This work was supported by NIH grants to T.W. (R01AI072060 and R01AI099123). G. Xie was supported by a Sealy Center for Vaccine Development Predoctoral Fellowship. We thank Dr. Richard Flavell (Howard Hughes Medical Institute, Yale University School of Medicine, New Haven) and Dr. Shizuo Akira (Osaka University, Japan) for providing the MyD88&#8211;/&#8211; mice and Dr. Y Cong (UTMB, Galveston) for providing OTII transgenic mice.

All animal experiments were approved by the Animal Care and Use Committee at the University of Texas Medical Branch.
1. Isolation of DCs from Non-infected and WNV-infected Mice
<ol>
	<li>Age- and sex- match 6-10 week-old, wild-type C57BL/6 (B6) and MyD88&#8722;/&#8722;mice. Inoculate intraperitoneally (i.p.) with 500 plaque forming unit (PFU) of WNV NS4B- P38G mutant. At day 3 post-infection, euthanize B6 and MyD88&#8722;/&#8722; mice with CO...

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WNV is a BL3 pathogen. Due to safety regulations, immunological assays with WNV-infected samples are often restricted by the availability of equipment at BL3 facilities or more lengthy and tedious to perform. In a recent study, we used two flow cytometry-based methods to study cell mediated immune responses during WNV infection5. In both assays, WNV-infected cells were treated with 1-2% PFA directly or with fixation/permeabilization solution containing 4% PFA. It is known that 1% PFA fixation of virus-infected...

West Nile virus (WNV), a neurotropic, plus-sensed flavivirus, is an emerging public health threat. Currently, no vaccines have been approved for human use1. An attenuated WNV strain, which has a P38G substitution in the nonstructural (NS)4B protein, is known to induce no lethality in mice but higher innate cytokines and T cell responses in mice than wild-type WNV NY99 strain2. Mice immunized with the NS4B-P38G mutant were all protected from a secondary challenge with lethal wild-type WNV. This suggests that the NS4B-P38G mutant has suitable features for an ideal vaccine candidate. The mechanisms by which the NS4B-P38G mutant induces high protective adaptive immunity are not clearly understood yet. Toll-like receptors (TLRs), which recognize pathogen-associated molecular patterns, play an essential role in the initiation of innate immunity to viral infection. The core TLR signaling pathway utilizes myeloid differentiation primary response gene 88 (MyD88) as the primary adaptor3,4. In a recent study, MyD88 signaling was shown to play an important role in development of cell mediated immunity during WNV NS4B- P38G mutant infection in mice5. Dentritic cells (DCs) are one of the most important antigen-presenting cells exhibiting the unique capacity to initiate primary T cell responses during viral infection6,7. CD4+ and CD8+ T-cells both contribute to long-lasting protective immunity and are important for host survival following wild-type WNV infection8,9. Two immunological assays were used in this study to assess the functions of these cells in the NS4B-P38G mutant infected mice.
First, an in vitro T cell priming assay was utilized to compare the antigen-presenting capability of DCs of WNV-infected wild-type and MyD88&#8722;/&#8722; mice. To increase sensitivity of the assay, na&#239;ve CD4+ T cells were isolated from OTII transgenic mice, which express a V&#945;2/V&#946;5 TCR specific for the chicken ovalbumin (OVA) peptide 323 - 339. DCs of WNV infected mice were purified, and co-cultured with carboxyfluorescein succinimidyl easter (CFSE)-labeled CD4+ T cells in the presence of OVA peptide. After 5 days of co-culture, cells were harvested and fixed with paraformaldehyde (PFA) and analyzed by flow cytometry. Proliferative assays have been traditionally carried out through incorporation of 5-bromo-2&#8217;-deoxyuridine (BrdU) or tritiated thymine deoxyriboside (3HTdr)10. Nevertheless, these assays are either radioactive and/or in need of special equipments at biosafety level (BL) 3 facilities, where WNV studies are conducted. The flow cytometric analysis of lymphocyte proliferation by serial halving of the fluorescence intensity of the vital dye CFSE has become more commonly used in immunological assays as the dye is more stably and evenly incorporated into cells, detected easily by flow cytometry, and is nonradioactive11. The assay also has the ability to assess the number of cell divisions. One major advantage of using this assay in WNV studies is that fixation of the infected cells with 1-2% PFA could inactivate WNV12, which will enable sample acquisition with a flow cytometer in a BL2 laboratory.
Next, a modified intracellular cytokine staining (ICS) procedure was used to study the role of MyD88 signaling in regulation of WNV specific T cell responses in NS4B-P38G mutant-infected mice. In this assay, splenocytes isolated from infected mice were treated in vitro with WNV specific peptides. Brefeldin A was added to retain the cytokines within the cell. After 5 hr incubation, cells were harvested, washed and stained for T cell subsets. Cells were then fixed in PFA, permeabilized and stained for interferon (IFN)-&#947; and analyzed by flow cytometry. As with other flow cytometry-based assay, once the cells are treated with fixation and permeabilization buffer containing PFA, infected samples can be transferred to a BL2 laboratory for further processing and analysis. In several published studies, we have used ICS to measure T cell effector functions in WNV-infected mice13,14. Although it&#8217;s well established, one major drawback of this assay is that the procedure is very lengthy and could be more time consuming when performed inside BL3 facilities. Here, a micro-centrifuge tube-based ICS method was shown to be more feasible, easier to proceed and less time consuming when performed within a BL3 laboratory.

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			<td style="width:153px;">Company</td>
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			<td height="20" style="height:20px;width:216px;">RPMI 1640</td>
			<td style="width:153px;">Invitrogen</td>
			<td align="right" style="width:119px;">11875</td>
			<td>warm up at 37C</td>
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			<td height="20" style="height:20px;">anti-CD11c magnetic beads&#160;</td>
			<td>Miltenyi Biotec</td>
			<td>130-052-001</td>
			<td>follow the manufacturer&#8217;s instructions</td>
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			<td height="20" style="height:20px;">anti-CD4 magnetic beads&#160;</td>
			<td>Miltenyi Biotec</td>
			<td>130-095-248</td>
			<td>follow the manufacturer&#8217;s instructions</td>
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			<td height="20" style="height:20px;">CFSE</td>
			<td style="width:153px;">Invitrogen</td>
			<td>C34554</td>
			<td></td>
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			<td height="20" style="height:20px;">OVA residue 323-339</td>
			<td>Genscript Corporation</td>
			<td>RP10610</td>
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			<td height="39" style="height:39px;width:216px;">Peptides</td>
			<td style="width:153px;">Proimmune</td>
			<td>PC0AD-D</td>
			<td></td>
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			<td height="58" style="height:58px;">Brefeldin A solution</td>
			<td style="width:153px;">BD Bioscience</td>
			<td align="right">555029</td>
			<td></td>
		</tr>
		<tr height="58">
			<td height="58" style="height:58px;width:216px;">Mouse Fc Blocker</td>
			<td style="width:153px;">e-Bioscience</td>
			<td>14-0161-85</td>
			<td></td>
		</tr>
		<tr height="58">
			<td height="58" style="height:58px;">APC-conjugated CD4&#160;</td>
			<td style="width:153px;">e-Bioscience</td>
			<td>17-0041-81</td>
			<td></td>
		</tr>
		<tr height="58">
			<td height="58" style="height:58px;">FITC-conjugated CD8&#160;</td>
			<td style="width:153px;">e- bioscience</td>
			<td>11-0081-82</td>
			<td></td>
		</tr>
		<tr height="58">
			<td height="58" style="height:58px;">Fixation/Permeabilization Solution</td>
			<td style="width:153px;">BD- Bioscience</td>
			<td align="right" style="width:119px;">554722</td>
			<td></td>
		</tr>
		<tr height="58">
			<td height="58" style="height:58px;">Permeabilization/wash buffer</td>
			<td style="width:153px;">BD- Bioscience</td>
			<td align="right">554723</td>
			<td></td>
		</tr>
		<tr height="58">
			<td height="58" style="height:58px;">anti-IFNg-PE&#160;</td>
			<td style="width:153px;">e-Bioscience</td>
			<td>12-7311-82</td>
			<td></td>
		</tr>
		<tr height="58">
			<td height="58" style="height:58px;width:216px;">Accuri flow cytometer</td>
			<td style="width:153px;">BD Bioscience</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
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in vitro analysis of myd88-mediated cellular immune response to west nile virus mutant strain infection

An attenuated West Nile virus (WNV), a nonstructural (NS) 4B-P38G mutant, induced higher innate cytokine and T cell responses than the wild-type WNV in mice. Recently, myeloid differentiation factor 88 (MyD88) signaling was shown to be important for initial T cell priming and memory T cell development during WNV NS4B-P38G mutant infection. In this study, two flow cytometry-based methods &#8211; an in vitro T cell priming assay and an intracellular cytokine staining (ICS) &#8211; were utilized to assess dendritic cells (DCs) and T cell functions. In the T cell priming assay, cell proliferation was analyzed by flow cytometry following co-culture of DCs from both groups of mice with carboxyfluorescein succinimidyl ester (CFSE) - labeled CD4+ T cells of OTII transgenic mice. This approach provided an accurate determination of the percentage of proliferating CD4+ T cells with significantly improved overall sensitivity than the traditional assays with radioactive reagents. A microcentrifuge tube system was used in both cell culture and cytokine staining procedures of the ICS protocol. Compared to the traditional tissue culture plate-based system, this modified procedure was easier to perform at biosafety level (BL) 3 facilities. Moreover, WNV- infected cells were treated with paraformaldehyde in both assays, which enabled further analysis outside BL3 facilities. Overall, these in vitro immunological assays can be used to efficiently assess cell-mediated immune responses during WNV infection.

In the T cell priming assay, CFSE labeled CD4+ T cells were cultured with purified DCs from the NS4B-P38G mutant-infected wild-type and MyD88&#8722;/&#8722; mice in the presence or absence of OVA peptides. Labeled T cells cultured alone with or without OVA for 5 days were used as negative controls. As shown in Figure 1A, total T cells were gated for analysis of fluorescence intensity on the FL1 channel. The marker was set up based on the freshly labeled CD4<sup...

Watch this Scientific Journal Video about In Vitro Analysis of Myd88-mediated Cellular Immune Response to West Nile Virus Mutant Strain Infection at JoVE.com

In Vitro Analysis of Myd88-mediated Cellular Immune Response to West Nile Virus Mutant Strain Infection

Two flow cytometry-based methods &#8211; an in vitro T cell priming assay and intracellular cytokine staining were utilized to measure antigen presenting capacity of dendritic cells and antigen-specific T cell responses to a West Nile virus mutant infection in mice.

In Vitro Analysis of Myd88-mediated Cellular Immune Response to West Nile Virus Mutant Strain Infection

An attenuated West Nile virus (WNV), a nonstructural (NS) 4B-P38G mutant, induced higher innate cytokine and T cell responses than the wild-type WNV in ...

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Immunology and Infection

8.1K visualizações.  The University of Texas Medical Branch. Two flow cytometry-based methods – an in vitro T cell priming assay and intracellular cytokine staining were utilized to measure antigen presenting capacity of dendritic cells and antigen-specific T cell responses to a West Nile virus mutant infection in mice.