Name: simultaneous study of the recruitment of monocyte subpopulations under flow in vitro
Uploaded: 2018-11-26T14:00:00
Description: Watch this Scientific Journal Video about Simultaneous Study of the Recruitment of Monocyte Subpopulations Under Flow In Vitro at JoVE.com

We thank Dr. Paul Bradfield for manuscript reading and feedbacks. A. S. received financial support from the Sir Jules Thorn Charitable Overseas Trust Reg.,

Human materials were used with the informed consent of volunteer donors and in accordance with the Swiss Ethics Committees on clinical research.
1. Isolation and Freezing of Human Umbilical Vein Endothelial Cells (HUVEC)
<ol>
	<li>Add 5 mL of coating solution to a T75 flask (0.1 mg/mL collagen G and 0.2% gelatin in phosphate buffered saline PBS at pH 7.4) for 30 min at 37 &#176;C before initiating HUVEC isolation.</li>
	<li>Clean the cord with PBS, wipe it with sterile compresses, and place ...

<ol>
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Here, we report a method detailing a study of how monocyte subpopulations transmigrate through the inflamed endothelial monolayer. The discussed method used confocal microscopy instead of phase-contrast microscopy, which is also used to study monocyte recruitment under flow3,11,19. One major advantage of using confocal microscopy for time-lapse imaging is the ability to unambiguously discriminate between transmigration and stron...

Monocytes constitute a phagocytic component of innate immunity that is essential for fighting pathogens, cleaning up damaged tissues, angiogenesis, and the pathophysiology of many diseases including cancers1,2,3. Monocytes are bone marrow-derived cells composed of heterogeneous subpopulations that circulate in the blood but can be recruited to the site of inflammation in peripheral tissue through specific molecular mechanisms. The recruitment cascades of monocytes, as for leukocytes in general, implicates different steps including capture, rolling, crawling, arrest, transendothelial migration (transmigration) and migration through the vessel wall (basement membrane and mural cells)4. These steps mainly involve inflammation-induced molecules on the endothelial luminal surface such as selectins, glycoprotein ligands, chemokines, intercellular and junctional adhesion molecules, and their receptors on leukocytes such as selectin ligands and integrins. Trafficking pathways through either the endothelial cell junctions (paracellular) or through the endothelial cell body (transcellular) can be used by leukocytes to cross the endothelial barrier5. Whilst monocytes have historically been documented to transmigrate through the transcellular route, potential divergences in their migratory pathway have been proposed as monocytes are no longer considered a homogeneous cell population. It is now becoming clear that monocyte diversity can be defined by each of their differences and commonalities, with respect to their distinctive extravasation cascades3,6. Therefore, in order to unambiguously discriminate between monocyte subpopulations, it is crucial to visualize and phenotype the behavior of each of these different subpopulations during the recruitment process.
Monocytes from human, pig, rat and mouse were subdivided into phenotypic subpopulations with certain ascribed functions and specific migratory behaviors7,8,9. For example, in humans, monocytes can be divided into three subsets based on their surface expression of CD14, a coreceptor for bacterial lipopolysaccharide, and CD16, the Fc-gamma receptor III. Human monocyte subpopulations include classical CD14+CD16-, intermediate CD14+CD16+ and non-classical CD14dimCD16+ cells6,9. The classical CD14+CD16- monocytes were shown to be mainly inflammatory whereas the pool of CD16+ monocytes were collectively found to present TIE2 expression and proangiogenic function10. Consistently, endothelial cell stimulation with inflammatory cytokines such as human tumor necrosis factor (TNF)&#945; or interleukin (IL-1)beta (conventional inflammation) is sufficient to trigger the complete recruitment of classical CD14+CD16- monocytes. However, simultaneous actions of vascular endothelial growth factor (VEGF)A and TNF&#945; (angiogenic factors-driven inflammation) are required to provoke the transmigration of the CD16+ proangiogenic pool of monocytes3. Historically, the traditional Transwell system under static conditions, the parallel plate flow chamber, and the &#181;-slide flow chambers have been used to quantitatively analyze the recruitment of one leukocyte population at a time in vitro11,12,13. Whilst these protocols have been validated, a more robust method that allowed the simultaneous analysis of multiple monocyte subpopulations would be considered more insightful. Such methodologies must account for multiple interactions and the differing frequencies of each respective population and also provide a mechanistic understanding of the similarities and specificities for the recruitment cascades that define each monocyte subset.
Here, we present a method based on the time-lapse imaging of monocyte recruitment under flow which allows the migratory cascades of different monocyte subpopulations to be studied simultaneously by using confocal microscopy. This method integrates certain critical features that mimic endothelial cell inflammation, as well as the hemodynamics of circulating monocytes in post-capillary venules, the main location of leukocyte recruitment in vivo. The proposed method uses human umbilical vein endothelial cells (HUVEC), which are generated through a well-established protocol of isolation from human umbilical cords. This clinical resource has the advantage of being easily available as a biological by-product, whilst also providing a reasonable yield of endothelial cells that can be isolated from the umbilical vein. We also used fluorescent dyes and immunofluorescence to distinguish between the different cellular components, and confocal microscopy to unambiguously define monocyte positioning (luminal vs. abluminal) over time. The protocol presented here has been developed to simultaneously measure the transmigration levels of monocyte subpopulations. Moreover, it should be noted that this methodology can be extended to study other leukocytes subpopulations and recruitment processes by use of different biomarkers and labelling.

<table>
	<tbody>
		<tr>
			<td>Tissue Culture Flasks 75 cm2</td>
			<td>TPP</td>
			<td>90076</td>
			<td>Routine culture of isolated HUVEC</td>
		</tr>
		<tr>
			<td>&#181;-Slide VI 0.4</td>
			<td>IBIDI</td>
			<td>80606</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge Tubes 15 mL</td>
			<td>TPP</td>
			<td>191015</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge Tubes 50 mL</td>
			<td>TPP</td>
			<td>191050</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagen G</td>
			<td>Biochrom</td>
			<td>L 7213</td>
			<td>For coating of cell culture flasks</td>
		</tr>
		<tr>
			<td>Gelatin</td>
			<td>Sigma-Aldrich</td>
			<td>1393</td>
			<td>For coating of cell culture flasks</td>
		</tr>
		<tr>
			<td>Dulbecco&#8217;s Phosphate Buffered Saline (without MgCl2 and CaCl2)</td>
			<td>Sigma-Aldrich</td>
			<td>D8537</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#8217;s Phosphate Buffered Saline (with MgCl2 and CaCl2)</td>
			<td>Sigma-Aldrich</td>
			<td>D8662</td>
			<td></td>
		</tr>
		<tr>
			<td>RPMI-1640 Medium</td>
			<td>Sigma-Aldrich</td>
			<td>R8758</td>
			<td></td>
		</tr>
		<tr>
			<td>3-Way Stopcocks</td>
			<td>BIO-RAD</td>
			<td>7328103</td>
			<td></td>
		</tr>
		<tr>
			<td>penicillin 10000 u/ml streptomycine 10000 ug/ml fungizone 25 ug/ml</td>
			<td>AMIMED</td>
			<td>4-02F00-H</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase type 1</td>
			<td>Worthington</td>
			<td>LS004216</td>
			<td></td>
		</tr>
		<tr>
			<td>Medium 199 1X avec Earle&#39;s salts, L-Glutamine, 25 mM Hepes</td>
			<td>GIBCO</td>
			<td>22340020</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Albumin Fraction V</td>
			<td>ThermoFisher</td>
			<td>15260037</td>
			<td></td>
		</tr>
		<tr>
			<td>Endothelial Cell Growth Supplement, 150mg</td>
			<td>Millipore</td>
			<td>02-102</td>
			<td></td>
		</tr>
		<tr>
			<td>Heparin Sodium</td>
			<td>Sigma-Aldrich</td>
			<td>H3149RT</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrocortisone</td>
			<td>Sigma-Aldrich</td>
			<td>H6909</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Ascorbic acid</td>
			<td>Sigma-Aldrich</td>
			<td>A 4544</td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA disodium salt dihydrate C10H14N2Na2O8 &#183; 2H2O</td>
			<td>APPLICHEM</td>
			<td>A2937.0500</td>
			<td></td>
		</tr>
		<tr>
			<td>CD144 (VE-Cadherin), human recombinant clone: REA199, FITC</td>
			<td>Miltenyi Biotech</td>
			<td>130-100-713</td>
			<td>AB_2655150</td>
		</tr>
		<tr>
			<td>CD31-PE antibody, human recombinant clone: REA730, PE</td>
			<td>Miltenyi Biotech</td>
			<td>130-110-807</td>
			<td>AB_2657280</td>
		</tr>
		<tr>
			<td>Anti-Podoplanin-APC, human recombinantclone: REA446, APC</td>
			<td>Miltenyi Biotech</td>
			<td>130-107-016</td>
			<td>AB_2653263</td>
		</tr>
		<tr>
			<td>BD Accuri C6 Plus</td>
			<td>BD Bioscience</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>&#181;-Slide I Luer</td>
			<td>IBIDI</td>
			<td>80176</td>
			<td></td>
		</tr>
		<tr>
			<td>CMFDA (5-chloromethylfluorescein diacetate)</td>
			<td>ThermoFisher</td>
			<td>C2925</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant human TNF&#945;</td>
			<td>Peprotech</td>
			<td>300-01A</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant human VEGFA</td>
			<td>Peprotech</td>
			<td>100-20</td>
			<td></td>
		</tr>
		<tr>
			<td>NE-1000 Programmable Syringe Pump</td>
			<td>KF Technology</td>
			<td>NE-1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Ficoll&#160;Paque Plus</td>
			<td>GE Healthcare</td>
			<td>17-1440-02</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-human CD14-PE, human recombinant clone: REA599, PE</td>
			<td>Miltenyi Biotech</td>
			<td>130-110-519</td>
			<td>AB_2655051</td>
		</tr>
		<tr>
			<td>Pan Monocyte Isolation Kit, human</td>
			<td>Miltenyi Biotech</td>
			<td>130-096-537</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-human CD16-PE, human recombinant clone: REA423, PE</td>
			<td>Miltenyi Biotech</td>
			<td>130-106-762</td>
			<td>AB_2655403</td>
		</tr>
		<tr>
			<td>LS columns</td>
			<td>Miltenyi Biotech</td>
			<td>130-042-401</td>
			<td></td>
		</tr>
		<tr>
			<td>QuadroMACS Separator</td>
			<td>Miltenyi Biotech</td>
			<td>130-090-976</td>
			<td></td>
		</tr>
		<tr>
			<td>Hoechst 33342, Trihydrochloride, Trihydrate</td>
			<td>ThermoFisher</td>
			<td>H1399</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicone tubing</td>
			<td>IBIDI</td>
			<td>10841</td>
			<td></td>
		</tr>
		<tr>
			<td>Elbow Luer Connector</td>
			<td>IBIDI</td>
			<td>10802</td>
			<td></td>
		</tr>
		<tr>
			<td>Female Luer Lock Coupler</td>
			<td>IBIDI</td>
			<td>10823</td>
			<td></td>
		</tr>
		<tr>
			<td>Luer Lock Connector Female</td>
			<td>IBIDI</td>
			<td>10825</td>
			<td></td>
		</tr>
		<tr>
			<td>In-line Luer Injection Port</td>
			<td>IBIDI</td>
			<td>10820</td>
			<td></td>
		</tr>
		<tr>
			<td>Ar1 confocal microscope</td>
			<td>Nikon</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>40X objective</td>
			<td>Nikon</td>
			<td>40x 0.6 CFI ELWD S Plane Fluor WD:3.6-2.8mm correction 0-2mm</td>
			<td></td>
		</tr>
		<tr>
			<td>ImageJ Software</td>
			<td>NIH</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
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simultaneous study of the recruitment of monocyte subpopulations under flow in vitro

The recruitment of monocytes from the blood to targeted peripheral tissues is critical to the inflammatory process during tissue injury, tumor development and autoimmune diseases. This is facilitated through a process of capture from free flow onto the luminal surface of activated endothelial cells, followed by their adhesion and transendothelial migration (transmigration) into the underlying affected tissue. However, the mechanisms that support the preferential and context-dependent recruitment of monocyte subpopulations are still not fully understood. Therefore, we have developed a method that allows the recruitment of different monocyte subpopulations to be simultaneously visualized and measured under flow. This method, based on time-lapse confocal imaging, allows for the unambiguous distinction between adherent and transmigrated monocytes. Here, we describe how this method can be used to simultaneously study the recruitment cascade of pro-angiogenic and non-angiogenic monocytes in vitro. Furthermore, this method can be extended to study the different steps of recruitment of up to three monocyte populations.

Determining the state of HUVEC activation induced by TNF&#945;
The bio-activity of the inflammatory cytokine TNF&#945; can be vary according to the batch and the repletion of freezing-thawing cycle. It is important to check the activation status of HUVEC with TNF&#945; treatment. This could be performed by staining in parallel some samples of confluent HUVEC for the inflammatory induction of selectins, ICAM-1 and VCAM-1<sup class="...

Watch this Scientific Journal Video about Simultaneous Study of the Recruitment of Monocyte Subpopulations Under Flow In Vitro at JoVE.com

Simultaneous Study of the Recruitment of Monocyte Subpopulations Under Flow In Vitro

Here, we present an integrated protocol that measures monocyte subpopulation trafficking under flow in vitro by use of specific surface markers and confocal fluorescence microscopy. This protocol can be used to explore sequential recruitment steps as well as to profile other leukocyte subtypes using other specific surface markers.

The recruitment of monocytes from the blood to targeted peripheral tissues is critical to the inflammatory process during tissue injury, tumor development ...

For this method can help answer key question in the field of inflammation and immunology. For example, what are the molecular mechanism of leukocyte adhesion and trans-endothelial migration. The main advantage of this technique is that it allows unlimited use discrimination between transmigration and strong addition of monocytes to endothelial monolayer.Although this method provides information about the recruitment of monocytes on the flow, it can also be adapted to other cells of the hematopoietic systems such as T-cells, B-cells, or derivatives of subpopulation thereof. After washing, label the human umbilical vein endothelial cells or HUVEC with 30 microliters of 37 degree Celsius M199 medium supplemented with one micromolar CMFDA for 10 minutes at 37 degree Celsius and 5%Carbon dioxide. At the end of the incubation, wash the cells with 150 microliters of complete M199 medium and incubate the culture in 150 microliters of fresh complete M199 medium for another 30 minutes.Then replace the supernatant with 150 microliters of complete M199 medium containing the appropriate experimental supplements and return the slide chamber culture to the incubator for six hours. For human PAN monocyte isolation, dilute a freshly collected blood sample in PBS supplemented with one millimolar EDTA at a one to one ratio and carefully layer 20 ml of the blood solution onto 20 ml of density gradient medium for density gradient separation by centrifugation. Collect the middle peripheral blood mononuclear cell platelet layer into a new 50 ml tube containing 40 ml of PBS supplemented with 1 millimolar EDTA and bring the final volume to 50 ml with additional PBS-EDTA After counting, isolate the monocytes with the PAN monocyte isolation kit according to the manufacturer's instruction.And wash the cells three times in M199 medium supplemented with 0.5%Bovine Serum Albumin, or BSA, to eliminate any traces of EDTA. The quality of monocyte isolation is critical for ensuring robust transmigration and adhesion result. Thus it is important to strictly follow the manufacturer's recommendation for the isolation.Resuspend the pellet at a 6 times 10 to the 6 monocytes per ml concentration in fresh M199 medium supplemented with 0.5%BSA and divide the cells into one 200 microliter aliquot per microcentrifuge tube per recruitment assay. Then place the cells at 37 degree Celsius for 20 minutes before their injection into the flow chamber. To prepare the fluidic system for the analysis, first insert a male luer connector into one end of an 8 cm long 3 mm thick piece of silicone tubing and connect the other end to an inline luer injection set.Then connect the luer connector to one end of a 40 cm long 3 mm thick piece of silicone tubing. Next, the 20 mm syringe to one end of a 1 m long 3mm thick piece of silicone tubing and insert a male luer connector to the other end. Then insert both male luer connectors into a female luer lock coupler and place the free end of the silicone tubing into a reservoir of 37 degree Celsius M199 medium supplemented with 0.5%BSA.Retract the plunger to fill the tubing with flow buffer and secure the syringe on the syringe pump. Then set the pump to the withdraw mode and specify the flow rate. To connect the slide chamber, clamp the silicone tubing around the female luer lock coupler and disconnect the two luer connector males from the coupler to allow them to be connected to the reservoir of the slide.Air bubbles not only disturb the image quality but also induce capillary sheer stress to the cells, leading to cell death. To avoid air bubbles, confirm the correct clamping of the tubing before inserting the luer into the reservoir. Then remove the clamps to confirm that the connection is not leaking and place the slide under the microscope.For imaging of the monocyte recruitment under flow, add 5 microliters of flourescence conjugated anti CD16 antibody and an appropriate nuclear dye to each aliquoted monocytes for a 10 minute incubation at room temperature and collect the cells with a brief centrifugation. Resuspend the pellet in 250 microliters of flow buffer and start the syringe pump. Add 30 microliters of one monocyte suspension to one chamber of the slide and select the 40X objective on the confocal microscope.Activate the appropriate fluorescent lasers and use the chamber with the labeled monocyte to set the acquisition parameters of the confocal microscope Next, select three fields of view within a half centimeter radius for multi position confocal imaging, and set a Z stack to the 10 to 12 micrometer range and the time lapse acquisition to run every one minute. After three minutes of imaging, inject 200 microliters of monocytes through the inline luer injection port and begin imaging the cellular interaction. After at least 30 minutes, stop the imaging and the flow and clamp the tubing to allow it to be disconnected from the slide.To determine the transmigration rate of the cells through the stimulated HUVECs, open image J and count the total number of adherent monocytes in each field to determine the cell count per square millimeter. Then count the number of transmigrated monocytes that are present in the basal plane underneath the endothelial cells as identified by the presence of a black hole zone around the nucleus. A simple way to check the activation status of the HUVECs after stimulation is to visualization of their elongation under inflammatory stress.Time lapse confocal imaging allows visualization of the monocytes at the apical plane where their phenotype can be assessed. Migrating cells undergoing transmigration move to the intercellular cell-to-cell junction before they disappear from the apical plane and reappear in the basal plane. Quantitation of the monocyte recruitment over time confirms that monocyte adhesion is followed by transmigration.The transmigration rate of CD16 positive monocyte is low when the endothelial cell are stimulated with TNF alpha only but increases when the endothelial cells are stimulated with both TNF alpha and vascular endothelial growth factor or VEGFA. HUVEC stimulation with TNF alpha and TNF alpha plus VEGFA induces an increase in the adherence to CD14 negative T, B and NK cells, compare to CD14 positive monocytes. In addition, HUVEC stimulation induces transmigration of the monocyte population only, as T, B and NK cells do not transmigrate under either TNF alpha or TNF alpha plus VEGFA stimulatory conditions.To perform an optimal monocyte recruitment assay, it is important that you plan your experiment in advance and do it at the same day. And when you purify the cells, make sure that your microscope is at 37 degrees so that you do not transfer the cells to different temperature during the experiment. To learn this procedure, all the methods like the profiling of HUVEC cytokine and chemokine expression as well as chemotaxis studies can be performed to answer additional question about the molecular mechanism that sustain the transmigration and adhesion of specific monocyte population.

simultaneous-study-recruitment-monocyte-subpopulations-under-flow

Research

JoVE Journal

Immunology and Infection

Human In Vitro Suppression as Screening Tool for the Recognition of an Early State of Immune Imbalance

Regulatory T cells (Tregs) are critical mediators of immune tolerance to self-antigens. In addition, they are crucial regulators of the immune response following an infection. Despite efforts to identify unique surface marker on Tregs, the only unique feature is their ability to suppress the proliferation and function of effector T cells. While it is clear that only in vitro assays can be used in assessing human Treg function, this becomes problematic when assessing the results from cross-sectional studies where healthy cells and cells isolated from subjects with autoimmune diseases (like Type 1 Diabetes-T1D) need to be compared. There is a great variability among laboratories in the number and type of responder T cells, nature and strength of stimulation, Treg:responder ratios and the number and type of antigen-presenting cells (APC) used in human in vitro suppression assays. This variability makes comparison between studies measuring Treg function difficult. The Treg field needs a standardized suppression assay that will work well with both healthy subjects and those with autoimmune diseases. We have developed an in vitro suppression assay that shows very little intra-assay variability in the stimulation of T cells isolated from healthy volunteers compared to subjects with underlying autoimmune destruction of pancreatic &beta;-cells. The main goal of this piece is to describe an in vitro human suppression assay that allows comparison between different subject groups. Additionally, this assay has the potential to delineate a small loss in nTreg function and anticipate further loss in the future, thus identifying subjects who could benefit from preventive immunomodulatory therapy1. Below, we provide thorough description of the steps involved in this procedure. We hope to contribute to the standardization of the in vitro suppression assay used to measure Treg function. In addition, we offer this assay as a tool to recognize an early state of immune imbalance and a potential functional biomarker for T1D.

Human In Vitro Suppression as Screening Tool for the Recognition of an Early State of Immune Imbalance

Tregs are potent suppressors of the immune system. There is a lack of unique surface markers to define them, hence, definitions of Tregs are primarily functional. Here we describe an optimized in vitro assay capable of identifying immune imbalance in subjects at risk to develop T1D.

Regulatory T cells (Tregs) are critical mediators of immune tolerance to self-antigens. In addition, they are crucial regulators of the immune response ...

Isolation of Human Umbilical Vein Endothelial Cells and Their Use in the Study of Neutrophil Transmigration Under Flow Conditions

Neutrophils are the most abundant type of white blood cell. They form an essential part of the innate immune system1. During acute inflammation, neutrophils are the first inflammatory cells to migrate to the site of injury. Recruitment of neutrophils to an injury site is a stepwise process that includes first, dilation of blood vessels to increase blood flow; second, microvascular structural changes and escape of plasma proteins from the bloodstream; third, rolling, adhesion and transmigration of the neutrophil across the endothelium; and fourth accumulation of neutrophils at the site of injury2,3. A wide array of in vivo and in vitro methods has evolved to enable the study of these processes4. This method focuses on neutrophil transmigration across human endothelial cells.
One popular method for examining the molecular processes involved in neutrophil transmigration utilizes human neutrophils interacting with primary human umbilical vein endothelial cells (HUVEC)5. Neutrophil isolation has been described visually elsewhere6; thus this article will show the method for isolation of HUVEC. Once isolated and grown to confluence, endothelial cells are activated resulting in the upregulation of adhesion and activation molecules. For example, activation of endothelial cells with cytokines like TNF-&alpha; results in increased E-selectin and IL-8 expression7. E-selectin mediates capture and rolling of neutrophils and IL-8 mediates activation and firm adhesion of neutrophils. After adhesion neutrophils transmigrate. Transmigration can occur paracellularly (through endothelial cell junctions) or transcellularly (through the endothelial cell itself). In most cases, these interactions occur under flow conditions found in the vasculature7,8.
The parallel plate flow chamber is a widely used system that mimics the hydrodynamic shear stresses found in vivo and enables the study of neutrophil recruitment under flow condition in vitro9,10. Several companies produce parallel plate flow chambers and each have advantages and disadvantages. If fluorescent imaging is needed, glass or an optically similar polymer needs to be used. Endothelial cells do not grow well on glass.
Here we present an easy and rapid method for phase-contrast, DIC and fluorescent imaging of neutrophil transmigration using a low volume ibidi channel slide made of a polymer that supports the rapid adhesion and growth of human endothelial cells and has optical qualities that are comparable to glass. In this method, endothelial cells were grown and stimulated in an ibidi &mu;slide. Neutrophils were introduced under flow conditions and transmigration was assessed. Fluorescent imaging of the junctions enabled real-time determination of the extent of paracellular versus transcellular transmigration.

This article first describes a procedure for isolating human endothelial cells from umbilical veins and then shows how to use these cells to examine neutrophil transmigration under flow conditions. By using a low-volume flow chamber made from a polymer with the optical characteristics of glass, live-cell fluorescent imaging of rare cell populations is also possible.

Neutrophils are the most abundant type of white blood cell. They form an essential part of the innate immune system1. During acute inflammation, ...

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 ...

A Flow Adhesion Assay to Study Leucocyte Recruitment to Human Hepatic Sinusoidal Endothelium Under Conditions of Shear Stress

Leucocyte infiltration into human liver tissue is a common process in all adult inflammatory liver diseases. Chronic infiltration can drive the development of fibrosis and progression to cirrhosis. Understanding the molecular mechanisms that mediate leucocyte recruitment to the liver could identify important therapeutic targets for liver disease. The key interaction during leucocyte recruitment is that of inflammatory cells with endothelium under conditions of shear stress. Recruitment to the liver occurs within the low shear channels of the hepatic sinusoids which are lined by hepatic sinusoidal endothelial cells (HSEC). The conditions within the hepatic sinusoids can be recapitulated by perfusing leucocytes through channels lined by human HSEC monolayers at specific flow rates. In these conditions leucocytes undergo a brief tethering step followed by activation and firm adhesion, followed by a crawling step and subsequent transmigration across the endothelial layer. Using phase contrast microscopy, each step of this &#39;adhesion cascade&#39; can be visualized and recorded followed by offline analysis. Endothelial cells or leucocytes can be pretreated with inhibitors to determine the role of specific molecules during this process.

Leucocyte recruitment to the liver occurs within the specialized channels of the hepatic sinusoids which are lined by unique hepatic sinusoidal endothelial cells. Phase contrast microscopy of leucocyte recruitment across human hepatic sinusoidal endothelium under conditions of physiological shear stress can facilitate the elucidation of the molecular mechanisms which underlie this process.

Leucocyte infiltration into human liver tissue is a common process in all adult inflammatory liver diseases. Chronic infiltration can drive the ...

Detection of Fluorescent Nanoparticle Interactions with Primary Immune Cell Subpopulations by Flow Cytometry

Engineered nanoparticles are endowed with very promising properties for therapeutic and diagnostic purposes. This work describes a fast and reliable method of analysis by flow cytometry to study nanoparticle interaction with immune cells. Primary immune cells can be easily purified from human or mouse tissues by antibody-mediated magnetic isolation. In the first instance, the different cell populations running in a flow cytometer can be distinguished by the forward-scattered light (FSC), which is proportional to cell size, and the side-scattered light (SSC), related to cell internal complexity. Furthermore, fluorescently labeled antibodies against specific cell surface receptors permit the identification of several subpopulations within the same sample. Often, all these features vary when cells are boosted by external stimuli that change their physiological and morphological state. Here, 50 nm FITC-SiO2 nanoparticles are used as a model to identify the internalization of nanostructured materials in human blood immune cells. The cell fluorescence and side-scattered light increase after incubation with nanoparticles allowed us to define time and concentration dependence of nanoparticle-cell interaction. Moreover, such protocol can be extended to investigate Rhodamine-SiO2 nanoparticle interaction with primary microglia, the central nervous system resident immune cells, isolated from mutant mice that specifically express the Green Fluorescent Protein (GFP) in the monocyte/macrophage lineage. Finally, flow cytometry data related to nanoparticle internalization into the cells have been confirmed by confocal microscopy.

Analysis of nanoparticle interaction with defined subpopulations of immune cells by flow cytometry.

Engineered nanoparticles are endowed with very promising properties for therapeutic and diagnostic purposes. This work describes a fast and reliable ...

Analyzing the Effects of Stromal Cells on the Recruitment of Leukocytes from Flow

Stromal cells regulate the recruitment of circulating leukocytes during inflammation through cross-talk with neighboring endothelial cells. Here we describe two in vitro &#8220;vascular&#8221; models for studying the recruitment of circulating neutrophils from flow by inflamed endothelial cells. A major advantage of these models is the ability to analyze each step in the leukocyte adhesion cascade in order, as would occur in vivo. We also describe how both models can be adapted to study the role of stromal cells, in this case mesenchymal stem cells (MSC), in regulating leukocyte recruitment.
Primary endothelial cells were cultured alone or together with human MSC in direct contact on Ibidi microslides or on opposite sides of a Transwell filter for 24 hr. Cultures were stimulated with tumor necrosis factor alpha (TNF&#945;) for 4 hr and incorporated into a flow-based adhesion assay. A bolus of neutrophils was perfused over the endothelium for 4 min. The capture of flowing neutrophils and their interactions with the endothelium was visualized by phase-contrast microscopy.
In both models, cytokine-stimulation increased endothelial recruitment of flowing neutrophils in a dose-dependent manner. Analysis of the behavior of recruited neutrophils showed a dose-dependent decrease in rolling and a dose-dependent increase in transmigration through the endothelium. In co-culture, MSC suppressed neutrophil adhesion to TNF&#945;-stimulated endothelium.
Our flow based-adhesion models mimic the initial phases of leukocyte recruitment from the circulation. In addition to leukocytes, they can be used to examine the recruitment of other cell types, such as therapeutically administered MSC or circulating tumor cells. Our multi-layered co-culture models have shown that MSC communicate with endothelium to modify their response to pro-inflammatory cytokines, altering the recruitment of neutrophils. Further research using such models is required to fully understand how stromal cells from different tissues and conditions (inflammatory disorders or cancer) influence the recruitment of leukocytes during inflammation.

The ability of inflamed endothelium to recruit leukocytes from flow is regulated by mesenchymal stromal cells. We describe two in vitro models incorporating primary human cells that can be used to assess neutrophil recruitment from flow and examine the role that mesenchymal stromal cells play in regulating this process.

Stromal cells regulate the recruitment of circulating leukocytes during inflammation through cross-talk with neighboring endothelial cells. Here we ...

In Vitro and In Vivo Model to Study Bacterial Adhesion to the Vessel Wall Under Flow Conditions

In order to cause endovascular infections and infective endocarditis, bacteria need to be able to adhere to the vessel wall while being exposed to the shear stress of flowing blood.
To identify the bacterial and host factors that contribute to vascular adhesion of microorganisms, appropriate models that study these interactions under physiological shear conditions are needed. Here, we describe an in vitro flow chamber model that allows to investigate bacterial adhesion to different components of the extracellular matrix or to endothelial cells, and an intravital microscopy model that was developed to directly visualize the initial adhesion of bacteria to the splanchnic circulation in vivo. These methods can be used to identify the bacterial and host factors required for the adhesion of bacteria under flow. We illustrate the relevance of shear stress and the role of von Willebrand factor for the adhesion of Staphylococcus aureus using both the in vitro and in vivo model.

In Vitro and In Vivo Model to Study Bacterial Adhesion to the Vessel Wall Under Flow Conditions

To study the interaction of bacteria with the blood vessels under shear stress, a flow chamber and an in vivo mesenteric intravital microscopy model are described that allow to dissect the bacterial and host factors contributing to vascular adhesion.

In order to cause endovascular infections and infective endocarditis, bacteria need to be able to adhere to the vessel wall while being exposed to the ...

A Simple Flow Cytometric Method to Measure Glucose Uptake and Glucose Transporter Expression for Monocyte Subpopulations in Whole Blood

Monocytes are innate immune cells that can be activated by pathogens and inflammation associated with certain chronic inflammatory diseases. Activation of monocytes induces effector functions and a concomitant shift from oxidative to glycolytic metabolism that is accompanied by increased glucose transporter expression. This increased glycolytic metabolism is also observed for trained immunity of monocytes, a form of innate immunological memory. Although in vitro protocols examining glucose transporter expression and glucose uptake by monocytes have been described, none have been examined by multi-parametric flow cytometry in whole blood. We describe a multi-parametric flow cytometric protocol for the measurement of fluorescent glucose analog 2-NBDG uptake in whole blood by total monocytes and the classical (CD14++CD16-), intermediate (CD14++CD16+) and non-classical (CD14+CD16++) monocyte subpopulations. This method can be used to examine glucose transporter expression and glucose uptake for total monocytes and monocyte subpopulations during homeostasis and inflammatory disease, and can be easily modified to examine glucose uptake for other leukocytes and leukocyte subpopulations within blood.

Monocytes are integral components of the human innate immune system that rely on glycolytic metabolism when activated. We describe a flow cytometry protocol to measure glucose transporter expression and glucose uptake by total monocytes and monocyte subpopulations in fresh whole blood.

Monocytes are innate immune cells that can be activated by pathogens and inflammation associated with certain chronic inflammatory diseases. Activation of ...

Characterization of Human Monocyte-derived Dendritic Cells by Imaging Flow Cytometry: A Comparison between Two Monocyte Isolation Protocols

Dendritic cells (DCs) are antigen presenting cells of the immune system that play a crucial role in lymphocyte responses, host defense mechanisms, and pathogenesis of inflammation. Isolation and study of DCs have been important in biological research because of their distinctive features. Although they are essential key mediators of the immune system, DCs are very rare in blood, accounting for approximately 0.1 - 1% of total blood mononuclear cells. Therefore, alternatives for isolation methods rely on the differentiation of DCs from monocytes isolated from peripheral blood mononuclear cells (PBMCs). The utilization of proper isolation techniques that combine simplicity, affordability, high purity, and high yield of cells is imperative to consider. In the current study, two distinct methods for the generation of DCs will be compared. Monocytes were selected by adherence or negatively enriched using magnetic separation procedure followed by differentiation into DCs with IL-4 and GM-CSF. Monocyte and MDDC viability, proliferation, and phenotype were assessed using viability dyes, MTT assay, and CD11c/ CD14 surface marker analysis by imaging flow cytometry. Although the magnetic separation method yielded a significant higher percentage of monocytes with higher proliferative capacity when compared to the adhesion method, the findings have demonstrated the ability of both techniques to simultaneously generate monocytes that are capable of proliferating and differentiating into viable CD11c+ MDDCs after seven days in culture. Both methods yielded &gt; 70% CD11c+ MDDCs. Therefore, our results provide insights that contribute to the development of reliable methods for isolation and characterization of human DCs.

This study compares two different methods of human monocyte isolation for obtaining in vitro dendritic cells (DCs). Monocytes are selected by adherence or negatively enriched by magnetic separation. Monocyte yield and viability along with MDDC viability, proliferation and CD11c/CD14 surface marker expression will be compared between both methods.

Dendritic cells (DCs) are antigen presenting cells of the immune system that play a crucial role in lymphocyte responses, host defense mechanisms, and ...

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 ...