Studies on canine distemper virus persistence in the central nervous system

Neuropathologic and molecular aspects of a canine distemper epizootic in red foxes in Germany

In the last fifteen years, an epidemic of canine distemper virus (CDV) with marked neurotropism has occurred in Europe after a longer period of endemic transmission. Many wildlife species have been infected, with red foxes (Vulpes vulpes) being particularly affected. Given that this species is assumed to mediate cross-species CDV infections to domestic and wild animals, tissue samples from foxes with confirmed CDV infection in North-Western Germany were investigated to better understand the neurotropic aspects of the disease. This analysis included histopathology, virus distribution and cell tropism, phenotyping of inflammatory responses and determination of the genotype of the viruses based on the phylogeny of the hemagglutinin (H) gene. The predominant lesion type is gliosis in both gray and white matter areas associated with an accumulation of Iba1+ macrophages/microglia and upregulation of major histocompatibility complex class II molecules in the brain, while sequestration of CD3+ T and Pax5+ B cell in CDV-infected foxes is limited. Demyelination is found in few foxes, characterized by reduced myelin staining with loss of CNPase+ oligodendrocytes in the cerebellar white matter and brainstem. In addition, axonal damage, characterized by β-amyloid precursor protein expression, is found mainly in these brain regions. In situ hybridization reveals a primary infection of the cerebral and cerebellar gray matter and brain stem. Iba1+ cells and NeuN+ neurons represent the main CDV targets. Sequencing of the CDV H open reading frame from fox tissues reveals that the virus strains belongs to three different sub-lineages of the Europe-1/South America-1 genotype, suggesting independent transmission lines.

One-step triplex PCR/RT-PCR to detect canine distemper virus, canine parvovirus and canine kobuvirus

To rapidly distinguish Canine distemper virus (CDV), canine parvovirus (CPV), and canine kobuvirus (CaKoV) in practice, a one-step multiplex PCR/RT-PCR assay was developed, with detection limits of 10^2.1 TCID₅₀ for CDV, 10^1.9 TCID₅₀ for CPV and 10³ copies for CaKoV. This method did not amplify nonspecific DNA or RNA from other canine viruses. Therefore, the assay provides a sensitive tool for the rapid clinical detection and epidemiological surveillance of CDV, CPV and CaKoV in dogs.

Expression of canine distemper virus receptor nectin-4 in the central nervous system of dogs

Canine distemper virus (CDV) exhibits lymphotropic, epitheliotropic, and neurotropic nature, and causes a severe systemic infection in susceptible animals. Initially, signaling lymphocyte activation molecule (SLAM) expressed on immune cells has been identified as a crucial cellular receptor for CDV. Currently, nectin-4 expressed in epithelia has been shown to be another receptor for CDV. Our previous study demonstrated that neurons express nectin-4 and are infected with CDV. In this study, we investigated the distribution pattern of nectin-4 in various cell types in the canine central nervous system and showed its relation to CDV infection to further clarify the pathology of disease. Histopathological, immunohistochemical and immunofluorescent analyses were done using formalin-fixed paraffin-embedded tissues of CDV-infected dogs. Dual staining of nectin-4 and CDV antigen or nectin-4 and brain cell markers was performed. Nectin-4 was detected in ependymal cells, epithelia of choroid plexus, meningeal cells, neurons, granular cells, and Purkinje's cells. CDV antigens were detected in these nectin-4-positive cells, further suggesting contribution of nectin-4 for the CDV neurovirulence. On the other hand, astrocytes did not express nectin-4, although they were frequently infected with CDV. Since astrocytes are negative for SLAM expression, they must express an unidentified CDV receptor, which also contributes to CDV neurovirulence.

SLAM- and nectin-4-independent noncytolytic spread of canine distemper virus in astrocytes

Measles and canine distemper viruses (MeV and CDV, respectively) first replicate in lymphatic and epithelial tissues by using SLAM and nectin-4 as entry receptors, respectively. The viruses may also invade the brain to establish persistent infections, triggering fatal complications, such as subacute sclerosis pan-encephalitis (SSPE) in MeV infection or chronic, multiple sclerosis-like, multifocal demyelinating lesions in the case of CDV infection. In both diseases, persistence is mediated by viral nucleocapsids that do not require packaging into particles for infectivity but are directly transmitted from cell to cell (neurons in SSPE or astrocytes in distemper encephalitis), presumably by relying on restricted microfusion events. Indeed, although morphological evidence of fusion remained undetectable, viral fusion machineries and, thus, a putative cellular receptor, were shown to contribute to persistent infections. Here, we first showed that nectin-4-dependent cell-cell fusion in Vero cells, triggered by a demyelinating CDV strain, remained extremely limited, thereby supporting a potential role of nectin-4 in mediating persistent infections in astrocytes. However, nectin-4 could not be detected in either primary cultured astrocytes or the white matter of tissue sections. In addition, a bioengineered "nectin-4-blind" recombinant CDV retained full cell-to-cell transmission efficacy in primary astrocytes. Combined with our previous report demonstrating the absence of SLAM expression in astrocytes, these findings are suggestive for the existence of a hitherto unrecognized third CDV receptor expressed by glial cells that contributes to the induction of noncytolytic cell-to-cell viral transmission in astrocytes.

IMPORTANCE

While persistent measles virus (MeV) infection induces SSPE in humans, persistent canine distemper virus (CDV) infection causes chronic progressive or relapsing demyelination in carnivores. Common to both central nervous system (CNS) infections is that persistence is based on noncytolytic cell-to-cell spread, which, in the case of CDV, was demonstrated to rely on functional membrane fusion machinery complexes. This inferred a mechanism where nucleocapsids are transmitted through macroscopically invisible microfusion events between infected and target cells. Here, we provide evidence that CDV induces such microfusions in a SLAM- and nectin-4-independent manner, thereby strongly suggesting the existence of a third receptor expressed in glial cells (referred to as GliaR). We propose that GliaR governs intercellular transfer of nucleocapsids and hence contributes to viral persistence in the brain and ensuing demyelinating lesions.

Establishment of reverse transcription loop-mediated isothermal amplification for rapid detection and differentiation of canine distemper virus infected and vaccinated animals

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A novel RT-LAMP method was developed to detect canine distemper virus (CDV).

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A set of four primers were designed to target the H gene for the specific detection of wild-type CDV variants.

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The assay was 100-fold more sensitive than conventional RT-PCR.

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The system showed a preference for wild-type CDV, and exhibited less sensitivity to CPV.

Although widespread vaccination against canine distemper virus (CDV) has been conducted for many decades, several canine distemper outbreaks in vaccinated animals have been reported frequently. In order to detect and differentiate the wild-type and vaccine strains of the CDV from the vaccinated animals, a novel reverse transcription loop-mediated isothermal amplification (RT-LAMP) method was developed. A set of four primers—two internal and two external—were designed to target the H gene for the specific detection of wild-type CDV variants. The CDV-H RT-LAMP assay rapidly amplified the target gene, within 60 min, using a water bath held at a constant temperature of 65 °C. The assay was 100-fold more sensitive than conventional RT-PCR, with a detection limit of 10⁻¹ TCID₅₀ ml⁻¹. The system showed a preference for wild-type CDV, and exhibited less sensitivity to canine parvovirus, canine adenovirus type 1 and type 2, canine coronavirus, and canine parainfluenza virus. The assay was validated using 102 clinical samples obtained from vaccinated dog farms, and the results were comparable to a multiplex nested RT-PCR assay. The specific CDV-H RT-LAMP assay provides a simple, rapid, and sensitive tool for the detection of canines infected with wild-type CDV from canines vaccinated with attenuated vaccine.

Human borna disease virus infection impacts host proteome and histone lysine acetylation in human oligodendroglia cells

Background

Borna disease virus (BDV) replicates in the nucleus and establishes persistent infections in mammalian hosts. A human BDV strain was used to address the first time, how BDV infection impacts the proteome and histone lysine acetylation (Kac) of human oligodendroglial (OL) cells, thus allowing a better understanding of infection-driven pathophysiology in vitro.

Methods

Proteome and histone lysine acetylation were profiled through stable isotope labeling for cell culture (SILAC)-based quantitative proteomics. The quantifiable proteome was annotated using bioinformatics. Histone acetylation changes were validated by biochemistry assays.

Results

Post BDV infection, 4383 quantifiable differential proteins were identified and functionally annotated to metabolism pathways, immune response, DNA replication, DNA repair, and transcriptional regulation. Sixteen of the thirty identified Kac sites in core histones presented altered acetylation levels post infection.

Conclusions

BDV infection using a human strain impacted the whole proteome and histone lysine acetylation in OL cells.

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A human strain of BDV (BDV Hu-H1) was used to infect human oligodendroglial cells (OL cells).

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This study is the first to reveal the host proteomic and histone Kac profiles in BDV-infected OL cells.

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BDV infection affected the expression of many transcription factors and several HATs and HDACs.

Proteomics reveal energy metabolism and mitogen-activated protein kinase signal transduction perturbation in human Borna disease virus Hu-H1-infected oligodendroglial cells

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A human strain of BDV (BDV Hu-H1) was used to infect human oligodendroglial cells (OL cells).

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Energy metabolism was the most significantly altered pathway in BDV Hu-H1-infected OL cells.

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The Raf/MEK/ERK signaling cascade was significantly perturbed in BDV Hu-H1-infected OL cells.

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BDV Hu-H1caused constitutive activation of the ERK1/2 pathway, but cell proliferation was down-regulated at the same time.

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BDV Hu-H1 manages to down-regulate cell proliferation, in the presence of activated but not translocated ERK–RSK complex.

Borna disease virus (BDV) is a neurotropic, non-cytolytic RNA virus which replicates in the cell nucleus targeting mainly hippocampal neurons, but also astroglial and oligodendroglial cells in the brain. BDV is associated with a large spectrum of neuropsychiatric pathologies in animals. Its relationship to human neuropsychiatric illness still remains controversial. We could recently demonstrate that human BDV strain Hu-H1 promoted apoptosis and inhibited cell proliferation in a human oligodendroglial cell line (OL cells) whereas laboratory BDV strain V acted contrariwise. Here, differential protein expression between BDV Hu-H1-infected OL cells and non-infected OL cells was assessed through a proteomics approach, using two-dimensional electrophoresis followed by matrix-assisted laser desorption ionization-time of flight tandem mass spectrometry. A total of 63 differential host proteins were identified in BDV Hu-H1-infected OL cells compared to non-infected OL cells. We found that most changes referred to alterations related to the pentose phosphate pathway, glyoxylate and dicarboxylate metabolism, the tricarboxylic acid (TCA) cycle, and glycolysis /gluconeogenesis. By manual querying, two differential proteins were found to be associated with mitogen-activated protein kinase (MAPK) signal transduction. Five key signaling proteins of this pathway (i.e., p-Raf, p-MEK, p-ERK1/2, p-RSK, and p-MSK) were selected for Western blotting validation. p-ERK1/2 and p-RSK were found to be significantly up-regulated, and p-MSK was found to be significantly down-regulated in BDV Hu-H1-infected OL cells compared to non-infected OL cell. Although BDV Hu-H1 constitutively activated the ERK–RSK pathway, host cell proliferation and nuclear translocation of activated pERK in BDV Hu-H1-infected OL cells were impaired. These findings indicate that BDV Hu-H1 infection of human oligodendroglial cells significantly perturbs host energy metabolism, activates the downstream ERK–RSK complex of the Raf/MEK/ERK signaling cascade, and disturbs host cell proliferation possibly through impaired nuclear translocation of pERK, a finding which warrants further research.

Immunopathogenic and neurological mechanisms of canine distemper virus

Canine distemper is a highly contagious viral disease caused by the canine distemper virus (CDV), which is a member of the Morbillivirus genus, Paramyxoviridae family. Animals that most commonly suffer from this disease belong to the Canidae family; however, the spectrum of natural hosts for CDV also includes several other families of the order Carnivora. The infectious disease presents worldwide distribution and maintains a high incidence and high levels of lethality, despite the availability of effective vaccines, and no specific treatment. CDV infection in dogs is characterized by the presentation of systemic and/or neurological courses, and viral persistence in some organs, including the central nervous system (CNS) and lymphoid tissues. An elucidation of the pathogenic mechanisms involved in canine distemper disease will lead to a better understanding of the injuries and clinical manifestations caused by CDV. Ultimately, further insight about this disease will enable the improvement of diagnostic methods as well as therapeutic studies.

Borna disease virus infection perturbs energy metabolites and amino acids in cultured human oligodendroglia cells

Background

Borna disease virus is a neurotropic, non-cytolytic virus that has been widely employed in neuroscientific research. Previous studies have revealed that metabolic perturbations are associated with Borna disease viral infection. However, the pathophysiological mechanism underlying its mode of action remains unclear.

Methodology

Human oligodendroglia cells infected with the human strain Borna disease virus Hu-H1 and non-infected matched control cells were cultured in vitro. At day 14 post-infection, a proton nuclear magnetic resonance-based metabonomic approach was used to differentiate the metabonomic profiles of 28 independent intracellular samples from Borna disease virus-infected cells (n = 14) and matched control cells (n = 14). Partial least squares discriminant analysis was performed to demonstrate that the whole metabonomic patterns enabled discrimination between the two groups, and further statistical testing was applied to determine which individual metabolites displayed significant differences between the two groups.

Findings

Metabonomic profiling revealed perturbations in 23 metabolites, 19 of which were deemed individually significant: nine energy metabolites (α-glucose, acetate, choline, creatine, formate, myo-inositol, nicotinamide adenine dinucleotide, pyruvate, succinate) and ten amino acids (aspartate, glutamate, glutamine, glycine, histidine, isoleucine, phenylalanine, threonine, tyrosine, valine). Partial least squares discriminant analysis demonstrated that the whole metabolic patterns enabled statistical discrimination between the two groups.

Conclusion

Borna disease viral infection perturbs the metabonomic profiles of several metabolites in human oligodendroglia cells cultured in vitro. The findings suggest that Borna disease virus manipulates the host cell’s metabolic network to support viral replication and proliferation.

Canine distemper virus persistence in demyelinating encephalitis by swift intracellular cell-to-cell spread in astrocytes is controlled by the viral attachment protein

The mechanism of viral persistence, the driving force behind the chronic progression of inflammatory demyelination in canine distemper virus (CDV) infection, is associated with non-cytolytic viral cell-to-cell spread. Here, we studied the molecular mechanisms of viral spread of a recombinant fluorescent protein-expressing virulent CDV in primary canine astrocyte cultures. Time-lapse video microscopy documented that CDV spread was very efficient using cell processes contacting remote target cells. Strikingly, CDV transmission to remote cells could occur in less than 6 h, suggesting that a complete viral cycle with production of extracellular free particles was not essential in enabling CDV to spread in glial cells. Titration experiments and electron microscopy confirmed a very low CDV particle production despite higher titers of membrane-associated viruses. Interestingly, confocal laser microscopy and lentivirus transduction indicated expression and functionality of the viral fusion machinery, consisting of the viral fusion (F) and attachment (H) glycoproteins, at the cell surface. Importantly, using a single-cycle infectious recombinant H-knockout, H-complemented virus, we demonstrated that H, and thus potentially the viral fusion complex, was necessary to enable CDV spread. Furthermore, since we could not detect CD150/SLAM expression in brain cells, the presence of a yet non-identified glial receptor for CDV was suggested. Altogether, our findings indicate that persistence in CDV infection results from intracellular cell-to-cell transmission requiring the CDV-H protein. Viral transfer, happening selectively at the tip of astrocytic processes, may help the virus to cover long distances in the astroglial network, “outrunning” the host’s immune response in demyelinating plaques, thus continuously eliciting new lesions.

Viral protein expression and phenotyping of inflammatory responses in the central nervous system of phocine distemper virus-infected harbor seals (Phoca vitulina)

The central nervous system (CNS) represents an important target organ of the phocine distemper virus (PDV). The aim of the present study was to characterize pathological changes in the CNS of harbor seals suffering from natural PDV-infection. The distribution of virus protein and mRNA was investigated by immunohistochemistry (IHC) and in situ hybridization, respectively. In addition, inflammatory and glial cells were characterized by IHC. Polioencephalitis with glial activation, neuronal death and perivascular mononuclear infiltrations in the cerebral cortex was the main histopathological finding. Inflammatory responses, dominated by CD3(+) T-cells and activated microglia/macrophages were associated with a prominent MHC-II upregulation within the CNS. Viral protein was found predominantly in neurofilament-expressing neurons within inflamed areas as demonstrated by immunohistochemical double-labeling. Morbillivirus nucleo-, phospho-, matrix-, fusion- and hemagglutinin-proteins were found in CNS-lesions. The expressions of viral matrix- and fusion-proteins were reduced in severely inflamed plaques. Comparison of viral protein and mRNA expression revealed a diminished amount of viral phosphoprotein preferentially associated with perivascular inflammation. In summary, CNS-lesions in PDV-infected seals are similar to canine distemper virus-induced acute polioencephalitis in dogs and measles virus inclusion body polioencephalitis in men, respectively.

Increase of pro-inflammatory cytokine expression in non-demyelinating early cerebral lesions in nervous canine distemper

Canine distemper virus (CDV) infection of the central nervous system results in lesions of the gray and white matter. While a biphasic disease process has been discussed for leukoencephalitis with a prominent loss of viral protein expression, polioencephalitis has been associated with virus persistence. Using semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR), expression of pro- and anti-inflammatory cytokines such as interleukin (IL)-1beta, IL-2, IL-6, IL-8, IL-10, IL-12, tumor necrosis factor-alpha (TNF)-alpha, interferon (IFN)-gamma, and transforming growth factor (TGF)-beta were studied in the cerebra of distemper dogs with white matter lesions in the cerebellum. Additionally, cytokine values were correlated with the degree of CDV infection, major histocompatibility complex class II (MHC II) expression, and infiltration of CD4-, CD8-, and CD3epsilon-positive lymphocytes. Cerebral CDV infection was not associated with detectable light microscopic lesions or infiltration of B and T lymphocytes. However, an increasing number of CDV-antigen-positive cells was associated with an upregulation of MHC II antigen. RT-PCR results revealed a significant upregulation of IL-6, IL-8, IL-12, and TNF-alpha in the cerebra of distemper dogs, whereas IL-10 and TGF-beta showed no significant increase. Elevated cytokine values were directly related to the presence of CDV antigen and MHC II upregulation. However, succeeding increases of the latter did not result in an additional proportional elevation of cytokine expression values. In summary, the present study demonstrates the expression of pro-inflammatory cytokines by resident neural cells following CDV infection. Furthermore, the lack of light microscopic changes indicates that additional factors besides cytokines are necessary for the development of a distemper-characteristic neuropathology.

Pathogenesis and immunopathology of systemic and nervous canine distemper

Canine distemper is a worldwide occurring infectious disease of dogs, caused by a morbillivirus, closely related to measles and rinderpest virus. The natural host range comprises predominantly carnivores. Canine distemper virus (CDV), an enveloped, negative-sense RNA virus, infects different cell types, including epithelial, mesenchymal, neuroendocrine and hematopoietic cells of various organs and tissues. CDV infection of dogs is characterized by a systemic and/or nervous clinical course and viral persistence in selected organs including the central nervous system (CNS) and lymphoid tissue. Main manifestations include respiratory and gastrointestinal signs, immunosuppression and demyelinating leukoencephalomyelitis (DL). Impaired immune function, associated with depletion of lymphoid organs, consists of a viremia-associated loss of lymphocytes, especially of CD4+ T cells, due to lymphoid cell apoptosis in the early phase. After clearance of the virus from the peripheral blood an assumed diminished antigen presentation and altered lymphocyte maturation cause an ongoing immunosuppression despite repopulation of lymphoid organs. The early phase of DL is a sequel of a direct virus-mediated damage and infiltrating CD8+ cytotoxic T cells associated with an up-regulation of pro-inflammatory cytokines such as interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-alpha and IL-12 and a lacking response of immunomodulatory cytokines such as IL-10 and transforming growth factor (TGF)-beta. A CD4+-mediated delayed type hypersensitivity and cytotoxic CD8+ T cells contribute to myelin loss in the chronic phase. Additionally, up-regulation of interferon-gamma and IL-1 may occur in advanced lesions. Moreover, an altered balance between matrix metalloproteinases and their inhibitors seems to play a pivotal role for the pathogenesis of DL. Summarized, DL represents a biphasic disease process consisting of an initial direct virus-mediated process and immune-mediated plaque progression. Immunosuppression is due to early virus-mediated lymphocytolysis followed by still poorly understood mechanisms affecting antigen presentation and lymphocyte maturation.

Synergistic inhibition in cell–cell fusion mediated by the matrix and nucleocapsid protein of canine distemper virus

Canine distemper virus (CDV) causes a chronic, demyelinating, progressive or relapsing neurological disease in dogs, because CDV persists in the CNS. Persistence of virulent CDV, such as the A75/17 strain has been reproduced in cell cultures where it is associated with a non-cytolytic infection with very limited cell-cell fusion. This is in sharp contrast to attenuated CDV infection in cell cultures, such as the Onderstepoort (OP) CDV strain, which produces extensive fusion activity and cytolysis. Fusion efficiency may be determined by the structure of the viral fusion protein per se but also by its interaction with other structural proteins of CDV. This was studied by combining genes derived from persistent and non-persistent CDV strains in transient transfection experiments. It was found that fusion efficiency was markedly attenuated by the structure of the fusion protein of the neurovirulent A75/17-CDV. Moreover, we showed that the interaction of the surface glycoproteins with the M protein of the persistent strain greatly influenced fusion activity. Site directed mutagenesis showed that the c-terminus of the M protein is of particular importance in this respect. Interestingly, although the nucleocapsid protein alone did not affect F/H-induced cell-cell fusion, maximal inhibition occurred when the latter was added to combined glycoproteins with matrix protein. Thus, the present study suggests that very limited fusogenicity in virulent CDV infection, which favours persistence by limiting cell destruction involves complex interactions between all viral structural proteins.

Involvement of morbilliviruses in the pathogenesis of demyelinating disease

Two members of the morbillivirus genus of the family Paramyxoviridae, canine distemper virus (CDV) and measles virus (MV), are well-known for their ability to cause a chronic demyelinating disease of the CNS in their natural hosts, dogs and humans, respectively. Both viruses have been studied for their potential involvement in the neuropathogenesis of the human demyelinating disease multiple sclerosis (MS). Recently, three new members of the morbillivirus genus, phocine distemper virus (PDV), porpoise morbillivirus (PMV) and dolphin morbillivirus (DMV), have been discovered. These viruses have also been shown to induce multifocal demyelinating disease in infected animals. This review focuses on morbillivirus-induced neuropathologies with emphasis on aetiopathogenesis of CNS demyelination. The possible involvement of a morbillivirus in the pathogenesis of multiple sclerosis is discussed.

Clinicopathological findings in dogs with distemper encephalomyelitis presented without characteristic signs of the disease

The clinical diagnosis of distemper is difficult in dogs presented with nervous deficits in the absence of extraneural signs and myoclonus. The aim of this study is to verify how the clinicopathological findings may suggest distemper encephalomyelitis in such cases. We prospectively investigated 20 necropsied dogs presented with neurological signs without those characteristic signs of distemper at the time of hospital admission. Eight out of 20 dogs were diagnosed with distemper encephalomyelitis at post mortem by reverse transcription-polymerase chain reaction (RT-PCR) and histological examination. Cerebellar and/or vestibular signs progressing to tetraparesis/plegia were frequent neurological signs. Abnormalities in hematologic findings were non-specific, nevertheless the cerebrospinal fluid evaluation could suggest canine distemper virus (CDV) infection by a lymphocytic pleocytosis. At post mortem chronic CDV encephalomyelitis was predominant. Our clinical results, as well as the predominance of chronic encephalomyelitis, differ from other studies about CDV encephalomyelitis with naturally infected dogs presenting extraneural signs and myoclonus.

Antemortem Diagnosis of CDV Infection by RT-PCR in Distemper Dogs with Neurological Deficits without the Typical Clinical Presentation

In dogs with neurological disturbances without myoclonus and extraneural signs, the clinical diagnosis of distemper is difficult perform. Considering the great infectious potential of the disease, the possibility of carrying out an antemortem diagnosis of distemper is important, particularly in hospitalized patients with neurological disease. The present study was carried out to evaluate RT-PCR for antemortem CDV detection in hospitalized dogs with neurological disturbances without the typical findings of distemper. We investigated five dogs with canine distemper virus (CDV) encephalomyelitis, in which the clinical diagnosis was not performed owing to the absence of characteristic signs of the disease, such as myoclonus and systemic signs. We observed an apparent high sensitivity of RT-PCR in urine samples for detection of CDV: four out of five urine samples were RT-PCR positive. The results of the present study suggest that urine is a good biological sample for antemortem CDV detection by RT-PCR in dogs with distemper encephalomyelitis in which the clinical diagnosis is likely to be difficult owing to the absence of suggestive distemper signs. The use of two different body fluids (urine and CSF) may increase the RT-PCR sensitivity for antemortem diagnosis of distemper in such cases.

Canine distemper virus associated proliferation of canine footpad keratinocytes in vitro

Infection of canine footpads with canine distemper virus (CDV) can result in so-called hard pad disease characterized by footpad epidermal proliferation and hyperkeratosis. Cultured canine footpad keratinocytes (CFK) were inoculated with a virulent canine distemper virus strain (A75/17-CDV) to study the effects of CDV-infection on keratinocyte proliferation. Infection was analyzed by immunohistochemistry and in situ hybridization for CDV nucleoprotein (N-protein) antigen and mRNA. CDV caused a persistent, non-cytocidal infection with spread from single cells to infection of the confluent cell layer 7 days post infection (p.i.). Absolute cell numbers were significantly higher in infected cultures compared to control cultures from day 4 until day 6 p.i. Infected cultures contained significantly more total DNA on day 5 p.i. compared to controls. Immunohistochemical investigation of proliferation markers Ki67 and BrdU demonstrated a nearly two-fold increase in numbers of positive cells on day 5 p.i. compared to controls. These findings demonstrate that canine distemper virus infection of canine footpad keratinocytes in vitro was associated with proliferation.

Canine distemper virus-induced depletion of uninfected lymphocytes is associated with apoptosis

Canine distemper virus (CDV), a negative stranded RNA morbillivirus, causes a multisystemic disease in dogs, which is associated with a severe immune suppression. The aim of the study was to examine the influence of early CDV infection on leukocyte depletion, lymphopenia and virus-induced cell death in dogs infected with a virulent CDV strain. From 10 infected dogs, peripheral blood leukocytes were harvested periodically, phenotyped and analyzed for CDV antigen content and apoptosis using Annexin V-FITC and propidium iodide labeling. CDV infection induced a severe CD3⁺ T cell and CD21⁺ B cell depletion in all animals at 3 days post-infection (d.p.i.). For dogs with severe distemper, developing virus persistence in the lymphoid tissue and central nervous system, this lymphopenia lasted until the end of the experiment. Increased levels of lymphocyte apoptosis were found at 3 d.p.i., and monocyte apoptosis at 6 d.p.i. This was more prominent in the group of animals with severe distemper. At 3 d.p.i. no leukocyte infection was detectable indicating that the early lymphocyte depletion and apoptosis was not a direct consequence of virus infection. Taken together, our results demonstrate that CDV-induced lymphopenia is an early event and that the degree of lymphocyte depletion correlates with the severity of disease and virus persistence in the lymphoid tissue and central nervous system.

Demyelination in canine distemper virus infection: a review

Canine distemper virus (CDV) causes severe immunosuppression and neurological disease in dogs, associated with demyelination, and is a model for multiple sclerosis in man. In the early stage of the infection, demyelination is associated with viral replication in the white matter. In acute demyelinating lesions there is massive down-regulation of myelin transcription and metabolic impairment of the myelin-producing cells, but there is no evidence that these cells are undergoing apoptosis or necrosis. Oligodendroglial change is related to restricted infection of these cells (transcription but no translation) and marked activation of microglial cells in acute lesions. Concomitant with immunological recovery during the further course of the disease, inflammation occurs in the demyelinating plaques with progression of the lesions in some animals. A series of experiments in vitro suggests that chronic inflammatory demyelination is due to a bystander mechanism resulting from interactions between macrophages and antiviral antibodies. Autoimmune reactions are also observed, but do not correlate with the course of the disease. The progressive or relapsing course of the disease is associated with viral persistence in the nervous system. Persistence of CDV in the brain appears to be favored by non-cytolytic selective spread of the virus and restricted infection, in this way escaping immune surveillance in the CNS. The CDV Fusion protein appears to play an important role in CDV persistence. Similarities between canine distemper and rodent models of virus-induced demyelination are discussed.

Non-cytocidal infection of keratinocytes by canine distemper virus in the so-called hard pad disease of canine distemper

A late, but not uncommon sequel to canine distemper virus (CDV) infection of dogs is thickening of footpads and nasal planum, the so-called hard pad disease, originally described as vacuolar degeneration of epidermal keratinocytes with inclusion body formation and massive hyperkeratosis. However, in a recent study of footpads of naturally CDV-infected dogs only hyperkeratosis was observed without any of the other changes. Instead, acanthosis was frequently noticed. CDV nucleoprotein was present in the suprabasal keratinocytes and eccrine epithelial glands only. No CDV nucleoprotein was present in basal keratinocytes. This observation in combination with lack of obvious cytocidal changes strongly suggested the possibility of a restricted viral infection with presence of viral mRNA but without protein expression. Therefore, the presence of CDV nucleoprotein mRNA was investigated using in situ hybridization and compared to the localization of the nucleoprotein in footpads of clinically healthy and distemper dogs. Viral nucleoprotein and nucleoprotein mRNA in nearly all cases co-localized to the same compartments and basal keratinocytes did not contain nucleoprotein mRNA. These findings dispute the idea of a restricted viral infection of footpad keratinocytes in dogs with natural CDV infection. Instead, a migration of the virus to the epidermal surface along with the proliferating and differentiating epithelium is the most likely explanation for the lack of virus antigen in basal keratinocytes.

Canine distemper, a re-emerging morbillivirus with complex neuropathogenic mechanisms

Paramyxoviruses are responsible for a wide variety of diseases both in humans and in animals. Common to many paramyxoviruses is the fact that they can cause neurological symptoms in their final host. Newly discovered paramyxoviruses, such as the Hendra and Nipah viruses, show the same pattern of pathogenesis as that of the paramyxoviruses already known. Canine distemper virus (CDV) is a well-studied member of the genus Morbillivirus. Study of the neuropathogenesis of CDV might give insight into disease mechanisms and suggest approaches for the prevention of other recently discovered paramyxovirus infections.

A new paraclinical CSF marker for hypoxia-like tissue damage in multiple sclerosis lesions

Recent studies on the immunopathology of multiple sclerosis revealed a heterogeneity in the patterns of demyelination, suggesting interindividual differences in the mechanism responsible for myelin destruction. One of these patterns of demyelination, characterized by oligodendrocyte dystrophy and apoptosis, closely mimics myelin destruction in acute white matter ischaemia. In the course of a systematic screening for virus antigen expression in multiple sclerosis brains, we identified a monoclonal antibody against canine distemper virus, which detects a cross-reactive endogenous brain epitope, highly expressed in this specific subtype of actively demyelinating multiple sclerosis lesions with little or no immunoreactivity in other active multiple sclerosis cases. The respective epitope, which is a phosphorylation-dependent sequence of one or more proteins of 50, 70 and 115 kDa, is also expressed in a subset of active lesions of different virus-induced inflammatory brain diseases, but is present most prominently and consistently in acute lesions of white matter ischaemia. Its presence is significantly associated with nuclear expression of hypoxia-inducible factor-1 alpha within the lesions of both inflammatory and ischaemic brain diseases. The respective epitope is liberated into the CSF and, thus, may become a useful diagnostic tool to identify clinically a defined multiple sclerosis subtype.

Varied persistent life cycles of Borna disease virus in a human oligodendroglioma cell line

Borna disease virus (BDV) establishes a persistent infection in the central nervous system of vertebrate animal species as well as in tissue cultures. In an attempt to characterize the life cycle of BDV in persistently infected cultured cells, we developed 30 clones by single-cell cloning from a human oligodendroglioma (OL) cell line after infection with BDV. According to the percentage of cells expressing the BDV major proteins, p40 (nucleoprotein) and p24 (phosphoprotein), the clones were classified into two types: type I (>20%) and type II (<20%). mRNAs corresponding to both proteins were detected by in situ hybridization (ISH) in a percentage of cells consistent with that for the protein expression in the two types. Surprisingly, ISH for the detection of the genomic RNA, mainly in type II, revealed a significantly larger cell population harboring the genomic RNA than that with the protein as well as the mRNA expression. By recloning from type II primary cell clones, the same phenotype was confirmed in the secondary cell clones obtained: i.e., low percentage of protein-positive cells and higher percentage of cells harboring the genomic RNA. After nerve growth factor treatment, the two types of clones showed increases in the percentage of cells expressing BDV-specific proteins that reached 80% in type II clones, in addition to increased expression levels per cell. Such enhancement might have been mediated by the activation of the mitogen-activated protein kinase in the clones as revealed by the detection of activated ERK1/2. Thus, our findings show that BDV may have established a persistent infection at low levels of viral expression in OL cells with the possibility of a latent infection.

Relation of clinical signs to pathological changes in 19 cases of canine distemper encephalomyelitis

In an attempt to associate the clinical neurological syndromes with the neuropathological features of canine distemper (CD), 19 spontaneous cases with neurological involvement were examined, before and after euthanasia. Seventeen dogs were less than one year of age and all except two (89.4%) were unvaccinated against CD. Various extraneural signs associated with CD encephalomyelitis (CDE) were seen in 15 dogs. Generalized or localized myoclonus was the most common sign observed (13/19). Seventeen of the dogs presented with signs suggestive of one neuroanatomical location of lesions. Of these animals, seven had signs of cerebral, two of cerebellar, four of cervical, one of cervicothoracic, two of thoracolumbar and two of lumbosacral syndrome. The diagnosis of CD was confirmed immunohistochemically (detection of CD viral antigen), serologically (neutralizing serum antibody titre > or = 16) and histopathologically (CDV inclusion bodies, type of central nervous system lesions). An association of the neuroanatomical lesion location and the histopathological findings was noted in 14 out of 17 dogs (82.3%). Myoclonus could be attributed to lower motor neuron damage in eight out of 13 dogs (61.5%).

A novel nonsuppurative meningoencephalitis in young greyhounds in Ireland

Fourteen 4- to 18-month-old vaccinated Greyhounds (10 males, 4 females) from three kennels in southern Ireland presented over a 2-year period with acute or insidious onset neurological signs. Head tilting, ataxia, recumbency, circling, and blindness were commonly observed, and animals were dull, dehydrated, and had lost weight. Hematologic and biochemical parameters reflected dehydration but were otherwise unremarkable. Microscopic examination revealed severe diffuse and focal gliosis and gemistocytosis accompanied by mononuclear cell perivascular cuffing in caudate nucleus and cortical gray matter of the cerebrum and in the periventricular gray matter of the anterior brainstem. Milder lesions were noted in the caudal brainstem, cranial spinal cord, and in the molecular layer of the cerebellum. This was accompanied by a lymphocyte and plasma cell infiltration of the cerebral and cerebellar meninges. Demyelination, neuropil necrosis, neuronophagia, and vasculitis were not observed. No inclusion bodies, fungi, or protozoal cysts were seen. Additional serologic and molecular pathology tests also failed to determine a cause, suggesting that these cases may represent a previously undiagnosed condition in the dog.

Partial protection and intrathecal invasion of CD8(+) T cells in acute canine distemper virus infection

Initial non-inflammatory demyelination in canine distemper virus infection (CDV) develops against a background of severe immunosuppression and is therefore, thought to be virus-induced. However, recently we found a marked invasion of T cells throughout the central nervous system (CNS) in dogs with acute distemper despite drastic damage to the immune system. In the present study, this apparent paradox was further investigated by immunophenotyping of lymphocytes, following experimental CDV challenge in vaccinated and non-vaccinated dogs. In contrast to CDV infected, unprotected dogs, vaccinated dogs did not become immunosuppressed and exhibited a strong antiviral immune response following challenge with virulent CDV. In unprotected dogs rapid and drastic lymphopenia was initially due to depletion of T cells. In peripheral blood, CD4(+) T cells were more sensitive and depleted earlier and for a longer time than CD8(+) cells which recovered soon. In the cerebrospinal fluid (CSF) we could observe an increase in the T cell to B cell and CD8(+) to CD4(+) ratios. Thus, partial protection of the CD8(+) cell population could explain why part of the immune function in acute distemper is preserved. As found earlier, T cells invaded the CNS parenchyma in these dogs but also in the protected challenged dogs, which did not develop any CNS disease at all. Since markers of T cell activation were upregulated in both groups of animals, this phenomenon could in part be related to non-specific penetration of activated T cells through the blood brain barrier. However, in diseased animals much larger numbers of T cells were found in the CNS than in the protected dogs, suggesting that massive invasion of T cells in the brain requires CDV expression in the CNS.

KAI1 gene is differently expressed in papillary and pancreatic cancer: influence on metastasis

AIM:To compare KAI1 in cancer of papilla of Vater and pancreas to evaluate whether there are differences in biologic behavior which might account for prognosis.METHODS:We compared the expression in 24 papillay and 29 pancreatic cancers using Northern blot analysis, immunochemical assay and in situ hybridization, and investigated whether early diagnosis or molecular differences predict the outcome in these tumor entities.RESULTS:By Northern blot analysis there is no statistical difference of KAI1 levels in normal and cancerous papilla. No association between KAI1 mRNA expression and tumor stage or tumor differentiation was found in the tumors. By immunohistochemical assay, KAI1 staining in cytoplasm of papillary cancer cells was similar to that of normal papillary cells. By in situ hybridization, the results of KAI1 mRNA expression in normal and cancerous papilla were similar to those with immunohistochemical assay. The normal and cancerous pancreas tissues were also analyzed by the methods used in papillary samples.CONCLUSION:Although the biologic roles of KAI1 have not been clarified, our results suggest that KAI1 may restrict the progression of malignant papillary cancer, but its expression might not have any effect on the characteristics of papillary tumor, whereas by the analysis of KAI1 gene, its reduced expression is closely related to the progression and metastases of pancreatic cancer.

Interleukin-1beta, -6, -12 and tumor necrosis factor-alpha expression in brains of dogs with canine distemper virus infection

Canine distemper virus infection in dogs is commonly associated with demyelinating central nervous system lesions. Investigations on viral protein expression by studying mRNA and protein distribution together with the characterization of CD4 and CD8 inflammatory cells and MHC class II up-regulation revealed a biphasic disease process. To further investigate the cellular interactions in the different plaque types the cerebella of 14 dogs with confirmed distemper infection were investigated for expression of interleukin (IL)-1beta, -6, -12 and tumor necrosis factor-alpha (TNF) by immunohistochemistry using rabbit polyclonal anti-cytokine antibodies. T-cells and astrocytes were identified with rabbit anti CD3- and GFAP-monoclonal and polyclonal antibodies, respectively; and microglia/macrophages were characterized by their ability to bind lectin from Bandeiraea simplicifolia (BS-1). To further name the cytokine expressing cells immunoenzymatic double staining using DAB and New Fuchsin was performed. White matter lesions were classified according to histopathological criteria into acute, subacute and chronic. Canine distemper virus nucleoprotein antigen was demonstrated in nearly all plaques, except in older plaques where virus was not present within the plaque but adjacent to the lesion. IL-1 expression was observed to varying degrees in all types of lesions. Most often IL-1 was present in CD3 and BS-1 positive cells in the brain parenchyma in earlier plaques and comprising perivascular cuffs found in chronic plaques. IL-6 expression was present in all lesions, and followed a similar distribution pattern as IL-1. IL-12 displayed very often a granular extracellular pattern of immunoreactivity, especially in the brain parenchyma, and was found only in individual perivascular cells. TNF staining, predominantly found in astrocytes, was present in lesions of various types; however, staining appeared to be stronger in acute lesions and decreased in chronic plaques. In the latter, TNF seemed to be more prominent in areas adjacent to the plaques. Summarizing, in early non-demyelinating lesions without overt inflammation TNF seemed to be important, whereas in distemper lesions with inflammatory infiltrates IL-1 and to a lesser degree IL-6 were more prominent. These results imply that TNF may be involved in the pathogenesis of early demyelination in nervous distemper.

Mammalian microsporidiosis

The phylum Microspora contains a diverse group of single-celled, obligate intracellular protozoa sharing a unique organelle, the polar filament, and parasitizing a wide variety of invertebrate and vertebrate animals, including insects, fish, birds, and mammals. Encephalitozoon cuniculi is the classic microsporidial parasite of mammals, and encephalitozoonosis in rabbits and rodents has been and continues to be recognized as a confounding variable in animal-based biomedical research. Although contemporary research colonies are screened for infection with this parasite, E. cuniculi remains a cause of morbidity and mortality in pet and conventionally raised rabbits. In addition, E. cuniculi is a potential pathogen of immature domestic dogs and farm-raised foxes. The recent discovery and identification of Encephalitozoon intestinalis, Encephalitozoon hellem, and Enterocytozoon bieneusi, in addition to E. cuniculi, as opportunistic pathogens of humans have renewed interest in the Microspora. Veterinary pathologists, trained in the comparative anatomy of multiple animal species and infectious disease processes, are in a unique position to contribute to the diagnosis and knowledge of the pathogenesis of these parasitic diseases. This review article covers the life cycle, ultrastructure, and biology of mammalian microsporaidia and the clinical disease and lesions seen in laboratory and domestic animals, particularly as they relate to Encephalitozoon species. Human microsporidial disease and animal models of human infection are also addressed. Often thought of as rabbit pathogens of historical importance, E. cuniculi and the related mammalian microsporidia are emerging as significant opportunistic pathogens of immunocompromised individuals.

Reduced expression of the metastasis suppressor gene KAI1 in advanced colon cancer and its metastases

BACKGROUND

The expression of the KAI1 gene and its gene product were studied in metastatic and non-metastatic human colorectal cancer to evaluate its role in the metastatic process.

METHODS

KAI1 mRNA and protein expression was examined in 36 primary colorectal carcinomas and 6 liver metastasis using Northern blot and Western blot analyses. Forty-six normal colonic tissue samples served as controls. The exact site of KAI1 expression was analyzed by in situ hybridization and by immunohistochemistry in primary tumors, in the corresponding normal tissues, in lymph node metastases and liver metastases.

RESULTS

Densitometric analysis of Northern blots revealed overexpression of KAI1 mRNA in 87% of colonic cancer tissues in comparison with the corresponding normal colonic tissues. This increase was 9.1-fold in median (P < .001). KAI1 mRNA expression was strongly dependent on tumor stage. Colorectal cancer at stages II and III revealed significantly higher KAI1 mRNA levels than stage IV tumors (P < .03 and P < .015, respectively) or normal controls. In addition, liver metastases showed reduced KAI1 mRNA expression when compared with their corresponding primary tumor. In situ hybridization confirmed the stage-dependent expression results obtained by Northern blots, in which the KAI1 mRNA signal was exhibited almost exclusively in the epithelial cells. Lymph node and liver metastases were largely devoid of KAI1 mRNA. Western blot analysis showed a highly significant increase of KAI1 protein level in stage II cancers in comparison with the normal colon (P < .001) but also in comparison with the more advanced tumor stages III and IV (P < .03) and P < .02, respectively), when metastases were already present. In accordance, KAI1 immunostaining decreased successively with the advance of the tumor stage and was absent in lymph node and liver metastases.

CONCLUSIONS

These data demonstrate that the KAI1 mRNA expression and the KAI1 protein level increase in an earlier tumor stage of colorectal cancer, decrease in advanced stages, and are lost in metastases. The loss of KAI1 might favor the ability of colorectal cancer cells to metastasize.

Restricted virus protein translation in canine distemper virus inclusion body polioencephalitis

In this study, inclusion body polioencephalitis, an uncommon form of canine distemper virus (CDV)-induced encephalitis, was investigated for viral protein and mRNA expression by immunohistochemistry (IH) and in situ hybridization and, in addition, infiltrating cells were characterized by IH. Lesions were predominantly found in the grey matter of the brain stem and the immune response, dominated by T cells, was associated with a strong MHC II upregulation. Abundant expression of all viral protein mRNAs and reduced or lacking protein translation, especially of the matrix protein were the most important findings, indicating that restricted virus infection in the grey matter might represent a mechanism for viral persistence in distemper polioencephalitis.

Alteration of the leptin network in late morbid obesity induced in mice by brain infection with canine distemper virus

Viruses can induce progressive neurologic disorders associated with diverse pathological manifestations, and therefore, viral infection of the brain can impair differentiated neural functions, depending on the initial viral tropism. We have previously reported that canine distemper virus (CDV) targets certain mouse brain structures, including the hypothalamus, early and selectively. Infected mice exhibit acute encephalitis, with late disease, characterized by motor impairment or obesity syndrome, appearing in some of the surviving mice several months after the initial viral replication. In the present study, we show viral persistence in the hypothalami of obese mice, as demonstrated by low, but still significant, levels of CDV nucleoprotein transcripts, associated with a dramatic decrease in F gene mRNAs. Given the pivotal role of the hypothalamus in obesity (eating behavior, energy consumption, and neuroendocrine function) and that of leptin, the adipose tissue-derived satiety factor acting through hypothalamic receptors, we analyzed the leptin networks in both obese and nonobese mice. The discrepancy found between the chronic and dramatic increase in blood leptin levels and the occurrence of obesity may be due to leptin resistance in the brain. In fact, expression of the long leptin receptor isoform, representing the functional leptin receptor, was specifically downregulated in the hypothalami of obese mice, explaining their inability to generate an adequate response to leptin in the brain. Intriguingly, during the acute phase of infection, its expression was increased in CDV-targeted structures in all infected mice and remained high in obese mice in all CDV-targeted structures, except for the hypothalamus. The biphasic change in hypothalamic leptin receptor expression seen during the progression of CDV-induced obesity provides a new paradigm for understanding mechanisms of neuroendocrinological, virus-induced abnormalities.

Identification of CD4+ and CD8+ T cell subsets and B cells in the brain of dogs with spontaneous acute, subacute-, and chronic-demyelinating distemper encephalitis

CD4 and CD8 antigen expression of T cells as well as B cell and canine distemper virus (CDV) antigen distribution were immunohistologically examined in the cerebellum of dogs with spontaneous distemper encephalitis. Cellular and viral antigen expression were evaluated at intralesional and extralesional sites and in the perivascular space. Histologically, acute and subacute non-inflammatory encephalitis and subacute inflammatory and chronic plaques were distinguished. Demyelination was a feature of all subacute and chronic lesions, although the majority of plaques exhibited no or only a low level of active demyelination as demonstrated by single macrophages with luxol fast blue positive material in their cytoplasm. CDV antigen expression, observed in all distemper brains, was reduced in chronic plaques. CD4+, CD8+, and B cells were absent in controls and in some brains with acute encephalitis. A mild infiltration of CD8+ cells was noticed in the neuropil of the remaining brains with acute and all brains with subacute non-inflammatory encephalitis. Single CD4+ cells were found in two brains with acute and in all brains with subacute non-inflammatory encephalitis. Numerous CD8+ and CD4+ cells and few B cells, with a preponderance of CD8+ cells, were detected in subacute inflammatory and chronic lesions. In contrast, in perivascular infiltrates (PVI) of subacute and chronic lesions a dominance of CD4+ cells was detected. The dominating CD8+ cells in acute and subacute non-inflammatory encephalitis might be involved in viral clearance or contribute as antibody-independent cytotoxic T cells to early lesion development. In subacute inflammatory and chronic lesions CD8+ cells may function as cytotoxic effector cells and CD4+ cells by initiating a delayed-type hypersensitivity reaction. The simultaneous occurrence of perivascular B and CD4+ cells indicated that an antibody-mediated cytotoxicity could synergistically enhance demyelination. Summarized, temporal and spatial distribution of CD4+, CD8+ and B cells and virus antigen in early and late lesions support the hypothesis of a heterogeneous in part immune-mediated plaque pathogenesis in distemper demyelination.

KAI1, a new metastasis suppressor gene, is reduced in metastatic hepatocellular carcinoma

Down-regulation of KAI1 expression has been shown to be associated with formation of metastases or disease progression in prostate and pancreatic cancer. In the present study we analyzed the expression pattern of KAI1 in metastatic and nonmetastatic hepatocellular carcinomas (HCCs) in comparison with normal livers to evaluate whether alteration of KAI1 also facilitates the metastatic ability in this malignancy. Thirty-nine primary HCCs and 10 normal liver tissue samples were studied for KAI1 messenger RNA (mRNA) expression with use of Northern blot analysis and in situ hybridization. By Northern blot analysis, moderate to strong KAI1 mRNA expression was present in normal liver samples. In contrast, KAI1 mRNA expression in tissue samples of primary HCCs was markedly decreased compared with normal controls. The normal/tumor ratio of KAI1 mRNA expression was 2.6:1 (P <.01). Primary HCCs that gave rise to metastasis showed significantly lower KAI1 mRNA levels than nonmetastasized HCCs (P <. 05). As seen by in situ hybridization, moderate to strong cytoplasmic KAI1 mRNA staining was present in almost all normal hepatocytes. Bile ducts, blood vessels, and connective tissue showed no or only faint KAI1 mRNA expression in the normal liver samples. In nonmetastatic HCCs, the cancer cells exhibited in situ hybridization signals that were similar to the normal controls. In contrast, most of the primary HCC cells in samples with metastases showed only faint or moderate KAI1 mRNA expression predominantly in the perinuclear regions. When KAI1 mRNA expression of primary hepatocellular cancer cells was compared with metastasized cancer cells in lymph nodes, with intrahepatic satellite metastasis, or with peritoneal metastasis in the same patients, significantly lower (P <.01) KAI1 mRNA levels were present in the metastasized HCC cells. Reduced KAI1 mRNA in HCC cells seems to influence their metastatic ability and thereby enhances the malignant potential of HCC.

Experimental old dog encephalitis (ODE) in a gnotobiotic dog

Experimental infection of a gnotobiotic Beagle dog with the neurovirulent R252 strain of canine distemper virus (R252-CDV) resulted in long-term central nervous system (CNS) infection; cerebral and brain stem lesions were consistent with old dog encephalitis (ODE). Eight clinical cycles of relapsing cortical and subcortical signs were documented over 33 months and were corroborated by the presence of both chronic and active inflammatory demyelinating lesions within the neuraxis. Immunocytochemistry revealed that CDV antigen was restricted to neurons. Attempts to use fresh brain tissue to directly transmit the infection to CDV-susceptible gnotobiotic dogs were unsuccessful. Reisolation of infectious virus from the infected dog required prolonged culture and coculture of brain explant cells with CDV-susceptible Vero cell monolayers. These findings demonstrate that ODE is a variant of virulent CDV-induced canine neurologic disease that can evolve de novo within the CNS of subclinically infected dogs in the absence of external sources of reinfection. The highly cell-associated nature of the virus, when first recovered from this dog, suggests that the virus was present within the CNS in a replication-defective form.

Cytokine mRNA expression in whole blood samples from dogs with natural canine distemper virus infection

Cytokines are soluble polypeptides with many physiological functions and a special role during infection and inflammation. Little is known about cytokine regulation in naturally occurring viral diseases of animals. Especially the role of cytokines in the development and progression of lesions in canine distemper virus (CDV) infection in dogs is largely unknown. Whole blood samples from 14 dogs with CDV infection and three dogs suffering from non-distemper diseases were examined for mRNA of pro-inflammatory cytokines such as interleukin-1beta (IL-1), interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-12 (IL-12), tumor necrosis factor-alpha (TNF), interferon-gamma (IFN), and the anti-inflammatory transforming growth factor-beta1 (TGF) using reverse transcription polymerase chain reaction (RT-PCR). Blood samples from the three dogs that showed no clinical abnormalities during a pre-vaccination physical examination served as control. CDV infection was confirmed by post-mortem immunohistochemistry for CDV nucleoprotein. The degree of immunoreactivity and the number of virus antigen positive organs were expressed as antigen index. IFN transcripts were not identified in any dog and IL-8 transcripts were present in RNA isolates from all 20 dogs. None of the other cytokines was detected in control animals. IL-1 and IL-6 were each found in one non-distemper dog and TGF transcripts were amplified in two dogs with non-distemper disease. The following transcripts were found in variable numbers in distemper dogs: IL-1 (7/14 dogs), IL-6 (3/14 dogs), IL-12 (3/14 dogs), TNF (8/14 dogs), and TGF (10/14 dogs) with multiple cytokines in ten dogs. No cytokine transcripts were detected in three distemper dogs. There was no obvious correlation between cytokine mRNA expression and respiratory and gastrointestinal tract diseases. In the CNS, demyelination was frequently associated with IL-1, IL-12, TNF and TGF mRNA expression in the blood. IL-6 transcripts were found only in animals with early CNS lesions and TGF was the only detectable cytokine in an animal with chronic demyelination. Lack of detectable cytokine transcripts in whole blood samples was associated with a high antigen index and viremia, indicating that an overwhelming virus infection may suppress cytokine production, possibly due to paralysis of the immune system. Simultaneous occurrence of pro- and anti-inflammatory cytokines in whole blood preparation from most of the dogs with distemper, indicated a complex most likely disease stage dependent orchestrated cytokine expression.

Reduced KAI1 expression in pancreatic cancer is associated with lymph node and distant metastases

KAI1 belongs to a structurally distinct family of membrane glycoproteins, which function via cell-cell and cell-extracellular matrix interactions, thereby potentially influencing the ability of cancer cells to invade tissues and to metastasize into lymph nodes and distant organs. In the present study, we examined KAI1 expression in lymph node and liver metastases in comparison with primary pancreatic cancer to evaluate its influence on metastasis. KAI1 mRNA analysis was performed by Northern blot analysis and in situ hybridization. In addition, the respective protein was studied by immunostaining. Fourteen primary pancreatic cancer samples in which no lymph node metastases were present and 25 primary pancreatic cancer samples in which lymph node metastases were present at the time of tumor resection were included. In 20 of these cases, primary pancreatic cancer tissues and corresponding lymph node metastases from the same patient were studied. Furthermore, 11 liver metastases were available for KAI1 analysis. Increased steady-state levels of KAI1 mRNA were found in 33/39 (85%) primary pancreatic cancers in comparison with normal controls. Statistical analysis of KAI1 mRNA levels and clinical parameters of the patients revealed that KAI1 mRNA levels were significantly higher in non-metastasized tumors compared with tumors in which lymph node or distant metastases were present. In lymph node metastases KAI1 mRNA expression was lower than in the corresponding primary tumors: In 14 of 20 lymph node metastases no KAI1 mRNA expression and in 6 of 20 lymph node metastases only weak KAI1 mRNA levels were present in some cancer cells. Cancer cells of distant metastases were devoid of or exhibited low KAI1 mRNA levels compared with those of primary pancreatic cancers. A similar pattern was observed by immunostaining. These data support the hypothesis that KAI1 gene expression might influence the metastatic ability of pancreatic cancer cells in vivo. Reduction of KAI1 appears to promote cancer cell spread in lymph nodes and distant organs.

In vivo and in vitro detection of canine distemper virus nucleoprotein gene with digoxigenin-labelled RNA, double-stranded DNA probes and oligonucleotides by in situ hybridization

A single-stranded RNA, two double-stranded (ds) DNA probes and 10 oligonucleotides labelled with digoxigenin were comparatively evaluated for their usefulness to detect canine distemper virus (CDV) nucleoprotein RNA in in vitro infected Vero cells and in tissues of dogs with spontaneous CDV infection by in situ hybridization (ISH). In addition, results were compared to CDV nucleoprotein antigen distribution as demonstrated by immunohistochemistry. The RNA probe was derived from the virulent A75/17 strain, the DNA and oligonucleotide probes from the avirulent Onderstepoort strain of CDV. The two DNA probes were 287 and 126 base pairs long. For ISH, various factors including fixatives, proteolytic digestion, probe concentration, hybridization conditions and detection systems were compared. All probes were suitable for demonstration of CDV RNA in in vitro infected cells, regardless of the CDV strain employed. In vivo CDV nucleic acid was detected by RNA and the dsDNA probes. However, the probes varied substantially with respect to sensitivity and specificity. The CDV RNA probe was far superior in sensitivity when compared to the DNA probes. Furthermore, the shorter DNA probe displayed a higher sensitivity, indicating that length of the probe is an important parameter when selecting probes. Oligonucleotides displayed only rarely a positive signal and caused frequently hybridization signals in the nucleus, which where considered not specific for CDV. Summarized, the present study reveals that RNA probes are currently the most sensitive tool for detection of CDV RNA in tissues.

Determinants of persistence in canine distemper viruses

Viral persistence in the central nervous system is the driving force behind the chronic progressive disease caused by natural canine distemper virus (CDV) infection in dogs. Persistence of CDV is associated with non-cytolytic spread and impaired viral budding. Since budding is to a large extend dependent on the nucleocapsid-(N) and matrixproteins (M) of the virus, we analyzed the nucleotide- and deduced amino acid sequences of the corresponding genes of a spectrum of CDV strains, that differ with respect to virulence and persistence in vivo and in vitro. The wild type CDV (A75/17), which is capable of causing a persistent infection in vivo was compared to two tissue culture adapted CDV strains (passaged A75/17-CDV and Rockborn-CDV), which CDV strains, that differ with respect to virulence and persistence in vivo and in vitro. The wild type CDV (A75/17), which is capable of causing a persistent infection in vivo was compared to two tissue culture adapted CDV strains (passaged A75/17-CDV and Rockborn-CDV), which retain a residual virulence and the capacity to spontaneously persist in vitro. A modified distemper virus (Snyder Hill-CDV), which is neurovirulent but not capable of causing a persistent infection in vivo, and an avianized virus (Onderstepoort-CDV) which is completely apathogenic and spreads by budding in cell cultures were also examined. Differences were found in the C-terminal of the nucleocapsid protein, which--comparing the two extremes of the spectrum (wild A75/17-CDV and OP-CDV)--lead to changes of the predicted protein structure. Such changes could affect the budding process and thus play a role in persistence. Marked changes in the M-gene were found in its non-coding region: the nucleotide sequences of the SH-CDV and OP-CDV differed considerably from the other three strains. Moreover, an additional second open reading frame was detected in the 'non-coding' region of the M gene in the wild A75-CDV, the two tissue culture adapted CDV strains and SH-CDV, but not in OP-CDV. The presence of this additional open reading frame correlated with the ability to cause a spontaneous persistent infection in vitro. Our findings support the notion that both N- and M-genes of CDV harbor determinants of viral persistence.

Abundant expression of viral nucleoprotein mRNA and restricted translation of the corresponding viral protein in inclusion body polioencephalitis of canine distemper

Brain and other tissues of three dogs aged 4-21 months with inclusion body polioencephalitis caused by canine distemper virus (CDV) were examined for CDV nucleoprotein (N) antigen and mRNA distribution. Two animals (nos 3 and 1) had suddenly shown central nervous system (CNS) signs 4 days and 5 months, respectively, after vaccination with a modified live CDV vaccine; animal no. 2 had shown similar signs 4 weeks after vaccination with an unknown product. Lesions in the CNS, which were restricted to the grey matter, occurred most frequently in the diencephalon, mesencephalon, medulla oblongata and, in one animal, in the cerebral cortex. Changes were characterized by mild to moderate perivascular lymphohistiocytic cuffs, loss of neurons, neuronal necrosis, glial nodules, and oedema. Intranuclear and cytoplasmic inclusion bodies, especially prominent in neurons, were observed. By in-situ hybridization, CDV N mRNA expression was confirmed with a non-radioactively labelled N-specific mRNA probe. The corresponding RNA translation product was detected immunohistochemically with a proteinspecific monoclonal antibody. Viral antigen and mRNA were observed in the same cell types and brain compartments. However, the number of cells expressing N mRNA exceeded the number of cells containing viral antigen greatly in two animals and slightly in one. Some areas with abundant viral mRNA expression were almost completely devoid of viral antigen. mRNA and the corresponding translation product were demonstrated in neurons and less frequently in astrocytes, but not in perivascular inflammatory cells. It would appear that distemper inclusion-body polioencephalitis may be due to a non-productive CDV infection of neurons, characterized by abundant expression of CDV N mRNA and reduced translation of the corresponding viral protein. These findings suggest that in distemper the pathogenesis of grey-matter lesions differs substantially from that of white-matter lesions, which constitute the most common manifestation of distemper encephalitis.

In vivo detection of porcine reproductive and respiratory syndrome virus RNA by in situ hybridization at different times postinfection

We studied the distribution of porcine reproductive and respiratory syndrome virus (PRRSV) RNA in tissues by in situ hybridization at different times postinfection (p.i.). The probe used for in situ hybridization was prepared by reverse transcription of PRRSV RNA, followed by PCR amplification of the cDNA. The sequence amplified corresponded to 433 bp from PRRSV open reading frame 7, which is contained in the nucleocapsid protein gene and which is highly conserved in both European and American strains (H. Mardassi, L. Wilson, S. Mounir, and S. Dea, J. Clin. Microbiol. 32:2197-2203, 1994). An immunohistochemical technique was used to detect PRRSV antigen in tissue from virus-infected animals by using a monoclonal antibody specific for the PRRSV nucleocapsid protein (E.A. Nelson, J. Christopher-Hennings, T. Drew, G. Wensvoort, J.E. Collins, and D.A. Benfield, J. Clin. Microbiol. 31:3184-3189, 1993). The detection of PRRSV RNA was conducted in tissues of 6-week-old pigs that had been infected with one of three different field PRRSV isolates and collected at times ranging from 4 to 42 days p.i. Hybridization signals specific for PRRSV RNA were detected in lung, lymphoid tissues, alveolar macrophages (obtained by lavage at the time of necropsy), Peyer's patches, and kidney. The PRRSV-positive cells in these tissues appeared to be predominantly macrophages. In lung tissue we also obtained evidence suggesting the involvement of type II pneumocytes in the replication of PRRSV. During the acute period of infection there was a close correlation between the detection of RNA and the detection of nucleocapsid protein in individual cells. At later times p.i. (28 and 42 days p.i.), instead, more cells containing only PRRSV RNA than those containing PRRSV RNA and also expressing PRRSV nucleocapsid protein were detected. These results suggest that PRRSV RNA might persist in the tissues of infected animals for a longer time than PRRSV antigen expression.

Restricted infection with canine distemper virus leads to down-regulation of myelin gene transcription in cultured oligodendrocytes

Canine distemper virus (CDV) induces oligodendroglial degeneration and multifocal demyelination in the central nervous system. The mechanism of oligodendrocyte degeneration is not understood but it has been shown that there is a restricted infection of these cells without viral protein production. Using a combination of immunocytochemistry and in situ hybridization we were able to demonstrate the transcription of the entire virus genome throughout the whole observation period (7-35 days after infection) in oligodendrocytes in CDV-infected brain cell cultures. Therefore, the lack of viral protein and particle production can not be explained on the basis of a defective viral transcription. The present study also shows that a restricted infection of oligodendrocytes with CDV down-regulates the transcription of the major myelin genes coding for proteolipid protein, myelin basic protein (MBP) and myelin-associated glycoprotein in a very similar way. Using densitometry for in situ hybridization products of MBP in populations of normal and infected oligodendrocytes, an effect could be observed long before morphological changes were detectable. The present results strongly suggest that demyelination in distemper is induced by a restricted CDV infection of oligodendrocytes which down-regulates the expression of a variety of cellular genes, in particular those coding for myelin proteins. Consequently, the infected cells are no longer able to synthesize all the membrane compounds which are necessary for maintaining their structural integrity.