Name: Molecular Diffusion in Plasma Membranes of Primary Lymphocytes Measured by Fluorescence Correlation Spectroscopy (Video) | JoVE Journal
Uploaded: 2017-02-01T12:30:00.000+00:00
Duration: 12 min 6 s
Description: Learn fluorescence correlation spectroscopy to measure protein diffusion in primary lymphocyte membranes using live-cell imaging. This method reveals membrane receptor dynamics for immunology and cancer immunotherapy research.

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We thank Dr. Vladana Vukojevi&#231;, Center for Molecular Medicine, Karolinska Institutet for the maintenance of the Zeiss Confocor 3 instrument and for helpful tips regarding cell measurements.&#160;This study was funded by grants from Vetenskapsr&#229;det (grant number 2012- 1629), Magnus Bergvalls stiftelse, and from Stiftelsen Claes Groschinskys minnesfond.

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<li>Liu, P., Ahmed, S., Wohland, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+F-techniques%3A+advances+in+receptor+protein+studies%5BTitle%5D)+AND+%22Trends+Endocrinol+Metab%22%5BJournal%5D)">The F-techniques: advances in receptor protein studies.</a> Trends Endocrinol Metab. 19, 181-190 (2008).</li>
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<li>Bacia, K., Haustein, E., Schwille, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Fluorescence+correlation+spectroscopy%3A+principles+and+applications%5BTitle%5D)+AND+%22Cold+Spring+Harb+Protoc%22%5BJournal%5D)">Fluorescence correlation spectroscopy: principles and applications.</a> Cold Spring Harb Protoc. , 709-725 (2014).</li>
<li>Haustein, E., Schwille, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Fluorescence+correlation+spectroscopy%3A+novel+variations+of+an+established+technique%5BTitle%5D)+AND+%22Annu+Rev+Biophys+Biomol+Struct%22%5BJournal%5D)">Fluorescence correlation spectroscopy: novel variations of an established technique.</a> Annu Rev Biophys Biomol Struct. 36, 151-169 (2007).</li>
<li>Widengren, J., Thyberg, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((FCS+cell+surface+measurements--photophysical+limitations+and+consequences+on+molecular+ensembles+with+heterogenic+mobilities%5BTitle%5D)+AND+%22Cytometry+A%22%5BJournal%5D)">FCS cell surface measurements--photophysical limitations and consequences on molecular ensembles with heterogenic mobilities.</a> Cytometry A. 68, 101-112 (2005).</li>
<li>North, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Seeing+is+believing%3F+A+beginners%27+guide+to+practical+pitfalls+in+image+acquisition%5BTitle%5D)+AND+%22J+Cell+Biol%22%5BJournal%5D)">Seeing is believing? A beginners' guide to practical pitfalls in image acquisition.</a> J Cell Biol. 172, 9-18 (2006).</li>
<li>Meinhardt, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Influence+of+NK+cell+magnetic+bead+isolation+methods+on+phenotype+and+function+of+murine+NK+cells%5BTitle%5D)+AND+%22J+Immunol+Methods%22%5BJournal%5D)">Influence of NK cell magnetic bead isolation methods on phenotype and function of murine NK cells.</a> J Immunol Methods. 378, 1-10 (2012).</li>
<li>Bacia, K., Schwille, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Practical+guidelines+for+dual-color+fluorescence+cross-correlation+spectroscopy%5BTitle%5D)+AND+%22Nat+Protoc%22%5BJournal%5D)">Practical guidelines for dual-color fluorescence cross-correlation spectroscopy.</a> Nat Protoc. 2, 2842-2856 (2007).</li>
<li>Gendron, P. O., Avaltroni, F., Wilkinson, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Diffusion+coefficients+of+several+rhodamine+derivatives+as+determined+by+pulsed+field+gradient-nuclear+magnetic+resonance+and+fluorescence+correlation+spectroscopy%5BTitle%5D)+AND+%22J+Fluoresc%22%5BJournal%5D)">Diffusion coefficients of several rhodamine derivatives as determined by pulsed field gradient-nuclear magnetic resonance and fluorescence correlation spectroscopy.</a> J Fluoresc. 18, 1093-1101 (2008).</li>
<li>Petrasek, Z., Schwille, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Precise+measurement+of+diffusion+coefficients+using+scanning+fluorescence+correlation+spectroscopy%5BTitle%5D)+AND+%22Biophys+J%22%5BJournal%5D)">Precise measurement of diffusion coefficients using scanning fluorescence correlation spectroscopy.</a> Biophys J. 94, 1437-1448 (2008).</li>
<li>Stromqvist, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+modified+FCCS+procedure+applied+to+Ly49A-MHC+class+I+cis-interaction+studies+in+cell+membranes%5BTitle%5D)+AND+%22Biophys+J%22%5BJournal%5D)">A modified FCCS procedure applied to Ly49A-MHC class I cis-interaction studies in cell membranes.</a> Biophys J. 101, 1257-1269 (2011).</li>
<li>Widengren, J., Mets, U., Rigler, R. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/j100036a009">Fluorescence Correlation Spectroscopy of Triplet-States in Solution - a Theoretical and Experimental-Study.</a> J Phys Chem. 99, 13368-13379 (1995).</li>
<li>Humpolickova, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Probing+diffusion+laws+within+cellular+membranes+by+Z-scan+fluorescence+correlation+spectroscopy%5BTitle%5D)+AND+%22Biophys+J%22%5BJournal%5D)">Probing diffusion laws within cellular membranes by Z-scan fluorescence correlation spectroscopy.</a> Biophys J. 91, L23-L25 (2006).</li>
<li>Guo, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Bayesian+approach+to+the+analysis+of+fluorescence+correlation+spectroscopy+data+II%3A+application+to+simulated+and+in+vitro+data%5BTitle%5D)+AND+%22Anal+Chem%22%5BJournal%5D)">Bayesian approach to the analysis of fluorescence correlation spectroscopy data II: application to simulated and in vitro data.</a> Anal Chem. 84, 3880-3888 (2012).</li>
<li>Ries, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Automated+suppression+of+sample-related+artifacts+in+Fluorescence+Correlation+Spectroscopy%5BTitle%5D)+AND+%22Opt+Express%22%5BJournal%5D)">Automated suppression of sample-related artifacts in Fluorescence Correlation Spectroscopy.</a> Opt Express. 18, 11073-11082 (2010).</li>
<li>Chiu, C. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Intracellular+kinetics+of+the+androgen+receptor+shown+by+multimodal+Image+Correlation+Spectroscopy+%28mICS%29%5BTitle%5D)+AND+%22Sci+Rep%22%5BJournal%5D)">Intracellular kinetics of the androgen receptor shown by multimodal Image Correlation Spectroscopy (mICS).</a> Sci Rep. 6, 22435(2016).</li>
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</ol>

The authors have nothing to disclose.

This protocol for FCS can be used for the assessment of the molecular dynamics of surface molecules on all types of immune cells (murine, human, or other species). FCS measures spatio-temporal molecular dynamics down to single-molecule resolution in live cells. The molecular density, as well as the diffusion rate and clustering dynamics of the proteins of interest, can be extracted from the autocorrelation curves.
The fluorescent labeling is of pivotal importance for successful FCS experiments...

Many immune cells functions rely on molecular diffusion and interactions within membranes. Biological membranes are complex, and many factors that may be important for the function of immune cells can influence the speed of translational diffusion of proteins within cellular membranes1. We recently showed that natural killer (NK) cells, lymphocytes belonging to the innate immune system, exhibit differential diffusion of two studied proteins at the cell membrane depending on the state of NK cell activation2.
Fluorescence correlation spectroscopy (FCS) is a technique that is capable of quantifying molecular diffusion rates within biological membranes. It reports the average diffusion rate of fluorescently labeled molecules in a fixed volume, typically the focus of a confocal microscope. It is based on the measurement of the fluctuations in fluorescence that occur upon molecular movement in a system in steady state. FCS has been widely used for studying the diffusion of fluorescent dyes and proteins, both in solution and within lipid membranes. Other output parameters affecting the diffusion rate can also be indirectly studied in this fashion (e.g., conformational changes of proteins or interactions of molecules on cell membranes)3,4. FCS stands out compared to other techniques due to its high sensitivity, allowing the possibility for single-molecule detection. It works well for molecular concentrations in the nanomolar to millimolar range, which is typical for endogenous expression levels of most proteins5. Furthermore, FCS can give an approximation of the absolute number of proteins within the studied volume, while most other techniques only give relative information about protein expression levels. Other methods to measure molecular diffusion rates within membranes include fluorescence recovery after photobleaching (FRAP), single particle tracking (SPT), multiple pinhole FCS, and image correlation methods. FRAP and image correlation methods are ensemble techniques, which generally do not give information about the absolute number of molecules10. Compared to SPT, the throughput of FCS is higher in regard to characterizing the population average. The analysis is also less demanding since the average diffusion rate of the molecules present within the laser focus is measured, rather than the rate of single molecules. Also, unless specialized microscopes are available11, SPT cannot give any information about concentrations, since standard SPT labeling must be very low to allow for the identification of single molecules. On the other hand, FCS requires the molecules under study to be mobile. It will simply not detect any putative immobile fractions or molecules moving very slowly. The diffusion rate of molecules that reside within the focus longer than approximately one tenth of the acquisition time will not be correctly represented in FCS measurements3,12. Therefore, diffusion coefficients recorded by FCS tend to be faster than diffusion rates reported from techniques like FRAP and SPT, where the close-to-immobile and very slow fractions are taken into account as well. SPT will also give a more detailed description of the variability of diffusion rates within the molecular population than FCS will.
FCS quantifies the fluctuation of fluorescence intensity over time within the excited volume. In the case of membrane measurements, this translates to the illuminated area of the membrane. In this paper, we utilize the fact that such fluctuations are induced by molecules exhibiting Brownian diffusion and are thus moving in and out of the excitation volume. There are also several other possible sources for the fluctuations in the fluorescence signal, such as blinking or the presence of a triplet state in the fluorophores, environmental effects, binding-unbinding of the ligand, or movement of the entire cell membrane. These putative error sources need to be taken into consideration when designing an FCS experiment in order to accurately interpret the results12,13. Typically, lateral diffusion rates in biological membranes are low due to crowding and interactions, both between membrane proteins and between proteins and the cytoskeleton. Historically, the use of FCS in membranes has thus been hampered by the lack of photo-stable fluorophores, which are required to avoid bleaching during the extended transit times through the excitation focus14. However, today, there are plenty of options for suitable photo-stable dyes. Significant improvements in detectors and other hardware also allow the detection of fluorescent proteins and dyes of lower brightness. Here, a basic protocol for the application of FCS using murine primary lymphocytes, where the protein of interest is labeled with a fluorescently tagged antibody, is described. An approach to fit the autocorrelation curves in order to extract the diffusion coefficient and the molecular density is also shown. The protocol aims at being easily followed by immunologists with no previous experience of techniques to study the diffusion of molecules. However, a basic understanding of confocal microscopy is expected (to gain this basic understanding, see reference15). This protocol can relatively easily be adapted to other suspension cells, both cell lines and primary cells. For more experienced FCS users, more refined analysis methods exist, some of which are described in the discussion.

<table><tbody><tr><td>MACS NK Cell Isolation Kit mouse II</td><td>Miltenyi Biotec Norden&lt;sup&gt;AB&lt;/sup&gt;</td><td>130-096-892</td><td>Negative selection of NK cells</td></tr><tr><td>Fetal Bovine Serum</td><td>Sigma-Adlrich</td><td>F7524</td><td>Heat inactivated</td></tr><tr><td>Phosphate Buffered Saline</td><td>-</td><td>-</td><td>Made in house&amp;nbsp;</td></tr><tr><td>Roswell Park Memorial Institute medium 1640</td><td>PAA The Cell Culture Company&amp;nbsp;</td><td>E15-848</td><td>Transparent medium</td></tr><tr><td>Antibody clone 2.4G2</td><td>Thermo Fischer Scientific</td><td>553140</td><td>For blocking Fc-receptors.</td></tr><tr><td>Anti-Ly49A antibody&amp;nbsp;</td><td></td><td></td><td>Monoclonal antibody made in house and conjugated in house to Alexa fluor 647</td></tr><tr><td>Clone JR9.318</td><td></td><td></td><td></td></tr><tr><td>Anti-H-2Dd antibody&amp;nbsp;</td><td>BD Pharmingen</td><td>558915</td><td>Conjugated in house to MFP488</td></tr><tr><td>Clone 34.5.8S</td><td></td><td></td><td></td></tr><tr><td>MFP488</td><td>Mobiotech</td><td>MFP-A2181</td><td>Fluorescent dye for antibody conjugation.</td></tr><tr><td>Poly-L-Lysine</td><td>Sigma-Aldrich</td><td>P8920</td><td>Diluted in distilled water (1.10)</td></tr><tr><td>Poly-L-Lysine (20 kDa) grafted with polyethylene glycol (2 kDa)</td><td>SuSoS AG</td><td>PLL(20)-g[3.5]-PEG(2)</td><td>Diluted in PBS (pH 7.4) to 0.5 mg/ml.</td></tr><tr><td>Rhodamine 110 chloride</td><td>Sigma-Aldrich</td><td>432202</td><td>Known diffusion coefficient: 3.3 &amp;times; 10&lt;sup&gt;&amp;minus;10&lt;/sup&gt; m&lt;sup&gt;2&lt;/sup&gt;/sec &lt;sup&gt;19&lt;/sup&gt;</td></tr><tr><td>Alexa fluor 647</td><td>Thermo Fisher Scientific&amp;nbsp;</td><td>A20006</td><td>Known diffusion coefficient: 4.4 &amp;times; 10&lt;sup&gt;&amp;minus;10&lt;/sup&gt; m&lt;sup&gt;2&lt;/sup&gt;/sec &lt;sup&gt;20&lt;/sup&gt;</td></tr><tr><td>Confocal microscope&amp;nbsp;</td><td>Zeiss</td><td>LSM510</td><td></td></tr><tr><td>Software: Confocor 3</td><td>Zeiss</td><td></td><td></td></tr><tr><td>Software: Matlab with curve fitting toolbox</td><td>Matlab</td><td>Version R2013b</td><td></td></tr><tr><td>Nunc Lab-Tek Chambered Coverglass</td><td>Thermo-scientific&amp;nbsp;</td><td>155411</td><td>8 wells, 1.0 borosilicate bottom</td></tr></tbody></table>

molecular diffusion in plasma membranes of primary lymphocytes measured by fluorescence correlation spectroscopy

Molecular Diffusion in Plasma Membranes of Primary Lymphocytes Measured by Fluorescence Correlation Spectroscopy

Fluorescence correlation spectroscopy (FCS) is a powerful technique for studying the diffusion of molecules within biological membranes with high spatial and temporal resolution. FCS can quantify the molecular concentration and diffusion coefficient of fluorescently labeled molecules in the cell membrane. This technique has the ability to explore the molecular diffusion characteristics of molecules in the plasma membrane of immune cells in steady state (i.e., without processes affecting the result during the actual measurement time). FCS is suitable for studying the diffusion of proteins that are expressed at levels typical for most endogenous proteins. Here, a straightforward and robust method to determine the diffusion rate of cell membrane proteins on primary lymphocytes is demonstrated. An effective way to perform measurements on antibody-stained live cells and commonly occurring observations after acquisition are described. The recent advancements in the development of photo-stable fluorescent dyes can be utilized by conjugating the antibodies of interest to appropriate dyes that do not bleach extensively during the measurements. Additionally, this allows for the detection of slowly diffusing entities, which is a common feature of proteins expressed in cell membranes. The analysis procedure to extract molecular concentration and diffusion parameters from the generated autocorrelation curves is highlighted. In summary, a basic protocol for FCS measurements is provided; it can be followed by immunologists with an understanding of confocal microscopy but with no other previous experience of techniques for measuring dynamic parameters, such as molecular diffusion rates.

A typical result will generate an autocorrelation curve with a transit time in the range of 10 msec to 400 msec for membrane proteins. The number of molecules can vary between 0.5 to around 200 per μm2 for endogenously expressed proteins. Check carefully that the CPM is not lower than expected. This may mean that there is an influence of the background signal. As a rule of thumb, the CPM signal on cells that is accepted for analysis should not be lower than 33% of the CPM for f...

A method to measure protein diffusion in membranes of primary immune cells using fluorescence correlation spectroscopy (FCS) is described. In this paper, the use of antibodies for fluorescent labeling is illustrated.

Fluorescence correlation spectroscopy (FCS) is a powerful technique for studying the diffusion of molecules within biological membranes with high spatial ...

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Molecular Diffusion in Plasma Membranes of Primary Lymphocytes Measured by Fluorescence Correlation Spectroscopy

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