We thank Lee Tuddenham (IBMC, Strasbourg) for amplifying and titrating MCMV-Luc and Thomas Baumert (INSERM U748, Strasbourg) for permission to use the animal facility of the Institute of Virology. Financial support from INSERM, Universit&eacute; de Strasbourg and Agence Nationale de la Recherche (ANR-08-MIEN-005-01) is acknowledged. The initial participation of Sonia Beroud and Laetitia Lelieur during their Master project is also acknowledged.

1. Preparation of Viral Suspension
<ol>
	<li>Obtain the Smith strain of MCMV expressing Luciferase (MCMV-Luc 15) from Ulrich Koszninowski's laboratory. In this recombinant, the Luciferase gene is inserted in the ie2 locus of the MCMV genome.</li>
	<li>To amplify MCMV-Luc, infect a murine bone marrow stromal cell line (M2-10B4, ATCC #CRL-1972) with MCMV at different multiplicity of infection (MOI, 0.001 to 1) 16. For this, add virus to cultured cells in serum free medium at 37 &deg;C. Afte...

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The authors declare no competing financial interest.	
	Ethics statement	
	Animals were maintained under pathogen-free conditions in the animal care facility of the Institut d'Immunologie et d'H&eacute;matologie. Handling of mice and experimental procedures were conducted in accordance with the French Law for the Protection of Laboratory Animals. The procedure was approved by the service v&eacute;terinaire de la Pr&eacute;fecture du Bas-Rhin (France) under the authorization number A-67-345.

Using in vivo imaging technology to monitor MCMV-Luc dissemination in mice neonates, we were able to observe viral spread to the brain of mutant animals, as opposed to wild-type. Further dissection of the animal and ex vivo imaging of the brain confirmed the presence of luminescent virus in the central nervous system. In addition, we also performed immunohistochemistry (not shown) on brain thin sections with an antibody specific for MCMV E1 early protein and observed that indeed, MCMV is present in the ...

Human Cytomegalovirus (HCMV/HHV-5) is a member of the &beta;-herpesvirus family. HCMV is a highly prevalent, opportunistic pathogen which is usually acquired during early life as an asymptomatic infection 1. Like all herpesviruses, HCMV persists throughout the entire life of the host whose immune system tightly controls viral replication. Episodes of viral reactivation mostly occur in immunocompromised individuals such as transplant patients receiving drugs to prevent graft rejection 2. In adults, HCMV has also been linked to glioblastomas 3. In addition, HCMV is a prominent pathogen for newborns with immature immunity 4-6. Primary infection in the developing fetus or neonate can have severe consequences. HCMV infection is the most common infectious cause of congenital birth defects and childhood disorders in developed countries. It is estimated that the incidence of neonatal HCMV infection affects 0.5-1% of all live births among which 5-10% will suffer from severe symptoms such as microcephaly or cerebellar hypoplasia. In addition, 10% of the infected infants with subclinical viral infection will later develop sequellae leading to mental retardation, hearing loss, visual defects or seizure and epilepsy 7,8.	
	As opposed to other human herpesviruses such as Herpes Simplex 1 (HSV-1/HHV-1) which can be inoculated to mice via different routes of injection 9, cytomegalovirus replication is species specific. This feature has severely hampered investigations of HCMV pathogenesis which are performed in different animal models (mouse, rat, guinea pig, rhesus monkey) and their respective genuine host-specific CMVs. All CMVs exhibit significant similarities in genome size and organization, tissue tropism and regulation of gene expression. They also induce similar pathologies in their respective host. Despite genomic diversity between HCMV and mouse cytomegalovirus (MCMV) (50% of the ORFs present in the human virus are identified in the murine CMV), the mouse model has recently proved to be advantageous, mostly because mutant strains can be tested for their ability to control viral replication in vivo. This has led to a genetic screen which enabled an estimation of the number of mouse genes expressed at the adult stage which compose the "resistome" to this virus 10. Altogether, this indicates that MCMV-infected mice represent an attractive model for the study of host-virus interactions in adults. The exploration of congenital CMV infection is more complex because differences in placental layer organization between human and mice impair the mother-to-fetus transmission of the viral infection in mice. Recently, direct injection of MCMV in the placenta on day 12.5 of gestation has enabled brain infection of mice neonates which led to hearing impairment 11. However, most investigations now use intraperitoneal injection of 4-20 hr-old neonates to provide systemic viral dissemination potentially leading to hematogenous brain infection, a model which is more relevant than that of an intracranial injection. This protocol provided important insights into CMV pathogenesis and more particularly, it was demonstrated that MCMV infection of newborns results in viral replication in neuronal and glial cells located in inflammatory foci which are infiltrated with mononuclear cells like macrophages 12. This report also described altered morphogenesis of the cerebellum accompanied with diminished granular neuron proliferation and migration and the induction of multiple interferon-stimulated genes. The essential role of CD8+T cells for the control of MCMV in the central nervous system was also reported by the same group 13. An important aspect to consider when analyzing the pathological effect of a microbe is the dynamics of the infection. In the case of MCMV, it is particularly crucial to explore and quantify the progression of viral dissemination into the developing brain in order to understand and anticipate the magnitude of the future neurobiological injuries. Traditionally, the quantification of the progression of an infection requires the regular sacrifice of infected animals to titer the pathogen in tissues, such as the brain, which are otherwise inaccessible. This type of protocol is now challenged by necessary improvement of animal welfare and the 3Rs (Reduce, Refine, Replace) principles 14. Using in vivo imaging technologies may allow a drastic reduction of the number of animals which are necessary in in vivo infection experiments. Here, we report and describe a time-course analysis of viral dissemination into the brain upon intraperitoneal MCMV-Luc injection to mouse neonates. Using the same animals, we tracked and monitored in vivo the sites of intense viral replication during a 2-week period.

<table border="1">
		<tbody>
		 <tr>
			<td></td>
			<td></td>
			<td></td>
			<td>Reagent/Material</td>
		 </tr>
		 <tr>
			<td>DMEM</td>
			<td>Fisher Scientific</td>
			<td>W3523A</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Methylene blue</td>
			<td>Sigma Aldrich</td>
			<td>319112</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Insulin needles</td>
			<td>VWR</td>
			<td>613-4897</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Ketamine</td>
			<td>CentraVet</td>
			<td>Ket 201</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Xylazine/Vetranal</td>
			<td>Sigma Aldrich</td>
			<td>46995</td>
			<td></td>
		 </tr>
		 <tr>
			<td>DPBS</td>
			<td>DUTSCHER</td>
			<td>P0436500</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Luciferin</td>
			<td>Caliper</td>
			<td>760504</td>
			<td></td>
		 </tr>
		 <tr>
			<td>gentamycin</td>
			<td>Sigma Aldrich</td>
			<td>G1272</td>
			<td></td>
		 </tr>
		 <tr>
			<td>penicillin/streptomycin</td>
			<td>Gibco</td>
			<td>15070</td>
			<td></td>
		 </tr>
		 <tr>
			<td>carboxymethylcellulose</td>
			<td>Sigma Aldrich</td>
			<td>C4888</td>
			<td></td>
		 </tr>
		 <tr>
			<td>formaldehyde</td>
			<td>Sigma Aldrich</td>
			<td>F8775</td>
			<td></td>
		 </tr>
		 <tr>
			<td>crystal violet</td>
			<td>Sigma Aldrich</td>
			<td>C3886</td>
			<td></td>
		 </tr>
		 <tr>
			<td></td>
			<td></td>
			<td></td>
			<td>Equipment</td>
		 </tr>
		 <tr>
			<td>IVIS 50</td>
			<td>Caliper/Perkin Elmer</td>
			<td></td>
			<td></td>
		 </tr>
		</tbody>
 </table>

use of in vivo imaging to monitor the progression of experimental mouse cytomegalovirus infection in neonates

Human Cytomegalovirus (HCMV or HHV-5) is a life-threatening pathogen in immune-compromised individuals. Upon congenital or neonatal infection, the virus can infect and replicate in the developing brain, which may induce severe neurological damage, including deafness and mental retardation. Despite the potential severity of the symptoms, the therapeutic options are limited by the unavailability of a vaccine and the absence of a specific antiviral therapy. Furthermore, a precise description of the molecular events occurring during infection of the central nervous system (CNS) is still lacking since observations mostly derive from the autopsy of infected children. Several animal models, such as rhesus macaque CMV, have been developed and provided important insights into CMV pathogenesis in the CNS. However, despite its evolutionary proximity with humans, this model was limited by the intracranial inoculation procedure used to infect the animals and consistently induce CNS infection. Furthermore, ethical considerations have promoted the development of alternative models, among which neonatal infection of newborn mice with mouse cytomegalovirus (MCMV) has recently led to significant advances. For instance, it was reported that intraperitoneal injection of MCMV to Balb/c neonates leads to infection of neurons and glial cells in specific areas of the brain. These findings suggested that experimental inoculation of mice might recapitulate the deficits induced by HCMV infection in children. Nevertheless, a dynamic analysis of MCMV infection of neonates is difficult to perform because classical methodology requires the sacrifice of a significant number of animals at different time points to analyze the viral burden and/or immune-related parameters. To circumvent this bottleneck and to enable future investigations of rare mutant animals, we applied in vivo imaging technology to perform a time-course analysis of the viral dissemination in the brain upon peripheral injection of a recombinant MCMV expressing luciferase to C57Bl/6 neonates.

A representative experiment is illustrated in Figure 1. Upon intraperitoneal injection of 50 PFUs of MCMV-Luc (Panel A shows a similar injection performed with Methylene blue to visualize the subcutaneous route of the needle), neonates were anesthetized and received simultaneously 0.3 mg of the luciferase substrate (Luciferin, Caliper). Fifteen minutes later, animals were placed ventral side up in the acquisition chamber of the IVIS 50 (In Vivo Imaging System, Caliper) and the light emitted by the whole ...

Watch this Scientific Journal Video about Use of In vivo Imaging to Monitor the Progression of Experimental Mouse Cytomegalovirus Infection in Neonates at JoVE.com

Use of In vivo Imaging to Monitor the Progression of Experimental Mouse Cytomegalovirus Infection in Neonates

Human Cytomegalovirus (HCMV) infection of neonates represents an important cause of mental retardation, yet the molecular events leading to virus-induced pathogenesis are still poorly understood. To investigate the dynamics of brain infection, we adapted whole-animal in vivo imaging to perform time-course analysis of neonates infected with a luciferase-recombinant virus.

Use of In vivo Imaging to Monitor the Progression of Experimental Mouse Cytomegalovirus Infection in Neonates

Human Cytomegalovirus (HCMV or HHV-5) is a life-threatening  pathogen in immune-compromised individuals. Upon congenital or neonatal  infection, the virus ...

use-vivo-imaging-to-monitor-progression-experimental-mouse

Research

JoVE Journal

Immunology and Infection

14.8K visualizações.  Université de Strasbourg. O citomegalovírus (HCMV) A infecção humana de recém-nascidos representa uma importante causa de retardo mental, mas os eventos moleculares que levam à induzida por vírus patogênese ainda são pouco compreendidos. Para investigar a dinâmica da infecção cerebral, adaptamos todo-animais In vivo Imagiologia para realizar a análise tempo-curso de recém-nascidos infectados com um vírus recombinante luciferase.