Developmental disorders of the mouse brain induced by murine cytomegalovirus: Animal models for congenital cytomegalovirus infection

Developmental disorders induced by congenital cytomegalovirus (CMV) infection mainly involve the central nervous system. The type and degree of the brain disorders seems to depend on infection time during gestation, virulence, route of infection and viral susceptible cells in each embryonal stage. Since transplacental transmission has been reported not to occur with murine CMV (MCMV), we developed mouse models for congenital CMV infection by surgical injection of MCMV into the mouse conceptus or embryo at different gestational stages. For the early stage, the mouse embryos were not infected with MCMV even after injecting the virus into the blastocysts, which were developed in the pseudo-pregnant mothers or cultured in vitro. Isolated whole mouse embryos of day 7.5 of gestation (E7.5), adsorbed with a high titer of MCMV and cultured for 3 days, were susceptible to MCMV infection. Therefore, the mouse embryo acquires the susceptibility around this period. Microphthalmia and cerebral atrophy were induced in mouse embryos after injection of MCMV into the conceptus on E8.5. Viral antigen-positive cells were widely distributed in the mesenchyme around the oral and nasal cavities and in the mesenchyme around the brain, especially the endothelial cells of vessels and the perivascular mesodermal cells, then infection extends to the eyes, brain or choroid plexus. This finding suggests that mesenchymal infection may be the critical step in disrupting organogenesis, resulting in brain disorders. For the late stage, mouse embryos were infected with MCMV by injecting the virus into the cerebral ventricles on E15.5. Brains of the offspring showed massive necrosis with gliomesodermal proliferation in the cerebral cortex. Viral antigen-positive cells were observed in laminar array in the lesion-free cortex and the hippocampus, suggesting that the infected cells migrate in association with the lamina formation. Imrnuno-histochemical double-staining showed that brain cells susceptible to MCMV infection may be mainly neuronal and endothelial cells, resulting in cerebral atrophy with reduction of neuronal cells and cystic lesions, presumably due to ischemic vascular changes.     

Susceptibility of mouse embryo to murine cytomegalovirus infection in early and mid-gestation stages

Summary The susceptibility of mouse embryonic cells to murine cytomegalovirus (MCMV) infection was studied by injecting the virus in the early and mid-gestation stages. For the early stage, blastocysts from BDF1 mice were injected with MCMV or minimal essential medium (MEM) by micromanipulator and returned to the uteri of pseudopregnant ICR mice. On day 11 of gestation, the embryos were examined immunohistochemically, using antibody specific to the early antigen of MCMV, and the placentae were examined by plaque assay. No infection was detected by either method. Furthermore, no infection was detected in MCMV-infected blastocysts that were cultured and examined for infection by immunofluorescence. For mid-gestation embryos, the conceptus was injected with MCMV on day 8.5 of gestation and was subjected to immunohistochemical analysis from day 10.5 to 12.5 of gestation. Viral antigen-positive cells were first observed in the placentae, then antigen-positive cells appeared among the blood cells, endothelial and mesodermal cells of the embryos. On day 12.5 of gestation, clusters of viral antigen-positive cells were sometimes observed in the hearts and livers. Although the incidence was lower, viral antigen-positive cells were also observed in the neuroectoderm and the eyes. These results suggest that MCMV does not infect early embryos and that infection first occurs in the placenta of postimplantation embryos, whence it extends through the blood cells to the endothelial and mesodermal cells of different embryonic regions, eventually extending to the neuroectoderm.     

Microphthalmia and cerebral atrophy induced in mouse embryos by infection with murine cytomegalovirus in midgestation.

Microphthalmia and cerebral atrophies were induced in mouse embryos after injection of murine cytomegalovirus (MCMV) into the conceptus at midgestation. The concepti of ICR mice on day 8.5 of gestation were injected with MCMV through the uterine wall, then pregnancies were allowed to continue. On day 15.5 of gestation, microphthalmia was observed in 19.2% of the MCMV-injected embryos (1 x 10(4) plaque-forming units). As the survival rate decreased when pregnancies were allowed to continue further, incidence of microphthalmia decreased, whereas cerebral atrophies, determined by examining the histological sections, were observed in 17.6% of the surviving mouse fetuses on day 18.5 of gestation. Microphthalmia was confirmed by microscopically measuring the eyes on the serial coronal sections. There were two types of microphthalmia: one with marked hypoplastic eye with periglobular mesenchymal proliferation, the other with small eye and lens without the mesenchymal proliferation. Immunohistochemical analysis was performed using antibodies specific to the nuclear antigen of MCMV. Viral antigen-positive cells were widely distributed in the mesenchymes around the oral and nasal cavities and in the mesenchymes around the brain, especially in the endothelial cells of the vessels and the perivascular mesodermal cells. In the eyes, viral antigen-positive cells were observed in mononuclear blood cells in the cavities of the vitreous bodies. These results suggest that the primary target of congenital cytomegalovirus infection may be the mesenchymal cells; then the infection extends to the eyes and brain. In addition, the mesenchymal infection may also disrupt their organogenesis, resulting in microphthalmia and cerebral atrophy. This experimental system may provide a model similar to congenital cytomegalovirus infection in humans.     

Murine cytomegalovirus infection of cultured mouse embryos.

Isolated mouse whole embryos of 7.5 days' gestation were infected with murine cytomegalovirus (MCMV) and cultured in pure rat serum. Although the MCMV infection had little effect on the survival and development of the embryos during 3 days of cultivation, immunohistochemical analysis of their serial sections using monoclonal antibody showed MCMV-infected cells in various portions of the embryos. This monoclonal antibody, when tested with the use of infected cultured mouse fibroblasts, reacted with nuclear antigen within 2 hours after infection and also reacted with nuclear inclusions in the late phase of infection. The viral antigen-positive cells detected by the monoclonal antibody were present in almost all of the ectoplacental cone and the yolk sac and in about 82% of the embryos. In the embryos, antigen-positive cells were frequently observed in the epithelium of the digestive tracts, endothelial cells of the blood vessels, and the mesodermal cells. In some of the embryos, viral antigen-positive cells were clearly observed in a small percentage of the blood cells. These findings indicate that blood cells, in addition to cell migration during embryogenesis, may play an important role in transmission of infectious virus into the embryos. Mouse whole embryo culture infected with MCMV can provide a model for the study of cellular tropism related to congenital infection by cytomegalovirus.     

Viral DNA detected by in situ hybridization in the developing mouse brain infected with murine cytomegalovirus.

To investigate the pathogenesis of brain abnormalities caused by congenital cytomegalovirus (CMV) infection, we previously reported experimental murine models of brain damage induced by intraventricular injection of murine CMV (MCMV) at the late stage of gestation. In the present study, viral DNA-positive cells in the damaged brain at different postnatal stages detected by in situ hybridization were compared with viral antigen-positive cells detected by an immunoperoxidase method using a monoclonal antibody against the immediate early antigen. At birth, the number of viral DNA-positive cells almost equalled that of viral antigen-positive cells. Seven to ten days after birth, the number of viral DNA-positive cells in the brain of MCMV-injected mice was one-fifth that of viral antigen-positive cells. Viral DNA-positive cells were more numerous in the hippocampus than in the cortex, and their density was dependent on the presence of viral antigen-positive cells. Dotted reaction products were observed in the nuclei of viral DNA-positive cells. These cells were rarely detected in lesions of later stages such as atrophy of the cortex and hippocampus, or the wall of the cystic lesions. These results suggest that viral DNA-positive cells detected by in situ hybridization are infected cells in which viral DNA replication is occurring actively.     

Viral DNA Detected by In Situ Hybridization in the Developing Mouse Brain Infected with Murine Cytomegalovirus

To investigate the pathogenesis of brain abnormalities caused by congenital cytomegalovirus (CMV) infection, we previously reported experimental murine models of brain damage induced by intraventricular injection of murine CMV (MCMV) at the late stage of gestation. In the present study, viral DNA-positive cells in the damaged brain at different postnatal stages detected by in situ hybridization were compared with viral antigen-positive cells detected by an immunoperoxidase method using a monoclonal antibody against the immediate early antigen. At birth, the number of viral DNA-positive cells almost equalled that of viral antigen-positive cells. Seven to ten days after birth, the number of viral DNA-positive cells in the brain of MCMV-injected mice was one-fifth that of viral antigen-positive cells. Viral DNA-positive cells were more numerous in the hippocampus than in the cortex, and their density was dependent on the presence of viral antigen-positive cells. Dotted reaction products were observed in the nuclei of viral DNA-positive cells. These cells were rarely detected in lesions of later stages such as atrophy of the cortex and hippocampus, or the wall of the cystic lesions. These results suggest that viral DNA-positive cells detected by in situ hybridization are infected cells in which viral DNA replication is occurring actively. Acta Pathol Jpn 41: 661–667, 1991.     

Differential expression of the immediate-early and early antigens in neuronal and glial cells of developing mouse brains infected with murine cytomegalovirus.

Brain disorders induced by congenital cytomegalovirus (CMV) infection may appear at a later time after birth as a consequence of persistent infection and/or the activation of a latent infection of the neural cells. We have analyzed the infection dynamics of the neural cells in the neonatal mouse brains infected with murine CMV (MCMV) in the late stage of gestation. First we prepared a rat monoclonal antibody to the major immediate-early (IE)-89K antigen and then used the antibody for comparison of the expression of early and late viral genes in the developing mouse brains. The cells expressing the IE-89K antigen were mostly localized in the ventricular and subventricular zones and were preferentially double stained with anti-glial fibrillary acidic protein and anti-nestin antibodies. In contrast, the cells expressing the early nuclear antigen, detected by the monoclonal antibody D5, were diffusely distributed in the cortex and the hippocampus and were mostly double labeled with anti-neuron-specific enolase antibody. In neonatal mouse brains infected congenitally with recombinant MCMV, which expressed lacZ as a late gene, the number of the early nuclear antigen-positive cells was much higher than that of the beta-galactosidase-expressing cells, the number of which was almost the same as that of the IE-89K antigen-positive cells. In addition, the distribution of viral DNA-rich cells detected by DNA-DNA hybridization was similar to that of the IE-89K antigen-positive cells. These results suggest that CMV may persistently infect neuronal cells, whereas lytic infection may preferentially occur in the glial cells in the developing brain.     

Cytomegalovirus-induced pneumonitis and myocarditis in newborn mice

Summary Genetically determined resistance to the lethal effects of infection with murine cytomegalovirus (MCMV) has been reported previously in adult and newborn mice. We examined the pathogenesis of MCMV infection in resistant (CBA, H-2^k) and susceptible (BALB/c, H-2^d) mice infected intraperitoneally on the day of birth. BALB/c mice developed a severe interstitial pneumonitis and myocarditis 10 days post-infection. Their pulmonary and cardiac tissues contained high MCMV titres and large numbers of MCMV-antigen positive cells. MCMV also infected the endothelial and myointimal cells of the coronary arteries in newborn BALB/c mice. Only limited infection and pathological changes were seen in CBA mice. Since the severe disease in BALB/c mice resembles the pneumonitis and less frequently reported myocarditis observed after perinatal HCMV infection, the newborn mouse model will be useful for studying the consequences and treatment of such infections, the influence of the host genotype on disease severity and the possible association between perinatal HCMV infection and atherosclerosis.     

Multifactorial protective mechanisms to limit viral replication in the lung of mice during primary murine cytomegalovirus infection

In this article, we investigated the protective host immune mechanisms against acute murine cytomegalovirus (MCMV) infection. For this purpose, we used various knockout mice lacking molecules, which include interferon-gamma (IFN-gamma), interferon-gamma receptor (IFN-gamma-R), interferon regulatory factor-1 (IRF-1), inducible nitric oxide synthase (iNOS), and perforin. We also used mutant mice lacking Fas molecule. When we infected these mice with MCMV and determined the viral titers in their lungs at different time points, we found that IFN-gamma, IFN-gamma-R, IRF-1, iNOS, and perforin-deficient mice developed significantly higher titers of infectious MCMV in the lung, compared to those observed in their respective wild-type controls. In the lungs of Fas-mutant mice, viral titers were similar to those obtained in wild-type mice.     

Pathogenesis of cytomegalovirus infection. Distribution of viral products, immune complexes and autoimmunity during latent murine infection.

During studies on the mechanisms of virus latency, reactivation and resultant tissue injury in mice infected with murine cytomegalovirus (MCMV) in utero or at birth, we found the occurrence of three distinct pathological groups. In the first group, mice died within 4 weeks of exposure to virus and showed evidence of tissue injury due to MCMV in multiple tissues and organs of the body. The second group consisted of mice which survived the initial infection and was composed of a minority (about 25%) which shed virus (chronically infected). The third group (about 75%) consisted of mice in which shedding of virus could not be detected (latently infected). Study of the latter group indicated that virus was not detected in brain, thymus, liver, kidneys, urine or serum by co-cultivation techniques or by cellular DNA-MCMV DNA hybridization. In contrast, virus could be activated from spleen cells by co-cultivation with allogenic but not syngeneic feeder cells and MCMV-DNA was detected in amounts equivalent to 3 to 4 virus genomes per 100 spleen cells. In both the latently infected and chronically infected mice, in all strains studied evidence of virus-antivirus immune complex deposits in the renal glomeruli occurred. Only one of the six infected strains (C57 Br/cdJ) studied showed manifestations of autoimmune disease with the formation of antibodies to nuclear antigens, DNA and soluble nucleoprotein.     

Functional disorder of primary immunity responding to respiratory syncytial virus infection in offspring mice exposed to a flame retardant,decabrominated diphenyl ether,perinatally

Perinatal exposure to a representative flame retardant, decabrominated diphenyl ether (DBDE), was shown previously to increase viral titers in the lungs of respiratory syncytial virus (RSV)‐infected offspring on day 5 post‐infection, resulting in exacerbation of pneumonia. In this study, the significant increase of pulmonary viral titers was confirmed even on day 1 post‐infection and the effect on the primary immune response to RSV infection were examined to assess a mode of DBDE action on developmental immunotoxicity. On day 1 after infection, the secretion of both TNF‐α and IL‐6 decreased significantly in the bronchoalveolar lavage fluid prepared from RSV‐infected offspring exposed to DBDE perinatally, but IL‐1β increased. However, in ex vivo lipopolysaccharide stimulation test, the productivity of TNF‐α in the bronchoalveolar lavage cells, which are mainly primary immune cells responding to RSV infection, prepared from offspring mice exposed to DBDE perinatally was not lower than that in the control. The primary immune cells retained normally the ability of cytokine production after the DBDE exposure. Gene expressions of innate pattern recognition receptors (Toll‐like receptor 3 and 4, melanoma differentiation‐associated gene‐5, and retinoic acid‐inducible gene I) in lung tissues were not affected by DBDE exposure. Because the levels of TNF‐α, IL‐6, and IL‐1β are known to be elevated in the lungs of RSV‐infected mice, these irregular productions due to perinatal DBDE exposure indicate a disorder of the primary immune response to RSV infection. Thus, perinatal exposure to DBDE was suggested to cause a functional disorder of primary immunity responding to RSV infection. J. Med. Virol. 82:1075–1082, 2010. © 2010 Wiley‐Liss, Inc.     

A murine model of dual infection with cytomegalovirus and Pneumocystis carinii: effects of virus-induced immunomodulation on disease progression

Despite the use of antimicrobial prophylaxis, cytomegalovirus (CMV) and Pneumocystis carinii (PC) pneumonia (PCP) are both leading causes of morbidity and mortality in immunocompromised patients. It has previously been reported that CMV infection modulates host immune responses with a variety of mechanisms which include the suppression of helper T cell functions and antigen presenting cell (APC) functions, both of which are critical for PCP resolution. However, the mechanisms of these interactions and other possible immune regulatory effects are not clearly understood. In this study, we investigated the impact of murine CMV (MCMV) induced immunomodulation on the progression of PCP in a co-infection model. Initial results show that dually infected mice had evidence of more severe PC disease, which include a greater loss of body weight, an excess lung PC burden and delayed clearance of PC from lungs, compared to mice with PC infection alone. At day 7 post-infection, dually infected mice had reduced numbers of MHC-II expressing cells in the lung interstitium and lymph nodes and reduced migration of CD11c+ cells to both the tracheobronchial lymph nodes and alveolar spaces. Dual infected mice showed elevated numbers of specific CD8 responses concomitant with a decrease in activated CD4+ T cells in both the lymph nodes and in alveolar spaces when compared to mice infected with MCMV alone. These data suggest that MCMV infection inhibits the immune responses generated against PC which contribute to the delayed clearance of the organism.     

Acute cytomegalovirus infections in leukemic mice.

Mice infected with 2 x 10(3) plaque-forming units of mouse cytomegalovirus (MCMV) 3 days after receiving 300 to 400 spleen focus-forming units of Friend leukemia virus developed a more severe MCMV infection than did normal animals. Increased severity was demonstrated by the increased amounts of MCMV recoverable from the salivary glands of leukemic mice 1 to 5 weeks postinfection. In addition, the difference in the number of virus isolations from the kidneys, spleens, livers, and lungs of animals (74 to 120) coinfected with MCMV and Friend leukemia virus compared with animals (49 of 120) infected with MCMV alone was significant (P less than 0.01). Both the 50% lethal dose and 50% infectious dose of MCMV in leukemic mice were lower than in normal animals. MCMV and Friend leukemia virus appear to interact by suppressing the ability of infected spleen cells to respond to mitogen-induced stimulation. The observations of increased severity of MCMV infections in leukemic mice closely parallel the situation observed in human leukemia patients who are at an increased risk of disease due to human cytomegalovirus infections. This mouse model may be useful in assessing the effect of antiviral (cytomegalovirus) therapy.     

A flow cytometry-based method for detecting antibody responses to murine cytomegalovirus infection

An assay based on target cells infected with green fluorescent protein labeled murine cytomegalovirus (GFP-MCMV) and dual color flow cytometry for detecting antibody to MCMV is described. After optimizing conditions for this technique, kinetics of anti-MCMV IgG antibody response was tested in susceptible (BALB/c) and resistant (C57BL/6) mouse strains following primary MCMV infection. Previously published antibody kinssetics were confirmed in susceptible mice, with peak IgG response seen approximately 8 weeks after primary infection, decreasing by 20 weeks after infection. In contrast, MCMV resistant C57BL/6 mice showed significantly lower IgG antibody responses than susceptible mice. Although several techniques have been previously described to detect murine antibody responses to MCMV, including nuclear anti-complement immunofluorescence, viral immunoblotting, complement fixation, indirect immunofluorescence, indirect hemagglutination, and enzyme-liked immunosorbent assay techniques, these techniques are all time consuming and laborious. The technique presented is a simple time efficient alternative to detect previous MCMV antibody responses in experimentally infected mice.     

Protective effect of black seed oil from Nigella sativa against murine cytomegalovirus infection

In this study, antiviral effect of black seed oil (BSO) from Nigella sativa was investigated using murine cytomegalovirus (MCMV) as a model. The viral load and innate immunity mediated by NK cells and Mφ during early stage of the infection were analyzed. Intraperitoneal (i.p.) administration of BSO to BALB/c mice, a susceptible strain of MCMV infection, strikingly inhibited the virus titers in spleen and liver on day 3 of infection with 1x10(5) PFU MCMV. This effect coincided with an increase in serum level of IFN-gamma. Although BSO treatment decreased both number and cytolytic function of NK cells on day 3 of infection, it increased numbers of Mφ and CD4(+) T cells. On day 10 of infection, the virus titer was undetectable in spleen and liver of BSO-treated mice, while it was detectable in control mice. Although spleen of both control and BSO-treated mice showed similar CTL activities on day 10 after infection, serum level of IFN-gamma in BSO-treated mice was higher. Furthermore, BSO treatment upregulated suppressor function of Mφ in spleen. These results show that BSO exhibited a striking antiviral effect against MCMV infection which may be mediated by increasing of Mφ number and function, and IFN-gamma production.     

Distribution of mouse cytomegalovirus in organs of white mice experimentally infected by natural route

One, 10, 21-day-old and adult mice were inoculated by peroral and/or intranasal routes with mouse cytomegalovirus (MCMV). In animals surviving generalized infection, the virus could be demonstrated in salivary glands up to 123 days postinfection (p.i.). In mouse females which had eaten their infected and diseased offspring, the virus was detectable in salivary glands up to day 121, p.i. On day 16 p.i., the virus was present in salivary glands, lungs and kidneys of mice of different age groups, but no virus was recovered from their Gasserian ganglia. These results were compared with those obtained after infection with murine alpha herpesvirus.     

Correlation between natural killer cell activation in the bone marrow and haemopoietic dysfunction following cytomegalovirus infection of mice.

We describe here the activation of natural killer (NK) cells in the bone marrows and spleens of mice infected with murine cytomegalovirus (MCMV). NK activity at these sites peaked at day 2 to 3 post-infection (p.i.) and declined between days 6 and 10 p.i. in BALB/c and C57BL/6 mice. In BALB/c mice, the increases in NK activity coincided with depletion of colony-forming units of the granulocyte-monocyte lineage (CFU-GM) from the marrow. CFU-GM depletion in MCMV-infected C57BL/6 mice was less severe, despite the presence of activated NK cells in the marrow. Treatment of BALB/c mice with anti-asialo GM1 prior to MCMV infection resulted in less severe CFU-GM depletion at day 2 p.i. than infection with MCMV alone. When homozygous C57BL/6 or CBA/CaH bg/bg mice were infected with MCMV, depletion of marrow CFU-GM was more severe than in their heterozygous littermates. Finally, we observed some inhibition of colony formation when marrow cells from MCMV-infected and uninfected BALB/c donors were mixed and incubated prior to the CFU-GM assay. These results suggest that activated NK cells may contribute to depletion of haemopoietic cells soon after MCMV infection of BALB/c mice, but may limit the loss of these cells in C57BL/6 and CBA/CaH mice.     

Cytomegalovirus infection of murine testicular interstitial Leydig cells.

We studied the susceptibility of mouse testicular interstitial Leydig cells to cytomegalovirus both in vivo and in vitro. The in vivo studies included intratesticular and intraperitoneal infection of 6-week-old mice with murine cytomegalovirus (MCMV); the in vitro studies involved an MCMV-Leydig cell interaction using a Leydig tumor cell line (I-10). MCMV-specific antigens were detected in interstitial Leydig cells in sections of MCMV-inoculated testes by an indirect immunofluorescence test. MCMV DNA was also localized in the same testes cells derived from mice, which received intratesticular and intraperitoneal MCMV inoculations, respectively, by in situ DNA-RNA hybridization. Cytopathic effects were seen in MCMV-infected I-10 cell cultures 2 or more days after exposure to MCMV. The infected cells showed intranuclear inclusions characteristic of cytomegalovirus when stained with May-Grunwald-Giemsa stain. The indirect immunofluorescence test was also positive with MCMV-infected I-10 cells. MCMV DNA was detected in these cells by in situ DNA-RNA cytohybridization, and the presence of viral particles in MCMV-infected I-10 cells was confirmed by electron microscopy. Thus, we conclude that the interstitial Leydig cell is susceptible to MCMV infection both in vivo and in vitro.     

Interstitial pneumonia and subclinical infection after intranasal inoculation of murine cytomegalovirus.

Although cytomegalovirus (CMV) infections are common throughout the world, little is known about the means of person-to-person transmission. To determine whether infection could be established by a respiratory route, studies were conducted in a murine CMV (MCMV) model by using intranasal inoculation. The infectious dose which resulted in pulmonary and systemic infection of half the mice was 100 plaque-forming units of MCMV. Here, infection was subclinical, but virus replicated in the lungs and subsequently disseminated via the blood to other organs within 7 days. The serum immunofluorescence antibody titer peaked by day 21. None of these mice died, although focal peribronchial interstitial pneumonitis was found in infected animals. In mice given greater than or equal to 10(4) plaque-forming units of MCMV intranasally, severe diffuse interstitial pneumonitis resulted uniformly, closely resembling that seen in immunocompromised patients and in newborn infants, and 20% of the animals died. Normal pulmonary architecture was obliterated by sheets of histiocytes, many containing MCMV intranuclear inclusions, and by accumulation of proteinaceous fluid in the interstitial and alveolar spaces. Of relevance to human disease, these experiments show that MCMV as a sole pathogen can cause severe interstitial pneumonitis in normal mice and that subclinical systemic infection results from respiratory inoculation of small amounts of virus.