Demyelination in experimental canine distemper virus infection: immunological, pathologic, and immunohistological studies

Caprine arthritis encephalitis virus-induced apoptosis associated with brain lesions in naturally infected kids

Acute demyelinating leucoencephalomyelitis was the most conspicuous microscopic change in the brain and spinal cord of kids infected with caprine arthritis encephalitis virus (CAEV). TUNEL positivity and labelling of anti-bax and anti-caspases-3, -8 and -9 were found in a distinct population of glial cells, mainly at the edges of the demyelinated plaques and perivascular areas and, to a lesser extent, in neurons. Double labelling revealed that most of these apoptotic cells in the demyelinated plaques were astrocytes and a few were oligodendroglia. In contrast, expression of bcl-2, an anti-apoptotic protein, was found mainly in neurons of the brainstem and cerebellum and motor neurons of the spinal cord, but was restricted in glial cells. These results suggest that apoptosis plays an important role in the pathogenesis of CAE demyelinating encephalitis.

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.

Histopathological Features of Spinal Cord Lesions in Dogs with Distemper-Associated Demyelinating Leucoencephalomyelitis

Demyelinating leucoencephalomyelitis (DLEM) is one of the pathological presentations of canine distemper, but its histological characteristics and topographical distribution of spinal cord injuries have been poorly explored. Seventeen dogs submitted for necropsy to a veterinary pathology service (2006-2008) and diagnosed with distemper-associated DLEM were investigated. Seventy-two of 231 spinal cord sections from these animals had histological lesions, which consistently affected the white matter. The lumbosacral region was mostly affected (13/17), followed by the thoracolumbar (11/17), cervical (9/17) and cervicothoracic (9/17) regions. Among the 72 affected cord sections, lesions in the lateral (42/72) and dorsal funiculi (31/72) were the most common. Demyelination (17/17), astrocytosis (17/17), microgliosis (17/17), gemistocytes (11/17) and non-suppurative inflammation (10/17) were frequently seen in the white matter. Grey matter changes were less common, and included gliosis (8/17), non-suppurative inflammation (7/17) and malacia (5/17). Acute lesions were most prevalent (13/17) but it was common (10/17) for the same dog to have lesions at different stages of evolution in distinct spinal cord regions. Pathological changes in several spinal cords did not correlate with the reported clinical signs and some dogs did not present with spinal cord-related clinical signs. Our results highlight important aspects of the distribution and morphology of spinal cord lesions in dogs with distemper-associated DLEM, and may assist clinicians and pathologists in the diagnosis of spontaneous cases of this important infectious disease and contribute to further studies concerning distemper pathogenesis.

Temporal overexpression of IL-22 and Reg3γ differentially impacts the severity of experimental autoimmune encephalomyelitis

IL-22 is an alpha-helical cytokine which belongs to the IL-10 family of cytokines. IL-22 is produced by RORγt+ innate and adaptive lymphocytes, including ILC3, γδ T, iNKT, Th17 and Th22 cells and some granulocytes. IL-22 receptor is expressed primarily by non-haematopoietic cells. IL-22 is critical for barrier immunity at the mucosal surfaces in the steady state and during infection. Although IL-22 knockout mice were previously shown to develop experimental autoimmune encephalomyelitis (EAE), a murine model of multiple sclerosis (MS), how temporal IL-22 manipulation in adult mice would affect EAE course has not been studied previously. In this study, we overexpressed IL-22 via hydrodynamic gene delivery or blocked it via neutralizing antibodies in C57BL/6 mice to explore the therapeutic impact of IL-22 modulation on the EAE course. IL-22 overexpression significantly decreased EAE scores and demyelination, and reduced infiltration of IFN-γ+IL-17A+Th17 cells into the central nervous system (CNS). The neutralization of IL-22 did not alter the EAE pathology significantly. We show that IL-22-mediated protection is independent of Reg3γ, an epithelial cell-derived antimicrobial peptide induced by IL-22. Thus, overexpression of Reg3γ significantly exacerbated EAE scores, demyelination and infiltration of IFN-γ+IL-17A+ and IL-17A+GM-CSF+Th17 cells to CNS. We also show that Reg3γ may inhibit IL-2-mediated STAT5 signalling and impair expansion of Treg cells in vivo and in vitro. Finally, Reg3γ overexpression dramatically impacted intestinal microbiota during EAE. Our results provide novel insight into the role of IL-22 and IL-22-induced antimicrobial peptide Reg3γ in the pathogenesis of CNS inflammation in a murine model of MS.

Increased frequency of canine distemper virus-specific antibodies in multiple sclerosis

BACKGROUND AND PURPOSE

Canine distemper virus (CDV) is a candidate agent in the etiology of multiple sclerosis (MS). Elevated anti-CDV levels were previously found in the sera from MS patients compared with controls. We now investigated whether there was an age-related association with the presence of antibodies specific to CDV-hemagglutinin (H) protein in MS.

METHODS

Sera from patients with MS, other neurological diseases, and inflammatory and/or autoimmune diseases, and healthy individuals were screened for anti-CDV in an ELISA using linear peptides of the CDV-H protein as antigen. Antibody levels to measles and varicella-zoster virus were measured and served as controls.

RESULTS

Analysis of the new cohort of MS patients and controls confirmed our initial finding of elevated anti-CDV-H levels in MS patients. An increase in measles but not varicella-zoster virus antibody levels was found in MS patients compared with healthy controls. Data from the new cohort of patients and controls were combined with data from the original study and analyzed with respect to age distribution of anti-CDV IgG. Mean CDV antibody levels were significantly elevated in each decade from 20 to 50 years of age in MS compared with healthy and disease controls. Antibody levels to measles virus were not consistently elevated during this age span. A striking relationship (p < .0001, odds ratio = 5.0) was observed between elevated anti-CDV-H levels and diagnosis of MS.

CONCLUSIONS

The finding that anti-CDV levels are elevated in MS patients of all ages provides substantial evidence of a strong association between elevated anti-CDV and MS.

Neurotoxic potential of reactive astrocytes in canine distemper demyelinating leukoencephalitis

Canine distemper virus (CDV) causes a fatal demyelinating leukoencephalitis in young dogs resembling human multiple sclerosis. Astrocytes are the main cellular target of CDV and undergo reactive changes already in pre-demyelinating brain lesions. Based on their broad range of beneficial and detrimental effects in the injured brain reactive astrogliosis is in need of intensive investigation. The aim of the study was to characterize astrocyte plasticity during the course of CDV-induced demyelinating leukoencephalitis by the aid of immunohistochemistry, immunofluorescence and gene expression analysis. Immunohistochemistry revealed the presence of reactive glial fibrillary acidic protein (GFAP)+ astrocytes with increased survivin and reduced aquaporin 4, and glutamine synthetase protein levels, indicating disturbed blood brain barrier function, glutamate homeostasis and astrocyte maladaptation, respectively. Gene expression analysis revealed 81 differentially expressed astrocyte-related genes with a dominance of genes associated with neurotoxic A1-polarized astrocytes. Accordingly, acyl-coA synthetase long-chain family member 5+/GFAP+, and serglycin+/GFAP+ cells, characteristic of A1-astrocytes, were found in demyelinating lesions by immunofluorescence. In addition, gene expression revealed a dysregulation of astrocytic function including disturbed glutamate homeostasis and altered immune function. Observed findings indicate an astrocyte polarization towards a neurotoxic phenotype likely contributing to lesion initiation and progression in canine distemper leukoencephalitis.

Interferon-Stimulated Genes-Mediators of the Innate Immune Response during Canine Distemper Virus Infection

The demyelinating canine distemper virus (CDV)-leukoencephalitis represents a translational animal model for multiple sclerosis. The present study investigated the expression of type I interferon (IFN-I) pathway members in CDV-induced cerebellar lesions to gain an insight into their role in lesion development. Gene expression of 110 manually selected genes in acute, subacute and chronic lesions was analyzed using pre-existing microarray data. Interferon regulatory factor (IRF) 3, IRF7, signal transducer and activator of transcription (STAT) 1, STAT2, MX protein, protein kinase R (PKR), 2'-5'-oligoadenylate synthetase (OAS) 1 and interferon-stimulated gene (ISG) 15 expression were also evaluated using immunohistochemistry. Cellular origin of STAT1, STAT2, MX and PKR were determined using immunofluorescence. CDV infection caused an increased expression of the antiviral effector proteins MX, PKR, OAS1 and ISG15, which probably contributed to a restricted viral replication, particularly in neurons and oligodendrocytes. This increase might be partly mediated by IRF-dependent pathways due to the lack of changes in IFN-I levels and absence of STAT2 in astrocytes. Nevertheless, activated microglia/macrophages showed a strong expression of STAT1, STAT2 and MX proteins in later stages of the disease, indicating a strong activation of the IFN-I signaling cascade, which might be involved in the aggravation of bystander demyelination.

Accumulation of Extracellular Matrix in Advanced Lesions of Canine Distemper Demyelinating Encephalitis

In demyelinating diseases, changes in the quality and quantity of the extracellular matrix (ECM) may contribute to demyelination and failure of myelin repair and axonal sprouting, especially in chronic lesions. To characterize changes in the ECM in canine distemper demyelinating leukoencephalitis (DL), histochemical and immunohistochemical investigations of formalin-fixed paraffin-embedded cerebella using azan, picrosirius red and Gomori`s silver stain as well as antibodies directed against aggrecan, type I and IV collagen, fibronectin, laminin and phosphacan showed alterations of the ECM in CDV-infected dogs. A significantly increased amount of aggrecan was detected in early and late white matter lesions. In addition, the positive signal for collagens I and IV as well as fibronectin was significantly increased in late lesions. Conversely, the expression of phosphacan was significantly decreased in early and more pronounced in late lesions compared to controls. Furthermore, a set of genes involved in ECM was extracted from a publically available microarray data set and was analyzed for differential gene expression. Gene expression of ECM molecules, their biosynthesis pathways, and pro-fibrotic factors was mildly up-regulated whereas expression of matrix remodeling enzymes was up-regulated to a relatively higher extent. Summarized, the observed findings indicate that changes in the quality and content of ECM molecules represent important, mainly post-transcriptional features in advanced canine distemper lesions. Considering the insufficiency of morphological regeneration in chronic distemper lesions, the accumulated ECM seems to play a crucial role upon regenerative processes and may explain the relatively small regenerative potential in late stages of this disease.

REVIEW ■ : The Epidemiology of Multiple Sclerosis: Clues to the Etiology of a Mysterious Disease

The etiology of multiple sclerosis (MS) has not yet been defined. Based on analysis of prevalence, incidence, and migration studies, it is likely that one or more environmental factors, probably infectious in origin, initiates the disease. Canine distemper virus appears to be an attractive candidate in this regard. Because the risk of acquiring MS is greater in multiplex families (particularly in identical twins), certain ethnic and religious groups, and individuals with the human leukocyte antigen DW2, genetic predisposition is an important determinant in disease expression. NEUROSCIENTIST 2:172-180, 1996

New aspects of the pathogenesis of canine distemper leukoencephalitis

Canine distemper virus (CDV) is a member of the genus morbillivirus, which is known to cause a variety of disorders in dogs including demyelinating leukoencephalitis (CDV-DL). In recent years, substantial progress in understanding the pathogenetic mechanisms of CDV-DL has been made. In vivo and in vitro investigations provided new insights into its pathogenesis with special emphasis on axon-myelin-glia interaction, potential endogenous mechanisms of regeneration, and astroglial plasticity. CDV-DL is characterized by lesions with a variable degree of demyelination and mononuclear inflammation accompanied by a dysregulated orchestration of cytokines as well as matrix metalloproteinases and their inhibitors. Despite decades of research, several new aspects of the neuropathogenesis of CDV-DL have been described only recently. Early axonal damage seems to represent an initial and progressive lesion in CDV-DL, which interestingly precedes demyelination. Axonopathy may, thus, function as a potential trigger for subsequent disturbed axon-myelin-glia interactions. In particular, the detection of early axonal damage suggests that demyelination is at least in part a secondary event in CDV-DL, thus challenging the dogma of CDV as a purely primary demyelinating disease. Another unexpected finding refers to the appearance of p75 neurotrophin (NTR)-positive bipolar cells during CDV-DL. As p75NTR is a prototype marker for immature Schwann cells, this finding suggests that Schwann cell remyelination might represent a so far underestimated endogenous mechanism of regeneration, though this hypothesis still remains to be proven. Although it is well known that astrocytes represent the major target of CDV infection in CDV-DL, the detection of infected vimentin-positive astrocytes in chronic lesions indicates a crucial role of this cell population in nervous distemper. While glial fibrillary acidic protein represents the characteristic intermediate filament of mature astrocytes, expression of vimentin is generally restricted to immature or reactive astrocytes. Thus, vimentin-positive astrocytes might constitute an important cell population for CDV persistence and spread, as well as lesion progression. In vitro models, such as dissociated glial cell cultures, as well as organotypic brain slice cultures have contributed to a better insight into mechanisms of infection and certain morphological and molecular aspects of CDV-DL. Summarized, recent in vivo and in vitro studies revealed remarkable new aspects of nervous distemper. These new perceptions substantially improved our understanding of the pathogenesis of CDV-DL and might represent new starting points to develop novel treatment strategies.

Transcriptional changes in canine distemper virus-induced demyelinating leukoencephalitis favor a biphasic mode of demyelination

Canine distemper virus (CDV)-induced demyelinating leukoencephalitis in dogs (Canis familiaris) is suggested to represent a naturally occurring translational model for subacute sclerosing panencephalitis and multiple sclerosis in humans. The aim of this study was a hypothesis-free microarray analysis of the transcriptional changes within cerebellar specimens of five cases of acute, six cases of subacute demyelinating, and three cases of chronic demyelinating and inflammatory CDV leukoencephalitis as compared to twelve non-infected control dogs. Frozen cerebellar specimens were used for analysis of histopathological changes including demyelination, transcriptional changes employing microarrays, and presence of CDV nucleoprotein RNA and protein using microarrays, RT-qPCR and immunohistochemistry. Microarray analysis revealed 780 differentially expressed probe sets. The dominating change was an up-regulation of genes related to the innate and the humoral immune response, and less distinct the cytotoxic T-cell-mediated immune response in all subtypes of CDV leukoencephalitis as compared to controls. Multiple myelin genes including myelin basic protein and proteolipid protein displayed a selective down-regulation in subacute CDV leukoencephalitis, suggestive of an oligodendrocyte dystrophy. In contrast, a marked up-regulation of multiple immunoglobulin-like expressed sequence tags and the delta polypeptide of the CD3 antigen was observed in chronic CDV leukoencephalitis, in agreement with the hypothesis of an immune-mediated demyelination in the late inflammatory phase of the disease. Analysis of pathways intimately linked to demyelination as determined by morphometry employing correlation-based Gene Set Enrichment Analysis highlighted the pathomechanistic importance of up-regulated genes comprised by the gene ontology terms “viral replication” and “humoral immune response” as well as down-regulated genes functionally related to “metabolite and energy generation”.

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.

Neuropatologia da cinomose canina: 70 casos (2005-2008)

Este estudo teve como objetivo realizar uma investigação anátomo-patológica detalhada das lesões e sua distribuição no sistema nervoso central (SNC) de cães com cinomose. Foram avaliadas secções padronizadas do encéfalo e da medula espinhal de 70 cães. Os casos foram agrupados de acordo com a idade dos cães e classificados conforme a evolução das lesões. Os resultados permitem concluir que: (1) encefalomielite induzida pelo vírus da cinomose canina é mais prevalente em filhotes e adultos; (2) lesões macroscópicas no SNC ocorrem com baixa freqüência; (3) o encéfalo é mais acometido do que a medula espinhal; (4) as cinco regiões anatômicas mais afetadas do encéfalo são, em ordem decrescente de freqüência, o cerebelo, o diencéfalo, o lobo frontal, a ponte e o mesencéfalo; (5) a região anatômica mais afetada da medula espinhal é o segmento cervical cranial (C1-C5); (6) lesões subagudas e crônicas são mais comuns do que lesões agudas; (7) desmielinização é a lesão mais prevalente e ocorre principalmente no cerebelo, na ponte e no diencéfalo, quase sempre acompanhada de astrogliose e inflamação não-supurativa; (8) na maior parte dos casos em que há astrogliose, observam-se astrócitos gemistocíticos, freqüentemente com formação de sincícios; (9) leptomeningite não-supurativa, malacia e necrose cortical laminar são lesões relativamente freqüentes no encéfalo, mas não na medula espinhal; (10) corpúsculos de inclusão no encéfalo são muito comuns, ocorrem principalmente em astrócitos e com freqüência menor em neurônios; no entanto, independentemente da célula afetada, são vistos predominantemente no núcleo; (11) uma classificação da encefalite na cinomose com base em síndromes clínicas relacionadas com a idade do cão é imprecisa.

Immunohistochemical demonstration of the putative canine distemper virus receptor CD150 in dogs with and without distemper

Signaling lymphocyte activation molecule (SLAM) or CD150 can function as a receptor for the canine distemper virus (CDV) in vitro. The expression of SLAM was studied using immunohistochemistry in order to evaluate the presence and distribution of the receptor in dogs in vivo. Additionally, receptor expression was assessed after experimental infection of dogs with CDV. In 7 control dogs without distemper virus, the receptor was found in various tissues, mostly on cells morphologically identified as lymphocytes and macrophages. In 7 dogs with early distemper lesions characterized by presence of the virus, higher numbers of SLAM-expressing cells were found in multiple tissues recognized as targets of CDV compared with those in control dogs. These findings suggest that SLAM, a putative distemper receptor, is expressed in dogs in vivo. Additionally, virus infection is associated with up-regulation of SLAM, potentially causing an amplification of virus in the host.

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.

Microglial cell activation in demyelinating canine distemper lesions

Microglia cells are the principal immune effector elements of the brain responding to any pathological event. To elucidate the possible role of microglia in initial non-inflammatory demyelination in canine distemper virus (CDV) infection, microglia from experimentally CDV infected dogs were isolated ex vivo by density gradient centrifugation and characterized immunophenotypically and functionally using flow cytometry. Results from dogs with demyelinating lesions were compared to results from recovered dogs and two healthy controls. CDV antigen could be detected in microglia of dogs with histopathologically confirmed demyelination. Microglia of these dogs showed marked upregulation of the surface molecules CD18, CD11b, CD11c, CD1c, MHC class I and MHC class II and a tendency for increased expression intensity of ICAM-1 (CD54), B7-1 (CD80), B7-2 (CD86), whereas no increased expression was found for CD44 and CD45. Functionally, microglia exhibited distinctly enhanced phagocytosis and generation of reactive oxygen species (ROS). It was concluded that in CDV infection, there is a clear association between microglial activation and demyelination. This strongly suggests that microglia contribute to acute myelin destruction in distemper.

Canine distemper virus infection: proliferation of canine footpad keratinocytes

The proliferation of footpad keratinocytes of canine distemper virus (CDV)-infected dogs was investigated. Footpads of 19 dogs inoculated experimentally with a virulent distemper strain (A75/17) and of two noninoculated control dogs were collected at necropsy. Dogs were divided into four groups according to results of the postmortem examination: dogs with severe distemper (group 1), dogs with mild distemper (group 2), inoculated dogs without distemper (group 3) and noninoculated dogs (group 4). There was no distinct difference of epidermal thickness among the four groups. Infection of the footpad epidermis with CDV was demonstrated using immunohistochemistry for viral nucleoprotein and in situ hybridization for nucleoprotein messenger ribonucleic acid (mRNA). Only group 1 dogs had viral antigen and mRNA in the footpad epidermis with the same distribution. Footpad epidermis of group 1 dogs had more mitotic figures in the basal layer, and significantly more basal keratinocytes were positive for the proliferation markers Ki-67 and proliferating cell nuclear antigen. Double-staining for Ki-67 and viral nucleoprotein identified rare double-labeled basal keratinocytes. These findings suggest that the presence of CDV particles in the footpad epidermis is associated with keratinocyte proliferation.

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.

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.

Studies on canine distemper virus persistence in the central nervous system

Chronic progressive demyelination in canine distemper virus (CDV) infection is associated with persistence of the virus in the nervous system. We studied persistence by examining expression of CDV mRNA corresponding to all genes of the virus as well as genomic CDV RNA in brain sections of dogs with acute and chronic demyelinating disease. All virus mRNAs were expressed in acute demyelinating lesions in a way similar to that seen in lymphoid tissues, the primary replication site of CDV. Their distribution corresponded very well with immunohistochemical detection of virus protein. In contrast, much more CDV mRNA than virus protein was found in gray matter areas suggesting that translation of CDV can be impaired in nervous distemper. Virus protein and RNA were cleared from chronic inflammatory demyelinating lesions. mRNA corresponding to the distal genes (F; H; L) of CDV disappeared first in inflammatory lesions for technical reasons associated with the particular mode of transcription of morbilliviruses. CDV RNA and protein persisted in chronically ill dogs in other areas of the CNS in which inflammation had not occurred. Our results suggest that persistence of CDV is favored by non-cytolytic spread of the virus and restricted infection of certain cells with reduced viral protein expression. Both tend to delay immune recognition of the virus.

The neurobiology of canine distemper virus infection

Canine distemper virus (CDV) invades the nervous system and replicates in neurons and glial cell of the white matter during a period of severe viral induced immunosuppression. Demyelination occurs in infected white matter areas in the absence of inflammation. The mechanism of demyelination is not apparent because there is no ultrastructural evidence of viral replication in the oligodendrocytes, the myelin producing cells. However, brain tissue culture studies have shown that oligodendrocytes support transcription of all CDV genes and later on degenerate, although no viral proteins can be found in these cells. It remains to be shown how such a restricted infection leads to demyelination. Concomitant with immunologic recovery during the further course of the disease, inflammation occurs in the demyelinating lesions with progression of the lesions in some animals. A series of experiments in vitro suggested that chronic demyelination is due to a bystander mechanism associated with the virus-induced immune response in which antibody dependent cell-mediated reactions play an important role. The progressive, or even relapsing, course of the disease is associated with viral persistence in the nervous system. Persistence of CDV in the brain appears to be due to non-cytolytic selective spread of the virus with very limited budding. In this way CDV escaped immune surveillance.

Evidence for multiple sclerosis as an infectious disease

Evidence for a viral cause of multiple sclerosis (MS) is indirect since no infectious agent has been reproducibly isolated from MS tissues nor has viral genome or antigen been consistently identified. The occurrence of spontaneous human and animal models of demyelination, serologic studies, and epidemiologic data provide persuasive circumstantial evidence for an infectious trigger in this disease. Potential mechanisms for viral induced demyelination include persistent infection of host tissues or immune mediated organ damage either in the presence or absence of the infectious agent. Any proposed viral candidate should cause demyelination in animals or man and the pattern of infection should be consistent with the unique geographic features of MS epidemiology. In addition, serologic studies should support an infection by the agent and/or viral genome should be detected in MS tissues. At this time no virus can be unequivocally linked to MS but cumulative evidence is more supportive of canine distemper virus than other viruses.

Determination of the IgG index for the detection of intrathecal immunoglobulin synthesis in dogs using an ELISA

The IgG index is a calculated quotient using IgG and albumin contents of cerebrospinal fluid (CSF) and serum to detect intrathecal IgG synthesis, which is important in the diagnosis of inflammatory infectious diseases of the central nervous system (CNS). An ELISA to measure IgG and albumin contents in blood and CSF was developed to determine the IgG index. Twenty-three normal dogs and 98 dogs with various neurological diseases were examined. In most dogs with infectious inflammatory diseases, with the exception of the acute form of nervous canine distemper, there was an elevation of the IgG index. Tumours of the CNS had an IgG index within the normal range. An elevation was found in lymphoid tumours or meningiomas with secondary cellular infiltration. Degenerative diseases, spinal cord compression and ischaemic myelopathy due to fibrocartilagenous embolism had normal or only slightly elevated IgG indices. In seven cases with inflammatory lesions there was no obvious CSF pleocytosis but the IgG index was elevated. In 17 cases in which infectious inflammatory disease was suspected, based on elevated CSF cell counts, inflammation could be excluded after determination of the IgG index. The reproducibility of the technique was found to be good and, considering the limited amount of time, expense and effort required, the determination of the IgG index in dogs is a useful extension of the conventional CSF examination.

Pathogenesis of virus-induced demyelination

Demyelination is a component of several viral diseases of humans. The best known of these are subacute sclerosing panencephalitis (SSPE) and progressive multifocal leukoencephalopathy (PML). There are a number of naturally occurring virus infections of animals that involve demyelination and many of these serve as instructive models for human demyelinating diseases. In addition to the naturally occurring diseases, many viruses have been shown to be capable of producing demyelination in experimental situations. In discussing virus-associated demyelinating disease, the chapter reviews the architecture and functional organization of the CNS and considers what is known of the interaction of viruses with CNS cells. It also discusses the immunology of the CNS that differs in several important aspects from that of the rest of the body. Experimental models of viral-induced demyelination have also been considered. Viruses capable of producing demyelinating disease have no common taxonomic features; they include both DNA and RNA viruses, enveloped and nonenveloped viruses. The chapter attempts to summarize the important factors influencing viral demyelination, their common features, and possible mechanisms.

Myelitis and meningitis

Animals with meningomyelitis have clinical neurologic signs that typically range from paraspinal discomfort to tetraplegia; however, most affected animals also show evidence of multifocal CNS involvement with brain stem and cerebral cortical structures being affected most commonly. The cause, duration, and host response to the disease process will determine the clinical signs in individual animals. Confirmation of a specific causative agent is difficult, but CSF analysis and immunotesting of serum and CSF yield the most rewarding diagnostic results. Successful treatment is based on formulation of an appropriate and aggressive therapeutic regimen. In some diseases, no effective treatment is available, and some animals may develop permanent neurologic disabilities.

Cerebrospinal fluid analysis

Accurate interpretation of cerebrospinal fluid (CSF) changes can only be made in the context of the differential diagnosis for each case. The routine analysis of CSF cell number and type as well as CSF total protein can provide information that suggests a specific mechanism or disease, but is often inconclusive. Further information obtained from CSF protein electrophoresis and immunoglobulin determination and calculation of an albumin quota and IgG index can lend additional support for the suspected mechanism of disease. Paired serum and CSF antibody titers for specific organisms can be useful to confirm the presence of a systemic or nervous system infection. Current research on detecting antibodies against nervous tissue components in CSF should result in better diagnostic capabilities and understanding of the pathophysiology of certain disorders in the future.

Canine distemper virus-immune complexes induce bystander degeneration of oligodendrocytes

Demyelination in chronic canine distemper encephalitis may be the result of a bystander effect in which the antiviral immune response is involved. In the present report we demonstrate that canine distemper virus-antiviral antibody immune complexes induce oligodendroglial degeneration in mixed brain cell cultures, particularly at the level of the cell processes. The involvement of macrophages as effector cells in this process was confirmed by depletion of these cells from the cultures which prevented the immune complex-mediated oligodendroglial degeneration. Canine distemper virus-immune complex-induced oligodendroglial pathology is thought to be mediated by toxic factors released from stimulated macrophages, this bystander effect demonstrated here in vitro may be relevant to the mechanisms of demyelination in vivo, in which virus persistence plays an important role.

Viral expression in experimental canine distemper demyelinating encephalitis

We have characterized the relationship between the expression of canine distemper virus (CDV) and demyelinating lesions in the white matter of the cerebellum of experimentally infected dogs. In animals which had demyelinating lesions, CDV proteins (N, P, F and H) were expressed and infectious virus could be recovered from brain tissue. Viral proteins (N, P, F and H) were detected by monoclonal antibodies and immunocytochemistry within demyelinating lesions as well as in scattered glial cells in areas of the white matter which lacked detectable lesions. Many cell types, including astrocytes, neurons, ependymal cells, choroid plexus cells, meningeal cells and perivascular inflammatory cells were labelled for viral antigen. We conclude from our results that the mechanism of demyelination in canine distemper virus-induced encephalitis involves expression of viral gene products at the lesion site.

Ultrastructural and biochemical findings in brain cell cultures infected with canine distemper virus

To study the pathomechanism of demyelination in canine distemper (CD), dog brain cell cultures were infected with virulent A75/17-CD virus (CDV) and examined ultrastructurally. Special attention was paid to the oligodendrocytes, which were specifically immunolabelled. In addition, cerebroside sulfotransferase (CST), an enzyme specific for oligodendrocyte activity was assayed during the course of the infection. Infection and maturation as well as CDV-induced changes were found in astrocytes and brain macrophages. Infection of oligodendrocytes was rarely seen, although CST activity of the culture markedly decreased and vacuolar degeneration of these cells occurred, resulting in their complete disappearance. We concluded that the degeneration of oligodendrocytes and demyelination is not due to direct virus-oligodendrocyte interaction, but due to CDV-induced events in other glial cells.

Selective degeneration of oligodendrocytes mediated by reactive oxygen species

The mechanism underlying demyelination in inflammatory canine distemper encephalitis is uncertain. Macrophages and their secretory products are thought to play an important effector role in this lesion. Recently, we have shown that anti-canine distemper virus antibodies, known to occur in chronic inflammatory lesions, stimulate macrophages leading to the secretion of reactive oxygen species (ROS). To investigate whether ROS could be involved in demyelination, dog glial cell cultures were exposed to xanthine/xanthine oxidase (X/XO), a system capable of generating O2-. This treatment resulted in a specific time-dependent degeneration and loss of oligodendrocytes, the myelin producing cells of the central nervous system. Initial degeneration was not associated with a decrease in viability of oligodendrocytes as judged by trypan blue and propidium iodide exclusion. Astrocytes and brain macrophages were not affected morphologically by this treatment. Further, an evaluation of the effect of several ROS scavengers, transition metal chelators and inhibitors of poly (ADP-ribose) polymerase suggests that a metal dependent formation of .OH or a similar highly oxidizing species could be responsible for the observed selective damage to oligodendrocytes.

Antibody-induced generation of reactive oxygen radicals by brain macrophages in canine distemper encephalitis: a mechanism for bystander demyelination

The mechanism of inflammatory demyelination in canine distemper encephalitis (CDE) is uncertain but macrophages are thought to play an important effector role in this lesion. Serum and cerebrospinal fluid (CSF), containing anti-canine distemper virus and anti-myelin antibodies from dogs with CDE were tested for their ability to generate reactive oxygen species (ROS) in macrophages in primary dog brain cell cultures using a chemiluminescence (CL) assay. The majority of serum samples and several CSF samples from animals with inflammatory demyelination elicited a CL signal in infected dog brain cell cultures. In contrast, none of these samples induced a positive response in uninfected cultures which contained large numbers of myelin antigen-presenting cells, although defined anti-myelin antibodies lead to a marked secretion of ROS in this system. It was concluded that antiviral antibody-induced secretion of ROS, known to be highly toxic for brain tissue, may play an important role in white matter damage in inflammatory lesions supporting a previous hypothesis of bystander demyelination in CDE. No evidence was found for a similar antibody-dependent cellular cytotoxicity-like mechanism mediated by anti-myelin antibodies in CDE, which does not support the concept of autoimmunity in this disease.

Antiviral antibodies stimulate production of reactive oxygen species in cultured canine brain cells infected with canine distemper virus

Canine distemper is characterized mainly by respiratory, enteric, and nervous symptoms. Infection of the central nervous system results in demyelination, to which inflammation has been shown to contribute significantly. It has been proposed that macrophages play a major role as effector cells in this process. We report that cultured dog brain cells contain a population of macrophages capable of producing reactive oxygen species as measured by luminol-dependent chemiluminescence. In cultures infected with canine distemper virus, a burst of reactive oxygen is triggered by antiviral antibody. This response depends on the presence of viral antigens on the surfaces of infected cells and is mediated by the interaction of antigen-bound antibody with Fc receptors on the macrophages. Since there is no evidence in vitro or in vivo that oligodendrocytes, the cells forming myelin, are infected, our observation supports the hypothesis that "innocent bystander killing" is important in demyelination caused by canine distemper virus. Reactive oxygen species released from macrophages may contribute to destruction of myelin.

Chronic relapsing demyelinating encephalomyelitis associated with persistent spontaneous canine distemper virus infection

This is the first report of spontaneous canine distemper virus (CDV) infection in a dog associated with chronic progressive multiphasic neurological disease. Initial neurological deficits in the pelvic limbs progressed rapidly to paraplegia with almost complete remission after 9 weeks. Then another acute episode occurred with severe thoracic limb deficits and cerebellar dysfunction and progressive neurological deterioration over 3 months with rising serum neutralizing (SN) anti-CDV titers in the serum and cerebrospinal fluid (CSF). Three neuropathologically distinct lesions of spinal cystic necrosis, chronic demyelinating foci in the cerebellum and acute demyelinating encephalitis in the pons were identified. Persistent CDV antigen was demonstrated immunocytochemically only in acute lesions and atypically restricted to neurons. However, the immunological mechanism associated with the distinct remissions and exacerbations and CDV antigen clearance from chronic demyelinating lesions but persistence in acute lesions, despite a vigorous anti-CDV serologic response, was not defined.

Naturally occurring canine distemper virus encephalitis: distribution and expression of viral polypeptides in nervous tissues

Formalin-fixed brain tissues from 16 dogs with naturally occurring canine distemper virus (CDV) infection were investigated immunohistochemically by a panel of eight monoclonal antibodies (mAb) directed against four structural CDV proteins. Three mAb recognizing different epitopes of the polymerase (P-1, P-2, P-3) protein, two clones identifying different epitopes on each, the nucleocapsid (NP-1, NP-2) and fusion (F-2, F-3) protein, and one mAb directed against the hemagglutinin (H-2) protein were used. The immunoreactivity of the clones was tested on formalin-fixed, paraffin-embedded Vero cells, which were lytically infected with the neurotropic R252 (R252-CDV) or the Onderstepoort (CDV/Ond) strain of CDV. Clones directed against the H-2 and F-3 epitope recognized CDV/Ond but not R252-CDV. The remaining six clones showed positive immunoreaction with both CDV strains. In vivo expression and distribution of the individual proteins and their epitopes varied substantially between animals and within lesions from the same animal. The NP-2 epitope showed positive immunostaining in all 16 cases. The P-2 epitope was demonstrated in 13, the NP-1 epitope in 12, the P-3 epitope in 9, and the P-1 epitope in 3 brains, but staining was severely reduced compared with the NP-2 epitope and restricted to areas with strong NP-2 expression. Immunostaining was prominent in early and subacute and reduced in chronic demyelinating lesions. mAb directed against the H and F protein showed no immunoreaction in diseased brains.

Comparative analysis of virus-specific antibodies and immunoglobulins in serum and cerebrospinal fluid of subacute measles virus-induced encephalomyelitis (SAME) in rats and subacute sclerosing panencephalitis (SSPE)

The intrathecal humoral immune response was analysed in patients with subacute sclerosing panencephalitis (SSPE) and Lewis rats with subacute measles virus (MV)-induced encephalomyelitis (SAME). SSPE patients as well as SAME rats revealed oligoclonal, intrathecal antibody synthesis with MV specificity. SAME rats synthesized MV-specific antibodies intracerebrally to a higher extent than SSPE patients. Although a restricted isoelectric pattern of MV-specific antibodies was detected in the cerebrospinal fluid (CSF) of SSPE patients as well as of SAME rats, the heterogeneity within clusters of immunoglobulin bands was higher in the rat specimens. Increase in the blood-brain barrier permeability for albumin was exclusively detected in SAME rats but not in SSPE patients. These data suggest that the rat model offers excellent opportunities to study the initial humoral events in MV-induced encephalitides.

Demyelination in canine distemper encephalomyelitis: an ultrastructural analysis

A morphological study of selected white matter lesions was carried out in three dogs with canine distemper encephalomyelitis. Two dogs had experimental infections while the third was a spontaneous case. Two stages were identified in the process of demyelination. The earliest evidence of myelin injury was a ballooning change in myelin sheaths involving single or multiple axons. This was followed by a progressive stripping of compact sheaths by the cytoplasmic fingers of phagocytic cells which infiltrated and removed myelin lamellae. Some axonal necrosis also accompanied these changes. Where demyelination occurred, canine distemper viral nucleocapsids were found in astrocytes, macrophages, ependymal cells and infiltrating lymphocytes. In contrast, oligodendrocytes were conspicuous by their apparent lack of infection. Thus it seems that myelin loss cannot be ascribed to oligodendrocyte infection. Perturbed astrocyte function following canine distemper viral infection may cause oedema of myelin sheaths, leading to ballooning and primary demyelination. Cells which phagocytosed myelin were mainly identified as microglial cells with lesser involvement by astrocytes. Rarely, oligodendrocytes also acted as macrophages. Myelin debris was engulfed in bulk or as small droplets into coated pits. Remyelination was present in established plaques although not in great abundance, perhaps due to the diminished oligodendrocyte numbers and a relative increase in immature forms of these cells. These observations are compared to similar changes observed in other demyelinating diseases of animals and man.

Neuropathology and neurovirulence of canine distemper virus plaque isolates in the hamster

The relationship between neuropathological abnormalities, antibody response and neurovirulence of plaque isolates has been studied in an experimental model of canine distemper in the hamster. Genetic virus variance influenced neurovirulence and the experimental evidence supports the hypothesis that the mechanism of this effect may be through the modulating effect of circulating antibody. Large plaque virus (LPV) produced severe encephalitis with little early antibody response and a high degree of pathological abnormality. Small plaque virus (SPV) produced mild chronic encephalitis and early antibody response. Microscopically, histological abnormalities in this group were qualitatively similar to those seen with LPV but generally of lesser degree. Immunosuppression in SPV infected animals increased the severity of the encephalitis, reflected by the increase in inflammation and inclusion formation. Combined SPV and LPV infection produced high antibody levels and less severe disease than LPV infection alone with an intermediate pattern of histological abnormality.

Demyelinating canine distemper encephalomyelitis: measurement of myelin basic protein in cerebrospinal fluid

Beagle dogs were experimentally infected with the Cornell A75-17 strain of canine distemper virus. At three time points post-infection (PI), immunoreactive myelin basic protein (MBP) was measured in cerebrospinal fluid (CSF). Levels were correlated with neuropathological findings, interferon in CSF and virus isolation from the brain. CSF from animals inoculated with Cornell A75-17 strain often showed detectable immunoreactive MBP late in the disease course. As anticipated from earlier morphological studies, CSF drawn around day 20 PI lacked MBP while subsequent samples were positive. Dogs with severe demyelination had elevated values of immunoreactive MBP while dogs with only mild inflammation had little or none. Release of MBP or MBP peptides into CSF of dogs with canine distemper may be a valuable laboratory test in studies of the natural history of this disease and in assessing the response to treatment. Whether an immune response to MBP plays an immunopathogenic role in the chronic, demyelinating phase of canine distemper encephalitis remains to be determined.

Potential role of paramyxoviruses in multiple sclerosis

At the present time, the cause of multiple sclerosis (MS) remains unknown, although it seems likely that one or more infectious agents triggers the disease, perhaps through an autoimmune mechanism. In this article, evidence linking the paramyxoviruses, canine distemper, and measles to MS is reviewed.

Focal perivascular alterations of white matter in herpes simplex encephalitis--a histological and immunocytochemical study

Several cases of human herpes simplex encephalitis treated with Vidarabin have been investigated with the histological and immunocytochemical techniques. Cases with a subacute evolution revealed areas of focal perivascular myelin destruction in the white matter. The distribution of herpes simplex antigen did not show any preferential localization of the virus in perivascular oligoglial cells. In contrast, a spatial and temporal relationship has been found between the appearance of immunoglobulin-bearing cells around the vessels and that of areas of focal perivascular myelin damage. Therefore, it is postulated that the areas of focal destruction of myelin are not related to the cytotoxic effect of the virus but are rather dependent on the immune response of the host.

Studies on the intrathecal humoral immune response in canine distemper encephalitis

Albumin and IgG were quantitated in paired cerebrospinal fluid (CSF) and serum samples from dogs with demyelinating canine distemper virus (CDV) infection by means of rocket immunoelectrophoresis. The IgG index as indicator for intrathecal immunoglobulin synthesis was normal in animals with non-inflammatory demyelinating lesions and elevated in dogs with inflammatory myelin lesions. Specific antibodies against CDV and myelin were quantitated in CSF and serum from 8 dogs with an elevated IgG index. Eight of these dogs had significant amounts of antimyelin antibody and 4 dogs had neutralizing anti-CDV antibody in the CSF. Whereas the pathogenetic significance of antimyelin antibodies remains uncertain, the intrathecal antiviral immune response provides a plausible explanation for immunopathologic destruction of myelin in distemper.

Canine distemper virus clearance in chronic inflammatory demyelination

The distribution of canine distemper virus (CDV) antigen was examined in the brains of 14 dogs with chronic nervous distemper using a monoclonal antibody against a major viral protein. In ten of these dogs, neutralizing anti-CDV antibody titers were determined in serum and unconcentrated cerebrospinal fluid (CSF). In 19% of the inflammatory demyelinating lesions, large amounts of CDV antigen were found; in 34% of these lesions only residual traces of virus were seen and in almost half of the lesions (47%) no CDV could be demonstrated. In four dogs neutralizing antibodies were found in the serum only; in one dog in the CSF only and in 5 dogs both in serum and CSF. Because of the correlation between the presence of inflammation, intrathecal antiviral antibodies and disappearance of CDV from the lesions, it was concluded that the inflammatory response in distemper is associated with viral clearance from the lesions. Associated immune-mediated cytotoxic reactions could explain exacerbation of the initial virus-induced demyelinating lesions. Despite the presence of an apparently effective intrathecal antiviral immune response, fresh non-inflammatory lesions as a result of viral replication and spread in the white matter coexisted with inflammatory ones in which viral clearance had taken place. The role and mechanism of such virus persistence are discussed.

Canine distemper virus does not infect oligodendrocytes in vitro

Dissociated canine brain cell cultures were infected with virulent canine distemper virus (CDV). Double immunofluorescent labelling was done to simultaneously demonstrate viral antigen and specific glial cell markers. Virus containing oligodendrocytes were not found at any stage of the infection. A certain proportion of the infected cells were shown to be astrocytes. It was concluded that CDV has no obvious tropism for oligodendrocytes which could explain the mechanism of demyelination in distemper in vivo.

Viruses and demyelinating disease of the central nervous system

In MS, there are many mechanisms by which viruses can produce demyelinating diseases in humans and experimental demyelinating infections in animals.

Spread and distribution of viral antigen in nervous canine distemper

Canine distemper virus (CDV) antigen was demonstrated immunocytochemically in the central nervous system (CNS) of 19 dogs killed from 16 to 170 days after infection. In the earliest lesions, infection of glial cells preceded demyelination, and the degree of myelin destruction correlated with the amount of viral antigen in the tissue. It was concluded that initial demyelination in distemper is directly viral-induced, but the nature of the infected glial cells remains uncertain. Ependymal infection and spread of virus in the subependymal white matter was often seen, suggesting invasion of CDV into the CNS along the CSF pathways. Inflammation during the latter stages of the infection appeared to be associated with viral clearance from the CNS in most dogs. In two dogs with chronic progressive neurologic distemper, viral antigen was still present in the brain suggesting that viral persistence and associated immunologic reactions may contribute to further myelin damage. With the exception of one dog that survived for 6 months after infection, viral antigen was no longer detected in the dogs that had recovered.

A leukoencephalomyelopathy of rottweiler dogs

Two adult rottweiler dogs were evaluated for slowly progressive ataxia and paresis of all four limbs of over seven months duration. On neurologic examination, signs referable to a lesion in the cervical spinal cord affecting motor and sensory white matter tracts were found. Both dogs were necropsied and were found to have demyelinating lesions in the spinal cord, brain stem, and deep cerebellar white matter. Primary morphologic alterations were intact naked axons and thinly myelinated axons accompanied by reactive astrogliosis. The spinal cord lesions tended to have bilateral symmetry and were found in the lateral funiculi and occasionally in the dorsal funiculi. The cause and pathogenesis of the lesion were not determined.