We thank Peter Staeheli for providing B6.A2G-Mx1 mice and Semra &#214;zcelik for technical advice.
This work was supported by the German Research Foundation through SFB829 and KN536/16, and the K&#246;ln Fortune Program/Faculty of Medicine, University of Cologne.

Ethics statement.
The preparation of epidermal sheets from sacrificed animals is carried out in strict accordance with the recommendations of the Guide of Landesamt f&#252;r Natur, Umwelt and Verbraucherschutz, Northrhine-Westphalia (Germany). The study was approved by LANUV NRW (Number 8.84-02.05.20.13.018).
1. Preparation of Instruments and Culture Media
<ol>
	<li>Cultivate epidermal sheets in Dulbecco&#8217;s modified Eagle&#8217;s medium (DMEM)/high glucose co...

<ol>
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D., Cross, A., Orr, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+truncated+form+of+herpes+simplex+virus+type+1+immediate-early+protein+Vmw110+is+expressed+in+a+cell+type+dependent+manner.">A truncated form of herpes simplex virus type 1 immediate-early protein Vmw110 is expressed in a cell type dependent manner.</a> Virology. 197, 751-756 (1993).</li><li>Horisberger, M. A., Staeheli, P., Haller, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interferon+induces+a+unique+protein+in+mouse+cells+bearing+a+gene+for+resistance+to+influenza+virus.">Interferon induces a unique protein in mouse cells bearing a gene for resistance to influenza virus.</a> Proc. Natl. Acad. Sci. USA. 80, 1910-1914 (1983).</li><li>Christian, A. E., Haynes, M. P., Phillips, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+cyclodextrins+for+manipulating+cellular+cholesterol+content.">Use of cyclodextrins for manipulating cellular cholesterol content.</a> J. Lipid Res. 38, 2264-2272 (1997).</li><li>Ilangumaran, S., Hoessli, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+cholesterol+depletion+by+cyclodextrin+on+the+sphingolipid+microdomains+of+the+plasma+membrane.">Effects of cholesterol depletion by cyclodextrin on the sphingolipid microdomains of the plasma membrane.</a> Biochem. J. 335, 433-440 (1998).</li><li>Yancey, P. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cellular+cholesterol+efflux+mediated+by+cyclodextrins:+Demonstration+of+kinetic+pools+and+mechanism+of+efflux.">Cellular cholesterol efflux mediated by cyclodextrins: Demonstration of kinetic pools and mechanism of efflux.</a> J. Biol. Chem. 271, 16026-16034 (1996).</li><li>Montgomery, R. I., Warner, M. S., Lum, B. J., Spear, P. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Herpes+simplex+virus-1+entry+into+cells+mediated+by+a+novel+member+of+the+TNF/NGF+receptor+family.">Herpes simplex virus-1 entry into cells mediated by a novel member of the TNF/NGF receptor family.</a> Cell. 87, 427-436 (1996).</li><li>Geraghty, R. J., Krummenacher, C., Cohen, G. H., Eisenberg, R. J., Spear, P. 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The authors declare that they have no competing financial interests.

When epidermal sheets of adult skin from C57BL/6 are infected with HSV-1 at approximately 100 PFU/cell, we observe infection in nearly all cells of the basal layer in the interfollicular epidermis while lower virus doses correlate with less infected cells and a slower progress of infection. In general, hair follicles show a variable number of infected cells; while most of the rather small keratinocytes lining the developing hair follicles are infected, only the hair germ of the adult hair follicle is completely infected....

Herpes simplex virus (HSV) can cause a range of diseases in humans from mild uncomplicated mucocutaneous lesions to life-threatening infections. HSV type 1 (HSV-1) is dominantly associated with orofacial infections and encephalitis, whereas HSV type 2 (HSV-2) more likely causes genital infections1. While there is significant progress in understanding how HSV enters cells in culture, initiates infection and produces viral progeny, we know little about the viral invasion pathway(s) into tissue at the cellular level2. For studies of HSV skin or mucosal infections, mice, rabbits and guinea pigs have been used as animal models. Skin infection was established by intradermal injection or by scratching the skin in the presence of virus, and disease development was correlated with virus production. These methods helped to understand various aspects of disease pathogenesis, and are used to evaluate antiviral drugs. To study HSV infection at the tissue level, organotypic human skin models have been applied. As the rate of infection is restricted in these raft cultures, only a limited number of studies investigating infection, viral spread and the effects of antiviral components have been published3-6.
In order to characterize cellular determinants that play a role during HSV-1 infection in the intact epithelium, we established a protocol for ex vivo infection studies of murine epidermis7. Skin was prepared from newborns or from the tails of adult mice. Since HSV-1 could not infect complete skin samples, which were submerged in virus-containing medium, we separated the epidermis from the dermis by dispase II treatment. After floating of the epidermal sheets on virus-containing medium, infected cells can be visualized in the epidermal basal layer at various times postinfection (p.i.)7. To visualize the initiation of infection in individual cells prior to viral replication and virus production, we stained with an antibody against the infected-cell protein&#160;0 (ICP0), which is one of the first proteins expressed during HSV-1 infection. The cellular localization of ICP0 passes through distinct phases during early infection. While ICP0 is present in nuclear foci during an early stage of viral gene expression, relocalization of ICP0 to the cytoplasm indicates a subsequent phase of infection8.
We used the ex vivo infection assay of epidermal sheets from different mouse models to test the potential role of various cellular factors during infection. To address the impact of Rac1 as a key regulator of actin dynamics, we infected the epidermis of mice with a keratinocyte-specific deletion of the rac1 gene9. This model allowed us to study the consequences of deficient Rac1 on the efficiency of HSV-1 infection in epidermal keratinocyte layers. The comparison to infected epidermis of control littermates revealed no significant difference, indicating that the absence of Rac1 had no effect on the initiation of infection in the basal layer of the epidermis7. The use of further mouse models allowed us to address which cellular receptors mediate entry into the epidermis. Infecting epidermal sheets from either nectin-1- or HVEM-deficient mice with HSV-1 revealed that the initial viral entry into tissue strongly depends on the presence of nectin-110. Furthermore, our results demonstrate that HVEM can also serve as receptor in murine epidermis, although less efficiently than nectin-110.
To address the spatial distribution of infected cells in the epidermal layers, we visualize ICP0 expression in tissue sections and epidermal whole mounts (Figure 1). In cryosections of complete skin, no ICP0-expressing cells are detected (Figure 1). In contrast, cryosections of epidermal sheets demonstrate cytoplasmic ICP0 expression in the basal layer already at 3 hours p.i. (Figure 1). At later times, viral spreading to suprabasal layers can be visualized. The spatial distribution of infected cells in the basal layer can be easily followed in epidermal whole mounts (Figure 1). Upon infection with HSV-1 at 100 PFU/cell, approximately 50% of the basal keratinocytes in the interfollicular epidermis show ICP0 expression at 1.5 hr p.i. At this time point most infected cells express nuclear ICP0. The relocalization of ICP0 to the cytoplasm indicating a later stage of early gene expression is present in nearly all cells at 3 hr p.i. (Figure 1). These modes of visualizing infected cells upon ex vivo HSV-1 infection provide a powerful assay to study the effect of inhibitors or of deleted/mutated cellular components on viral entry and spread in tissue.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>DMEM/high glucose/GlutaMAX</td>
			<td>Life Technologies</td>
			<td align="right">31966047</td>
			<td>needed for cultivation of epidermal sheets</td>
		</tr>
		<tr>
			<td>dispase II powder</td>
			<td>Roche</td>
			<td align="right">4942078001</td>
			<td>has to be solved in heated PBS</td>
		</tr>
		<tr>
			<td>enzyme-free cell dissociation solution</td>
			<td>Sigma</td>
			<td>C5914</td>
			<td>needed for very gentle dissociation of epidermal sheets</td>
		</tr>
		<tr>
			<td>TrypLE select cell dissociation solution</td>
			<td>Life Technologies</td>
			<td>12563-029</td>
			<td>needed for dissociation of epidermal sheets</td>
		</tr>
		<tr>
			<td>chelex 100 resin</td>
			<td>Bio-Rad</td>
			<td>142-2832</td>
			<td>needed for chelation of polyvalent metal ions from the fetal calf serum</td>
		</tr>
		<tr>
			<td>gelatin from cold water fish skin&#160;</td>
			<td>Sigma</td>
			<td>G7765</td>
			<td>needed for minimization of non-specific antibody binding</td>
		</tr>
		<tr>
			<td>Keratin 14 Polyclonal Antibody (AF64) (conc.: 1 mg/ml)</td>
			<td>Covance</td>
			<td>PRB-155P</td>
			<td>used to visualize the intermediate filament keratin 14 which is a marker of the basal layer of the epidermis</td>
		</tr>
		<tr>
			<td>Mouse IgG (H+L) Secondary Antibody, Alexa Fluor&#174; 488 conjugate (conc.: 2 mg/ml)</td>
			<td>Life Technologies</td>
			<td>A-11029</td>
			<td>used as secondary antibodies</td>
		</tr>
		<tr>
			<td>Rabbit IgG (H+L) Secondary Antibody, Alexa Fluor&#174; 555 conjugate (conc.: 2 mg/ml)</td>
			<td>Life Technologies</td>
			<td>A-21429</td>
			<td>used as secondary antibodies</td>
		</tr>
		<tr>
			<td>4&#8242;,6-Diamidino-2-phenylindole dihydrochloride (DAPI dihydrochloride)&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; (conc.: 0.1 mg/ml)</td>
			<td>Sigma</td>
			<td align="right">36670</td>
			<td>used to counterstain the nucleus</td>
		</tr>
	</tbody>
</table>

ex vivo infection of murine epidermis with herpes simplex virus type 1

To enter its human host, herpes simplex virus type 1 (HSV-1) must overcome the barrier of mucosal surfaces, skin, or cornea. HSV-1 targets keratinocytes during initial entry and establishes a primary infection in the epithelium, which is followed by latent infection of neurons. After reactivation, viruses can become evident at mucocutaneous sites that appear as skin vesicles or mucosal ulcers. How HSV-1 invades skin or mucosa and reaches its receptors is poorly understood. To investigate the invasion route of HSV-1 into epidermal tissue at the cellular level, we established an ex vivo infection model of murine epidermis, which represents the site of primary and recurrent infection in skin. The assay includes the preparation of murine skin. The epidermis is separated from the dermis by dispase II treatment. After floating the epidermal sheets on virus-containing medium, the tissue is fixed and infection can be visualized at various times postinfection by staining infected cells with an antibody against the HSV-1 immediate early protein ICP0. ICP0-expressing cells can be observed in the basal keratinocyte layer already at 1.5 hr postinfection. With longer infection times, infected cells are detected in suprabasal layers, indicating that infection is not restricted to the basal keratinocytes, but the virus spreads to other layers in the tissue. Using epidermal sheets of various mouse models, the infection protocol allows determining the involvement of cellular components that contribute to HSV-1 invasion into tissue. In addition, the assay is suitable to test inhibitors in tissue that interfere with the initial entry steps, cell-to-cell spread and virus production. Here, we describe the ex vivo infection protocol in detail and present our results using nectin-1- or HVEM-deficient mice.

The challenge of the method is to prepare epidermal sheets into which HSV-1 can penetrate from the basal layer. The critical step is the separation of the epidermis from the dermis by dispase II treatment, which, depending on the mouse strain, needs to be adapted. The concentration of dispase II can range from 2.5 to 5 mg/ml, and the time of incubation from 20 to 45 min. The staining of the intermediate filament protein keratin 14 readily allows predicting whether the basal epidermal layer can be infected or whether it w...

Watch this Scientific Journal Video about Ex Vivo Infection of Murine Epidermis with Herpes Simplex Virus Type 1 at JoVE.com

Ex Vivo Infection of Murine Epidermis with Herpes Simplex Virus Type 1

The skin is one target tissue of the human pathogen herpes simplex virus type 1 (HSV-1). To explore the invasion route of HSV-1 into tissue, we established an ex vivo infection model of murine epidermal sheets which represent the outermost layer of skin.

Ex Vivo Infection of Murine Epidermis with Herpes Simplex Virus Type 1

To enter its human host, herpes simplex virus type 1 (HSV-1) must overcome the barrier of mucosal surfaces, skin, or cornea. HSV-1 targets keratinocytes ...

ex-vivo-infection-of-murine-epidermis-with-herpes-simplex-virus-type-1

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Immunology and Infection

11.0K Görüntüleme.  University of Cologne. The skin is one target tissue of the human pathogen herpes simplex virus type 1 (HSV-1). To explore the invasion route of HSV-1 into tissue, we established an ex vivo infection model of murine epidermal sheets which represent the outermost layer of skin.