Modulation of major histocompatibility class II protein expression by varicella-zoster virus

Varicella zoster virus immune evasion strategies

The capacity of varicella zoster virus (VZV) to cause varicella (chickenpox) relies upon multiple steps, beginning with inoculation of the host at mucosal sites with infectious virus in respiratory droplets. Despite the presence of a powerful immune defense system, this virus is able to disseminate from the site of initial infection to multiple sites, resulting in the emergence of distinctive cutaneous vesiculopustular lesions. Most recently, it has been proposed that the steps leading to cutaneous infection include VZV infecting human tonsillar CD4(+) T cells that express skin homing markers that allow them to transport VZV directly from the lymph node to the skin during the primary viremia. It has also been proposed that dendritic cells (DC) of the respiratory mucosa may be among the first cells to encounter VZV and these cells may transport virus to the draining lymph node. These various virus-host cell interactions would all need to occur in the face of an intact host immune response for the virus to successfully cause disease. Significantly, following primary exposure to VZV, there is a prolonged incubation period before emergence of skin lesions, during which time the adaptive immune response is delayed. For these reasons, it has been proposed that VZV must encode functions which benefit the virus by evading the immune response. This chapter will review the diverse array of immunomodulatory mechanisms identified to date that VZV has evolved to at least transiently limit immune recognition.

Respiratory syncytial virus impairs macrophage IFN-alpha/beta- and IFN-gamma-stimulated transcription by distinct mechanisms

Macrophages are the primary lung phagocyte and are instrumental in maintenance of a sterile, noninflamed microenvironment. IFNs are produced in response to bacterial and viral infection, and activate the macrophage to efficiently counteract and remove pathogenic invaders. Respiratory syncytial virus (RSV) inhibits IFN-mediated signaling mechanisms in epithelial cells; however, the effects on IFN signaling in the macrophage are currently unknown. We investigated the effect of RSV infection on IFN-mediated signaling in macrophages. RSV infection inhibited IFN-beta- and IFN-gamma-activated transcriptional mechanisms in primary alveolar macrophages and macrophage cell lines, including the transactivation of important Nod-like receptor family genes, Nod1 and class II transactivator. RSV inhibited IFN-beta- and IFN-gamma-mediated transcriptional activation by two distinct mechanisms. RSV impaired IFN-beta-mediated signal transducer and activator of transcription (STAT)-1 phosphorylation through a mechanism that involves inhibition of tyrosine kinase 2 phosphorylation. In contrast, RSV-impaired transcriptional activation after IFN-gamma stimulation resulted from a reduction in the nuclear STAT1 interaction with the transcriptional coactivator, CBP, and was correlated with increased phosphorylation of STAT1beta, a dominant-negative STAT1 splice variant, in response to IFN-gamma. In support of this concept, overexpression of STAT1beta was sufficient to repress the IFN-gamma-mediated expression of class II transactivator. These results demonstrate that RSV inhibits IFN-mediated transcriptional activation in macrophages, and suggests that paramyxoviruses modulate an important regulatory mechanism that is critical in linking innate and adaptive immune mechanisms after infection.

Influenza A virus abrogates IFN-gamma response in respiratory epithelial cells by disruption of the Jak/Stat pathway

The innate immunity to viral infections induces a potent antiviral response mediated by interferons (IFN). Although IFN-gamma is detected during the acute stages of illness in the upper respiratory tract secretions and in the serum of influenza A virus-infected individuals, control of influenza A virus is not dependent upon IFN-gamma as evidenced by studies using anti-IFN-gamma Ab and IFN-gamma(-/-) mice. Thus, we hypothesized that IFN-gamma is not critical in host survival because influenza A virus has mechanisms to evade the antiviral activity of IFN-gamma. To test this, A549 cells, an epithelial cell line derived from lung adenocarcinoma, were infected with influenza virus strain A/Aichi/2/68 (H3N2) (Aichi) and/or stimulated with IFN-gamma to detect IFN-gamma-stimulated MHC class II expression. Influenza A virus infection inhibited IFN-gamma-induced up-regulation of HLA-DRalpha mRNA and the IFN-gamma induction of class II transactivator (CIITA), an obligate mediator of MHC class II expression. Nuclear translocation of Stat1alpha upon IFN-gamma stimulation was significantly inhibited in influenza A virus-infected cells and this was associated with a decrease in Tyr701 and Ser727 phosphorylation of Stat1alpha. Thus, influenza A virus subverts antiviral host defense mediated by IFN-gamma through effects on the intracellular signaling pathways.

WSSV infection activates STAT in shrimp

Although the JAK/STAT signaling pathway is usually involved in antiviral defense, a recent study suggested that STAT might be annexed by WSSV (white spot syndrome virus) to enhance the expression of a viral immediate early gene in infected shrimps. In the present study, we clone and report the first full-length cDNA sequence for a crustacean STAT from Penaeus monodon. Alignment and comparison with the deduced amino acid sequences of other STATs identified several important conserved residues and functional domains, including the DNA binding domain, SH2 domain and C-terminal transactivation domain. Based on these conserved sequences, a phylogenetic analysis suggested that shrimp STAT belongs to the ancient STAT family, while the presence of the functional domains suggested that shrimp STAT might share similar functions and regulating mechanisms with the well-known STATs isolated from model organisms. Real-time PCR showed a decreased transcription level of shrimp STAT after WSSV infection, but a Western blot analysis using anti-phosphorylated STAT antibody showed an increased level of phosphorylated (activated) STAT in the lymphoid organ of shrimp after WSSV infection. We further show that a primary culture of lymphoid organ cells from WSSV-infected shrimp resulted in activated STAT being translocated from the cytoplasm to the nucleus. This report provides experimental evidence that shrimp STAT is activated in response to WSSV infection. Our results support an earlier finding that WSSV does not disrupt JAK/STAT pathway, but on the contrary benefits from STAT activation in the shrimp host.

Varicella-zoster virus modulates NF-kappaB recruitment on selected cellular promoters

Intercellular adhesion molecule 1 (ICAM-1) expression is down-regulated in the center of cutaneous varicella lesions despite the expression of proinflammatory cytokines such as gamma interferon and tumor necrosis factor alpha (TNF-alpha). To study the molecular basis of this down-regulation, the ICAM-1 induction of TNF-alpha was analyzed in varicella-zoster virus (VZV)-infected melanoma cells (MeWo), leading to the following observations: (i) VZV inhibits the stimulation of icam-1 mRNA synthesis; (ii) despite VZV-induced nuclear translocation of p65, p52, and c-Rel, p50 does not translocate in response to TNF-alpha; (iii) the nuclear p65 present in VZV-infected cells is no longer associated with p50 and is unable to bind the proximal NF-kappaB site of the icam-1 promoter, despite an increased acetylation and accessibility of the promoter in response to TNF-alpha; and (iv) VZV induces the nuclear accumulation of the NF-kappaB inhibitor p100. VZV also inhibits icam-1 stimulation of TNF-alpha by strongly reducing NF-kappaB nuclear translocation in MRC5 fibroblasts. Taken together, these data show that VZV interferes with several aspects of the immune response by inhibiting NF-kappaB binding and the expression of target genes. Targeting NF-kappaB activation, which plays a central role in innate and adaptive immune responses, leads to obvious advantages for the virus, particularly in melanocytes, which are a site of viral replication in the skin.

Marek's disease virus up-regulates major histocompatibility complex class II cell surface expression in infected cells

Many herpesviruses modulate major histocompatibility complex (MHC) expression on the cell surface as an immune evasion mechanism. We report here that Marek's disease virus (MDV), a lymphotrophic avian alphaherpesvirus, up-regulates MHC class II cell surface expression in infected cells, contrary to all other herpesviruses examined to date. This MDV-induced class II up-regulation was detected both in vitro and in vivo. This effect was not solely an indirect effect of interferon, which is a highly potent natural inducer of MHC class II expression, since MHC class II up-regulation in cultured primary fibroblast cells was confined to the infected cells only. MHC class II up-regulation was also observed in infected cells of the bursa of Fabricius during the lytic phase of MDV infection in birds and upon reactivation of MDV from latency in an MDV-transformed cell line. As MDV is a strictly cell-associated virus and requires activated T cells for its life cycle, this up-regulation of MHC class II in infected cells may contribute to virus spread within the infected host by increasing the chance of contact between productively infected cells and susceptible activated T cells.

Molecular studies of Varicella zoster virus

VZV is a highly cell-associated member of the Herpesviridae family and one of the eight herpesviruses to infect humans. The virus is ubiquitous in most populations worldwide, primary infection with which causes varicella, more commonly known as chickenpox. Characteristic of members of the alphaherpesvirus sub-family, VZV is neurotropic and establishes latency in sensory neurones. Reactivation from latency, usually during periods of impaired cellular immunity, causes herpes zoster (shingles). Despite being one of the most genetically stable human herpesviruses, nucleotide alterations in the virus genome have been used to classify VZV strains from different geographical regions into distinct clades. Such studies have also provided evidence that, despite pre-existing immunity to VZV, subclinical reinfection and reactivation of reinfecting strains to cause zoster is also occurring. During both primary infection and reactivation, VZV infects several PBMC and skin cell lineages. Difficulties in studying the pathogenesis of VZV because of its high cell association and narrow host range have been overcome through the development of the VZV severe combined immunodeficient mouse model carrying human tissue implants. This model has provided a valuable tool for studying the importance of individual viral proteins during both the complex intracellular replication and assembly of new virions and for understanding the underlying mechanism of attenuation of the live varicella vaccine. In addition, a rat model has been developed and successfully used to uncover which viral proteins are important for both the establishment and maintenance of latent VZV infection.

Varicella-zoster virus influences the activities of components and targets of the ERK signalling pathway

Varicella-zoster virus (VZV) is ultimately dependent upon its host cell for replication. To ensure its reproduction, VZV reorganizes various cellular functions by taking advantage of pre-existing signalling pathways. Recently, it was demonstrated that the activation of stress-related mitogen-activated protein kinase pathways following infection led to increased phosphorylation of cellular transcription factors involved in VZV gene expression. Here, it was shown that members of the extracellular signal-regulated kinase (ERK) pathway are also influenced following VZV infection: c-Raf remained inactive in infected MeWo cells, whereas MEK1/2 and ERK1/2 were phosphorylated transiently, reaching their highest level of phosphorylation at between 10 and 12 h post-infection. Inhibition of this pathway resulted in a severe reduction in viral progeny and in an increased apoptotic response, indicating that the functionality of this cascade is essential for successful high-rate replication. In addition, the activities of Bad, a cytoplasmic target of ERK via ribosomal S6 kinase, and the nuclear-localized target c-Myc were analysed. Bad is a member of the Bcl-2 family and has a key function in regulating apoptosis. Pro-apoptotic functions of Bad are repressed by phosphorylation. A 10-fold increase in Bad phosphorylation at Ser-112 was detected following infection, which was suppressed after inhibition of ERK. The transcription factor c-Myc is involved in the regulation of cell growth and apoptosis. By performing immunoblots and quantitative RT-PCR, suppression of c-Myc expression was demonstrated at both the transcriptional and translational levels in VZV-infected cells. These results suggest that VZV optimizes the conditions for its replication in different ways: upregulation of proviral-acting systems and suppression of potentially antiviral-acting systems.

A tale of 2 alpha-herpesviruses: lessons for vaccinologists

Of the 8 known herpesviruses that affect human beings, we only have successful vaccines against varicella zoster virus. This brief review compares the pathogenesis of varicella zoster virus with that of the closely related alpha-herpesviruses herpes simplex virus 1 and 2, for which we have no satisfactory vaccines. The main objective of this review is to learn lessons from the success of varicella zoster virus vaccine that could be exploited for the development of successful vaccines against herpes simplex virus and perhaps against other herpes viruses.

Regulation of MHC class II gene expression by the class II transactivator

MHC class II molecules are pivotal for the adaptive immune system, because they guide the development and activation of CD4+ T helper cells. Fulfilling these functions requires that the genes encoding MHC class II molecules are transcribed according to a strict cell-type-specific and quantitatively modulated pattern. This complex gene-expression profile is controlled almost exclusively by a single master regulatory factor, which is known as the class II transactivator. As we discuss here, differential activation of the three independent promoters that drive expression of the gene encoding the class II transactivator ultimately determines the exquisitely regulated pattern of MHC class II gene expression.

T-cell tropism and the role of ORF66 protein in pathogenesis of varicella-zoster virus infection

The pathogenesis of varicella-zoster virus (VZV) involves a cell-associated viremia during which infectious virus is carried from sites of respiratory mucosal inoculation to the skin. We now demonstrate that VZV infection of T cells is associated with robust virion production and modulation of the apoptosis and interferon pathways within these cells. The VZV serine/threonine protein kinase encoded by ORF66 is essential for the efficient replication of VZV in T cells. Preventing ORF66 protein expression by stop codon insertion (pOka66S) impaired the growth of the parent Oka (pOka) strain in T cells in SCID-hu T-cell xenografts in vivo and reduced formation of VZV virions. The lack of ORF66 protein also increased the susceptibility of infected T cells to apoptosis and reduced the capacity of the virus to interfere with induction of the interferon (IFN) signaling pathway following exposure to IFN-gamma. However, preventing ORF66 protein expression only slightly reduced growth in melanoma cells in culture and did not diminish virion formation in these cells. The pOka66S virus showed only a slight defect in growth in SCID-hu skin implants compared with intact pOka. These observations suggest that the ORF66 kinase plays a unique role during infection of T cells and supports VZV T-cell tropism by contributing to immune evasion and enhancing survival of infected T cells.

An influx of macrophages is the predominant local immune response in ovine pulmonary adenocarcinoma

Infection with a retrovirus, Jaagsiekte sheep retrovirus (JSRV), causes ovine pulmonary adenocarcinoma (OPA). The excess production of surfactant proteins by alveolar tumour cells results in increased production of pulmonary fluid, which is characteristically expelled through the nostrils of affected sheep. The immune response to JSRV and the tumour is poorly understood: no JSRV-specific circulating antibodies or T cells have been detected to date. The aim of the present study was to obtain phenotypic evidence for a local immune response in OPA lungs. Specific-pathogen free lambs were infected intratracheally with JSRV. When clinical signs of OPA were apparent, the lungs were removed at necropsy and immunohistochemistry (IHC) was performed on lung sections using a panel of mouse anti-sheep mAbs. No influx of dendritic cells, B cells, CD4, CD8 or gammadelta T cells was seen in the neoplastic nodules or in their periphery. MHC Class II-positive cells were found intratumourally, peritumourally and in the surrounding alveolar lumina. In the tumours, many of these cells were shown to be fibroblasts and the remainder were likely to be mature macrophages. In the alveolar lumen, the MHC Class II-positive cells were CD14-positive and expressed high levels of IFN-gamma. They appeared to be immature monocytes or macrophages which then differentiated to become CD14-negative as they reached the periphery of the tumours. A high level of MHC Class I expression was detected on a range of cells in the OPA lungs but the tumour nodules themselves contained no MHC Class I-positive cells. On the basis of these findings, it is proposed that the lack of an effective immune response in OPA could result from a mechanism of peripheral tolerance in which the activity of the invading macrophages is suppressed by the local environment, possibly as a consequence of the inhibitory properties of the surfactant proteins.

The varicella-zoster virus-mediated delayed host shutoff: open reading frame 17 has no major function, whereas immediate-early 63 protein represses heterologous gene expression

We reported that varicella-zoster virus (VZV) causes a delayed host shutoff during its replicative cycle. VZV open reading frame 17 (ORF17) is the homologue of the herpes simplex virus (HSV) UL41 gene encoding the virion host shutoff (vhs) protein which is responsible for the shutoff effect observed in HSV-infected cells. In the present study, we demonstrated that ORF17 is expressed as a late protein during the VZV replicative cycle in different infected permissive cell lines which showed a delayed shutoff of cellular RNA. A cell line with stable expression of VZV ORF17 was infected with VZV. In these cells, VZV replication and delayed host shutoff remained unchanged when compared to normal infected cells. ORF17 was not capable of repressing the expression of the beta-gal reporter gene under the control of the human cytomegalovirus immediate-early gene promoter or to inhibit the expression of a CAT reporter gene under the control of the human GAPDH promoter, indicating that ORF17 has no major function in the VZV-mediated delayed host shutoff. To determine whether other viral factors are involved in the host shutoff, a series of cotransfection assays was performed. We found that the immediate-early 63 protein (IE63) was able to downregulate the expression of reporter genes under the control of the two heterologous promoters, indicating that this viral factor can be involved in the VZV-mediated delayed host shutoff. Other factors can be also implicated to modulate the repressing action of IE63 to achieve a precise balance between the viral and cellular gene expression.

Relationship between polymorphism of class II transactivator gene promoters and chronic hepatitis B

AIM: To investigate the relationship between the polymorphism of class II transactivator (CIITA) gene promoters and chronic hepatitis B (CHB).

METHODS: Genomic DNA was prepared from peripheral blood leukocytes. Promoters I, III and IV of gene were analyzed respectively with polymerase chain reaction single strand conformation polymorphism (PCR-SSCP) in 65 patients with CHB, 26 patients with acute hepatitis B (AHB) and 85 normal controls.

RESULTS: No abnormal migration was found in PCR-SSCP analysis of the three promoters in the three groups. Also, no sequential difference was observed at the three promoters among the CHB patients, AHB patients and normal controls.

CONCLUSION: No polymorphism in promoters I, III and IV of CIITA gene exists in CHB patients, ABH patients and normal controls, suggesting that the promoter of CIITA gene might be a conserved domain.

Herpes simplex virus and varicella-zoster virus: why do these human alphaherpesviruses behave so differently from one another?

Members of the Herpesviridae family of viruses are classified into the alpha, beta and gamma subfamilies. The alpha subfamily is estimated to have diverged from the beta and gamma subfamilies 200-220 million years ago. The ancestors of the herpes simplex virus (HSV) and the varicella-zoster virus (VZV), two ubiquitous and clinically important human pathogens, appeared 70-80 million years ago. As these viruses coevolved with their specific primate hosts, genetic rearrangements led to the development of the contemporary alphaherpesviruses and their distinct complement of genes. Here the distinct features of HSV and VZV are discussed in terms of their transmissibility, clinical picture, tissue tropism, establishment of latency/reactivation and immune evasion, which can, at least in part, be explained by differences in their genomes.

The host response to smallpox: analysis of the gene expression program in peripheral blood cells in a nonhuman primate model

Smallpox has played an unparalleled role in human history and remains a significant potential threat to public health. Despite the historical significance of this disease, we know little about the underlying pathophysiology or the virulence mechanisms of the causative agent, variola virus. To improve our understanding of variola pathogenesis and variola-host interactions, we examined the molecular and cellular features of hemorrhagic smallpox in cynomolgus macaques. We used cDNA microarrays to analyze host gene expression patterns in sequential blood samples from each of 22 infected animals. Variola infection elicited striking and temporally coordinated patterns of gene expression in peripheral blood. Of particular interest were features that appear to represent an IFN response, cell proliferation, immunoglobulin gene expression, viral dose-dependent gene expression patterns, and viral modulation of the host immune response. The virtual absence of a tumor necrosis factor alpha/NF-kappaB-activated transcriptional program in the face of an overwhelming systemic infection suggests that variola gene products may ablate this response. These results provide a detailed picture of the host transcriptional response during smallpox infection, and may help guide the development of diagnostic, therapeutic, and prophylactic strategies.

The human histocompatibility leukocyte antigen (HLA) haplotype is associated with the onset of postherpetic neuralgia after herpes zoster

In some herpes zoster patients, pain persists for more than 3 months or more after healing of vesicular eruptions; this condition is termed postherpetic neuralgia (PHN). We have recently reported the association of the human histocompatibility leukocyte antigens (HLA) haplotype, HLA-A*3303-B*4403-DRB1*1302 with PHN patients; however, it has not been determined whether the haplotype is also associated with herpes zoster that did not develop subsequent PHN. To distinguish whether the haplotype is associated with herpes zoster or the development of PHN, we examined if herpes zoster patients without subsequently PHN are also associated with the HLA haplotype or not. Herpes zoster patients were followed up for more than 6 months, and HLA alleles and haplotypes were compared among the PHN patients (n = 52) the herpes zoster patients who did not develop PHN (n = 42) and healthy controls (n = 125). The frequencies of the risk haplotype in the PHN patients, in the healthy controls and in the herpes zoster patients without subsequent PHN were 16.3, 5.2 and 4.8%, respectively. While the frequency of the risk haplotype was significantly higher in the PHN patients than in the healthy controls (P = 0.0006) no difference was observed between the herpes zoster patients without subsequent PHN and the healthy controls. No significant association was found between the duration of symptoms or the site of herpes zoster and the HLA alleles and the haplotype. These results suggest that the HLA-A*3303-B*4403-DRB1*1302 haplotype plays an important role in the development of PHN after herpes zoster, but not in the onset of herpes zoster.

Herpes simplex virus 1 gene products occlude the interferon signaling pathway at multiple sites

Earlier studies have shown that herpes simplex virus 1 (HSV-1) blocks the interferon response pathways, at least at two sites, by circumventing the effects of activation of protein kinase R by double-stranded RNA and interferon and through the degradation of promyelocytic leukemia protein (PML) since interferon has no antiviral effects in PML(-/-) cells. Here we report on two effects of viral genes on other sites of the interferon signaling pathway. (i) In infected cells, Jak1 kinase associated with interferon receptors and Stat2 associated with the interferon signaling pathway rapidly disappear from infected cells. The level of interferon alpha receptor is also reduced, albeit less drastically at times after 4 h postinfection. Other members of the Stat family of proteins were either decreased in amount or posttranslationally processed in a manner different from those of mock-infected cells. The decrease in the levels of Jak1 and Stat2 may account for the decrease in the formation of complexes consisting of Stat1 or ISGF3 and DNA sequences containing the interferon-stimulated response elements after exposure to interferon. (ii) The disappearance of Jak1 and Stat2 was related at least in part to the function of the virion host shutoff protein, the product of the viral U(L)41 gene. Consistent with this observation, a mutant lacking the U(L)41 gene and treated with interferon produced lesser amounts of a late protein (U(L)38) than the wild-type parent. We conclude that HSV-1 blocks the interferon signaling pathways at several sites.

Absence of intercellular adhesion molecule 1 expression in varicella zoster virus-infected keratinocytes during herpes zoster: another immune evasion strategy?

Downregulation of major histocompatibility complex (MHC) class I, MHC-II, and intercellular adhesion molecule 1 (ICAM-1) expression in infected cell lines allows some viruses to escape host immunity. In skin lesions of varicella zoster virus (VZV), MHC-II transcripts were demonstrated in keratinocytes around vesicles, but not in VZV-infected cells. Whether other immunoevasive mechanisms are present during herpes zoster (HZ) is not yet elucidated. The aim of the study was to disclose the temporal immunohistochemical expression of immune escape mechanisms during HZ. Sequential skin biopsies were performed in 5 HZ patients. VZV IE63, CD1a, CD3, CD4, CD8, CD56, CD68, L1, HLA-DR, HLA-ABC, interleukin (IL)-6, IL-10, interferon gamma (IFNgamma), tumor necrosis factor alpha (TNFalpha), and ICAM-1 expressions were assessed on frozen sections using immunohistochemistry. Controls consisted of normal skin, herpes simplex virus (HSV) skin infections, and other distinct bullous skin diseases. HLA-DR and ICAM-1 expressions were not observed in VZV- and HSV-infected keratinocytes, contrasting with their upregulation in the surrounding epidermis and inside nonviral blisters. However, HLA-ABC expressions were not inhibited in VZV-infected keratinocytes. Furthermore, the CD4/CD8 ratio remained unmodified during the infection evolution, and this ratio was variable among patients. Increased IFNgamma, TNFalpha, and IL-6 expressions were present, but IL-10 expression only increased in later stages. In contrast to in vitro MHC-I and MHC-II downregulation, VZV infection is related to MHC-II but not MHC-I expression on infected keratinocytes. The absence of ICAM-1 expression on infected keratinocytes may reduce their antigen presentation capacities to LFA-1 ligand-bearing T cells. This may represent another VZV-associated immune escape mechanism. Increased IFNgamma, TNFalpha, and IL-6 expressions suggest a TH1 profile.

Interferon gamma expression and clinical features in patients with acute retinal necrosis syndrome

BACKGROUND

Interferon gamma (IFN-gamma) has been reported to play an important role during virus infections. The purpose of this study was to examine the relationship between IFN-gamma expression and the clinical course of patients with acute retinal necrosis syndrome (ARN) associated with the varicella-zoster virus (VZV).

METHODS

Six patients with ARN were studied. The aqueous and/or vitreous were examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay during the follow-up period. The presence of VZV genome was also determined by PCR. The results were correlated with the clinical data and features and compared with patients with other ocular diseases.

RESULTS

A statistically significant higher level of IFN-gamma was detected in the aqueous and/or vitreous in eyes with ARN than in eyes with other ocular diseases. A statistically significant positive correlation was observed between the level of IFN-gamma in the vitreous and the final visual acuity. IFN-gamma was reduced to undetectable levels within 30 days after the initial eye symptoms. Three of five patients had severe inflammation initially, and the visual acuity gradually recovered with the disappearance of VZV and higher levels of IFN-gamma. Conversely, the other 2 patients showed mild inflammation, had a slow decrease of visual acuity with persistent VZV, and lower levels of IFN-gamma expression.

CONCLUSION

Our results suggest that IFN-gamma may be one of the factors that plays an important role in the clinical course of VZV-associated ARN.

Clinical and genetic risk factors of herpes zoster in patients with systemic lupus erythematosus

OBJECTIVE

The aim of this study was to determine the clinical and genetic risk factors that influence herpes zoster occurrence in patients with systemic lupus erythematosus (SLE).

METHODS

Three hundred three SLE patients meeting the American College of Rheumatology criteria were enrolled in this study. Herpes zoster was diagnosed when classic grouped vesicles were noted. Medical records were reviewed retrospectively to collect clinical information. For Fc gamma receptor IIa (Fc gamma RIIa) and Fc gamma RIIIa genotyping, polymerase chain reaction (PCR) using allele-specific primers was performed. The PCR sequence-specific oligonucleotide probe method was utilized in human HLA-DRB1 genotyping.

RESULTS

Forty-two cases (13.9%) of zoster occurred among 303 SLE patients. The incidence of zoster in patients with SLE was 32.5/1,000 patients per year. Patients who developed zoster had higher rates of lupus nephritis (P = 0.018) and positive anti-Sm antibody (P = 0.019). However, Fc gamma RIIa and Fc gamma RIIIa polymorphism and the HLA-DRB1 genotype did not influence herpes zoster occurrence.

CONCLUSION

Systemic lupus erythematosus patients with lupus nephritis or anti-Sm antibody are at higher risk of herpes zoster. Fc gamma RIIa (H/R131), Fc gamma RIIIa (F/V176), and HLA-DRB1 genetic polymorphisms did not influence the occurrence of herpes zoster in these patients.

Differential HLA gene expression in measles vaccine seropositive and seronegative subjects: a pilot study

This is the first study using GeneChip technology to elucidate genetic determinants of the measles vaccine response. A comparative gene expression study was conducted using Affymetrix's Human GeneChip U-95A in 5 human subjects immunized with a 'booster' dose of measles vaccine (Attenuax, Merck) to determine whether serologically distinct subjects exhibit differential expression of human leukocyte antigen (HLA) genes. Healthy individuals aged 15-25 y, previously immunized with 2 doses of measles-mumps-rubella-II (MMR-II) vaccine, were classified as measles vaccine immunoglobulin G-specific antibody seronegatives (n = 2) and seropositives (n = 3). Changes in expression of HLA genes in seronegatives and seropositives were studied on days 7 and 14 post-measles vaccination using Microarray Suite 5.0 (MAS 5.0). There was increased expression of the HLA class I-B (p = 0.0002), HLA class II cluster of DMA, DMB, TAP1, TAP2 (p = 0.0007) and HLA-DR (p = 0.0001) genes, and decreased expression of HLA class I MICB molecule (p = 1), HLA class I-A (p = 0.9999) and major histocompatibility complex class III HSP 70 (p = 0.9999) genes on day 7 or day 14 postvaccination in seropositives compared with seronegatives. These results suggest an association between antibody response and differential HLA gene activation and may explain one potential mechanism underlying measles vaccine non-response.

The varicella-zoster virus induces apoptosis in vitro in subpopulations of primary human peripheral blood mononuclear cells

Varicella-zoster virus (VZV), a member of Herpesviridae, subfamily alpha-Herpesvirinae, is pathogenic exclusively in the human. Chickenpox is the result of primary infection of VZV. During the viremic stage, VZV infects peripheral blood mononuclear cells (PBMC) and spreads to the periphery. In skin cells it causes typical lesions. Apoptosis has been demonstrated in different cell types by other alpha-herpesviruses. VZV-infected T lymphocytes, B lymphocytes, and monocytes, respectively, were examined in this in vitro study by flow cytometry, immunofluorescence and electron microscopy. All infected cell types showed signs of apoptosis: a lower DNA content, DNA fragmentation, loss of membrane integrity, and an altered nuclear morphology. The results observed led to the suggestion that VZV can induce apoptosis during infection in vivo in the PBMC subpopulations.

Susceptibility of mice deficient in the MHC class II transactivator to infection with Mycobacterium tuberculosis

Major histocompatibility complex (MHC) class II antigen presentation and subsequent CD4+ T-cell activation are critical for acquired immunity to Mycobacterium tuberculosis infection. MHC class II gene expression is primarily controlled by the master transactivator CIITA protein. Without functional CIITA protein, MHC class II expression is lost, impairing immune responses and increasing susceptibility to infection. In this study, we compared protective immune responses of CIITA-deficient mice and wild-type C57BL/6 controls with low dose aerosol M. tuberculosis infection. After aerogenic challenge, CIITA-/- mice failed to limit mycobacterial growth (2.5 and 2.0 log10 > WT lung and spleen CFUs, respectively, at day 58). Lung histopathology involved extensive necrosis, severe pneumonitis and overwhelming inflammation in the gene knockout mice. Mean survival time for CIITA-/- mice was significantly reduced (57 versus >300 days for WT). This extreme sensitivity to tuberculous infection was largely attributed to the absence of CD4+ cells. Flow cytometric studies detected virtually no CD4+ cells in CIITA-/- mouse spleens after infection versus elevated numbers in WT spleens. Failed CD4+ T-cell expansion markedly reduced interferon-gamma (IFN-gamma production in CIITA-/- mice versus WT controls. These results suggest the necessity of a functional CIITA pathway for controlling tuberculous infections and that interventions targeting CIITA expression may be useful antimycobacterial therapeutics.

Varicella-zoster virus productively infects mature dendritic cells and alters their immune function

Mature dendritic cells (DCs) are potent antigen-presenting cells essential for initiating successful antiviral immune responses and would therefore serve as an ideal target for viruses seeking to evade or delay the immune response by disrupting their function. We have previously reported that VZV productively infects immature DCs (A. Abendroth, G. Morrow, A. L. Cunningham, and B. Slobedman, J. Virol. 75:6183-6192, 2001), and in the present study we assessed the ability of VZV to infect mature DCs. Mature DCs were generated from immature monocyte-derived DCs by lipopolysaccharide treatment before being exposed to VZV-infected fibroblasts. On day 4 postexposure, flow cytometry analysis revealed that 15 to 45% of mature DCs were VZV antigen positive, and immunofluorescent staining together with infectious-center assays demonstrated that these cells were fully permissive for the complete VZV replicative cycle. VZV infection of mature DCs resulted in a selective downregulation of cell surface expression of the functionally important immune molecules major histocompatibility complex (MHC) class I, CD80, CD83, and CD86 but did not alter MHC class II expression. Immunofluorescent staining showed that the downregulation of cell surface CD83 was concomitant with a retention of CD83 in cytoplasmic vesicles. Importantly, VZV infection of mature DCs significantly reduced their ability to stimulate the proliferation of allogeneic T lymphocytes. These data demonstrate that mature DCs are permissive for VZV and that infection of these cells reduces their ability to function properly. Thus, VZV has evolved yet another immune evasion strategy that would likely impair immunosurveillance and enhance the chances for lifelong persistence in the human population.

Subversion of B lymphocyte signaling by infectious agents

Infectious agents and their hosts interact in a complex manner, involving not only superficially apparent mechanisms, but also the signaling machinery that governs host cells responses. Thus, signaling events, surface molecule expression, and transcriptional control may be affected in various cell types, with profound consequences for the function of individual cells and organ systems. Studies of the biochemistry of cell signaling and cell invasion by infectious agents have begun to detail the interplay between elements of infectious organisms and the host at the molecular level. Consequently, the resulting interferences with lymphocyte signaling may disturb the function of the immune system. In B cells, alterations of immune receptor signaling has implications for human diseases. By affecting the mechanisms of the host's immune defense, this may not only lead to inadequate elimination of an infectious agent, but also to autoimmunity or neoplasia.

Microarray analysis of host cell gene transcription in response to varicella-zoster virus infection of human T cells and fibroblasts in vitro and SCIDhu skin xenografts in vivo

During primary infection, varicella-zoster virus (VZV) is spread via lymphocytes to skin, where it induces a rash and establishes latency in sensory ganglia. A live, attenuated varicella vaccine (vOka) was generated by using the VZV Oka strain (pOka), but the molecular basis for vOka attenuation remains unknown. Little is known concerning the effects of wild-type or attenuated VZV on cellular gene regulation in the host cells that are critical for pathogenesis. In this study, transcriptional profiles of primary human T cells and fibroblasts infected with VZV in cell culture were determined by using 40,000-spot human cDNA microarrays. Cellular gene transcription in human skin xenografts in SCID mice that were infected with VZV in vivo was also evaluated. The profiles of cellular gene transcripts that were induced or inhibited in infected human foreskin fibroblasts (HFFs), T cells, and skin in response to pOka and vOka infection were similar. However, significant alterations in cellular gene regulation were observed among the three differentiated human cell types that were examined, suggesting specific differences in the biological consequences of VZV infection related to the target cell. Changes in cellular gene transcription detected by microarray analysis were confirmed for selected genes by quantitative real-time reverse transcription-PCR analysis of VZV-infected cells. Interestingly, the transcription of caspase 8 was found to be decreased in infected T cells but not in HFFs or skin, which may signify a tissue-specific antiapoptosis mechanism. The use of microarrays to demonstrate differences in effects on host cell genes in primary, biologically relevant cell types provides background information for experiments to link these various response phenotypes with mechanisms of VZV pathogenesis that are important for the natural course of human infection.

Paramyxovirus strategies for evading the interferon response

Two genera, the Respirovirus (Sendai virus (SeV) and human parainfluenza virus (hPIV3) and the Rubulavirus (simian virus (SV) 5, SV41, mumps virus and hPIV2), of the three in the subfamily Paramyxovirinae inhibit interferon (IFN) signalling to circumvent the IFN response. The viral protein responsible for the inhibition is the C protein for respirovirus SeV and the V protein for the rubulaviruses, both of which are multifunctional accessory proteins expressed from the P gene. SeV suppresses IFN-stimulated tyrosine phosphorylation of signal transducers and activators of transcription (STATs) at an early phase of infection and further inhibits the downstream signalling without degrading any of the signalling components in most cell lines. On the contrary, the Rubulavirus V protein targets Stat1 or Stat2 for degradation. Proteasome-mediated degradation appears to be involved in most cases. Studies on the molecular mechanisms by which paramyxoviruses evade the IFN response will offer important information for modulating the JAK-STAT pathway, designing novel antiviral drugs and recombinant live vaccines, and improving paramyxovirus expression vectors for gene therapy.

Varicella-zoster virus (VZV) ORF17 protein induces RNA cleavage and is critical for replication of VZV at 37 degrees C but not 33 degrees C

Varicella-zoster virus (VZV) open reading frame 17 (ORF17) is homologous to herpes simplex virus (HSV) UL41, which encodes the viral host shutoff protein (vhs). HSV vhs induces degradation of mRNA and rapid shutoff of host protein synthesis. An antibody to ORF17 protein detected a 46-kDa protein in VZV-infected cells. While HSV vhs is located in virions, VZV ORF17 protein was not detectable in virions. ORF17 protein induced RNA cleavage, but to a substantially lesser extent than HSV-1 vhs. Expression of ORF17 protein did not inhibit expression from a beta-galactosidase reporter plasmid, while HSV type 1 vhs abolished reporter expression. Two VZV ORF17 deletion mutants were constructed to examine the role of ORF17 in virus replication. While the ORF17 VZV mutants grew to peak titers that were similar to those of the parental virus at 33 degrees C, the ORF17 mutants grew to 20- to 35-fold-lower titers than parental virus at 37 degrees C. ORF62 protein was distributed in a different pattern in the nuclei and cytoplasm of cells infected with an ORF17 deletion mutant at 37 degrees C compared to 33 degrees C. Inoculation of cotton rats with the ORF17 deletion mutant resulted in a level of latent infection similar to that produced by inoculation with the parental virus. The importance of ORF17 protein for viral replication at 37 degrees C but not at 33 degrees C suggests that this protein may facilitate the growth of virus in certain tissues in vivo.

Latent cytomegalovirus down-regulates major histocompatibility complex class II expression on myeloid progenitors

Following primary infection, human cytomegalovirus (CMV) establishes a lifelong latent infection in bone marrow-derived myeloid lineage cells. Although downmodulation of major histocompatibility complex (MHC) class I and class II protein levels occurs during active viral replication, little is known about the modulation of these proteins during latent infection. When analyzed by flow cytometry, latently infected adherent cells collected from granulocyte macrophage progenitor (GM-P) cultures exhibited a striking reduction in MHC class II antigen present on the cell surface starting very early after exposure to virus that continued for more than 2 weeks. In comparison, cell surface levels of the monocyte cell surface marker CD14 remained unaltered in these cells. A recombinant virus (RV798) lacking the virus genes US2-US11 retained the ability to downmodulate MHC class II levels during latent infection. Immunoblot and immunofluorescent antibody staining analyses showed that the reduction in MHC class II surface levels during latency was associated with a block in protein trafficking. HLA-DR was retained within cytoplasmic vesicles that also contained HLA-DM. Thus, downmodulation remained independent of all previously characterized MHC class I and class II immunomodulatory viral gene products and involved a mechanism not previously ascribed to any viral function. These data show that latent infection is accompanied by reduced cell surface expression of MHC class II proteins, a strategy that would afford the virus escape from immunosurveillance and increase the chances for lifelong latent infection.

Cell surface major histocompatibility complex class II proteins are regulated by the products of the gamma(1)34.5 and U(L)41 genes of herpes simplex virus 1

Modulation of host immune responses has emerged as a common strategy employed by herpesviruses both to establish life-long infections and to affect recovery from infection. Herpes simplex virus 1 (HSV-1) blocks the major histocompatibility complex (MHC) class I antigen presentation pathway by inhibiting peptide transport into the endoplasmic reticulum. The interaction of viral gene products with the MHC class II pathway, however, has not been thoroughly investigated, although CD4(+) T cells play an important role in human recovery from infection. We have investigated the stability, distribution, and state of MHC class II proteins in glioblastoma cells infected with wild-type HSV-1 or mutants lacking specific genes. We report the following findings. (i) Wild-type virus infection caused a decrease in the accumulation of class II protein on the surface of cells and a decrease in the endocytosis of lucifer yellow or dextran conjugated to fluorescein isothiocyanate but no decrease in the total amount of MHC class II proteins relative to the levels seen in mock-infected cells. (ii) Although the total amount of MHC class II protein remained unchanged, the amounts of cell surface MHC class II proteins were higher in cells infected with the U(L)41-negative mutant, which lacks the virion host shutoff protein, and especially high in cells infected with the gamma(1)34.5-negative mutant. We conclude that infected cells attempt to respond to infection by increased acquisition of antigens and transport of MHC class II proteins to the cell surface and that these responses are blocked in part by the virion host shutoff protein encoded by the U(L)41 gene and in large measure by the direct or indirect action of the infected cell protein 34.5, the product of the gamma(1)34.5 gene.

Specific inhibition of interferon signal transduction pathways by adenoviral infection

Adenoviral evolution has generated strategies to resist host cell antiviral systems, but molecular mechanisms for evasion of interferon (IFN) effects by adenoviruses during late-phase infection are poorly defined. In this study, we examined adenovirus type 5 (AdV) effects on IFN-gamma-dependent gene expression and Janus family kinase-signal transducer and activator of transcription signaling components in human tracheobronchial epithelial cells. We found that AdV infection specifically inhibited IFN-gamma-dependent gene expression in airway epithelial cells without evidence of epithelial cell injury or generation of a soluble extracellular inhibitor. Furthermore, infection with AdV for 18-24 h blocked phosphorylation/activation of the Stat1 transcription factor that regulates IFN-gamma-dependent genes. Although AdV also inhibited IFN-alpha-dependent phosphorylation of Stat1 and Stat2, interleukin-4-dependent phosphorylation of the related transcription factor Stat6 was not affected, indicating that the virus selectively affected specific signaling pathways. Our results indicate that AdV inhibition of the IFN-gamma signal transduction cascade occurs through loss of ligand-induced receptor complex assembly and consequent component phosphorylation and suggest that lack of complex assembly is due to decreased expression of the IFN-gammaR2 chain of the IFN-gamma receptor. IFN-gammaR2 is required at an early step in Janus family kinase-signal transducer and activator of transcription pathway activation and is expressed at low levels in airway epithelial cells, supporting the concept that adenoviral down-regulation of the level of this IFN-gamma receptor component allows for persistent modulation of IFN-gamma-dependent gene expression.

Feline immunodeficiency virus lacks sensitivity to the antiviral activity of feline IFN-gamma

The antiviral activity of recombinant feline interferon-gamma (rFeIFN-gamma) against feline immunodeficiency virus (FIV) was investigated. A persistently FIV(Bang)-infected feline T cell line (FeT-J/Bang) was treated with either rFeIFN-omega, rFeIFN-gamma, or recombinant human IFN-alpha2 (rHuIFN-alpha2), and the culture fluids were tested for antiviral activity by reverse transcriptase (RT) assay. FeT-J/Bang cell cultures treated with rFeIFN-omega showed dose-dependent inhibition of RT activity. In contrast, rFeIFN-gamma treatment had no antiviral effect on FIV replication but instead caused a statistically significant enhancement on day 9 of culture. Antiviral activity of rFeIFN-gamma was also tested on feline peripheral blood mononuclear cells (PBMC). PBMC cultures were inoculated with FIV(Bang) and simultaneously treated with either rFeIFN-omega, rFeIFN-gamma, or rHuIFN-alpha2. FeIFN-gamma had no effect on FIV replication, unlike the rFeIFN-omega and rHuIFN-alpha2, which had strong anti-FIV effects. In another study, rFeIFN-gamma treatment was initiated 3 days before FIV(Bang) infection, the day of FIV(Bang) infection, or 3 days post-FIV(Bang) infection and then tested for antiviral activity. The time of initiating rFeIFN-gamma treatment had no effect on the antiviral activity. Hence, these results suggest that unlike rHuIFN-alpha2 and rFeIFN-omega, rFeIFN-gamma has no inhibitory effect on FIV replication in PBMC but causes a slight enhancement in a feline T cell line.

Inhibition of IFN-gamma signaling by an Epstein-Barr virus immediate-early protein

Viruses have evolved elaborate mechanisms to target many aspects of the host's immune response. The cytokine IFN-gamma plays a central role in resistance of the host to infection via direct antiviral effects as well as modulation of the immune response. In this study, we demonstrate that the Epstein-Barr virus (EBV) immediate-early protein, BZLF1, inhibits the IFN-gamma signaling pathway. BZLF1 decreases the ability of IFN-gamma to activate a variety of important downstream target genes, such as IRF-1, p48, and CIITA, and prevents IFN-gamma-induced class II MHC surface expression. Additionally, BZLF1 inhibits IFN-gamma-induced STAT1 tyrosine phosphorylation and nuclear translocation. Finally, we demonstrate that BZLF1 decreases expression of the IFN-gamma receptor, suggesting a mechanism by which EBV may escape antiviral immune responses during primary infection.

Antiviral actions of interferons

Tremendous progress has been made in understanding the molecular basis of the antiviral actions of interferons (IFNs), as well as strategies evolved by viruses to antagonize the actions of IFNs. Furthermore, advances made while elucidating the IFN system have contributed significantly to our understanding in multiple areas of virology and molecular cell biology, ranging from pathways of signal transduction to the biochemical mechanisms of transcriptional and translational control to the molecular basis of viral pathogenesis. IFNs are approved therapeutics and have moved from the basic research laboratory to the clinic. Among the IFN-induced proteins important in the antiviral actions of IFNs are the RNA-dependent protein kinase (PKR), the 2',5'-oligoadenylate synthetase (OAS) and RNase L, and the Mx protein GTPases. Double-stranded RNA plays a central role in modulating protein phosphorylation and RNA degradation catalyzed by the IFN-inducible PKR kinase and the 2'-5'-oligoadenylate-dependent RNase L, respectively, and also in RNA editing by the IFN-inducible RNA-specific adenosine deaminase (ADAR1). IFN also induces a form of inducible nitric oxide synthase (iNOS2) and the major histocompatibility complex class I and II proteins, all of which play important roles in immune response to infections. Several additional genes whose expression profiles are altered in response to IFN treatment and virus infection have been identified by microarray analyses. The availability of cDNA and genomic clones for many of the components of the IFN system, including IFN-alpha, IFN-beta, and IFN-gamma, their receptors, Jak and Stat and IRF signal transduction components, and proteins such as PKR, 2',5'-OAS, Mx, and ADAR, whose expression is regulated by IFNs, has permitted the generation of mutant proteins, cells that overexpress different forms of the proteins, and animals in which their expression has been disrupted by targeted gene disruption. The use of these IFN system reagents, both in cell culture and in whole animals, continues to provide important contributions to our understanding of the virus-host interaction and cellular antiviral response.

The MHC class II transactivator: prey and hunter in infectious diseases

The MHC class II transcriptional activator (CIITA) is the major regulator of expression of MHC class II genes. Thus, CIITA plays a fundamental role in the regulation of the immune response. Here, we discuss our findings on the dual role of CIITA during infections, as the target (prey) for certain pathogens but the host effector (hunter) against other pathogens, including HIV-1. This dual role is placed in an evolutionary context as a rather peculiar example of a strategy used by pathogens to evade host defenses and a counteraction of the host to minimize the survival and spread of the pathogen.

The bare lymphocyte syndrome and the regulation of MHC expression

The bare lymphocyte syndrome (BLS) is a hereditary immunodeficiency resulting from the absence of major histocompatibility complex class II (MHCII) expression. Considering the central role of MHCII molecules in the development and activation of CD4(+) T cells, it is not surprising that the immune system of the patients is severely impaired. BLS is the prototype of a "disease of gene regulation." The affected genes encode RFXANK, RFX5, RFXAP, and CIITA, four regulatory factors that are highly specific and essential for MHCII genes. The first three are subunits of RFX, a trimeric complex that binds to all MHCII promoters. CIITA is a non-DNA-binding coactivator that functions as the master control factor for MHCII expression. The study of RFX and CIITA has made major contributions to our comprehension of the molecular mechanisms controlling MHCII genes and has made this system into a textbook model for the regulation of gene expression.

Varicella-zoster virus infection of human dendritic cells and transmission to T cells: implications for virus dissemination in the host

During primary varicella-zoster virus (VZV) infection, it is presumed that virus is transmitted from mucosal sites to regional lymph nodes, where T cells become infected. The cell type responsible for VZV transport from the mucosa to the lymph nodes has not been defined. In this study, we assessed the susceptibility of human monocyte-derived dendritic cells to infection with VZV. Dendritic cells were inoculated with the VZV strain Schenke and assessed by flow cytometry for VZV and dendritic cell (CD1a) antigen expression. In five replicate experiments, 34.4% +/- 6.6% (mean +/- SEM) of CD1a(+) cells were also VZV antigen positive. Dendritic cells were also shown to be susceptible to VZV infection by the detection of immediate-early (IE62), early (ORF29), and late (gC) gene products in CD1a(+) dendritic cells. Infectious virus was recovered from infected dendritic cells, and cell-to-cell contact was required for transmission of virus to permissive fibroblasts. VZV-infected dendritic cells showed no significant decrease in cell viability or evidence of apoptosis and did not exhibit altered cell surface levels of major histocompatibility complex (MHC) class I, MHC class II, CD86, CD40, or CD1a. Significantly, when autologous T lymphocytes were incubated with VZV-infected dendritic cells, VZV antigens were readily detected in CD3(+) T lymphocytes and infectious virus was recovered from these cells. These data provide the first evidence that dendritic cells are permissive to VZV and that dendritic cell infection can lead to transmission of virus to T lymphocytes. These findings have implications for our understanding of how virus may be disseminated during primary VZV infection.

Immune evasion mechanisms of varicella-zoster virus

Varicella-zoster virus can to modulate the expression of class I and class II major histocompatibility (MHC) molecules. MHC class I expression is downregulated in VZV-infected T cells as well as in fibroblasts. VZV-infected cells do not respond to exposure to interferon-gamma (IFN-gamma) by upregulation of MHC class II expression. However, MHC class II expression is induced when cells are treated with IFN-gamma before VZV infection. These effects on MHC class I and class II expression can be expected to interfere transiently with adaptive immune responses of the host, mediated by CD4 and CD8 T cells, ensuring that the virus has sufficient opportunity for transmission to susceptible contracts.

The role of gamma interferon in antimicrobial immunity

Gamma interferon (IFN-gamma) is an important cytokine in the host defense against infection by viral and microbial pathogens. IFN-gamma induces a variety of physiologically significant responses that contribute to immunity. Treatment of animal cells with IFN-gamma or infection with viral or microbial pathogens leads to changes in the level of expression of several target genes as revealed by DNA microarray analyses. The signaling pathways leading to the induction of IFN-gamma-regulated gene products and, in some cases, their biochemical functions have been defined in exquisite detail. Studies of transgenic mutant mice deficient in proteins of the IFN-gamma response pathway firmly establish the importance of IFN-gamma in immunity.

Varicella-zoster virus retains major histocompatibility complex class I proteins in the Golgi compartment of infected cells

We sought to examine the effects of varicella-zoster virus (VZV) infection on the expression of major histocompatibility complex class I (MHC I) molecules by human fibroblasts and T lymphocytes. By flow cytometry, VZV infection reduced the cell surface expression of MHC I molecules on fibroblasts significantly, yet the expression of transferrin receptor was not affected. Importantly, when human fetal thymus/liver implants in SCID-hu mice were inoculated with VZV, cell surface MHC I expression was downregulated specifically on VZV-infected human CD3+ T lymphocytes, a prominent target that sustains VZV viremia. The stage in the MHC I assembly process that was disrupted by VZV in fibroblasts was examined in pulse-chase and immunoprecipitation experiments in the presence of endoglycosidase H. MHC I complexes continued to be assembled in VZV-infected cells and were not retained in the endoplasmic reticulum. In contrast, immunofluorescence and confocal microscopy showed that VZV infection resulted in an accumulation of MHC I molecules which colocalized to the Golgi compartment. Inhibition of late viral gene expression by treatment of infected fibroblasts with phosphonoacetic acid did not influence the modulation of MHC I expression, nor did transfection of cells with plasmids expressing immediate early viral proteins. However, cells transfected with a plasmid carrying the early gene ORF66 did result in a significant downregulation of MHC I expression, suggesting that this gene encodes a protein with an immunomodulatory function. Thus, VZV downregulates MHC I expression by impairing the transport of MHC I molecules from the Golgi compartment to the cell surface; this effect may enable the virus to evade CD8+ T-cell immune recognition during VZV pathogenesis, including the critical phase of T-lymphocyte-associated viremia.

Immune evasion as a pathogenic mechanism of varicella zoster virus

Varicella zoster virus (VZV) is a human herpesvirus that causes varicella (chickenpox) during primary infection, establishes latency in dorsal root ganglia and may reactivate years later, producing herpes zoster. VZV must evade antiviral immunity during three important stages of viral pathogenesis, including the cell-associated viremia characteristic of primary infection, persistence in dorsal root ganglia during latency and the initial period of VZV reactivation. Our observations about the immunomodulatory effects of VZV document its capacity to interfere with adaptive immunity mediated by CD4 as well as CD8 T cells, ensuring the survival of the virus in the human population from generation to generation.

Modulation of host immune responses by clinically relevant human DNA and RNA viruses

Numerous mechanisms allow viruses to evade host immune surveillance, and new evasion strategies continue to be identified. In addition to interference with antigen processing and presentation, direct viral modulation of host immune responses can also be achieved by altering the host cytokine milieu and the development of immunoregulatory cells. A better understanding of these viral evasion strategies will help to define critical host defense mechanisms and will lead to novel immune-based therapeutic strategies in the future.