This project has been funded in part with federal funds from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under CEIRS contract P01AI097092-04S1 (P.E.L.).

The experiments preformed in this manuscript were done following Icahn School of Medicine&#8217;s institutional code of ethics and regulations.
1. Expression of Influenza Virus Hemagglutinin via Transfection or Infection
Transfection:
<ol>
	<li>Plate Human Embryonic Kidney (HEK 293T) cells at a density of 2 x 104 cells/well in a white tissue culture treated 96-well plate and let it sit for 4 h in a 37 &#176;C incubator (with 5% CO2).</li>
	<li>Transfect cells with 100 ng of DNA coding for viral hemagglutinin and 0.2 &#956;L of transfection reagent per well in a total volume of 50 &#956;L. 
	NOTE: Both plasmid and transfectant reagent are diluted in 1x&#160;Opti-Minimum Essential Media (MEM) Reduced Serum Medium.</li>
	<li>After incubating plates in a 37 &#176;C incubator with 5% CO2 for 18 h, remove transfection media.</li>
</ol>
2. Infection
<ol>
	<li>Plate A549 or Madin Darby canine kidney cells at a density of 2 x 104 cells/well in a white tissue culture treated 96-well plate and grow for at least 18 h in a 37 &#176;C incubator with 5% CO2.</li>
	<li>Dilute virus in 1x&#160;MEM and infect cells at a multiplicity of infection of 3, 1, or 0.33 for 1 h in a 37 &#176;C incubator with 5% CO2. Total volume should equal 100 &#956;L. 
	NOTE: 10x&#160;MEM is diluted with water to make a 1x&#160;MEM working stock for virus dilution mentioned above.</li>
	<li>After infection, remove the inoculum and add 100 &#956;L of 1x&#160;MEM into the plate in the absence of trypsin.</li>
	<li>Grow infected cells for 18 to 24 h in a 37 &#176;C incubator with 5% CO2.</li>
</ol>
3. Assessing the FcRg/NFAT-mediated Activation of Luciferase Activity by Monoclonal Antibodies or Sera
<ol>
	<li>First, replace growth media of transfected or infected cells with 25 &#181;L of assay media (1x&#160;RPMI 1640 supplemented with 4% (vol/vol) low IgG fetal bovine sera).</li>
	<li>In a separate 96-well plate, perform four-fold dilutions of the antibodies of interest starting at 30 &#956;g/mL using the assay media. Perform dilutions in triplicates and an example plate layout is illustrated in Figure 1A. Make sure to include a control that excludes antibody (no antibody control) as well as a background control (assay buffer alone). 
	NOTE: For both the &#8216;no antibody&#8217; and background controls, add 25 &#181;L of assay buffer instead of antibody.</li>
	<li>Transfer 25 &#956;L of the serially diluted antibodies from Step 3.2 to corresponding wells on plate of transfected cells or infected cells.</li>
	<li>Incubate plate in a 37 &#176;C incubator (with 5% CO2) for 15 min.</li>
	<li>Add 25 &#956;L of the appropriate modified effector Jurkat cell expressing murine FcgRIV or human FcgRIIIa (75,000 of cells/well). Total volume for each well should be 75&#160;&#181;L and the starting final concentration of the antibody is at 10 &#181;g/mL (Figure 1B). 
	NOTE: For the background control, add 25 &#181;L of assay buffer instead of effector cells. To examine antibody-dependent cell-mediated phagocytosis, a modified Jurkat cell expressing the human FcgRIIa can be used.</li>
	<li>Incubate plate in a 37 &#176;C incubator with 5% CO2 for 6 h.</li>
	<li>Thaw and warm luciferase substrate buffer in a 37 &#176;C water for about 1 h before use. 
	NOTE: To make the luciferase substrate buffer, reconstitute lyophilized luciferase assay substrate in assay buffer provided. The reconstituted substrate buffer can be stored at -30 &#176;C to -10 &#176;C for up to six weeks.</li>
	<li>Add 75 &#956;L/well of luciferase substrate buffer to all wells except for the background control.</li>
	<li>Read on a luminometer.</li>
	<li>Calculate fold induction with the following equation: Fold induction = (Induced value-Background value) / (No mAb value-Background value).</li>
</ol>

<ol>
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Authors declare no conflicts of interest.

The method described here allows the user to measure the ability of an HA-specific monoclonal antibody to engage the murine Fc&#947;RIV. The target antigen, influenza virus hemagglutinin, is expressed on the surface of cells after infection by virus or transfection of plasmid DNA. The assay is further amenable to using different surface-expressed viral proteins in combination with other Fc&#947;Rs (humans or murine). Additionally, we have used sera samples to assess the ability of antibodies in a polyclonal context to induce Fc effector functions (data not shown), which may provide more relevant information when studying the adaptive immune response induced by infection or vaccination. We additionally speculate that the assay can be modified to measure the induction of antibodies that recognize internal viral proteins by directly coating the plates with soluble protein. However, this methodology has not been rigorously tested.
Induction of antibody-dependent effector functions can be affected by several factors including but not limited to the effector to target ratio (number of effectors cells added per well), the concentration of antibody used, the length of incubation between effector and target cells, and the concentration of low IgG serum used in the assay buffer.
Historically, the standard assay to measure the antibody-dependent cellular cytotoxicity activity of antibodies or polyclonal sera involves primary natural killer (NK) cells harvested from donors. Engagement of Fc&#947;R and activation of the intracellular pathway is typically determined by the expression of activation markers CD107a and/or IFN-&#947;19,23,24,31. Although the classical assay uses more relevant effector cells as they have not been genetically engineered, donor variation due to allelic differences in the Fc&#947;R may affect NK cell activation and result in batch to batch variation. Alternative assays used as surrogates for ADCC activity include an Fc&#947;R dimer-based ELISA or a chromium release killing assay25. Though the use of an Fc&#947;R dimer-based ELISA is high throughput, the assay may not be physiologically relevant as this assay does not use effector cells32. While the chromium release assay measures direct killing, it is not high throughput and requires primary NK cells which again are donor dependent33. One recent method describe the use of murine T-cell hybridomas stably expressing chimeric Fc&#947;R-CD3&#950; chain molecules and measures activation through the secretion of IL-2. The assay described is similar to the described method here, which makes use of a modified T-cell as a surrogate for an effector cell expressing a singular activating Fc&#947;R34. Alternatively, a cell line (NK92.05-CD16) expressing the Fc&#947;RIIIa can be used as the effector cell and upregulation of the degranulation antigen CD107a is used as an activation marker. However, the use of virions and viral peptides on ELISA plates on the latter protocol should be noted as proteins coated onto hydrophobic surfaces may not always recapitulate the physiological structure of antigens35.
The method described here is a 96-well format assay, makes use of physiologically relevant and natively expressed viral targets and can be modified for murine or human antibodies. The genetically modified Jurkat cells can be maintained in culture and cryopreserved36. Though currently the effector cells express only one activating Fc&#947;R, the many advantages of using this protocol described in this study should be taken into consideration when measuring antibody-dependent cell-mediated effector function.

Immunity provided by the seasonal influenza vaccine has traditionally been assessed by the hemagglutination inhibition (HI) assay1, which measures the presence of antibodies that target the receptor binding site of the hemagglutinin. These HI-active antibodies can confer sterilizing immunity, but are generally narrow in their breadth of protection, providing immunity to only a select few strains of influenza virus. The isolation and characterization of broadly reactive monoclonal antibodies that recognize the hemagglutinin (HA) suggest the development of a universal influenza vaccine is within reach2,3,4,5,6,7,8. One of the major aims of a universal influenza vaccine is to induce a strong antibody response towards the conserved regions of the influenza virus9,10,11,12,13,14,15,16. Broadly reactive antibodies that recognize these conserved epitopes, composed of both neutralizing and non-neutralizing antibodies17,18, have been shown to require Fc-Fc&#947;R interactions for optimal protection in vivo and highlight the contribution of Fc-mediated immunity to the overall immune response to influenza virus19,20.
Correlates of protection are crucial in assessing immunity to infection. These metrics allow scientists and clinicians to estimate the efficacy of vaccines, the significance of the data, and the course of treatment. The only established correlate of protection against influenza virus infection is the hemagglutination inhibition assay. A titer of 1:40 is associated with a 50% reduction in the risk of illness1,21 &#8211; and reflects the presence of antibodies that inhibit agglutination by targeting the receptor binding site located on the globular head of the HA. However, it should also be noted that T-cell responses may be a better correlate of protection against influenza virus infection in the elderly. Interestingly, a recent report suggests that neuraminidase inhibition activity may be a better predictor of immunity to influenza22. Fortunately, typical in vitro assays such as neutralization or neuraminidase inhibition assays can measure HA stalk- or neuraminidase-specific antibodies. Most of these conventional in vitro assays, however, only take into account the function of the antigen binding region of the antibody and do not measure the role of the Fc region. Additionally, the contribution of non-neutralizing antibodies that protect via Fc receptor engagement in vivo are not detected17,18. In order to measure protection afforded by antibodies that induce Fc-mediated immunity such as antibody dependent cell mediated cytotoxicity (ADCC), a robust in vitro assay is needed.
The method described below assesses the ability of murine monoclonal antibodies to induce Fc-mediated functions through the use of a genetically modified Jurkat cell line expressing an activating murine type 1 FcR, Fc&#947;RIV. Antibody engagement of the Fc&#947;R transduces intracellular signaling that triggers nuclear factor of activated T-cells-mediated luciferase activity. The assay has several advantages over traditional techniques that require isolation and culture of primary effector cells and the use of flow cytometry to detect activation of Fc-mediated effector functions19,23,24,25,26. First, the protocol described here can easily be adapted to incorporate different viral targets, Fc&#947;Rs, and antibodies from different species (human and murine). Second, the use of a modified Jurkat cell line expressing an Fc&#947;R with a luciferase reporter gene under a nuclear factor of activated T-cell (NFAT) allows for a large format assay that can be easily analyzed using a plate reader measuring luminescence. Here, the traditional activation of primary effector cells is replaced with the induction of NFAT-luciferase upon antibody engagement of an Fc&#947;R on the surface of the Jurkat cell. This 96-well plate format assay allows for the measurement of up to four different samples in triplicates with seven dilutions &#8211; a number of samples that could be cumbersome using traditional techniques. There are additional points to consider with this assay that may affect the design of experiments and the interpretation of data. The viral target must be expressed on the cell surface in order for antibody recognition. To mitigate this, the target antigen (e.g. an internal viral protein) may be directly coated on the surface of a plate. However, this has not yet been rigorously tested. Additionally, the modified Jurkat cell line expresses only one type of activating Fc&#947;R and does not express any inhibitory Fc&#947;Rs, while primary cell lines express all receptors in a physiological context.
We have previously used this assay to demonstrate that epitope specificity in a polyclonal context plays a crucial role in regulating Fc-mediated effector functions and that optimal activation of antibody-dependent cell-mediated response requires two points of contact27,28. Here, we describe a method that assesses the ability of stalk-specific monoclonal antibodies to engage and activate the murine activating Fc&#947;RIV. Although there are exceptions29,30, a large number of broadly reactive antibodies target the antigenically conserved stalk region of the hemagglutinin and thus play an important role in the development of a universal influenza vaccine.

<table border="0" cellpadding="0" cellspacing="0" width="921">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">A549 cells&#160;</td>
			<td style="width:141px;">ATCC</td>
			<td style="width:184px;">CCL-185</td>
			<td style="width:353px;">Adenocarcinomic human alveolar basal epithelial cells</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">HEK 293T cells</td>
			<td style="width:141px;">ATCC</td>
			<td style="width:184px;">CRL-3216</td>
			<td>Human embryonic kidney cells</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Lipofectamine 2000</td>
			<td style="width:141px;">Life Technologies&#160;</td>
			<td style="width:184px;">11668019</td>
			<td>Transfection reagent</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1X Opti-MEM Reduced Serum Medium</td>
			<td>ThermoFisher Scientific</td>
			<td style="width:184px;">51985-034</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">White tissue culture treated 96-well plate</td>
			<td>Corning, Inc.&#160;</td>
			<td>3917</td>
			<td>Assay plates</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">10X MEM</td>
			<td style="width:141px;">Gibco</td>
			<td style="width:184px;">11430-030</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Jurkat cell expressing murine FcgRIV</td>
			<td style="width:141px;">Promega</td>
			<td style="width:184px;">M1201</td>
			<td>Kit provides includes cells, Bio-Glo Luciferase assay system, 1X RPMI and low IgG serum</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Jurkat cell expressing human FcgRIIIa</td>
			<td style="width:141px;">Promega</td>
			<td style="width:184px;">G7010</td>
			<td>Kit provides includes cells, Bio-Glo Luciferase assay system, 1X RPMI and low IgG serum</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Jurkat cell expressing human FcgRIIa</td>
			<td style="width:141px;">Promega</td>
			<td style="width:184px;">G9901</td>
			<td>Kit provides includes cells, Bio-Glo Luciferase assay system, 1X RPMI and low IgG serum</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Luminometer</td>
			<td>BioTek</td>
			<td>Synergy H1 Multi-Mode reader</td>
			<td>Luminescence plate reader</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Bio-Glo Luciferase Assay System</td>
			<td style="width:141px;">Promega</td>
			<td style="width:184px;">G7940</td>
			<td>Contains luciferase assay buffer and luciferase assay substrate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Madin Darby canine kidney cells</td>
			<td style="width:141px;">ATCC</td>
			<td style="width:184px;">CCL-34</td>
			<td>Canine kidney cells</td>
		</tr>
	</tbody>
</table>

a method to assess fc-mediated effector functions induced by influenza hemagglutinin specific antibodies

Antibodies play a crucial role in coupling the innate and adaptive immune responses against viral pathogens through their antigen binding domains and Fc-regions. Here, we describe how to measure the activation of Fc effector functions by monoclonal antibodies targeting the influenza virus hemagglutinin with the use of a genetically engineered Jurkat cell line expressing an activating type 1 Fc-Fc&#947;R. Using this method, the contribution of specific Fc-Fc&#947;R interactions conferred by immunoglobulins can be determined using an in vitro assay.

We demonstrated that a stalk-specific mAb, 6F12, but not head-specific a head-specific mAb, PY102, was able to activate primary natural killer cells by upregulating CD107a and interferon&#160;&#947;19. To model the ability of a stalk-specific antibody to activate primary human NK cells, we show that a stalk-specific mAb, 6F12, can robustly activate the modified Jurkat cell expressing the murine Fc&#947;RIV by ~14-fold. On the other hand, the head-specific mAb, PY102 and the control IgG do not (Figure 2)28.
To investigate if the multiplicity of infection (MOI) can affect the induction of Jurkat cells expressing the murine Fc&#947;RIV, we infected MDCK cells with X31 (a reassortant influenza A virus expressing the hemagglutinin and neuraminidase of A/Hong Kong/1/68 (H3N2) virus with the internal segments of A/Puerto Rico/8/34 (H1N1)) with an MOI of 3, 1, or 0.33. Twenty four hours later, Jurkat cells expressing murine Fc&#947;RIV and mAb 9H10 were added unto the infected MDCK cells. In Figure 3, we show that cells infected with an MOI of 3 can induce the luminescence around 3-fold higher than MDCK cells infected with an MOI of 0.33.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56256/56256fig1.jpg" /> 
Figure 1: A schematic of a sample plate layout and composition of the experimental groups. (A) The starting concentration for each antibody sample is at 10 &#181;g/mL and serially diluted across the plate (column 1 to column 12) 4-fold. Each sample is done in triplicates. Row G is reserved for the no mAb control and Row H is background. (B) Final volume for each experimental group before addition of luciferase substrate buffer is 75 &#181;L. Of note, the sample and &#8216;no mAb groups&#8217; have 25 &#181;L of effector cells added, while the background control groups have 75 &#181;L of assay media. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56256/56256fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56256/56256fig2.jpg" /> 
Figure 2: Induction of modified Jurkat cells expressing FcgR by a stalk monoclonal antibody. A549 cells were infected with A/Puerto Rico/8/34 (H1N1) with an MOI of 3. At 24 hours post infection, murine Fc&#947;RIV-expressing Jurkat cells in combination with PY102, 6F12 or a IgG control were added. Induction of Jurkat cells were assessed by luminescence signal generated by firefly luciferase under the NFAT response element. Error bars = standard deviations. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56256/56256fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56256/56256fig3.jpg" /> 
Figure 3: The multiplicity of infection affects induction of a stalk-specific antibody. MDCK cells were infected with X31 (H3N2) with an MOI of 3, 1, or 0.33. At 24 h post infection, FcgR-expressing Jurkat cells in combination with 9H10 (starting dilution of 10 &#181;g/mL) added. Induction of Jurkat cells were assessed by luminescence signal generated by firefly luciferase under the NFAT response element. Error bars = standard deviations. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56256/56256fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about A Method to Assess Fc-mediated Effector Functions Induced by Influenza Hemagglutinin Specific Antibodies at JoVE.com

A Method to Assess Fc-mediated Effector Functions Induced by Influenza Hemagglutinin Specific Antibodies

We describe a method to measure the activation of Fc-mediated effector functions by antibodies that target the influenza virus hemagglutinin. This assay can also be adapted to assess the ability of monoclonal antibodies or polyclonal sera targeting other viral surface glycoproteins to induce Fc-mediated immunity.

Antibodies play a crucial role in coupling the innate and adaptive immune responses against viral pathogens through their antigen binding domains and ...

a-method-to-assess-fc-mediated-effector-functions-induced-influenza

Nanyang Technological University

Research

JoVE Journal

Immunology and Infection

7.6K Views.  Icahn School of Medicine at Mount Sinai. We describe a method to measure the activation of Fc-mediated effector functions by antibodies that target the influenza virus hemagglutinin. This assay can also be adapted to assess the ability of monoclonal antibodies or polyclonal sera targeting other viral surface glycoproteins to induce Fc-mediated immunity.

Video: A Method to Assess Fc-mediated Effector Functions Induced by Influenza Hemagglutinin Specific Antibodies

Methods to Assess Beta Cell Death Mediated by Cytotoxic T Lymphocytes

Type 1 diabetes (T1D) is a T cell mediated autoimmune disease. During the pathogenesis, patients become progressively more insulinopenic as 
insulin production is lost, presumably this results from the destruction of pancreatic beta cells by T cells. Understanding the mechanisms of beta cell death during 
the development of T1D will provide insights to generate an effective cure for this disease. Cell-mediated lymphocytotoxicity (CML) assays have historically used the 
radionuclide Chromium 51 (51Cr) to label target cells. These targets are then exposed to effector cells and the release of 51Cr from target 
cells is read as an indication of lymphocyte-mediated cell death. Inhibitors of cell death result in decreased release of 51Cr.
 As effector cells, we used an activated autoreactive clonal population of CD8+ Cytotoxic T lymphocytes (CTL) isolated from a mouse stock transgenic for both the alpha and beta chains of the AI4 T cell receptor (TCR). Activated AI4 T cells were co-cultured with 51Cr labeled target NIT cells for 16 hours, release of 51Cr was recorded to calculate specific lysis 
Mitochondria participate in many important physiological events, such as energy production, regulation of signaling transduction, and apoptosis. The study of beta cell mitochondrial functional changes during the development of T1D is a novel area of research. Using the mitochondrial membrane potential dye Tetramethyl Rhodamine Methyl Ester (TMRM) and confocal microscopic live cell imaging, we monitored mitochondrial membrane potential over time in the beta cell line NIT-1. For imaging studies, effector AI4 T cells were labeled with the fluorescent nuclear staining dye Picogreen. NIT-1 cells and T cells were co-cultured in chambered coverglass and mounted on the microscope stage equipped with a live cell chamber, controlled at 37&deg;C, with 5% CO2, and humidified. During these experiments images were taken of each cluster every 3 minutes for 400 minutes.
Over a course of 400 minutes, we observed the dissipation of mitochondrial membrane potential in NIT-1 cell clusters where AI4 T cells were attached. In the simultaneous control experiment where NIT-1 cells were co-cultured with MHC mis-matched human lymphocyte Jurkat cells, mitochondrial membrane potential remained intact. This technique can be used to observe real-time changes in mitochondrial membrane potential in cells under attack of cytotoxic lymphocytes, cytokines, or other cytotoxic reagents.

Cell-mediated lymphocytotoxicity (CML) assays can be used to test autoreactive responses and study mechanisms of cell death in vitro. However, using live-cell confocal microscopic imaging techniques with fluorescent dyes, the type and kinetics of cell death as well as the pathways utilized can be studied in greater detail.

Type 1 diabetes (T1D) is a T cell mediated autoimmune disease.  During the pathogenesis, patients become progressively more insulinopenic as 
insulin ...

Quantitative Analyses of all Influenza Type A Viral Hemagglutinins and Neuraminidases using Universal Antibodies in Simple Slot Blot Assays

Hemagglutinin (HA) and neuraminidase (NA) are two surface proteins of influenza viruses which are known to play important roles in the viral life cycle and the induction of protective immune responses1,2. As the main target for neutralizing antibodies, HA is currently used as the influenza vaccine potency marker and is measured by single radial immunodiffusion (SRID)3. However, the dependence of SRID on the availability of the corresponding subtype-specific antisera causes a minimum of 2-3 months delay for the release of every new vaccine. Moreover, despite evidence that NA also induces protective immunity4, the amount of NA in influenza vaccines is not yet standardized due to a lack of appropriate reagents or analytical method5. Thus, simple alternative methods capable of quantifying HA and NA antigens are desirable for rapid release and better quality control of influenza vaccines.
Universally conserved regions in all available influenza A HA and NA sequences were identified by bioinformatics analyses6-7. One sequence (designated as Uni-1) was identified in the only universally conserved epitope of HA, the fusion peptide6, while two conserved sequences were identified in neuraminidases, one close to the enzymatic active site (designated as HCA-2) and the other close to the N-terminus (designated as HCA-3)7. Peptides with these amino acid sequences were synthesized and used to immunize rabbits for the production of antibodies. The antibody against the Uni-1 epitope of HA was able to bind to 13 subtypes of influenza A HA (H1-H13) while the antibodies against the HCA-2 and HCA-3 regions of NA were capable of binding all 9 NA subtypes. All antibodies showed remarkable specificity against the viral sequences as evidenced by the observation that no cross-reactivity to allantoic proteins was detected. These universal antibodies were then used to develop slot blot assays to quantify HA and NA in influenza A vaccines without the need for specific antisera7,8. Vaccine samples were applied onto a PVDF membrane using a slot blot apparatus along with reference standards diluted to various concentrations. For the detection of HA, samples and standard were first diluted in Tris-buffered saline (TBS) containing 4M urea while for the measurement of NA they were diluted in TBS containing 0.01% Zwittergent as these conditions significantly improved the detection sensitivity. Following the detection of the HA and NA antigens by immunoblotting with their respective universal antibodies, signal intensities were quantified by densitometry. Amounts of HA and NA in the vaccines were then calculated using a standard curve established with the signal intensities of the various concentrations of the references used. 
Given that these antibodies bind to universal epitopes in HA or NA, interested investigators could use them as research tools in immunoassays other than the slot blot only.

A simple slot blot method was developed for the quantification of influenza viral hemagglutinin and neuraminidase using universal antibodies targeting their most conserved sequences identified through bioinformatics analyses. This innovative approach may provide a useful alternative to quantitative determination of all viral hemagglutinin and neuraminidase.

Hemagglutinin (HA) and neuraminidase (NA) are two surface proteins of influenza viruses which are known to play important roles in the viral life cycle ...

High-throughput Detection Method for Influenza Virus

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, precise diagnosis of the infecting strain and rapid high-throughput screening of vast numbers of clinical samples is paramount to control the spread of pandemic infections. Current clinical diagnoses of influenza infections are based on serologic testing, polymerase chain reaction, direct specimen immunofluorescence and cell culture 1,2.
Here, we report the development of a novel diagnostic technique used to detect live influenza viruses. We used the mouse-adapted human A/PR/8/34 (PR8, H1N1) virus 3 to test the efficacy of this technique using MDCK cells 4. MDCK cells (104 or 5 x 103 per well) were cultured in 96- or 384-well plates, infected with PR8 and viral proteins were detected using anti-M2 followed by an IR dye-conjugated secondary antibody. M2 5 and hemagglutinin 1 are two major marker proteins used in many different diagnostic assays. Employing IR-dye-conjugated secondary antibodies minimized the autofluorescence associated with other fluorescent dyes. The use of anti-M2 antibody allowed us to use the antigen-specific fluorescence intensity as a direct metric of viral quantity. To enumerate the fluorescence intensity, we used the LI-COR Odyssey-based IR scanner. This system uses two channel laser-based IR detections to identify fluorophores and differentiate them from background noise. The first channel excites at 680 nm and emits at 700 nm to help quantify the background. The second channel detects fluorophores that excite at 780 nm and emit at 800 nm. Scanning of PR8-infected MDCK cells in the IR scanner indicated a viral titer-dependent bright fluorescence. A positive correlation of fluorescence intensity to virus titer starting from 102-105 PFU could be consistently observed. Minimal but detectable positivity consistently seen with 102-103 PFU PR8 viral titers demonstrated the high sensitivity of the near-IR dyes. The signal-to-noise ratio was determined by comparing the mock-infected or isotype antibody-treated MDCK cells.
Using the fluorescence intensities from 96- or 384-well plate formats, we constructed standard titration curves. In these calculations, the first variable is the viral titer while the second variable is the fluorescence intensity. Therefore, we used the exponential distribution to generate a curve-fit to determine the polynomial relationship between the viral titers and fluorescence intensities. Collectively, we conclude that IR dye-based protein detection system can help diagnose infecting viral strains and precisely enumerate the titer of the infecting pathogens.

This method describes the use of Infrared dye based imaging system for detection of H1N1 in bronchioalveolar lavage (BAL) fluid of infected mice at a high sensitivity. This methodology can be performed in a 96- or 384-well plate, requires &lt;10 &mu;l volume of test material and has the potential for concurrent screening of multiple pathogens.

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, ...

In Vitro Assay to Evaluate the Impact of Immunoregulatory Pathways on HIV-specific CD4 T Cell Effector Function

T cell exhaustion is a major factor in failed pathogen clearance during chronic viral infections. Immunoregulatory pathways, such as PD-1 and IL-10, are upregulated upon this ongoing antigen exposure and contribute to loss of proliferation, reduced cytolytic function, and impaired cytokine production by CD4 and CD8 T cells. In the murine model of LCMV infection, administration of blocking antibodies against these two pathways augmented T cell responses. However, there is currently no in vitro assay to measure the impact of such blockade on cytokine secretion in cells from human samples. Our protocol and experimental approach enable us to accurately and efficiently quantify the restoration of cytokine production by HIV-specific CD4 T cells from HIV infected subjects.
Here, we depict an in vitro experimental design that enables measurements of cytokine secretion by HIV-specific CD4 T cells and their impact on other cell subsets. CD8 T cells were depleted from whole blood and remaining PBMCs were isolated via Ficoll separation method. CD8-depleted PBMCs were then incubated with blocking antibodies against PD-L1 and/or IL-10R&#945; and, after stimulation with an HIV-1 Gag peptide pool, cells were incubated at 37 &#176;C, 5% CO2. After 48 hr, supernatant was collected for cytokine analysis by beads arrays and cell pellets were collected for either phenotypic analysis using flow cytometry or transcriptional analysis using qRT-PCR. For more detailed analysis, different cell populations were obtained by selective subset depletion from PBMCs or by sorting using flow cytometry before being assessed in the same assays. These methods provide a highly sensitive and specific approach to determine the modulation of cytokine production by antigen-specific T-helper cells and to determine functional interactions between different populations of immune cells.

In Vitro Assay to Evaluate the Impact of Immunoregulatory Pathways on HIV-specific CD4 T Cell Effector Function

We developed an in vitro assay to investigate the role of immunoregulatory pathways in the regulation of cytokine secretion by HIV-specific CD4 T cells.

T cell exhaustion is a major factor in failed pathogen clearance during chronic viral infections. Immunoregulatory pathways, such as PD-1 and IL-10, are ...

In vitro Coculture Assay to Assess Pathogen Induced Neutrophil Trans-epithelial Migration

Mucosal surfaces serve as protective barriers against pathogenic organisms.&#160;Innate immune responses are activated upon sensing pathogen leading to the infiltration of tissues with migrating inflammatory cells, primarily neutrophils.&#160;This process has the potential to be destructive to tissues if excessive or held in an unresolved state.&#160; Cocultured in vitro models can be utilized to study the unique molecular mechanisms involved in pathogen induced neutrophil trans-epithelial migration.&#160;This type of model provides versatility in experimental design with opportunity for controlled manipulation of the pathogen, epithelial barrier, or neutrophil.&#160;Pathogenic infection of the apical surface of polarized epithelial monolayers grown on permeable transwell filters instigates physiologically relevant basolateral to apical trans-epithelial migration of neutrophils applied to the basolateral surface.&#160;The in vitro model described herein demonstrates the multiple steps necessary for demonstrating neutrophil migration across a polarized lung epithelial monolayer that has been infected with pathogenic P. aeruginosa (PAO1).&#160;Seeding and culturing of permeable transwells with human derived lung epithelial cells is described, along with isolation of neutrophils from whole human blood and culturing of PAO1 and nonpathogenic K12 E. coli (MC1000).&#160; The emigrational process and quantitative analysis of successfully migrated neutrophils that have been mobilized in response to pathogenic infection is shown with representative data, including positive and negative controls.&#160;This in vitro model system can be manipulated and applied to other mucosal surfaces.&#160;Inflammatory responses that involve excessive neutrophil infiltration can be destructive to host tissues and can occur in the absence of pathogenic infections.&#160;A better understanding of the molecular mechanisms that promote neutrophil trans-epithelial migration through experimental manipulation of the in vitro coculture assay system described herein has significant potential to identify novel therapeutic targets for a range of mucosal infectious as well as inflammatory diseases.

In vitro Coculture Assay to Assess Pathogen Induced Neutrophil Trans-epithelial Migration

Neutrophil trans-epithelial migration in response to mucosal bacterial infection contributes to epithelial injury and clinical disease.&#160;An in vitro model has been developed that combines pathogen, human neutrophils, and polarized human epithelial cell layers grown on transwell filters to facilitate investigations towards unraveling the molecular mechanisms orchestrating this phenomenon.

Mucosal surfaces serve as protective barriers against pathogenic organisms.&#160;Innate immune responses are activated upon sensing pathogen leading to ...

Expression of Functional Recombinant Hemagglutinin and Neuraminidase Proteins from the Novel H7N9 Influenza Virus Using the Baculovirus Expression System

The baculovirus expression system is a powerful tool for expression of recombinant proteins. Here we use it to produce correctly folded and glycosylated versions of the influenza A virus surface glycoproteins - the hemagglutinin (HA) and the neuraminidase (NA). As an example, we chose the HA and NA proteins expressed by the novel H7N9 virus that recently emerged in China. However the protocol can be easily adapted for HA and NA proteins expressed by any other influenza A and B virus strains. Recombinant HA (rHA) and NA (rNA) proteins are important reagents for immunological assays such as ELISPOT and ELISA, and are also in wide use for vaccine standardization, antibody discovery, isolation and characterization. Furthermore, recombinant NA molecules can be used to screen for small molecule inhibitors and are useful for characterization of the enzymatic function of the NA, as well as its sensitivity to antivirals. Recombinant HA proteins are also being tested as experimental vaccines in animal models, and a vaccine based on recombinant HA was recently licensed by the FDA for use in humans. The method we describe here to produce these molecules is straight forward and can facilitate research in influenza laboratories, since it allows for production of large amounts of proteins fast and at a low cost. Although here we focus on influenza virus surface glycoproteins, this method can also be used to produce other viral and cellular surface proteins.

Here we describe a way to express correctly folded and functional influenza virus surface antigens derived from the novel Chinese H7N9 virus in insect cells. The technique can be adapted to express ectodomains of any viral or cellular surface proteins.

The baculovirus expression system is a powerful tool for expression of  recombinant proteins. Here we use it to produce correctly folded and  glycosylated ...

In Vitro Disassembly of Influenza A Virus Capsids by Gradient Centrifugation

Acid-triggered molecular processes closely control cell entry of many viruses that enter through the endocytic system. In the case of influenza A virus (IAV), virus fusion with the endosomal membrane as well as the subsequent disassembly of the viral capsid, called uncoating, is governed by the ionic conditions inside endocytic vesicles. The early steps in the virus life cycle are hard to study because endosomes cannot be directly accessed experimentally, creating the need for an in vitro approach. Here, we describe a method based on velocity gradient centrifugation of purified virions through a two-layer glycerol gradient, which enables analysis of the IAV core and its stability. The gradient contains a non-ionic detergent (NP-40) in its lower layer to remove the viral membrane by solubilization as the virus sediments toward the bottom. At neutral pH, viral cores are pelleted as stable structures. The major core components, matrix protein (M1) and the viral ribonucleoproteins (vRNPs), can be clearly identified in the pellet fraction by SDS-PAGE. Decreasing the pH to 6.0 or lower in the bottom layer selectively removes M1 from the pellet followed by release of vRNPs at more acidic conditions. Viral protein bands on Coomassie-stained gels can be subjected to densitometric quantification to monitor intermediate states of IAV disassembly. Besides pH, other factors that influence viral core stability can be assessed, such as salt concentration and putative viral uncoating factors, simply by modifying the detergent-containing glycerol layer accordingly. Taken together, the presented technique allows highly reproducible and quantitative analysis of viral uncoating in vitro. It can be applied to other enveloped viruses that undergo complex uncoating processes.

In Vitro Disassembly of Influenza A Virus Capsids by Gradient Centrifugation

Disassembly of influenza A virus cores during virus entry into host cells is a multistep process. We describe an in vitro method to analyze the early stages of viral uncoating. In this approach, velocity gradient centrifugation is used to biochemically dissect the steps that initiate uncoating under defined conditions.

Acid-triggered molecular processes closely control cell entry of many viruses that enter through the endocytic system. In the case of influenza A virus ...

Applying Fluorescence Resonance Energy Transfer (FRET) to Examine Effector Translocation Efficiency by Coxiella burnetii during siRNA Silencing

Coxiella burnetii, the causative agent of Q fever, is an intracellular pathogen that relies on a Type IV Dot/Icm Secretion System to establish a replicative niche. A cohort of effectors are translocated through this system into the host cell to manipulate host processes and allow the establishment of a unique lysosome-derived vacuole for replication. The method presented here involves the combination of two well-established techniques: specific gene silencing using siRNA and measurement of effector translocation using a FRET-based substrate that relies on &#946;-lactamase activity. Applying these two approaches, we can begin to understand the role of host factors in bacterial secretion system function and effector translocation. In this study we examined the role of Rab5A and Rab7A, both important regulators of the endocytic trafficking pathway. We demonstrate that silencing the expression of either protein results in a decrease in effector translocation efficiency. These methods can be easily modified to examine other intracellular and extracellular pathogens that also utilize secretion systems. In this way, a global picture of host factors involved in bacterial effector translocation may be revealed.

Applying Fluorescence Resonance Energy Transfer FRET to Examine Effector Translocation Efficiency by Coxiella burnetii during siRNA Silencing

Investigating the interactions between bacterial pathogens and their hosts is an important area of biological research. Here, we describe the necessary techniques to measure effector translocation by Coxiella burnetii during siRNA gene silencing using BlaM substrate.

Coxiella burnetii, the causative agent of Q fever, is an intracellular pathogen that relies on a Type IV Dot/Icm Secretion System to establish a ...

Fluorescence-based Neuraminidase Inhibition Assay to Assess the Susceptibility of Influenza Viruses to The Neuraminidase Inhibitor Class of Antivirals

The neuraminidase (NA) inhibitors are the only class of antivirals approved for the treatment and prophylaxis of influenza that are effective against currently circulating strains. In addition to their use in treating seasonal influenza, the NA inhibitors have been stockpiled by a number of countries for use in the event of a pandemic. It is therefore important to monitor the susceptibility of circulating influenza viruses to this class of antivirals. There are different types of assays that can be used to assess the susceptibility of influenza viruses to the NA inhibitors, but the enzyme inhibition assays using either a fluorescent substrate or a chemiluminescent substrate are the most widely used and recommended. This protocol describes the use of a fluorescence-based assay to assess influenza virus susceptibility to NA inhibitors. The assay is based on the NA enzyme cleaving the 2&#8242;-(4-Methylumbelliferyl)-&#945;-D-N-acetylneuraminic acid (MUNANA) substrate to release the fluorescent product 4-methylumbelliferone (4-MU). Therefore, the inhibitory effect of an NA inhibitor on the influenza virus NA is determined based on the concentration of the NA inhibitor that is required to reduce 50% of the NA activity, given as an IC50 value.

We describe the use of a phenotypic fluorescence-based neuraminidase inhibition assay to assess the susceptibility of influenza A and B viruses to the neuraminidase inhibitor class of antivirals.

The neuraminidase (NA) inhibitors are the only class of antivirals approved for the treatment and prophylaxis of influenza that are effective against ...

Generation of Escape Variants of Neutralizing Influenza Virus Monoclonal Antibodies

Influenza viruses exhibit a remarkable ability to adapt and evade the host immune response. One way is through antigenic changes that occur on the surface glycoproteins of the virus. The generation of escape variants is a powerful method in elucidating how viruses escape immune detection and in identifying critical residues required for antibody binding. Here, we describe a protocol on how to generate influenza A virus escape variants by utilizing human or murine monoclonal antibodies (mAbs) directed against the viral hemagglutinin (HA). With the use of our technique, we previously characterized critical residues required for the binding of antibodies targeting either the head or stalk of the novel avian H7N9 HA. The protocol can be easily adapted for other virus systems. Analyses of escape variants are important for modeling antigenic drift, determining single nucleotide polymorphisms (SNPs) conferring resistance and virus fitness, and in the designing of vaccines and/or therapeutics.

We describe a method by which we identify critical residues required for the binding of human or murine monoclonal antibodies that target the viral hemagglutinin of influenza A viruses. The protocol can be adapted to other virus surface glycoproteins and their corresponding neutralizing antibodies.

Influenza viruses exhibit a remarkable ability to adapt and evade the host immune response. One way is through antigenic changes that occur on the surface ...