Ultrastructural features of fetal erythroid precursors infected with parvovirus B19 in vitro: evidence of cell death by apoptosis

Molecular insights and promise of oncolytic virus based immunotherapy

Discovering a therapeutic that can counteract the aggressiveness of this disease's mechanism is crucial for improving survival rates for cancer patients and for better understanding the most different types of cancer. In recent years, using these viruses as an anticancer therapy has been thought to be successful. They mostly work by directly destroying cancer cells, activating the immune system to fight cancer, and expressing exogenous effector genes. For the treatment of tumors, oncolytic viruses (OVs), which can be modified to reproduce only in tumor tissues and lyse them while preserving the healthy non-neoplastic host cells and reinstating antitumor immunity which present a novel immunotherapeutic strategy. OVs can exist naturally or be created in a lab by altering existing viruses. These changes heralded the beginning of a new era of less harmful virus-based cancer therapy. We discuss three different types of oncolytic viruses that have already received regulatory approval to treat cancer as well as clinical research using oncolytic adenoviruses. The primary therapeutic applications, mechanism of action of oncolytic virus updates, future views of this therapy will be covered in this chapter.

Pearson syndrome: a rare inborn error of metabolism with bone marrow morphology providing a clue to diagnosis

Pearson syndrome is a rare disorder of mitochondrial metabolism presenting in infancy with transfusion dependent refractory anaemia and multisystem involvement. We report a case of a 3-month-old infant presenting with anaemia requiring multiple transfusions. The presence of lactic acidosis, hyperglycaemia and cytoplasmic vacuoles in erythroid precursors on bone marrow aspiration study helped to suspect the diagnosis. However, the baby succumbed to metabolic crisis before he could be offered definitive therapy. This case report aims to emphasise the typical bone marrow aspiration finding which serves as a useful marker for establishing the diagnosis of this rare disorder, which is mostly fatal without bone marrow transplantation.

Review: Oncolytic virotherapy, updates and future directions

Oncolytic viruses (OVs) are viral strains that can infect and kill malignant cells while spare their normal counterparts. OVs can access cells through binding to receptors on their surface or through fusion with the plasma membrane and establish a lytic cycle in tumors, while leaving normal tissue essentially unharmed. Multiple viruses have been investigated in humans for the past century. IMLYGIC™ (T-VEC/Talimogene Laherparepvec), a genetically engineered Herpes Simplex Virus, is the first OV approved for use in the United States and the European Union for patients with locally advanced or non-resectable melanoma.

Although OVs have a favorable toxicity profile and are impressively active anticancer agents in vitro and in vivo the majority of OVs have limited clinical efficacy as a single agent. While a virus-induced antitumor immune response can enhance oncolysis, when OVs are used systemically, the antiviral immune response can prevent the virus reaching the tumor tissue and having a therapeutic effect. Intratumoral administration can provide direct access to tumor tissue and be beneficial in reducing side effects.

Immune checkpoint stimulation in tumor tissue has been noted after OV therapy and can be a natural response to viral-induced oncolysis. Also for immune checkpoint inhibition to be effective in treating cancer, an immune response to tumor neoantigens and an inflamed tumor microenvironment are required, both of which treatment with an OV may provide. Therefore, direct and indirect mechanisms of tumor killing provide rationale for clinical trials investigating the combination of OVs other forms of cancer therapy, including immune checkpoint inhibition.

Human Parvoviruses

Parvovirus B19 (B19V) and human bocavirus 1 (HBoV1), members of the large Parvoviridae family, are human pathogens responsible for a variety of diseases. For B19V in particular, host features determine disease manifestations. These viruses are prevalent worldwide and are culturable in vitro, and serological and molecular assays are available but require careful interpretation of results. Additional human parvoviruses, including HBoV2 to -4, human parvovirus 4 (PARV4), and human bufavirus (BuV) are also reviewed. The full spectrum of parvovirus disease in humans has yet to be established. Candidate recombinant B19V vaccines have been developed but may not be commercially feasible. We review relevant features of the molecular and cellular biology of these viruses, and the human immune response that they elicit, which have allowed a deep understanding of pathophysiology.

Virotherapy of digestive tumors with rodent parvovirus: overview and perspectives

INTRODUCTION

Toolan's H-1 parvovirus (H-1PV) exerts a cytotoxic/oncolytic effect, predominantly mediated by its non-structural protein (NS1). This rat parvovirus is harmless, unlike other parvoviruses, and its antitumor potential may be useful to clinicians as its oncolytic action appears to be true in numerous non-digestive and digestive cancers.

AREAS COVERED

After a brief review of parvovirus genus and biology, we summarize the proposed mechanisms to explain the cytotoxicity of H-1PV to tumors which results in dysregulation of cell transcription, cell-cycle arrest, termination of cell replication, activation of cellular stress response and induction of cell death. Viral oncolysis induces a strong tumor-specific immune response leading to the recognition and elimination of minimal residual disease. As the action of H-1PV is not limited to the digestive tract, we initially analyse studies performed in non-digestive cancers such as glioma (as the virus is able to cross the blood brain barrier), and then focused more particularly on the results in digestive cancers.

EXPERT OPINION

Based on the results of studies showing little H-1PV toxicity to living bodies, we advocate for the use of the parvovirus in cancers such as melanoma, glioma and pancreatic ductal adenocarcinoma in addition to conventional chemotherapy.

Parvovirus B19 Achievements and Challenges

Parvovirus B19 is a widespread human pathogenic virus, member of the Erythrovirus genus in the Parvoviridae family. Infection can be associated with an ample range of pathologies and clinical manifestations, whose characteristics and outcomes depend on the interplay between the pathogenetic potential of the virus, its adaptation to different cellular environments, and the physiological and immune status of the infected individuals. The scope of this review is the advances in knowledge on the biological characteristics of the virus and of virus-host relationships; in particular, the interactions of the virus with different cellular environments in terms of tropism and ability to achieve a productive replicative cycle, or, on the contrary, to establish persistence; the consequences of infection in terms of interference with the cell physiology; the process of recognition of the virus by the innate or adaptive immune system, hence the role of the immune system in controlling the infection or in the development of clinical manifestations. Linked to these issues is the continuous effort to develop better diagnostic algorithms and methods and the need for development of prophylactic and therapeutic options for B19V infections.

Diagnosis, management and possibilities to prevent parvovirus B19 infection in pregnancy

Human parvovirus B19 (B19V) infection in pregnancy can cause severe fetal anemia and nonimmune hydrops fetalis, which may be associated with spontaneous abortion and fetal death. Approximately 30–40% of women of child-bearing age are not immune to B19V infection. The risk to fetal life is particularly high if maternal infection occurs during the first 20 weeks of gestation. In this article we intend to give an overview on the molecular biology, epidemiology and management of B19V infection during pregnancy. These data will be combined with an assessment of the clinical situation of the infected fetus and the possibilities for avoiding and/or preventing B19V infection in pregnant women. Currently B19V infection is the causative agent of one of the most frequently occurring infectious complications in pregnancy that endangers fetal life, and so the necessity to develop a preventive vaccine is discussed.

Parvovirus B19 antibodies and correlates of infection in pregnant women attending an antenatal clinic in central Nigeria

Human parvovirus B19 infection is associated with spontaneous abortion, hydrops foetalis, intrauterine foetal death, erythema infectiosum (5th disease), aplastic crisis and acute symmetric polyarthropathy. However, data concerning Nigerian patients with B19 infection have not been published yet. The purpose of this study was to establish the prevalence of B19 IgG and IgM antibodies, including correlates of infection, among pregnant women attending an antenatal clinic in Nigeria. Subsequent to clearance from an ethical committee, blood samples were collected between August-November 2008 from 273 pregnant women between the ages of 15-40 years who have given their informed consent and completed self-administered questionnaires. Recombinant IgG and IgM enzyme linked immunosorbent assay kits (Demeditec Diagnostics, Germany) were used for the assays. Out of the 273 participants, 111 (40.7%) had either IgG or IgM antibodies. Out of these, 75 (27.5%) had IgG antibodies whereas 36 (13.2%) had IgM antibodies, and those aged 36-40 years had the highest prevalence of IgG antibodies. Significant determinants of infection (p < 0.05) included the receipt of a blood transfusion, occupation and the presence of a large number of children in the household. Our findings have important implications for transfusion and foeto-maternal health policy in Nigeria. Routine screening for B19 IgM antibodies and accompanying clinical management of positive cases should be made mandatory for all Nigerian blood donors and women of childbearing age.

Herpes virus infection can cause intervertebral disc degeneration

It has been proposed that intervertebral disc degeneration might be caused by low-grade infection. The purpose of the present study was to assess the incidence of herpes viruses in intervertebral disc specimens from patients with lumbar disc herniation. A polymerase chain reaction based assay was applied to screen for the DNA of eight different herpes viruses in 16 patients and two controls. DNA of at least one herpes virus was detected in 13 specimens (81.25%). Herpes Simplex Virus type-1 (HSV-1) was the most frequently detected virus (56.25%), followed by Cytomegalovirus (CMV) (37.5%). In two patients, co-infection by both HSV-1 and CMV was detected. All samples, including the control specimens, were negative for Herpes Simplex Virus type-2, Varicella Zoster Virus, Epstein Barr Virus, Human Herpes Viruses 6, 7 and 8. The absence of an acute infection was confirmed both at the serological and mRNA level.

To our knowledge this is the first unequivocal evidence of the presence of herpes virus DNA in intervertebral disc specimens of patients with lumbar disc herniation suggesting the potential role of herpes viruses as a contributing factor to the pathogenesis of degenerative disc disease.

Phosphoinositide 3-kinase signalling pathway involvement in a truncated apoptotic cascade associated with motility loss and oxidative DNA damage in human spermatozoa

Human spermatozoa are characterized by poor functionality and abundant DNA damage that collude to generate the high incidences of male infertility and miscarriage seen in our species. Although apoptosis has been suggested as a possible cause of poor sperm quality, the ability of these cells to enter an apoptotic state and the factors that might trigger such an event are unresolved. In the present study we provide evidence that the commitment of these cells to apoptosis is negatively regulated by PI3K (phosphoinositide 3-kinase)/AKT. If PI3K activity is inhibited, then spermatozoa default to an apoptotic cascade characterized by rapid motility loss, mitochondrial reactive oxygen species generation, caspase activation in the cytosol, annexin V binding to the cell surface, cytoplasmic vacuolization and oxidative DNA damage. However, the specialized physical architecture of spermatozoa subsequently prevents endonucleases activated during this process from penetrating the sperm nucleus and cleaving the DNA. As a result, DNA fragmentation does not occur as a direct result of apoptosis in spermatozoa as it does in somatic cells, even though oxidative DNA adducts can clearly be detected. We propose that this unusual truncated apoptotic cascade prepares spermatozoa for silent phagocytosis within the female tract and prevents DNA-damaged spermatozoa from participating in fertilization.

Nuclear envelope disruption involving host caspases plays a role in the parvovirus replication cycle

Parvoviruses are small, nonenveloped, single-stranded DNA viruses which replicate in the nucleus of the host cell. We have previously found that early during infection the parvovirus minute virus of mice (MVM) causes small, transient disruptions of the nuclear envelope (NE). We have now investigated the mechanism used by MVM to disrupt the NE. Here we show that the viral phospholipase A2, the only known enzymatic domain on the parvovirus capsid, is not involved in causing NE disruption. Instead, the virus utilizes host cell caspases, which are proteases involved in causing NE breakdown during apoptosis, to facilitate these nuclear membrane disruptions. Studies with pharmacological inhibitors indicate that caspase-3 in particular is involved. A caspase-3 inhibitor prevents nuclear lamin cleavage and NE disruption in MVM-infected mouse fibroblast cells and reduces nuclear entry of MVM capsids and viral gene expression. Caspase-3 is, however, not activated above basal levels in MVM-infected cells, and other aspects of apoptosis are not triggered during early MVM infection. Instead, basally active caspase-3 is relocalized to the nuclei of infected cells. We propose that NE disruption involving caspases plays a role in (i) parvovirus entry into the nucleus and (ii) alteration of the compartmentalization of host proteins in a way that is favorable for the virus.

Advances in human B19 erythrovirus biology

Since its discovery, human parvovirus B19 (B19V), now termed erythrovirus, has been associated with many clinical situations (neurological and myocardium infections, persistent B19V DNAemia) in addition to the prototype clinical manifestations, i.e., erythema infectiosum and erythroblastopenia crisis. In 2002, the use of new molecular tools led to the characterization of three different genotypes of human B19 erythrovirus. Although the genomic organization is conserved, the geographic distribution of the different genotypes varies worldwide, and the nucleotidic divergences can impact the molecular diagnosis of B19 virus infection. The cell cycle of the virus remains partially unresolved; however, recent studies have shed light on the mechanism of cell entry and the interactions of B19V proteins with apoptosis pathways.

Infection in systemic lupus erythematosus: friend or foe?

Infectious agents have long been implicated in the pathogenesis of systemic lupus erythematosus. Common viruses, such as the Epstein-Barr virus, transfusion transmitted virus, parvovirus and cytomegalovirus, have an increased prevalence in patients with systemic lupus erythematosus. They may contribute to disease pathogenesis through triggering autoimmunity via structural or functional molecular mimicry, encoding proteins that induce cross-reactive immune responses to self antigens or modulate antigen processing, activation, or apoptosis of B and T cells, macrophages or dendritic cells. Alternatively, some infectious agents, such as malaria, Toxoplasma gondii and Helicobacter pylori, may have a protective effect. Vaccinations may play dual roles by protecting against friend and foe alike.

Fetal anaemia as a cause of fetal injury: diagnosis and management

PURPOSE OF REVIEW

This review provides up-to-date information on the diagnosis and management of fetal anaemia.

RECENT FINDINGS

Exciting advances in the field of red blood cell isoimmunization are phasing out the need for invasive procedures. Rhesus blood group genotyping using fetal DNA in maternal plasma has been introduced into clinical practice with remarkable success. The role of middle cerebral artery peak systolic velocity in screening for fetal anaemia has been confirmed in various causes of fetal anaemia. A recent review of a successful Iran national screening programme for thalassaemia provided a timely and valuable educational opportunity. The value of intrauterine transfusion as a treatment for fetal anaemia was demonstrated by both high success rate and low procedure-related pregnancy loss rate.

SUMMARY

Fetal anaemia is one of the severe fetal conditions that affect the worldwide population. Rhesus isoimmunization remains an important health issue despite the recommendation for anti-D immunoglobulin prophylaxis and injection after sensitizing events. Noninvasive ultrasound diagnostic methods have replaced traditional invasive procedures in the assessment of fetus at risk of anaemia due to various causes, including red blood cell isoimmunization, parvovirus B19 infection and thalassaemia. The increased availability of intrauterine transfusion will help to improve the prognosis of these anaemic fetuses.

Naturally occurring parvovirus-associated feline hypogranular cerebellar hypoplasia-- A comparison to experimentally-induced lesions using immunohistology

Three cases of feline cerebellar hypoplasia are presented. At the time of examination, the ages of the cats ranged from 2 months to 1 year. Necropsy revealed cerebellar and pons hypoplasia. Polymerase chain reaction for parvoviral deoxyribonucleic acid was positive in cerebellar tissue. Cell-specific immunolabeling was used to characterize the lesions, which were characterized into 2 types. In type 1 lesions, the cortex was nearly agranular, with an extremely thin molecular layer; the Purkinje cells were randomly placed and oriented, and their stunted main dendrite produced a thorn-covered atrophic dendritic tree; the basket cell axons ran randomly and had dysmorphic endings; and myelinated fibers were severely reduced in folia axes. In type 2 lesions, the cortex was hypogranular; the Purkinje cells were linearly organized, but their main dendrite extended too far in the molecular layer before giving up smooth, bent secondary dendrites; many basket cells were located along the cerebellar surface, and their axons ran at right angle to the surface; myelinated fibers were moderately reduced. Defects in climbing fiber synapse translocation and elimination were evident in both types of lesion. This immunohistologic study allowed a comparison between lesions in these spontaneous cerebellar hypoplasia cases with those documented when using silver impregnation studies after perinatal experimental cerebellar damage. Such a comparison is consistent with viral infection that occurs before birth in all 3 cases. Progress in parvovirus biology knowledge suggests that viral NS1 protein cytotoxicity might explain degenerative changes in the Purkinje cells that were present, in addition to the development defect.

Intrauterine therapy for parvovirus B19 infected symptomatic fetus using B19 IgG-rich high titer gammaglobulin

Parvovirus B19-infected hydrops fetalis was treated using gammaglobulin injection into the peritoneal cavity (GIFPeC) with B19-IgG-rich immunoglobulin. Fetal anemia and hydrops resolved, and B19-DNA in fetal ascites decreased despite no change in maternal B19-IgG or B19-DNA. Gammaglobulin injection into the peritoneal cavity is thus useful for treating hydrops fetalis while avoiding intrauterine blood-transfusion risks.

Parvovirus B19: the causative agent of dilated cardiomyopathy or a harmless passenger of the human myocard?

Parvovirus B19 infections may cause a widespread benign and self-limiting disease in children and adults known as erythema infectiosum (fifth disease). Several further manifestations are associated with B19 infections, such as arthralgias, arthritis, leucopenia and thrombocytopenia, anaemia and vasculitis and spontaneous abortion and hydrops fetalis in pregnant women. Persistent infections with continuous virus production may occur in immunocompetent as well as in immunosuppressed individuals. Parvovirus B19 infections have been frequently implicated as a cause or trigger of various forms of autoimmune diseases affecting joints, connective tissue and large and small vessels. Autoimmune neutropenia, thrombocytopenia and haemolytic anaemia are known as sequelae of B19 infections. The molecular basis of the autoimmune phenomena is unclear. Many patients with these long-lasting symptoms are not capable of eliminating the virus or controlling its propagation. Furthermore, latent viral genomes have been detected in cells of various organs and tissues by PCR. At present, it is not clear if these cells produce viral proteins and/or infectious B19 particles, if the virus genome can be reactivated to productive replication and if the presence of viral DNA indicates a causative role of parvovirus B19 with distinct diseases.

Pathogenesis of aleutian mink disease parvovirus and similarities to b19 infection

Aleutian mink disease parvovirus (ADV) is an unusual member of the autonomous parvoviruses in both its replication and pathogenesis. Infection of newborn mink kits results in an acute disease typified by virus replication in type II pneumocytes in the lung. This replication is permissive and cytopathic, characterized by the production of high levels of viral replicative intermediates and infectious progeny. However, infection of adult Aleutian mink leads to a chronic form of the disease termed Aleutian disease (AD). In this case, virus replication occurs predominantly in lymph node macrophages and is restricted, with viral DNA replication, RNA transcription, protein expression and production of infectious progeny occurring at low levels. B19 is the only autonomous parvovirus known to infect humans. The primary site of virus replication in both children and adults is in erythrocyte precursors in the blood and bone marrow, although viral genomes have been detected in various other tissues. B19 infection often causes a self-limiting disease although persistent infection of B19 can occur in both immuno-compromised and -competent people. Perhaps the most striking similarity between infection with ADV or with B19 is the important role the humoral immune response to infection has in pathogenesis. It can be both protective and pathogenic. Due to of the central role of antibody in the disease caused by either virus, understanding the specific roles of antibody production in protection, antibody-mediated enhancement of infection, the establishment of persistent infection and immune-mediated pathology will provide insight into the pathogenesis of these infections. A second similarity between the two viruses is the ability to establish persistent infection. Persistence of ADV is associated with restricted replication. Although many cellular factors may contribute to restricted virus replication, the interactions between the major non-structural protein, NS1, and the cells are likely to be critical. Parallels exist between the expression and post-translational modification of ADV and B19 NS1 proteins that may contribute to restriction of virus replication. Thus, a study of the regulation of NS1 expression and its interactions with cell signalling pathways may lead to increased understanding of the restricted replication of these two viruses, and perhaps of persistent infection.

Human parvovirus B19 VP2 empty capsids bind to human villous trophoblast cells in vitro via the globoside receptor

BACKGROUND: Pregnant women acutely infected with human parvovirus B19 (B19) may transmit the virus to the developing fetus. The mechanism whereby the virus interacts with the placenta is unknown. It is known that globoside receptor is required for successful infection of the target cells, which are the highly undifferentiated, actively dividing colony and burst-form units of the erythroid series. Globoside is present on trophoblast cells which have intimate contact with maternal blood, and may therefore serve as a potential route for B19 transmission into the fetal compartment. OBJECTIVES: The purpose of this study was to determine whether B19 VP2 capsids could bind to villous trophoblast cells in vitro and whether globoside was involved. METHODS: Binding of B19 VP2 empty capsid to first-trimester villous trophoblast cells was assessed by multiple approaches, including ICC using either biotinylated B19 VP2 empty capsid or unlabeled B19 VP2 empty capsid. Quantification of viral binding involved I125-labeled B19 VP2 empty capsid. Competition studies included excess unlabeled empty capsids or pretreatment with globoside-specific IgM antibody. RESULTS: Linear binding of B19 VP2 capsid to purified villous trophoblast cells in vitro was clearly demonstrated (R2= 0.9524). Competition studies revealed specificity of I125-labeled B19 VP2 capsid binding to villous trophoblast cells when pretreatment with either 60-fold excess unlabeled B19 capsid or globoside-specific IgM antibody took place. The results illustrated B19's ability to bind in a specific manner to globoside-containing villous trophoblast cells. CONCLUSION: We speculate that the globoside present on trophoblast cells may play a role in viral binding in vivo, which may facilitate B19 transmission across the maternal-fetal interface.

Human Parvovirus B19 nonstructural protein transactivates the p21/WAF1 through Sp1

The expression of human Parvovirus B19 nonstructural protein 1 (NS1) induces cell cycle arrest at the G1 phase and is accompanied by increased expression of the cyclin-dependent kinase inhibitor, p21/WAF1. Here, we provide direct evidence that NS1 mediates the transactivation of p21/WAF1. Up-regulation of p21/WAF1 by wild-type NS1 but not an NS1 mutant deleted of its NTP binding motif was observed. We also demonstrated that the wild-type NS1 is unable to induce G1 arrest in p21-deficient cells. Using reporter plasmids containing various mutants of the p21/WAF1 promoter, luciferase assay further revealed that the binding sites of the promoter to the transcription factor Sp1 are critical for NS1-mediated transactivation. Indeed Sp1 interacts only with the wild-type NS1 but not the NS1 mutant. These results indicate a cooperative contribution of NS1 and Sp1 to the transactivation of p21/WAF1, which leads to G1 arrest.

Human Parvovirus B19 Transgenic Mice Become Susceptible to Polyarthritis

Human parvovirus B19 (B19) often causes acute polyarthritis in adults. In this paper, we analyzed nucleotide sequences of the B19 genome of patients with rheumatoid arthritis (RA), and then introduced the nonstructural protein 1 (NS1) gene of B19 into C57BL/6 mice that had a genetic origin not susceptible to arthritis. The transgenic mice developed no lesions spontaneously, but were susceptible to type II collagen (CII)-induced arthritis. B19 NS1 was expressed in synovial cells on the articular lesions that were histologically characteristic of granulomatous synovitis and pannus formation in cartilage and bone. Serum levels of anti-CII Abs and TNF-alpha increased in NS1 transgenic mice to the same levels as those of DBA/1 mice, which were susceptible to polyarthritis. Stimulation with CII increased secretion of Th1-type- and Th2-type cytokines in NS1 transgenic mice, indicating that a nonpermissive H-2(b) haplotype in the wild type of C57BL/6 mice can be made susceptible to polyarthritis through the expression of NS1. This study is the first to show that a viral agent from the joints in humans can cause CII-induced arthritis resembling RA.

Advances in the biology, diagnosis and host-pathogen interactions of parvovirus B19

Increased recognition of parvovirus B19 (B19), an erythrovirus, as a significant human pathogen that causes fetal loss and severe disease in immunocompromised patients has resulted in intensive efforts to understand the pathogenesis of B19-related disease, to improve diagnostic strategy that is deployed to detect B19 infection and blood-product contamination and, finally, to elucidate the nature of the cellular immune response that is elicited by the virus in diverse patient cohorts. It is becoming clear that at least three related erythrovirus strains (B19, A6/K71 and V9) are circulating in the general population and that viral entry into target cells is mediated by an expanding range of cellular receptors, including P antigen and beta-integrins. Persistent infection by B19 is emerging as a contributory factor in autoimmune disease, a hypothesis that is constrained by the detection of B19 in the skin of apparently healthy individuals. B19 infection during pregnancy may account for thousands of incidences of fetal loss per annum in Europe, North America and beyond, yet there is currently only minimal screening of pregnant women to assess serological status, and thereby risk of infection, upon becoming pregnant. Whilst major advances in diagnosis of B19 infection have taken place, including standardization of serological and DNA-based detection methodologies, blood donations that are targeted at high-risk groups are only beginning to be screened for B19 IgG and DNA as a means of minimizing exposure of at-risk patients to the virus. It is now firmly established that a Th1-mediated cellular immune response is mounted in immunocompetent individuals, a finding that should contribute to the development of an effective vaccine to prevent B19 infection in selected high-risk groups, including sickle-cell anaemics.

Evidence of parvovirus B19 infection in patients of pre-eclampsia and eclampsia with dyserythropoietic anaemia

Parvovirus B19 (PVB19) infection can induce transient anaemia in patients with increased erythropoiesis. However, the dynamic change within the bone marrow after PVB19 infection is not well understood. Increased erythropoiesis is a physiological phenomenon in puerperital women. Nevertheless, anaemia as a result of PVB19 infection in puerperital women has never been reported. We report one patient with eclampsia and two patients with pre-eclampsia who had transient, severe anaemia during the puerperital period because of PVB19 infection. Viral genomes were detected in the peripheral blood during the anaemic period by polymerase chain reaction and became undetectable after the anaemia was resolved. Viral genomes and protein could also be detected in bone marrow by in situ hybridization and immunohistochemical staining, respectively. Serial aspiration cytology of bone marrow showed severe dysplastic change involving erythroid precursors with a few apoptotic cells at the initial onset of anaemia, markedly increased apoptotic cells that was confirmed by the increased expression of activated caspase 3, around the nadir of anaemia, and a normal marrow picture without features of apoptosis after recovery from anaemia. Our data indicates that PVB19 infection can induce transient, severe dyserythropoietic anaemia in puerperital women with pre-eclampsia/eclampsia and the pathogenetic mechanism may probably involve the induction of apoptosis following PVB19 infection.

Parvovirus B19 and the pathogenesis of anaemia

Human parvovirus B19 (B19) infection causes human bone marrow failure, by affecting erythroid-lineage cells which are well-known target cells for B19. The anaemia induced by B19 infection is of minor clinical significance in healthy children and adults, however, it becomes critical in those afflicted with haemolytic diseases. This condition is called transient aplastic crisis, and the pathogenesis is explained by the short life-span of red blood cells. Similarly, fetuses are thought to be severely affected by B19-intrauterine infection in the first and second trimester, as the half-life of red blood cells is apparently shorter than RBC at the bone marrow haematopoietic stage. On the other hand, B19 is also the causative agent of persistent anaemia in immunocompromised patients, transplant recipients and infants. The deficiencies of appropriate immune responses to B19 impair viral elimination in vivo, which results in enlargement of B19-infected erythroid-lineage cells. The B19-associated damage of erythroid lineage cells is due to cytotoxicity mediated by viral proteins. B19-infected erythroid-lineage cells show apoptotic features, which are thought to be induced by the non-structural protein, NS1, of B19. In addition, B19 infection induces cell cycle arrests at the G(1) and G(2) phases. The G(1) arrest is induced by NS1 expression prior to apoptosis induction in B19-infected cells, while the G(2) arrest is induced not only by infectious B19 but also by UV-inactivated B19, which lacks the ability to express NS1. In this review, we address the clinical manifestations and molecular mechanisms for B19-induced anaemia in humans and a mouse model, and of B19-induced cell cycle arrests in erythroid cells.

Parvovirus infects cardiac myocytes in hydrops fetalis

Parvovirus infection during pregnancy is an important cause of hydrops fetalis. It is attributed to anemia caused by viral-induced destruction of red blood cells. Infection of other organs has been reported including the heart, liver, and lungs. Few of these reports, however, convincingly demonstrate virions within the functional parenchyma of the tissue. This is of particular concern regarding myocardium in the context of hydrops fetalis which is, in part, due to cardiac failure. The problem in routine pathology practice is that most fetuses with the infection are macerated. This, in part, probably explains the paucity of published information on cardiac involvement. This study examined five cases of fatal hydrops fetalis with variable maceration with serologically proven parvovirus B19 infection. Transmission electron microscopy of cardiac tissue demonstrated intranuclear virions in both erythroid precursor cells and in cardiac myocytes in three of these cases. In each of these, immuno-gold electron microscopy provided confirmatory evidence of parvovirus infection. Virions were not identifiable where maceration had caused disintegration of nuclei in the myocytes. In addition, virions were absent in the three negative control cases where retroplacental hemorrhage was confirmed as the cause of death. This study suggests that parvovirus infection of cardiac myocytes may play a more important role in causing hydrops fetalis than previously realized. It also demonstrates that maceration should not discourage the use of electron microscopy.

Parvovirus B19 and autoimmune diseases

Parvovirus B19 (B19) causes many clinical disorders, of which the most common are erythema infectiosum, aplastic crisis complicating chronic hemolytic anemia, and hydrops fetalis. In young adults, the skin eruption caused by B19 is accompanied with polyarthritis and polyarthralgia in 60% of the cases. The joint abnormalities predominate in the hands and feet and usually resolve within a week (range 2-21 d). Serological tests show IgM antibodies against B19, confirming the diagnosis of recent infection. Protracted polyarthritis occurs in some patients and seems associated with the DR4 histocompatibility alleles. Rheumatoid factors can be produced transiently in these patients. Other autoantibodies produced in the wake of B19 infection include anti-nuclear antibodies, anti-DNA, anti-SSA/SSB, and anti-phospholipids. Acute B19 infection can simulate early rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE) (lupus-like eruption over the cheeks, cytopenia, etc.). In addition, there have been a few reports of erosive RA or SLE developing shortly after a B19 infection, with positive PCR tests for B19 DNA in synovial tissue or blood cells. Studies in large series indicate that B19 is probably an extremely rare cause of RA or SLE. Vasculitides affecting the small vessels (Henoch-Schonlein purpura, Wegener's granulomatosis), medium-sized vessels (periarteritis nodosa), and large vessels (giant cell arteritis) can occur after B19 infection. Here again, the number of clinical cases is small.

Role of endogenous retroviruses in autoimmune diseases

Endogenous retroviruses (ERVs) correspond to the integrated proviral form of infectious retroviruses that are trapped within the genome by mutations. Endogenous retroviruses represent a key molecular link between the host genome and infectious viral particles. Proteins encoded by ERVs are recognized by antiviral immune responses and become targets of autoreactivity. Activation of ERVs, such as human ERV-K or a human T-cell lymphotropic virus-related endogenous sequence, may also mediate pathogenicity of Epstein-Barr virus. Endogenous retrovirus peptides can directly regulate immune responses. Thus, molecular mimicry and immunomodulation by ERVs may account for self-reactivity and abnormal T- and B-cell functions in autoimmune disorders.

Apoptotic activity in villous trophoblast cells during B19 infection correlates with clinical outcome: assessment by the caspase-related M30 Cytodeath antibody

Human parvovirus B19 (B19) infection during pregnancy can result in horizontal transmission of the virus and congenital infection. The main targets for B19 replication are the erythroid precursor cell of the colony and burst forming units. The cellular receptor necessary for B19 infectivity is globoside. Other non-erythroid cells can express this receptor, including megakaryocytes, endothelial cells, cardiac myocytes and placental trophoblast cells. B19 infection of globoside-containing erythroid cells results in cell death via apoptosis. We asked whether globoside-containing placental trophoblast cells, although not permissive for complete viral replication, would show evidence of apoptotic activity as a result of B19 infection. Placentas from 26 pregnancies with documented maternal and/or congenital B19 infection, 14 with poor outcomes and 12 with good outcomes were examined for evidence of apoptosis using the caspase-related M30 Cytodeath monoclonal antibody (Mab). M30 Mab recognizes a caspase 3 directed cleavage event within cytokeratin 18, a protein widely distributed in epithelial cells, of which trophoblast cells are classified. The results of the immunohistochemical analysis revealed a significant number of M30-staining placental villous trophoblast cells from B19-complicated pregnancies with poor outcomes compared to B19-complicated pregnancies with good outcomes or the 24 age-matched controls (P< 0.001). This is the first description of an association between B19-complicated pregnancies ending in foetal death and increased apoptosis within placental villous trophoblast cells. Damage due to premature death of the protective barrier of the placental trophoblast layer may compromise its integrity and play a role in pathogenesis.

Parvovirus B19 and erythroid cells

Parvovirus B19 is a human erythrovirus, i.e. which induces the death of erythroid progenitors. In such cells, until now only ubiquitous transcription factors have been described to regulate promoter driven gene expression. Their possible interactions with erythroid specific transcription factors merit further investigations. Effectively, the high level of replication of B19 in erythroid cells is not well understood. In addition to apoptosis, necrosis or inhibition of cell growth, the death of B19 infected erythroid progenitors has been never clearly reported as the result of immunological attack: this mecanism will merit further investigations. The interactions with other cell types in vitro remain at present not well defined but many obstacles have been mentioned which counteract B19 expression.

A transgenic mouse model for non-immune hydrops fetalis induced by the NS1 gene of human parvovirus B19

Human parvovirus B19 (B19) infection during pregnancy is associated with the adverse foetal outcome known as non-immune hydrops fetalis (NIHF). Although B19 is known to infect erythroid-lineage cells in vivo as well as in vitro, the mechanism leading to the occurrence of NIHF is not clear. To investigate the possible involvement of the B19 non-structural protein NS1 in NIHF, three independent lines of transgenic mice were generated that expressed NS1 under the control of the Cre-loxP system and the GATA1 promoter. Two of the three lines expressed NS1 in erythroid-lineage cells. Most of the transgenic mice died at the embryonic stage, some of which developed hydropic changes caused by severe anaemia at embryonic day 15.5 (E15.5). Histological examination of embryos at E15.5 showed significantly fewer erythropoietic islands in the liver parenchyma, whereas their hearts showed no abnormal signs, such as cardiomegaly and apoptotic cells. The NS1-transgenic mouse lines established here provide an animal model for human NIHF and suggest that NS1 plays a crucial role in the adverse outcome associated with intrauterine B19 infection in humans.

Caspase activation is required for permissive replication of Aleutian mink disease parvovirus in vitro

Aleutian mink disease parvovirus (ADV) is distinct among the parvoviruses as infection in vivo is persistent, restricted, and noncytopathic. In contrast, infections with other more prototypic parvoviruses, like mink enteritis virus (MEV), are acute, cytopathic, and characterized by permissive replication in vivo. Although apoptosis results in the death of cells acutely infected by parvoviruses, the role of apoptosis in ADV infections is unknown. Permissive infection of ADV resulted in apoptosis of Crandell feline kidney (CrFK) cells as indicated by TUNEL staining, Annexin-V staining, and characteristic changes in cell morphology. Pretreatment of infected cells with caspase 3 or broad-spectrum caspase inhibitors prevented apoptosis. In addition, treatment of infected cells with these inhibitors caused a 2 log(10) reduction in the yield of infectious virus compared to untreated cultures. This block in replication preceded substantial viral DNA amplification and gene expression. However, inhibitors of caspases 1, 6, and 8 did not have this effect. MEV also induced caspase-dependent apoptosis following infection of CrFK cells, although production of infectious progeny was not affected by inhibition of apoptosis. Thus, permissive replication of ADV in vitro depended upon activation of specific caspases. If ADV infection of cells in vivo fails to initiate caspase activation, the requirement of caspase activity for replication may not be met, thus providing a possible mechanism for persistent, restricted infection.

E5 protein of human papillomavirus type 16 protects human foreskin keratinocytes from UV B-irradiation-induced apoptosis

The human papillomavirus type 16 (HPV16) E5 protein associates with the epidermal growth factor receptor (EGFR) and enhances the activation of the EGFR after stimulation by EGF in human keratinocytes. Phosphatidylinositol 3-kinase (PI3K) and ERK1/2 mitogen-activated protein kinase (ERK1/2 MAPK), two signal molecules downstream of the EGFR, have been recognized as participants in two survival signal pathways in response to stress. The fact that E5 can enhance EGFR activation suggests that E5 might act as a survival factor. To test this hypothesis, the apoptotic response of UV B-irradiated primary keratinocytes infected with either control retrovirus, LXSN, or HPV16 2E5-expressing recombinant retrovirus was quantitated. Under the same conditions, LXSN-infected cells showed extensive apoptosis, while E5-expressing cells demonstrated a significant reduction in UV B-irradiation-induced apoptosis. The E5-mediated protection against apoptosis was blocked by wortmannin and PD98059, specific inhibitors of the PI3K and ERK1/2 MAPK pathways, respectively, suggesting that the PI3K and ERK1/2 MAPK pathways are involved in this process. Western blot analysis showed that Akt (also named protein kinase B), which is a downstream effector of PI3K, and ERK1/2 MAPK were activated by EGF. When cells were stimulated by EGF and irradiated by UV B, the levels of phospho-Akt and phospho-ERK1/2 activated by EGF in E5-expressing cells were about twofold greater than those in LXSN-infected cells. Two other UV-activated stress pathways, p38 and JNK, were activated to the same level during UV B irradiation in both LXSN-infected cells and E5-expressing cells, indicating that E5 protein did not affect these two pathways. After UV B irradiation, p53 was activated in both LXSN-infected cells and E5-expressing cells, and cell cycle analysis showed that nearly all cells in both cell populations were growth arrested. These data suggest that unlike HPV16 E6, which blocks apoptosis by inactivation of p53, HPV16 E5 protects cells from apoptosis by enhancing the PI3K-Akt and ERK1/2 MAPK signal pathways.

Expression of p53 and Ki-67 antigen in bone marrow giant proerythroblasts associated with human parvovirus B19 infection

Giant proerythroblasts are hallmarks of human parvovirus B19 infection. We attempted to characterize these cells in 5 patients with parvovirus B19-induced pure red cell aplasia using immunostaining of paraffin-embedded bone marrow sections with antibodies against erythroid-lineage-specific proteins, viral capsid antigen VP-1, and apoptosis- and cell-cycle-related proteins. Giant proerythroblasts are immunohistochemically consistent with early erythroid precursors of cells in the differentiation stage of CD34-, cytoplasmic spectrin+, glycophorin A-, and band-3-. VP-1 was expressed in the nucleus and cytoplasm of small- to medium-sized spectrin+ erythroid cells but not in giant proerythroblasts. The giant proerythroblasts displayed nuclear staining for p53 (41%+/-16%) and Ki-67 antigen (100%+/-0%) and cytoplasmic staining for Bax (65%+/-11%) and procaspase-3 (78%+/-10%), whereas they were not stained for p21Wafl/Cip1, active form of caspase-3, or terminal deoxynucleotidyltransferase-mediated deoxyuridine nick-end labeling (TUNEL). Antiapoptotic proteins, Bcl-2 and Mcl-1, were not expressed in the giant cells, and Bcl-x was infrequently expressed in these cells (11%+/-4%). These immunohistochemical findings suggest that giant proerythroblasts are proliferating erythroid precursors with accumulation of nonfunctional p53.

Induction of apoptosis in vitro by the 17-kDa nonstructural protein of infectious bursal disease virus: possible role in viral pathogenesis

Infectious bursal disease virus (IBDV) causes severe immunodeficiency in young chickens by destroying the precursors of antibody-producing B cells in the bursa of Fabricius. It has been shown that IBDV infection induces apoptosis in chicken embryo and tissue culture cells. We previously reported that an IBDV mutant lacking the expression of 17-kDa nonstructural (NS) protein exhibited decreased apoptotic effects in cell culture as compared to the parental IBDV, suggesting that the NS protein may be involved in induction of apoptosis. Here, we report that the NS protein of IBDV alone is capable of inducing apoptosis in cell culture. Transfection of chicken B-lymphocyte cell line (RP9) and chicken embryo fibroblast cells with a plasmid DNA, containing the NS protein gene under the control of the immediate-early promoter-enhancer region of human cytomegalovirus, induced programmed cell death in both cell lines. Apoptosis changes, such as chromatin condensation, DNA fragmentation, and the appearance of apoptotic nuclear bodies, were observed in cell cultures 48-h posttransfection. As reported earlier, the mutant IBDV grew to lower titers with slower replication kinetics and lower cytopathogenicity when compared to that of the parental virus. Here, we demonstrate that the mutant virus is closely associated with cells and its yield from the supernatant was approximately 30-fold lower than the wild-type due to increased cell association, indicating a deficiency in lysis of virus-infected cells. Taken together, our results indicate that the NS protein of IBDV is highly cytotoxic, which brings about the release of the viral progeny from cells, and thus play an important role in viral pathogenesis.

Propagation of rat parvovirus in thymic lymphoma cell line C58(NT)d and subsequent appearance of a resistant cell clone after lytic infection

Rat parvovirus (RPV) is nonpathogenic in rats but causes persistent lymphocytotropic infection. We found that RPV was propagated in rat thymic lymphoma cell line C58(NT)D and induced apoptosis. Interestingly, a resistant subclone, C58(NT)D/R, from surviving cells after lytic infection had differentiated phenotypic modifications, such as increased cell adherence, resistance to apoptosis, and suppressed tumorigenicity.

Apoptosis in feline panleukopenia and canine parvovirus enteritis

Tissue samples of cats and dogs with panleukopenia and parvovirus enteritis, respectively, were examined for the presence of viral antigen-positive cells and apoptotic cells by immunohistochemistry and by TUNEL assay (Terminal Transferase-Mediated dUTP Nick End Labelling). Compared to control animals, infected cats and dogs generally had more TUNEL-positive cells. Cell types positive for parvovirus antigen, for example digestive tract epithelial and mesenchymal cells, and lymphocytes and macrophages in lymphoid tissues were also positive for TUNEL signals. Occasionally, TUNEL signal and viral antigen were present in the same tissue areas, suggesting a direct viral trigger of apoptosis. More frequently, however, there was no complete overlap of antigen and TUNEL-positive areas. The results of this study indicate that apoptotic cell death contributes significantly to the widespread tissue damage of parvovirus infection in cats and dogs.

Potential dengue virus-triggered apoptotic pathway in human neuroblastoma cells: arachidonic acid, superoxide anion, and NF-kappaB are sequentially involved

Direct in vivo evidence for the susceptibility of human neuronal cells to dengue virus has not been reported. In this study, we demonstrated that type 2 dengue (DEN-2) virus infection induced extensive apoptosis in the human neuroblastoma cell line SK-N-SH. Phospholipase A(2) (PLA(2)) was activated by DEN-2 infection, which led to the generation of arachidonic acid (AA). Inhibition of PLA(2) activity by the PLA(2) inhibitors, AACOCF(3) and ONO-RS-082, diminished DEN-2 virus-induced apoptosis. In contrast, the cyclooxygenase inhibitors aspirin and indomethacin, thought to increase AA accumulation by blocking AA catabolism, enhanced apoptosis. Exogenous AA induced apoptosis in a dose-dependent manner. Superoxide anion, which is thought to be generated through the AA-activated NADPH oxidase, was increased after infection. Pretreatment with superoxide dismutase (SOD) protected cells against DEN-2 virus-induced apoptosis. Furthermore, generation of superoxide anion was blocked by AACOCF(3). In addition, the transcription factors, NF-kappaB and c-Jun, were found to be activated after DEN-2 virus infection. However, pretreatment of cells with oligodeoxynucleotides containing NF-kappaB, but not c-Jun, binding sites (transcription factor decoy) strongly prevented dengue virus-induced apoptosis. The finding that AACOCF(3) and SOD significantly block activation of NF-kappaB suggests that this activation is derived from the AA-superoxide anion pathway. Our results indicate that DEN-2 virus infection of human neuroblastoma cells triggers an apoptotic pathway through PLA(2) activation to superoxide anion generation and subsequently to NF-kappaB activation. This apoptotic effect can be either directly derived from the action of AA and superoxide anion on mitochondria or indirectly derived from the products of apoptosis-related genes activated by NF-kappaB.

Haematological consequences of parvovirus B19 infection

Parvovirus B19, a member of the Erythrovirus genus, is the only member of the Parvoviridae family known to be pathogenic in humans. Erythroviruses are so named because of their tropism and selective replication in erythroid progenitor cells. Haematological consequences of B19 infection arise due to a direct cytotoxic effect on erythroid progenitors in bone marrow with interruption of erythrocyte production. In addition, the physiology of host haematopoiesis and competence of the immune response each determines clinical manifestations of B19 infection: in individuals with underlying haemolytic disorders, B19 infection causes transient aplastic crisis; in immunocompromised patients, persistent B19 infection may develop that manifests as pure red cell aplasia and chronic anaemia; B19 infection in utero may result in fetal death, hydrops fetalis, or congenital anaemia. Diagnosis is based on examination of bone marrow and B19 virological studies. Treatment of persistent infection with immunoglobulin leads to a prompt resolution of the anaemia.

Human immunodeficiency virus type 1 vpr induces apoptosis through caspase activation

Human immunodeficiency virus type 1 (HIV-1) Vpr is a 96-amino-acid protein that is found associated with the HIV-1 virion. Vpr induces cell cycle arrest at the G(2)/M phase of the cell cycle, and this arrest is followed by apoptosis. We examined the mechanism of Vpr-induced apoptosis and found that HIV-1 Vpr-induced apoptosis requires the activation of a number of cellular cysteinyl aspartate-specific proteases (caspases). We demonstrate that ectopic expression of anti-apoptotic viral proteins, which inhibit caspase activity, and addition of synthetic peptides, which represent caspase cleavage sites, can inhibit Vpr-induced apoptosis. Finally, inhibition of caspase activity and subsequent inhibition of apoptosis results in increased viral expression, suggesting that therapeutic strategies aimed at reducing Vpr-induced apoptosis in vivo require careful consideration.

Genetic and metabolic control of the mitochondrial transmembrane potential and reactive oxygen intermediate production in HIV disease

Redox mechanims play important roles in replication of human immunodeficiency virus type 1 (HIV-1) and cellular susceptibility to apoptosis signals. Viral replication and accelerated turnover of CD4+ T cells occur throughout a prolonged asymptomatic phase in patients infected by HIV-1. Disease development is associated with steady loss of CD4+ T cells by apoptosis, increased rate of opportunistic infections and lymphoproliferative diseases, disruption of energy metabolism, and generalized wasting. Such pathological states are preceded by: (i) depletion of intracellular antioxidants, glutathione (GSH) and thioredoxin (TRX), (ii) increased reactive oxygen species (ROS) production, and (iii) changes in mitochondrial transmembrane potential (deltapsi(m)). Disruption of deltapsi(m) appears to be the point of no return in the effector phase of apoptosis. Viral proteins Tat, Nef, Vpr, protease, and gp120, have been implicated in initiation and/or intensification of oxidative stress and disruption of deltapsi(m). Redox-sensitive transcription factors, NF-kappaB, AP-1, and p53, support expression of viral genes and proinflammatory lymphokines. ROS regulate apoptosis signaling through Fas, tumor necrosis factor (TNF), and related cell death receptors, as well as the T-cell receptor. Oxidative stress in HIV-infected donors is accompanied by increased glucose utilization both on the cellular and organismal levels. Generation of GSH and TRX from their corresponding oxidized forms is dependent on NADPH provided through the pentose phosphate pathway of glucose metabolism. This article seeks to delineate the genetic and metabolic bases of HIV-induced oxidative stress. Such understanding should lead to development of effective antioxidant therapies in HIV disease.

Possible interactions between the NS-1 protein and tumor necrosis factor alpha pathways in erythroid cell apoptosis induced by human parvovirus B19

Human erythroid progenitor cells are the main target cells of the human parvovirus B19 (B19), and B19 infection induces a transient erythroid aplastic crisis. Several authors have reported that the nonstructural protein 1 (NS-1) encoded by this virus has a cytotoxic effect, but the underlying mechanism of NS-1-induced primary erythroid cell death is still not clear. In human erythroid progenitor cells, we investigated the molecular mechanisms leading to apoptosis after natural infection of these cells by the B19 virus. The cytotoxicity of NS-1 was concomitantly evaluated in transfected erythroid cells. B19 infection and NS-1 expression induced DNA fragmentation characteristic of apoptosis, and the commitment of erythroid cells to undergo apoptosis was combined with their accumulation in the G(2) phase of the cell cycle. Since B19- and NS-1-induced apoptosis was inhibited by caspase 3, 6, and 8 inhibitors, and substantial caspase 3, 6, and 8 activities were induced by NS-1 expression, there may have been interactions between NS-1 and the apoptotic pathways of the death receptors tumor necrosis factor receptor 1 and Fas. Our results suggest that Fas-FasL interaction was not involved in NS-1- or B19-induced apoptosis in erythroid cells. In contrast, these cells were sensitized to tumor necrosis factor alpha (TNF-alpha)-induced apoptosis. Moreover, the ceramide level was enhanced by B19 infection and NS-1 expression. Therefore, our results suggest that there may be a connection between the respective apoptotic pathways activated by TNF-alpha and NS-1 in human erythroid cells.

Induction of apoptosis in murine coronavirus-infected cultured cells and demonstration of E protein as an apoptosis inducer

We demonstrated that infection of 17Cl-1 cells with the murine coronavirus mouse hepatitis virus (MHV) induced caspase-dependent apoptosis. MHV-infected DBT cells did not show apoptotic changes, indicating that apoptosis was not a universal mechanism of cell death in MHV-infected cells. Expression of MHV structural proteins by recombinant vaccinia viruses showed that expression of MHV E protein induced apoptosis in DBT cells, whereas expression of other MHV structural proteins, including S protein, M protein, N protein, and hemagglutinin-esterase protein, failed to induce apoptosis. MHV E protein-mediated apoptosis was suppressed by a high level of Bcl-2 oncogene expression. Our data showed that MHV E protein is a multifunctional protein; in addition to its known function in coronavirus envelope formation, it also induces apoptosis.