Many signaling circuits face a fundamental tradeoff between accelerating their response speed while maintaining final levels below a cytotoxic threshold. Here, we describe a transcriptional circuitry that dynamically converts signaling inputs into faster rates without amplifying final equilibrium levels. Using time-lapse microscopy, we find that transcriptional activators accelerate human cytomegalovirus (CMV) gene expression in single cells without amplifying steady-state expression levels, and this acceleration generates a significant replication advantage. We map the accelerator to a highly self-cooperative transcriptional negative-feedback loop (Hill coefficient ~ 7) generated by homo-multimerization of the virus’s essential transactivator protein IE2 at nuclear PML bodies. Eliminating the IE2-accelerator circuit reduces transcriptional strength through mislocalization of incoming viral genomes away from PML bodies and carries a heavy fitness cost. In general, accelerators may provide a mechanism for signal-transduction circuits to respond quickly to external signals without increasing steady-state levels of potentially cytotoxic molecules.

Cytomegalovirus (CMV) infection has been linked to inflammation-related disease processes in the human host, including vascular diseases and chronic transplant rejection. The mechanisms through which CMV affects the pathogenesis of these diseases are for the most part unknown. To study the contributing role of the host immune response to CMV in these chronic inflammatory processes, we examined endothelial cell interactions with peripheral blood mononuclear cells (PBMC). Endothelial cultures were monitored for levels of fractalkine induction as a marker for initiating the host inflammatory response. Our results demonstrate that in the presence of CMV antigen PBMC from normal healthy CMV-seropositive donors produce soluble factors that induce fractalkine in endothelial cells. This was not observed in parallel assays with PBMC from seronegative donors. Examination of subset populations within the PBMC further revealed that CMV antigenstimulated CD4؉ T cells were the source of the factors, gamma interferon and tumor necrosis factor alpha, driving fractalkine induction. Direct contact between CD4؉ cells and the endothelial monolayers is required for this fractalkine induction, where the endothelial cells appear to provide antigen presentation functions. These findings indicate that CMV may represent one member of a class of persistent pathogens where the antigen-specific T-cell response can result in the induction of fractalkine, leading to chronic inflammation and endothelial cell injury.

Human cytomegalovirus (CMV) infection has been linked to inflammatory diseases that involve vascular endothelial damage, including vascular disease and chronic transplant rejection. We previously reported that the host CD4(+) T-cell response to CMV antigen presented by endothelial cells can produce interferon-gamma and tumor necrosis factor-alpha at levels sufficient to drive induction of fractalkine, a key marker of inflammation, in endothelial cells. In this work, we report that donors with high frequencies of antigen-specific T cells to CMV (high responders) induce higher levels of activation-associated chemokines such as fractalkine, RANTES (regulated on activation, normal T cell expressed and secreted), and macrophage inflammatory protein-1beta, together with cell-adhesion markers in endothelial cells compared with donors with low levels of CMV-specific T cells (low responders). High-responder cultures had higher levels of leukocyte recruitment and adherence to the endothelial monolayers associated with progressive damage and loss of the endothelial cells. These processes that led to endothelial destruction only required viral antigen and did not require infectious virus. Our findings further support that CMV may represent one member of a class of persistent pathogens in which a high antigen-specific T-cell response defines an important risk factor for development of chronic inflammation and endothelial cell injury.

Human cytomegalovirus (CMV) infection has been linked to inflammatory diseases, including vascular disease and chronic transplant rejection, that involve vascular endothelial damage. We have previously shown that the host CD4(+) T-cell response to CMV antigen can produce IFNgamma and TNFalpha at levels sufficient to drive induction of fractalkine, a key marker of inflammation in endothelial cells. We have also observed a major pathogenic effect in which endothelial cell damage and loss follow the induction of fractalkine and up-regulation of cell adhesion markers in the presence of peripheral blood mononuclear cells (PBMCs) from donors with a high CMV-specific T-cell frequency. In this report, we show that the fractalkine-CX(3)CR1 interaction resulting in recruitment of natural killer (NK) cells and monocyte-macrophages plays an important role in mediating this endothelial damage. Supportive evidence for frac-talkine's key role is shown by the ability of specific antibody to CX(3)CR1 to reduce significantly CX(3)CR1(+)-bearing cell chemoattraction and to protect against endothelial damage. These findings support CMV as a member of a class of persistent pathogens in which a high T-cell response and chemokine-mediated effects are a risk factor for development of chronic inflammation and endothelial cell injury.

e Infection by human cytomegalovirus (CMV) elicits a strong humoral immune response and robust anti-CMV antibody production. Diagnosis of virus infection can be carried out by using a variety of serological assays; however, quantification of serum antibodies against CMV may not present an accurate measure of a patient's ability to control a virus infection. CMV strains that express green fluorescent protein (GFP) fusion proteins can be used as screening tools for evaluating characteristics of CMV infection in vitro. In this study, we employed a CMV virus strain, AD169, that ectopically expresses a yellow fluorescent protein (YFP) fused to the immediate-early 2 (IE2) protein product (AD169 IE2-YFP ) to quantify a CMV infection in human cells. We created a high-throughput cell-based assay that requires minimal amounts of material and provides a platform for rapid analysis of the initial phase of virus infection, including virus attachment, fusion, and immediate-early viral gene expression. The AD169 IE2-YFP cell infection system was utilized to develop a neutralization assay with a monoclonal antibody against the viral surface glycoprotein gH. The high-throughput assay was extended to measure the neutralization capacity of serum from CMV-positive subjects. These findings describe a sensitive and specific assay for the quantification of a key immunological response that plays a role in limiting CMV dissemination and transmission. Collectively, we have demonstrated that a robust high-throughput infection assay can analyze the early steps of the CMV life cycle and quantify the potency of biological reagents to attenuate a virus infection.T he coevolution of human herpesviruses with their hosts over the past millions of years has led to the development of complex strategies of immune evasion that allow persistent viral infection despite the presence of an active immune response (1). A comprehensive understanding of cytomegalovirus (CMV) infection is essential to delineate the molecular and cellular interactions necessary for priming a targeted humoral immune response and how a pathogen may coopt these processes to establish a persistent and lifelong infection (2). Furthermore, a more complete comprehension of CMV entry, replication, and immune evasion is paramount in developing strategies to diagnose and alleviate CMV disease in immunocompromised patients such as transplant recipients, AIDS patients, and neonates.Analysis of viral protein expression during CMV infection can be useful in studying viral entry, cellular manipulation, and egress. The replication cycle of CMV is temporally controlled and regulated by different segments of the viral genome. The replicative cycle is divided into immediate-early (IE), early (E), and late (L) phases of replication. CMV IE proteins are produced first and appear within 6 h postinfection (hpi). IE proteins are potent transactivators that stimulate the transcription of E genes (3, 4). IE1 and IE2 are the best-characterized IE gene products and are essential for viral replication a...