Cytomegalovirus infection and viral-induced transformation of human endothelial cells

Inflammation in HIV and Its Impact on Atherosclerotic Cardiovascular Disease

People living with HIV have a 1.5- to 2-fold increased risk of developing cardiovascular disease. Despite treatment with highly effective antiretroviral therapy, people living with HIV have chronic inflammation that makes them susceptible to multiple comorbidities. Several factors, including the HIV reservoir, coinfections, clonal hematopoiesis of indeterminate potential (CHIP), microbial translocation, and antiretroviral therapy, may contribute to the chronic state of inflammation. Within the innate immune system, macrophages harbor latent HIV and are among the prominent immune cells present in atheroma during the progression of atherosclerosis. They secrete inflammatory cytokines such as IL (interleukin)-6 and tumor necrosis-α that stimulate the expression of adhesion molecules on the endothelium. This leads to the recruitment of other immune cells, including cluster of differentiation (CD)8+ and CD4+ T cells, also present in early and late atheroma. As such, cells of the innate and adaptive immune systems contribute to both systemic inflammation and vascular inflammation. On a molecular level, HIV-1 primes the NLRP3 (NLR family pyrin domain containing 3) inflammasome, leading to an increased expression of IL-1β, which is important for cardiovascular outcomes. Moreover, activation of TLRs (toll-like receptors) by HIV, gut microbes, and substance abuse further activates the NLRP3 inflammasome pathway. Finally, HIV proteins such as Nef (negative regulatory factor) can inhibit cholesterol efflux in monocytes and macrophages through direct action on the cholesterol transporter ABCA1 (ATP-binding cassette transporter A1), which promotes the formation of foam cells and the progression of atherosclerotic plaque. Here, we summarize the stages of atherosclerosis in the context of HIV, highlighting the effects of HIV, coinfections, and antiretroviral therapy on cells of the innate and adaptive immune system and describe current and future interventions to reduce residual inflammation and improve cardiovascular outcomes among people living with HIV.

A novel cytomegalovirus-induced regulatory-type T-cell subset increases in size during older life and links virus-specific immunity to vascular pathology

Background. Cytomegalovirus (CMV) infection directly targets vascular endothelium and smooth muscle and at older ages is associated with accelerated vascular pathology and mortality. CMV-specific cellular immunity might directly contribute to this process.

Methods. Conventional ex vivo activation–induced T-cell responses to 19 dominant CMV antigens, along with CMV-specific inducible regulatory-type CD4⁺ T cells (iTregs), were measured in healthy older people, using a novel protocol that included classic Treg markers alongside the activation marker CD134. Measurements were correlated with diastolic, systolic, and mean arterial blood pressure, a surrogate marker for arterial stiffness.

Results. CMV-specific iTregs recognized the same antigens as conventional CD4⁺ T cells and were significantly more frequent at older ages. They suppressed antigen-specific and nonspecific proliferation and in large part expressed Foxp3. Frequencies of CMV-specific iTregs and CD8⁺ T cells (summated response) were significantly associated with diastolic and mean arterial pressures. Confounders, including age, body mass index, smoking, antihypertensive medication use, or C-reactive protein levels, did not explain these observations.

Conclusions. A novel CMV-induced regulatory-type CD4⁺ T-cell subset is readily detectable in CMV-infected people and, like the aggregate CD8⁺ T-cell response to the most dominant CMV antigens, is quantitatively associated with arterial stiffness in older life. Whereas CD8⁺ effector T cells might directly cause vascular injury, iTregs may attenuate this response.

Humoral immunity to cytomegalovirus and chronic graft-versus-host disease

Human cytomegalovirus (HCMV) is an important cause of morbidity and mortality in patients with chronic graft-versus-host disease (cGVHD), but the underlying mechanisms are not understood. The aim of this investigation was to determine whether humoral immune responses to the HCMV antigens were quantitatively different in hematopoietic cell transplant (HCT) recipients who developed cGVHD from those who did not. Antibodies to HCMV and its proteins UL94 and UL70 were quantitated in 79 cGVHD and 30 non-cGVHD patients by enzyme-linked immunosorbent assays (ELISAs). Mean levels of antibodies to the whole HCMV and to its protein UL94 were not significantly different between the cGVHD and the non-cGVHD subjects. However, the levels of antibodies to HCMV UL70 were significantly higher in non-cGVHD subjects than in those with cGVHD (20.91±15.63 versus 15.00±10.35 ng/mL; p=0.03). This suggests that anti-UL70 antibodies might play a protective role in the development of cGVHD.

Human cytomegalovirus attenuates interleukin-1beta and tumor necrosis factor alpha proinflammatory signaling by inhibition of NF-kappaB activation

Viral infection is associated with a vigorous inflammatory response characterized by cellular infiltration and release of the proinflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF-alpha). In the present study, we identified a novel function of human cytomegalovirus (HCMV) that results in inhibition of IL-1 and TNF-alpha signaling pathways. The effect on these pathways was limited to cells infected with the virus, occurred at late times of infection, and was independent of cell type or virus strain. IL-1 and TNF-alpha signaling pathways converge at a point upstream of NF-kappaB activation and involve phosphorylation and degradation of the NF-kappaB inhibitory molecule IkappaBalpha. The HCMV inhibition of IL-1 and TNF-alpha pathways corresponded to a suppression of NF-kappaB activation. Analysis of IkappaBalpha phosphorylation and degradation suggested that HCMV induced two independent blocks in NF-kappaB activation, which occurred upstream from the point of convergence of the IL-1 and TNF-alpha pathways. We believe that the ability of HCMV to inhibit these two major proinflammatory pathways reveals a critical aspect of HCMV biology, with possible importance for immune evasion, as well as establishment of infection in cell types persistently infected by this virus.

A cyclooxygenase-2 homologue encoded by rhesus cytomegalovirus is a determinant for endothelial cell tropism

Cyclooxygenase-2 (COX-2) is a cellular enzyme in the eicosanoid synthetic pathway that mediates the synthesis of prostaglandins from arachidonic acid. The eicosanoids function as critical regulators of a number of cellular processes, including the acute and chronic inflammatory response, hemostasis, and the innate immune response. Human cytomegalovirus (HCMV), which does not encode a viral COX-2 isoform, has been shown to induce cellular COX-2 expression. Importantly, although the precise role of COX-2 in CMV replication is unknown, COX-2 induction was shown to be critical for normal HCMV replication. In an earlier study, we identified an open reading frame (Rh10) within the rhesus cytomegalovirus (RhCMV) genome that encoded a putative protein (designated vCOX-2) with high homology to cellular COX-2. In the current study, we show that vCOX-2 is expressed with early-gene kinetics during RhCMV infection, resulting in production of a 70-kDa protein. Consistent with the expression of a viral COX-2 isoform, cellular COX-2 expression was not induced during RhCMV infection. Finally, analysis of growth of recombinant RhCMV with vCOX-2 deleted identified vCOX-2 as a critical determinant for replication in endothelial cells.

Human papillomavirus, cytomegalovirus, and adeno-associated virus infections in pregnant and nonpregnant women with cervical intraepithelial neoplasia

Two hundred eight cervical specimens from two groups of subjects, 165 nonpregnant women and 53 pregnant women with cervical intraepithelial neoplasia (CIN) of grades I to III, were positive by PCR analyses for human papillomaviruses (HPVs), adeno-associated virus type 2 (AAV 2), and human cytomegalovirus (HCMV) in 67, 6, and 4.1% of the cases, respectively. The presence of AAV 2 infection was more frequently associated with pregnancy (17 versus 2.4%) and HPV-positive cervices (odds ratio = 6.358) than HCMV was. Increased HPV infection was strongly associated (P < 0.001) with a higher CIN grade, but there is no evidence that AAV 2 and HCMV infections have any impact on CIN development.

Characterization of the rhesus cytomegalovirus US28 locus

Human cytomegalovirus (CMV) US28 (and the related open reading frame [ORF] US27) are G-protein-coupled receptor homologs believed to play a role in viral pathogenesis. In vitro, US28 has been shown to bind and internalize ligands, as well as activate intracellular signaling in response to certain chemokines, and to initiate the migration of smooth muscle cells to chemokine gradients. To assess the role of US28 in vivo, we examined the rhesus model and sequenced and characterized the rhesus CMV US28 locus. We found that rhesus CMV carries five tandem homologs of US28, all widely divergent from US28 and from each other. By reverse transcription-PCR and Northern analysis, we demonstrated expression of these ORFs in infected cells. With stable cell lines expressing these ORFs, we analyzed the homolog's binding and signaling characteristics across a wide range of chemokines and found one (RhUS28.5) to have a ligand binding profile similar to that of US28. In addition, we localized US28 and the rhesus CMV homolog RhUS28.5 to the envelope of infectious virions, suggesting a role in viral entry or cell tropism.

Transcriptional activation of the promoter of human cytomegalovirus immediate early gene (CMV-IE) by the hepatitis B viral X protein (HBx) through the NF-kappaB site

The reactivation of latent cytomegalovirus (CMV) in a human by another viral infection may induce virus-related symptoms. Based on this presumption, we investigated the effect of HBx on the activation of the CMV-IE, which is also known as a transactivator and potential oncogene. The HBx transactivated the CMV-IE promoter by up to 4- and 18-fold factors in human liver HepG2 and lung fibroblast MRC-5 cells, respectively. Cotransfection of HBx with each transcription factor presented in the CMV-IE promoter showed that only NF-kappaB synergistically activated the promoter by up to a 14-fold factor. Serial deletion assays and point mutation analysis showed that the third NF-kappaB site (nt -267 to -258) and the second one (nt -162 to -153) appeared as the major responsible site and minor one, respectively, for the transactivation. These results suggest the possibility that the HBV infection of a cell previously infected by CMV would exert influence on the reactivation of the latent cytomegalovirus in a human to induce virus-related symptoms.

Experimental inoculation of male mice with murine cytomegalovirus and effect on offspring

BACKGROUND

Murine cytomegalovirus (MCMV) was used to examine aspects of viral infection in male mice, and its possible transmission to their offspring.

METHODS AND RESULTS

FVB/N mice inoculated intratesticularly with 5x10(5) plaque forming units (PFU) of MCMV, developed peritoneal haemorrhagic exudates, spleen hypertrophy and acute local infection. Infectiousness was detected until 15 days post-inoculation (D15 PI) in the genital organs, and virus DNA up to D35 PI. Testicular endothelial and Leydig cells were infected, and peritubular cells severely damaged. Spermatogenesis was affected, but neither germ cells nor Sertoli cells were infected. No virus was found in the epididymal epithelial cells. Viral DNA was detected in cells extracted from vas deferens samples until D15 PI. Neither infectious virus nor viral DNA were found in spermatozoa recovered from uterine fluid, fertilized oocytes, blastocysts, fetal tissues or newborn animals following the mating of infected males with uninfected females.

CONCLUSIONS

MCMV harboured in the male genital organs was not transmitted to their offspring, even when mating occurred during the acute phase of CMV disease. Although the infection may have had an impact on spermatogenesis, fertility was not affected. These results do not support the hypothesis of conceptus MCMV infection by the fertilizing spermatozoon in natural conception.

Bacterial invasion and transcytosis in transfected human brain microvascular endothelial cells

Most cases of neonatal bacterial meningitis develop as a result of a hematogenous spread, but it is not clear how circulating bacteria cross the blood-brain barrier. Attempts to answer these questions have been hampered by the lack of a reliable model of the human blood-brain barrier. Human brain microvascular endothelial cells (HBMEC) were isolated and transfected with a pBR322 based plasmid containing simian virus 40 large T antigen (SV40-LT). The transfected HBMEC exhibited similar brain endothelial cell characteristics as the primary HBMEC, i.e. gamma glutamyl transpeptidase and a high transendothelial electrical resistance. Escherischia coli and Citrobacter spp, two important Gram-negative bacilli causing neonatal meningitis, were found to transcytose across primary and transfected HBMEC, without affecting the integrity of the monolayer. In addition, E. coli and C. freundii invaded transfected HBMEC as shown previously with primary HBMEC. We conclude that E. coli and C. freundii are able to invade and transcytose HBMEC and these bacterial-HBMEC interactions are similar between primary and transfected HBMEC. Therefore, our transfected HBMEC should be useful for studying pathogenesis of CNS infections.

Strain specific effects of cytomegalovirus on endothelial cells: implications for investigating the relationship between CMV and cardiac allograft vasculopathy

BACKGROUND

Cytomegalovirus (CMV) has been associated with the development of chronic allograft rejection. Attempts to delineate pathogenetic mechanisms for this association have characteristically used well-established laboratory strains for in vitro investigation and rodent strains for in vivo studies. There is substantial genetic heterogeneity not only among different laboratory strains, but also between laboratory strains and clinical isolates, and genetic differences between human and animal strains are profound. Given these genetic differences, one would anticipate differences in biological activity between strains.

METHODS

Vascular endothelial cells were infected with two laboratory strains of CMV (Towne and AD-169) as well as two individual clinical CMV isolates, after genetic typing with six segments of the genome (including early and late genes). mRNA expression coding for a panel of mesenchymal growth factors was studied using quantitative reverse transcription, polymerase chain reaction. Major histocompatibility complex (MHC) expression was investigated using flow cytometry.

RESULTS

There was substantial genetic variability between clinical and laboratory isolates. There did not appear to be differences in overall infectivity by the different strains as determined by expression of immediate-early antigen at 24 hours (5-10% of endothelial cells positive for immediate-early. Two growth factors, platelet-derived growth factor-A and basic fibroblast growth factor were augmented by one of the two clinical strains of CMV (Clin 2) (P=0.0091 and P=0.0018, respectively). Transforming growth factor -alpha and insulin-like growth factor expression were significantly reduced by both clinical strains and AD-169. Two other growth factors, heparin-binding epidermal growth factor and transforming growth factor-beta were not altered by infection with any strain. No strain altered MHC class II expression. MHC class I expression was increased with one of the two clinical strains (Clin 1, P=0.0006) and decreased by AD-169 (P=0.0016). Clin 2 and Towne had no effect on MHC class I expression.

CONCLUSIONS

These data demonstrate that the genetic heterogeneity of CMV is associated with differences in transplant-relevant biologic activity even among clinical isolates. The relationship between CMV and chronic rejection may be difficult to determine given the heterogeneous nature of this complex virus.

Human cytomegalovirus and human herpesvirus 6 genes that transform and transactivate

This review is an update on the transforming genes of human cytomegalovirus (HCMV) and human herpesvirus 6 (HHV-6). Both viruses have been implicated in the etiology of several human cancers. In particular, HCMV has been associated with cervical carcinoma and adenocarcinomas of the prostate and colon. In vitro transformation studies have established three HCMV morphologic transforming regions (mtr), i.e., mtrI, mtrII, and mtrIII. Of these, only mtrII (UL111A) is retained and expressed in both transformed and tumor-derived cells. The transforming and tumorigenic activities of the mtrII oncogene were localized to an open reading frame (ORF) encoding a 79-amino-acid (aa) protein. Furthermore, mtrII protein bound to the tumor suppressor protein p53 and inhibited its ability to transactivate a p53-responsive promoter. In additional studies, the HCMV immediate-early protein IE86 (IE2; UL122) was found to interact with cell cycle-regulatory proteins such as p53 and Rb. However, IE86 exhibited transforming activity in vitro only in cooperation with adenovirus E1A. HHV-6 is a T-cell-tropic virus associated with AIDS-related and other lymphoid malignancies. In vitro studies identified three transforming fragments, i.e., SalI-L, ZVB70, and ZVH14. Of these, only SalI-L (DR7) was retained in transformed and tumor-derived cells. The transforming and tumorigenic activities of SalI-L have been localized to a 357-aa ORF-1 protein. The ORF-1 protein was expressed in transformed cells and, like HCMV mtrII, bound to p53 and inhibited its ability to transactivate a p53-responsive promoter. HHV-6 has also been proposed to be a cofactor in AIDS because both HHV-6 and human immunodeficiency virus type 1 (HIV-1) have been demonstrated to coinfect human CD4(+) T cells, causing accelerated cytopathic effects. Interestingly, like the transforming proteins of DNA tumor viruses such as simian virus 40 and adenovirus, ORF-1 was also a transactivator and specifically up-regulated the HIV-1 long terminal repeat when cotransfected into CD4(+) T cells. Finally, based on the interactions of HCMV and HHV-6 transforming proteins with tumor suppressor proteins, a scheme is proposed for their role in oncogenesis.

Cytomegalovirus infection and cardiac allograft vasculopathy

There is a wealth of clinical and experimental evidence indicating the interaction of cytomegalovirus (CMV) infection and rejection in cardiac and other solid organ allografts. A plausible explanation for this association comes from data showing that therapy with biologicals, sepsis, and rejection, all lead to the release of TNF-alpha which, upon binding to its receptor, activates NF-kB. TNF-alpha is also able to stimulate the activity of the CMV-IE enhancer/promoter region. CMV infection of several cell lines leads to NF-kB activation. NF-kB binding sites are present in regulatory regions of various cellular and viral genes, including the IE enhancer region of CMV. In a reciprocal situation, CMV infection, most likely via gamma-interferon, leads to upregulation of MHC antigens in the transplant and, thereby, to increased transplant immunogenicity. Thus, a vicious circle is induced. We have investigated in detail the pathobiology of CMV and allograft vasculopathy (chronic rejection) in experimental animals, using aortic and cardiac allografts as well as a trachea model. The results may be summarized as follows: Infection of the recipient with rat CMV results in an early inflammatory response in the aortic and cardiac allograft vascular adventitia and intima (endothelialitis) and in the airway wall of tracheal allografts. This early inflammatory response leads to enhanced intimal thickness in aortic and cardiac allografts and enhanced luminal occlusion of tracheal allografts. Timewise, this coincides with early activation of intragraft inflammatory leukocytes and increased mRNA of various growth factors and cytokines. When the recipients receive gancyclovir, the enhanced intimal response in aortic and cardiac allografts and luminal occlusion in tracheal allografts is entirely abolished. Gancyclovir treatment dramatically reduces the inflammatory response in the allograft, and thereby growth factor synthesis in response to injury. However, gancyclovir does not prevent the expression of IE antigen of CMV, suggested to inactivate tumor suppressor protein p53 predisposing smooth muscle cells to increased growth. Taken together, the effect of CMV infection on cardiac allograft dysfunction is bidirectional and biphasic. The bidirectional nature emerges from the observations that acute CMV infection may accelerate acute rejection, and, on the other hand, acute alloimmune response-associated cytokine response may activate latent CMV infection. The biphasic effect of CMV on allograft dysfunction refers to its early and late detrimental effects, i.e. during the time of acute and chronic rejection. These two effects of CMV on allograft dysfunction emphasize the need for precise diagnosis of CMV infection in transplant recipients and pre-emptive or prophylactic anti-viral therapy. The benefits of this strategy may not be evident during the early post-transplant period, but 5-10 years after transplantation they manifest as better graft survival.

Two clinical isolates and the Toledo strain of cytomegalovirus contain endothelial cell tropic variants that are not present in the AD169, Towne, or Davis strains

The highly fibroblast-passaged AD169, Towne, and Davis strains of cytomegalovirus (CMV) were found to have a restricted capacity to infect endothelial cells in vitro. Although such replication could be increased by a combination of low speed centrifugation and sodium butyrate treatment, the extracellular virus produced was infectious for fibroblasts but not for endothelial cells. In contrast, the low passage Toledo strain, and a low passage fibroblast-grown clinical isolate of CMV, C1F, could be continually passaged in endothelial cells, giving the strains C1FE and Toledo.E. Whilst, using the conditions described above, initial infection of endothelial cells with AD169 or C1F resulted in similar titres of extracellular virus as assayed on fibroblasts, only the virus from the C1F strain was infectious for endothelial cells. Passage of C1F in fibroblasts decreased its ability to infect endothelial cells, whilst retaining equal ability to infect fibroblasts. Although endothelial-cell-passaged cell-free C1FE virus was endothelial cell-tropic, it was still much more infectious for fibroblasts than for endothelial cells. It is concluded that the C1F and Toledo strains, but not the AD169, Towne, or Davis strains, contained endothelial cell tropic variants, which could be lost on passage through fibroblasts, but retained on passage through endothelial cells. Furthermore, virus in an ex vivo source of CMV, a blood specimen, was found to be more tropic for fibroblasts than for endothelial cells, suggesting that in vivo CMV exists as quasi strains with different cell tropism, some of which might be lost in vitro by passage in an inappropriate cell type.

Human cytomegalovirus infection induces mRNA expression and secretion of plasminogen inhibitor type-1 in endothelial cells

The aim of the study was to investigate whether infection of endothelial cells with human cytomegalovirus (HCMV) perturbs expression and production of plasminogen activator inhibitor type-1 (PAI-1). mRNA expression of PAI-1 was investigated by isolating total RNA from HCMV-infected and control cells, followed by Northern blotting and probing with 32P-labelled PAI-1 probe. Sandwich ELISA was used to investigate PAI-1 production. HCMV induced the expression of PAI-1-mRNA at 2-5 days postinfection (maximum expression was at 3 days postinfection which was 40% higher than control). HCMV also induced secretion of PAI-1 at 2-5 days postinfection. These results indicate that infection of endothelial cells with HCMV disturbs PAI-1 expression and production in these cells.

Human cytomegalovirus persistently infects aortic endothelial cells

Endothelial cells (EC) have been implicated as constituting an important cell type in the pathogenesis of human cytomegalovirus (HCMV). Microvascular and macrovascular EC exhibit different biochemical and functional properties depending on the organ of origin. Phenotypic differences between microvascular and macrovascular EC may alter the ability of these cells to support HCMV replication. In this study, we compared the replication of HCMV in primary macrovascular aortic EC (AEC) with that in brain microvascular EC (BMVEC). An examination of IE72, pp65, and gB viral antigen expression in BMVEC and AEC by immunoflourescence revealed similar frequencies of infected cells. Intracellular production of virus was 3 log units greater in BMVEC than in AEC, while equal quantities of extracellular virus were produced in both cell types. HCMV infection of BMVEC resulted in rapid cellular lysis, while the virus was nonlytic and continuously released from HCMV-infected AEC for the life span of the culture. An examination of infected cells by electron microscopy revealed the formation of abundant nucleocapsids in both AEC and BMVEC. However, significant amounts of mature viral particles were only detected in the cytoplasm of BMVEC. These observations indicate that levels of HCMV replication in EC obtained from different organs are distinct and suggest that persistently infected AEC may serve as a reservoir of virus.

Modulation of HLA class I antigen and ICAM-2 on endothelial cells after in vitro infection with human cytomegalovirus

The aim of the present work is to investigate the expression of HLA class I antigen and intercellular adhesion molecule-2 (ICAM-2) on the surface of human umbilical cord endothelial cells (HUVEC) after infection with human cytomegalovirus (HCMV). The expression of HLA class I antigen and ICAM-2 were determined (using antibodies against HLA class I antigen and ICAM-2) by attachment inhibition assay and flow cytometric analysis. Attachment inhibition assay demonstrated that HCMV increased the expression of HLA class I antigen. This was confirmed by flow cytometric analysis, which showed an increase in HLA class I antigen expression on HCMV-infected HUVEC. The results of the expression of ICAM-2 using attachment inhibition assay revealed that ICAM-2 is involved significantly in the increased adhesion of T lymphocytes to HCMV-infected HUVEC. However, flow cytometric analysis revealed that there were no changes in the expression of ICAM-2 on HCMV-infected HUVEC. One possible explanation for this is that HCMV induces the activation of ICAM-2 on the surface of HCMV-infected endothelial cells without affecting its expression.

Human cytomagalovirus IE1 and IE2 proteins are mutagenic and mediate "hit-and-run" oncogenic transformation in cooperation with the adenovirus E1A proteins

Some epidemiological studies have suggested a possible link between human cytomegalovirus (HCMV) infection and various malignancies, and HCMV has been shown to transform cultured cells. However, viral DNA is not detected in most transformants, and the mechanism by which HCMV might contribute to oncogenesis has remained obscure. Here we show that the HCMV immediate early 1 and 2 genes can cooperate with the adenovirus E1A gene to generate transformed foci of primary baby rat kidney cells. HCMV gene expression is transient and viral DNA is not present in clonal cell lines derived from the transformed foci. We find that the HCMV immediate early proteins are mutagenic, and we propose that HCMV has the potential to contribute to oncogenesis through a "hit-and-run" mechanism, by inducing mutations in cellular genes.

Increased frequency of specific locus mutation following human cytomegalovirus infection

The effect of human cytomegalovirus (HCMV) infection on the frequency of mutations at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus was studied in Chinese hamster lung V79 cells. When V79 cells were infected with HCMV (strain AD169) at multiplicities of 0.1 to 50 plaque forming units (PFU) per cell the presumptive mutation frequency, as determined by the number of 6-thioguanine-resistant (TGr) colonies, was increased up to 16.8-fold (P < 0.005), depending on the multiplicity of infection. Increases in the mutation frequency at the hprt locus were also observed for other laboratory-adapted HCMV strains (C-87, Davis) and for low passage clinical isolates (82-1, 84-2). The expression time required for the maximum increase in TGr colonies was 3 days and was consistent among the HCMV strains evaluated in this study. UV-irradiation of HCMV stock up to a dose of 9.6 x 10(4) ergs/mm2 increased the mutation frequency, but further exposure to UV light or to heat (56 degrees for 30 min) significantly decreased the frequency of TGr-resistant colonies, suggesting that expression of HCMV genes was involved in the mutation process. HCMV-induced TGr cells demonstrated substantially reduced (> 96%) incorporation of [3H]hypoxanthine. PCR analysis of the hprt locus demonstrated deletions in 9 of 19 HCMV-induced TGr colonies randomly selected for further study, while 2 of 17 spontaneously developed TGr colonies demonstrated deletions. Although insertions were not detected in spontaneously developed clones, 3 of 19 HCMV-induced TGr clones had insertions in the hprt gene. Neither HCMV-specific DNA sequences nor HCMV-specific proteins were detected in the TGr clones obtained after HCMV infection. Infection of V79 cells with HCMV also increased their sensitivity to mutation with N-methyl-N'-nitro-N-nitrosoguanidine, giving a synergistic enhancement of the mutation frequency. These results indicate that HCMV infection has the capacity to induce mutations in the cellular genome and increase the sensitivity of infected cells to mutation by genotoxic chemicals. Although inactivated HCMV particles are responsible for a modest increase in the mutation frequency, expression of HCMV genes is associated with a substantial enhancement of the mutation frequency.

Comparison of the infectivity of the laboratory strain AD169 and a clinical isolate of human cytomegalovirus to human smooth muscle cells

The results displayed by human cytomegalovirus (HCMV) IE/E antigen expression and virus release into the supernatant at various times post infection with a clinical isolate (C3/p5) and AD169 laboratory strain of HCMV, illustrated differences in the biology of these viruses on the various cell lines. While AD169 strain was shown to infect fibroblasts efficiently, it showed a low infectivity profile to smooth muscle cells, whereas C3/p5 displayed comparable infectivity characteristics on both cell lines. Neither virus demonstrated propensity for infecting endothelial cells, although passaging of the C3/p5 for additional 11 passages in endothelial cells provided virus capable of infecting endothelial cells efficiently. These results show that HCMV is capable of infecting smooth muscle cells which could be of relevance to the proposed role of HCMV in atherogenesis and provides further evidence on the adaptation of AD169 to fibroblasts.

A dual role for endothelial cells in cytomegalovirus infection? A study of cytomegalovirus infection in a series of rat endothelial cell lines

Several clinical findings point to the involvement of microvascular endothelial cells in cytomegalovirus-related pathology. In this study the interactions of cytomegalovirus (CMV) with microvascular endothelial cells was investigated in an in vitro rat model. A series of rat endothelial cell lines, considered representative for the heterogeneity of heart microvascular endothelium in vivo, were infected with rat CMV (RCMV). The course of infection and production of infectious virus were examined using immunofluorescence staining and plaque titration assays, and was compared with infection of fully permissive rat fibroblasts. These endothelial cell lines displayed differences in susceptibility to CMV infection. Two endothelial cell lines (RHEC 50 and 191) were practically non-permissive, while four endothelial cell lines (RHEC 3, 10, 11 and 116) were partly permissive for CMV infection. In contrast to CMV infection in fibroblasts, only limited infection of the permissive endothelial cell lines was observed without spreading of CMV infection through the monolayer, although infectious virus was produced. Detachment of infected endothelial cells and recovery of the monolayer with time was observed. The detached endothelial cells were able to transmit CMV infection to fibroblast monolayers, but not to endothelial monolayers. Our in vitro results demonstrate differences in permissiveness for RCMV between the series of rat endothelial cell lines, which is suggestive for endothelial heterogeneity to CMV infection in vivo. Our findings indicate that endothelial cells are relatively resistant to CMV infection and that, upon infection, the endothelial monolayer may dispose of the virus via detachment of the infected cells. This points to a dual role for the endothelium in CMV infection in vivo: a barrier for CMV infection (by the endothelial monolayer) on the one hand and spreading of CMV infection (by detached infected cells) on the other hand.

Cytomegalovirus infection-enhanced chronic kidney allograft rejection is linked with intercellular adhesion molecule-1 expression

In human kidney allografts, association of acute rejection and glomerulopathy with cytomegalovirus (CMV) infection has been demonstrated. To investigate the effect of CMV infection on the development of experimental chronic kidney allograft rejection, heterotopic kidney allografts from DA (Ag-B4, RT1a1) rat donors to WF (Ag-B2, RT1u) rat recipients were used. The animals received cyclosporine A (CsA) 5 mg/kg/day s.c. either for 1 or 12 weeks. Two groups of recipients were infected with 10(5) plaque-forming units of rat CMV (RCMV) and two other groups were left noninfected and used as controls. The grafts were removed 12 weeks after transplantation for histology and immunohistochemistry. RCMV infection significantly enhanced the development of chronic kidney allograft rejection in rats on continuous CsA the intensity of interstitial inflammation (P < 0.025), particularly the degree of pyroninophilic cells in the inflammatory infiltrate (P < 0.025), the glomerular mesangial matrix increase (P < 0.05) and capillary basement membrane thickening (P < 0.01), the extent of endothelial cell swelling (P < 0.025) and intimal proliferation (P < 0.025) in the graft vasculature, and the extent of tubular epithelial atrophy (P < 0.025). Chronic allograft damage index (CADI) was significantly increased to 4.3 +/- 0.8 in RCMV-infected allografts, compared to 0.8 +/- 0.4 in noninfected (P < 0.02). In addition, RCMV infection significantly increased the number of acute rejection episodes (serum creatinine > 200 mumol/liter, P < 0.05) and almost doubled the end-stage serum creatinine. RCMV infection significantly increased ICAM-1 expression on the vascular endothelium (P < 0.05) and tubular epithelial cells (P < 0.01), and was linked with enhanced interstitial, glomerular, and tubular inflammation. In 80% of allografts on continuous CsA, RCMV antigens could be observed in sporadic inflammatory cells one week after infection and in tubular epithelial cells at 12 weeks. In heavily inflamed allografts where the CsA treatment was discontinued at one week, enhancement of RCMV infection on the histological changes attributable to chronic kidney allograft rejection could not be demonstrated. Our results show that during CsA immunosuppression, RCMV infection enhances chronic kidney allograft rejection associated with increased interstitial inflammation as well as vascular endothelial and tubular epithelial ICAM-1 expression.

Chronic rejection and late renal allograft dysfunction

Renal transplantation is currently standard therapy for end-stage kidney disease for children. Despite the considerable improvement in short-term results, the expected allograft half-life has remained the same. This is due to chronic rejection/late graft dysfunction which has proved resistant to therapeutic attempts. During the last few years the multifactorial pathogenesis of chronic renal allograft rejection has been clarified to some extent. Early injury by immunological and non-immunological mechanisms is followed by vascular remodelling due to repetitive cycles of cytokine release, upregulation of growth factors, and vascular smooth muscle cell proliferation. This leads to typical concentric arteriosclerosis and ischemia. Secondary kidney-specific mechanisms are initiated by the reduction in functioning renal mass and lead to gradual progression of chronic rejection. There is no single optimal therapy. Several attempts to influence the pathophysiological cascade have been promising. Attention should be focused on minimizing early immunological/non-immunological injury in order to attenuate future progression of chronic rejection. A significant prolongation of allograft half-life may be achieved during the next decade with the introduction of new therapeutic agents and comprehensive approach to treatment. This would be especially beneficial for pediatric recipients, reducing the need for retransplantation in adulthood.

Cytomegalovirus antigen expression, endothelial cell proliferation, and intimal thickening in rat cardiac allografts after cytomegalovirus infection

BACKGROUND

Cardiac allograft arteriosclerosis is the primary cause of late death in heart transplant recipients. Clinical studies have suggested that humoral and cellular immune response, hyperlipidemia, and cytomegalovirus (CMV) infection may amplify the disease. In this study, the role of CMV infection in the development of rat cardiac allograft arteriosclerosis is investigated.

METHODS AND RESULTS

Heterotopic rat cardiac allografts were performed from the DA to the WF rat strains. To prevent rejection, the recipients received triple-drug (cyclosporine A 20 mg.kg-1.d-1, azathioprine 2 mg.kg-1.d-1, and methylprednisolone 0.5 mg.kg-1.d-1) immunosuppression postoperatively. Recipient rats were infected intraperitoneally (n = 21) with 10(5) plaque-forming units of rat CMV (RCMV) 1 day after transplantation or were left uninfected and used as controls (n = 18). The grafts were removed 7 and 14 days and 1 and 3 months after transplantation. In 42% (9 of 21) of cardiac allografts in RCMV-infected rats, an intramural, mononuclear cell inflammation of small intramyocardial arterioles was observed compared with none in uninfected rats (P = .005). Acute RCMV infection was associated with an early perivascular inflammatory cell response of helper T (W3/25), cytotoxic T (OX8), and NK (3.2.3) cells, macrophages (OX42), and major histocompatibility complex class II expression around small intramyocardial arterioles and capillaries. No upregulation of interleukin-2 receptor expression was seen. In arteries and small intramyocardial arterioles, RCMV infection was associated with a significant endothelial cell proliferation and a clear increase in intimal thickening. Significant endothelial cell proliferation was also observed in the capillaries after RCMV infection. Immunohistochemistry revealed specific focal RCMV early and late antigen expression in epicardial and interstitial ED1-immunoreactive mononuclear cell infiltrates and around small arterioles of RCMV-infected cardiac allografts. Occasionally, media cells of stenosed small intramyocardial arterioles also showed strong focal RCMV antigen expression. In addition, infectious RCMV could be recovered by plaque assay in cardiac allografts expressing RCMV antigens.

CONCLUSIONS

These results demonstrate a productive RCMV infection in cardiac allograft structures and suggest that RCMV infection accelerates cardiac allograft arteriosclerosis, particularly in small intramyocardial arterioles mediated by inflammatory responses in the vascular wall and perivascular space.

Cytomegalovirus and atherosclerosis

Finding that an avian herpesvirus can cause atherosclerosis in chickens prompted studies of human herpesviruses in human atherosclerosis. Antigens and nucleic acid sequences of cytomegalovirus (CMV), a widespread member of the herpesvirus family, were found in arterial lesions in human atherosclerosis, but infectious virus has not been observed. In atherosclerosis patients, high levels of CMV antibodies are present, suggesting the presence of virus that had been activated from a latent state. Atherosclerosis also develops in immune-suppressed heart transplant patients infected with CMV. The properties of CMV are consistent with its involvement at several levels of the atherogenic process. If this concept is correct, immunization with a CMV vaccine should prevent CMV infection and atherosclerosis.

Some nucleoside analogs with anti-human immunodeficiency virus activity inhibit replication of Epstein-Barr virus

The effects of (+)-beta-D-dioxolane-cytosine ((+)-D-beta-DOC), (-)-beta-L-dioxolane-cytosine ((-)-L-beta-DOC), (+)-beta-D-oxathiolane-cytosine ((+)-D-beta-OTC), (-)-beta-L-oxathiolane-cytosine ((-)-L-beta-OTC, or 3TC), 3'-azido-2',3'-dideoxy-5-methyl-cytidine (5-Me-AZDC), and 3'-azido-2',3'-dideoxyuridine (AZDU) on Epstein-Barr virus (EBV) DNA replication in vitro were tested in P3HR-1 cells. Two anti-EBV drugs, 3'-azido-3'-deoxythymidine (AZT) and 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG, or ganciclovir), were used as positive controls. The inhibitory effects on EBV DNA synthesis were quantified by membrane filter and Southern blot hybridizations with an EBV-specific probe BamHI-W fragment. The 50% effective doses (ED50) for EBV DNA replication were 0.15, 0.83, 1.5, 8.3, 14, and 7.7 microM for DHPG, (-)-L-beta-DOC, (+)-D-beta-DOC, (+)-D-beta-OTC, (-)-L-beta-OTC, and AZT, respectively. In contrast, 5-Me-AZDC and AZDU were not effective at concentrations as high as 30 microM. These results indicated that both (-)-L-beta-DOC and (+)-D-beta-DOC were more potent than AZT, which has previously been shown to have anti-EBV activity. (-)-L-beta-DOC and (+)-D-beta-DOC have also been previously demonstrated to suppress the infectivity of human immunodeficiency virus type 1 (HIV-1). Thus, (-)-L-beta-DOC represents the first nucleoside analog with L-configuration exhibiting significant antiviral activities against both EBV and HIV.

Human cytomegalovirus (HCMV) immediate-early enhancer/promoter specificity during embryogenesis defines target tissues of congenital HCMV infection

Congenital human cytomegalovirus (HCMV) infection is a common cause of deafness and neurological disabilities. Many aspects of this prenatal infection, including which cell types are infected and how infection proceeds, are poorly understood. Transcription of HCMV immediate-early (IE) genes is required for expression of all other HCMV genes and is dependent on host cell transcription factors. Cell type-specific differences in levels of IE transcription are believed to underlie differences in infection permissivity. However, DNA transfection experiments have paradoxically suggested that the HCMV major IE enhancer/promoter is a broadly active transcriptional element with little cell type specificity. In contrast, we show here that expression of a lacZ gene driven by the HCMV major IE enhancer/promoter -524 to +13 segment is restricted in transgenic mouse embryos to sites that correlate with known sites of congenital HCMV infection in human fetuses. This finding suggests that the IE enhancer/promoter is a major determinant of HCMV infection sites in humans and that transcription factors responsible for its regulation are cell type-specifically conserved between humans and mice. The lacZ expression patterns of these transgenic embryos yield insight into congenital HCMV pathogenesis by providing a spatiotemporal map of the sets of vascular, neural, and epithelial cells that are likely targets of infection. These transgenic mice may constitute a useful model system for investigating IE enhancer/promoter regulation in vivo and for identifying factors that modulate active and latent HCMV infections in humans.

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. Immunohistochemical 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.

Cytomegalovirus (CMV) and Helicobacter pylori (HP) found in oral mucosal ulcers

The possible involvement of Cytomegalovirus (CMV) and Helicobacter pylori (HP) in oral mucosal ulcers is suggested by their role in the development of ulceration at other mucosal sites of the gastrointestinal tract. A series of 29 incisional biopsies from 29 consecutive and apparently immunocompetent patients attending the clinic for oral ulceration were examined by routine histopathology as well as by in situ hybridisation (ISH) with biotinylated CMV and HP DNA probes. In 14/29 biopsies, Giemsa staining disclosed spiral bacteria. Six (20.7%) of these 14 Giemsa-positive samples showed HP DNA on ISH and 3 ulcers (10.3%) contained CMV DNA. In none of the specimens were CMV and HP detected simultaneously. Two of the ulcers containing CMV DNA were found on the labial mucosa and one on the posterior palatal mucosa, whereas all HP DNA-positive ulcers were located on the buccal mucosa. The results indicate that CMV and HP DNA can be found in separate oral mucosal ulcers in apparently immunocompetent adults.

Active cytomegalovirus infection of arterial smooth muscle cells in immunocompromised rats. A clue to herpesvirus-associated atherogenesis?

The susceptibility of medial and neointimal arterial smooth muscle cells (SMCs) to acute cytomegalovirus (CMV) infection was investigated in immunocompetent and immunocompromised rats. The left common carotid artery of all the rats was injured by balloon catheterization. On days 14 and 17 after injury, rats were either intravenously infected with a rat CMV (RCMV) or mock-infected. Active RCMV infection was shown in the neointima of the injured arteries of immunosuppressed rats, characterized by specific cytopathological changes in hematoxylin-eosin-stained sections and by the presence of early viral antigens and the presence of the virus at different stages of maturation at the electron-microscopic level. Viral genome was shown as well by use of in situ hybridization procedures. However, medial cells were hardly ever infected, and RCMV did not infect neointimal parts that were recovered by endothelial cells. No infection was seen in control right carotid arteries or in the injured arteries of immunocompetent rats. Acute intimal RCMV infection was accompanied by infiltration of inflammatory cells, predominantly mononuclear cells that stained positive with an ED-1 monoclonal antibody. The majority of infected neointimal cells were SMCs containing smooth muscle actin. No changes were found in medial or neointimal cross-sectional areas of the infected arteries. In the present study, an active RCMV infection of arterial SMCs was established in vivo, and it was concluded that neointimal SMCs are far more susceptible than are medial SMCs and that the absence of endothelium and immunosuppression are necessary conditions for arterial RCMV infection.

The effect of short-chain fatty acids on the susceptibility of human umbilical vein endothelial cells to human cytomegalovirus infection

We have compared the replication of three strains of human cytomegalovirus (HCMV), HCMV AD-169, HCMV Towne, or HCMV RC-256, an insertional mutant of Towne containing the LacZ gene of E. coli, in human umbilical vein endothelial cells (HUVEC) and human forskin fibroblasts (HFF). We also examine the effects of salts of short-chain fatty acids on the susceptibility of HUVEC to infection by HCMV. All three virus strains replicated in both cell types, but 10-to 100-fold less virus was produced in HUVEC cells than HFF. For all virus strains, expression of HCMV IE-1 antigen in HFF was > 70% 24 h after inoculation. In contrast, the number of HUVEC exhibiting IE-1 antigen at 24 h was < 15%. Treatment of HUVEC with sodium butyrate, sodium hexanoate, or sodium propionate prior to virus inoculation increased the IE-1 and late HCMV antigen expression in a dose- and time-dependent manner. Virus yield was also increased. This increased susceptibility was inhibited by cycloheximide and tunicamycin, indicating a requirement for new cellular protein synthesis. Treatment with both sodium hexanoate and propionate after virus inoculation increased HUVEC susceptibility to HCMV infection. Treatment of HUVEC with sodium butyrate after virus inoculation also increased HCMV IE-1 antigen expression, but only after removal of the drug. These studies demonstrate that the susceptibility of HUVEC to HCMV infection can be increased by the treatment of the host cell with salts of short-chain fatty acids, such as sodium butyrate, before or after virus inoculation.

HCMV strain comparison by restriction analysis of genomic virus DNA and of a PCR-amplified DNA fragment

BACKGROUND

Human cytomegalovirus (HCMV) is ubiquitous and a major cause of disease in the immunocompromised which include the unborn fetus. HCMV strains are closely related and may be difficult to differentiate.

OBJECTIVES

To analyze new HCMV isolates and highly passaged strains by conventional restriction fragment length polymorphism (RFLP) analysis of HCMV DNA and restriction analysis (RA) of a PCR-amplified a-sequence fragment to identify epidemiological relatedness.

STUDY DESIGN

DNA from 14 low-passaged clinical isolates and the high-passaged strains S348 and AD169 were analyzed by RFLP analysis of BamHI, PstI or HpaII digestion as well as by PCR a-sequence amplification. The laboratory results were compared according to epidemiological findings.

RESULTS

Of the 14 clinical isolates 13 could be distinguished from each other by RFLP analysis. Isolates from an infant and its mother had identical restriction fragment patterns. Eight of 13 clinical isolates were differentiated from each other by comparing a-sequence PCR fragments according to length and the presence of cleavage sites for 6 different restriction enzymes. The mother-infant isolates were identical by the a-sequence PCR criteria. All 14 low-passaged isolates differed from the high-passaged S384 and AD169 strains by both distinguishing approaches.

CONCLUSIONS

Both RFLP and PCR-amplified a-sequence fragment analysis clearly differentiated between low- and high-passaged HCMV isolates and are useful epidemiological tools for determining viral strain relatedness.

Interleukin-1 production and cell-activation response to cytomegalovirus infection of vascular endothelial cells

Human cytomegalovirus (HCMV) is a source of major complications in immunosuppressed individuals, and endothelial involvement in HCMV infection is well documented. Traditionally laboratory strains of HCMV have been used in experimental investigations in vitro; however the continuous propagation of these strains in fibroblasts have attenuated the virus making it unsuitable for infecting other cell systems such as endothelial cells. In this study a recent clinical isolate of HCMV was propagated through several passages in endothelial cells and was used to investigate the effect of HCMV infection of human umbilical vein endothelial cells (HUVEC) on IL-1 production and cell proliferation. Infection of HUVEC with the clinical isolate of HCMV (at multiplicity of infection 5:1) suppressed the production of IL-1 alpha (82%) and IL-1 beta (99%) at 5 h post infection; the levels returned to that of the control within 24h post infection. Ultraviolet inactivated (but not heat killed) virus produced similar suppression confirming that a thermolabile viral structural protein or intact virion were responsible for this suppression. Infection of HUVEC with the clinical isolate increased the number of these cells and the rate of their proliferation. An increase of infected HUVEC number under quiescent growth conditions continued as the infection progressed (6-10 days post infection), exhibiting, at 3 days post infection, 5 times the number of uninfected HUVEC (control) which did not tolerate the quiescent culture conditions for more than 4 days. Live virus is responsible for this increase because UV-inactivated virus did not maintain the proliferation of HUVEC. These studies suggest that while infection of HUVEC with a recent clinical isolate of HCMV suppressed the production of IL-1 at early hours after infection, it increased the proliferation of these cells at later stages of infection.

Cytomegalovirus infection enhances smooth muscle cell proliferation and intimal thickening of rat aortic allografts

Inbred DA (AG-B4, RT1a) and WF (AG-B2, RT1v) rats were used as donors and recipients of aortic allografts. The recipient rats were inoculated i.p. either on day 1 (early infection) or on day 60 (late infection) with 10(5) plaque-forming units of rat cytomegalovirus (RCMV). The control rats were left noninfected. The presence of viral infection was demonstrated by plaque assays from biopsies of the salivary glands, liver, and spleen at sacrifice. The rats received 300 microCi[3H]thymidine by i.v. injection 3 h before sacrifice, and the grafts were removed at various time points for histology, immunohistochemistry, and autoradiography. RCMV infection significantly enhanced the generation of allograft arteriosclerosis. Infection at the time of transplantation had two important effects. First, the infection was associated with an early, prominent inflammatory episode and proliferation of inflammatory cells in the allograft adventitia. Second, the viral infection doubled the proliferation rate of smooth muscle cells and the arteriosclerotic alterations in the intima. In late infection the impact of RCMV infection on the allograft histology was nearly nonexistent. RCMV infection showed no effect in syngeneic grafts. These results suggest that early infection is more important to the generation of accelerated allograft arteriosclerosis than late infection, and that an acute alloimmune response must be associated with virus infection, to induce accelerated allograft arteriosclerosis. RCMV-infected aortic allografts, as described here, provide the first experimental model to investigate the interaction between the virus and the vascular wall of the transplant.

Murine cytomegalovirus interacts with major histocompatibility complex class I molecules to establish cellular infection

The expression of stable, correctly folded major histocompatibility complex class I molecules conferred susceptibility to murine cytomegalovirus (MCMV) in cells which were previously resistant to infection, demonstrating that these molecules interact critically with MCMV to initiate infection. All class I molecules could potentiate MCMV infection but H-2Dd and Kb molecules were most efficient. Monoclonal antibodies specific for the alpha 1 and/or alpha 2 domains of Dd and Kb inhibited infection. Infection of L cells transfected with hybrid major histocompatibility complex class I molecules demonstrated that allelic control of susceptibility to MCMV mapped to the alpha 1 domain of Dd when in correct configuration with the alpha 2 and alpha 3 domains. In MCMV-resistant RMA-S cells, an improvement in the conformation of class I molecules introduced susceptibility to infection.

Definition of a subset of human peripheral blood mononuclear cells that are permissive to human cytomegalovirus infection

The identity of cells responsible for transmission of human cytomegalovirus (HCMV) in blood products or bone marrow transplants is unknown. We have tested the capacity of HCMV to in vitro infect human peripheral blood mononuclear cells (PBMC) from healthy donors and found that certain PBMC are permissive to HCMV infection. In vitro-infected viable cells were double stained for surface expression of different HMCV proteins and for cell-type-specific antigens to allow the identification of sensitive cells. All analysis were performed on viable cells, using HCMV-specific monoclonal antibodies and automated flow cytofluorimetry. PBMC were infected either with the laboratory-adapted HCMV strain AD169 or with a virus isolate obtained from a viremic patient. Up to 25% of all PBMC could express the major immediate-early antigen as well as the pp65 antigen, known at the lower matrix protein. Infected cells were mainly CD14+ monocytes, but also a small population of large CD8+ cells were susceptible to HCMV infection. CD19+ B lymphocytes were resistant to HCMV infection. Different populations of infected cells were enriched by using Dynabeads coated with cell-type-specific antibodies, and the presence of infectious virus was demonstrated by incubating the selected and sonicated cell material on human fibroblasts. Only material from infected monocytes and from CD3+ CD8+ cells gave rise to HCMV-specific plaques. The presence of HCMV mRNA as a sign of active viral transcription of the major immediate-early and late pp150 genes in infected cells was demonstrated by using nested reversed polymerase chain reaction. A common denominator was found for all cells that could be infected with HCMV. The CD13 antigen, a 130- to 150-kDa integral membrane protein identical to the enzyme aminopeptidase N, was expressed on all HCMV-permissive cells.

An immortalized human fibroblast cell line is permissive for human cytomegalovirus infection

Human foreskin fibroblasts (HFF) were immortalized via retrovirus-mediated gene transfer of the E6 and E7 genes of human papillomavirus type 16. An immortalized fibroblast (IF) cell line which was morphologically akin to the parental cell line was isolated. The IF cell line was evaluated for permissiveness to human cytomegalovirus (HCMV) infection after the IF cell line surpassed the normal passage limitation of diploid fibroblasts. Western immunoblot analysis of representative HCMV-encoded immediate-early (72-kDa), early (gB), and late (gH) gene products demonstrated that the IF cell line produced these proteins analogous to those produced by the parental HFF cells. Similar quantities of infectious virus were produced in the IF and HFF cell lines as determined in one-step growth curve experiments. Compared with the HFF cells, morphologically identical plaques were produced in the IF cell line in approximately 10 to 12 days postinfection. These findings indicate that fibroblast cell lines immortalized with transforming genes of human papillomavirus retain complete permissiveness to HCMV infection and support plaque formation. The IF cell line will be useful for future genetic analysis of HCMV.

Cytomegalovirus- and interferon-related effects on human endothelial cells. Cytomegalovirus infection reduces upregulation of HLA class II antigen expression after treatment with interferon-gamma

Cultured human umbilical vein endothelial cells (HUVEs) were infected with human cytomegalovirus (HCMV) strain AD169. Up to 50% HUVEs proved to be positive for HCMV early nuclear antigens 24 hours after inoculation with virus. Following infection kinetics of surface expression of HLA class I and II, intercellular adhesion molecule (ICAM-1) and endothelial lymphocyte adhesion molecule (ELAM-1) on HUVEs were investigated by means of flow cytometry. A slight increase in HLA class I expression was observed, whereas expression of HLA class II (DR, DP, DQ) antigens was not induced by infection with HCMV. Furthermore, when compared with uninfected cells treated with interferon-gamma (IFN-gamma), reduced enhancement of HLA-DR expression was conspicuous in HCMV-infected cells treated with IFN-gamma. There is evidence that only a portion of HUVE is affected in its ability to upregulate HLA class II antigens. While expression of ICAM-1 was found to be enhanced between 8 and 20 hours after infection with a maximum at 12 hours after infection, no modulation of ELAM-1 was seen.

HMEC-1: Establishment of an Immortalized Human Microvascular Endothelial Cell Line

The study of human microvascular endothelial cells has been limited, because these cells are difficult to isolate in pure culture, are fastidious in their in vitro growth requirements, and have a very limited lifespan. In order to overcome these difficulties, we have transfected human dermal microvascular endothelial cells (HMEC) with a PBR-322-based plasmid containing the coding region for the simian virus 40 A gene product, large T antigen, and succeeded in immortalizing them. These cells, termed CDC/EU.HMEC-1 (HMEC-1), have been passaged 95 times to date and show no signs of senescence, whereas normal microvascular endothelial cells undergo senescence at passages 8-10. HMEC-1 exhibit typical cobblestone morphology when grown in monolayer culture, express and secrete von Willebrand's Factor, take up acteylated low-density lipoprotein, and rapidly form tubes when cultured on matrigel. HMEC-1 grow to densities three to seven times higher than microvascular endothelial cells and require much less stringent growth medium. HMEC-1 will grow in the absence of human serum, whereas microvascular endothelial cells require culture medium supplemented with 30% human serum. These cells express other cell-surface molecules typically associated with endothelial cells, including CD31 and CD36 and epitopes identified by monoclonal antibodies EN4 and PAL-E. They also express the cell adhesion molecules ICAM-1 and CD44 and following stimulation with interferon-gamma express major histocompatibility complex class II antigens. HMEC-1 specifically bind lymphocytes in cell adhesion assays. Thus HMEC-1 is the first immortalized human microvascular endothelial cell line that retains the morphologic, phenotypic, and functional characteristics of normal human microvascular endothelial cells.

Comparison of MRC-5 and continuous cell lines for detection of cytomegalovirus in centrifugation cultures

Continuous cell lines were assessed for use for rapid human cytomegalovirus (HCMV) detection procedures combining tissue culture, centrifugation, and immediate early antigen (IEA) immunostaining. Human cells (MRC-5 embryonic fibroblasts, U-373MG astrocytoma cells, differentiated teratocarcinoma (Tera-2) cells), murine cells (BALB/c-3T3 and Y-1 cells), BHK21 hamster cells, and mink lung (ML) cells were first inoculated with HCMV laboratory strain. IEA synthesizing cells were detected by immunoperoxidase assay using a monoclonal antibody. ML cells and differentiated Tera-2 cells exhibited more positive cells than MRC-5 cells. BHK21, and MRC-5 cells were equivalent in sensitivity whereas U-373MG, BALB/c-3T3, and Y-1 cells had only reduced IEA positive cells. When 63 urine specimens were inoculated onto MRC-5, ML and differentiated Tera-2 cells, 20 (31.7%) were positive in MRC-5 cells versus 18 (28.5%) in ML or Tera-2 cells. Moreover, greater numbers of infected cells were detected in MRC-5 cells than in these two cell lines. MRC-5 cells were superior for detection of HCMV in clinical samples by centrifugation cultures.

The effects of beta-2-microglobulin on the infectivity of murine cytomegalovirus

The role of beta-2-microglobulin (beta 2m) in murine cytomegalovirus (MCMV) infection of susceptible (H-2d) and resistant (H-2k) murine embryo fibroblasts (MEF) and peritoneal macrophages was evaluated using serum-free virus (SF-MCMV). The infectivity of SF-MCMV was significantly lower than virus propagated in serum, although the concentrations of virions were similar. Infection of cells with SF-MCMV was assessed by measuring the proportion of cells expressing viral antigens, the sizes of plaques formed in fibroblast monolayers and TCID50 titers. Infection of susceptible fibroblasts was significantly increased 1.6-4.7 fold by the addition of whole FCS, a less than 20 kDa FCS fraction, or purified human beta 2m. These supplements also significantly enhanced infection of susceptible macrophages and increased TCID50 titers by 3.5-10 fold in susceptible MEF. In relatively resistant H-2k cells, the TCID50 titer and the proportion of cells expressing viral antigens after infection with SF-MCMV were not affected by beta 2m or FCS, but plaque sizes were increased 2.5-3 fold in resistant BALB.K MEF. When human or murine beta 2m was added to infected cultures, immunogold electron microscopy revealed these proteins to be always associated extracellularly with the tegument material of disrupted multicapsid virions, but rarely with the envelope of intact virions. However, no murine beta 2m was found in association with the envelope or tegument of SF-MCMV. These relatively modest effects of beta 2m which were restricted to genetically susceptible cells, may be due to tegument-bound beta 2m facilitating infection by capsids, or the stabilisation of the conformation of Class 1 molecules by exogenous beta 2m, promoting MCMV binding to the target cell.

Cytomegalovirus infection induces vascular injury in the rat

The role of cytomegalovirus (CMV) in the early development of atherosclerosis was studied in a rat model. Arterial samples derived from virus-infected normo- and hypercholesterolaemic animals were investigated by light microscopy at 1, 4, 8 and 16 weeks post infection. Early atherogenic lesions comparable to those seen in non-infected hypercholesterolaemic rats were found in CMV-infected normocholesterolaemic and hypercholesterolaemic animals, starting at 1 week post infection. The changes consisted of minimal endothelial cell damage, as shown by the en face technique, and a more than 10-fold increase in the number of leukocytes adhering to the aortic intima. The increased adhesion of leukocytes was observed in infected normocholesterolaemic rats but only in the non-infected rats which were hypercholesterolaemic. The infection of hypercholesterolaemic rats did not enhance this effect although it resulted in increased migration of the leukocytes into the subendothelial space. CMV infection of normocholesterolaemic rats induced lipid accumulation in the endothelium. In these animals approximately 1% of the endothelial cells contained lipid at 1 week post infection. In the non-infected hypercholesterol-fed animals 10% of the cells contained lipid. CMV infection in these rats induced an extra increase of the lipid-containing endothelial area. The changes in the CMV infected animals largely corresponded with the intimal injury observed in the hypercholesterolaemic rats. These results support the hypothesis that CMV may be one of the factors involved in atherogenesis.