A functional role for neutralizing antibodies in Borna disease: influence on virus tropism outside the central nervous system

Comparative study of virus and lymphocyte distribution with clinical data suggests early high dose immunosuppression as potential key factor for the therapy of patients with BoDV-1 infection

ABSTRACTBorna disease virus 1 (BoDV-1) was just recently shown to cause predominantly fatal encephalitis in humans. Despite its rarity, bornavirus encephalitis (BVE) can be considered a model disease for encephalitic infections caused by neurotropic viruses and understanding its pathomechanism is of utmost relevance. Aim of this study was to compare the extent and distribution pattern of cerebral inflammation with the clinical course of disease, and individual therapeutic procedures. For this, autoptic brain material from seven patients with fatal BVE was included in this study. Tissue was stained immunohistochemically for pan-lymphocytic marker CD45, the nucleoprotein of BoDV-1, as well as glial marker GFAP and microglial marker Iba1. Sections were digitalized and counted for CD45-positive and BoDV-1-positive cells. For GFAP and Iba1, a semiquantitative score was determined. Furthermore, detailed information about the individual clinical course and therapy were retrieved and summarized in a standardized way. Analysis of the distribution of lymphocytes shows interindividual patterns. In contrast, when looking at the BoDV-1-positive glial cells and neurons, a massive viral involvement in the brain stem was noticeable. Three of the seven patients received early high-dose steroids, which led to a significantly lower lymphocytic infiltration of the central nervous tissue and a longer survival compared to the patients who were treated with steroids later in the course of disease. This study highlights the potential importance of early high-dose immunosuppressive therapy in BVE. Our findings hint at a promising treatment option which should be corroborated in future observational or prospective therapy studies.ABBREVIATIONS: BoDV-1: Borna disease virus 1; BVE: bornavirus encephalitis; Cb: cerebellum; CNS: central nervous system; FL: frontal lobe; GFAP: glial fibrillary acid protein; Hc: hippocampus; Iba1: ionized calcium-binding adapter molecule 1; Iba1act: general activation of microglial cells; Iba1nod: formation of microglial nodules; IL: insula; Me: mesencephalon; Mo: medulla oblongata; OL: occipital lobe; pASS: per average of 10 screenshots; patearly: patients treated with early high dose steroid shot; patlate: patients treated with late or none high dose steroid shot; Po: pons; So: stria olfactoria; Str: striatum.

Borna disease virus 1 infection in alpacas: Comparison of pathological lesions and viral distribution to other dead-end hosts

Borna disease is a progressive meningoencephalitis caused by spillover of the Borna disease virus 1 (BoDV-1) to horses and sheep and has gained attention due to its zoonotic potential. New World camelids are also highly susceptible to the disease; however, a comprehensive description of the pathological lesions and viral distribution is lacking for these hosts. Here, the authors describe the distribution and severity of inflammatory lesions in alpacas (n = 6) naturally affected by this disease in comparison to horses (n = 8) as known spillover hosts. In addition, the tissue and cellular distribution of the BoDV-1 was determined via immunohistochemistry and immunofluorescence. A predominant lymphocytic meningoencephalitis was diagnosed in all animals with differences regarding the severity of lesions. Alpacas and horses with a shorter disease duration showed more prominent lesions in the cerebrum and at the transition of the nervous to the glandular part of the pituitary gland, as compared to animals with longer disease progression. In both species, viral antigen was almost exclusively restricted to cells of the central and peripheral nervous systems, with the notable exception of virus-infected glandular cells of the Pars intermedia of the pituitary gland. Alpacas likely represent dead-end hosts similar to horses and other spillover hosts of BoDV-1.

Vaccination against Borna Disease: Overview, Vaccine Virus Characterization and Investigation of Live and Inactivated Vaccines

(1) Background: Vaccination of horses and sheep against Borna disease (BD) was common in endemic areas of Germany in the 20th century but was abandoned in the early 1990s. The recent occurrence of fatal cases of human encephalitis due to Borna disease virus 1 (BoDV-1) has rekindled the interest in vaccination. (2) Methods: The full genomes of the BD live vaccine viruses "Dessau" and "Giessen" were sequenced and analyzed for the first time. All vaccination experiments followed a proof-of-concept approach. Dose-titration infection experiments were performed in rabbits, based on both cell culture- and brain-derived viruses at various doses. Inactivated vaccines against BD were produced from concentrated cell culture supernatants and investigated in rabbits and horses. The BoDV-1 live vaccine "Dessau" was administered to horses and antibody profiles were determined. (3) Results: The BD live vaccine viruses "Dessau" and "Giessen" belong to clusters 3 and 4 of BoDV-1. Whereas the "Giessen" virus does not differ substantially from field viruses, the "Dessau" virus shows striking differences in the M gene and the N-terminal part of the G gene. Rabbits infected with high doses of cell-cultured virus developed neutralizing antibodies and were protected from disease, whereas rabbits infected with low doses of cell-cultured virus, or with brain-derived virus did not. Inactivated vaccines were administered to rabbits and horses, following pre-defined vaccination schemes consisting of three vaccine doses of either adjuvanted or nonadjuvanted inactivated virus. Their immunogenicity and protective efficacy were compared to the BD live vaccine "Dessau". Seventy per cent of horses vaccinated with the BD live vaccine "Dessau" developed neutralizing antibodies after vaccination. (4) Conclusion: Despite a complex evasion of immunological responses by bornaviruses, some vaccination approaches can protect against clinical disease. For optimal effectiveness, vaccines should be administered at high doses, following vaccination schemes consisting of three vaccine doses as basic immunization. Further investigations are necessary in order to investigate and improve protection against infection and to avoid side effects.

Avian Bornavirus Research—A Comprehensive Review

Avian bornaviruses constitute a genetically diverse group of at least 15 viruses belonging to the genus Orthobornavirus within the family Bornaviridae. After the discovery of the first avian bornaviruses in diseased psittacines in 2008, further viruses have been detected in passerines and aquatic birds. Parrot bornaviruses (PaBVs) possess the highest veterinary relevance amongst the avian bornaviruses as the causative agents of proventricular dilatation disease (PDD). PDD is a chronic and often fatal disease that may engulf a broad range of clinical presentations, typically including neurologic signs as well as impaired gastrointestinal motility, leading to proventricular dilatation. It occurs worldwide in captive psittacine populations and threatens private bird collections, zoological gardens and rehabilitation projects of endangered species. In contrast, only little is known about the pathogenic roles of passerine and waterbird bornaviruses. This comprehensive review summarizes the current knowledge on avian bornavirus infections, including their taxonomy, pathogenesis of associated diseases, epidemiology, diagnostic strategies and recent developments on prophylactic and therapeutic countermeasures.

Optimal Expression of the Envelope Glycoprotein of Orthobornaviruses Determines the Production of Mature Virus Particles

An RNA virus-based episomal vector (REVec) whose backbone is Borna disease virus 1 (BoDV-1) can provide long-term gene expression in transduced cells. To improve the transduction efficiency of REVec, we evaluated the role of the viral envelope glycoprotein (G) of the genus Orthobornavirus, including that of BoDV-1, in the production of infectious particles. By using G-pseudotype assay in which the lack of G in G-deficient REVec (ΔG-REVec) was compensated for expression of G, we found that excess expression of BoDV-1-G does not affect particle production itself but results in uncleaved and aberrant mature G expression in the cells, leading to the production of REVec particles with low transduction titers. We revealed that the expression of uncleaved G in the cells inhibits the incorporation of mature G and vgRNA into the particles. This feature of G was conserved among mammalian and avian orthobornaviruses; however, the cleavage efficacy of canary bornavirus 1 (CnBV-1)-G was exceptionally not impaired by its excess expression, which led to the production of the pseudotype ΔG-REVec with the highest titer. Chimeric G proteins between CnBV-1 and -2 revealed that the signal peptide of CnBV-1-G was responsible for the cleavage efficacy through the interaction with intracellular furin. We showed that CnBV-1 G leads to the development of pseudotyped REVec with high transduction efficiency and a high-titer recombinant REVec. Our study demonstrated that the restricted expression of orthobornavirus G contributes to the regulation of infectious particle production, the mechanism of which can improve the transduction efficiency of REVec.IMPORTANCE Most viruses causing persistent infection produce few infectious particles from the infected cells. Borna disease virus 1, a member of the genus Orthobornavirus, is an RNA virus that persistently infects the nucleus and has been applied to vectors for long-term gene expression. In this study, we showed that, common among orthobornaviruses, excessive G expression does not affect particle production itself but reduces the production of infectious particles with mature G and genomic RNA. This result suggested that limited G expression contributes to suppressing abnormal viral particle production. On the other hand, we found that canary bornavirus 1 has an exceptional G maturation mechanism and produces a high-titer virus. Our study will contribute to not only understanding the mechanism of infectious particle production but also improving the vector system of orthobornaviruses.

Age-dependent development and clinical characteristics of an experimental parrot bornavirus-4 (PaBV-4) infection in cockatiels (Nymphicus hollandicus)

Parrot bornavirus (PaBV) is a pathogen often found in psittacine populations. Infected, clinically healthy carrier birds are of major importance for epidemiology, but the underlying pathomechanism of this carrier status is poorly understood. The age, implying the maturation status of the immune system, at the time of infection might be significant for the clinical outcome. Therefore, two groups of 11 cockatiels of different ages (adult and newly hatched) were inoculated with a PaBV-4 isolate intravenously. The trial lasted for 233 days and all birds were observed for clinical signs, PaBV-RNA shedding and anti-PaBV antibody production. At the end of the trial, histopathology, immunohistochemistry, PCR and virus re-isolation were performed. All 22 birds seroconverted and shed PaBV-RNA during the investigation period; the juvenile group earlier and more homogeneously. Nine of 11 birds of the adult group developed clinical signs; five birds died or had to be euthanized before the end of the study. In the juvenile group none of the birds developed clinical signs and only one bird died due to bacterial septicaemia. Eight birds of the adult group, but none of the juvenile group, showed a dilatation of the proventriculus. PaBV-RNA detection and virus re-isolation were successful in all birds. Immunohistochemically, PaBV antigen was found in all birds. Histopathology revealed mononuclear infiltrations in organs in birds of both groups, but the juveniles were less severely affected in the brain.Thus, PaBV infection at an age with a more naïve immune system makes the production of carrier birds more likely.RESEARCH HIGHLIGHTS PaBV infection at a young age might favour the development of carrier birds.Cockatiels infected at a very young age showed inflammation but no clinical signs.The juvenile group started seroconversion and PaBV-RNA shedding earlier.Seroconversion and PaBV-RNA shedding occurred more homogeneously in the juveniles.

Evolutionary Selection of the Nuclear Localization Signal in the Viral Nucleoprotein Leads to Host Adaptation of the Genus Orthobornavirus

Adaptation of the viral life cycle to host cells is necessary for efficient viral infection and replication. This evolutionary process has contributed to the mechanism for determining the host range of viruses. Orthobornaviruses, members of the family Bornaviridae, are non-segmented, negative-strand RNA viruses, and several genotypes have been isolated from different vertebrate species. Previous studies revealed that some genotypes isolated from avian species can replicate in mammalian cell lines, suggesting the zoonotic potential of avian orthobornaviruses. However, the mechanism by which the host specificity of orthobornaviruses is determined has not yet been identified. In this study, we found that the infectivity of orthobornaviruses is not determined at the viral entry step, mediated by the viral glycoprotein and matrix protein. Furthermore, we demonstrated that the nuclear localization signal (NLS) sequence in the viral nucleoprotein (N) has evolved under natural selection and determines the host-specific viral polymerase activity. A chimeric mammalian orthobornavirus, which has the NLS sequence of avian orthobornavirus N, exhibited a reduced propagation efficiency in mammalian cells. Our findings indicated that nuclear transport of the viral N is a determinant of the host range of orthobornaviruses, providing insights into the evolution and host adaptation of orthobornaviruses.

Update on immunopathology of bornavirus infections in humans and animals

Knowledge on bornaviruses has expanded tremendously during the last decade through detection of novel bornaviruses and endogenous bornavirus-like elements in many eukaryote genomes, as well as by confirmation of insectivores as reservoir species for classical Borna disease virus 1 (BoDV-1). The most intriguing finding was the demonstration of the zoonotic potential of lethal human bornavirus infections caused by a novel bornavirus of different squirrel species (variegated squirrel 1 bornavirus, VSBV-1) and by BoDV-1 known as the causative agent for the classical Borna disease in horses and sheep. Whereas a T cell-mediated immunopathology has already been confirmed as key disease mechanism for infection with BoDV-1 by experimental studies in rodents, the underlying pathomechanisms remain less clear for human bornavirus infections, infection with other bornaviruses or infection of reservoir species. Thus, an overview of current knowledge on the pathogenesis of bornavirus infections focusing on immunopathology is given.

In vivo biodistribution analysis of transmission competent and defective RNA virus-based episomal vector

RNA virus-based episomal vector (REVec) is an emerging viral vector system that mediates long-term stable gene expression in variety of cell types in vitro. However, little is known about its tissue tropism and persistence of gene expression in vivo. Here, to evaluate the feasibility of REVec for in vivo gene delivery, we conducted biodistribution analysis of transmission competent REVec and transmission defective ΔG-REVec in Lewis rats. Following intracranial administration of REVec, transgene expression was detected in various tissues. In contrast, transgene expression was only observed in the brain after ΔG-REVec administration. Low levels of vector shedding in the feces and blood and of neutralizing antibody in the serum were detected after REVec injection. In the brain, microglia, astrocytes and neurons were susceptible to REVec-mediated transduction. However, the animals administered with REVec, but not with ΔG-REVec showed a significant decrease in body weight compared to mock treated animals. Additionally, CD8 T cell infiltration was observed in the brain of these animals. In summary, we demonstrated that REVec promotes long-term transgene expression in vivo without causing high vector shedding or neutralizing antibody production; however, suggests the need to attenuate vector associated pathogenicity in the future.

The pathogenesis of bornaviral diseases in mammals

Natural bornavirus infections and their resulting diseases are largely restricted to horses and sheep in Central Europe. The disease also occurs naturally in cats, and can be induced experimentally in laboratory rodents and numerous other mammals. Borna disease virus-1 (BoDV-1), the cause of most cases of mammalian Borna disease, is a negative-stranded RNA virus that replicates within the nucleus of target cells. It causes severe, often lethal, encephalitis in susceptible species. Recent events, especially the discovery of numerous new species of bornaviruses in birds and a report of an acute, lethal bornaviral encephalitis in humans, apparently acquired from squirrels, have revived interest in this remarkable family of viruses. The clinical manifestations of the bornaviral diseases are highly variable. Thus, in addition to acute lethal encephalitis, they can cause persistent neurologic disease associated with diverse behavioral changes. They also cause a severe retinitis resulting in blindness. In this review, we discuss both the pathological lesions observed in mammalian bornaviral disease and the complex pathogenesis of the neurologic disease. Thus infected neurons may be destroyed by T-cell-mediated cytotoxicity. They may die as a result of excessive inflammatory cytokine release from microglia. They may also die as a result of a ‘glutaminergic storm’ due to a failure of infected astrocytes to regulate brain glutamate levels.

Surface glycoprotein of Borna disease virus mediates virus spread from cell to cell

Borna disease virus (BDV) is a non-segmented negative-stranded RNA virus that maintains a strictly neurotropic and persistent infection in affected end hosts. The primary target cells for BDV infection are brain cells, e.g. neurons and astrocytes. The exact mechanism of how infection is propagated between these cells and especially the role of the viral glycoprotein (GP) for cell-cell transmission, however, are still incompletely understood. Here, we use different cell culture systems, including rat primary astrocytes and mixed cultures of rat brain cells, to show that BDV primarily spreads through cell-cell contacts. We employ a highly stable and efficient peptidomimetic inhibitor to inhibit the furin-mediated processing of GP and demonstrate that cleaved and fusion-active GP is strictly necessary for the cell-to-cell spread of BDV. Together, our quantitative observations clarify the role of Borna disease virus-glycoprotein for viral dissemination and highlight the regulation of GP expression as a potential mechanism to limit viral spread and maintain persistence. These findings furthermore indicate that targeting host cell proteases might be a promising approach to inhibit viral GP activation and spread of infection.

The bicolored white-toothed shrew Crocidura leucodon (HERMANN 1780) is an indigenous host of mammalian Borna disease virus

Borna disease (BD) is a sporadic neurologic disease of horses and sheep caused by mammalian Borna disease virus (BDV). Its unique epidemiological features include: limited occurrence in certain endemic regions of central Europe, yearly varying disease peaks, and a seasonal pattern with higher disease frequencies in spring and a disease nadir in autumn. It is most probably not directly transmitted between horses and sheep. All these features led to the assumption that an indigenous virus reservoir of BDV other than horses and sheep may exist. The search for such a reservoir had been unsuccessful until a few years ago five BDV-infected shrews were found in a BD-endemic area in Switzerland. So far, these data lacked further confirmation. We therefore initiated a study in shrews in endemic areas of Germany. Within five years 107 shrews of five different species were collected. BDV infections were identified in 14 individuals of the species bicolored white-toothed shrew (Crocidura leucodon, HERMANN 1780), all originating from BD-endemic territories. Immunohistological analysis showed widespread distribution of BDV antigen both in the nervous system and in epithelial and mesenchymal tissues without pathological alterations. Large amounts of virus, demonstrated by presence of viral antigen in epithelial cells of the oral cavity and in keratinocytes of the skin, may be a source of infection for natural and spill-over hosts. Genetic analyses reflected a close relationship of the BDV sequences obtained from the shrews with the regional BDV cluster. At one location a high percentage of BDV-positive shrews was identified in four consecutive years, which points towards a self-sustaining infection cycle in bicolored white-toothed shrews. Analyses of behavioral and population features of this shrew species revealed that the bicolored white-toothed shrew may indeed play an important role as an indigenous host of BDV.

Epidemiology and host spectrum of Borna disease virus infections

Borna disease virus (BDV) has gained lot of interest because of its zoonotic potential, ability to introduce cDNA of its RNA transcripts into host genomes, and ability to cause severe neurobehavioural diseases. Classical Borna disease is a progressive meningoencephalomyelitis in horses and sheep, known in central Europe for centuries. According to current knowledge, BDV or a close relative also infects several other species, including humans at least occasionally, in central Europe and elsewhere, but the existence of potential 'human Borna disease' with its suspected neuropsychiatric symptoms is highly controversial. The recent detection of endogenized BDV-like genes in primate and various other vertebrate genomes confirms that at least ancient bornaviruses did infect our ancestors. The epidemiology of BDV is largely unknown, but accumulating evidence indicates vectors and reservoirs among small wild mammals. The aim of this review is to bring together the current knowledge on epidemiology of BDV infections. Specifically, geographical and host distribution are addressed and assessed in the critical light of the detection methods used. We also review some salient clinical aspects.

Vertical transmission of avian bornavirus in Psittaciformes: avian bornavirus RNA and anti-avian bornavirus antibodies in eggs, embryos, and hatchlings obtained from infected sun conures (Aratinga solstitialis)

Fertilized eggs were obtained from four pairs of sun conures (Aratinga solstitialis) infected with avian bornavirus (ABV) genotype 2, as determined by the sequence of the P24 gene. ABV RNA could be detected in early embryos of all four pairs. ABV RNA also was detected in brain, liver, and eyes of late-stage embryos of one of the pairs (Pair 4) and in blood of a 2-wk-old hatchling of this pair, demonstrating that vertical transmission can occur. ABV RNA could be detected in the liver but not in the brain or eyes of the late-stage embryos of another pair (Pair 3). Although it could be detected in the undeveloped eggs of the female parent and 8-day-old embryos, bornaviral RNA could not be found in the brain and liver of the late-stage embryos or in feathers and blood of young (5-9-wk-old) hatchlings of a third pair (Pair 2). At 11 wk, ABV RNA could be detected again in feathers and blood of these hatchlings and in the brain of one of the hatchlings of Pair 2 that suddenly died. ABV RNA could however be detected in throat swabs of the 5- and 9-wk-old hatchlings and their parents (Pair 2). Although the continued presence of ABV RNA in feathers and blood below the detection level of the reverse transcription-PCR used cannot be excluded, this result also may be attributable to feeding by the infected parents. Analysis by enzyme-linked immunosorbent assay showed that egg yolks and serum of late-stage embryos contain variable amounts of non-neutralizing anti-ABV-P40, -P10, -P24, and -P16 antibodies, the ratio of which reflected the antibody ratio in the serum of the female parent. Antibodies against the viral glycoprotein, which are considered neutralizing in mammals, and against ABV RNA polymerase were not detected. Whereas 5-wk-old hatchlings of the pair (Pair 2) that produced ABV RNA-free late-stage embryos were free of anti-ABV antibodies, such antibodies could be detected again in the serum of these hatchlings at 9 wk of age, before the age that bornaviral RNA could again be detected in feathers and blood. At 16 wk, these antibodies became abundant. The finding that late-stage embryos, presumably free of ABV RNA, can be obtained from eggs from infected parents suggests that hand- or foster-raising of such birds may be a method to obtain birnavirus-free offspring from some infected birds.

[Bornaviruses]

Bornaviridae is an enveloped animal virus carrying an 8.9 kb non-segmented, negative-strand RNA genome. The genus bornavirus contains two members infecting vertebrates, Borna disease virus (BDV) and avian bornavirus (ABV), which could preferably infect the nervous systems. BDV causes classical Borna disease, a progressive meningoencephalomyelitis, in horses and sheep, and ABV is known to induce proventricular dilatation disease, a fatal disease characterized by a lymphocytic, plasmacytic inflammation of central and peripheral nervous tissues, in multiple avian species. Recent evidences have demonstrated that bornavirus is unique among RNA viruses as they not only establish a long-lasting, persistent infection in the nucleus, but also integrate their own DNA genome copy into the host chromosome. In this review, I outline the recent knowledge about the unique virological characteristics of bornaviruses, as well as the diseases caused by the infection of BDV and ABV.

Intracerebral Borna disease virus infection of bank voles leading to peripheral spread and reverse transcription of viral RNA

Bornaviruses, which chronically infect many species, can cause severe neurological diseases in some animal species; their association with human neuropsychiatric disorders is, however, debatable. The epidemiology of Borna disease virus (BDV), as for other members of the family Bornaviridae, is largely unknown, although evidence exists for a reservoir in small mammals, for example bank voles (Myodes glareolus). In addition to the current exogenous infections and despite the fact that bornaviruses have an RNA genome, bornavirus sequences integrated into the genomes of several vertebrates millions of years ago. Our hypothesis is that the bank vole, a common wild rodent species in traditional BDV-endemic areas, can serve as a viral host; we therefore explored whether this species can be infected with BDV, and if so, how the virus spreads and whether viral RNA is transcribed into DNA in vivo.We infected neonate bank voles intracerebrally with BDV and euthanized them 2 to 8 weeks post-infection. Specific Ig antibodies were detectable in 41%. Histological evaluation revealed no significant pathological alterations, but BDV RNA and antigen were detectable in all infected brains. Immunohistology demonstrated centrifugal spread throughout the nervous tissue, because viral antigen was widespread in peripheral nerves and ganglia, including the mediastinum, esophagus, and urinary bladder. This was associated with viral shedding in feces, of which 54% were BDV RNA-positive, and urine at 17%. BDV nucleocapsid gene DNA occurred in 66% of the infected voles, and, surprisingly, occasionally also phosphoprotein DNA. Thus, intracerebral BDV infection of bank vole led to systemic infection of the nervous tissue and viral excretion, as well as frequent reverse transcription of the BDV genome, enabling genomic integration. This first experimental bornavirus infection in wild mammals confirms the recent findings regarding bornavirus DNA, and suggests that bank voles are capable of bornavirus transmission.

Antigen tissue distribution of Avian bornavirus (ABV) in psittacine birds with natural spontaneous proventricular dilatation disease and ABV genotype 1 infection

Tissues of 10 psittacines from aviary 1 ("case birds") and 5 psittacines from different aviaries were investigated for the presence of Avian bornavirus (ABV) antigen by immunohistochemistry using a polyclonal serum specific for the viral nucleocapsid (N) protein. Seven of 10 case birds had clinical signs, and necropsy findings consistent with proventricular dilatation disease (PDD) while 3 case birds and the 5 birds from other aviaries did not exhibit signs and lesions of this disease. In birds with clinical signs of PDD, ABV antigen was largely limited to neuroectodermal cells including neurons, astroglia, and ependymal cells of the central nervous system, neurons of the peripheral nervous system, and adrenal cells. ABV antigen was present in the nuclei and cytoplasm of infected cells. In 2 case birds that lacked signs and lesions of PDD, viral antigen had a more widespread distribution and was present in nuclei and cytoplasm of epithelial cells of the alimentary and urogenital tract, retina, heart, skeletal muscle, and skin in addition to the mentioned neuroectodermal cells. ABV RNA was identified by reverse transcription polymerase chain reaction (RT-PCR) in tissues of all 7 case birds available for testing from aviary 1, including 4 birds with PDD lesions and the 3 birds without PDD lesions. Sequencing and phylogenetic analysis indicated the presence of ABV genotype 1 in all cases. Findings further substantiate a role of ABV in PDD of psittacine bird species.

Borna disease virus (BDV) circulating immunocomplex positivity in addicted patients in the Czech Republic: a prospective cohort analysis

BACKGROUND

Borna disease virus (BDV) is an RNA virus belonging to the family Bornaviridae. Borna disease virus is a neurotropic virus that causes changes in mood, behaviour and cognition. BDV causes persistent infection of the central nervous system. Immune changes lead to activation of infection. Alcohol and drug dependence are associated with immune impairment.

METHODS

We examined the seropositivity of BDV circulating immunocomplexes (CIC) in patients with alcohol and drug dependence and healthy individuals (blood donors). We examined 41 addicted patients for the presence of BDV CIC in the serum by ELISA at the beginning of detoxification, and after eight weeks of abstinence. This is the first such study performed in patients with alcohol and drug dependence.

RESULTS

BDV CIC positivity was detected in 36.59% of addicted patients on day 0 and in 42.86% on day 56. The control group was 37.3% positive. However, we did not detect higher BDV CIC positivity in addicted patients in comparison with blood donors (p = 0.179). The significantly higher level of BDV CIC was associated with lower levels of GGT (gamma glutamyl transferase) (p = 0.027) and approached statistical significance with the lower age of addicted patients (p = 0.064). We did not find any association between BDV CIC positivity and other anamnestic and demographic characteristics.

CONCLUSIONS

In our study addicted patients did not have significantly higher levels of BDV CIC than the control group. The highest levels of BDV CIC were detected in patients with lower levels of GGT and a lower age.

TRIAL REGISTRATION

This study was approved by the ethical committee of the University Hospital Medical Faculty of Charles University in Pilsen, Czech Republic (registration number 303/2001).

Visualizing viral dissemination in the mouse nervous system, using a green fluorescent protein-expressing Borna disease virus vector

Borna disease virus (BDV) frequently persists in the brain of infected animals. To analyze viral dissemination in the mouse nervous system, we generated a mouse-adapted virus that expresses green fluorescent protein (GFP). This viral vector supported GFP expression for up to 150 days and possessed an extraordinary staining capacity, visualizing complete dendritic arbors as well as individual axonal fibers of infected neurons. GFP-positive cells were first detected in cortical areas from where the virus disseminated through the entire central nervous system (CNS). Late in infection, GFP expression was found in the sciatic nerve, demonstrating viral spread from the central to the peripheral nervous system.

Distribution of Borna disease virus antigen and RNA in tissues of naturally infected bicolored white-toothed shrews, Crocidura leucodon, supporting their role as reservoir host species

Borna disease is a severe viral-induced disorder of the central nervous system of horses, sheep, and a few other animal species, occurring in certain areas of central Europe. Pathogenesis and epidemiology of natural Borna disease virus (BDV) infections are still not fully understood; several unique epidemiologic features, however, point toward the existence of BDV reservoir populations other than the final hosts. In this study, 69 mice and 12 shrews were trapped and examined. The virus distribution was investigated in detail in 2 BDV-positive bicolored white-toothed shrews, Crocidura leucodon, by immunohistochemistry and TaqMan real-time reverse transcription polymerase chain reaction (RT-PCR). RT-PCR amplification products were sequenced, and the sequences were compared. These shrews had been collected in a BDV-endemic geographical region using live traps and did not show obvious clinical or pathological disease signs. BDV antigen and nucleic acid were identified in several organs, including the brain, mainly in nerve tissue and neurons, respectively, but also in parenchymal cells (eg, hepatocytes, Leydig cells) and epithelial cells, particularly of the respiratory and urogenital tract.

Avian bornaviruses in psittacine birds from Europe and Australia with proventricular dilatation disease

Birds with this disease display bornaviral antigen in neural and extraneural tissues.

To determine whether avian bornaviruses (ABVs) were a factor in proventricular dilatation disease (PDD), we used immunohistochemistry, reverse transcription–PCR, and nucleotide sequence analysis to examine paraffin wax–embedded or frozen tissue samples of 31 psittacine birds with this disease. PDD is a fatal disease of psittacine birds associated with nonsuppurative encephalitis and ganglioneuritis of the upper intestinal tract. Tissue samples had been collected from 1999 through 2008 in Austria, Switzerland, Hungary, and Australia. Immunohistochemical demonstration of viral antigen within the brain and vegetative nerve system of the gastrointestinal tract provides strong evidence for a causative role of ABVs in this condition. Partial sequences of nucleoprotein (p40) and matrix protein (gp18) genes showed that virus in most of our cases belonged to the ABV-2 and ABV-4 groups among the 5 genogroups described so far. Viral sequences of 2 birds did not match any of the described sequences and clustered together in a new branch termed ABV-6.

Analysis of naturally occurring avian bornavirus infection and transmission during an outbreak of proventricular dilatation disease among captive psittacine birds

A proventricular dilatation disease (PDD) outbreak provided the opportunity to investigate the transmissibility of avian Bornavirus (ABV) and its linkage to PDD under natural conditions. Upon exposure to a bird with a fatal case of PDD, 10 birds became symptomatic and died. ABV2 RNA was recovered from available tissues. Further screening revealed that 12/46 exposed birds were ABV2(+). Three chicks boarded at this aviary developed PDD. They harbored the same ABV2 isolate and transmitted it to five of eight chicks in their home aviary. These findings demonstrate that ABV infection precedes the development of PDD. ABV-specific Western blotting and reverse transcription-PCR indicate that ABV2 is not strictly neurotropic.

Role of Borna disease virus in neuropsychiatric illnesses: are we inching closer?

The biological cause of psychiatric illnesses continues to be under intense scrutiny. Among the various neurotropic viruses, Borna disease virus (BDV) is another virus that preferentially targets the neurons of the limbic system and has been shown to be associated with behavioural abnormalities. Presence of various BDV markers, including viral RNA, in patients with affective and mood disorders have triggered ongoing debate worldwide regarding its aetiopathogenic relationship. This article analyses its current state of knowledge and recent advances in diagnosis in order to prove or refute the association of BDV in causation of human neuropsychiatric disorders. This emerging viral causative association of behavioural disorders, which seems to be inching closer, has implication not only for a paradigm shift in the treatment and management of neuropsychiatric illnesses but also has an important impact on the public health systems.

Cell-to-cell spread of Borna disease virus proceeds in the absence of the virus primary receptor and furin-mediated processing of the virus surface glycoprotein

Borna disease virus (BDV) is an enveloped virus with a nonsegmented negative-strand RNA genome whose organization is characteristic of Mononegavirales. BDV cell entry follows a receptor-mediated endocytosis pathway, which is initiated by the recognition of an as-yet-unidentified receptor at the cell surface by the virus glycoprotein G. BDV G is synthesized as a precursor (GPC) that is cleaved by the cellular protease furin to produce the mature glycoproteins GP1 and GP2, which have been implicated in receptor recognition and pH-dependent fusion events, respectively. BDV is highly neurotropic and its spread in cultured cells proceeds in the absence of detectable extracellular virus or syncytium formation. BDV spread has been proposed to be strictly dependent on the expression and correct processing of BDV G. Here we present evidence that cell-to-cell spread of BDV required neither the expression of cellular receptors involved in virus primary infection, nor the furin-mediated processing of BDV G. We also show that in furin-deficient cells, the release of BDV particles induced by the treatment of BDV-infected cells with hypertonic buffer was not significantly affected, while virion infectivity was dramatically impaired, correlating with the decreased incorporation of BDV G species into viral particles. These findings support the view that the propagation of BDV within the central nervous systems of infected hosts involves both a primary infection that follows a receptor-mediated endocytosis pathway and a subsequent cell-to-cell spread that is independent of the expression of the primary receptor and does not require the processing of BDV G into GP1 and GP2.

Constitutive activation of the transcription factor NF-kappaB results in impaired borna disease virus replication

The inducible transcription factor NF-kappaB is commonly activated upon RNA virus infection and is a key player in the induction and regulation of the innate immune response. Borna disease virus (BDV) is a neurotropic negative-strand RNA virus, which replicates in the nucleus of the infected cell and causes a persistent infection that can lead to severe neurological disorders. To investigate the activation and function of NF-kappaB in BDV-infected cells, we stably transfected the highly susceptible neuronal guinea pig cell line CRL with a constitutively active (IKK EE) or dominant-negative (IKK KD) regulator of the IKK/NF-kappaB signaling pathway. While BDV titers were not affected in cells with impaired NF-kappaB signaling, the expression of an activated mutant of IkappaB kinase (IKK) resulted in a strong reduction in the intracellular viral titer in CRL cells. Electrophoretic mobility shift assays and luciferase reporter gene assays revealed that neither NF-kappaB nor interferon regulatory factors (IRFs) were activated upon acute BDV infection of wild-type or vector-transfected CRL cells. However, when IKK EE-transfected cells were used as target cells for BDV infection, DNA binding to an IRF3/7-responsive DNA element was detectable. Since IRF3/7 is a key player in the antiviral interferon response, our data indicate that enhanced NF-kappaB activity in the presence of BDV leads to the induction of antiviral pathways resulting in reduced virus titers. Consistent with this observation, the anti-BDV activity of NF-kappaB preferentially spread to areas of the brains of infected rats where activated NF-kappaB was not detectable.

Prevention of virus persistence and protection against immunopathology after Borna disease virus infection of the brain by a novel Orf virus recombinant

The Parapoxvirus Orf virus represents a promising candidate for novel vector vaccines due to its immune modulating properties even in nonpermissive hosts such as mouse or rat. The highly attenuated Orf virus strain D1701 was used to generate a recombinant virus (D1701-VrVp40) expressing nucleoprotein p40 of Borna disease virus, which represents a major antigen for the induction of a Borna disease virus-specific humoral and cellular immune response. Infection with Borna disease virus leads to distinct neurological symptoms mediated by the invasion of activated specific CD8+ T cells into the infected brain. Usually, Borna disease virus is not cleared from the brain but rather persists in neural cells. In the present study we show for the first time that intramuscular application of the D1701-VrVp40 recombinant protected rats against Borna disease, and importantly, virus clearance from the infected brain was demonstrated in immunized animals. Even 4 and 8 months after the last immunization, all immunized animals were still protected against the disease. Initial characterization of the immune cells attracted to the infected brain areas suggested that D1701-VrVp40 mediated induction of B cells and antibody-producing plasma cells as well as T cells. These findings suggest the induction of various defense mechanisms against Borna disease virus. First studies on the role of antiviral cytokines indicated that D1701-VrVp40 immunization did not lead to an enhanced early response of gamma or alpha interferon or tumor necrosis factor alpha. Collectively, this study describes the potential of the Orf virus vector system in mediating long-lasting, protective antiviral immunity and eliminating this persistent virus infection without provoking massive neuronal damage.

Exploring the cerebellum with a new tool: neonatal Borna disease virus (BDV) infection of the rat's brain

Cerebellar pathology has been associated with a number of developmental behavioral disorders, including autism spectrum disorders. Despite the fact that perinatal virus infections have been implicated in neurodevelopmental damage, few animal models have been developed to study the pathogenesis involved. One of the most interesting in vivo models of virus-induced cerebellar damage is the neonatal Borna disease virus (BDV) infection of the rat brain. The present review describes molecular, cellular, neuroanatomical, neurochemical and behavioral features of the BDV model and also provides a basis for a new understanding of the pathogenic mechanisms of cerebellar malformation and associated behavioral deficits.

Borna disease virus

Borna disease virus, a negative-strand RNA virus, infects a wide variety of warm-blooded animals. Depending on the age of the host and the integrity of its immune response, infection may be asymptomatic or cause a broad spectrum of behavioral disorders. Unusual features of Borna disease virus biology include nuclear localization of replication and transcription; diverse strategies for regulation of gene expression; and interaction with signaling pathways resulting in subtle neuropathology. Although the question of human infection remains unresolved, burgeoning interest in this unique pathogen has provided tools for exploring the pharmacology and neurochemistry of neuropsychiatric disorders potentially linked to infection. Analysis of rodent models of infection has yielded insights into mechanisms by which neurotropic agents and/or immune factors may impact developing or mature central nervous system circuitry to effect complex disturbances in movement and behavior.

Control of central nervous system viral persistence by neutralizing antibody

Replication of the neurotropic JHM strain of mouse hepatitis virus within the central nervous system is controlled by cellular immunity. However, following initial clearance, virus reactivates in the absence of humoral immunity. Viral recrudescence is prevented by the transfer of antiviral antibody (Ab). To characterize the specificity and biological functions of Ab critical for maintaining viral persistence, monoclonal Abs specific for the viral spike, matrix, and nucleocapsid proteins were transferred into infected B-cell-deficient mice following initial virus clearance. Neutralizing immunoglobulin G (IgG) but not IgA anti-spike Ab suppressed virus recrudescence, reduced viral antigen in most cell types except oligodendroglia, and was associated with reduced demyelination. Nonneutralizing monoclonal Abs specific for the spike, matrix, and nucleocapsid proteins did not prevent recrudescence, demonstrating that neutralization is critical for maintaining JHM mouse hepatitis virus persistence within the central nervous system. Ab-mediated protection was not associated with alterations in virus-specific T-cell function or inflammation. Furthermore, neutralizing Ab delayed but did not prevent virus recrudescence. These data indicate that following acute viral clearance cellular immunity is ineffective in controlling virus recrudescence and suggest that the continued presence of neutralizing Ab is the essential effector in maintaining viral persistence within the central nervous system.

Bornavirus and the brain

Borna disease virus (BDV) causes central nervous system (CNS) disease that is frequently manifested by behavioral abnormalities. BDV is a nonsegmented, negative, single-stranded RNA virus. On the basis of its unique genetic and biologic features, BDV is the prototypic member of a new virus family, Bornaviridae, within the order Mononegavirales. Therefore, the investigation of the molecular and cell biology of BDV may provide new insights about virus-cell interactions in the CNS. BDV is an important model system for the investigation of viral persistence in the CNS. Serologic and molecular epidemiologic studies suggest that BDV can infect humans. Despite controversy about potential association with human neuropsychiatric illnesses, BDV affords an intriguing model for the study of these illnesses. Neonatal BDV-infected rats display neurodevelopmental, physiologic, and neurobehavioral abnormalities that closely parallel some of the main features associated with several human mental disorders.

Humoral immune response against Borna disease virus (BDV) in experimentally and naturally infected cats

In order to investigate the peripheral and intracerebral humoral immune response against Borna disease virus (BDV) in cats, serum and cerebrospinal fluid (CSF) samples from experimentally and naturally BDV-infected cats were analysed in two different test systems (indirect enzyme-linked immunosorbent assay and indirect immunofluorescent test). The experimentally infected cats developed high antibody titres against the major immunogenic BDV-proteins, p24 and p40. In contrast, the naturally infected cats showed a comparatively weak humoral immune response. The experimentally infected cats were inoculated with either BDV laboratory strain V or a feline BDV-isolate. Some differences existed between the two groups of cats. The former group developed a higher response against p40, whereas the latter group showed, beside the p40-response, a more pronounced p24-response, similar to the situation in the naturally infected cats.

Bornavirus tropism and targeted pathogenesis: virus-host interactions in a neurodevelopmental model

Animal models provide unique opportunities to explore interactions between host and environment. Two models have been established based on Bornavirus infection that provide new insights into mechanisms by which neurotropic agents and/or immune factors may impact developing or mature CNS circuitry to effect complex disturbances in movement and behavior. Distinct losses in DA pathways in the adult infection model, and the associated dramatic movement disorder that accompanies it, make it an intriguing model for tardive dyskinesia and dystonic syndromes. The neuropathologic, physiologic, and neurobehavioral features of BDV infection of neonates indicate that it not only provides a useful model for exploring the mechanisms by which viral and immune factors may damage developing neurocircuitry, but also has significant links to the range of biologic, neurostructural, locomotor, cognitive, and social deficits observed in serious neuropsychiatric illnesses such as autism.

High-dose Borna disease virus infection induces a nucleoprotein-specific cytotoxic T-lymphocyte response and prevention of immunopathology

Experimental Borna disease virus (BDV) infection of rats and natural infection of horses and sheep leads to severe central nervous system disease based on immunopathological pathways. The virus replicates slowly, and the cellular immune response results in immunopathology. CD8(+) T cells exert effector cell functions, and their activity results in the destruction of virus-infected cells. Previously, Oldach and colleagues (D. Oldach, M. C. Zink, J. M. Pyper, S. Herzog, R. Rott, O. Narayan, and J. E. Clements, Virology 206:426-434, 1995) have reported protection against Borna disease after inoculation of high-dose cell-adapted BDV. Here we show that the outcome of the infection, i.e., immunopathology versus protection, is simply dependent on the amount of virus used for infection. High-dose BDV (10(6) FFU) triggers an early virus-specific reaction of the immune system, as demonstrated by strong cellular and humoral responses. In particular, the early presence and function of nucleoprotein-specific CD8(+) T cells could be demonstrated in the brain. We present evidence that in a noncytolytic and usually persistent virus infection, high-dose input virus mediates early control of the pathogen due to an efficient induction of an antiviral immune mechanism. From these data, we conclude that immune reactivity, in particular the cytotoxic T-cell response, determines whether the virus is controlled with prevention of the ensuing immunopathological disease or whether a persistent infection is established.

Borna disease virus infection of adult and neonatal rats: models for neuropsychiatric disease

Animal models provide unique opportunities to explore interactions between host and environment. Two models have been established based on Borna disease virus infection that provide new insights into mechanisms by which neurotropic agents and/or immune factors may impact developing or mature CNS circuitry to effect complex disturbances in movement and behavior. Note in press: Since this chapter was submitted, several manuscripts have been published that extend findings reported here and support the relevance of BDV infections of neonatal Lewis rats as models for investigating mechanisms of neurodevelopmental damage in autism. Behavioral abnormalities, including disturbed play behavior and chronic emotional overactivity, have been described by Pletnikov et al. (1999); inhibition of responses to novel stimuli were described by Hornig et al. (1999); loss of Purkinje cells following neonatal BDV infection has been demonstrated by Eisenman et al. (1999), Hornig et al. (1999), and Weissenböck et al. (2000); and alterations in cytokine gene expression have been reported by Hornig et al. (1999), Plata-Salaman et al. (1999) and Sauder et al. (1999).

Experimental infection of mice with Borna disease virus (BDV): replication and distribution of the virus after intracerebral infection

To develop an animal model resembling natural asymptomatic Borna disease virus (BDV) infections, BDV He/80 rat brain homogenate was passaged four times in adult SJL/J mice. Within 12 months of observation, mice did not develop overt signs of disease. Nucleotide sequencing of the rat isolate and the mouse isolates at the fourth passage revealed no difference in the deduced amino acids. Viral RNA was found in brain, heart, kidney, lung, liver, and urinary bladder. Infectious virus was isolated from brain, but also from heart and lung tissue. Immunohistochemically, BDV was demonstrated in nerves in the abdominal cavity, ganglion coeliacum, and adrenal glands, but not in organ parenchyma. Occasionally, viral RNA was detected in mononuclear blood cells.

MEK-specific inhibitor U0126 blocks spread of Borna disease virus in cultured cells

Borna disease virus (BDV) is a highly neurotropic virus that causes Borna disease, a virus-induced immune-mediated encephalomyelitis, in a variety of warm-blooded animals. Recent studies reported that BDV can be detected in patients with psychiatric disorders. BDV is noncytopathic, replicates in the nucleus of infected cells, and spreads intraaxonally in vivo. Upon infection of susceptible cultured cells, virus can be detected in foci. Little is known about the cellular components required for BDV replication. Here, we show that the cellular Raf/MEK/ERK signaling cascade is activated upon infection with BDV. In the presence of the MEK-specific inhibitor U0126, cells get infected with BDV; however, there is a block in virus spread to neighboring cells. The effect of the inhibitor on virus spread was still observed when the compound was added 2 h postinfection but not if treatment was initiated as late as 4 h after infection. Our results provide new insights into the BDV-host cell interaction and show that virus infection can be controlled with drugs interfering with a cellular signaling pathway. Since concentrations of the MEK inhibitor required to block BDV focus formation are not toxic for the host cells, our finding may be important with respect to antiviral drug development.

Borna disease virus

Borna disease virus (BDV) is unique amongst animal RNA viruses in its molecular biology and capacity to cause persistent, noncytolytic CNS-infection in a wide variety of host species. Unlike other non-segmented negative-strand RNA animal viruses, BDV replicates in the nucleus of the host cell where splicing is employed for expression of a very compact genome. Epidemiological studies indicate a broad host range and geographical distribution, and some investigators have proposed that human infection may result in neuropsychiatric disorders. Experimental Borna disease in neonatal and adult rats provides an intriguing model for immune-mediated disturbances of brain development and function.

Borna disease virus: a mystery as an emerging zoonotic pathogen

For Central European veterinarians, Borna disease (BD) has been known for a long time as a sporadically occurring, progressive viral polioencephalomyelitis predominantly affecting horses and sheep and-as discovered in the last decade-an increasing number of domestic and zoo animals. The aetiological agent, the Borna disease virus (BDV), a negative-sense, single-stranded RNA virus classified in the new virus family Bornaviridae within the order Mononegavirales, can induce severe clinical signs typically of a viral encephalitis with striking behavioural disturbances. After an incubation period lasting a few weeks to several months, BDV-infection causes locomotor and sensory dysfunctions followed by paralysis and death. Natural infections seem to be subclinical in most cases. BD received world-wide attention when it was reported that sera and/or cerebrospinal fluids from neuro-psychiatric patients can contain BDV-specific antibodies. Since infected animals produce BDV-specific antibodies only after virus replication, it was assumed that the broad spectrum of BDV-susceptible species also includes man. However, reports describing the presence of other BDV-markers, i.e. BDV-RNA or BDV-antigen, in peripheral blood leukocytes or brain tissue of neuro-psychiatric patients are highly controversial and, therefore, the role of BDV in human neuro-psychiatric disorders is questionable. (c) 2001 Harcourt Publishers Ltd.

Neutralizing antibodies in persistent borna disease virus infection: prophylactic effect of gp94-specific monoclonal antibodies in preventing encephalitis

Borna disease virus (BDV) infection triggers an immune-mediated encephalomyelitis and results in a persistent infection. The immune response in the acute phase of the disease is characterized by a cellular response in which CD8(+) T cells are responsible for the destruction of virus-infected brain cells. CD4(+) T cells function as helper cells and support the production of antiviral antibodies. Antibodies generated in the acute phase of the disease against the nucleoprotein and the phosphoprotein are nonneutralizing. In the chronic phase of the disease, neutralizing antibodies directed against the matrix protein and glycoprotein are synthesized. In the present work, the biological role of the neutralizing-antibody response to BDV was further investigated. By analyzing the blood of rats infected intracerebrally with BDV, a highly neurotropic virus, nucleic acid could be detected between 30 and 50 days after infection. Neutralizing antibodies were found between 60 and 100 days after infection. Furthermore, we produced hybridomas secreting BDV-specific neutralizing monoclonal antibodies. These antibodies, directed against the major glycoprotein (gp94) of BDV, were able to prevent Borna disease if given prophylactically. These data suggest that the late appearance of BDV-specific neutralizing antibodies is due to the presence of BDV in the blood of chronically infected rats. Furthermore, these antibodies have the potential to neutralize the infectious virus when given early, which is an important finding with respect to the development of a vaccine.

Borna disease in horses

Borna disease is a sporadically occurring, progressive viral polioencephalomyelitis that primarily affects horses and sheep. The etiological agent, Borna disease virus (BDV), is an enveloped, single-stranded RNA virus that has been classified in the new virus family Bornaviridae within the order Mononegavirales. Serological evidence of BDV infection has been found in an increasing number of countries throughout the world. After an incubation period lasting a few weeks to several months, BDV infection can cause locomotor and sensory dysfunction followed by paralysis and death. Borna disease is the result of a virus-induced immunopathological reaction. BDV-specific antibodies and viral RNA have been found in humans with various psychiatric disorders.

Pathogenesis of borna disease virus: granulocyte fractions of psychiatric patients harbor infectious virus in the absence of antiviral antibodies

Borna disease virus (BDV) causes acute and persistent infections in various vertebrates. During recent years, BDV-specific serum antibodies, BDV antigen, and BDV-specific nucleic acid were found in humans suffering from psychiatric disorders. Furthermore, viral antigen was detected in human autopsy brain tissue by immunohistochemical staining. Whether BDV infection can be associated with psychiatric disorders is still a matter of debate; no direct evidence has ever been presented. In the present study we report on (i) the detection of BDV-specific nucleic acid in human granulocyte cell fraction from three different psychiatric patients and (ii) the isolation of infectious BDV from these cells obtained from a patient with multiple psychiatric disorders. In leukocyte preparations other than granulocytes, either no BDV RNA was detected or positive PCR results were obtained only if there was at least 20% contamination with granulocytes. Parts of the antigenome of the isolated virus were sequenced, demonstrating the close relationship to the prototype BDV strains (He/80 and strain V) as well as to other human virus sequences. Our data provide strong evidence that cells in the granulocyte fraction represent the major if not the sole cell type harboring BDV-specific nucleic acid in human blood and contain infectious virus. In contrast to most other reports of putative human isolates, where sequences are virtually identical to those of the established laboratory strains, this isolate shows divergence in the region previously defined as variable in BDV from naturally infected animals.

General and specific immunosuppression caused by antiviral T-cell responses

Immunosuppression caused by the non-cytopathic lymphocytic choriomeningitis virus (LCMV) (an RNA virus) is mediated by antiviral cytotoxic T cells that destroy LCMV-infected cells, also of the immune system. While this immunopathological destruction of antigen-presenting cells, macrophages and follicular dendritic cells and of some CD4+ T cells causes general immunosuppression and impairs immune response to third party antigens, it also enhances exhaustion/deletion of LCMV-specific CD8+ T-cell responses. LCMV seems in addition to infect neutralizing antibody-producing B cells via the specific receptor; immunopathological LCMV specific CD8+ T-cell-mediated elimination of these infected B cells (but not of uninfected internal virus antigen-specific B cells) causes a highly specific immunosuppression that delays neutralizing antibody responses and thereby enhances virus persistence. Both generalized and specific immunosuppression by CD8+ T-cell-mediated immunopathology may be involved in human infections with HIV, hepatitis B virus or hepatitis C virus.

Borna disease virus nucleoprotein (p40) is a major target for CD8(+)-T-cell-mediated immune response

Experimental infection of rats with Borna disease virus (BDV) and natural BDV infection of horses and sheep leads to a virus-induced T-cell-mediated immunopathology in the central nervous system. Earlier work revealed the importance of the BDV-specific T-cell response and of CD8(+) effector cells in particular in the destruction of virus-infected cells. Evidence was also presented that this major histocompatibility complex class I-restricted lysis detected in vitro might play a functional role in the immunopathogenesis of Borna disease. The present study employed different vaccinia virus recombinants expressing single BDV-specific proteins to investigate the specificity of the cytolytic CD8(+)-T-cell response, revealing a major epitope on the BDV nucleoprotein p40. In contrast, no direct evidence in favor of the presence of in vivo relevant cytotoxic T-lymphocyte epitopes on other BDV-specific proteins was found.