Human cytomegalovirus replicates in primary human bone marrow cells

Jeor S, Almeida-Porada G. Perivascular stromal cells as a potential reservoir of human cytomegalovirus

Human cytomegalovirus (HCMV) infection is an important cause of morbidity and mortality among both solid organ and hematopoietic stem cell transplant recipients. Identification of cells throughout the body that can potentially serve as a viral reservoir is essential to dissect mechanisms of cell tropism and latency and to develop novel therapies. Here, we tested and compared the permissivity of liver-, brain-, lung (LNG)- and bone marrow (BM)-derived perivascular mesenchymal stromal cells (MSC) to HCMV infection and their ability to propagate and produce infectious virus. Perivascular MSC isolated from the different organs have in common the expression of CD146 and Stro-1. While all these cells were permissive to HCMV infection, the highest rate of HCMV infection was seen with LNG-MSC, as determined by viral copy number and production of viral particles by these cells. In addition, we showed that, although the supernatants from each of the HCMV-infected cultures contained infectious virus, the viral copy number and the quantity and timing of virus production varied among the various organ-specific MSC. Furthermore, using quantitative polymerase chain reaction, we were able to detect HCMV DNA in BM-MSC isolated from 7 out of 19 healthy, HCMV-seropositive adults, suggesting that BM-derived perivascular stromal cells may constitute an unrecognized natural HCMV reservoir.

Human cytomegalovirus sequences expressed in latently infected individuals promote a latent infection in vitro

Latency enables human cytomegalovirus (HCMV) to persist in the hematopoietic cells of infected individuals indefinitely and prevents clearance of the pathogen. Despite its critical importance to the viral infectious cycle, viral mechanisms that contribute to latency have not been identified. We compared the ability of low-passage clinical and laboratory-adapted strains of HCMV to establish a latent infection in primary human CD34(+) cells. The low-passage strains, Toledo and FIX, established an infection with the hallmarks of latency, whereas the laboratory strains, AD169 and Towne, replicated producing progeny virus. We hypothesized that ULb' region of the genome, which is unique to low-passage strains, may encode a latency-promoting activity. We created and analyzed recombinant viruses lacking segments or individual open reading frames (ORFs) in the ULb' region. One 5-kb segment, and more specifically the UL138 ORF, was required for HCMV to establish and/or maintain a latent infection in hematopoietic progenitor cells infected in vitro. This is the first functional demonstration of a virus-coded sequence required for HCMV latency. Importantly, UL138 RNA was expressed in CD34(+) cells and monocytes from HCMV-seropositive, healthy individuals. UL138 might be a target for antivirals against latent virus.

Transfusion-Transmitted Cytomegalovirus: Lessons From a Murine Model

Transfusion-transmitted cytomegalovirus (CMV) infection (TT-CMV) continues to complicate blood transfusion therapy, which can lead to severe morbidity or mortality in immunocompromised or immuno-immature recipients. The biological mechanisms that underlie TT-CMV (eg, viral latency in donor monocytes or stimulatory signals in the transfusion recipient leading to cytomegalovirus reactivation) are difficult to study in humans, but can be addressed in animal models. In this review, we discuss a mouse blood transfusion model, which can be used to investigate these issues as well as to validate methods to prevent TT-CMV in at-risk patients.

Human cytomegalovirus inhibits cytokine-induced macrophage differentiation

Human cytomegalovirus (HCMV) infection in immunocompromised patients is associated with impaired immunological function. Blood monocytes, which differentiate into macrophage effector cells, are of central importance for immune reactivity. Here, we demonstrate that HCMV transiently blocks cytokine-induced differentiation of monocytes into functionally active phagocytic macrophages. In HCMV-treated cultures, the cells had classical macrophage markers but lacked the classical morphological appearance of macrophages and had impairments in migration and phagocytosis. Even at very low multiplicities of infection, macrophage differentiation was almost completely inhibited. The inhibition appeared to be mediated by a soluble factor released upon viral treatment of monocytes. Human immunodeficiency virus or measles virus had no such effects. These findings suggest that HCMV impairs immune function by blocking certain aspects of cytokine-induced differentiation of monocytes and demonstrate an efficient pathway for this virus to evade immune recognition that may have clinical implications for the generalized immunosuppression often observed in HCMV-infected patients.

Human cytomegalovirus (HCMV) infection in osteosarcoma cell line suppresses GM-CSF production by induction of TGF-beta

This study was performed to elucidate the possible mechanism of the disturbance of hemopoiesis by HCMV infection. Saos-2 cells constitutively express mRNA of GM-CSF, and its expression was profoundly decreased by HCMV infection, which required full replication of the virus and was mediated by soluble factors released from the HCMV-infected Saos-2 cells. TGF-beta1 production was statistically and significantly increased from one day after HCMV infection. Expression and production of GM-CSF in Saos-2 cells were restored when a culture supernatant of HCMV-infected Saos-2 cells was reacted with neutralizing anti-TGF-beta antibody. Conclusively, HCMV inhibits GM-CSF expression in Saos-2 cells partly by the increased production of TGF-beta1.

Cytomegalovirus mediated myelosuppression

Cytomegalovirus (CMV) has long been associated with myelosuppression. Evidence for this association has been provided from in vitro studies, statistical analysis of clinical studies, informative case reports, and murine models. Reports differ as to how CMV mediates myelosuppression. Some data indicate direct infection of hematopoietic progenitors and their progeny, others indicate that the supportive microenvironment is infected and thereby its supportive function compromised. In this report we review data suggesting that the severity of myelosuppression in patients is associated with particular CMV genotypes identified by variations in the glycoprotein B gene.

CMV and blood transfusions

Among the human herpesviruses, cytomegalovirus (CMV) is the only one that has assumed significant importance in blood transfusion. Transfusion transmission of CMV (TT-CMV) to seronegative immunocompromised patients can lead to lethal CMV disease. Studies over the past 30 years have demonstrated that monocytes latently infected with CMV represent the primary vector for TT-CMV, and that TT-CMV can be largely abrogated by transfusing at-risk patients with either seronegative units or blood filtered to remove white blood cells. However, the small number of cases of breakthrough TT-CMV that follow transfusion of either seronegative or filtered blood still produce morbidity and mortality. These circumstances have motivated ongoing efforts to provide improved protection from TT-CMV, including the use of CMV DNA amplification for blood screening, and pathogen inactivation to sterilise all blood components prior to transfusion.

Human cytomegalovirus infection of bone marrow myofibroblasts enhances myeloid progenitor adhesion and elicits viral transmission

Human cytomegalovirus (CMV) infection of bone marrow transplant recipients can cause pancytopenia, as well as life-threatening interstitial pneumonia. CMV replicates actively in bone marrow stromal cells, whereas it remains latent in hematopoietic progenitors. Our aim was to study the influence of CMV infection on adherence of CD34(+) cells to the myofibroblastic component of human bone marrow and examine transmission of virus from myofibroblasts to CD34(+) cells. We show that smooth actin, but not fibronectin, organization is markedly modified by CMV infection of bone marrow stromal myofibroblasts. Nonetheless, CMV infection led to increased adherence of the CD34(+) progenitor cell line, KG1a, relative to adherence to uninfected myofibroblasts from the same donors. Adherence of CD34(+) cells to infected bone marrow myofibroblasts resulted in transfer of virions and viral proteins through close cell-to-cell contacts. This phenomenon may play a role in the pathophysiology of CMV bone marrow infection and in eventual virus dissemination.

Superoxide generation by monocytes following infection with human cytomegalovirus

A significant level of superoxide (O2-) generation was observed in a U937-derived subclone following infection with human cytomegalovirus (HCMV). Although there were no detectable levels of viral mRNA and/or protein expression, HCMV DNA content transiently increased immediately before O2- generation. Similarly, O2- generation was also observed in peripheral blood monocytes derived from healthy donors.

Spread of Human Cytomegalovirus (HCMV) After Infection of Human Hematopoietic Progenitor Cells: Model of HCMV Latency

Clinical experience and laboratory data suggest that human cytomegalovirus (HCMV) is present in peripheral blood of seropositive individuals in a latent or persistent state and can be transmitted via blood products and be reactivated in seropositive imunocompromised patients. The pathophysiology of HCMV latency and the nature of HCMV interaction with hematopoietic cells remains unknown. In this study, we investigated the infection of bone marrow (BM) progenitor cells and their progeny as a model of HCMV latency. A clinical isolate and the recombinant laboratory strain Towne/lox containing the Escherichia coli β galactosidase (β-gal) gene regulated by immediately early (IE) HCMV promoter were used to infect highly purified CD34+ cells. Although the infection of these cells with a clinical isolate was associated with an inhibition of proliferation by 59%, an expansion of progeny derived from these cells was possible. Polymerase chain reaction analysis and staining for β-gal have shown that HCMV persisted in infected BM CD34+ cells and their progeny for up to 4 weeks. However, IE and late gene products (mRNA and protein) were detected only late in the course of infection and their expression correlated with terminal macrophage differentiation of the CD34+-derived progeny. Although early infection of CD34+ progenitor cells was not productive (as shown by the plaque assay), infectious virus could be recovered from the terminally differentiated cultures. BM progenitor cells may serve as a reservoir of the latent virus with limited transcription. Proliferation and monocytic maturation of infected progenitors may lead to the numerical expansion of HCMV-infected cells, which serve as a source of HCMV dissemination and reactivation.

Spread of Human Cytomegalovirus (HCMV) After Infection of Human Hematopoietic Progenitor Cells: Model of HCMV Latency

Clinical experience and laboratory data suggest that human cytomegalovirus (HCMV) is present in peripheral blood of seropositive individuals in a latent or persistent state and can be transmitted via blood products and be reactivated in seropositive imunocompromised patients. The pathophysiology of HCMV latency and the nature of HCMV interaction with hematopoietic cells remains unknown. In this study, we investigated the infection of bone marrow (BM) progenitor cells and their progeny as a model of HCMV latency. A clinical isolate and the recombinant laboratory strain Towne/lox containing the Escherichia coli β galactosidase (β-gal) gene regulated by immediately early (IE) HCMV promoter were used to infect highly purified CD34+ cells. Although the infection of these cells with a clinical isolate was associated with an inhibition of proliferation by 59%, an expansion of progeny derived from these cells was possible. Polymerase chain reaction analysis and staining for β-gal have shown that HCMV persisted in infected BM CD34+ cells and their progeny for up to 4 weeks. However, IE and late gene products (mRNA and protein) were detected only late in the course of infection and their expression correlated with terminal macrophage differentiation of the CD34+-derived progeny. Although early infection of CD34+ progenitor cells was not productive (as shown by the plaque assay), infectious virus could be recovered from the terminally differentiated cultures. BM progenitor cells may serve as a reservoir of the latent virus with limited transcription. Proliferation and monocytic maturation of infected progenitors may lead to the numerical expansion of HCMV-infected cells, which serve as a source of HCMV dissemination and reactivation.

Growth of Newcastle disease virus in chicken macrophages

Chicken macrophages were isolated from chicken peripheral blood, cultured in vitro, and infected with Newcastle disease virus (NDV) after reaching semiconfluence. Infected macrophages supported the growth and replication of NDV. Virus-infected macrophages exhibited features of apoptosis as determined by agarose gel electrophoresis, thymidine release assays and flow cytometry. Electron microscopical examination also showed the appearance of intact virus particles, fragmented chromatin and apoptotic bodies. This evidence demonstrates that NDV infection of chicken macrophages causes chicken macrophages to undergo apoptosis.

Cytomegalovirus as a cause of pancytopenia

Human cytomegalovirus, HCMV, infects most of the population by adulthood; The primary infection is often accompanied by transient neutropenia and thrombocytopenia, and is followed by a period asymtomatic viral latency. In the setting of bone marrow transplantation, however, the immunosuppressed state of the recipient enables HCMV to re-activate or to infect the individual and cause serious sequelae. These range from hepatitis and gastrointestinal disease to interstitial pneumonia and hematologic abnormalities, which are more common in the allograft. Little is currently known about the mechanisms by which HCMV causes these hematologic abnormalities. In this review, we discuss experimental models which are helping investigators understand the immunology and pathology of CMV infection. We also summarize the vivo studies of the effects of HCMV on human hematopoiesis. Several possible mechanisms that could explain the deleterious effect of HCMV on human hematopoietic function include: 1) alteration of accessory cell function by inducing the production of inhibitory cytokines; 2) perturbation of stromal cell function resulting in a decreased production of hematopoietic factors or by altering cell surface adhesion molecule expression; 3) by direct infection of the hematopoietic stem or progenitor cells. It is likely that the pathogenesis of this syndrome is multifactorial therefore requiring a broad therapeutic approach. This would include the use of the antiviral agents, hematopoietic growth factors and donor derived HCMV specific cytolytic cells.

Cell types involved in replication and distribution of human cytomegalovirus

As the number of patients suffering from severe HCMV infections has steadily increased, there is a growing need to understand the molecular mechanisms by which the virus causes disease. The factors that control infection at one time and the events leading to virus multiplication at another time are only beginning to be understood. The interaction of HCMV with different host cells is one key for elucidating these processes. Through modern techniques, much has been learned about the biology of HCMV infections in culture systems. In addition to endothelial cells, epithelial cells, and smooth muscle cells, fibroblasts are one cell population preferentially infected in solid tissues in vivo. From these sites of multiplication, the virus may be carried by peripheral monocytes and circulating endothelial cells to reach distant sites of the body. This would explain the multiorgan involvement in acute HCMV infection and the modes of viral transmission. From what has been learned mainly from human fibroblast culture systems, future studies will focus on how HCMV regulates the expression of its putative 200 genes in different host cells at different stages of cell differentiation and activation to result in viral latency and pathogenesis.

Stereochemical Aspects of the anti-HCMV Activity of Cytidine Nucleoside Analogues

The remarkable selectivity of the β-L enantiomers of 2′,3′-dideoxycytidine analogues against the viral polymerases of HIV and HBV has stimulated our interest in targeting β-L enantiomers of anti-HCMV cytidine analogues. Indeed, Ara-C, FIAC and DMDC are cytidine analogues with β-D configuration that show significant potency as anti-HCMV agents but lack selectivity. β-L enantiomers have therefore been synthesized and evaluated together with four other nucleoside analogues, and the β-L. enantiomers were found not to be inhibitory to HCMV replication. However, the three α-L isomers, α-L-Ara-C, α-L-Xylo-C and α-L-FMAU, emerged with activity against HCMV and have provided new approaches for the treatment of viral diseases with nucleoside analogues possessing the unusual L-configuration.

The role of human cytomegalovirus in haematological diseases

Infection with HCMV in healthy individuals generally results in mild or subclinical illness. Pathogenic infections occur predominantly in immunodeficient patients, such as transplant recipients, neonates and patients with AIDS. Primary infection is frequently latent or chronic and PBLs represent sites for virus latency and persistence. HCMV can be recovered from PMNL, monocytes and T-lymphocytes. Although virus-related cases of haematopoietic dysfunction are seen infrequently in infected normal persons, the importance of HCMV as a pathogenic agent in haematopoiesis is dramatically illustrated in the case of patients receiving BMT. Primary or reactivated HCMV infections are a common feature in BMT recipients, enhancing failure of marrow engraftment, GVHD, and many opportunistic infections. HCMV can infect both haematopoietic progenitor cells and stromal elements, identifying the entire haematopoietic system as a target for HCMV dissemination and latency. As a result, lympho- and myelosuppression can be due to both direct inhibition of progenitor cell growth as well as the failure of stem cell self-renewal due to stromal cell dysfunction. HCMV can also exert suppressive effects on immune cell function by direct and indirect mechanisms. These effects can have dire consequences, particularly when a state of immunosuppression already exists, as in the HIV infection. The diverse effects of CMV on the lymphohaematopoietic system are summarized in Figure 1.

Rabies virus replication in primary murine bone marrow macrophages and in human and murine macrophage-like cell lines: implications for viral persistence

To determine whether rabies viruses replicate in macrophage or macrophage-like cells, several human and murine macrophage-like cell lines, as well as primary cultures of murine bone marrow macrophages, were incubated with the Evelyn-Rokitnicki-Abelseth (ERA) virus and several different street rabies viruses (SRV). ERA rabies virus replicated well in human monocytic U937 and THP-1 cells and murine macrophage IC-21 cells, as well as primary cultures of murine macrophages. Minimal replication was detected in murine monocytic WEHI-3BD- and PU5-1R cells, and ERA virus did not replicate in murine monocytic P388D1 or J774A.1 cells. A tissue culture-adapted SRV of bat origin also replicated in IC-21 and U937 cells. Non-tissue culture-adapted SRV isolated from different animal species, particularly bats, replicated minimally in U937, THP-1, IC-21 cells and primary murine bone marrow macrophages. To determine whether rabies virus replication is dependent upon the state of differentiation of the macrophage-like cell, human promyelocytic HL-60 cells were differentiated with 12-O-tetradecanoylphorbol-13-acetate (TPA). ERA rabies virus replicated in the differentiated HL-60 cells but not in undifferentiated HL-60 cells. Persistent infections were established in macrophage-like U937 cells with ERA rabies virus and SRV, and infectious SRV was isolated from adherent bone marrow cells of mice that had been infected 96 days previously. Virus harvested from persistently infected U937 cells and the adherent bone marrow cells had specifically adapted to each cell. This specificity was shown by the inability of the viruses to infect macrophages other than U937 cells and primary bone marrow macrophages, respectively. Virus titers of the persistently infected U937 cells fluctuated with extended cell passage. After 30 passages, virus released from the cells had lost virulence as shown by its inability to kill intracranially inoculated mice. However, the avirulent virus released from the persistently infected cells was more efficient in infecting and replicating in naive U937 cells than the virus which was used to establish the persistent infection. These results suggest that macrophages may serve as reservoirs of infection in vivo, sequestering virus which may subsequently be activated from its persistent state, resulting in clinical infection and death.

Human cytomegalovirus latent infection of granulocyte-macrophage progenitors

We have investigated the interaction of human cytomegalovirus (CMV) with cultured primary granulocyte-macrophage progenitors, a suspected natural site of viral latency, and have established conditions for latent infection and reactivation in this cell population. Progenitor cells from human fetal liver or bone marrow maintained a CD14+, CD15+, CD33+ cell surface phenotype during propagation in suspension culture. Exposure to human CMV did not reduce growth or alter the phenotype of these cells during a 4-week culture period. Viral replication was not detectable in these cells, although viral DNA, as measured by PCR analysis, persisted in a high proportion of cultured cells in the absence of delayed early (beta) gene expression. Viral gene expression was restricted such that only ie1 region transcripts were detected by PCR analysis of cDNA, and these transcripts were estimated to be present in no less than 2-5% of latently infected cells. Most of these transcripts remained unspliced, a result that strikingly contrasts with the splicing pattern normally seen during viral replication in permissive cells. Latent virus reactivated after prolonged, 16- to 21-day cocultivation of infected granulocyte-macrophage progenitors with permissive cells, results that support a role for the myelomonocytic cell population as a biological reservoir of latent human CMV and suggest that these cells may be the source of CMV DNA PCR-positive monocytes found in the peripheral blood of healthy carriers.

Human cytomegalovirus infection of the monocyte/macrophage lineage in bone marrow

Peripheral blood monocytes (PBM) are one site of persistence of human cytomegalovirus (HCMV) in healthy carriers. However, because PBM circulate only briefly before entering the tissues and are difficult to infect with HCMV, it has been suggested that they may acquire HCMV during development in the bone marrow. Consistent with this, we show evidence that bone marrow progenitors from healthy HCMV carriers contain endogenous HCMV DNA as detected by PCR. We also show that bone marrow precursors are readily infected by clinical isolates of HCMV in vitro but that no viral gene expression occurs until these cells become differentiated. In contrast, incubation of these cells at any developmental stage with the laboratory strain AD169 resulted in few cells expressing viral immediate-early genes, and this correlated with a lack of entry of AD169 virus. These observations are consistent with bone marrow progenitors acting as a reservoir for HCMV and transmitting the viral genome to PBM, in the absence of lytic-gene expression, until they leave the circulation and undergo tissue-specific differentiation to macrophages.

Human cytomegalovirus replication correlates with differentiation in a hematopoietic progenitor cell line and can be modulated by HIV-1

Human cytomegalovirus (HCMV) infection of a CD34+ hematopoietic progenitor cell line (TF1) was studied before and after TPA differentiation. TF1 cells were found to be infected but the virus does not replicate, while differentiated TF1 cells can be infected and allow HCMV complete replication. In the same system we studied the interaction between HCMV and HIV and found that while contact between HIV gp 120 and the HCMV-infected cell has an inhibitory effect, exogenous Tat protein stimulates HCMV replication. The interaction between HCMV and HIV in hematopoietic progenitor cells is complex and depends on several factors that can have opposite effects.

Human cytomegalovirus in a SCID-hu mouse: thymic epithelial cells are prominent targets of viral replication

Animal models of human cytomegalovirus (CMV) infections have not been available to study pathogenesis or to evaluate antiviral drugs. Severe combined immunodeficient mice implanted with human fetal tissues (SCID-hu) were found to support CMV replication and may provide a model for this species-specific virus. When conjoint implants of human fetal thymus and liver were inoculated with a low-passage-number isolate of CMV, strain Toledo, consistent high-level viral replication was detected 5, 12, 15, 28, and 35 days after inoculation and virus replication continued for up to 9 months. Other human tissue implants, including lung and colon, were also found to support viral growth but with greater variability in levels and for a shorter duration. As expected, the species specificity of human CMV was preserved in this model such that virus was detected in the human conjoint thymus/liver implant but not in surrounding mouse tissues. The majority of virus-infected cells were localized in the thymic medulla rather than cortical region of the implant and immunofluorescence analysis identified epithelial cells rather than any hematopoietic cell population as the principal hosts for viral replication. Finally, treatment of infected animals with ganciclovir reduced viral replication, thereby demonstrating the value of this system for evaluating antiviral therapies. This animal model opens the way for a range of investigations not previously possible with human CMV.

Persistence of cytomegalovirus in human long-term bone marrow culture: relationship to hemopoiesis

Using pre-established human long-term marrow culture (LTMC), we studied cytomegalovirus (CMV) replication in this system after in vitro infection of nonadherent cells obtained from these cultures with CMV AD-169. After infection with 5 immediate-early antigen foci/cell CMV was detectable for 63-123 days (peak titer 2.0 x 10(3)-1.3 x 10(9)) in the supernatants of LTMC. Lower MOI resulted in a delay in the detection and longer persistence of CMV in LTMC although peak titers were unchanged. CMV infection was associated with destruction of the stromal layer, appearance of a subset of large (23 microns) CMV-infected mononuclear cells in the nonadherent fraction, and early differentiation of nonadherent cells into a homogenous population of macrophage-like cells. CMV infection resulted in a reduction and premature disappearance of committed progenitors (BFU-E, CFU-GM) in LTMC. Persistence of CMV in LTMC was linked to ongoing hemopoiesis. Human bone marrow may be an important site for CMV replication during acute infection and CMV persistence.

NF-kappa B activation of the cytomegalovirus enhancer is mediated by a viral transactivator and by T cell stimulation

The expression of cytomegalovirus alpha (immediate early) genes is under control of an enhancer that carries signals for strong constitutive expression as well as response elements for transactivation by viral proteins. We have used synthetic oligonucleotides representing the 16, 18 and 19 bp repeat elements within the enhancer to investigate the role of virus-induced cellular transcription factors in enhancer activation. We show that the transcription factor NF-kappa B, which binds to the 18 bp repeat, plays a central role in enhancer activation in infected human fibroblasts and that activation is mediated by the product of the viral gene ie1. The simian immunodeficiency virus kappa B site can functionally substitute for the 18 bp element in transient transactivation assays and can also compete efficiently for specific binding to the 18 bp repeat element in vitro. Point mutations in the NF-kappa B site within the 18 bp element disrupt ie1-mediated transactivation and binding. We have found that the characteristics of the 18 bp binding factor from human fibroblasts are indistinguishable from NF-kappa B induced by phorbol ester plus mitogen treatment of T lymphocytes, as determined by gel mobility shift assay as well as protection of the binding site from chemical cleavage. Furthermore, T cell stimulation mediates activation of the viral enhancer via kappa B sites, an observation that may be important in the interaction of cytomegalovirus with the naturally infected human host. Thus, NF-kappa B plays a central role as a target for enhancer activation via viral and cellular factors.

Hybridization techniques provide improved sensitivity for HCMV detection and allow quantitation of the virus in clinical samples

Hybridization techniques (slot-blot and in-situ hybridization assays) and immunostaining using murine monoclonal antibodies directed against different proteins of the human cytomegalovirus (HCMV) were compared for their sensitivity and specificity for detection of HCMV. A model system with HCMV infected human embryonic lung fibroblasts and lung biopsy specimens obtained from patients with culture positive HCMV interstitial pneumonia were used for evaluation of these techniques. The hybridization techniques were found to provide an improved sensitivity compared to immunostaining. Additionally a good correlation was found between the virus dose determined by TCID50 and the amount of viral DNA detected by slot-blot hybridization and by the number of autoradiographic silver grains per 100 cells per 2 weeks exposure time detected in the infected fibroblasts by in-situ hybridization. Thus, at least in the model system quantification of the virus was achieved by hybridization assays.

Failure in generating hemopoietic stem cells is the primary cause of death from cytomegalovirus disease in the immunocompromised host

We have shown in a murine model system for cytomegalovirus (CMV) disease in the immunocompromised host that CMV infection interferes with the earliest detectable step in hemopoiesis, the generation of the stem cell CFU-S-I, and thereby prevents the autoreconstitution of bone marrow after sublethal irradiation. The antihemopoietic effect could not be ascribed to a direct infection of stem cells. The failure in hemopoiesis was prevented by adoptive transfer of antiviral CD8+ T lymphocytes and could be overcome by syngeneic bone marrow transplantation. CD8+ T lymphocytes and bone marrow cells both mediated survival, although only CD8+ T lymphocytes were able to limit virus multiplication in host tissues. We concluded that not the cytopathic effect of virus replication in host tissues, but the failure in hemopoiesis, is the primary cause of death in murine CMV disease.

Pathogenesis of murine cytomegalovirus infection: identification of infected cells in the spleen during acute and latent infections

Spleen cells which replicate murine cytomegalovirus (MCMV) during acute infection in vivo were identified by electron microscopy and combined immunocytochemical staining and in situ cytohybridization. Most infected cells, as defined by in situ hybridization for viral RNA with MCMV-specific probes, were shown to be positive for factor VIII-related antigen and negative for Ia, Thy-1, and F4/80 antigens. Electron microscopic ultrastructural observations indicated that the infected cells in the spleen are predominantly sinusoidal-lining cells. We also studied reactivation of MCMV from latently infected mice by cocultivation of spleen cells with mouse embryo fibroblasts. Virus was only recovered from cells in preparations of stromal (or reticular) fragments, and not from spleen cell suspensions. Neither removal of immunoglobulin-bearing cells from the stromal fragments by panning nor depletion of Thy-1- and Ia-bearing stromal cells by treatment with monoclonal antibodies and complement reduced the frequency of reactivation of MCMV. These data suggest that T lymphocytes, mature B lymphocytes, and other Ia-bearing cells are not predominant reservoirs of latent MCMV.

Cytomegalovirus infection in pregnancy

Cytomegalovirus (CMV) is the most common agent of prenatal (peri- and early postnatal) infection of the newborn with an incidence of 0.2-2.0% (5-10%) depending on the socio-economic status. Only one out of 20 congenitally CMV-infected newborns shows serious symptoms. Another two may reveal mental retardation and other significant handicaps in later age. Perinatal CMV infection occasionally causes atypical pneumonia, mostly combined with Pneumocystis carinii infections similar to reports of AIDS cases. The risk of vertical infection has been quantified. About 2-4% of pregnant seronegative women (40-60% of all) pass a primary, 10-20% of seropositives a recurrent CMV infection. Every third primary infection may result in vertical CMV transmission with poor prognosis in about 25% (40%) of the offspring infected (in the first half of pregnancy). Sources of vertical infection are semen, maternal cell-associated viraemia, ascending genital virus (prenatally), cervical secretion (perinatally), breast milk and saliva (early postnatally). Laboratory diagnosis of CMV infection is performed by many virological and immunological techniques for detecting viral infectivity, structural components, humoral and cellular immunoresponses. Routine diagnostic service is mainly established by virus cultivation in human fibroblasts and by ELISAs on antibodies and antigens.