Name: antibody labeling with fluorescent dyes using magnetic protein a and protein g beads
Uploaded: 2016-09-15T14:00:00
Description: Watch this Scientific Journal Video about Antibody Labeling with Fluorescent Dyes Using Magnetic Protein A and Protein G Beads at JoVE.com

1. Antibody Capture onto High Capacity Magnetic Protein A or Magnetic Protein G Beads
<ol>
	<li>Uniformly re-suspend magnetic beads by gentle shaking. Keep the suspension uniform when aliquoting beads.</li>
	<li>Add 50 &#181;l of bead slurry to a 1.5 ml microcentrifuge tube. Place in the magnetic stand for 10 sec. Carefully remove the storage buffer.</li>
	<li>Add 250 &#181;l of antibody binding buffer.</li>
	<li>Mix and place in the magnetic stand for 10 sec. Carefully remove the binding buffer.</li>
	<li>Add 1.0 ml o...

<ol>
	<li>Colwill, K., Graslund, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+roadmap+to+generate+renewable+protein+binders+to+the+human+proteome.">A roadmap to generate renewable protein binders to the human proteome.</a> Nat Methods. 8 (7), 551-558 (2011).</li><li>Silverstein, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Labeled+antigens+and+antibodies:+the+evolution+of+magic+markers+and+magic+bullets.">Labeled antigens and antibodies: the evolution of magic markers and magic bullets.</a> Nat Immunol. 5 (12), 1211-1217 (2004).</li><li>Day, J. J., 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=Chemically+modified+antibodies+as+diagnostic+imaging+agents.">Chemically modified antibodies as diagnostic imaging agents.</a> Curr Opin Chem Biol. 14 (6), 803-809 (2010).</li><li>Cunningham, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Overview+of+flow+cytometry+and+fluorescent+probes+for+flow+cytometry.">Overview of flow cytometry and fluorescent probes for flow cytometry.</a> Methods Mol Biol. 588, 319-326 (2010).</li><li>Eaton, S. 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=A+guide+to+modern+quantitative+fluorescent+western+blotting+with+troubleshooting+strategies.">A guide to modern quantitative fluorescent western blotting with troubleshooting strategies.</a> J Vis Exp. (93), e52099 (2014).</li><li>Dundas, C. M., Demonte, D., Park, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Streptavidin-biotin+technology:+improvements+and+innovations+in+chemical+and+biological+applications.">Streptavidin-biotin technology: improvements and innovations in chemical and biological applications.</a> Appl Microbiol Biotechnol. 97 (21), 9343-9353 (2013).</li><li>Kraeber-Bodere, F., 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=Radioimmunoconjugates+for+the+treatment+of+cancer.">Radioimmunoconjugates for the treatment of cancer.</a> Semin Oncol. 41 (5), 613-622 (2014).</li><li>Leal, 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=Antibody-drug+conjugates:+an+emerging+modality+for+the+treatment+of+cancer.">Antibody-drug conjugates: an emerging modality for the treatment of cancer.</a> Ann N Y Acad Sci. 1321, 41-54 (2014).</li><li>Drachman, J. G., Senter, P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antibody-drug+conjugates:+the+chemistry+behind+empowering+antibodies+to+fight+cancer.">Antibody-drug conjugates: the chemistry behind empowering antibodies to fight cancer.</a> Hematology Am Soc Hematol Educ Program. 2013, 306-310 (2013).</li><li>Hermanson, G. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Bioconjugate Techniques. , 380-382 (1996).</li><li>Shrestha, D., Bagosi, A., Szollosi, J., Jenei, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparative+study+of+the+three+different+fluorophore+antibody+conjugation+strategies.">Comparative study of the three different fluorophore antibody conjugation strategies.</a> Anal Bioanal Chem. 404 (5), 1449-1463 (2012).</li><li>Vira, S., Mekhedov, E., Humphrey, G., Blank, P. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent-labeled+antibodies:+Balancing+functionality+and+degree+of+labeling.">Fluorescent-labeled antibodies: Balancing functionality and degree of labeling.</a> Anal Biochem. 402 (2), 146-150 (2010).</li><li>Isa, 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=High-throughput+screening+system+to+identify+small+molecules+that+induce+internalization+and+degradation+of+HER2.">High-throughput screening system to identify small molecules that induce internalization and degradation of HER2.</a> ACS Chem Biol. 9 (10), 2237-2241 (2014).</li><li>Liao-Chan, S., 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=Quantitative+assessment+of+antibody+internalization+with+novel+monoclonal+antibodies+against+Alexa+fluorophores.">Quantitative assessment of antibody internalization with novel monoclonal antibodies against Alexa fluorophores.</a> PLoS One. 10 (4), e0124708 (2015).</li><li>Riedl, T., van Boxtel, E., Bosch, M., Parren, P. W., Gerritsen, A. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-Throughput+Screening+for+Internalizing+Antibodies+by+Homogeneous+Fluorescence+Imaging+of+a+pH-Activated+Probe.">High-Throughput Screening for Internalizing Antibodies by Homogeneous Fluorescence Imaging of a pH-Activated Probe.</a> J Biomol Screen. 21 (1), 12-23 (2016).</li><li>Nath, N., 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=Homogeneous+plate+based+antibody+internalization+assay+using+pH+sensor+fluorescent+dye.">Homogeneous plate based antibody internalization assay using pH sensor fluorescent dye.</a> J Immunol Methods. 431, 11-21 (2016).</li><li>Lundberg, E., Sundberg, M., Graslund, T., Uhlen, M., Svahn, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+method+for+reproducible+fluorescent+labeling+of+small+amounts+of+antibodies+on+solid+phase.">A novel method for reproducible fluorescent labeling of small amounts of antibodies on solid phase.</a> J Immunol Methods. 322 (1-2), 40-49 (2007).</li><li>Strachan, 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=Solid-phase+biotinylation+of+antibodies.">Solid-phase biotinylation of antibodies.</a> J Mol Recognit. 17 (3), 268-276 (2004).</li><li>Dezfouli, 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=Magnetic+bead+assisted+labeling+of+antibodies+at+nanogram+scale.">Magnetic bead assisted labeling of antibodies at nanogram scale.</a> Proteomics. 14 (1), 14-18 (2014).</li><li>Nath, N., Godat, B., Benink, H., Urh, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On-bead+antibody-small+molecule+conjugation+using+high-capacity+magnetic+beads.">On-bead antibody-small molecule conjugation using high-capacity magnetic beads.</a> J Immunol Methods. 426, 95-103 (2015).</li><li>Lund, L. N., 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=Exploring+variation+in+binding+of+Protein+A+and+Protein+G+to+immunoglobulin+type+G+by+isothermal+titration+calorimetry.">Exploring variation in binding of Protein A and Protein G to immunoglobulin type G by isothermal titration calorimetry.</a> J Mol Recognit. 24 (6), 945-952 (2011).</li><li>Safarik, I., Safarikova, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Magnetic+techniques+for+the+isolation+and+purification+of+proteins+and+peptides.">Magnetic techniques for the isolation and purification of proteins and peptides.</a> Biomagn Res Technol. 2 (1), 7 (2004).</li><li>Flygare, J. A., Pillow, T. H., Aristoff, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antibody-drug+conjugates+for+the+treatment+of+cancer.">Antibody-drug conjugates for the treatment of cancer.</a> Chem Biol Drug Des. 81 (1), 113-121 (2013).</li><li>Shen, B. Q., 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=Conjugation+site+modulates+the+in+vivo+stability+and+therapeutic+activity+of+antibody-drug+conjugates.">Conjugation site modulates the in vivo stability and therapeutic activity of antibody-drug conjugates.</a> Nat Biotechnol. 30 (2), 184-189 (2012).</li><li>Acchione, M., Kwon, H., Jochheim, C. M., Atkins, W. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+linker+and+conjugation+chemistry+on+antigen+binding,+Fc+receptor+binding+and+thermal+stability+of+model+antibody-drug+conjugates.">Impact of linker and conjugation chemistry on antigen binding, Fc receptor binding and thermal stability of model antibody-drug conjugates.</a> MAbs. 4 (3), 362-372 (2012).</li></ol>

The goal of this study was to develop a method to label antibodies, present in the cell media at low concentrations, with a variety of small molecules. Such a method will allow a large number of antibodies, during the early stages of antibody discovery, to be labeled with small molecules and screened using a biologically relevant assay. One such assay is the receptor-mediated antibody internalization assay where internalization may vary between antibodies even with similar binding affinities. Hence, it is important to sc...

Antibodies labeled with small molecules are perhaps the most commonly used reagents in biology1,2. Antibodies labeled with fluorescent dyes and biotin are extensively used in imaging, immunoassays, flow cytometry, western blots, and immunoprecipitation among other applications3-6. Radiolabeled antibodies3,7 find extensive use in imaging and therapy, antibodies labeled with cytotoxic drugs (ADCs) are offering new options for the treatment of cancers, and two ADCs have already been approved for therapeutic use8. In spite of their extensive use, the methods for labeling antibodies have remained surprisingly unchanged and typically involve multiple reactions and desalting steps9-12. Solution methods work very well in cases where only a few antibodies need to be labeled and are available in highly purified form at high concentration and in sufficient volumes. However, for newer applications like ADCs, there is a need to label antibodies at the early hybridoma stage so that they can be screened for biologically relevant properties, for example, receptor-mediated antibody internalization13-16. At the hybridoma stage, sample volumes are limited, antibodies are expressed at low concentrations and a number of samples are large, hence solution based labeling methods are not suitable.
To simplify and improve the throughput of the traditional antibody labeling methods, a few alternative approaches have been proposed17,18. One approach is to use non-magnetic Protein A affinity beads packed in small columns to capture antibodies followed by the labeling reaction and elution of labeled and purified protein. This method can be used to label antibodies directly from cell media, however, the use of columns can be laborious. A magnetic bead based method has recently been reported19 that eliminates the use of columns and improves throughput but due to the limited antibody binding capacity of the beads, only nanogram to low microgram quantities of the antibodies could be labeled.
We recently developed and used high capacity magnetic Protein A and Protein G beads (&#62;20 mg of Human IgG/ml of settled beads) to label antibodies present in cell media with small molecules20. The high capacity of the beads allows tens to hundreds of micrograms of antibody to be labeled conveniently and the rapid magnetic response of the beads simplifies handling and processing of a large number of samples in parallel. Using fluorescent dyes as surrogates for small molecules, we show that the method is compatible with amine and thiol labeling chemistry and offers high recoveries of labeled and very pure antibodies.
This protocol and the accompanying video describe on-bead labeling of mouse antibodies present in the cell media using Magnetic Protein A and Protein G beads. The protocol is divided into four sections: Section 1 describes the capture of antibodies onto the bead from biological samples. Following capture, the labeling of antibodies with fluorescent dye using amine chemistry or using thiol chemistry is described in sections 2 and section 3, respectively. Finally, section 4 describes the method for the calculations of the antibody concentration and the dye to antibody ratio.

<table border="0" cellpadding="0" cellspacing="0" width="592">
	<tbody>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Magne Protein A Beads</td>
			<td style="width:103px;">Promega Corporation</td>
			<td style="width:119px;">&#160;G8781</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Magne Protein G Beads</td>
			<td style="width:103px;">Promega Corporation&#160;</td>
			<td style="width:119px;">&#160;G7471</td>
			<td></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">AlexaFluor 532-SE (Succinimidyl Ester)</td>
			<td style="width:103px;">Life Technologies</td>
			<td style="width:119px;">A20001</td>
			<td></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">AlexaFluor 532-ME (Malemide)</td>
			<td style="width:103px;">Life Technologies</td>
			<td style="width:119px;">A10255</td>
			<td></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">AlexaFluor 647-ME (Maleimide)</td>
			<td style="width:103px;">Life Technologies</td>
			<td style="width:119px;">A20347</td>
			<td></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Fluorescein-ME (Maleimide)</td>
			<td style="width:103px;">Life Technologies</td>
			<td style="width:119px;">F-150</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Magnetic Stand</td>
			<td style="width:103px;">Promega</td>
			<td style="width:119px;">Z5332</td>
			<td></td>
		</tr>
	</tbody>
</table>

antibody labeling with fluorescent dyes using magnetic protein a and protein g beads

Antibodies labeled with small molecules like fluorescent dyes, cytotoxic drugs, and radioactive tracers are essential tools in biomedical research, immunodiagnostics and more recently as therapeutic agents. Traditional methods for labeling antibodies with small molecules require purified antibodies at relatively high concentration, involve multiple dialysis steps and have limited throughput. However, several applications, including the field of Antibody Drug Conjugates (ADCs), will benefit from new methods that will allow labeling of antibodies directly from cell media. Such methods may allow antibodies to be screened in biologically relevant assays, for example, the receptor-mediated antibody internalization assay in the case of ADCs. Here, we describe a method (on-bead method) that enables labeling of small amounts of antibodies directly from cell media. This approach utilizes high capacity magnetic Protein A and Protein G affinity beads to capture antibodies from the cell media followed by labeling with small molecules using either amine or thiol chemistry and subsequent elution of the labeled antibodies. Taking fluorescent dyes as surrogates for small molecules, we demonstrate the on-bead labeling of three different mouse antibodies directly from cell media using both amine and thiol labeling chemistry. The high binding affinity of antibodies to Protein A and Protein G ensures high recoveries as well as high purity of the labeled antibodies. In addition, use of magnetic beads allows multiple samples to be handled manually, thereby significantly improving labeling throughput.

A schematic for labeling antibodies with small molecules using high capacity magnetic Protein A and Protein G beads is shown in Figure 1. Antibodies captured on the magnetic Protein G beads can be labeled with small molecules, for example fluorescent dyes, using either amine chemistry which labels primary amines of the lysine amino acids or using thiol chemistry which labels at the reduced thiols in the hinge region of the antibodies. Affinity between antibodies and Prote...

Watch this Scientific Journal Video about Antibody Labeling with Fluorescent Dyes Using Magnetic Protein A and Protein G Beads at JoVE.com

Antibody Labeling with Fluorescent Dyes Using Magnetic Protein A and Protein G Beads

The on-bead method for labeling antibodies with small molecules enables labeling of a small amount of antibodies directly from cell media. This method is compatible with amine and thiol chemistry, and can handle multiple samples in parallel, manually or using automated platforms.

Antibodies labeled with small molecules like fluorescent dyes, cytotoxic drugs, and radioactive tracers are essential tools in biomedical research, ...

The overall goal of this method is to label antibodies with fluorescent dies from purified samples or directly from cell medium using magnetic protein A or G beads. This method can be used to optimize the labeling chemistry of even small amount of antibodies within the cell medium. Leading to better downstream application of the antibodies.The main advantages of this technique are that the antibodies do not require purification, amine or thiol chemistry can be used, and the method can be automated or manual. Begin by uniformly re-suspending the beads with gentle shaking. Then, add 50 microliters of beads to a 1.5 milliliter microsentrifuge tube.Then, place the tube in a magnetic stand. After 10 seconds, carefully replace the storage buffer with 250 microliters of antibody-binding buffer and mix the beads well. After another 10 seconds, carefully replace the binding buffer with one milliliter of the antibody of interest.And mix the sample for 60 minutes at room temperature. At the end of the incubation, return the tubes to the magnet and remove the supernatant when the beads have moved to the sides of the tube. Then, rinse the beads and antibody mixture by two 10 second washes with 250 microliters of antibody-binding wash buffer per wash.To label the antibodies using amine chemistry, after the second wash, replace the wash buffer with 100 microliters of amine conjugation buffer and add 2.5 microliters of freshly prepared amine-reactive dye per 100 micrograms of anitbody. Vortex the sample for 60 minutes at room temperature to keep the beads in suspension during the labeling. Then, return the tube to the magnet for 10 seconds and remove the supernatant.Wash the beads two times with antibody-binding wash buffer, as just demonstrated. Then, replace the wash buffer with 50 microliters of elution buffer and mix the beads for five minutes. Return the tube to the magnet for 10 seconds and transfer the eluted antibody to a new microcentrifuge tube containing five microliters of neutralization buffer.Elute the antibody one more time, as just demonstrated, pulling the eluted samples. Then, measure the absorbance of the antibody-dye conjugate at 280 nanometers and at the lambda max for the dye. To label the antibodies using thiol chemistry, after the second wash, replace the wash buffer with 250 microliters of thiol conjugation buffer and mix the beads with gentle pipetting.After 10 seconds, wash the beads two times with antibody-binding wash buffer. Then, replace the wash buffer with 100 microliters of thiol conjugation buffer and add DTT to a final concentration of 2.5 millimolar. Mix the beads for another 60 minutes.Then, return the beads to the magnet for 10 seconds and discard the buffer. Next, add 250 microliters of thiol-conjugation buffer to the beads with gentle mixing. After 10 seconds, wash the beads two times with antibody-binding wash buffer, replacing the second wash with 100 microliters of fresh thiol-conjugation buffer.Now, add 2.5 microliters of freshly prepared thiol-reactive dye per 100 micrograms of antibody and mix the beads for 60 minutes at room temperature. At the end of the incubation, return the tube to the magnet for 10 seconds. And replace the supernatant with 250 microliters of fresh thiol-conjugation buffer with gentle mixing.After 10 seconds, wash the beads two times. Then, replace the wash buffer with 50 microliters of elution buffer and elute the conjugated antibody two times, as just demonstrated. Then, measure the absorbance of the antibody-dye conjugate at 280 nanometers and at the lambda max for the dye.The strong affinity between the antibodies and Protein G, the robust affinity of the magnet for the beads, and the optimization of the method prior to the bead purification together result in a nominal loss of antibody during the labeling reaction, as evidenced by the efficient recovery of three different mouse antibody isotypes after fluorescent dilabeling compared to simple purification. This recovery is also evident in Coomassie gels, where the low non-specific binding properties of the magnetic G Protein beads result in the presence of highly purified fluorescence-dilabeled heavy and light chains. On bead labeling with magnetic Protein A beads, it is also compatible with multiple fluorescent dyes, resulting in high recovery and good dye-to-antibody ratios.Once mastered, this technique can be completed in two to three hours, if it is performed properly. Allowing multiple samples to be handled manually or an automated platform for improved throughput. While attempting this procedure, it is important to remember to keep the magnetic beads in suspension at all times.Choose the appropriate volume of magnetic beads for the sample. And optimize the amount of fluorescent dye for the antibody of interest. Following this procedure, the labeled antibodies should be tested to determine functionality using relevant biological assays, like ELISA, facts, or cell-based assays.After watching this video, you should have a good understanding of how to label purified and unpurified antibodies with fluorescent tags or other small molecules, like biotin or cytotoxic drugs, using magnetic Protein A or G beads.

antibody-labeling-with-fluorescent-dyes-using-magnetic-protein

Research

JoVE Journal

Immunology and Infection

Specific Marking of HIV-1 Positive Cells using a Rev-dependent Lentiviral Vector Expressing the Green Fluorescent Protein

Most of HIV-responsive expression vectors are based on the HIV promoter, the long terminal repeat (LTR). While responsive to an early HIV protein, Tat, the LTR is also responsive to cellular activation states and to the local chromatin activity where the integration has occurred. This can result in high HIV-independent activity, and has restricted the usefulness of LTR-based reporter to mark HIV positive cells 1,2,3. Here, we constructed an expression lentiviral vector that possesses, in addition to the Tat-responsive LTR, numerous HIV DNA sequences that include the Rev-response element and HIV splicing sites 4,5,6. The vector was incorporated into a lentiviral reporter virus, permitting highly specific detection of replicating HIV in living cell populations. The activity of the vector was measured by expression of the green fluorescence protein (GFP). The application of this vector as reported here offers a novel alternative approach to existing methods, such as in situ PCR or HIV antigen staining, to identify HIV-positive cells. The vector can also express therapeutic genes for basic or clinical experimentation to target HIV-positive cells.

We have developed a lentiviral vector that possesses, in addition to the Tat-responsive LTR, the Rev-response element (RRE) that can regulate reporter gene expression in an HIV-1 Tat- and Rev-dependent fashion. The vector permits the specific detection of replicating HIV in living cells via the expression of GFP.

Most of HIV-responsive expression vectors are based on the HIV promoter, the long terminal repeat (LTR). While responsive to an early HIV protein, Tat, ...

A Calcium Bioluminescence Assay for Functional Analysis of Mosquito (Aedes aegypti) and Tick (Rhipicephalus microplus) G Protein-coupled Receptors

Arthropod hormone receptors are potential targets for novel pesticides as they regulate many essential physiological and behavioral processes. The majority of them belong to the superfamily of G protein-coupled receptors (GPCRs). We have focused on characterizing arthropod kinin receptors from the tick and mosquito. Arthropod kinins are multifunctional neuropeptides with myotropic, diuretic, and neurotransmitter function. Here, a method for systematic analyses of structure-activity relationships of insect kinins on two heterologous kinin receptor-expressing systems is described. We provide important information relevant to the development of biostable kinin analogs with the potential to disrupt the diuretic, myotropic, and/or digestive processes in ticks and mosquitoes.
The kinin receptors from the southern cattle tick, Boophilus microplus (Canestrini), and the mosquito Aedes aegypti (Linnaeus), were stably expressed in the mammalian cell line CHO-K1. Functional analyses of these receptors were completed using a calcium bioluminescence plate assay that measures intracellular bioluminescence to determine cytoplasmic calcium levels upon peptide application to these recombinant cells. This method takes advantage of the aequorin protein, a photoprotein isolated from luminescent jellyfish. We transiently transfected the aequorin plasmid (mtAEQ/pcDNA1) in cell lines that stably expressed the kinin receptors. These cells were then treated with the cofactor coelenterazine, which complexes with intracellular aequorin. This bond breaks in the presence of calcium, emitting luminescence levels indicative of the calcium concentration. As the kinin receptor signals through the release of intracellular calcium, the intensity of the signal is related to the potency of the peptide.
This protocol is a synthesis of several previously described protocols with modifications; it presents step-by-step instructions for the stable expression of GPCRs in a mammalian cell line through functional plate assays (Staubly et al., 2002 and Stables et al., 1997). Using this methodology, we were able to establish stable cell lines expressing the mosquito and the tick kinin receptors, compare the potency of three mosquito kinins, identify critical amino acid positions for the ligand-receptor interaction, and perform semi-throughput screening of a peptide library. Because insect kinins are susceptible to fast enzymatic degradation by endogenous peptidases, they are severely limited in use as tools for pest control or endocrinological studies. Therefore, we also tested kinin analogs containing amino isobutyric acid (Aib) to enhance their potency and biostability. This peptidase-resistant analog represents an important lead in the development of biostable insect kinin analogs and may aid in the development of neuropeptide-based arthropod control strategies.

A Calcium Bioluminescence Assay for Functional Analysis of Mosquito Aedes aegypti and Tick Rhipicephalus microplus G Protein-coupled Receptors

This protocol provides instructions for clonal-cell line selection and a calcium bioluminescence assay to analyze the structure-activity relationships of synthesized arthropod neuropeptides on their cognate GPCRs. This assay can be used for receptor deorphanization and structure-activity relationship studies for synthetic analog design and peptide/drug-lead discovery.

Arthropod hormone receptors are potential targets for novel pesticides as they regulate many essential physiological and behavioral processes.  The ...

Colorectal Cancer Cell Surface Protein Profiling Using an Antibody Microarray and Fluorescence Multiplexing

The current prognosis and classification of CRC relies on staging systems that integrate histopathologic and clinical findings. However, in the majority of CRC cases, cell dysfunction is the result of numerous mutations that modify protein expression and post-translational modification1.
A number of cell surface antigens, including cluster of differentiation (CD) antigens, have been identified as potential prognostic or metastatic biomarkers in CRC. These antigens make ideal biomarkers as their expression often changes with tumour progression or interactions with other cell types, such as tumour-infiltrating lymphocytes (TILs) and tumour-associated macrophages (TAMs).
The use of immunohistochemistry (IHC) for cancer sub-classification and prognostication is well established for some tumour types2,3. However, no single &#x2018;marker&#x2019; has shown prognostic significance greater than clinico-pathological staging or gained wide acceptance for use in routine pathology reporting of all CRC cases. 
A more recent approach to prognostic stratification of disease phenotypes relies on surface protein profiles using multiple 'markers'. While expression profiling of tumours using proteomic techniques such as iTRAQ is a powerful tool for the discovery of biomarkers4, it is not optimal for routine use in diagnostic laboratories and cannot distinguish different cell types in a mixed population. In addition, large amounts of tumour tissue are required for the profiling of purified plasma membrane glycoproteins by these methods. 
In this video we described a simple method for surface proteome profiling of viable cells from disaggregated CRC samples using a DotScan CRC antibody microarray. The 122-antibody microarray consists of a standard 82-antibody region recognizing a range of lineage-specific leukocyte markers, adhesion molecules, receptors and markers of inflammation and immune response5, together with a satellite region for detection of 40 potentially prognostic markers for CRC. Cells are captured only on antibodies for which they express the corresponding antigen. The cell density per dot, determined by optical scanning, reflects the proportion of cells expressing that antigen, the level of expression of the antigen and affinity of the antibody6. 
For CRC tissue or normal intestinal mucosa, optical scans reflect the immunophenotype of mixed populations of cells. Fluorescence multiplexing can then be used to profile selected sub-populations of cells of interest captured on the array. For example, Alexa 647-anti-epithelial cell adhesion molecule (EpCAM; CD326), is a pan-epithelial differentiation antigen that was used to detect CRC cells and also epithelial cells of normal intestinal mucosa, while Phycoerythrin-anti-CD3, was used to detect infiltrating T-cells7. The DotScan CRC microarray should be the prototype for a diagnostic alternative to the anatomically-based CRC staging system.

We described a procedure for the disaggregation of colorectal cancer (CRC) to produce viable single cells, which are then captured on customized antibody microarrays recognizing surface antigens (DotScan CRC microarray). Sub-populations of cells bound to the microarray can be profiled by fluorescence multiplexing using monoclonal antibodies tagged with fluorescent dyes.

The current prognosis and classification of CRC relies on staging systems that integrate histopathologic and clinical findings. However, in the majority ...

Protein Misfolding Cyclic Amplification of Prions

Prions are infectious agents that cause the inevitably fatal transmissible spongiform encephalopathy (TSE) in animals and humans9,18. The prion protein has two distinct isoforms, the non-infectious host-encoded protein (PrPC) and the infectious protein (PrPSc), an abnormally-folded isoform of PrPC 8.
One of the challenges of working with prion agents is the long incubation period prior to the development of clinical signs following host inoculation13. This traditionally mandated long and expensive animal bioassay studies. Furthermore, the biochemical and biophysical properties of PrPSc are poorly characterized due to their unusual conformation and aggregation states.
PrPSc can seed the conversion of PrPC to PrPSc in vitro14. PMCA is an in vitro technique that takes advantage of this ability using sonication and incubation cycles to produce large amounts of PrPSc, at an accelerated rate, from a system containing excess amounts of PrPC and minute amounts of the PrPSc seed19. This technique has proven to effectively recapitulate the species and strain specificity of PrPSc conversion from PrPC, to emulate prion strain interference, and to amplify very low levels of PrPSc from infected tissues, fluids, and environmental samples6,7,16,23 .
This paper details the PMCA protocol, including recommendations for minimizing contamination, generating consistent results, and quantifying those results. We also discuss several PMCA applications, including generation and characterization of infectious prion strains, prion strain interference, and the detection of prions in the environment.

Protein misfolding cyclic amplification (PMCA) is an in vitro assay for the study of prion conversion and strain and species barriers. It can also be used as a prion detection assay.

Prions  are infectious agents that cause the inevitably fatal transmissible spongiform  encephalopathy (TSE) in animals and humans9,18. The prion protein ...

Monitoring Changes in Membrane Polarity, Membrane Integrity, and Intracellular Ion Concentrations in Streptococcus pneumoniae Using Fluorescent Dyes

Membrane depolarization and ion fluxes are events that have been studied extensively in biological systems due to their ability to profoundly impact cellular functions, including energetics and signal transductions. While both fluorescent and electrophysiological methods, including electrode usage and patch-clamping, have been well developed for measuring these events in eukaryotic cells, methodology for measuring similar events in microorganisms have proven more challenging to develop given their small size in combination with the more complex outer surface of bacteria shielding the membrane. During our studies of death-initiation in Streptococcus pneumoniae (pneumococcus), we wanted to elucidate the role of membrane events, including changes in polarity, integrity, and intracellular ion concentrations. Searching the literature, we found that very few studies exist. Other investigators had monitored radioisotope uptake or equilibrium to measure ion fluxes and membrane potential and a limited number of studies, mostly in Gram-negative organisms, had seen some success using carbocyanine or oxonol fluorescent dyes to measure membrane potential, or loading bacteria with cell-permeant acetoxymethyl (AM) ester versions of ion-sensitive fluorescent indicator dyes. We therefore established and optimized protocols for measuring membrane potential, rupture, and ion-transport in the Gram-positive organism S. pneumoniae. We developed protocols using the bis-oxonol dye DiBAC4(3) and the cell-impermeant dye propidium iodide to measure membrane depolarization and rupture, respectively, as well as methods to optimally load the pneumococci with the AM esters of the ratiometric dyes Fura-2, PBFI, and BCECF to detect changes in intracellular concentrations of Ca2+, K+, and H+, respectively, using a fluorescence-detection plate reader. These protocols are the first of their kind for the pneumococcus and the majority of these dyes have not been used in any other bacterial species. Though our protocols have been optimized for S. pneumoniae, we believe these approaches should form an excellent starting-point for similar studies in other bacterial species.

Monitoring Changes in Membrane Polarity, Membrane Integrity, and Intracellular Ion Concentrations in Streptococcus pneumoniae Using Fluorescent Dyes

Unlike that seen for eukaryotes, there is a paucity of studies that detail membrane depolarization and ion concentration changes in bacteria, primarily as their small size makes conventional methods of measurement difficult. Here, we detail protocols for monitoring such events in the significant Gram-positive pathogen Streptococcus pneumoniae utilizing fluorescence techniques.

Membrane depolarization and ion fluxes are events that have been studied extensively in biological systems due to their ability to profoundly impact ...

Inoculating Anopheles gambiae Mosquitoes with Beads to Induce and Measure the Melanization Immune Response

The stimulation of immune responses is a common tool in invertebrate studies to examine the efficacy and the mechanisms of immunity. This stimulation is based on the injection of non-pathogenic particles into insects, as the particles will be detected by the immune system and will induce the production of immune effectors. We focus here on the stimulation of the melanization response in the mosquito Anopheles gambiae. The melanization response results in the encapsulation of foreign particles and parasites with a dark layer of melanin. To stimulate this response, mosquitoes are inoculated with beads in the thoracic cavity using microcapillary glass tubes. Then, after 24 hr, the mosquitoes are dissected to retrieve the beads. The degree of melanization of the bead is measured using image analysis software. Beads do not have the pathogenic effects of parasites, or their capacity to evade or suppress the immune response. These injections are a way to measure immune efficacy and the impact of immune stimulations on other life history traits, such as fecundity or longevity. It is not exactly the same as directly studying host-parasite interactions, but it is an interesting tool to study immunity and its evolutionary ecology.

Inoculating Anopheles gambiae Mosquitoes with Beads to Induce and Measure the Melanization Immune Response

Through inoculation with beads, the described technique enables the stimulation of the mosquito melanization response in the hemolymph circulating system. The amount of melanin covering the beads can be measured after dissection as a measure of the immune response.

The stimulation of immune responses is a common tool in invertebrate studies to examine the efficacy and the mechanisms of immunity. This stimulation is ...

A Protein Microarray Assay for Serological Determination of Antigen-specific Antibody Responses Following Clostridium difficile Infection

We provide a detailed overview of a novel high-throughput protein microarray assay for the determination of anti-Clostridium difficile antibody levels in human sera and in separate preparations of polyclonal intravenous immunoglobulin (IVIg). The protocol describes the methodological steps involved in sample preparation, printing of arrays, assay procedure, and data analysis. In addition, this protocol could be further developed to incorporate diverse clinical samples including plasma and cell culture supernatants. We show how protein microarray can be used to determine a combination of isotype (IgG, IgA, IgM), subclass (IgG1, IgG2, IgG3, IgG4, IgA1, IgA2), and strain-specific antibodies to highly purified whole C. difficile toxins A and B (toxinotype 0, strain VPI 10463, ribotype 087), toxin B from a C. difficile toxin-B-only expressing strain (CCUG 20309), a precursor form of a B fragment of binary toxin, pCDTb, ribotype-specific whole surface layer proteins (SLPs; 001, 002, 027), and control proteins (tetanus toxoid and Candida albicans). During the experiment, microarrays are probed with sera from individuals with C. difficile infection (CDI), individuals with cystic fibrosis (CF) without diarrhea, healthy controls (HC), and from individuals pre- and post-IVIg therapy for the treatment of CDI, combined immunodeficiency disorder, and chronic inflammatory demyelinating polyradiculopathy. We encounter significant differences in toxin neutralization efficacies and multi-isotype specific antibody levels between patient groups, commercial preparations of IVIg, and sera before and following IVIg administration. Also, there is a significant correlation between microarray and enzyme-linked immunosorbent assay (ELISA) for antitoxin IgG levels in serum samples. These results suggest that microarray could become a promising tool for profiling antibody responses to C.difficile antigens in vaccinated or infected humans. With further refinement of antigen panels and a reduction in production costs, we anticipate that microarray technology may help optimize and select the most clinically useful immunotherapies for C. difficile infection in a patient-specific manner.

A Protein Microarray Assay for Serological Determination of Antigen-specific Antibody Responses Following Clostridium difficile Infection

This article describes a simple protein microarray method for profiling humoral immune responses to a 7-plex panel of highly purified Clostridium difficile antigens in human sera. The protocol can be extended for the determination of specific antibody responses in preparations of polyclonal intravenous immunoglobulin.

We provide a detailed overview of a novel high-throughput protein microarray assay for the determination of anti-Clostridium difficile antibody levels in ...

TurboID-Based Proximity Labeling for In Planta Identification of Protein-Protein Interaction Networks

Proximity labeling (PL) techniques using engineered ascorbate peroxidase (APEX) or Escherichia coli biotin ligase BirA (known as BioID) have been successfully used for identification of protein-protein interactions (PPIs) in mammalian cells. However, requirements of toxic hydrogen peroxide (H2O2) in APEX-based PL, longer incubation time with biotin (16&#8211;24 h), and higher incubation temperature (37 &#176;C) in BioID-based PL severely limit their applications in plants. The recently described TurboID-based PL addresses many limitations of BioID and APEX. TurboID allows rapid proximity labeling of proteins in just 10&#8201;min under room temperature (RT) conditions. Although the utility of TurboID has been demonstrated in animal models, we recently showed that TurboID-based PL performs better in plants compared to BioID for labeling of proteins that are proximal to a protein of interest. Provided here is a step-by-step protocol for the identification of protein interaction partners using the N-terminal Toll/interleukin-1 receptor (TIR) domain of the nucleotide-binding leucine-rich repeat (NLR) protein family as a model. The method describes vector construction, agroinfiltration of protein expression constructs, biotin treatment, protein extraction and desalting, quantification, and enrichment of the biotinylated proteins by affinity purification. The protocol described here can be easily adapted to study other proteins of interest in Nicotiana and other plant species.

Described here is a proximity labeling method for identification of interaction partners of the TIR domain of the NLR immune receptor in Nicotiana benthamiana leaf tissue. Also provided is a detailed protocol for the identification of interactions between other proteins of interest using this technique in Nicotiana and other plant species.

Proximity labeling (PL) techniques using engineered ascorbate peroxidase (APEX) or Escherichia coli biotin ligase BirA (known as BioID) have been ...

Analysis of SARS-CoV-2 Using Dual-Reporter and Multiplex Technology

Profiling of Surface Protein Epitopes on Viral Particles by Multiplex Dual-Reporter Strategy

Membrane proteins on enveloped viruses play an important role in many biological functions involving virus attachment to target cell receptors, fusion of viral particles to host cells, host-virus interactions, and disease pathogenesis. Furthermore, viral membrane proteins on virus particles and presented on host cell surfaces have proven to be excellent targets for antivirals and vaccines. Here, we describe a protocol to investigate surface proteins on intact severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) particles using the dual-reporter flow cytometric system. The assay exploits multiplex technology to obtain a triple detection of viral particles by three independent affinity reactions. Magnetic beads conjugated to recombinant human angiotensin-converting enzyme-2 (ACE2) were used to capture viral particles from the supernatant of cells infected with SARS-CoV-2. Then, two detection reagents labeled with R-phycoerythrin (PE) or Brilliant Violet 421 (BV421) were applied simultaneously. As a proof-of-concept, antibody fragments targeting different epitopes of the SARS-CoV-2 surface protein Spike (S1) were used. The detection of viral particles by three independent affinity reactions provides strong specificity and confirms the capture of intact virus particles. Dose-dependency curves of SARS-CoV-2 infected cell supernatant were generated with replicate coefficient variances (mean/SD) &#706;14%. Good assay performance in both channels confirmed that two virus surface target protein epitopes are detectable in parallel. The protocol described here could be applied for (i) high-multiplex, high-throughput profiling of surface proteins expressed on enveloped viruses; ii) detection of active intact viral particles; and (iii) assessment of specificity and affinity of antibodies and antiviral drugs for surface epitopes of viral antigens.The application can be potentially extended to any type of extracellular vesicles and bioparticles, exposing surface antigens in body fluids or other liquid matrices.

Author Spotlight: Advancing Antiviral Strategies Through Novel Immunocapture and Mass Spectrometry Techniques

Here, we describe a newly developed multiplex fluorescent immunoassay that uses a dual-reporter flow cytometric system to concurrently detect two unique spike protein epitopes on intact severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral particles that had been captured by angiotensin-converting enzyme-2-coupled magnetic microspheres.

Membrane proteins on enveloped viruses play an important role in many biological functions involving virus attachment to target cell receptors, fusion of ...

Quick and Early Detection of Rabies Antibodies to Evaluate the Immune Response in a Patient

Detection of Rabies IgG and IgM Antibodies Using the Rabies Indirect Fluorescent Antibody Test

The rabies indirect fluorescent antibody (IFA) test was developed to detect various rabies-specific antibody isotypes in sera or cerebral spinal fluid. This test provides rapid results and can be used to detect rabies antibodies in several different scenarios. The rabies IFA test is especially useful for the quick and early detection of antibodies to evaluate the immune response in a patient who has developed rabies. Although other methods for antemortem rabies diagnosis take precedence, this test may be utilized to demonstrate recent rabies virus exposure through antibody detection. The IFA test does not provide a virus-neutralizing antibody (VNA) titer, but the pre-exposure prophylaxis (PrEP) response can be evaluated through positive or negative antibody presence. This test can be utilized in various situations and can provide results for a number of different targets. In this study, we used several paired serum samples from individuals who received PrEP and demonstrated their rabies antibody presence over time using the IFA test.

Author Spotlight: Rabies-Specific Antibody Isotypes Detection in Sera or Cerebral Spinal Fluid Using an IFA Test 

The aim of this manuscript is to examine the use of the rabies indirect fluorescent antibody test for the detection of rabies-specific IgG and IgM antibodies.

The rabies indirect fluorescent antibody (IFA) test was developed to detect various rabies-specific antibody isotypes in sera or cerebral spinal fluid. ...