Varicella-zoster virus immune evasion

Immunobiology of Varicella-Zoster Virus Infection

Varicella-zoster virus (VZV) causes clinically significant illness during acute and recurrent infection accompanied by robust innate and acquired immune responses. Innate immune cells in skin and ganglion secrete type I interferon (IFN-I) and proinflammatory cytokines to control VZV. Varicella-zoster virus subverts pattern recognition receptor sensing to modulate antigen presentation and IFN-I production. During primary infection, VZV hijacks T cells to disseminate to the skin and establishes latency in ganglia. Durable T- and B-cell memory formed within a few weeks of infection is boosted by reactivation or re-exposure. Antigen-specific T cells are recruited and potentially retained in VZV-infected skin to counteract reactivation. In latently VZV-infected ganglia, however, virus-specific T cells have not been recovered, suggesting that local innate immune responses control VZV latency. Antibodies prevent primary VZV infection, whereas T cells are fundamental to resolving disease, limiting severity, and preventing reactivation. In this study, we review current knowledge on the interactions between VZV and the human immune system.

Effector and Central Memory Poly-Functional CD4(+) and CD8(+) T Cells are Boosted upon ZOSTAVAX(®) Vaccination

ZOSTAVAX(®) is a live attenuated varicella-zoster virus (VZV) vaccine that is licensed for the protection of individuals ≥50 years against shingles and its most common complication, postherpetic neuralgia. While IFNγ responses increase upon vaccination, the quality of the T cell response has not been elucidated. By using polychromatic flow cytometry, we characterized the breadth, magnitude, and quality of ex vivo CD4(+) and CD8(+) T cell responses induced 3-4 weeks after ZOSTAVAX vaccination of healthy adults. We show, for the first time that the highest frequencies of VZV-specific CD4(+) T cells were poly-functional CD154(+)IFNγ(+)IL-2(+)TNFα(+) cells, which were boosted upon vaccination. The CD4(+) T cells were broadly reactive to several VZV proteins, with immediate early (IE) 63 ranking the highest among them in the fold rise of poly-functional cells, followed by IE62, gB, open reading frame (ORF) 9, and gE. We identified a novel poly-functional ORF9-specific CD8(+) T cell population in 62% of the subjects, and these were boosted upon vaccination. Poly-functional CD4(+) and CD8(+) T cells produced significantly higher levels of IFNγ, IL-2, and TNFα compared to mono-functional cells. After vaccination, a boost in the expression of IFNγ by poly-functional IE63- and ORF9-specific CD4(+) T cells and IFNγ, IL-2, and TNFα by ORF9-specific poly-functional CD8(+) T cells was observed. Responding poly-functional T cells exhibited both effector (CCR7(-)CD45RA(-)CD45RO(+)), and central (CCR7(+)CD45RA(-)CD45RO(+)) memory phenotypes, which expressed comparable levels of cytokines. Altogether, our studies demonstrate that a boost in memory poly-functional CD4(+) T cells and ORF9-specific CD8(+) T cells may contribute toward ZOSTAVAX efficacy.

A negative feedback modulator of antigen processing evolved from a frameshift in the cowpox virus genome

Coevolution of viruses and their hosts represents a dynamic molecular battle between the immune system and viral factors that mediate immune evasion. After the abandonment of smallpox vaccination, cowpox virus infections are an emerging zoonotic health threat, especially for immunocompromised patients. Here we delineate the mechanistic basis of how cowpox viral CPXV012 interferes with MHC class I antigen processing. This type II membrane protein inhibits the coreTAP complex at the step after peptide binding and peptide-induced conformational change, in blocking ATP binding and hydrolysis. Distinct from other immune evasion mechanisms, TAP inhibition is mediated by a short ER-lumenal fragment of CPXV012, which results from a frameshift in the cowpox virus genome. Tethered to the ER membrane, this fragment mimics a high ER-lumenal peptide concentration, thus provoking a trans-inhibition of antigen translocation as supply for MHC I loading. These findings illuminate the evolution of viral immune modulators and the basis of a fine-balanced regulation of antigen processing.

Virus-infected or malignant transformed cells are eliminated by cytotoxic T lymphocytes, which recognize antigenic peptide epitopes in complex with major histocompatibility complex class I (MHC I) molecules at the cell surface. The majority of such peptides are derived from proteasomal degradation in the cytosol and are then translocated into the ER lumen in an energy-consuming reaction via the transporter associated with antigen processing (TAP), which delivers the peptides onto MHC I molecules as final acceptors. Viruses have evolved sophisticated strategies to escape this immune surveillance. Here we show that the cowpox viral protein CPXV012 inhibits the ER peptide translocation machinery by allosterically blocking ATP binding and hydrolysis by TAP. The short ER resident active domain of the viral protein evolved from a reading frame shift in the cowpox virus genome and exploits the ER-lumenal negative feedback peptide sensor of TAP. This CPXV012-induced conformational arrest of TAP is signaled by a unique communication across the ER membrane to the cytosolic motor domains of the peptide pump. Furthermore, this study provides the rare opportunity to decipher on a molecular level how nature plays hide and seek with a pathogen and its host.

Varicella zoster virus vaccines: potential complications and possible improvements

Varicella zoster virus (VZV) is the causative agent of varicella (chicken pox) and herpes zoster (shingles). After primary infection, the virus remains latent in sensory ganglia, and reactivates upon weakening of the cellular immune system due to various conditions, erupting from sensory neurons and infecting the corresponding skin tissue. The current varicella vaccine (v-Oka) is highly attenuated in the skin, yet retains its neurovirulence and may reactivate and damage sensory neurons. The reactivation is sometimes associated with postherpetic neuralgia (PHN), a severe pain along the affected sensory nerves that can linger for years, even after the herpetic rash resolves. In addition to the older population that develops a secondary infection resulting in herpes zoster, childhood breakthrough herpes zoster affects a small population of vaccinated children. There is a great need for a neuro-attenuated vaccine that would prevent not only the varicella manifestation, but, more importantly, any establishment of latency, and therefore herpes zoster. The development of a genetically-defined live-attenuated VZV vaccine that prevents neuronal and latent infection, in addition to primary varicella, is imperative for eventual eradication of VZV, and, if fully understood, has vast implications for many related herpesviruses and other viruses with similar pathogenic mechanisms.

Downregulation of the H-2Kd gene by siRNA affects the cytotoxicity of murine LAK cells

To investigate the effect of the H-2K^d gene on the lymphocyte membrane, we constructed a small interfering RNA (siRNA) that targets the H-2K^d gene and compared the cytotoxicity of mouse lymphokine-activated killer (LAK) cells with different H-2K^d expression states. H-2K^d-targeting siRNA was transfected into spleen lymphocytes of BALB/C mice. Flow cytometry (FCM) was then performed to examine the expression of the H-2K^d gene in the transfected and control cells. Additionally, the cytotoxicity of the transfected cells toward the H22 and K562 cell lines was evaluated in vitro using the LDH release assay. H-2K^d-targeting siRNA significantly reduced the expression levels of the target protein, whereas pure transMessenger and non-silencing siRNA did not inhibit H-2K^d expression at the concentrations tested. The cytotoxicity of siRNA-treated LAK cells toward H22 and K562 cells was reduced significantly. The knockdown of H-2K^d gene expression by siRNA may be associated with LAK cell cytotoxicity toward neoplasm cell lines.

ORF7 of varicella-zoster virus is a neurotropic factor

Varicella-zoster virus (VZV) is the causative agent of chickenpox and herpes zoster (shingles). After the primary infection, the virus remains latent in sensory ganglia and reactivates upon weakening of the cellular immune system due to various conditions, erupting from sensory neurons and infecting the corresponding skin tissue. The current varicella vaccine is highly attenuated in the skin and yet retains its neurovirulence and may reactivate and damage sensory neurons. The factors involved in neuronal invasion and establishment of latency are still elusive. Previously, we constructed a library of whole-gene deletion mutants carrying a bacterial artificial chromosome sequence and a luciferase marker in order to perform a comprehensive VZV genome functional analysis. Here, screening of dispensable gene deletion mutants in differentiated neuronal cells led to the identification of ORF7 as the first known, likely a main, VZV neurotropic factor. ORF7 is a virion component localized to the Golgi compartment in infected cells, whose deletion causes loss of polykaryon formation in epithelial cell culture. Interestingly, ORF7 deletion completely abolishes viral spread in human nervous tissue ex vivo and in an in vivo mouse model. This finding adds to our previous report that ORF7 is also a skin-tropic factor. The results of our investigation will not only lead to a better understanding of VZV neurotropism but could also contribute to the development of a neuroattenuated vaccine candidate against shingles or a vector for delivery of other antigens.

Expression of the genes encoding human leucocyte antigens-A, -B, -DP, -DQ and -G in gastric cancer patients

This study compared the expression of the genes encoding human leucocyte antigens (HLA)-A, -B, -DP, -DR and -G in peripheral blood mononuclear cells (PBMCs) in gastric cancer patients and healthy controls. Using reverse transcription-polymerase chain reaction, levels of classical HLA-A, -B, -DP and -DR and non-classical HLA-G mRNA were studied in 43 gastric cancer patients and 22 controls. In addition, the levels of HLA-A,B,C and -G antigens on the surface of PBMCs were measured in 30 gastric cancer patients and 15 controls using flow cytometry. The mean fluorescence intensity of HLA-A,B,C antigen in the gastric cancer group was significantly lower than in controls. The HLA-G antigen was mainly present on CD4(+)CD8(-) T-lymphocytes. The percentage of CD4(+)CD8(-) T-lymphocytes positive for HLA-G antigen was significantly lower in the gastric cancer group compared with the healthy controls. Levels of HLA-A, -B and -G mRNA in the gastric cancer group were significantly lower than in controls. The HLA-G mRNA levels were significantly lower in gastric cancer of histological grades III and IV than in grades I and II. These data may provide a novel diagnostic and research tool for gastric cancer.

Genome-wide mutagenesis reveals that ORF7 is a novel VZV skin-tropic factor

The Varicella Zoster Virus (VZV) is a ubiquitous human alpha-herpesvirus that is the causative agent of chicken pox and shingles. Although an attenuated VZV vaccine (v-Oka) has been widely used in children in the United States, chicken pox outbreaks are still seen, and the shingles vaccine only reduces the risk of shingles by 50%. Therefore, VZV still remains an important public health concern. Knowledge of VZV replication and pathogenesis remains limited due to its highly cell-associated nature in cultured cells, the difficulty of generating recombinant viruses, and VZV's almost exclusive tropism for human cells and tissues. In order to circumvent these hurdles, we cloned the entire VZV (p-Oka) genome into a bacterial artificial chromosome that included a dual-reporter system (GFP and luciferase reporter genes). We used PCR-based mutagenesis and the homologous recombination system in the E. coli to individually delete each of the genome's 70 unique ORFs. The collection of viral mutants obtained was systematically examined both in MeWo cells and in cultured human fetal skin organ samples. We use our genome-wide deletion library to provide novel functional annotations to 51% of the VZV proteome. We found 44 out of 70 VZV ORFs to be essential for viral replication. Among the 26 non-essential ORF deletion mutants, eight have discernable growth defects in MeWo. Interestingly, four ORFs were found to be required for viral replication in skin organ cultures, but not in MeWo cells, suggesting their potential roles as skin tropism factors. One of the genes (ORF7) has never been described as a skin tropic factor. The global profiling of the VZV genome gives further insights into the replication and pathogenesis of this virus, which can lead to improved prevention and therapy of chicken pox and shingles.

The Varicella Zoster Virus (VZV) is the causative agent of chicken pox and shingles. The long-term efficacy of the current chickenpox vaccine is yet to be determined, and the current shingles vaccine fails to provide protective immunity for a substantial number of individuals. Shingles can also lead to post-herpetic neuralgia (PHN), a debilitating condition associated with an intractable pain that can linger for life. Therefore, VZV remains an important public health concern. We use growth-rate analysis of our genome-wide deletion library to determine the essentiality of all known VZV genes, including novel annotations for 51% of the VZV proteome. We also discovered a novel skin-tropic factor encoded by ORF7. Overall, our identification of genes essential for VZV replication and pathogenesis will serve as the basis for multiple in-depth genetic studies of VZV, which can lead to improved prevention and therapy of chicken pox and shingles. For example, essential genes may be appealing drug targets and genes whose deletion causes a substantial growth defect may be prospective candidates for novel live attenuated vaccines.

Advances in the understanding of the pathogenesis and epidemiology of herpes zoster

The primary varicella zoster virus (VZV) infection results in chickenpox (varicella), which is transmitted via the airborne route. VZV is highly infectious, but in the USA the incidence of varicella has been reduced by 76-87% as a result of the varicella vaccine. The virus establishes latency in the dorsal root ganglia during varicella and, when reactivated, travels along the sensory nerve axons to cause shingles (herpes zoster [HZ]). There are over 1 million cases of HZ in the USA each year, with an estimated lifetime attack rate of 30%. The incidence of HZ, which causes significant morbidity, increases with age and reaches approximately 10 cases per 1,000 patient-years by age 80. Cell-mediated immunity (CMI) is known to decline with age as part of immunosenescence, and decreased CMI is associated with reactivation of VZV. This article provides an overview of our emerging understanding of the epidemiology and pathogenesis of varicella and HZ, in addition to exploring the current theories on latency and reactivation. Understanding the risk factors for developing HZ and the complications associated with infection, particularly in older people, is important for prompt diagnosis and management of HZ in primary care, and they are therefore also reviewed.

An efficient protocol for VZV BAC-based mutagenesis

Varicella-zoster virus (VZV) causes both varicella (chicken pox) and herpes zoster (shingles). As a member of the human herpesvirus family, VZV contains a large 125-kb DNA genome, encoding 70 unique open reading frames (ORFs). The genetic study of VZV has been hindered by the large size of viral genome, and thus the functions of the majority of these ORFs remain unclear. Recently, an efficient protocol has been developed based on a luciferase-containing VZV bacteria artificial chromosome (BAC) system to rapidly isolate and study VZV ORF deletion mutants.

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.

Molecular mechanisms of viral immune evasion proteins to inhibit MHC class I antigen processing and presentation

Viral products inhibit MHC class I antigen processing and presentation via three major pathways: inhibition of major histocompatibility complex (MHC) class I expression on cells, blockade of peptide trafficking and loading on MHC class I molecules, and inhibition of peptide generation in host cells. Viral products also interfere with IFN-gamma -mediated JAK/STAT signal transduction in cells. These results imply that viral proteins probably inhibit the function of IFN-gamma in MHC class I antigen presentation via inactivation of JAK/STAT signal transduction in host cells. Mechanisms of viral products to inhibit IFN-gamma -mediated MHC class I antigen presentation were summarized in this literature review.

The varicellovirus UL49.5 protein blocks the transporter associated with antigen processing (TAP) by inhibiting essential conformational transitions in the 6+6 transmembrane TAP core complex

TAP translocates virus-derived peptides from the cytosol into the endoplasmic reticulum, where the peptides are loaded onto MHC class I molecules. This process is crucial for the detection of virus-infected cells by CTL that recognize the MHC class I-peptide complexes at the cell surface. The varicellovirus bovine herpesvirus 1 encodes a protein, UL49.5, that acts as a potent inhibitor of TAP. UL49.5 acts in two ways, as follows: 1) by blocking conformational changes of TAP required for the translocation of peptides into the endoplasmic reticulum, and 2) by targeting TAP1 and TAP2 for proteasomal degradation. At present, it is unknown whether UL49.5 interacts with TAP1, TAP2, or both. The contribution of other members of the peptide-loading complex has not been established. Using TAP-deficient cells reconstituted with wild-type and recombinant forms of TAP1 and TAP2, TAP was defined as the prime target of UL49.5 within the peptide-loading complex. The presence of TAP1 and TAP2 was required for efficient interaction with UL49.5. Using deletion mutants of TAP1 and TAP2, the 6+6 transmembrane core complex of TAP was shown to be sufficient for UL49.5 to interact with TAP and block its function. However, UL49.5-induced inhibition of peptide transport was most efficient in cells expressing full-length TAP1 and TAP2. Inhibition of TAP by UL49.5 appeared to be independent of the presence of other peptide-loading complex components, including tapasin. These results demonstrate that UL49.5 acts directly on the 6+6 transmembrane TAP core complex of TAP by blocking essential conformational transitions required for peptide transport.

Neuropathology of viral infections of the central nervous system

Many viral infections of the nervous system cause stereotyped pathologic features and overlapping clinical and imaging features. Neuroimaging usually offers neuroanatomical localization of the pathology, degree of involvement of the nervous system, and response to therapy during follow up in a few instances. Neuroimaging is a useful adjunct for diagnosis.

A highly efficient protocol of generating and analyzing VZV ORF deletion mutants based on a newly developed luciferase VZV BAC system

Varicella Zoster Virus (VZV) is the causative agent for both varicella (chicken pox) and herpes zoster (shingles). As a member of the human herpesvirus family, VZV contains a large DNA genome, encoding 70 unique open reading frames (ORFs). The functions of the majority of these ORFs remain unknown. Recently, the full-length VZV (P-Oka strain) genome was cloned as a VZV bacteria artificial chromosome (BAC) and additionally a firefly luciferase cassette was inserted to generate a novel luciferase VZV BAC. In this study, a highly efficient protocol has been developed exploiting the new luciferase VZV BAC system to rapidly isolate and characterize VZV ORF deletion mutants by growth curve analysis in cell culture.

Phase-dependent immune evasion of herpesviruses

Viruses employ various modes to evade immune detection. Two possible evasion modes are a reduction of the number of epitopes presented and the mimicry of host epitopes. The immune evasion efforts are not uniform among viral proteins. The number of epitopes in a given viral protein and the similarity of the epitopes to host peptides can be used as a measure of the viral attempts to hide this protein. Using bioinformatics tools, we here present a genomic analysis of the attempts of four human herpesviruses (herpes simplex virus type 1-human herpesvirus 1, Epstein-Barr virus-human herpesvirus 4, human cytomegalovirus-human herpesvirus 5, and Kaposi's sarcoma-associated herpesvirus-human herpesvirus 8) and one murine herpesvirus (murine herpesvirus 68) to escape from immune detection. We determined the full repertoire of CD8 T-lymphocyte epitopes presented by each viral protein and show that herpesvirus proteins present many fewer epitopes than expected. Furthermore, the epitopes that are presented are more similar to host epitopes than are random viral epitopes, minimizing the immune response. We defined a score for the size of the immune repertoire (the SIR score) based on the number of epitopes in a protein. The numbers of epitopes in proteins expressed in the latent and early phases of infection were significantly smaller than those in proteins expressed in the lytic phase in all tested viruses. The latent and immediate-early epitopes were also more similar to host epitopes than were lytic epitopes. A clear trend emerged from the analysis. In general, herpesviruses demonstrated an effort to evade immune detection. However, within a given herpesvirus, proteins expressed in phases critical to the fate of infection (e.g., early lytic and latent) evaded immune detection more than all others. The application of the SIR score to specific proteins allows us to quantify the importance of immune evasion and to detect optimal targets for immunotherapy and vaccine development.

Evolutionary genetics of Carpodacus mexicanus, a recently colonized host of a bacterial pathogen, Mycoplasma gallisepticum

We present molecular data documenting how introduction to the eastern United States and an epizootic involving a bacterial pathogen has affected the genetic diversity of house finches, a cardueline songbird. Population bottlenecks during introduction can cause loss of genetic variation and may negatively affect a population's ability to adapt to novel stressors such as disease. Although a genome-wide survey using Amplified Fragment Length Polymorphism (AFLP) markers suggests little loss of genetic diversity in introduced populations, an epizootic of bacterial Mycoplasma has nonetheless caused dramatic declines in the eastern US population. Sequence analysis of a candidate gene for pathogen resistance in the Major Histocompatibity Complex (MHC) in pre- and post-epizootic population samples reveals allele frequency shifts since introduction of the pathogen, but similar shifts are also observed in control populations not exposed to the bacteria, and in a neutral non-coding locus. Expression studies using a novel subtractive hybridization approach indicate decreased expression of the class II MHC locus upon exposure to Mycoplasma, a pattern also seen in MHC class I loci in mice infected with cytomegalovirus and consistent with manipulation of the finch immune system by Mycoplasma. These results will be further expanded using experimental studies as well as examination of evolution of the pathogen genome itself.

Anatomical mapping of human herpesvirus reservoirs of infection

Following primary infection, all eight human herpesviruses persist lifelong in the human host. However, a mapping of all anatomic sites of human herpesvirus persistence is lacking. Fresh tissue specimens representing approximately 40 major anatomic sites from eight autopsies were screened using a recently developed real-time PCR method for detection of all eight human herpesviruses. Patients with evidence of active herpesvirus infection (herpes simplex 1 (HSV-1), herpes simplex 2 (HSV-2), varicella-zoster virus (VZV), Epstein-Barr virus (EBV), cytomegalovirus (CMV), herpesvirus 6 (HHV-6), herpesvirus 7 (HHV-7), and herpesvirus 8 (HHV-8)) at the time of death were excluded to avoid detection of widely disseminated infection. Despite this precaution, widespread HSV-1 positivity (with blood positivity) was detected in one case-an elderly male who died of cardiac arrest. In a middle-aged male with HIV-AIDS, HSV-1 was found in neural and pharyngeal tissues, skin, cartilage, bone, and urinary bladder, whereas in two other cases, HSV-1 was restricted to neural tissues. HSV-2 was detected in a single site, the anus, in the male with HIV-AIDS. VZV was detected only twice, once in the adrenal gland and once in the small intestine. CMV was detected in three cases, most commonly in nasal mucosa, trachea, thyroid, intestine, and liver. EBV was detected in all eight cases, especially in nasal mucosa, tonsil, spleen, lymph node, tongue, and intestine, but in only two of six whole-blood specimens. HHV-6, like EBV, was detected in all eight cases, most commonly in salivary glands, thyroid, stomach, intestines, liver, and pancreas. HHV-7, like EBV and HHV-6, was detected in all eight cases, most commonly in salivary glands, tonsil, lymph nodes, and bone marrow. HHV-8 was detected in only two sites (both lymph nodes) from two cases. Herpesviruses were detected in three of six whole-blood specimens, including HSV-1, EBV, HHV-6, and HHV-7. These results represent the most comprehensive mapping of herpesvirus tissue distribution in humans reported to date.

Varicella-Zoster-Virus Folliculitis Promoted Clonal Cutaneous Lymphoid Hyperplasia

Post herpes zoster (HZ) reactions have been associated with panoply of neoplastic, inflammatory, and fibro-inflammatory cutaneous disorders. Varicella zoster virus (VZV) DNA has not been identified in most of these reports. After an episode of HZ, a healthy, active 90-year-old female developed ulcerative nodules in the affected trigeminal V1 dermatome and the contra-lateral trigeminal region over a 1-year period. Excision and/or biopsy of all these lesions showed similar pathologic changes that consisted of herpetic folliculitis, adjacent dense mixed nodular lymphocytic infiltrates with germinal centers (cutaneous lymphoid hyperplasia (CLH)), and in the deeper excision specimens, an obliterative vasculitis of a vessel with smooth muscle in its wall. Immunophenotype analysis revealed a mixed, predominate T- and B-cell population without loss of pan-T cell antigens or aberrant expression by B cells of T-cell antigens. Polymerase chain reaction for herpetic DNA was positive for VZV DNA. Lymphocyte gene rearrangement analysis revealed 2 distinct, anatomically and chronologically, monoclonal B-cell populations and a monoclonal T-cell population in one nodule. Treatment with valacyclovir has lead to almost complete resolution of her cutaneous nodules after 6 months of therapy. In this case, it can be surmised that persistence of VZV infection and lack of effective cell-mediated immunity lead to development of both immunopathology (vasculitis) and excessive lymphoid cell proliferation (CLH).

Herpesviral Fcgamma receptors: culprits attenuating antiviral IgG?

Production of IgG in response to virus infection is central to antiviral immune effector functions and a hallmark of B cell memory. Antiviral antibodies (Abs) recognising viral glycoproteins or protein antigen displayed on the surface of virions or virus-infected cells are crucial in rendering the virus noninfectious and in eliminating viruses or infected cells, either acting alone or in conjunction with complement. In many instances, passive transfer of Abs is sufficient to protect from viral infection. Herpesviruses (HV) are equipped with a large array of immunomodulatory functions which increase the efficiency of infection by dampening the antiviral immunity. Members of the α- and β-subfamily of the Herpesviridae are distinct in encoding transmembrane glycoproteins which selectively bind IgG via its Fc domain. The Fc-binding proteins constitute viral Fcγ receptors (vFcγRs) which are expressed on the cell surface of infected cells. Moreover, vFcγRs are abundantly incorporated into the envelope of virions. Despite their molecular and structural heterogeneity, the vFcγRs generally interfere with IgG-mediated effector functions like antibody (Ab)-dependent cellular cytolysis, complement activation and neutralisation of infectivity of virions. vFcγRs may thus contribute to the limited therapeutic potency of antiherpesviral IgG in clinical settings. A detailed molecular understanding of vFcγRs opens up the possibility to design recombinant IgG molecules resisting vFcγRs. Engineering IgG with a better antiviral efficiency represents a new therapeutic option against herpesviral diseases.

A Chimeric Antibody to Varicella-Zoster Virus Glycoprotein E

Varicella-Zoster virus (VZV) immune globulin (VZIG) derived from pooled human serum is currently used in immunotherapy of VZV-associated complications of chickenpox and shingles. We developed a mouse-human chimeric antibody against a VZV glycoprotein E (gE) epitope as a safer replacement for VZIG. Variable (V) heavy- and V kappa light-chain exons, derived from an anti-VZV gE antibody secreting mouse hybridoma cell line, were cloned into expression vectors containing an immunoglobulin promoter and enhancer, and human IgG1 or kappa constant (C) region genes. The expression vectors were cotransfected into mouse myeloma cell line (NSO), generating transformants that secreted chimeric human-mouse IgGs. The chimeric and the parent mouse antibody were indistinguishable in their antigen binding specificity. VZV gE chimeric antibody may prove to be a prophylactic antibody that could provide significant advantages over VZIG in having defined specificity, lessened possibility of contamination with viral pathogens, and consistent availability.

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.

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.

Measurement of cell-mediated immunity with a Varicella-Zoster Virus-specific interferon-gamma ELISPOT assay: responses in an elderly population receiving a booster immunization

An interferon-gamma ELISPOT assay has been developed for assessment of cellular immune responses to Varicella-Zoster Virus (VZV) in large, multi-center clinical vaccine trials. We show that the assay performed best when testing peripheral blood mononuclear cells (PBMCs) that had been isolated and then frozen on the same day as blood was drawn, and that freezing PBMCs from blood that was stored overnight before processing resulted in dramatically reduced responses. This assay was used to monitor cell-mediated immunity (CMI) in response to a booster immunization with an investigational live, attenuated VZV vaccine in an elderly population that had been vaccinated 8-10 years previously. The booster vaccine elicited a 1.6- to 1.7-fold rise in the VZV-specific cellular immune response as measured by the ELISPOT assay. The increase from pre to post booster vaccination response was more pronounced (approximately 2.2-fold rise) in a subset of subjects who had received two prior immunizations with a live, attenuated vaccine.

Memory cytotoxic T cell responses to viral tegument and regulatory proteins encoded by open reading frames 4, 10, 29, and 62 of varicella-zoster virus

Cytotoxic T cell recognition of tegument and regulatory proteins encoded by open reading frames (ORFs) 4, 10, 29, and 62 of varicella-zoster virus (VZV) was evaluated using limiting dilution conditions to estimate the precursor frequencies of memory T cells specific for these proteins in immune subjects. Responder cell frequencies for ORFs 4, 10, and 62 gene products, which are virion tegument components and function as immediate early viral transactivating proteins, were equivalent. CTLp recognition of VZV proteins made in latently infected cells, which include ORF4 and ORF62 proteins, was not maintained preferentially when compared to ORF10 protein, which has not been shown to be expressed during latency. T cell recognition of ORF29 protein, the major DNA binding protein, which is expressed during replication but not incorporated into the virion tegument, was less common than responses to ORFs 4, 10, and 62 gene products. Older individuals had diminished numbers of memory CTLp that lysed autologous targets expressing IE62 protein; these responses were increased after immunization with live attenuated varicella vaccine to the range observed in younger adults. Adaptive immunity to VZV is characterized by a broad repertoire of memory CTL responses to proteins that comprise the virion tegument and regulate viral gene expression in infected cells.

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.

Association of HLA-A*3303-B*4403-DRB1*1302 haplotype, but not of TNFA promoter and NKp30 polymorphism, with postherpetic neuralgia (PHN) in the Japanese population

Herpes zoster is a common disease caused by reactivation of the varicella zoster virus (VZV). In a small number of herpes zoster patients, pain persists beyond 4 weeks or more after healing of vesicular eruptions; this condition is termed postherpetic neuralgia (PHN). Positive associations of human histocompatibility leukocyte antigens (HLA) class I antigens, A33 and B44, with PHN in the Japanese population have been reported. Our hypothesis is that susceptibility genes to PHN might exist in the HLA region and the study objective is to further examine possible associations of genes in HLA class I, II and III regions, HLA-A, -B, -DRB1, tumor necrosis factor alpha (TNFA) promoter, and a natural killer cell activating receptor, NKp30 polymorphisms with PHN. Although TNFA or NKp30 in the class III region had been considered as a candidate locus, we found no associations of TNFA promoter or NKp30 polymorphisms with PHN in this study. We demonstrated that HLA-A*3303, -B*4403 and -DRB1*1302 alleles were significantly associated with PHN (P = 0.0007 for A*3303, P = 0.001 for B*4403 and P = 0.001 for DRB1*1302). The frequency of the HLA-A*3303-B*4403-DRB1*1302 haplotype was also significantly higher in the PHN patients than in the healthy controls (P = 0.0039). Our results suggest that this haplotype might be related to the pathogenesis of PHN.

Herpes viruses hedge their bets

Static latency is the hallmark of all herpes viruses. The varicella zoster virus, for instance, causes varicella (chickenpox), and after a latent phase of between 5 and 40 years, it can give rise to herpes zoster (shingles). This latency and the subsequent reactivation has intrigued and puzzled virologists. Although several factors have been suggested, it is unknown what triggers reactivation. However, latency can be explained with a simple evolutionary model. Here, we demonstrate that a simple, yet efficient, bet-hedging strategy might have evolved in a number of viruses, especially those belonging to the herpes virus family and most importantly in varicella zoster virus. We show that the evolution of latency can be explained by the population dynamics of infectious diseases in fluctuating host populations.

Characterization of varicella-zoster virus gene 21 and 29 proteins in infected cells

Varicella-zoster virus (VZV) transcription is limited in latently infected human ganglia. Note that much of the transcriptional capacity of the virus genome has not been analyzed in detail; to date, only VZV genes mapping to open reading frames (ORFs) 4, 21, 29, 62, and 63 have been detected. ORF 62 encodes the major immediate-early virus transcription transactivator IE62, ORF 29 encodes the major virus DNA binding protein, and ORF 21 encodes a protein associated with the developing virus nucleocapsid. We analyzed the cellular location of proteins encoded by ORF 21 (21p) and ORF 29 (29p), their phosphorylation state during productive infection, and their ability form a protein-protein complex. The locations of both 21p and 29p within infected cells mimic those of their herpes simplex virus type 1 (HSV-1) homologues (UL37 and ICP8); however, unlike these homologues, 21p is not phosphorylated and neither 21p nor 29p exhibits a protein-protein interaction. Transient transfection assays to determine the effect of 21p and 29p on transcription from VZV gene 20, 21, 28, and 29 promoters revealed no significant activation of transcription by 21p or 29p from any of the VZV gene promoters tested, and 21p did not significantly modulate the ability of IE62 to activate gene transcription. A modest increase in IE62-induced activation of gene 28 and 29 promoters was seen in the presence of 29p; however, IE62-induced activation of gene 28 and 29 promoters was reduced in the presence of 21p. A Saccharomyces cerevisiae two-hybrid analysis of 21p indicated that the protein can activate transcription when tethered within a responsive promoter. Together, the data reveal that while VZV gene 21 and HSV-1 UL37 share homology at the nucleic acid level, these proteins differ functionally.

Development and validation of a gamma interferon ELISPOT assay for quantitation of cellular immune responses to varicella-zoster virus

Cell-mediated immunity appears to be critical for the prevention and control of varicella-zoster virus (VZV) infection and complications arising from zoster. Current assays of VZV-specific cell-mediated immunity are cumbersome or lack sensitivity. We have developed a gamma interferon ELISPOT assay that provides a direct measure of the number of T cells secreting a cytokine following stimulation with antigen. This assay is extremely sensitive and specific, with the ability to detect gamma interferon spot-forming cells (SFC) in the range of 10 to 1,000 SFC per million peripheral blood mononuclear cells (PBMCs). This assay has been validated by demonstrating the following: (i) the response detected is mediated almost entirely by CD4+ T cells, (ii) ELISPOT responses from fresh-frozen PBMCs are equivalent to those from freshly isolated cells, (iii) frozen PBMCs can be shipped on dry ice for up to 48 h without loss of activity, (iv) frozen PBMC samples can be stored in liquid nitrogen over long periods (>22 months) without any significant change in response, and (v) the numbers of ELISPOTs counted using a computer-based imaging system are equivalent to those counted by humans but have lower variability. The ability to use frozen cells is facilitated by the use of a recombinant nuclease (Benzonase) that can prevent cell clumping when samples are thawed. Frozen PBMC samples can be cycled through multiple changes in storage between liquid nitrogen and dry ice without any change in response being detected. This facilitates collection of samples at one site and testing performed at a remote location. This VZV ELISPOT assay provides a new versatile tool for monitoring cellular immune responses either during a herpes zoster disease outbreak or following vaccination.

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.

Genetic resistance factor for HIV-1 and immune response to varicella zoster virus

A 32 bp deletion in the chemokine receptor CCR5 gene modulates HIV-1 infection. However, whether this CCR5 gene variation modifies immunity to common herpesvirus infections is unknown. We investigated whole blood IgG concentrations of 157 normal adult blood donors. Also we assessed whether the 32 bp deletion of CCR5 (delta32CCR5) was associated with circulating IgG to four herpesviruses: varicella zoster virus, Epstein-Barr virus, cytomegalovirus, and herpes simplex virus type 1 and type 2. Individuals who carried delta32CCR5 were 9.2 times more likely to be seronegative for varicella zoster virus than non-carriers (95% CI 2.9-29.1), but no differences were seen for the other herpesviruses studied. Variation in CCR5 may modulate humoral immunity to varicella zoster virus.

Viral immune evasion strategies and the underlying cell biology

Evasion of the immune system by viruses is a well-studied field. It remains a challenge to understand how these viral tactics affect pathogenesis and the viral lifecycle. At the same time, the study of viral proteins involved in immune evasion has helped us to better understand a number of cellular processes at the molecular level. Here we review recent data on different viral tactics for immune evasion and highlight what these viral interventions might teach us about cell biology.

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

We sought to investigate the effects of varicella-zoster virus (VZV) infection on gamma interferon (IFN-gamma)-stimulated expression of cell surface major histocompatibility complex (MHC) class II molecules on human fibroblasts. IFN-gamma treatment induced cell surface MHC class II expression on 60 to 86% of uninfected cells, compared to 20 to 30% of cells which had been infected with VZV prior to the addition of IFN-gamma. In contrast, cells that were treated with IFN-gamma before VZV infection had profiles of MHC class II expression similar to those of uninfected cell populations. Neither IFN-gamma treatment nor VZV infection affected the expression of transferrin receptor (CD71). In situ and Northern blot hybridization of MHC II (MHC class II DR-alpha) RNA expression in response to IFN-gamma stimulation revealed that MHC class II DR-alpha mRNA accumulated in uninfected cells but not in cells infected with VZV. When skin biopsies of varicella lesions were analyzed by in situ hybridization, MHC class II transcripts were detected in areas around lesions but not in cells that were infected with VZV. VZV infection inhibited the expression of Stat 1alpha and Jak2 proteins but had little effect on Jak1. Analysis of regulatory events in the IFN-gamma signaling pathway showed that VZV infection inhibited transcription of interferon regulatory factor 1 and the MHC class II transactivator. This is the first report that VZV encodes an immunomodulatory function which directly interferes with the IFN-gamma signal transduction via the Jak/Stat pathway and enables the virus to inhibit IFN-gamma induction of cell surface MHC class II expression. This inhibition of MHC class II expression on VZV-infected cells in vivo may transiently protect cells from CD4(+) T-cell immune surveillance, facilitating local virus replication and transmission during the first few days of cutaneous lesion formation.

Human pathogen subversion of antigen presentation

Many pathogens have co-evolved with their human hosts to develop strategies for immune evasion that involve disruption of the intracellular pathways by which antigens are bound by class I and class II molecules of the major histocompatibility complex (MHC) for presentation to T cells. Here the molecular events in these pathways are reviewed and pathogen interference is documented for viruses, extracellular and intracellular bacteria and intracellular parasites. In addition to a general review, data from our studies of adenovirus, Chlamydia trachomatis and Coxiella burnetii are summarized. Adenovirus E19 is the first viral gene product described that affects class I MHC molecule expression by two separate mechanisms, intracellular retention of the class I heavy chain by direct binding and by binding to the TAP transporter involved in class I peptide loading. Coxiella and Chlamydia both affect peptide presentation by class II MHC molecules as a result of their residence in endocytic compartments, although the properties of the parasitophorous vacuoles they form are quite different. These examples of active interference with antigen presentation by viral gene products and passive interference by rickettsiae and bacteria are typical of the strategies used by these different classes of pathogens, which need to evade different types of immune responses. Pathogen-host co-evolution is evident in these subversion tactics for which the pathogen crime seems tailored to fit the immune system punishment.