Human cytomegalovirus (HCMV) is a recognized cause of disease in the fetus, the allograft recipient and AIDS patients. More recently, it has been recognized as a pathogen for those admitted to intensive care units, for the elderly and for the general population. The epidemiology and molecular and cellular pathology of this virus are summarized to provide an overarching model of pathogenesis, able to account for these varying clinical presentations. In brief, HCMV has the potential to spread in the bloodstream to all organs, but only produces overt disease if the viral load increases to high levels. This is normally prevented by a robust immune response, so that the infected individual usually remains asymptomatic. However, this benefit comes at the cost of committing more and more immunological resources to controlling HCMV with time, so that the overall function of the immune system is impaired. Fortunately, recent progress in developing novel antiviral drugs and vaccines suggests the possibility that the diverse effects of HCMV may soon become controllable at the individual and population level, respectively.

Human cytomegalovirus (HCMV) persists as a subclinical, lifelong infection in the normal human host, but reactivation from latency in immunocompromised subjects results in serious disease. Latency and reactivation are defining characteristics of the herpesviruses and are key to understanding their biology; however, the precise cellular sites in which HCMV is carried and the mechanisms regulating its latency and reactivation during natural infection remain poorly understood. Here we present evidence, based entirely on direct analysis of material isolated from healthy virus carriers, to show that myeloid dendritic cell (DC) progenitors are sites of HCMV latency and that their ex vivo differentiation to a mature DC phenotype is linked with reactivation of infectious virus resulting from differentiation-dependent chromatin remodeling of the viral major immediate-early promoter. Thus, myeloid DC progenitors are a site of HCMV latency during natural persistence, and there is a critical linkage between their differentiation to DC and transcriptional reactivation of latent virus, which is likely to play an important role in the pathogenesis of HCMV infection. P rimary infection of healthy individuals with human cytomegalovirus (HCMV) is often asymptomatic and results in lifelong persistence in the host, a characteristic of all herpes viruses. However, primary infection and reactivation of latent HCMV causes serious disease in immunosuppressed transplant recipients and in advanced HIV infection (1-3). Transfusionmediated HCMV disease can be prevented by leukocyte depletion (4) of blood, but infectious virus cannot be detected in the blood of healthy carriers, suggesting that HCMV is transmitted as latent virus in the peripheral blood leukocyte population. Accumulating evidence has shown that HCMV is carried latently in mononuclear cells of the myeloid lineage during lifelong latency in naturally infected individuals (5-8). Differentiation of monocytes to macrophages in vitro is reported to induce immediate-early (IE) lytic gene expression from latent virus (9), and groups have intermittently reported that infectious virus can be recovered after differentiation of monocytes to macrophages through explant culture (10) and, more recently, by allogeneic T cell stimulation (11), suggesting that reactivation of latent virus is associated with both the differentiation and activation state of myeloid cells.The major IE genes of HCMV, driven by the viral major IE promoter͞enhancer (MIEP), are the two most abundantly transcribed genes at IE times of virus lytic infection (12), and their proteins play a critical role in control of viral early and late gene expression (for review, see ref. 12). Consistent with the differentiation-dependent induction of IE gene expression observed above, there is a clear correlation between the differentiation state of the cell and the regulation of HCMV IE gene expression in vitro. Thus, in transfection assays, the MIEP is transcriptionally repressed in undifferentiated but transcriptionally active ...

No abstract

No abstract

We previously carried out T2D linkage analysis in the families of many of our stage 1 cases (10). None of the 10 loci in Table 1 had large T2D logarithm of the odds (LOD) scores, although those for FTO and TCF7L2 were 0.63 and 0.60 and so were nominally significant. LOD scores for six of the 10 loci were greater than 0.2, as compared to 2.2 that would be expected for random genome locations. This suggests enrichment for T2D-associated loci in regions with modest evidence of T2D linkage (P = 0.01) but that the power of the linkage approach was insufficient to distinguish these signals from background noise.The ability to construct a list of ten robust and replicated T2D-associated loci (Table 1) represents a landmark in efforts to identify genetic variants that predispose to complex human diseases, although the specific predisposing variants and even the relevant genes remain to be defined. We examined the combined risk of T2D based on these 10 loci in our stage 1 + 2 sample by constructing a logistic regression model and predicting T2D risk for each person (8). We found a fourfold variation in T2D risk from the lowest to highest predicted risk groups, which is of potential interest for a personalized preventive-medicine program (Fig. 2). However, these predictions from our data may be biased as compared to predictions based on the general population, likely owing to the overestimation of ORs due to the "winner's curse," enrichment for familial T2D cases, and exclusion of individuals with impaired glucose tolerance or impaired fasting glucose.Thirty years ago, James V. Neel labeled T2D as "the geneticist's nightmare" (32), predicting that the discovery of genetic factors in T2D would be thoroughly challenging. Until recently, his prediction has proven true. Although large samples and collaboration among three groups were required, we can confidently state that new diabetes risk factors have been identified. Each gene discovery points to a pathway that contributes to pathogenesis, and all of these proteins and their relevant pathways represent potential drug targets for the prevention or treatment of diabetes. Based on the number of other interesting results observed in these studies, it is likely that there are additional T2D-predisposing loci to be found. Even though much remains to be done, we are at last awakening from Jim Neel's nightmare.

Human cytomegalovirus (HCMV) is a frequent cause of major disease following primary infection or reactivation from latency in immunocompromised patients. Infection of non-permissive mononuclear cells is used for analyses of HCMV latency in vitro. Using this approach, it is shown here that repression of lytic gene expression following experimental infection of CD34 Primary infection of healthy individuals with human cytomegalovirus (HCMV) is often asymptomatic and results in lifelong persistence of the virus within the host, a common feature of all herpesvirus infections. However, primary infection and reactivation of latent HCMV are responsible for serious disease in both immunosuppressed transplant recipients and during advanced human immunodeficiency virus infection (Adler, 1983;Rubin, 1990). The health threat posed by the reactivation of latent HCMV has resulted in considerable efforts from a number of laboratories to identify the sites of latency and potential mechanisms responsible for controlling the progression of HCMV latency to reactivation. These studies include the study of naturally infected cells ex vivo and experimentally infected model systems in vitro.Analysis of peripheral blood mononuclear cells identified monocytes as one site of HCMV carriage in healthy individuals (Bevan et al., 1991;Taylor-Wiedeman et al., 1991). Monocytes represent a short-lived population of cells subject to constant renewal from myeloid precursors residing in the bone marrow. Analysis of these self-renewing CD34 + mononuclear haematopoietic progenitor cells showed that they also harboured HCMV genomes in naturally infected individuals (Kondo et al., 1996;Mendelson et al., 1996) and thus could represent an important reservoir of HCMV latency in vivo. Haematopoietic progenitors can differentiate into a number of cell types, including monocytes, macrophages, dendritic cells (DCs) and granulocytes, and in a recent analysis we showed that DCs generated ex vivo from healthy seropositive carriers reactivated HCMV and that latency and reactivation in these cells may be controlled by chromatin remodelling of the major immediate-early promoter (MIEP) to regulate lytic gene expression (Reeves et al., 2005). However, overall, the analysis of HCMV latency ex vivo has been complicated severely by the low frequency of genome-positive mononuclear cells, which is predicted to be around only 0?01 % of the total population (Slobedman & Mocarski, 1999). Consequently, many studies have relied on experimental infection of primary cells and of cell lines to try to model the events that occur during latency and reactivation of HCMV in the myeloid lineage.A number of these studies have shown that experimental infection of CD34 + cells is non-permissive and that a 'latent infection' is established during extended culture of these cells (Kondo et al., 1994;Minton et al., 1994;Movassagh et al., 1996;Sindre et al., 1996). Such non-permissive infection is defined by the absence of lytic gene expression; however, it is worth noting that a small numbe...

Upon herpesvirus infection, viral DNA becomes associated with nuclear structures known as nuclear domain 10 (ND10). The role of ND10 during herpesvirus infection has long been contentious; data arguing for a role for ND10 in repression of infection have been countered by other data showing little effect of ND10 on virus infection. Here we show that knockdown of human Daxx (hDaxx) expression, an important component of ND10, prior to infection with human cytomegalovirus resulted in increased levels of viral immediate early RNA and protein expression and that this correlated with an increased association of the major immediate early promoter with markers of transcriptionally active chromatin. Conversely, we also show that stable overexpression of hDaxx renders cells refractory to cytomegalovirus immediate early gene expression. Intriguingly, this hDaxxmediated repression appears to be restricted to cells stably overexpressing hDaxx and is not recapitulated in transient transfection assays. Finally, hDaxx-mediated repression of cytomegalovirus major immediate early gene expression was overcome by infecting at higher virus titers, suggesting that an incoming viral structural protein or viral DNA is responsible for overcoming the repression of viral gene expression in hDaxx superexpressing cells. These data suggest that hDaxx in ND10 functions at the site of cytomegalovirus genome deposition to repress transcription of incoming viral genomes and that this repression is mediated by a direct and immediate effect of hDaxx on chromatin modification around the viral major immediate early promoter. Human cytomegalovirus (HCMV)3 is an extremely widespread, opportunistic pathogen of considerable clinical significance. Primary infection of healthy, immunocompetent individuals with HCMV is normally asymptomatic. However, as is the case with all herpesviruses, after the initial control of primary infection by the immune system, HCMV establishes lifelong latency in the host. During latency and throughout the lifetime of the infected individual, the herpesviruses can reactivate. Although generally asymptomatic, such reactivation can result in severe disease. As such, the disease burden of herpesviruses can be life-long and particularly severe when associated with immunosuppression, such as in transplant patients and in human immunodeficiency virus-infected patients who have developed immunodeficiency (1, 2).After infection with herpes simplex virus-1, the viral genomes appear to co-localize with cellular nuclear structures known as nuclear domain 10 (ND10) and give rise to replication centers in close proximity to these sites (3, 4). ND10 are discrete interchromosomal accumulations of a number of proteins, many of which are transcriptional repressors. Intriguingly, many of the human herpesviruses encode an immediate early protein, which functions to destroy or redistribute components of ND10 (5-17), and a number of studies have attempted to address the role of ND10 during infection. One of the first observations was that ICP0 (int...

Human cytomegalovirus (HCMV) infection remains a major cause of morbidity in patient populations. In certain clinical settings, it is the reactivation of the pre-existing latent infection in the host that poses the health risk. The prevailing view of HCMV latency was that the virus was essentially quiescent in myeloid progenitor cells and that terminal differentiation resulted in the initiation of the lytic lifecycle and reactivation of infectious virus. However, our understanding of HCMV latency and reactivation at the molecular level has been greatly enhanced through recent advancements in systems biology approaches to perform global analyses of both experimental and natural latency. These approaches, in concert with more classical reductionist experimentation, are furnishing researchers with new concepts in cytomegalovirus latency and suggest that latent infection is far more active than first thought. In this review, we will focus on new studies that suggest that distinct sites of cellular latency could exist in the human host, which, when coupled with recent observations that report different transcriptional programmes within cells of the myeloid lineage, argues for multiple latent phenotypes that could impact differently on the biology of this virus in vivo. Finally, we will also consider how the biology of the host cell where the latent infection persists further contributes to the concept of a spectrum of latent phenotypes in multiple cell types that can be exploited by the virus.