions, such as chemotaxis, reverse migration, phagocytosis, degranulation of cytotoxic enzymes and metabolites, and release of DNA as neutrophil extracellular traps (NETs). Neutrophils not only have tightly regulated signaling themselves, but also participate in the regulation of other components of the immune system. As fresh neutrophils are terminally differentiated, short-lived, and highly variable among individuals, it is important to make the most of the collected samples. Researchers often need to perform screening assays to assess an overview of the many neutrophil functions that may be affected by specific conditions under evaluation. A set of tests following a single isolation process of normal density neutrophils was developed to address this need, seeking a balance between speed, comprehensiveness, cost, and accuracy. The results can be used to reason and guide in-depth follow-up studies. This procedure can be carried out in an average time of 4 h and includes the evaluation of cell viability, reactive oxygen species (ROS) production, real-time migration, and phagocytosis of yeast on glass slides, leaving enough cells for more detailed approaches like omics studies. Moreover, the procedure includes a way to easily observe a preliminary suggestion of NETs after fast panoptic staining observed by light microscopy, with a lack of specific markers, albeit enough to indicate if further efforts in that way would be worthwhile. The diversity of functions tested combines common points among tests, reducing the analysis time and expenses. The procedure was named NeutroFun Screen, and although having&#160;limitations, it balances the aforementioned factors. Furthermore, the aim of this work is not a definite test set, but rather a guideline that can easily be adjusted to each lab&#39;s resources and demands.

The density-based isolation method used in this study (Figure 1) met the criteria for the proposed experiments. Neutrophil parameters obtained from this method included viability &#8805;98%, purity &#8805;94%, and cell yield &#8805;1.5 x 107, with no activation detectable&#160;by the screening tests. Two relevant steps in the isolation of PMNs are anticoagulation and RBC removal. Keeping the anticoagulated blood tube or syringe at a gentle rocking before layering over the density ...

Watch this Scientific Journal Video about Balancing Speed, Cost, and Accuracy in Neutrophil Function Assessment with NeutroFun Screen Protocol at JoVE.com

Author Spotlight: Balancing Speed, Cost, and Accuracy in Neutrophil Function Assessment with NeutroFun Screen Protocol 

This protocol features a set of neutrophil functional assays to be used as a screening method to cover functions from different signaling pathways. The protocol includes an initial and simple evaluation of cell viability, purity, reactive oxygen species production, real-time migration, phagocytosis, and a preliminary suggestion of neutrophil extracellular traps.

A Set of Screening Techniques for a Quick Overview of the Neutrophil Function

Neutrophils are known as one of the first lines of defense in the innate immune response and can perform many particular cellular functions, such as ...

a-set-screening-techniques-for-quick-overview-neutrophil

Research

JoVE Journal

Immunology and Infection

2.4K Views.  University of Brasilia. This protocol features a set of neutrophil functional assays to be used as a screening method to cover functions from different signaling pathways. The protocol includes an initial and simple evaluation of cell viability, purity, reactive oxygen species production, real-time migration, phagocytosis, and a preliminary suggestion of neutrophil extracellular traps.

Video: Author Spotlight: Balancing Speed, Cost, and Accuracy in Neutrophil Function Assessment with NeutroFun Screen Protocol 

Microfluidic Platform for Measuring Neutrophil Chemotaxis from Unprocessed Whole Blood

Neutrophils play an essential role in protection against infections and their numbers in the blood are frequently measured in the clinic. Higher neutrophil counts in the blood are usually an indicator of ongoing infections, while low neutrophil counts are a warning sign for higher risks for infections. To accomplish their functions, neutrophils also have to be able to move effectively from the blood where they spend most of their life, into tissues, where infections occur. Consequently, any defects in the ability of neutrophils to migrate can increase the risks for infections, even when neutrophils are present in appropriate numbers in the blood. However, measuring neutrophil migration ability in the clinic is a challenging task, which is time consuming, requires large volume of blood, and expert knowledge. To address these limitations, we designed a robust microfluidic assays for neutrophil migration, which requires a single droplet of unprocessed blood, circumvents the need for neutrophil separation, and is easy to quantify on a simple microscope. In this assay, neutrophils migrate directly from the blood droplet, through small channels, towards the source of chemoattractant. To prevent the granular flow of red blood cells through the same channels, we implemented mechanical filters with right angle turns that selectively block the advance of red blood cells. We validated the assay by comparing neutrophil migration from blood droplets collected from finger prick and venous blood. We also compared these whole blood (WB) sources with neutrophil migration from samples of purified neutrophils and found consistent speed and directionality between the three sources. This microfluidic platform will enable the study of human neutrophil migration in the clinic and the research setting to help advance our understanding of neutrophil functions in health and disease.

This protocol details an assay designed to measure human neutrophil chemotaxis from one droplet of whole blood with robust reproducibility. This approach circumvents the need for neutrophil separation and requires only a few minutes of assay preparation time. The microfluidic chip enables the repeated measure of neutrophil chemotaxis over time in infants or small mammals, where sample volume is limited.

Neutrophils play an essential role in protection against infections and their numbers in the blood are frequently measured in the clinic. Higher ...

Bioengineering

Neutrophil Isolation and Analysis to Determine their Role in Lymphoma Cell Sensitivity to Therapeutic Agents

Neutrophils are the most abundant (40% to 75%) type of white blood cells and among the first inflammatory cells to migrate towards the site of inflammation. They are key players in the innate immune system and play major roles in cancer biology. Neutrophils have been proposed as key mediators of malignant transformation, tumor progression, angiogenesis and in the modulation of the antitumor immunity; through their release of soluble factors or their interaction with tumor cells. To characterize the specific functions of neutrophils, a fast and reliable method is coveted for in vitro isolation of neutrophils from human blood. Here, a density gradient separation method is demonstrated to isolate neutrophils as well as mononuclear cells from the blood. The procedure consists of layering the density gradient solution such as Ficoll carefully above the diluted blood obtained from patients diagnosed with chronic lymphocytic leukemia (CLL), followed by centrifugation, isolation of mononuclear layer, separation of neutrophils from RBCsby dextran then lysis of residual erythrocytes. This method has been shown to isolate neutrophils &#8805; 90 % pure. To mimic the tumor microenvironment, 3-dimensional (3D) experiments were performed using basement membrane matrix such as Matrigel. Given the short half-life of neutrophils in vitro, 3D experiments with fresh human neutrophils cannot be performed. For this reason promyelocytic HL60 cells are differentiated along the granulocytic pathway using the differentiation inducers dimethyl sulfoxide (DMSO) and retinoic acid (RA). The aim of our experiments is to study the role of neutrophils on the sensitivity of lymphoma cells to anti-lymphoma agents. However these methods can be generalized to study the interactions of neutrophils or neutrophil-like cells with a large range of cell types in different situations.

Neutrophils are the most abundant type of white blood cells. The isolation of neutrophils from human blood by density gradient separation method and the differentiation of human promyelocytic (HL60) cells along the granulocytic pathway are described here; to test their role on sensitivity of lymphoma cells to anti-lymphoma agents.

Neutrophils are the most abundant (40% to 75%) type of white blood cells and among the first inflammatory cells to migrate towards the site of ...

An All-on-chip Method for Rapid Neutrophil Chemotaxis Analysis Directly from a Drop of Blood

Neutrophil migration and chemotaxis are critical for our body's immune system. Microfluidic devices are increasingly used for investigating neutrophil migration and chemotaxis owing to their advantages in real-time visualization, precise control of chemical concentration gradient generation, and reduced reagent and sample consumption. Recently, a growing effort has been made by the microfluidic researchers toward developing integrated and easily operated microfluidic chemotaxis analysis systems, directly from whole blood. In this direction, the first all-on-chip method was developed for integrating the magnetic negative purification of neutrophils and the chemotaxis assay from small blood volume samples. This new method permits a rapid sample-to-result neutrophil chemotaxis test in 25 min. In this paper, we provide detailed construction, operation and data analysis method for this all-on-chip chemotaxis assay with a discussion on troubleshooting strategies, limitations and future directions. Representative results of the neutrophil chemotaxis assay testing a defined chemoattractant, N-Formyl-Met-Leu-Phe (fMLP), and sputum from a chronic obstructive pulmonary disease (COPD) patient, using this all-on-chip method are shown. This method is applicable to many cell migration-related investigations and clinical applications.

This article provides the detailed method of performing a rapid neutrophil chemotaxis assay by integrating the on-chip neutrophil isolation from whole blood and the chemotaxis test on a single microfluidic chip.

Neutrophil migration and chemotaxis are critical for our body's immune system. Microfluidic devices are increasingly used for investigating neutrophil ...

Bioparticle Microarrays for Chemotactic and Molecular Analysis of Human Neutrophil Swarming in vitro

Neutrophil swarming is a cooperative process by which neutrophils seal off a site of infection and promote tissue reorganization. Swarming has classically been studied in vivo in animal models showing characteristic patterns of cell migration. However, in vivo models have several limitations, including intercellular mediators that are difficult to access and analyze, as well as the inability to directly analyze human neutrophils. Because of these limitations, there is a need for an in vitro platform that studies swarming with human neutrophils and provides easy access to the molecular signals generated during swarming. Here, a multistep microstamping process is used to generate a bioparticle microarray that stimulates swarming by mimicking an in vivo infection. The bioparticle microarray induces neutrophils to swarm in a controlled and stable manner. On the microarray, neutrophils increase in speed and form stable swarms around bioparticle clusters. Additionally, supernatant generated by the neutrophils was analyzed and 16 proteins were discovered to have been differentially expressed over the course of swarming. This in vitro swarming platform facilitates direct analysis of neutrophil migration and protein release in a reproducible, spatially controlled manner.

This protocol generates bioparticle microarrays that provide spatially controlled neutrophil swarming. It provides easy access to the mediators that neutrophils release during migration and allows for quantitative imaging analysis.

Neutrophil swarming is a cooperative process by which neutrophils seal off a site of infection and promote tissue reorganization. Swarming has classically ...

Standardized In vitro Assays to Visualize and Quantify Interactions between Human Neutrophils and Staphylococcus aureus Biofilms

Neutrophils are the first line of defense deployed by the immune system during microbial infection. In vivo, neutrophils are recruited to the site of infection where they use processes such as phagocytosis, production of reactive oxygen and nitrogen species (ROS, RNS, respectively), NETosis (neutrophil extracellular trap), and degranulation to kill microbes and resolve the infection. Interactions between neutrophils and planktonic microbes have been extensively studied. There have been emerging interests in studying infections caused by biofilms in recent years. Biofilms exhibit properties, including tolerance to killing by neutrophils, distinct from their planktonic-grown counterparts. With the successful establishment of both in vitro and in vivo biofilm models, interactions between these microbial communities with different immune cells can now be investigated. Here, techniques that use a combination of traditional biofilm models and well-established neutrophil activity assays are tailored specifically to study neutrophil and biofilm interactions. Wide-field fluorescence microscopy is used to monitor the localization of neutrophils in biofilms. These biofilms are grown in static conditions, followed by the addition of neutrophils derived from human peripheral blood. The samples are stained with appropriate dyes prior to visualization under the microscope. Additionally, the production of ROS, which is one of the many neutrophil responses against pathogens, is quantified in the presence of a biofilm. The addition of immune cells to this established system will expand the understanding of host-pathogen interactions while ensuring the use of standardized and optimized conditions to measure these processes accurately.

Standardized In vitro Assays to Visualize and Quantify Interactions between Human Neutrophils and Staphylococcus aureus Biofilms

The present protocol describes the study of neutrophil-biofilm interactions. Staphylococcus aureus biofilms are established in vitro and incubated with peripheral blood-derived human neutrophils. The oxidative burst response from neutrophils is quantified, and the neutrophil localization within the biofilm is determined by microscopy.

Neutrophils are the first line of defense deployed by the immune system during microbial infection. In vivo, neutrophils are recruited to the site of ...

Quantifying NET Formation Using Dual-Dye Live Cell Analysis

Real-Time High Throughput Technique to Quantify Neutrophil Extracellular Traps Formation in Human Neutrophils

Neutrophils are myeloid-lineage cells that form a crucial part of the innate immune system. The past decade has revealed additional key roles that neutrophils play in the pathogenesis of cancer, autoimmune diseases, and various acute and chronic inflammatory conditions by contributing to the initiation and perpetuation of immune dysregulation through multiple mechanisms, including the formation of neutrophil extracellular traps (NETs), which are structures crucial in antimicrobial defense. Limitations in techniques to quantify NET formation in an unbiased, reproducible, and efficient way have restricted our ability to further understand the role of neutrophils in health and diseases. We describe an automated, real-time, high-throughput method to quantify neutrophils undergoing NET formation using a live cell imaging platform coupled with a membrane permeability-dependent dual-dye approach using two different DNA dyes to image intracellular and extracellular DNA. This methodology is able to help assess neutrophil physiology and test molecules that can target NET formation.

Author Spotlight: Quantifying Neutrophil Extracellular Traps in Disease and Drug Screening Using Dual-Color Live-Cell Imaging

We present an automated high-throughput method to quantify neutrophil extracellular traps (NETs) utilizing the live cell analysis system, coupled with a membrane permeability-dependent dual-dye approach.

Neutrophils are myeloid-lineage cells that form a crucial part of the innate immune system. The past decade has revealed additional key roles that ...

Screening of β2 Integrin Activation Inhibitors in Human Neutrophils

A Flow Cytometry-Based High-Throughput Technique for Screening Integrin-Inhibitory Drugs

This protocol aims to establish a method for identifying small molecular antagonists of &#946;2 integrin activation, utilizing conformational-change-reporting antibodies and high-throughput flow cytometry. The method can also serve as a guide for other antibody-based high-throughput screening methods. &#946;2 integrins are leukocyte-specific adhesion molecules that are crucial in immune responses. Neutrophils rely on integrin activation to exit the bloodstream, not only to fight infections but also to be involved in multiple inflammatory diseases. Controlling &#946;2 integrin activation presents a viable approach for treating neutrophil-associated inflammatory diseases. In this protocol, a monoclonal antibody, mAb24, which specifically binds to the high-affinity headpiece of &#946;2 integrins, is utilized to quantify &#946;2 integrin activation on isolated primary human neutrophils. N-formylmethionyl-leucyl-phenylalanine (fMLP) is used as a stimulus to activate neutrophil &#946;2 integrins. A high-throughput flow cytometer capable of automatically running 384-well plate samples was used in this study. The effects of 320 chemicals on &#946;2 integrin inhibition are assessed within 3 h. Molecules that directly target &#946;2 integrins or target molecules in the G protein-coupled receptor-initiated integrin inside-out activation signaling pathway can be identified through this approach.

Author Spotlight: Development of a Method for Identifying Small Molecular Antagonists of &#946;2 Integrin Activation 

This protocol describes a flow cytometry-based, high-throughput screening method to identify small-molecule drugs that inhibit &#946;2 integrin activation on human neutrophils.

This protocol aims to establish a method for identifying small molecular antagonists of &#946;2 integrin activation, utilizing ...

The MUB40 Peptide for Use in Detecting Neutrophil-Mediated Inflammation Events

Here, we provide a protocol involving the use of MUB40, a synthesized peptide with the ability to bind glycosylated lactoferrin stored at high concentrations in specific and tertiary granules of neutrophils. This protocol details how MUB40&#160;conjugated directly to a fluorophore can be used to stain neutrophils in fixed/permeabilized tissues as well as how this can be used in live-cell imaging to assay for neutrophil activation and de-granulation. Neutrophil detection methods are limited to species-specific monoclonal antibodies, which are not always suitable for certain applications. MUB40 does not penetrate the cell membrane and is thus excluded from lactoferrin stored in non-activated/non-permeabilized neutrophils. MUB40 has the added benefit of recognizing lactoferrin from a broad host range, making it especially useful for comparing results in studies involving multiple research models, reducing the number of duplicate reagents, and simplifying protocols through single-step staining.

The MUB40 Peptide for Use in Detecting Neutrophil-Mediated Inflammation Events

Here, we present a protocol to detect the presence of neutrophils in fixed/permeabilized histology sections and assess the activation state of live purified neutrophils. In particular, the MUB40&#160;peptide binds lactoferrin present in neutrophil-specific and tertiary granules. Exposure of the granule contents through either permeabilization or neutrophil activation allows for the marking of neutrophils.

Here, we provide a protocol involving the use of MUB40, a synthesized peptide with the ability to bind glycosylated lactoferrin stored at high ...

Biology

Isolation of Human Neutrophils from Whole Blood and Buffy Coats

Neutrophils (PMNs) are the most abundant leukocytes in human circulation, ranging from 40 to 70% of total blood leukocytes. They are the first cells recruited at the site of inflammation via rapid extravasation through vessels. There, neutrophils perform an array of functions to kill invading pathogens and mediate immune signaling. Freshly purified neutrophils from human blood are the model of choice for study, as no cell line fully replicates PMN functions and biology. However, neutrophils are short-lived, terminally differentiated cells and are highly susceptible to activation in response to physical (temperature, centrifugation speed) and biological (endotoxin, chemo- and cytokines) stimuli. Therefore, it is crucial to follow a standardized, reliable, and fast method to obtain pure and non-activated cells. This protocol presents an updated protocol combining density gradient centrifugation, red blood cell (RBC) sedimentation, and RBC lysis to obtain high PMN purity and minimize cell activation. Furthermore, methods to assess neutrophil isolation quality, viability, and purity are also discussed.

This protocol details a method for the isolation of neutrophils from whole blood, buffy coats, or leukapheresis membranes, achieving good yield, high purity, and minimal cell activation. We utilize gradient purification, red blood cell (RBC) sedimentation, and RBC lysis to obtain a high-quality/purity neutrophil preparation.

Neutrophils (PMNs) are the most abundant leukocytes in human circulation, ranging from 40 to 70% of total blood leukocytes. They are the first cells ...

Real-Time Microscopy for Studying NETosis Kinetics and Screening Inhibitors

Real-Time, High-Throughput Microscopic Quantification of Human Neutrophil Extracellular Trap Release and Assessing the Pharmacology of Antagonists

Neutrophils play an important role in innate immune defense by using several strategies, including the release of neutrophil extracellular traps (NETs) in a process referred to as NETosis. However, in the past two decades, it has become clear that the accumulation of NETs in tissues contributes to the pathophysiology of multiple inflammatory and autoimmune diseases. Therefore, interest in the development of NETosis antagonists has risen. Variable and non-standardized methods to detect and analyze NETosis were developed concomitantly, each with its own advantages and limitations. Here, we describe a real-time microscopy method for the quantification of human NET release, allowing to study NETosis as well as NET inhibition in a high-throughput manner. The surface area-based semi-automated analysis recognizes NETs and distinguishes them from non-netting activated neutrophils. We demonstrate that the non-physiological NETosis inducers, calcium ionophore and phorbol-12-myristate-13-acetate (PMA), trigger the release of NETs with different characteristics and kinetics. Furthermore, we show that this approach allows studying NET release in response to disease-relevant stimuli, including immune complexes, N-Formylmethionine-leucyl-phenylalanine (fMLF), monosodium urate crystals, and calcium pyrophosphate crystals. To exemplify the utility of this method to study NETosis antagonists, we used CIT-013, a first-in-class monoclonal antibody inhibitor of NET release. CIT-013 targets citrullinated histone H2A and H4 and efficiently inhibits NET release with an IC50 of 4.6 nM. Other anti-histone antibodies tested lacked this NETosis-inhibitory capacity. Altogether, we demonstrate that this protocol enables specific, reliable, and reproducible high-throughput quantification of NETs, enhancing the study of NET release characteristics, kinetics, and pharmacology of NETosis antagonists.

This defined protocol describes a real-time high-throughput microscopy approach to visualize and quantify human neutrophil extracellular trap (NET) release in vitro. The reproducible method allows investigation of the characteristics and kinetics of NET release upon stimulation with distinct NETosis inducers and enables assessment of the pharmacology of NETosis antagonists.

Neutrophils play an important role in innate immune defense by using several strategies, including the release of neutrophil extracellular traps (NETs) in ...

A Set of Screening Techniques for a Quick Overview of the Neutrophil Function

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Chapters in this video

Microfluidic Platform for Measuring Neutrophil Chemotaxis from Unprocessed Whole Blood

Neutrophil Isolation and Analysis to Determine their Role in Lymphoma Cell Sensitivity to Therapeutic Agents

An All-on-chip Method for Rapid Neutrophil Chemotaxis Analysis Directly from a Drop of Blood

Bioparticle Microarrays for Chemotactic and Molecular Analysis of Human Neutrophil Swarming in vitro

Standardized In vitro Assays to Visualize and Quantify Interactions between Human Neutrophils and Staphylococcus aureus Biofilms

Real-Time High Throughput Technique to Quantify Neutrophil Extracellular Traps Formation in Human Neutrophils

A Flow Cytometry-Based High-Throughput Technique for Screening Integrin-Inhibitory Drugs

The MUB₄₀ Peptide for Use in Detecting Neutrophil-Mediated Inflammation Events

Isolation of Human Neutrophils from Whole Blood and Buffy Coats

Real-Time, High-Throughput Microscopic Quantification of Human Neutrophil Extracellular Trap Release and Assessing the Pharmacology of Antagonists