Impact of oxidative stress on human cytomegalovirus replication and on cytokine-mediated stimulation of endothelial cells

Host Mitochondrial Requirements of Cytomegalovirus Replication

Purpose of Review

Metabolic rewiring of the host cell is required for optimal viral replication. Human cytomegalovirus (HCMV) has been observed to manipulate numerous mitochondrial functions. In this review, we describe the strategies and targets HCMV uses to control different aspects of mitochondrial function.

Recent Findings

The mitochondria are instrumental in meeting the biosynthetic and bioenergetic needs of HCMV replication. This is achieved through altered metabolism and signaling pathways. Morphological changes mediated through biogenesis and fission/fusion dynamics contribute to strategies to avoid cell death, overcome oxidative stress, and maximize the biosynthetic and bioenergetic outputs of mitochondria.

Summary

Emerging data suggests that cytomegalovirus relies on intact, functional host mitochondria for optimal replication. HCMV large size and slow replication kinetics create a dependency on mitochondria during replication. Targeting the host mitochondria is an attractive antiviral target.

Postoperative hyperglycemia may negatively impact cytomegalovirus infection in seropositive liver transplant recipients: a retrospective cohort study

The aim of the study was to evaluate the association between postoperative hyperglycemia and CMV infection. We analyzed 741 CMV seropositive recipients, of livers from seropositive living donors, who underwent preemptive CMV treatment without CMV prophylaxis. The primary outcome was early CMV infection within 1 month after surgery. Hyperglycemia was defined when mean postoperative blood glucose concentration was >180 mg/dl based on previous research and guidelines. Survival analysis was performed using the Fine and Gray model by accounting for the competing risk of CMV infection-unrelated death. Of the 741 recipients (hyperglycemic group, n = 287; nonhyperglycemic group, n = 454), 372 (50.2%) recipients developed cytomegalovirus (CMV) infection within 1 month after surgery. CMV infection risk was significantly higher in hyperglycemic group than in nonhyperglycemic group in univariable analysis [hazard ratio (HR) 1.34, 95% confidence interval (CI), 1.08-1.66; P = 0.007] and in multivariable analysis (HR 1.25, 95% CI 1.0-1.54; P = 0.038). CMV infection risk was also significantly associated with recipient age, graft ischemia time, model for end-stage liver disease score, and preoperative neutrophil-to-lymphocyte ratio (P < 0.05). In conclusion, preventing postoperative hyperglycemia appears to be an important factor decreasing the risk of CMV infection in seropositive liver transplant recipients undergoing preemptive CMV treatment.

Cytomegalovirus and HIV: A Dangerous Pas de Deux

Human immunodeficiency virus (HIV)-infected adults who take stable antiretroviral therapy (ART) are at risk for early onset of age-related diseases. This is likely due to a complex interaction between traditional risk factors, HIV infection itself, and other factors, such as underlying immune dysfunction and persistent inflammation. HIV disrupts the balance between the host and coinfecting microbes, worsening control of these potential pathogens. For example, HIV-infected adults are more likely than the general population to have subclinical bursts of cytomegalovirus (CMV) replication at mucosal sites. Production of antigens can activate the immune system and stimulate HIV replication, and it could contribute to the pathogenesis of adverse outcomes of aging, like cardiovascular disease and neurocognitive impairment. Further investigation of the relationships between CMV, immune dysfunction, and unsuccessful aging during chronic HIV infection is warranted.

Inhibition of cyclophilin A suppresses H2O2-enhanced replication of HCMV through the p38 MAPK signaling pathway

Human cytomegalovirus (HCMV) infection can be accelerated by intracellular and extracellular hydrogen peroxide (H₂O₂) stimulation, mediated by the activation of the p38 mitogen‐activated protein kinase (MAPK) pathway. However, it remains unknown whether host gene expression is involved in H₂O₂‐upregulated HCMV replication. Here, we show that the expression of the host gene, cyclophilin A (CyPA), could be facilitated by treatment with H₂O₂ in a dose‐dependent manner. Experiments with CyPA‐specific siRNA, or with cyclosporine A, an inhibitor of CyPA, confirmed that H₂O₂‐mediated upregulation of HCMV replication is specifically mediated by upregulation of CyPA expression. Furthermore, depletion or inhibition of CyPA reduced H₂O₂‐induced p38 activation, consistent with that of H₂O₂‐upregulated HCMV lytic replication. These results show that H₂O₂ is capable of activating ROS‐CyPA–p38 MAPK interactions to enhance HCMV replication.

The Putative Role of Viruses, Bacteria, and Chronic Fungal Biotoxin Exposure in the Genesis of Intractable Fatigue Accompanied by Cognitive and Physical Disability

Patients who present with severe intractable apparently idiopathic fatigue accompanied by profound physical and or cognitive disability present a significant therapeutic challenge. The effect of psychological counseling is limited, with significant but very slight improvements in psychometric measures of fatigue and disability but no improvement on scientific measures of physical impairment compared to controls. Similarly, exercise regimes either produce significant, but practically unimportant, benefit or provoke symptom exacerbation. Many such patients are afforded the exclusionary, non-specific diagnosis of chronic fatigue syndrome if rudimentary testing fails to discover the cause of their symptoms. More sophisticated investigations often reveal the presence of a range of pathogens capable of establishing life-long infections with sophisticated immune evasion strategies, including Parvoviruses, HHV6, variants of Epstein-Barr, Cytomegalovirus, Mycoplasma, and Borrelia burgdorferi. Other patients have a history of chronic fungal or other biotoxin exposure. Herein, we explain the epigenetic factors that may render such individuals susceptible to the chronic pathology induced by such agents, how such agents induce pathology, and, indeed, how such pathology can persist and even amplify even when infections have cleared or when biotoxin exposure has ceased. The presence of active, reactivated, or even latent Herpes virus could be a potential source of intractable fatigue accompanied by profound physical and or cognitive disability in some patients, and the same may be true of persistent Parvovirus B12 and mycoplasma infection. A history of chronic mold exposure is a feasible explanation for such symptoms, as is the presence of B. burgdorferi. The complex tropism, life cycles, genetic variability, and low titer of many of these pathogens makes their detection in blood a challenge. Examination of lymphoid tissue or CSF in such circumstances may be warranted.

Hydrogen Peroxide Induce Human Cytomegalovirus Replication through the Activation of p38-MAPK Signaling Pathway

Human cytomegalovirus (HCMV) is a major risk factor in transplantation and AIDS patients, which induces high morbidity and mortality. These patients infected with HCMV experience an imbalance of redox homeostasis that cause accumulation of reactive oxygen species (ROS) at the cellular level. H₂O₂, the most common reactive oxygen species, is the main byproduct of oxidative metabolism. However, the function of H₂O₂ on HCMV infection is not yet fully understood and the effect and mechanism of N-acetylcysteine (NAC) on H₂O₂-stimulated HCMV replication is unclear. We, therefore, examined the effect of NAC on H₂O₂-induced HCMV production in human foreskin fibroblast cells. In the present study, we found that H₂O₂ enhanced HCMV lytic replication through promoting major immediate early (MIE) promoter activity and immediate early (IE) gene transcription. Conversely, NAC inhibited H₂O₂-upregulated viral IE gene expression and viral replication. The suppressive effect of NAC on CMV in an acute CMV-infected mouse model also showed a relationship between antioxidants and viral lytic replication. Intriguingly, the enhancement of HCMV replication via supplementation with H₂O₂ was accompanied with the activation of the p38 mitogen-activated protein kinase pathway. Similar to NAC, the p38 inhibitor SB203580 inhibited H₂O₂-induced p38 phosphorylation and HCMV upregulation, while upregulation of inducible ROS was unaffected. These results directly relate HCMV replication to H₂O₂, suggesting that treatment with antioxidants may be an attractive preventive and therapeutic strategy for HCMV.

The inverted CD4:CD8 ratio is associated with gender-related changes in oxidative stress during aging

Aging has been associated with increased generation of free radicals as well as immunosenescence. Previous studies have identified older individuals with inverted T CD4:CD8 cell ratio and increased immunity to cytomegalovirus (CMV). Here, we investigated markers of oxidative stress and antioxidant defences in older individuals with inverted CD4:CD8 T-cell ratio. Sixty-one subjects were identified with inverted CD4:CD8 ratio. Older individuals with a CD4:CD8 ratio <1 had increased levels of plasma advanced oxidation protein products (AOPP) and ferric reducing ability of plasma (FRAP), but reduced levels of thiobarbituric acid reactive substances (TBARS) as compared to subjects with normal CD4:CD8 ratio. The CMV IgG serology was negatively correlated with CD4:CD8 ratio. These markers were more evident among elderly men than women. Our data suggest a close relationship between chronic CMV infection and oxidative profile in older individuals in the midst of its influence on the peripheral T-cell subsets.

Increased osteoprotegerin predicts poor virological outcome during anticytomegalovirus therapy in solid organ transplant recipients

BACKGROUND

Cytomegalovirus (CMV) infection involves interaction between endothelial cells and leukocyte subsets that may promote vascular inflammation and lead to treatment failure in infected individuals. Osteoprotegerin is a marker of vascular and systemic inflammation but has not been investigated in relation to treatment outcome during CMV infection.

METHODS

We investigated whether circulating levels of osteoprotegerin are related to features of CMV disease and treatment outcomes during CMV infection in 291 solid organ transplant recipients receiving valganciclovir or ganciclovir in an international multicenter trial of CMV disease treatment (the VICTOR study).

RESULTS

Elevated plasma osteoprotegerin was associated with (i) certain disease characteristics including presence of tissue invasive disease (P<0.05) and increased viral load at baseline (P<0.05), (ii) poor virological outcome at day 49 after anti-CMV therapy, (iii) increased plasma levels of markers of inflammation (pentraxin 3 and C-reactive protein) and endothelial cell activation (von Willebrand factor) both at baseline and during follow-up.

CONCLUSION

Our finding indicates that elevated osteoprotegerin levels in solid organ transplant recipients with CMV infection may reflect vascular inflammation and is associated with late virological outcome in these patients.

Renal ischemia/reperfusion injury activates the enhancer domain of the human cytomegalovirus major immediate early promoter

Reactivation of latent human cytomegalovirus is of significant concern in immunocompromised transplant patients and is likely to occur through transcriptional activation of immediate early (ie) gene expression through mechanisms that are not well understood. TNF-mediated activation of NF-kappaB has been proposed to be one pathway leading to transcriptional activation of CMV ie gene expression. Using transgenic mice carrying a lacZ reporter gene under the control of the HCMV major ie promoter/enhancer (MIEP-lacZ mice) and MIEP-lacZ mice deficient in TNF receptor 1 and TNF receptor 2 (MIEP-lac Z TNFR DKO mice), we demonstrate that renal ischemia/reperfusion (I/R) injury activates the HCMV enhancer independently of TNF. Induction of MIEP-lacZ expression was preceded by TNFR-independent formation of reactive oxygen species (ROS), weak and transient activation of NF-kappaB and strong and sustained activation of AP-1. Our studies show that, in addition to TNF-mediated signaling, TNF-independent signaling induced by I/R injury can contribute to the activation of the HCMV enhancer. This likely occurs through ROS-mediated activation of AP-1. Targeting MAP kinase signaling pathways as well as NF-kappaB may be of therapeutic value in patients with CMV infection.

Human cytomegalovirus-induced upregulation of intercellular cell adhesion molecule-1 on villous syncytiotrophoblasts

Human cytomegalovirus (HCMV) is secreted apically from villous trophoblasts, thus congenital infection is not likely to occur by basal release across the basement membrane. As an alternative route, we hypothesize that an HCMV-infected villous syncytiotrophoblast (ST) upregulates intercellular adhesion molecule (ICAM)-1, causing blood monocytes to bind to the ST and induce apoptosis. Purified (>99.99%) populations of human villous trophoblasts were differentiated into an ST-like culture, infected with HCMV strain AD169, and assessed for ICAM-1 expression by immunofluorescence. Infection strongly upregulated ICAM-1 24 h after challenge. ICAM-1 was also stimulated by transfection with viral genes IE2-55, IE1-72, and IE2-86, but not by UV-inactivated virus. Infection with a green fluorescent protein recombinant virus allowed infection and ICAM-1 expression to be topographically located. We found that ICAM-1 was expressed on both infected and noninfected cells. Furthermore, antibody to tumor necrosis factor (TNF)alpha and, to a lesser extent, interleukin (IL)1 beta inhibited ICAM-1 upregulation on noninfected cells but not on infected cells. We conclude that HCMV IE proteins stimulate ICAM-1 expression on villous trophoblasts by paracrine release of TNF alpha and IL1 beta, as well as by a direct effect on infected cells.

Zinc-induced activation of the human cytomegalovirus major immediate-early promoter is mediated by metallothionein and nuclear factor-kappaB

We previously reported that major immediate-early promoter (MIEP) activity was regulated by intercellular zinc levels. In this report, we elucidate the mechanisms involved in this phenomenon. In luciferase reporter assays, zinc-induced activation of MIEP (-735/+62) was decreased with deletion of the promoter in stages, and MIEP (-117/+62) did not respond to zinc. The time course of the activity of MIEP responding to diethylenetriamine pentaacetic acid and zinc was not parallel with metallothionein (MT) promoter, which contains metal responsive elements. SV40 promoter that contains AP-1 binding sites, a candidate for the zinc-responsive motif in the MIEP, was not affected by zinc under our conditions. The activation of MIEP (-735/+62) by zinc was prevented with NF-kappaB decoy. When three kappaB motifs from the enhancer in the MIEP were inserted in the front of the zinc-nonresponsive MIEP (-117/+62), it became responsive to zinc. Moreover, overexpression of MT up-regulates the DNA binding of NF-kappaB and NF-kappaB-induced activation of transcription. These findings strongly suggest that MT and NF-kappaB act as mediator/regulator in zinc-induced activation of MIEP.

Inhibition of cytomegalovirus immediate early gene expression: a therapeutic option?

The replication cycle of the human cytomegalovirus (HCMV) is characterized by the expression of immediate early (IE), early (E), and late (L) gene regions. Current antiviral strategies are directed against the viral DNA polymerase expressed during the early phase of infection. The regulation of the IE-1 and IE-2 gene expression is the key to latency and active replication due to their transactivating and repressing functions. There is growing evidence that the pathogenic features of HCMV are largely due to the abilities of IE-1 and IE-2 to transactivate cellular genes. Consequently, current drugs used to inhibit HCMV infection would have no impact on IE-1 and IE-2-induced effects that are produced before the early phase. Moreover, when HCMV DNA replication is inhibited, IE gene products accumulate in infected cells causing disturbances of host cell functions. This review summarizes the biological functions of HCMV-IE gene expression, their relevance in pathogenesis, as well as efforts to develop novel treatment strategies directed against HCMV-IE expression.

Antiviral and immunomodulatory effects of desferrioxamine in cytomegalovirus-infected rat liver allografts with rejection

BACKGROUND

Cytomegalovirus (CMV) infection is associated with acute and chronic allograft rejection. We have recently shown that rat CMV increases portal inflammation and bile duct destruction in a model of rat liver allograft rejection. Desferrioxamine (DFO), an iron chelator and antioxidant, has recently been demonstrated to have antiviral as well as immunomodulatory effects in vitro. We therefore investigated whether DFO inhibits (a) CMV infection and (b) graft destruction in our rat model.

METHOD

One day after liver transplantation, PVG (RT1c) into BN(RT1n), the rats were infected with rat CMV (RCMV, Maastricht strain; 10(5) plaque-forming units i.p.). The effects of 100 mg/kg body weight and 200 mg/kg body weight DFO were examined.

RESULTS

In the untreated group, the grafts were uniformly RCMV culture-positive. In the group receiving 200 mg/kg DFO, RCMV replication was effectively inhibited. Inflammatory response in the graft, and especially the number of macrophages, was significantly reduced by DFO. Portal inflammation and bile duct destruction were also significantly reduced. In the untreated group, the bile duct epithelial cells were found to be strongly positive for tumor necrosis factor-alpha and this expression was clearly decreased by DFO. In addition, DFO significantly inhibited vascular cell adhesion molecule-1 expression on sinusoidal endothelial cells.

CONCLUSIONS

Our in vivo transplant study strongly supports the inhibitory effects of metal chelators on CMV infection and their possible usefulness in the treatment of CMV-induced pathogenic changes.

Cytomegalovirus and its association with hepatic artery thrombosis after liver transplantation

BACKGROUND

Hepatic artery thrombosis (HAT) is a cause of morbidity and graft loss in approximately 7% of patients after an orthotopic liver transplantation (OLT). Although technical problems are often thought to be the cause of HAT, in general the etiology remains unclear. Because cytomegalovirus (CMV) can infect endothelial cells in vitro and lead to a rapid procoagulant response, it can be hypothesized that, in the absence of CMV antibodies, latent CMV in an allograft may become activated and promote or contribute to vascular thrombosis. Therefore, the purpose of this study was to examine the relationship between CMV serology of the donor and recipient with the development of HAT after OLT.

METHODS

Between July 1988 and November 1995 (University of Wisconsin era), 490 OLTs were performed in 413 patients. Subsequently, four patients were excluded in whom the CMV serology results of the donor were not available. Sixteen of the 409 patients developed HAT within 30 days after liver transplantation. The control group consisted of the other 393 patients.

RESULTS

The incidence of HAT was 12.5% in 64 CMV D+R- patients and 0% in 52 CMV D-R- patients. However, in the other combinations (D+R+ and D-R+), the incidence was only 2.8% (P = 0.005). Eight of the 16 patients with HAT belonged to the CMV D+R- group.

CONCLUSIONS

We conclude that CMV-seronegative patients receiving a seropositive allograft may be at risk for early HAT. Seropositivity of the donor alone and of the recipient alone was not significantly related to the incidence of HAT. Prophylactic treatment with ganciclovir and/or anticoagulation should be evaluated to prevent this complication.

Metallothionein expression in human lung and its varying levels after lung transplantation. Toulouse Lung Transplantation Group

The aim of this study was to determine the lung levels of metallothionein (MT), a free radical scavenger, because oxygen-derivated free radicals (ODFRs) have been involved both in reperfusion injury of transplanted lungs and in cardiac or renal allograft destruction. First, MT localization was evaluated in 14 normal human lung biopsy specimens. Then, in lung transplant recipients, MT content in BAL fluid (BALF) and its transcription rate in alveolar macrophages (AMs) were determined. The BALFs of 69 patients were separated into six groups: lung transplant recipients in clinically stable condition (CSR), those with acute rejection (AR), asymptomatic cytomegalovirus infection (ACMV), cytomegalovirus pneumonitis (CMVP), bronchiolitis obliterans syndrome (BOS), and patients without transplants who served as control subjects (NTCs). In normal lungs, 83% of AMs were positively stained. MT staining was also observed in pleural endothelial cells and basal cells from bronchial epithelium. In lung transplant recipients, MT levels in BALF were significantly higher in patients with CSR, AR, ACMV, and CMVP compared with NTCs, while during BOS, MT had a significantly lower level compared with other lung transplant groups. However, no difference among groups was found concerning MT-II messenger RNA expression in AMs, showing that, as in normal lung, AMs are not the only cells that produce MT. These data report for the first time to our knowledge MT cell distribution in human lung with specific emphasis on its enhanced levels after lung transplantation, even in the absence of complication. Possible correlation among MT levels, ODFRs, cytokine levels, and corticosteroid treatment during complications of lung transplantation are discussed.

Activation of stress-activated MAP protein kinases up-regulates expression of transgenes driven by the cytomegalovirus immediate/early promoter

The immediate/early promoter/enhancer of cytomegalovirus (CMV promoter) is one of the most commonly used promoters for expression of transgenes in eukaryotic cells. In practice, the CMV promoter is often thought of as a constitutively active unregulated promoter. However, we have observed that transcription from the CMV promoter can be up-regulated by a variety of environmental stresses. Many forms of cellular stress stimulate MAP kinase signalling pathways, resulting in activation of stress-activated protein kinases [SAPKs, also called Jun N-terminal kinases (JNKs)] and p38 kinases. We have found that the same conditions that lead to activation of SAPK/JNKs and p38 kinases can also dramatically increase expression from the CMV promoter. Inhibitors of p38 kinases abolished basal transcription from the CMV promoter and completely blocked stress-induced up-regulation of the CMV promoter. Overexpression of a dominant negative JNK kinase had no effect on basal transcription, but significantly reduced up-regulation caused by stress. These results have grave implications for use of the CMV promoter. If the CMV promoter can be up-regulated by cellular stresses, inadvertent activation of the stress kinase pathways may complicate, if not invalidate, the interpretation of a wide range of experiments.

Multiple organ involvement during experimental cytomegalovirus infection is associated with disseminated vascular pathology

Since much of the pathogenesis of cytomegalovirus (CMV) disease is still unknown and vascular involvement may be of importance a rat model was used to study the nature and course of CMV-induced vascular pathology. In this model, local CMV infection was established by subcutaneous inoculation of rat-specific CMV (RCMV) in the sole of the foot. Sings of endothelial activation, including leucocyte adhesion, preceded detectable RCMV infection of these cells. ultimately, vasculitis and thrombotic occlusion were accompanied by diffuse tissue inflammation and necrosis. Generalized RCMV infection was induced in rats by intraperitoneal administration of the virus, which resulted in multiple organ pathology, including haemorrhages, inflammation, and gastrointestinal ulceration. RCMV-encoded antigens were found especially in mononuclear inflammatory cells in the organs and peripheral blood. In addition, multiple haemorrhages and disturbed haematological parameters indicated diffuse intravascular coagulopathy. In conclusion, this study provides evidence for extensive vascular involvement and haematological consequences during disseminated CMV infection. The nature and chronology of RCM-induced pathological vascular events were demonstrated, indicating the importance of endothelial damage. These data and further study may lead to a better understanding of the pathogenesis of CMV multiple-organ disease.

Monocytes harboring cytomegalovirus: interactions with endothelial cells, smooth muscle cells, and oxidized low-density lipoprotein. Possible mechanisms for activating virus delivered by monocytes to sites of vascular injury

Cytomegalovirus (CMV) infection and its periodic reactivation from latency may contribute to atherogenesis and restenosis. It is unknown how CMV is delivered to the vessel wall and is reactivated. We examined the following hypothesis: CMV, present in monocytes recruited to sites of vascular injury, is activated by endothelial cell (EC) or smooth muscle cell (SMC) contact and by oxidized low-density lipoproteins (oxLDLs). The CMV major immediate-early promoter (MIEP) controls immediate-early (IE) gene expression, and thereby viral replication. To determine whether elements of the vessel wall can activate CMV present in monocytes, we transiently transfected the promonocytic cell line HL-60 with a chloramphenicol acetyltransferase reporter gene construct driven by MIEP. MIEP activity increased 1.7 +/- 0.5-fold (P = .02) when the transfected HL-60 cells were cocultured with ECs, 4.5 +/- 1.5-fold when cocultured with SMCs (P = .03), and 2.0 +/- 0.5-fold (P = .01) when exposed to oxLDL. The combination of oxLDL and EC coculture increased MIEP activity over 7-fold. We also found that freshly isolated human monocytes, infected with endothelium-passaged CMV, were capable of transmitting infectious virus to cocultured ECs or SMCs. CMV-related progression of atherosclerosis or restenosis may, at least in part, involve monocyte delivery of the virus to the site of vascular injury, where the vascular milieu, ie, contact with ECs, SMCs, and oxLDL, can contribute to viral reactivation and/or replication by enhancing CMV IE gene expression. The virus may then infect neighboring ECs or SMCs, initiating a cascade of events predisposing to the development of atherogenesis-related processes.

The immunological role of biliary epithelial cells in human liver transplant rejection

From histopathological analyses after liver transplantation it is evident that the biliary epithilium is an important target for leucocytes of the graft recipient. Besides clinical and histopathological investigations undertaken by several authors it was also endeavoured to determine the immunological impact of the biliary epithelial cells (BEC) in vitro. As for the intrahepatic BEC, in vitro studies proved to be restricted owing to difficult isolation procedures and the limited number of cells yielded from transplanted organs. Therefore, studies on cultured extrahepatic BEC served as a model for the immunological features of the biliary epithelium in transplantation. Herein, in vivo and in vitro studies dealing with BEC and immunologically mediated hepatic disorders are reviewed in order to understand better the pathogenesis after liver transplantation. Furthermore, possible underlying mechanisms of BEC-directed immunity with regard to BEC-leucocyte interactions are discussed.

Expression of human leukocyte antigens class I and class II on cultured biliary epithelial cells after cytomegalovirus infection

The influence of cytomegalovirus (CMV) infection on the HLA expression on cultured biliary epithelial cells (BEC) was investigated. CMV-infection augmented expression of HLA class I but not of HLA class II. CMV reduced the IFN-gamma-mediated induction of the de novo expression of HLA class II while the stimulated expression of HLA class I was not impaired. Autologous but not allogeneic PBL responded to CMV-infected BEC. This response resulted in upregulation of HLA class I on BEC which was significantly higher compared with the expression on infected BEC alone or on uninfected BEC cocultured with autologous PBL. The results suggest that CMV modulates the immunogenic potential of BEC, which is important for the HLA and CMV-mediated pathomechanisms in vivo.

Intracellular thiol redox status affects rat cytomegalovirus infection of vascular cells

There is increasing evidence for cytomegalovirus (CMV) induced vascular pathology during acute infection in the immunocompromised host. Inflammation is involved in such processes, which is frequently associated with increased levels of oxidative mediators and reduced anti-oxidant protection. A relation between viral infection and oxidative stress has been recognized for human immunodeficiency virus and herpes simplex virus-1 infections, but little is known in this respect for CMV infections. We investigated if there is a relation between CMV infection of vascular cells and the intracellular redox status using an in vitro rat model. We measured intracellular glutathione levels and rat CMV (RCMV) permissiveness of rat heart endothelial cell lines (RHEC), rat smooth muscle cells (RSMC), and compared these with fully CMV-permissive rat fibroblasts (REF and Rat 2). In addition, the effects of the anti-oxidant N-acetylcysteine (NAC) and the glutathione synthesis inhibitor buthionine sulfoximide (BSO) on CMV permissiveness and replication were investigated in these cell lines. Finally, we investigated infection of vascular cells under inflammatory conditions in an in vivo rat model for acute CMV infection. The results show a very high endogenous glutathione level in RHEC compared to REF, Rat 2 cells and RSMC. This is associated with a low CMV permissiveness in RHEC as opposed to full permissiveness in REF, Rat 2 cells and RSMC in vitro. In addition, modulation of the intracellular thiol redox status affected CMV infection and replication only in RHEC, but not in RSMC and Rat 2 cells. During acute infection in vivo under immunosuppressed conditions rat endothelial cells first become activated and subsequently infected leading to vascular damage and pathology. This study suggests that a high endogenous thiol redox status may contribute to the apparent barrier function of endothelial cells with respect of CMV infection and that oxidative stress may facilitate CMV infection of the vascular wall.

Immunomodulatory properties of the metal chelators desferrioxamine and diethylenetriamine penta-acetic acid in vitro

In this study, we investigated the effects of the intracellular metal chelator desferrioxamine (DFO) and the extracellular metal chelator diethylenetriamine penta-acetic acid (DTPA), which were previously shown to have strong anticytomegalovirus potencies, on their ability to elicit immunomodulatory effects in vitro[fcn,3]. The results showed that nontoxic and in vivo attainable concentrations of both DFO and DTPA inhibited mitogen- and allogen-induced proliferation of peripheral blood lymphocytes. The immunomodulatory effects of DFO/DTPA seem to be due to the impaired expression of interleukin-2 receptor and the reduced secretion of interleukin-2. However, metal chelators were more effective than cyclosporine or tacrolimus (FK506) in our in vitro experiments. Moreover, cytotoxicity mediated by lymphokine-activated killer cells and natural killer cells and the expression of HLA and adhesion molecules on cytokine-stimulated endothelial cells were differentially impaired by DFO/DTPA. These results warrant further study of the immunological effects of metal chelators in vivo.