The described project was supported by funds from the Uniformed Services University of the Health Sciences to JJM. The opinions or assertions contained herein are the private ones of the authors and are not to be construed as official or reflecting the views of the Department of Defense, the Uniformed Services University of the Health Sciences or any other agency of the U.S. Government.
WGV performed all the experiments and analyzed the data; JJM designed and supervised the study; WGW and JJM wrote the paper.

The serum samples used to demonstrate the protocol described here were obtained from rhesus macaques that were housed and cared for in accordance with local, state and federal policies in an Association for Assessment and Accreditation of Laboratory Animal Care International (AAALAC)-accredited facility. All animal experiments were reviewed and approved by Institutional Animal Care and Use Committee and samples were acquired through a tissue sharing protocol.
1. Day 1
NOTE: Perform all the steps described below in a sterile laminar flow biosafety cabinet used for tissue culture in a BSL-2 laboratory.
<ol>
	<li>Thaw the serum samples at room temperature and transfer 100 &#181;L of each serum sample to a sterile tube. Heat inactivate for 30 min at 56&#176;C either in a water bath or a temperature-adjustable thermomixer. Make 10-fold serial dilutions of the serum sample ranging from 1:1 to 1:1,000 using cold RPMI-10 (RPMI with 10% fetal bovine serum).</li>
	<li>Transfer 10 &#181;L of serially diluted serum sample to each well of a sterile 96-well V-bottom plate. Include two sets of control wells, RPMI-10 with RVPs only and without serum sample, and RPMI-10 only without RVPs and without serum sample. Set up each serum sample and RPMI-10 controls in triplicates.</li>
	<li>Remove the Dengue-1, 2, 3 and 4 RVPs from the -80 &#176;C freezer and thaw them in a 37 &#176;C water bath. Transfer the thawed RVPs immediately to ice. Obtain approximately 170 &#181;L RVPs for each serum sample (10 &#181;L of RVPs x 3 wells for each serum dilution (1:1, 1:10, 1:100, 1:1,000) and 10 &#181;L of RVPs x 3 wells for each of the RPMI-10 with RVP only control wells).</li>
	<li>Pipette 10 &#181;L of RVPs into each well of the 96-well V-bottom plate containing the serum sample and to the RPMI-10 with RVPs (no serum) control wells. Do not add RVPs to the RPMI-10 only (no serum sample and no RVP) wells. Mix thoroughly by pipetting up and down 5&#8211;10 times. Add 10 &#181;L cold RPMI-10 in lieu of RVPs to each cold RPMI-10 only (no serum sample and no RVP) control wells.</li>
	<li>Transfer the 96-well V-bottom plate to an incubator and incubate the plate for 1 hour at 37 &#176;C in the presence of 5% CO2. While the 96-well V-bottom plate is incubating, clean the surface of the biosafety cabinet with 70% ethanol and run the UV light for 15 min.</li>
	<li>Remove a fully confluent T75 flask of K562 cells from the incubator, mix the cells well using a sterile 5 mL pipet, and transfer 5 mL of cells to a sterile 15 mL conical tube. 
	NOTE: The K562 cells are maintained in RPMI-10 and subcultured at 1 x 106/mL.</li>
	<li>Count the number of cells by removing 10 &#181;L cells from the sterile 15 mL conical tube and mix with 10 &#181;L tryphan blue. Count the cells using a hemocytometer to determine the total number of cells in the 15 mL conical tube.</li>
	<li>Centrifuge the 15 mL conical with cells at ~1,200 x g for 10 minutes, decant the supernatant, and resuspend the cells in warm RPMI-10 at a concentration of 80,000 cells/30 &#181;L of media (2.66 x 106 cells /mL).</li>
	<li>Remove the 96-well V-bottom plate from the incubator (step 1.6), transfer 30 &#181;L of K562 cells to each well of the 96-well V-bottom plate, and mix thoroughly by pipetting up and down 5&#8211;10 times. Transfer the 96-well V-bottom plate to an incubator and incubate the plate for 1 hr at 37 &#176;C in the presence of 5% CO2.</li>
	<li>After incubating for 1 h, remove the 96-well V-bottom plate from the incubator and centrifuge at ~1,200 x g for 5 minutes. After centrifugation, decant the media from the wells by turning the plate upside down into a container containing 10% bleach.</li>
	<li>Wash the cells in each well by resuspending them in 125 &#181;L of warm RPMI-10, mix thoroughly with a pipette, and centrifuge the plate at ~1,200 x g for 5 min. Decant the media by turning the plate upside down into a container containing 10% bleach. Repeat this wash step two times.</li>
	<li>After washing, add 100 &#181;L of warm RPMI-10 to each well, mix up and down with the pipet, and incubate the plate for 48 h at 37 &#176;C in the presence of 5% CO2.</li>
</ol>
2. Day 3
<ol>
	<li>Remove the 96-well V-bottom plate containing 100 &#181;L of cells and media/well from the incubator and move it to a biosafety cabinet . Using a multichannel pipette, mix the contents of each well and transfer the cells and media to a 96 well U-bottom plate or to pre-labeled 5 mL polypropylene tubes.</li>
	<li>Rinse each well in the 96-well V-bottom plate with 100 &#181;L of 1% Paraformaldehyde (PFA) in 1x Phosphate Buffered Saline (PBS) and transfer to the respective wells in the 96 well U-bottom plate or labeled 5 mL polypropylene tubes from step 2.1 to yield a final concentration of 0.5% PFA/well or tube. Mix thoroughly using a multichannel pipette, cover the plate with aluminum foil, and let it sit in the incubator for 30 minutes to fix the cells.</li>
	<li>Prepare the flow cytometer (see Table of Materials for example) by running unstained K562 cells to calibrate the side and forward scatter along with the fluorescence settings. The only fluorescence channel required is FL1, as GFP is the only fluorescence emitted from the cells. Acquire ~30,000&#8211;50,000 cells from each sample. 
	NOTE: Any flow cytometer capable of reading a single fluorescence can be used for acquiring the data, as cells infected with RVPs will only emit green fluorescence due to the presence of GFP, and no other fluorescence channel are needed.</li>
</ol>
3. Data Analysis
<ol>
	<li>Analyze data acquired on the flow cytometer using any flow cytometry analysis software (see Table of Materials).
	<ol>
		<li>Set the first gate based on FSC-A (forward scatter &#8211; area) vs FSC-H (forward scatter &#8211; height) to include single cells and exclude auto-fluorescent doublets from analysis12. Then, gate singlet-gated cells based on SSC-A (side scatter &#8211; area) vs FSC-A to exclude any autofluorescent debris.</li>
		<li>Analyze SSC-A vs FSC-A gated cells for the expression of GFP based on SSC-A vs GFP-A. Determine the percentage of GFP+ cells for each dilution of the serum and control samples by setting a gate around GFP+ cells.</li>
	</ol>
	</li>
	<li>Determine the average percentage of GFP+ cells for each serum sample dilution and control wells by dividing the total percentage of GFP+ cells in the triplicate wells by 3.</li>
	<li>Calculate fold-enhancement of infection by dividing the average percentage of GFP+ cells in the serum samples for each dilution divided by the average percentage of GFP+ cells in the RPMI-10 with RVPs (no serum sample) control wells.</li>
	<li>Graph fold-enhancement (y-axis) versus dilution (x-axis), and perform statistical analysis using ANOVA followed by Tukey&#39;s post-hoc test for multiple comparisons.</li>
</ol>

<ol><li>George, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Prior+exposure+to+zika+virus+significantly+enhances+peak+dengue-2+viremia+in+rhesus+macaques%5BTitle%5D)+AND+%22Sci+Rep%22%5BJournal%5D)">Prior exposure to zika virus significantly enhances peak dengue-2 viremia in rhesus macaques.</a> Sci Rep. 7 (1), 10498(2017).</li>
<li>Stettler, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Specificity%2C+cross-reactivity%2C+and+function+of+antibodies+elicited+by+Zika+virus+infection%5BTitle%5D)+AND+%22Science%22%5BJournal%5D)">Specificity, cross-reactivity, and function of antibodies elicited by Zika virus infection.</a> Science. 353 (6301), 823-826 (2016).</li>
<li>Mattia, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Dengue+reporter+virus+particles+for+measuring+neutralizing+antibodies+against+each+of+the+four+dengue+serotypes%5BTitle%5D)+AND+%22PLoS+One%22%5BJournal%5D)">Dengue reporter virus particles for measuring neutralizing antibodies against each of the four dengue serotypes.</a> PLoS One. 6 (11), e27252(2011).</li>
<li>Chiofalo, M. S., Teti, G., Goust, J. M., Trifiletti, R., La Via,, F, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Subclass+specificity+of+the+Fc+receptor+for+human+IgG+on+K562%5BTitle%5D)+AND+%22Cell+Immunol%22%5BJournal%5D)">Subclass specificity of the Fc receptor for human IgG on K562.</a> Cell Immunol. 114 (2), 272-281 (1988).</li>
<li>Klein, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Properties+of+the+K562+cell+line%2C+derived+from+a+patient+with+chronic+myeloid+leukemia%5BTitle%5D)+AND+%22Int+J+Cancer%22%5BJournal%5D)">Properties of the K562 cell line, derived from a patient with chronic myeloid leukemia.</a> Int J Cancer. 18 (4), 421-431 (1976).</li>
<li>Kliks, S. C., Nisalak, A., Brandt, W. E., Wahl, L., Burke, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Antibody-dependent+enhancement+of+dengue+virus+growth+in+human+monocytes+as+a+risk+factor+for+dengue+hemorrhagic+fever%5BTitle%5D)+AND+%22Am+J+Trop+Med+Hyg%22%5BJournal%5D)">Antibody-dependent enhancement of dengue virus growth in human monocytes as a risk factor for dengue hemorrhagic fever.</a> Am J Trop Med Hyg. 40 (4), 444-451 (1989).</li>
<li>Littaua, R., Kurane, I., Ennis, F. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Human+IgG+Fc+receptor+II+mediates+antibody-dependent+enhancement+of+dengue+virus+infection%5BTitle%5D)+AND+%22J+Immunol%22%5BJournal%5D)">Human IgG Fc receptor II mediates antibody-dependent enhancement of dengue virus infection.</a> J Immunol. 144 (8), 3183-3186 (1990).</li>
<li>Wang, T. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((IgG+antibodies+to+dengue+enhanced+for+FcgammaRIIIA+binding+determine+disease+severity%5BTitle%5D)+AND+%22Science%22%5BJournal%5D)">IgG antibodies to dengue enhanced for FcgammaRIIIA binding determine disease severity.</a> Science. 355 (6323), 395-398 (2017).</li>
<li>Dejnirattisai, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Cross-reacting+antibodies+enhance+dengue+virus+infection+in+humans%5BTitle%5D)+AND+%22Science%22%5BJournal%5D)">Cross-reacting antibodies enhance dengue virus infection in humans.</a> Science. 328 (5979), 745-748 (2010).</li>
<li>Kawiecki, A. B., Christofferson, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Zika+virus-induced+antibody+response+enhances+dengue+virus+serotype+2+replication+in+vitro%5BTitle%5D)+AND+%22J+Infect+Dis%22%5BJournal%5D)">Zika virus-induced antibody response enhances dengue virus serotype 2 replication in vitro.</a> J Infect Dis. 214 (9), 1357-1360 (2016).</li>
<li>Morens, D. M., Halstead, S. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Measurement+of+antibody-dependent+infection+enhancement+of+four+dengue+virus+serotypes+by+monoclonal+and+polyclonal+antibodies%5BTitle%5D)+AND+%22J+Gen+Virol%22%5BJournal%5D)">Measurement of antibody-dependent infection enhancement of four dengue virus serotypes by monoclonal and polyclonal antibodies.</a> J Gen Virol. 71 (Pt 12), 2909-2914 (1990).</li>
<li>Perfetto, S. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Amine+reactive+dyes%3A+an+effective+tool+to+discriminate+live+and+dead+cells+in+polychromatic+flow+cytometry%5BTitle%5D)+AND+%22J+Immunol+Methods%22%5BJournal%5D)">Amine reactive dyes: an effective tool to discriminate live and dead cells in polychromatic flow cytometry.</a> J Immunol Methods. 313 (1-2), 199-208 (2006).</li>
<li>Priyamvada, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((B+Cell+responses+during+secondary+dengue+virus+infection+are+dominated+by+highly+cross-reactive%2C+memory-derived+plasmablasts%5BTitle%5D)+AND+%22J+Virol%22%5BJournal%5D)">B Cell responses during secondary dengue virus infection are dominated by highly cross-reactive, memory-derived plasmablasts.</a> J Virol. 90 (12), 5574-5585 (2016).</li>
<li>Priyamvada, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Human+antibody+responses+after+dengue+virus+infection+are+highly+cross-reactive+to+Zika+virus%5BTitle%5D)+AND+%22Proc+Natl+Acad+Sci+U+S+A%22%5BJournal%5D)">Human antibody responses after dengue virus infection are highly cross-reactive to Zika virus.</a> Proc Natl Acad Sci U S A. 113 (28), 7852-7857 (2016).</li>
</ol>

The authors have nothing to disclose.

Flaviviruses such as DENV and ZIKV share significant evidence of homology in both their structural and non-structural proteins that generate antibodies that cross-react with each other13,14. These cross-reactive antibody responses have been shown to enhance of infection both in vivo and in vitro with either a heterologous serotype or other related flaviviruses1,2. The potential to cross ...

Antibody dependent enhancement (ADE) of infection is a process whereby partially cross-reactive antibody responses induced by a serotype of virus enhances uptake of another serotype of virus, leading to increased viral replication and viremia. ADE has been extensively documented in Dengue virus (DENV) infections where four major serotypes are prevalent. In a subset of patients, ADE is associated with Dengue hemorrhagic fever (DHF). We have recently shown that Zika virus (ZIKV) infection induced significantly high levels of DENV cross-reactive antibody responses that caused ADE of DENV in vitro and likely contributed to the enhancement of DENV viremia in vivo1,2. Antibody dependent enhancement assays are a valuable tool to assess the capacity of antibodies to enhance secondary infection with related viruses and provide valuable insights into the pathogenesis of flavivirus infections and inform the development of vaccines.
The assay described here uses DENV RVPs along with K562 cells that are normally impermissible to infection. RVPs are structurally intact replication incompetent DENV viral particles that encode a sub-genomic green fluorescent protein (GFP) replicon that is expressed after a single round of replication3. As such, cells that become infected with RVPs fluoresce green and can be readily detected using flow cytometry or microscopy. The RVPs used in this assay were obtained from commercial sources. They can, however, be generated against other viruses and used in the assay described in this manuscript. Meanwhile, K562 cells are an Fc&#947;III-receptor-expressing leukemia cell line that bind to the Fc region of antibodies and become infected in the presence of sub-neutralizing concentrations of antibody4,5.
ADE assays have been extensively used in studies investigating the risk factors for severe dengue and to delineate the mechanisms of in vitro ADE6,7,8.The ADE assay described here can be quickly and easily used to determine the capacity of serum to enhance in vitro infection using RVPs and flow cytometry, as compared to other assays used currently, which require either the determination of plaque forming units (pfu) in Vero cells or antibody staining of infected cells6,7,8,9,10,11, both of which are time consuming and labor intensive.

<table><tbody><tr><td>DENV 1-4 RVP</td><td>Integral Molecular</td><td>RVP-501</td><td></td></tr><tr><td>K562 cells</td><td>ATCC</td><td>CCL-243</td><td></td></tr><tr><td>RPMI</td><td>Corning</td><td>10-040-CV</td><td></td></tr><tr><td>FBS</td><td>GE lifesceinces</td><td>SH 30910.03</td><td>10% FBS in RPMI-10</td></tr><tr><td>Penicillin-Streptomycin</td><td>MP biomedicals</td><td>1670049</td><td>100 IU Pen/mL, 100 ug Strep/mL in RPMI-10</td></tr><tr><td>HEPES</td><td>Cellegro</td><td>25-060-Cl</td><td>0.025M in RPMI-10</td></tr><tr><td>MEM Non-essential Amino Acid Solution (100&amp;times;)</td><td>Sigma</td><td>M7145</td><td>1x in RPMI-10</td></tr><tr><td>Sodium Pyruvate</td><td>Cellegro</td><td>25-000-Cl</td><td>1mM in RPMI-10</td></tr><tr><td>L-glutamine</td><td>Fisher Scientific</td><td>MT25005CI&amp;nbsp;</td><td></td></tr><tr><td>Sterile V-bottom plates</td><td>Thomas Scientific</td><td>333-8001-01V</td><td></td></tr><tr><td>BD Falcon Polypropylene 5 ml FACS tubes</td><td>VWR</td><td>60819-728</td><td></td></tr><tr><td>Non-sterile U-bottom plates</td><td>Falcon</td><td>Ref 353910</td><td>A high throughput alternative to FACS tubes</td></tr><tr><td>5mL, sterile, serological pipette</td><td>Denville</td><td>P7127</td><td></td></tr><tr><td>200uL sterile pipette tips</td><td>Denville</td><td>P3020 CPS</td><td></td></tr><tr><td>20uL sterile pipette tips</td><td>Denville</td><td>P1121</td><td></td></tr><tr><td>50-200uL multichannel pipette</td><td>Denville</td><td>P3975-8-B</td><td></td></tr><tr><td>5-50uL multichannel pipette</td><td>Denville</td><td>P3975-9-B</td><td></td></tr><tr><td>20% formadehyde</td><td>Tousimis</td><td>&amp;nbsp;#1008B</td><td></td></tr><tr><td>Water Bath</td><td>ThermoFisher</td><td>TSCOL35</td><td></td></tr><tr><td>thermomixer</td><td>Eppendorf</td><td>2231000387</td><td>An alternative to a waterbath for heat inactivation</td></tr><tr><td>CO2 Incubator</td><td>ThermoFisher</td><td>13-998-213</td><td></td></tr><tr><td>Ethanol</td><td>Sigma Aldrich</td><td>E7023</td><td></td></tr><tr><td>Liquid Bleach</td><td>Fisher Scientific</td><td>NC9724348</td><td></td></tr><tr><td>Flowjo 9.8</td><td>TreeStar, Inc.</td><td></td><td>Flow cytometry analysis software</td></tr><tr><td>BD FACSDiva 6.1.2</td><td>Becton Dikinson</td><td></td><td></td></tr><tr><td>BD LSR II flow cytometer</td><td>Becton Dikinson</td><td></td><td></td></tr><tr><td>Liquid Bleach</td><td>Fisher Scientific</td><td>NC9724348</td><td></td></tr></tbody></table>

a simple flow cytometry based assay to determine in vitro antibody dependent enhancement of dengue virus using zika virus convalescent serum

Antibody dependent enhancement of infection has been shown to play a major role in Dengue viral pathogenesis. Traditional assays that measure the capacity of antibodies or serum to enhance infection in impermissible cell lines have relied on using viral output in the media followed by plaque assays to quantify infection. More recently, these assays have examined Dengue virus (DENV) infection in the cell lines using fluorescently labeled antibodies. Both these approaches have limitations that restrict the widespread use of these techniques. Here, we describe a simple in vitro assay using Dengue virus reporter viral particles (RVPs) that express green fluorescent protein and K562 cells to examine antibody dependent enhancement (ADE) of DENV infection using serum that was obtained from rhesus macaques 16 weeks after infection with Zika virus (ZIKV). This technique is reliable, involves minimal manipulation of cells, does not involve the use of live replication competent virus, and can be performed in a high throughput format to get a quantitative readout using flow cytometry. Additionally, this assay can be easily adapted to examine antibody dependent enhancement (ADE) of other flavivirus infections such as Yellow Fever virus (YFV), Japanese Equine Encephalitis virus (JEEV), West Nile virus (WNV) etc. where RVPs are available. The ease of setting up the assay, analyzing the data, and interpreting results makes it highly amenable to most laboratory settings.

Sera from 4 rhesus macaques were collected 16 weeks after infection with ZIKV and tested for their potential to enhance DENV-1, 2, 3 and 4 infection in K562 cells. The animals had peak viremia of ~1 x 105 copies of ZIKV RNA/mL of plasma by day 3 after infection that declined to levels that were below the limit of detection by 7 days after infection. No viremia was detected in the plasma at 16 weeks post-infection. Then, the RVP assay was performed and the collected data were an...

Watch this Scientific Journal Video about A Simple Flow Cytometry Based Assay to Determine In Vitro Antibody Dependent Enhancement of Dengue Virus Using Zika Virus Convalescent Serum at JoVE.com

A Simple Flow Cytometry Based Assay to Determine In Vitro Antibody Dependent Enhancement of Dengue Virus Using Zika Virus Convalescent Serum

We describe a simple and easy protocol for measuring antibody dependent enhancement of infection by Zika virus convalescent serum using Dengue virus Reporter Viral Particles.

A Simple Flow Cytometry Based Assay to Determine In Vitro Antibody Dependent Enhancement of Dengue Virus Using Zika Virus Convalescent Serum

Antibody dependent enhancement of infection has been shown to play a major role in Dengue viral pathogenesis. Traditional assays that measure the capacity ...

a-simple-flow-cytometry-based-assay-to-determine-vitro-antibody

Research

JoVE Journal

Immunology and Infection

8.8K Views.  Uniformed Services University. We describe a simple and easy protocol for measuring antibody dependent enhancement of infection by Zika virus convalescent serum using Dengue virus Reporter Viral Particles.

Video: A Simple Flow Cytometry Based Assay to Determine In Vitro Antibody Dependent Enhancement of Dengue Virus Using Zika Virus Convalescent Serum

Multiplexed Isothermal Amplification Based Diagnostic Platform to Detect Zika, Chikungunya, and Dengue 1

Zika, dengue, and chikungunya viruses are transmitted by mosquitoes, causing diseases with similar patient symptoms. However, they have different downstream patient-to-patient transmission potentials, and require very different patient treatments. Thus, recent Zika outbreaks make it urgent to develop tools that rapidly discriminate these viruses in patients and trapped mosquitoes, to select the correct patient treatment, and to understand and manage their epidemiology in real time.
Unfortunately, current diagnostic tests, including those receiving 2016 emergency use authorizations and fast-track status, detect viral RNA by reverse transcription polymerase chain reaction (RT-PCR), which requires instrumentation, trained users, and considerable sample preparation. Thus, they must be sent to &#34;approved&#34; reference laboratories, requiring time. Indeed, in August 2016, the Center for Disease Control (CDC) was asking pregnant women who had been bitten by a mosquito and developed a Zika-indicating rash to wait an unacceptable 2 to 4 weeks before learning whether they were infected. We very much need tests that can be done on site, with few resources, and by trained but not necessarily licensed personnel.
This video demonstrates an assay that meets these specifications, working with urine or serum (for patients) or crushed mosquito carcasses (for environmental surveillance), all without much sample preparation. Mosquito carcasses are captured on paper carrying quaternary ammonium groups (Q-paper) followed by ammonia treatment to manage biohazards. These are then directly, without RNA isolation, put into assay tubes containing freeze-dried reagents that need no chain of refrigeration. A modified form of reverse transcription loop-mediated isothermal amplification with target-specific fluorescently tagged displaceable probes produces readout, in 30 min, as a three-color fluorescence signal. This is visualized with a handheld, battery-powered device with an orange filter. Forward contamination is prevented with sealed tubes, and the use of thermolabile uracil DNA glycosylase (UDG) in the presence of dUTP in the amplification mixture.

Current multiplexed diagnostics to detect Zika, chikungunya, and dengue viruses require complex sample preparation and expensive instrumentation, and are difficult to use in low resource environments. We show a diagnostic that uses isothermal amplification with target-specific strand displaceable probes to detect and differentiate these viruses with high sensitivity and specificity.

Zika, dengue, and chikungunya viruses are transmitted by mosquitoes, causing diseases with similar patient symptoms. However, they have different ...

Biochemistry

Zika Virus Infectious Cell Culture System and the In Vitro Prophylactic Effect of Interferons

Zika Virus (ZIKV) is an emerging pathogen that is linked to fetal developmental abnormalities such as microcephaly, eye defects, and impaired growth. ZIKV is an RNA virus of the Flaviviridae family. ZIKV is mainly transmitted by mosquitoes, but can also be spread by maternal to fetal vertical transmission as well as sexual contact. To date, there are no reliable treatment or vaccine options available to protect those infected by the virus. The development of a reproducible, effective Zika virus infectious cell culture system is critical for studying the molecular mechanisms of ZIKV replication as well as drug and vaccine development. In this regard, a protocol describing a mammalian cell-based in vitro Zika virus culture system for viral production and growth analysis is reported here. Details on the formation of plaques by Zika virus on a cell monolayer and plaque assay for measuring viral titer are presented. Viral genome replication kinetics and double-stranded RNA genome replicatory intermediates are determined. This culture platform was utilized to screen against a library of a small set of cytokines resulting in the identification of interferon-&#945; (IFN-&#945;), IFN-&#946; and IFN-&#947; as potent inhibitors of Zika viral growth. In summary, an in vitro infectious Zika viral culture system and various virological assays are demonstrated in this study, which has the potential to greatly benefit the research community in elucidating further the mechanisms of viral pathogenesis and the evolution of viral virulence. Antiviral IFN-alpha can further be evaluated as a prophylactic, post-exposure prophylactic, and treatment option for Zika virus infections in high-risk populations, including infected pregnant women.

Zika Virus Infectious Cell Culture System and the In Vitro Prophylactic Effect of Interferons

Zika Virus (ZIKV), an emerging pathogen, is linked to fetal developmental abnormalities and microcephaly. The establishment of an effective infectious cell culture system is crucial for studies of ZIKV replication as well as vaccine and drug development. In this study, various virological assays pertaining to ZIKV are illustrated and discussed.

Zika Virus (ZIKV) is an emerging pathogen that is linked to fetal developmental abnormalities such as microcephaly, eye defects, and impaired growth. ZIKV ...

Zika Virus Specific Diagnostic Epitope Discovery

High-density peptide microarrays allow screening of more than six thousand peptides on a single standard microscopy slide. This method can be applied for drug discovery, therapeutic target identification, and developing of diagnostics. Here, we present a protocol to discover specific Zika virus (ZIKV) diagnostic peptides using a high-density peptide microarray. A human serum sample validated for ZIKV infection was incubated with a high-density peptide microarray containing the entire ZIKV protein translated into 3,423 unique 15 linear amino acid (aa) residues with a 14-aa residue overlap printed in duplicate. Staining with different secondary antibodies within the same array, we detected peptides that bind to Immunoglobulin M (IgM) and Immunoglobulin G (IgG) antibodies present in serum. These peptides were selected for further validation experiments. In this protocol, we describe the strategy followed to design, process, and analyze a high-density peptide microarray.

In this protocol, we describe a technique to discover Zika virus specific diagnostic peptides using a high-density peptide microarray. This protocol can readly be adapted for other emerging infectious diseases.

High-density peptide microarrays allow screening of more than six thousand peptides on a single standard microscopy slide. This method can be applied for ...

Evaluation of Zika Virus-specific T-cell Responses in Immunoprivileged Organs of Infected Ifnar1-/- Mice

The Zika virus (ZIKV) can induce inflammation in immunoprivileged organs (e.g., the brain and testis), leading to the Guillain-Barr&#233; syndrome and damaging the testes. During an infection with the ZIKV, immune cells have been shown to infiltrate into the tissues. However, the cellular mechanisms that define the protection and/or immunopathogenesis of these immune cells during a ZIKV infection are still largely unknown. Herein, we describe methods to evaluate the virus-specific T-cell functionality in these immunoprivileged organs of ZIKV-infected mice. These methods include a) a ZIKV infection and vaccine inoculation in Ifnar1-/- mice; b) histopathology, immunofluorescence, and immunohistochemistry assays to detect the virus infection and inflammation in the brain, testes, and spleen; c) the preparation of a tetramer of ZIKV-derived T-cell epitopes; d) the detection of ZIKV-specific T cells in the monocytes isolated from the brain, testes, and spleen. Using these approaches, it is possible to detect the antigen-specific T cells that have infiltrated into the immunoprivileged organs and to evaluate the functions of these T cells during the infection: potential immune protection via virus clearance and/or immunopathogenesis to exacerbate the inflammation. These findings may also help to clarify the contribution of T cells induced by the immunization against ZIKV.

Evaluation of Zika Virus-specific T-cell Responses in Immunoprivileged Organs of Infected Ifnar1-/- Mice

A protocol to evaluate antigen-specific T-cell responses in the immunoprivileged organs of the Ifnar1-/- murine model for the Zika virus (ZIKV) infection is described. This method is pivotal for investigating the cellular mechanisms of the protection and immunopathogenesis of ZIKV vaccines and is also valuable for their efficacy evaluation.

The Zika virus (ZIKV) can induce inflammation in immunoprivileged organs (e.g., the brain and testis), leading to the Guillain-Barr&#233; syndrome and ...

Quantification of Antibody-dependent Enhancement of the Zika Virus in Primary Human Cells

The recent emergence of the flavivirus Zika and neurological complications, such as Guillain-Barr&#233; syndrome and microcephaly in infants, has brought serious public safety concerns. Among the risk factors, antibody-dependent enhancement (ADE) poses the most significant threat, as the recent re-emergence of the Zika virus (ZIKV) is primarily in areas where the population has been exposed and is in a state of pre-immunity to other closely related flaviviruses, especially dengue virus (DENV). Here, we describe a protocol for quantifying the effect of human serum antibodies against DENV on ZIKV infection in primary human cells or cell lines.

We describe a method to evaluate the effect of pre-existing immunity against dengue virus on the Zika virus infection by using human serum, primary human cells, and infection quantification by quantitative real-time polymerase chain reaction.

The recent emergence of the flavivirus Zika and neurological complications, such as Guillain-Barr&#233; syndrome and microcephaly in infants, has brought ...

Isolation and Quantification of Zika Virus from Multiple Organs in a Mouse

The methods being presented demonstrate laboratory procedures for the isolation of organs from Zika virus infected animals and the quantification of viral load. The purpose of the procedure is to quantify viral titers in peripheral and CNS areas of the mouse at different time points post infection or under different experimental conditions to identify virologic and immunological factors that regulate Zika virus infection. The organ isolation procedures demonstrated allow for both focus forming assay quantification and quantitative PCR assessment of viral titers. The rapid organ isolation techniques are designed for the preservation of virus titer. Viral titer quantification by focus forming assay allows for the rapid throughput assessment of Zika virus. The benefit of the focus forming assay is the assessment of infectious virus, the limitation of this assay is the potential for organ toxicity reducing the limit of detection. Viral titer assessment is combined with quantitative PCR, and using a recombinant RNA copy control viral genome copy number within the organ is assessed with low limit of detection. Overall these techniques provide an accurate rapid high throughput method for the analysis of Zika viral titers in the periphery and CNS of Zika virus infected animals and can be applied to the assessment of viral titers in the organs of animals infected with most pathogens, including Dengue virus.

The goal of the protocol is to demonstrate the techniques used to investigate viral disease by isolating and quantifying Zika virus, from multiple organs in a mouse following infection.

The methods being presented demonstrate laboratory procedures for the isolation of organs from Zika virus infected animals and the quantification of viral ...

Vector Competence Analyses on Aedes aegypti Mosquitoes using Zika Virus

The procedures presented describe a generalized methodology to infect Aedes aegypti mosquitoes with Zika virus under laboratory conditions to determine the rate of infection, disseminated infection, and potential transmission of the virus in the mosquito population in question. These procedures are widely utilized with various modifications in vector competence evaluations globally. They are important in determining the potential role that a given mosquito (i.e., species, population, individual) may play in the transmission of a given agent.

Vector Competence Analyses on Aedes aegypti Mosquitoes using Zika Virus

The presented protocol can determine the vector competence of Aedes aegypti mosquito populations for a given virus, such as Zika, in a containment setting.

The procedures presented describe a generalized methodology to infect Aedes aegypti mosquitoes with Zika virus under laboratory conditions to determine ...

Virus Propagation and Cell-Based Colorimetric Quantification

Zika virus (ZIKV) is a mosquito-borne virus belonging to the genus Flavivirus. ZIKV infection has been associated with congenital brain abnormalities and potentially Guillain-Barr&#233; syndrome in adults. Research on ZIKV to understand the disease mechanisms is important to facilitate vaccine and treatment development. The method of quantifying viruses is crucial and fundamental in the field of virology. The focus forming assay (FFA) is a virus quantification assay that detects the viral antigen with antibodies and identifies the infection foci of cells using the peroxidase immunostaining technique. The current study describes the virus propagation and quantification protocol using both 24-well and 96-well (high throughput) formats. Compared with other similar studies, this protocol has further described foci size optimization, which can serve as a guide to expand the use of this assay for other viruses. Firstly, ZIKV propagation is performed in Vero cells for 3 days. The culture supernatant containing ZIKV is harvested and quantitated using the FFA. Briefly, the virus culture is inoculated onto Vero cells and incubated for 2-3 days. Foci formation is then determined after optimized staining processes, including cell fixation, permeabilization, blocking, antibody binding, and incubation with peroxidase substrate. The stained virus foci are visualized using a stereo microscope (manual counting in 24-well format) or software analyzer (automated counting in 96-well format). The FFA provides reproducible, relatively fast results (3-4 days) and is suitable to be used for different viruses, including non-plaque-forming viruses. Subsequently, this protocol is useful for the study of ZIKV infection and could be used to detect other clinically important viruses.

The present protocol describes the propagation of Zika virus (ZIKV) in Vero African green monkey kidney cells and the quantification of ZIKV using cell-based colorimetric immunodetection methods in 24-well and 96-well (high throughput) formats.

Zika virus (ZIKV) is a mosquito-borne virus belonging to the genus Flavivirus. ZIKV infection has been associated with congenital brain abnormalities and ...

Cell-Based Electrical Impedance Platform to Evaluate Zika Virus Inhibitors in Real Time

Cell-based electrical impedance (CEI)&#160;technology measures changes in impedance caused by a growing or manipulated adherent cell monolayer on culture plate wells embedded with electrodes. The technology can be used to monitor the consequences of Zika virus (ZIKV) infection and adherent cell replication in real time, as this virus is highly cytopathogenic. It is a straightforward assay that does not require the use of labels or invasive methods and has the benefit of providing real-time data. The kinetics of ZIKV infection are highly dependent on the employed cell line, virus strain, and multiplicity of infection (MOI), which cannot be easily studied with conventional endpoint assays. Furthermore, the CEI assay can also be used for the evaluation and characterization of antiviral compounds, which can also have dynamic inhibitory properties over the course of infection. This methods article gives a detailed explanation of the practical execution of the CEI assay and its potential applications in ZIKV research and antiviral research in general.

Here, we demonstrate the use of cell-based electrical impedance (CEI) as a very easy and straightforward method to study Zika virus infection and replication in human cells in real time. Furthermore, the CEI assay is useful for the evaluation of antiviral compounds.

Cell-based electrical impedance (CEI)&#160;technology measures changes in impedance caused by a growing or manipulated adherent cell monolayer on culture ...

An In Vitro Assay for Screening Interferons as Potent Inhibitors of Zika Virus Growth

Source: Contreras, D. et al., <a href="https://app.jove.com/v/54767">Zika Virus Infectious Cell Culture System and the In Vitro Prophylactic Effect of Interferons.</a> J. Vis. Exp. (2016)
The video demonstrates an in vitro assay for screening interferons with antiviral activity against the Zika virus, a human pathogen. Within the host cell, the Zika virus undergoes multiplication upon internalization, infecting neighboring cells and creating distinct zones or viral plaques. Type I interferon, acting as an antiviral agent, hinders virus multiplication, thereby preventing the formation of viral plaques in the host cell monolayer.

1. Screening Cytokine Library against Zika Virus Infection

	Seed naive Vero cells at 1 x 105 cells per well using a 12-well plate. Once the cells are ...

A Simple Flow Cytometry Based Assay to Determine In Vitro Antibody Dependent Enhancement of Dengue Virus Using Zika Virus Convalescent Serum

Summary

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Cell-Based Electrical Impedance Platform to Evaluate Zika Virus Inhibitors in Real Time

An In Vitro Assay for Screening Interferons as Potent Inhibitors of Zika Virus Growth