Hirschil Trust, Michael Saperstein Medical Scholars Research Funds, and the NYU Whitehead fellowship supported this work.

1. Coating the Microplate Wells
Note: The goal of this step is to coat polystyrene surfaces with ICAM-1 to serve as ligands for T cell LFA-1.
<ol>
	<li>Prepare the following solutions:
	<ol>
		<li>Prepare the coating solution by resuspending recombinant ICAM-1 with phosphate buffered saline (PBS) solution (137 mM NaCl,&#160;2.7 mM KCl,&#160;10 mM Na2HPO4,&#160;2 mM KH2PO4,&#160;pH 7.4) enriched with calcium (1 mM CaCl2) and magnesium (2 nM MgCl2). Make sure that the final concentration of ICAM-1 is 10 &#956;g/ml, made from a 0.7 mg/ml stock solution and kept in a -80 &#176;C freezer.</li>
		<li>Prepare the adhesion solution by enriching PBS with 0.5% human (or bovine) serum albumin (HSA/BSA), 2 mM MgCl2, and 1 mM CaCl2.</li>
		<li>Prepare the wash solution by adding 2 mM MgCl2 and 1 mM CaCl2 to PBS. Warm all solutions to 37 &#176;C before use.</li>
	</ol>
	</li>
	<li>Wash 24 wells with 50 &#956;l of wash solution. This will include unwashed wells, positive (PMA treated cells), and negative (uncoated wells) controls. For each condition set at least three wells (triplicate).</li>
	<li>Add 50 &#956;l of coating solution to each well. Do not add to the uncoated control wells. Incubate for one hour inside 37 &#176;C incubator.</li>
	<li>Aspirate the coating solution gently, without allowing the tip to touch the bottom of the wells. Wash once with 50 &#956;l of wash solution.</li>
	<li>Add 50 &#956;l of adhesion solution and incubate the microplate for one hr&#160;inside 37 &#176;C incubator.</li>
	<li>Aspirate gently and wash once with 50 &#956;l wash solution. Use the plate on the same day, however it is possible to keep it at 4 &#176;C over night, and use it the following day.</li>
</ol>
2. T Cell Isolation from Blood
<ol>
	<li>Add human T cell enrichment cocktail at 50 &#956;l/ml of whole blood (e.g. for 3 ml of anticoagulant (heparin, EDTA, or citrate) whole blood, add 150 &#956;l of cocktail). Mix well.</li>
	<li>Incubate 20 min&#160;at room temperature.</li>
	<li>To a 50&#160;ml centrifuge tube add 3 ml of treated blood and an equal volume of PBS (without calcium and magnesium) enriched with 1% D-glucose at room temperature. Mix gently with a Pasteur pipette.</li>
	<li>Add 15&#160;ml Ficoll-Paque PLUS to the centrifuge tube.</li>
	<li>Carefully layer the 6 ml diluted blood sample on the lymphocyte isolation medium.</li>
	<li>Centrifuge at 400 x g for 20 min&#160;at 20 &#176;C with break off.</li>
	<li>Draw off the upper layer using a clean Pasteur pipette, leaving the lymphocyte layer undisturbed at the interface. The upper layer of plasma may be saved for later use. Using a clean Pasteur pipette transfer the lymphocyte layer to a clean centrifuge tube.</li>
	<li>Add 3 volumes (9 ml) of PBS to the lymphocytes. Suspend the cells by gently drawing them in and out of a Pasteur pipette.</li>
	<li>Centrifuge at 400 x g for 5 min&#160;at 20 &#176;C.</li>
	<li>Remove the supernatant. The lymphocytes should now be suspended in the medium appropriate to the application. Transfer the cells to a T-75 culture flask in 20 ml RPMI 1640 media containing 10% FBS, 1% penicillin/streptomycin.</li>
</ol>
3. Preparation of the Cells
Note: A prerequisite is for the cells to be labeled with a fluorescent reagent. In this protocol use carboxy fluorescein succinimidyl ester (CFSE), however green fluorescent protein (GFP) expressing cells are an acceptable alternative.
<ol>
	<li>Count 2.4 x 106 T cells (1 x 105 for each well) using a hemocytometer.</li>
	<li>Resuspend the cells in culture media lacking serum (serum starvation). Incubate the cells for 2&#160;hr&#160;in the 37 &#176;C incubator.</li>
	<li>Centrifuge the cells for 5 min&#160;(400 x g). Aspirate the media and resuspend in 1 ml PBS.</li>
	<li>Add CFSE at 1:1,000 dilution (stock made to 5 mM). Cover from light and incubate for 8 min&#160;at room temperature.</li>
	<li>Stop the reaction by adding 10 ml of 37 &#176;C PBS and spin at 400 x g for 5 min.</li>
	<li>Re-suspend cell pellet with 1.2 ml of pre-warmed adhesion solution (1 x 105 cells per 50 &#956;l).</li>
</ol>
4. Stimulation of the Cells
Note: In order to initiate adhesion, cells must be stimulated. In the following experiment the cells are stimulated via the TCR using anti-CD3 crosslinking antibodies, however soluble SDF-1 could serve as an alternative. Depending on the goal of the experiments, various pharmacological reagents could be added before or during stimulation to study the impact on cellular adhesion. Phorbol myristate acetate (PMA) is a phorbol ester that is structurally similar to the second messenger diacyl glycerol (DAG) and therefore activates multiple kinases downstream the TCR (mainly Protein kinase C); here it is used as a positive control.
<ol>
	<li>Warm the microplate to 37 &#176;C.</li>
	<li>Divide the cells into 8 empty 1.5 ml tubes (150 &#956;l in each tube), one tube for each condition.</li>
	<li>Treat the cells accordingly:
	<ol>
		<li>Stimulate one tube with PMA at 10 ng/ml to serve as positive control. Keep three tubes untreated, to serve as control for stimulation (&#8220;no stimulation&#8221;), unwashed loading control (&#8220;no wash&#8221;), and control for ICAM-1 coating (&#8220;uncoated&#8221;).</li>
		<li>Stimulate four tubes with different concentrations of anti-CD3 antibodies (0.1, 1, 5, and 10 &#956;g/ml). Continue to the next step without delays.</li>
	</ol>
	</li>
	<li>Aliquot 50 &#956;l of stimulated cell mix into each empty well. The final number of cells per well is 1 x 105.</li>
	<li>Place the microplate in the 37 &#176;C incubator for 15 min. 
	Note: Some T cell lines require shorter stimulation time. During this time, the cells will settle down to the bottom of the wells and adhere to the target ligands.</li>
</ol>
5. Washing Away Non-adherent Cells
Note: The goal of this step is to remove cells that were not able to form tight contacts with the ligand-coated surfaces. Use a multichannel pipette for this step in order to ensure that the same physical forces are applied to all the wells. It is important to keep the indicated control wells unwashed to assist in the calculation of the percentage of adherent cells.
<ol>
	<li>Add 150 &#956;l of warm adhesion solution to each wells. Shake the plate gently for few seconds before removing the medium from the wells. Do not touch the bottom of the wells with the tips.</li>
	<li>Repeat this step three times. Change the direction of the pipette when pipetting the buffer in and out.</li>
</ol>
6. Determining the Percentage of Adherent Cells
Note: In this step a fluorescent plate reader is used to measure the fluorescent intensity within each well. The intensity is in direct correlation with the number of the adherent cells.
<ol>
	<li>Turn on the plate reader. Open the plate reader software by clicking the shortcut icon on the desktop.
	<ol>
		<li>From the &#8220;Task&#8221; menu click &#8220;New&#8221; to set up a new protocol.</li>
		<li>From the &#8220;Actions&#8221; menu choose the &#8220;Read&#8221; option. Click &#8220;Fluorescent intensity&#8221; and hit the &#8220;Ok&#8221; tab.</li>
		<li>From the drop down menu select &#8220;Excitation wavelength 485&#8221; and &#8220;Emission wavelength 528&#8221;. Hit the &#8220;Ok&#8221; tab.</li>
		<li>In &#8220;Optic&#8221; option menu select &#8220;Bottom&#8221; and hit the &#8220;Ok&#8221; tab. Go back to the &#8220;Actions&#8221; menu and set the temperature to 37 &#176;C and click &#8220;Ok&#8221;.</li>
		<li>Insert the microplate into the plate reader and click &#8220;Run&#8221;. The result will be exported into excel spreadsheet.</li>
	</ol>
	</li>
	<li>Calculate the percentage of adherent cells using the following formula: Percentage of adherent cells = (average fluorescent intensity read in the washed wells)/(average fluorescent intensity read in the unwashed cells) x 100%.</li>
</ol>

<ol>
	<li>Dustin, M. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membranes+as+messengers+in+T+cell+adhesion+signaling.">Membranes as messengers in T cell adhesion signaling.</a> Nat Immunol. 5 (4), 363-372 (2004).</li><li>Mor, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=GTPases+and+LFA-1+reciprocally+modulate+adhesion+and+signaling.">GTPases and LFA-1 reciprocally modulate adhesion and signaling.</a> Immunol Rev. 218, 114-125 (2007).</li><li>Rose, D. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integrin+modulation+and+signaling+in+leukocyte+adhesion+and+migration.">Integrin modulation and signaling in leukocyte adhesion and migration.</a> Immunol Rev. 218, 126-134 (2007).</li><li>Alon, R., Feigelson, S. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemokine-triggered+leukocyte+arrest:+force-regulated+bi-directional+integrin+activation+in+quantal+adhesive+contacts.">Chemokine-triggered leukocyte arrest: force-regulated bi-directional integrin activation in quantal adhesive contacts.</a> Curr Opin Cell Biol. 24 (5), 670-676 (2012).</li><li>Griffith, J. W., Luster, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Targeting+cells+in+motion:+migrating+toward+improved+therapies.">Targeting cells in motion: migrating toward improved therapies.</a> Eur J Immunol. 43 (6), 1430-1435 (2013).</li><li>Dustin, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+adhesion+molecules+and+actin+cytoskeleton+at+immune+synapses+and+kinapses.">Cell adhesion molecules and actin cytoskeleton at immune synapses and kinapses.</a> Curr Opin Cell Biol. 19 (5), 529-533 (2007).</li><li>Springer, T. A., Dustin, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integrin+inside-out+signaling+and+the+immunological+synapse.">Integrin inside-out signaling and the immunological synapse.</a> Curr Opin Cell Biol. 24 (1), 107-115 (2012).</li><li>Mor, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=D1+regulates+lymphocyte+adhesion+via+upregulation+of+Rap1+at+the+plasma+membrane.">D1 regulates lymphocyte adhesion via upregulation of Rap1 at the plasma membrane.</a> Mol Cell Biol. 29 (12), 3297-3306 (2009).</li><li>Bivona, T. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rap1+up-regulation+and+activation+on+plasma+membrane+regulates+T+cell+adhesion.">Rap1 up-regulation and activation on plasma membrane regulates T cell adhesion.</a> J Cell Biol. 164 (3), 461-470 (2004).</li><li>Zeltzer, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diminished+adhesion+of+CD4++T+cells+from+dialysis+patients+to+extracellular+matrix+and+its+components+fibronectin+and+laminin.">Diminished adhesion of CD4+ T cells from dialysis patients to extracellular matrix and its components fibronectin and laminin.</a> Nephrol Dial Transplant. 12 (12), 2618-2622 (1997).</li><li>Bhattacharyya, S. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Both+adhesion+to+immobilized+vitronectin+and+Fc+epsilon+RI+cross-linking+cause+enhanced+focal+adhesion+kinase+phosphorylation+in+murine+mast+cells.">Both adhesion to immobilized vitronectin and Fc epsilon RI cross-linking cause enhanced focal adhesion kinase phosphorylation in murine mast cells.</a> Immunology. 98 (3), 357-362 (1999).</li><li>Dustin, M. L., Groves, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Receptor+signaling+clusters+in+the+immune+synapse.">Receptor signaling clusters in the immune synapse.</a> Annu Rev Biophys. 41, 543-556 (2012).</li></ol>

The authors have nothing to disclose.

There are several assays to study signals to LFA-1 activation and T cell adhesion12. Flow cytometry is used to measure LFA-1 affinity states in living cells using monoclonal antibodies that bind selectively to either bended or extended LFA-1. One of the limitations of this method is that it does not take into account the integrins&#8217; avidity. Migration assays are useful tools but they measure migration, and not measly adhesion at a specific time point. Mouse models to study T lymphocyte migration (e.g....

T lymphocyte adhesion is a fundamental process in the immune response1. It is required for T cell interaction with endothelial cells decorating the capillary walls, for scanning antigen presenting cells (APC) within lymph nodes, and for the formation of immunological synapses (IS) with target cells2. These requirements are functionally and kinetically distinct. The process of lymphocytes extravasation consists of chemoattraction, rolling, firm adhesion, and transmigration. The transition from rolling to firm adhesion requires T cells to respond to a G protein coupled receptor signal rapidly. This response yields an integrin ligand interaction that slows and arrests the rolling cell3. An immediate change in integrin avidity mediates this process. Migration requires dynamic interactions betweenTcells and endothelial cells with the formation of adhesions at the &#39;front end&#39; and breakage of adhesions at the &#39;rear end&#39; with an interval of about a minute between forming and breaking4. The IS forms inminutes, but needs to remain intact for hours6.
Interestingly, one adhesion molecule, the integrin family member lymphocyte function associated antigen (LFA)- 1, is essential for all these processes5. LFA-1 mediates adhesion through interactions with several members of the immunoglobulin superfamily. The most extensively studied ligand with the highest affinity to LFA-1 is the intercellular adhesion molecule (ICAM)-1. Non-activated circulating lymphocytes express low affinity LFA-1 on the cell surface, and therefore are unable to adhere to ICAM-1-coated surfaces. LFA-1 affinity is variable and regulated by several signaling events such as G protein coupled receptor activation, cytokine stimulation, and signals mediated by T cell receptors (TCR).The resulting high affinity form of LFA-1 conveys intracellular activation to the extracellular space through interactions with ICAM-1. This pathway is termed inside-out signaling7. Likewise, signaling through LFA-1 from the extracellular space is called outside-in signaling.
The intracellular signaling cascades involved in inside-out and outside-in signaling are a major focus of current research. The small GTPase Rap1 has recently emerged as the key component of inside-out signaling that is common to both TCR ligation and cytokine signaling8. The critical role of Rap1 in integrin activation is highlighted by the discovery that overexpression of Rap1 stimulates integrin-dependent adhesion of T cells, whereas T cell adhesion is blocked by expression of dominant negative Rap19. These advances in our understanding of integrin regulation by Rap1 have been accomplished using in&#160;vitro tools. Among them is the static adhesion assay described here.
The overall goal of this method is to study T cell adhesiveness to ICAM-1 coated surfaces. More specifically, it is used to objectively measure and quantify LFA-1 affinity toward its counter ligands in live cells at real time, under different conditions. This technique uses polystyrene wells coated with ICAM-1 to mimic the cellular surfaces that the T cells interact with. Many previously described static T cell adhesion assays were experimentally complex. These assays often required for T cells to be radioactively labeled, utilized cultured bovine corneal cells to create an extracellular matrix as the substrate for T cell adhesion, or called for non-physiological T cell stimulation over an extended duration to promote T cell adhesion10. The use of fluorometric measurement to quantify T cells following the adhesion incubation is a more sensitive and accurate method of quantification as compared to flow cytometry and microscopy, as are utilized in many other assay systems11. Additionally, single cell microscopic analysis of integrin localization does not allow for the broad, population based analysis in the same way as the fluorometric measurement. While activation state-specific LFA-1 antibodies are commercially available, these antibodies offer low sensitivity relative to the method outlined here. The main advantage over alternative techniques is its simplicity and the ability to examine multiple experimental conditions simultaneously. When considering this method for a specific application, one should take into account that T cells should be negatively selected, freshly isolated, and labeled with a fluorescent marker.

<table><tbody><tr><td>Plate reader</td><td>BioTek</td><td>Synergy H1 Hybrid</td><td></td></tr><tr><td>Multichannel pipette</td><td>Fisher</td><td>21-377-829</td><td></td></tr><tr><td>96-well microplate with optical bottom</td><td>Corning Costar</td><td>3603</td><td></td></tr><tr><td>Recombinant ICAM-1</td><td>R&amp;amp;D Systems</td><td>ADP4-050</td><td></td></tr><tr><td>Anti-CD3 antibodies</td><td>Ancell</td><td>144-020</td><td></td></tr><tr><td>PMA</td><td>Sigma-Aldrich</td><td>79346</td><td></td></tr><tr><td>BSA</td><td>Sigma-Aldrich</td><td>A2058</td><td></td></tr><tr><td>CFSE</td><td>Molecular Probes</td><td>C1157</td><td></td></tr><tr><td>RPMI</td><td>Gibco</td><td>11875-093</td><td></td></tr><tr><td>DPBS containing calcium and magnesium</td><td>Gibco</td><td>14190250</td><td></td></tr><tr><td>Peripheral lymphocytes</td><td>&lt;em&gt;e.g.&lt;/em&gt; mouse or human</td><td></td><td></td></tr><tr><td>Magnesium chloride</td><td>Sigma-Aldrich</td><td>M8266</td><td></td></tr><tr><td>Calcium chloride</td><td>Sigma-Aldrich</td><td>499609</td><td></td></tr><tr><td>Open Gen 5 software</td><td>BioTek</td><td>Version 2.01</td><td></td></tr><tr><td>Ficoll-Paque PLUS</td><td>GE Healthcare</td><td>71-7167-00</td><td></td></tr><tr><td>15 and 50 ml centrifuge tubes</td><td>Fisher</td><td>352099, 352070</td><td></td></tr><tr><td>Disposable plastic Pasteur pipettes</td><td>Fisher</td><td>13-711-7M</td><td></td></tr><tr><td>T-75 culture flasks</td><td>Fisher</td><td>50-754-1366</td><td></td></tr><tr><td>RosetteSep T cell enricment kit</td><td>StemCell Technologies</td><td>15061</td><td></td></tr></tbody></table>

static adhesion assay for the study of integrin activation in t lymphocytes

T lymphocyte adhesion is required for multiple T cell functions, including migration to sites of inflammation and formation of immunological synapses with antigen presenting cells. T cells accomplish regulated adhesion by controlling the adhesive properties of integrins, a class of cell adhesion molecules consisting of heterodimeric pairs of transmembrane proteins that interact with target molecules on partner cells or extracellular matrix. The most prominent T cell integrin is lymphocyte function associated antigen (LFA)-1, composed of subunits &#945;L and &#946;2, whose target is the intracellular adhesion molecule (ICAM)-1. The ability of a T cell to control adhesion derives from the ability to regulate the affinity states of individual integrins. Inside-out signaling describes the process whereby signals inside a cell cause the external domains of integrins to assume an activated state. Much of our knowledge of these complex phenomena is based on mechanistic studies performed in simplified in&#160;vitro model systems. The T lymphocyte adhesion assay described here is an excellent tool that allows T cells to adhere to target molecules, under static conditions, and then utilizes a fluorescent plate reader to quantify adhesiveness. This assay has been useful in defining adhesion-stimulatory or inhibitory substances that act on lymphocytes, as well as characterizing the signaling events involved. Although described here for LFA-1 - ICAM-1 mediated adhesion; this assay can be readily adapted to allow for the study of other adhesive interactions (e.g.&#160;VLA-4 - fibronectin).

Below is an example of adhesion assay using primary T cells stimulated with various concentrations of anti-CD3 antibodies. It is useful to know the fluorescence of unwashed cells (i.e. total loading). Unstimulated cells serve as a negative control and PMA treated cells are the positive control for anti-CD3 antibodies. Cells plated in uncoated wells serve as a control for ICAM-1. In a typical experiment the percentage of adherent PMA treated cells is between 40% to 50% while the percentage of unstimulated cells i...

Watch this Scientific Journal Video about Static Adhesion Assay for the Study of Integrin Activation in T Lymphocytes at JoVE.com

Static Adhesion Assay for the Study of Integrin Activation in T Lymphocytes

Static adhesion assay is a powerful tool that can be used to model the interactions between T lymphocytes and other cell types. Interactions are generated by injecting labeled T cells into wells coated with adhesion molecules, while a plate reader is used to quantify the number of adherent cells following serial washes.

T lymphocyte adhesion is required for multiple T cell functions, including migration to sites of inflammation and formation of immunological synapses with ...

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15.9K Views.  New York University School of Medicine. Static adhesion assay is a powerful tool that can be used to model the interactions between T lymphocytes and other cell types. Interactions are generated by injecting labeled T cells into wells coated with adhesion molecules, while a plate reader is used to quantify the number of adherent cells following serial washes.

Video: Static Adhesion Assay for the Study of Integrin Activation in T Lymphocytes

Human T Lymphocyte Isolation, Culture and Analysis of Migration In Vitro

The migration of T lymphocytes involves the adhesive interaction of cell surface integrins with ligands expressed on other cells or with extracellular matrix proteins. The precise spatiotemporal activation of integrins from a low affinity state to a high affinity state at the cell leading edge is important for T lymphocyte migration 1. Likewise, retraction of the cell trailing edge, or uropod, is a necessary step in maintaining persistent integrin-dependent T lymphocyte motility 2. Many therapeutic approaches to autoimmune or inflammatory diseases target integrins as a means to inhibit the excessive recruitment and migration of leukocytes 3. To study the molecular events that regulate human T lymphocyte migration, we have utilized an in vitro system to analyze cell migration on a two-dimensional substrate that mimics the environment that a T lymphocyte encounters during recruitment from the vasculature. T lymphocytes are first isolated from human donors and are then stimulated and cultured for seven to ten days. During the assay, T lymphocytes are allowed to adhere and migrate on a substrate coated with intercellular adhesion molecule-1 (ICAM-1), a ligand for integrin LFA-1, and stromal cell-derived factor-1 (SDF-1). Our data show that T lymphocytes exhibit a migratory velocity of ~15 &mu;m/min. T lymphocyte migration can be inhibited by integrin blockade 1 or by inhibitors of the cellular actomyosin machinery that regulates cell migration 2.

Human T Lymphocyte Isolation, Culture and Analysis of Migration In Vitro

T lymphocyte migration occurs during homing to lymphoid organs, exit from the vasculature, and entering into peripheral tissues. Here, we describe a protocol that can be used to analyze T lymphocyte migration in vitro.

The migration of T lymphocytes involves the adhesive interaction of cell surface integrins with ligands expressed on other cells or with extracellular ...

Adhesion Frequency Assay for In Situ Kinetics Analysis of Cross-Junctional Molecular Interactions at the Cell-Cell Interface

The micropipette adhesion assay was developed in 1998 to measure two-dimensional (2D) receptor-ligand binding kinetics1. The assay uses a human red blood cell (RBC) as adhesion sensor and presenting cell for one of the interacting molecules. It employs micromanipulation to bring the RBC into contact with another cell that expresses the other interacting molecule with precisely controlled area and time to enable bond formation. The adhesion event is detected as RBC elongation upon pulling the two cells apart. By controlling the density of the ligands immobilized on the RBC surface, the probability of adhesion is kept in mid-range between 0 and 1. The adhesion probability is estimated from the frequency of adhesion events in a sequence of repeated contact cycles between the two cells for a given contact time. Varying the contact time generates a binding curve. Fitting a probabilistic model for receptor-ligand reaction kinetics1 to the binding curve returns the 2D affinity and off-rate.
The assay has been validated using interactions of Fc&gamma; receptors with IgG Fc1-6, selectins with glycoconjugate ligands6-9, integrins with ligands10-13, homotypical cadherin binding14, T cell receptor and coreceptor with peptide-major histocompatibility complexes15-19.
The method has been used to quantify regulations of 2D kinetics by biophysical factors, such as the membrane microtopology5, membrane anchor2, molecular orientation and length6, carrier stiffness9, curvature20, and impingement force20, as well as biochemical factors, such as modulators of the cytoskeleton and membrane microenvironment where the interacting molecules reside and the surface organization of these molecules15,17,19.
The method has also been used to study the concurrent binding of dual receptor-ligand species3,4, and trimolecular interactions19 using a modified model21.
The major advantage of the method is that it allows study of receptors in their native membrane environment. The results could be very different from those obtained using purified receptors17. It also allows study of the receptor-ligand interactions in a sub-second timescale with temporal resolution well beyond the typical biochemical methods.
To illustrate the micropipette adhesion frequency method, we show kinetics measurement of intercellular adhesion molecule 1 (ICAM-1) functionalized on RBCs binding to integrin &alpha;L&beta;2 on neutrophils with dimeric E-selectin in the solution to activate &alpha;L&beta;2.

Adhesion Frequency Assay for In Situ Kinetics Analysis of Cross-Junctional Molecular Interactions at the Cell-Cell Interface

An adhesion frequency assay for measuring receptor-ligand interaction kinetics when both molecules are anchored on the surfaces of the interacting cells is described. This mechanically-based assay is exemplified using a micropipette-pressurized human red blood cell as adhesion sensor and integrin &alpha;L&beta;2 and intercellular adhesion molecule-1 as interacting receptors and ligands.

The micropipette adhesion assay was developed in 1998 to measure two-dimensional (2D) receptor-ligand binding kinetics1. The assay uses a human red blood ...

Bioengineering

Bead Aggregation Assays for the Characterization of Putative Cell Adhesion Molecules

Cell-cell adhesion is fundamental to multicellular life and is mediated by a diverse array of cell surface proteins. However, the adhesive interactions for many of these proteins are poorly understood. Here we present a simple, rapid method for characterizing the adhesive properties of putative homophilic cell adhesion molecules. Cultured HEK293 cells are transfected with DNA plasmid encoding a secreted, epitope-tagged ectodomain of a cell surface protein. Using functionalized beads specific for the epitope tag, the soluble, secreted fusion protein is captured from the culture medium. The coated beads can then be used directly in bead aggregation assays or in fluorescent bead sorting assays to test for homophilic adhesion. If desired, mutagenesis can then be used to elucidate the specific amino acids or domains required for adhesion. This assay requires only small amounts of expressed protein, does not require the production of stable cell lines, and can be accomplished in 4 days.

Here we present a simple, rapid method for characterizing the intrinsic adhesive properties of putative cell adhesion molecules. The secreted, epitope-tagged ectodomain of a cell adhesion molecule is captured from the culture medium on small, uniform functionalized beads. These beads can then be used immediately in simple bead aggregation assays.

Cell-cell adhesion is fundamental to multicellular life and is mediated by a diverse array of cell surface proteins. However, the adhesive interactions ...

Assay of Adhesion Under Shear Stress for the Study of T Lymphocyte-Adhesion Molecule Interactions

Overall, T cell adhesion is a critical component of function, contributing to the distinct processes of cellular recruitment to sites of inflammation and interaction with antigen presenting cells (APC) in the formation of immunological synapses. These two contexts of T cell adhesion differ in that T cell-APC interactions can be considered static, while T cell-blood vessel interactions are challenged by the shear stress generated by circulation itself. T cell-APC interactions are classified as static in that the two cellular partners are static relative to each other. Usually, this interaction occurs within the lymph nodes. As a T cell interacts with the blood vessel wall, the cells arrest and must resist the generated shear stress.1,2 These differences highlight the need to better understand static adhesion and adhesion under flow conditions as two distinct regulatory processes. The regulation of T cell adhesion can be most succinctly described as controlling the affinity state of integrin molecules expressed on the cell surface, and thereby regulating the interaction of integrins with the adhesion molecule ligands expressed on the surface of the interacting cell. Our current understanding of the regulation of integrin affinity states comes from often simplistic in vitro model systems. The assay of adhesion using flow conditions described here allows for the visualization and accurate quantification of T cell-epithelial cell interactions in real time following a stimulus. An adhesion under flow assay can be applied to studies of adhesion signaling within T cells following treatment with inhibitory or stimulatory substances. Additionally, this assay can be expanded beyond T cell signaling to any adhesive leukocyte population and any integrin-adhesion molecule pair.

This flow adhesion assay provides a simple, high impact model of T cell-epithelial cell interactions. A syringe pump is used to generate shear stress, and confocal microscopy captures images for quantification. The goal of these studies is to effectively quantify T cell adhesion using flow conditions.

Overall, T cell adhesion is a critical component of function, contributing to the distinct processes of cellular recruitment to sites of inflammation and ...

Imaging Integrin Tension and Cellular Force at Submicron Resolution with an Integrative Tension Sensor

Molecular tension transmitted by integrin-ligand bonds is the fundamental mechanical signal in the integrin pathway that plays significant roles in many cell functions and behaviors. To calibrate and image integrin tension with high force sensitivity and spatial resolution, we developed an integrative tension sensor (ITS), a DNA-based fluorescent tension sensor. The ITS is activated to fluoresce if sustaining a molecular tension, thus converting force to fluorescent signal at the molecular level. The tension threshold for ITS activation is tunable in the range of 10&#8211;60 pN that well covers the dynamic range of integrin tension in cells. On a substrate grafted with an ITS, the integrin tension of adherent cells is visualized by fluorescence and imaged at submicron resolution. The ITS is also compatible with cell structural imaging in both live cells and fixed cells. The ITS has been successfully applied to the study of platelet contraction and cell migration. This paper details the procedure for the synthesis and application of the ITS in the study of integrin-transmitted cellular force.

Integrin tension plays important roles in various cell functions. With an integrative tension sensor, integrin tension is calibrated with picoNewton (pN) sensitivity and imaged at submicron resolution.

Molecular tension transmitted by integrin-ligand bonds is the fundamental mechanical signal in the integrin pathway that plays significant roles in many ...

Dynamic Adhesion Assay for the Functional Analysis of Anti-adhesion Therapies in Inflammatory Bowel Disease

Gut homing of immune cells is important for the pathogenesis of inflammatory bowel diseases (IBD). Integrin-dependent cell adhesion to addressins is a crucial step in this process and therapeutic strategies interfering with adhesion have been successfully established. The anti-&#945;4&#946;7 integrin antibody, vedolizumab, is used for the clinical treatment of Crohn&#39;s disease (CD) and ulcerative colitis (UC) and further compounds are likely to follow.
The details of the adhesion procedure and the action mechanisms of anti-integrin antibodies are still unclear in many regards due to the limited available techniques for the functional research in this field.
Here, we present a dynamic adhesion assay for the functional analysis of human cell adhesion under flow conditions and the impact of anti-integrin therapies in the context of IBD. It is based on the perfusion of primary human cells through addressin-coated ultrathin glass capillaries with real-time microscopic analysis. The assay offers a variety of opportunities for refinements and modifications and holds potentials for mechanistic discoveries and translational applications.

Dynamic adhesion of immune cells to the vessel wall is a prerequisite for gut homing. Here, we present a protocol for a functional in vitro assay for the impact analysis of anti-integrin antibodies, chemokines or other factors on the dynamic cell adhesion of human cells using addressin-coated capillaries.

Gut homing of immune cells is important for the pathogenesis of inflammatory bowel diseases (IBD). Integrin-dependent cell adhesion to addressins is a ...

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 ...

Tension Gauge Tether Probes for Quantifying Growth Factor Mediated Integrin Mechanics and Adhesion

Multicellular organisms rely on interactions between membrane receptors and cognate ligands in the surrounding extracellular matrix (ECM) to orchestrate multiple functions, including adhesion, proliferation, migration, and differentiation. Mechanical forces can be transmitted from the cell via the adhesion receptor integrin to ligands in the ECM. The amount and spatial organization of these cell-generated forces can be modulated by growth factor receptors, including epidermal growth factor receptor (EGFR). The tools currently available to quantify crosstalk-mediated changes in cell mechanics and relate them to&#160;focal adhesions, cellular morphology, and signaling are limited. DNA-based molecular force sensors known as tension gauge tethers (TGTs) have been employed to quantify these changes. TGT probes are unique in their ability to both modulate the underlying force threshold and report piconewton scale receptor forces across the entire adherent cell surface at diffraction-limited spatial resolution. The TGT probes used here rely on the irreversible dissociation of a DNA duplex by receptor-ligand forces that generate a fluorescent signal. This allows quantification of the cumulative integrin tension (force history) of the cell. This article describes a protocol employing TGTs to study the impact of EGFR on integrin mechanics and adhesion formation. The assembly of&#160;the TGT mechanical sensing platform is systematically detailed and the procedure to image forces, focal adhesions, and cell spreading is outlined. Overall, the ability to modulate the underlying force threshold of the probe, the adhesion ligand, and the type and concentration of growth factor employed for stimulation make this a robust platform for studying the interplay of diverse membrane receptors in regulating integrin-mediated forces.

TGT surface is an innovative platform to study growth factor-integrin crosstalk. The flexible probe design, specificity of the adhesion ligand, and precise modulation of stimulation conditions allow robust quantitative assessments of EGFR-integrin interplay. The results highlight EGFR as a 'mechano-organizer' tuning integrin mechanics, influencing focal adhesion assembly and cell spreading.

Multicellular organisms rely on interactions between membrane receptors and cognate ligands in the surrounding extracellular matrix (ECM) to orchestrate ...

Biology

Imaging Single Platelet Migration Using a Three-Layer Coating System

An In Vitro Assay to Study Platelet Migration Using RGD-Functionalized Avidin-Biotin Tethers

Despite being anucleated cell fragments, platelets are now widely recognized for their multifaceted abilities. Not only do they form blood clots to prevent bleeding after injury, but they also fight infections and maintain vascular integrity during inflammatory diseases. While hemostatic plugs require the collective activation and aggregation of platelets, their role in protecting inflamed blood vessels is performed at the single-cell level. In this context, recent data have shown that platelets can migrate autonomously, a process dependent on the mechanosensing of their adhesive environment. Here, a detailed protocol for imaging single platelet migration is presented, utilizing a three-layer coating system consisting of a poly-L-lysine graft poly(ethylene glycol) (PLL-PEG)-biotin backbone (1), a fluorescent avidin linker (2), and biotin-cyclic Arg-Gly-Asp (cRGD) (3) as the platelet integrin-binding motif. This reductionist approach allows precise control of substrate adhesion properties and serves as a simple, standardized in vitro assay to study the mechanisms underlying platelet migration. The results indicate that migrating platelets binding to cRGD exert forces capable of disrupting the avidin-biotin bond. Furthermore, the density of biotin-cRGD significantly influences both platelet spreading and migration.

A detailed protocol for imaging single migrating platelets using RGD-functionalized avidin-biotin tethers with tunable density is provided, revealing that platelets generate enough force to rupture the avidin-biotin bond.

Despite being anucleated cell fragments, platelets are now widely recognized for their multifaceted abilities. Not only do they form blood clots to ...

An In Vitro Technique to Study T Cell Interaction with Supported Planar Lipid Bilayers

Source: Steblyanko, M., et al. <a href="https://appjove.unicartagenaproxy.elogim.com/v/58143">Assessment of the Synaptic Interface of Primary Human T Cells from Peripheral Blood and Lymphoid Tissue.</a> J. Vis. Exp. (2018).
This video demonstrates an in vitro technique to study immune synapse formation between primary human T cells and supported lipid bilayers (SLB). T cell surface proteins interact with respective ligands immobilized on SLB to form an immune synapse, followed by the movement of lytic granules towards the synapse, which is visualized using fluorescence microscopy.

Technika in vitro do badania interakcji limfocytów T z obsługiwanymi płaskimi dwuwarstwami lipidowymi

All procedures involving sample collection have been performed in accordance with the institute&#39;s IRB guidelines.
1. Isolation of CD4+ T Cells for an ...

Static Adhesion Assay for the Study of Integrin Activation in T Lymphocytes

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Imaging Integrin Tension and Cellular Force at Submicron Resolution with an Integrative Tension Sensor

Dynamic Adhesion Assay for the Functional Analysis of Anti-adhesion Therapies in Inflammatory Bowel Disease

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

Tension Gauge Tether Probes for Quantifying Growth Factor Mediated Integrin Mechanics and Adhesion

An In Vitro Assay to Study Platelet Migration Using RGD-Functionalized Avidin-Biotin Tethers

Technika in vitro do badania interakcji limfocytów T z obsługiwanymi płaskimi dwuwarstwami lipidowymi