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Intracellular Flow Cytometry

Overview
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Intracellular flow cytometry is a powerful technique for the identification of cell types and the analysis of signaling and functional responses within cell lines and heterogeneous cell samples. For some cell types, such as Th17 and regulatory T cells (Tregs), definitive identification depends on the combined use of surface and intracellular markers such as cytokines or transcription factors. Intracellular flow cytometry also provides rich information concerning cellular function and signaling responses. Fluorescent antibodies specific for cell surface markers can be combined with markers of apoptosis, proliferation and protein phosphorylation to determine which cell subsets respond to various stimuli or treatments. The combined use of multiple markers decreases data acquisition time and conserves precious samples, since more parameters can be measured on a per-cell basis. While western blotting and other methods are useful for the examination of single proteins expressed by entire cell populations, flow cytometry allows the detection of multiple proteins simultaneously at the level of individual cells.

 

BD Biosciences provides fluorochrome-conjugated antibodies, buffers, kits and protocols to facilitate intracellular flow cytometry. Our antibodies are tested in biologically relevant model systems. These established tools enable new discoveries in fields such as immunology, inflammation and stem cell biology. Find the tools and techniques, including BD fluorochrome-conjugated antibodies, buffers, kits and protocols that support intracellular cytokine staining and phosphoprotein and transcription factor detection by intracellular flow cytometry.

 

Protocols for intracellular flow cytometry

 

 

Basic principles of intracellular staining

 

While techniques for cell surface staining are relatively standard, optimal staining for intracellular markers often depends on the biology of the target protein. Depending on the protein’s location inside the cell, association with other molecules, and its stability, different cell preparation and staining methods are recommended. Cytokines, for example, are typically secreted proteins.

 

However, if they are trapped inside the cell, they can be stained as intracellular proteins using protein transport inhibitors such as BD GolgiStop™ (containing monensin) or BD GolgiPlug™ (containing brefeldin A). Cytokines are relatively accessible using the gentle fixation and permeabilization afforded by BD Cytofix/ Cytoperm™ Fixation and Permeabilization Solution.

 

In contrast to cytokines, transcription factors often are localized inside the nucleus and bound to DNA and other proteins. Phosphorylation of some proteins, such as Stat5, results in dimer formation that masks the phosphorylated epitope of interest. Also, intracellular phosphatases can quickly dephosphorylate these proteins. Therefore, after treatment, cells must be quickly fixed and subjected to stronger permeabilization conditions to allow the antibody to enter the nucleus and access the epitope within disrupted molecular complexes.

 

Cells are fixed and permeabilized (symbolized by dashed line membrane), stained, and analyzed by flow cytometry. For studies on cytokine production, cells are first treated with a protein transport inhibitor to allow accumulation of the target protein inside the cell.

BD Biosciences provides tools to support intracellular flow cytometry

To facilitate intracellular flow cytometry assays, BD has developed several kits, buffers and protocols. In addition, many fluorescent antibodies specific for key cell surface markers have been tested in several buffer systems to save time, sample and money. Buffers are available for:

 

Detection of cytokines 

BD Cytofix/Cytoperm™ Fixation/Permeabilization Solution (Cat. No. 554714) is suitable for staining most cytokines and cell surface markers. This buffer system can also be used to stain some transcription factors and other intracellular proteins. This buffer system contains mild detergents along with a formaldehyde-based fixative.

 

Transcription factors 

The BD Pharmingen™ Transcription Factor Buffer Set (Cat. No. 562574/562725) is designed for the staining of transcription factors alone or in combination with cell surface markers and cytokines. This buffer system contains mild detergents along with a formaldehyde-based fixative.

 

Detection of phosphorylated protein 

BD Phosflow™ Perm Buffer III (Cat. No. 558050) is the recommended permeabilization buffer for phosphoepitope detection by flow cytometry. Perm buffer III is a harsh alcohol-based buffer. Alternative permeabilization buffers also are available to accommodate particular experimental requirements. We also provide a convenient buffer compatibility tool, detailing many common clones and their compatibility with BD Phosflow™ Buffer protocols. 

 

The permeabilization technique used can negatively impact the detection of cell surface and other intracellular antigens. The same techniques that allow access to the nucleus and open up DNA/protein or protein/protein complexes can often denature cell surface antigens, preventing their detection by antibodies. While detection of different intracellular proteins might require different conditions, the basic principles are the same: cells are fixed and permeabilized and then stained intracellularly with fluorescent antibodies.

 

 

STAT phosphotyrosine epitopes are obscured by dimerization within activated cells.

Optimal cell permeabilization conditions vary by epitope location.

Cytokine Detection
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Transcription Factors
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Phosphorylation
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Multiplexing
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Resources
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For Research Use Only. Not for use in diagnostic or therapeutic procedures.

Alexa Fluor is a trademark of Life Technologies Corporation.

CF is a trademark of Biotium, Inc.

Cy is a trademark of Global Life Sciences Solutions Germany GmbH or an affiliate doing business as Cytiva.

Cytobank is a trademark of Beckman Coulter, Inc.