Persisting murine cytomegalovirus can reactivate and has unique transcriptional activity in ocular tissue

Retinal and Choroidal Pathologies in Aged BALB/c Mice Following Systemic Neonatal Murine Cytomegalovirus Infection

Although pathologies associated with acute virus infections have been extensively studied, the effects of long-term latent virus infections are less well understood. Human cytomegalovirus, which infects 50% to 80% of humans, is usually acquired during early life and persists in a latent state for the lifetime. The purpose of this study was to determine whether systemic murine cytomegalovirus (MCMV) infection acquired early in life disseminates to and becomes latent in the eye and if ocular MCMV can trigger in situ inflammation and occurrence of ocular pathology. This study found that neonatal infection of BALB/c mice with MCMV resulted in dissemination of virus to the eye, where it localized principally to choroidal endothelia and pericytes and less frequently to the retinal pigment epithelium (RPE) cells. MCMV underwent ocular latency, which was associated with expression of multiple virus genes and from which MCMV could be reactivated by immunosuppression. Latent ocular infection was associated with significant up-regulation of several inflammatory/angiogenic factors. Retinal and choroidal pathologies developed in a progressive manner, with deposits appearing at both basal and apical aspects of the RPE, RPE/choroidal atrophy, photoreceptor degeneration, and neovascularization. The pathologies induced by long-term ocular MCMV latency share features of previously described human ocular diseases, such as age-related macular degeneration.

Platelet-endothelial associations may promote cytomegalovirus replication in the salivary gland in mice

Platelet decline is a feature of many acute viral infections, including cytomegalovirus (CMV) infection in humans and mice. Platelet sequestration in association with other cells, including endothelium and circulating leukocytes, can contribute to this decline and influence the immune response to and pathogenesis of viral infection. We sought to determine if platelet-endothelial associations (PEAs) contribute to platelet decline during acute murine CMV (mCMV) infection, and if these associations affect viral load and production. Male BALB/c mice were infected with mCMV (Smith strain), euthanized at timepoints throughout acute infection and compared to uninfected controls. An increase in PEA formation was confirmed in the salivary gland at all post-inoculation timepoints using immunohistochemistry for CD41+ platelets co-localizing with CD34+ vessels. Platelet depletion did not change amount of viral DNA or timecourse of infection, as measured by qPCR. However, platelet depletion reduced viral titer of mCMV in the salivary glands while undepleted controls demonstrated robust replication in the tissue by plaque assay. Thus, platelet associations with endothelium may enhance the ability of mCMV to replicate within the salivary gland. Further work is needed to determine the mechanisms behind this effect and if pharmacologic inhibition of PEAs may reduce CMV production in acutely infected patients.

Suppressor of Cytokine Signaling 1 (SOCS1) and SOCS3 Are Stimulated within the Eye during Experimental Murine Cytomegalovirus Retinitis in Mice with Retrovirus-Induced Immunosuppression

AIDS-related human cytomegalovirus retinitis remains the leading cause of blindness among untreated HIV/AIDS patients worldwide. To study mechanisms of this disease, we used a clinically relevant animal model of murine cytomegalovirus (MCMV) retinitis with retrovirus-induced murine AIDS (MAIDS) that mimics the progression of AIDS in humans. We found in this model that MCMV infection significantly stimulates ocular suppressor of cytokine signaling 1 (SOCS1) and SOCS3, host proteins which hinder immune-related signaling by cytokines, including antiviral type I and type II interferons. The present study demonstrates that in the absence of retinal disease, systemic MCMV infection of mice without MAIDS, but not in mice with MAIDS, leads to mild stimulation of splenic SOCS1 mRNA. In sharp contrast, when MCMV is directly inoculated into the eyes of retinitis-susceptible MAIDS mice, high levels of intraocular SOCS1 and SOCS3 mRNA and protein are produced which are associated with significant intraocular upregulation of gamma interferon (IFN-γ) and interleukin-6 (IL-6) mRNA expression. We also show that infiltrating macrophages, granulocytes, and resident retinal cells are sources of intraocular SOCS1 and SOCS3 protein production during development of MAIDS-related MCMV retinitis, and SOCS1 and SOCS3 mRNA transcripts are detected in retinal areas histologically characteristic of MCMV retinitis. Furthermore, SOCS1 and SOCS3 are found in both MCMV-infected cells and uninfected cells, suggesting that these SOCS proteins are stimulated via a bystander mechanism during MCMV retinitis. Taken together, our findings suggest a role for MCMV-related stimulation of SOCS1 and SOCS3 in the progression of retinal disease during ocular, but not systemic, MCMV infection.IMPORTANCE Cytomegalovirus infection frequently causes blindness in untreated HIV/AIDS patients. This virus manipulates host cells to dysregulate immune functions and drive disease. Here, we use an animal model of this disease to demonstrate that cytomegalovirus infection within eyes during retinitis causes massive upregulation of immunosuppressive host proteins called SOCS. As viral overexpression of SOCS proteins exacerbates infection with other viruses, they may also enhance cytomegalovirus infection. Alternatively, the immunosuppressive effect of SOCS proteins may be protective against immunopathology during cytomegalovirus retinitis, and in such a case SOCS mimetics or overexpression treatment strategies might be used to combat this disease. The results of this work therefore provide crucial basic knowledge that contributes to our understanding of the mechanisms of AIDS-related cytomegalovirus retinitis and, together with future studies, may contribute to the development of novel therapeutic targets that could improve the treatment or management of this sight-threatening disease.

What we have learned from animal models of HCMV

Although human cytomegalovirus (HCMV) primary infection is generally asymptomatic, in immune-compromised patients HCMV increases morbidity and mortality. As a member of the betaherpesvirus family, in vivo studies of HCMV are limited due to its species specificity. CMVs from other species are often used as surrogates to express HCMV genes/proteins or used as models for inferring HCMV protein function in humans. Using innovative experiments, these animal models have answered important questions about CMV's life cycle, dissemination, pathogenesis, immune evasion, and host immune response. This chapter provides CMV biologists with an overview of the insights gained using these animal models. Subsequent chapters will provide details of the specifics of the experimental methods developed for each of the animal models discussed here.

Case of cytomegalovirus retinitis aggravated by sub-Tenon injection of triamcinolone acetonide with subsequent metastatic liver cancer

We report a case of cytomegalovirus (CMV) retinitis in an immunocompetent patient who was resistant to antiviral treatment, and in whom fatal metastatic liver cancer was later detected. A 74-year-old Japanese man visited our ophthalmology clinic in May 2011. He had a history of well controlled type 2 diabetes and colon cancer, and underwent successful surgical treatment in 2008. In April 2011, he was diagnosed with uveitis affecting his left eye and received posterior sub-Tenon injection of triamcinolone acetonide. He was referred to us because of aggravation of the retinal lesion. Funduscopic examination of the left eye revealed arcuate, whitish, necrotizing retinitis with hemorrhage along the temporal arcade of the retina. Polymerase chain reaction of the aqueous fluid was positive for CMV DNA. Because of diagnosis of CMV retinitis in his left eye, he was referred to an internist and investigated for systemic CMV infection or any serious disease which could cause immunocompromise, but neither was detected. Despite an intensive course of intravitreous ganciclovir and oral valganciclovir, the retinitis did not resolve. In June 2012, 14 months after the initial ocular symptoms, metastatic liver cancer was found and the patient passed away. When CMV retinitis is resistant to antiviral treatment or recurs in an immunocompetent patient, it is important that ophthalmologists undertake systemic investigation for occult malignancy.

Viral Infections of Laboratory Mice

Viral infections of laboratory mice have considerable impact on research results, and prevention of such infections is therefore of crucial importance. This chapter covers infections of mice with the following viruses: herpesviruses, mousepox virus, murine adenoviruses, polyomaviruses, parvoviruses, lactate dehydrogenase-elevating virus, lymphocytic choriomeningitis virus, mammalian orthoreovirus serotype 3, murine hepatitis virus, murine norovirus, murine pneumonia virus, murine rotavirus, Sendai virus, and Theiler’s murine encephalomyelitis virus. For each virus, there is a description of the agent, epizootiology, clinical symptoms, pathology, methods of diagnosis and control, and its impact on research.

Kinetics of ocular and systemic antigen-specific T-cell responses elicited during murine cytomegalovirus retinitis

Cytomegalovirus (CMV) reactivation in the retina of immunocompromized patients is a cause of significant morbidity as it can lead to blindness. The adaptive immune response is critical in controlling murine CMV (MCMV) infection in MCMV-susceptible mouse strains. CD8(+) T cells limit systemic viral replication in the acute phase of infection and are essential to contain latent virus. In this study, we provide the first evaluation of the kinetics of anti-viral T-cell responses after subretinal infection with MCMV. The acute response was characterized by a rapid expansion phase, with infiltration of CD8(+) T cells into the infected retina, followed by a contraction phase. MCMV-specific T cells displayed biphasic kinetics with a first peak at day 12 and contraction by day 18 followed by sustained recruitment of these cells into the retina at later time points post-infection. MCMV-specific CD8(+) T cells were also observed in the draining cervical lymph nodes and the spleen. Presentation of viral epitopes and activation of CD8(+) T cells was widespread and could be detected in the spleen and the draining lymph nodes, but not in the retina or iris. Moreover, after intraocular infection, antigen-specific cytotoxic activity was detectable and exhibited kinetics equivalent to those observed after intraperitoneal infection with the same viral dose. These data provide novel insights of how and where immune responses are initiated when viral antigen is present in the subretinal space.

Expression of Matrix Metalloproteinases 2 and 9 in Experimental Corneal Injury and Fungal Keratitis

PURPOSE

Levels of matrix metalloproteinases (MMPs) can be modulated during corneal infection, but little is known about MMP profiles during fungal keratitis. The purpose of this study was to determine the effect of corneal trauma and immunosuppressive treatment on the expression kinetics of MMP-2 and MMP-9 during experimental keratomycosis.

METHODS

Corneas of immunocompetent and cyclophosphamide-treated adult BALB/c mice were topically inoculated with 1 x 10 culturable units of Fusarium solani or mock-inoculated with or without superficial corneal scarification. Eyes were scored daily for disease severity and processed for zymography after 1.5 hours, 6 hours, 1 day, 4 days, or 8 days. Gelatinase activity was densitometrically quantitated and normalized to MMP-2 and MMP-9 controls.

RESULTS

MMP-9 levels in nontraumatized eyes transiently increased at 6 hours after fungal exposure, but this increase was inhibited by cyclophosphamide treatment. Corneal injury significantly induced early MMP-9 expression that returned to baseline levels within 4 days. Cyclophosphamide pretreatment reduced and delayed MMP-9 after scarification. Fusarium exposure dampened the MMP-9 response to corneal trauma in immunocompetent and cyclophosphamide-treated animals. Ocular levels of MMP-2 were not affected by scarification, fungal exposure, or immunosuppressive treatment.

CONCLUSIONS

Ocular MMP-9 levels, but not MMP-2 levels, increased soon after corneal injury. A similar, although muted, MMP-9 response occurs during early filamentous fungal keratitis, with a kinetic profile similar to corneal disease progression. The early stage of ulcerative keratitis may involve selective regulation of corneal matrix metalloproteinases, suggesting an initial opportunity for therapeutic intervention.

The human eye (retina): a site of persistent HCMV infection?

BACKGROUND

Human cytomegalovirus (HCMV) retinitis frequently occurs in severely naturally and iatrogenically immunocompromised patients. It has been shown that the immune-privileged retina is a major site of HCMV infection in AIDS patients. It is conceivable either that during the immunosuppression HCMV infection reactivates in various other organs viremically affecting the retina or that HCMV persisting in the retina may locally reactivate and result in HCMV retinitis.

METHODS

As there is still controversy about the sites of HCMV latency and persistence we investigated 75 eyes of HIV-seronegative patients undergoing enucleation due to a variety of malignant and non-viral benign ophthalmic disorders for the retinal presence of HCMV antigen and DNA.

RESULTS

None of the analyzed patients had symptoms of HCMV retinitis. Immunohistologic staining as well as Taq Man DNA PCR analysis showed all samples to be free of HCMV.

CONCLUSIONS

Our data suggest that the human eye is rather unlikely to be a site of productive or latent HCMV persistence.

Role for tumor necrosis factor alpha in murine cytomegalovirus transcriptional reactivation in latently infected lungs

Interstitial pneumonia is a major clinical manifestation of primary or recurrent cytomegalovirus (CMV) infection in immunocompromised recipients of a bone marrow transplant. In a murine model, lungs were identified as a prominent site of CMV latency and recurrence. Pulmonary latency of murine CMV is characterized by high viral genome burden and a low incidence of variegated immediate-early (IE) gene expression, reflecting a sporadic activity of the major IE promoters (MIEPs) and enhancer. The enhancer-flanking promoters MIEP1/3 and MIEP2 are switched on and off during latency in a ratio of approximately 2:1. MIEP1/3 latency-associated activity generates the IE1 transcript of the ie1/3 transcription unit but not the alternative splicing product IE3 that encodes the essential transactivator of early gene expression. Splicing thus appeared to be an important checkpoint for maintenance of latency. In accordance with previous work of others, we show here that signaling by the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha) activates IE1/3 transcription in vivo. As an addition to current knowledge, Poisson distribution analysis revealed an increased incidence of IE1/3 transcriptional events as well as a higher amount of transcripts per event. Notably, TNF-alpha promoted the splicing to IE3 transcripts, but transcription did not proceed to the M55/gB early gene. Moreover, the activated transcriptional state induced by TNF-alpha did not predispose latently infected mice to a higher incidence of virus recurrence after hematoablative treatment. In conclusion, TNF-alpha is an important inductor of IE gene transcriptional reactivation, whereas early genes downstream in the viral replicative cycle appear to be the rate-limiting checkpoint(s) for virus recurrence.

Improved detection and quantification of mouse cytomegalovirus by real-time PCR

During latent cytomegalovirus (CMV) infection, viral presence cannot be detected by plaque assay. Therefore, we assessed the applicability of real-time PCR for temporal determination of virus dissemination in two different mouse strains. Eight-week-old BALB/c and C57BL/6J mice were infected with mouse CMV (MCMV) and sacrificed at 1, 2, 4, 6, 14 and 28 days post infection. Real-time PCR was used to determine MCMV copy number in the heart, bone marrow cells, aorta and blood. In lung, liver, salivary gland and spleen the presence of MCMV was determined both by plaque assay and real-time PCR. In analogy with the plaque assay, the real-time PCR technique revealed higher numbers of MCMV genomic copies in all organs obtained from BALB/c mice when compared with C57BL/6J mice, demonstrating the applicability of the technique. A significant correlation was observed between both assays when a positive test result was seen with both assays. Nonetheless, lower viral infectivity titers were found compared to real-time PCR data. Thus, the real-time PCR technique is more sensitive in detecting the presence of MCMV and is therefore well suited for (dose-response) intervention studies aimed at studying virus eradication.

Human cytomegalovirus retinitis: pathogenicity, immune evasion and persistence

Human cytomegalovirus (HCMV) retinitis frequently occurs in severely naturally and iatrogenically immunocompromised patients. It has been shown that the immune-privileged retinal pigment epithelium (RPE) is a major site of persistent HCMV. Recently, evidence has accumulated to show that HCMV immediate early (IE) gene expression in RPE cells deviates ocular antiviral inflammation via FasL. Moreover, unlike in other cell types, the HCMV major IE1/2 enhancer promoter (MIEP) resists activation by proinflammatory stimuli mediated by the transcription factor NF-kappaB. However, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) found at elevated levels in transplant recipients and AIDS patients with retinitis sensitize RPE cells and other retinal cells to FasL-mediated apoptosis, thus contributing to retina destruction and necrosis rather than inflammation. These specific features of RPE cells in conjunction with deregulated immune responses of immunocompromised patients seem to contribute to virus persistence and pathogenesis within the immune-privileged ocular retina.