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

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.

Phenotypic and Transcriptional Changes of Pulmonary Immune Responses in Dogs Following Canine Distemper Virus Infection

Canine distemper virus (CDV), a morbillivirus within the family Paramyxoviridae, is a highly contagious infectious agent causing a multisystemic, devastating disease in a broad range of host species, characterized by severe immunosuppression, encephalitis and pneumonia. The present study aimed at investigating pulmonary immune responses of CDV-infected dogs in situ using immunohistochemistry and whole transcriptome analyses by bulk RNA sequencing. Spatiotemporal analysis of phenotypic changes revealed pulmonary immune responses primarily driven by MHC-II⁺, Iba-1⁺ and CD204⁺ innate immune cells during acute and subacute infection phases, which paralleled pathologic lesion development and coincided with high viral loads in CDV-infected lungs. CD20⁺ B cell numbers initially declined, followed by lymphoid repopulation in the advanced disease phase. Transcriptome analysis demonstrated an increased expression of transcripts related to innate immunity, antiviral defense mechanisms, type I interferon responses and regulation of cell death in the lung of CDV-infected dogs. Molecular analyses also revealed disturbed cytokine responses with a pro-inflammatory M1 macrophage polarization and impaired mucociliary defense in CDV-infected lungs. The exploratory study provides detailed data on CDV-related pulmonary immune responses, expanding the list of immunologic parameters potentially leading to viral elimination and virus-induced pulmonary immunopathology in canine distemper.

Pathogen Screening for Possible Causes of Meningitis/Encephalitis in Wild Carnivores From Saxony-Anhalt

Inflammation in meninges and/or brain is regularly noticed in red foxes and other wild carnivores during rabies control programs. Despite negative rabies virus (RABV) results, the etiologies of these cases remain unknown. Thus, the aim of this study was to provide an overview of the occurrence of pathogens that may cause diseases in the brains of wild carnivores and pose a risk to humans and other animals. In addition to RABV and canine distemper virus (CDV), a variety of pathogens, including members of Flaviviridae, Bornaviridae, Herpesviridae, Circoviridae, as well as bacteria and parasites can also cause brain lesions. In 2016 and 2017, brain samples of 1,124 wild carnivores were examined by direct fluorescent antibody test for RABV as well as (reverse-transcriptase) quantitative polymerase chain reaction (PCR) for the presence of CDV as part of a monitoring program in Saxony-Anhalt, Germany. Here, we applied similar methods to specifically detect suid herpesvirus 1 (SuHV-1), West Nile virus (WNV), Borna disease virus 1 (BoDV-1), canid alphaherpesvirus 1 (CaHV-1), canine parvovirus type 2 (CPV-2), fox circovirus (FoxCV), and Neospora caninum (N. caninum). Further, bacteriogical examination for the existence of Listeria monocytogenes (L. monocytogenes) and immunohistochemistry of selected cases to detect Toxoplasma gondii (T. gondii) antigen were performed. Of all pathogens studied, CDV was found most frequently (31.05%), followed by FoxCV (6.80%), CPV-2 (6.41%), T. gondii (4/15; 26.67%), nematode larvae (1.51%), L. monocytogenes (0.3%), and various other bacterial pathogens (1.42%). In 68 of these cases (6.05%), multiple pathogen combinations were present simultaneously. However, RABV, WNV, BoDV-1, SuHV-1, CaHV-1, and N. caninum were not detected. The majority of the histopathological changes in 440 animals were inflammation (320/440; 72.73%), predominantly non-suppurative in character (280/320; 87.50%), and in many cases in combination with gliosis, satellitosis, neuronophagia, neuronal necrosis, and/or vacuolization/demyelination, or in single cases with malacia. Thus, it could be shown that wild carnivores in Saxony-Anhalt are carriers mainly for CDV and sometimes also for other, partly zoonotic pathogens. Therefore, the existing monitoring program should be expanded to assess the spill-over risk from wild carnivores to humans and other animals and to demonstrate the role of wild carnivores in the epidemiology of these zoonotic pathogens.

Canine distemper virus increased the differentiation of CD4+CD8+ T cells and mRNA expression of inflammatory cytokines in peripheral blood lymphocyte from canine

BACKGROUND

Canine distemper virus (CDV) can cause a highly contagious disease to canid. However, how CDV affects peripheral blood lymphocyte (PBL) remains unclear.

METHODS

In this study, CDV infected PBL was cultured to investigate the effect of CDV on the differentiation of lymphocytes and the mRNA expression of inflammatory cytokines in PBL.

RESULTS

The results showed that CDV changed the phenotype of lymphocytes and increased the percentage of CD4⁺CD8⁺ T cells. To explore the effect of immune response of lymphocytes to CDV, the mRNA expression of pro- and anti-inflammatory cytokines was examined. Interleukin (IL-6, IL-12B), and tumor necrosis factor (TNF)-α mRNA expression was significantly increased at 12-48 h after CDV infection. IL-10 mRNA expression was dramatically enhanced at 12-36 h after CDV infection. However, IL-4 and transforming growth factor (TGF-β) were not response to CDV infection. These results indicated that PBL differentiated intoCD4⁺CD8⁺ T cells and improved the inflammatory response to CDV infection.

CONCLUSIONS

After CDV infection, PBL differentiated into CD4⁺CD8⁺ T cells and initiated inflammatory response.

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.

Comparative Immunopathology of Cetacean morbillivirus Infection in Free-Ranging Dolphins From Western Mediterranean, Northeast-Central, and Southwestern Atlantic

Cetacean morbillivirus (CeMV; Paramyxoviridae) causes epizootic and interepizootic fatalities in odontocetes and mysticetes worldwide. Studies suggest there is different species-specific susceptibility to CeMV infection, with striped dolphins (Stenella coeruleoalba), bottlenose dolphins (Tursiops truncatus), and Guiana dolphins (Sotalia guianensis) ranking among the most susceptible cetacean hosts. The pathogenesis of CeMV infection is not fully resolved. Since no previous studies have evaluated the organ-specific immunopathogenetic features of CeMV infection in tissues from infected dolphins, this study was aimed at characterizing and comparing immunophenotypic profiles of local immune responses in lymphoid organs (lymph nodes, spleen), lung and CNS in CeMV-molecularly (RT-PCR)-positive cetaceans from Western Mediterranean, Northeast-Central, and Southwestern Atlantic. Immunohistochemical (IHC) analyses targeted molecules of immunologic interest: caspase 3, CD3, CD20, CD57, CD68, FoxP3, MHCII, Iba1, IFNγ, IgG, IL4, IL10, lysozyme, TGFβ, and PAX5. We detected consistent CeMV-associated inflammatory response patterns. Within CNS, inflammation was dominated by CD3⁺ (T cells), and CD20⁺ and PAX5⁺ (B cells) lymphocytes, accompanied by fewer Iba1⁺, CD68⁺, and lysozyme⁺ histiocytes, mainly in striped dolphins and bottlenose dolphins. Multicentric lymphoid depletion was characterized by reduced numbers of T cells and B cells, more pronounced in Guiana dolphins. Striped dolphins and bottlenose dolphins often had hyperplastic (regenerative) phenomena involving the aforementioned cell populations, particularly chronically infected animals. In the lung, there was mild to moderate increase in T cells, B cells, and histiocytes. Additionally, there was a generalized increased expression of caspase 3 in lymphoid, lung, and CNS tissues. Apoptosis, therefore, is believed to play a major role in generalized lymphoid depletion and likely overt immunosuppression during CeMV infection. No differences were detected regarding cytokine immunoreactivity in lymph nodes, spleen, and lung from infected and non-infected dolphins by semiquantitative analysis; however, there was striking immunoreactivity for IFNγ in the CNS of infected dolphins. These novel results set the basis for tissue-specific immunophenotypic responses during CeMV infection in three highly susceptible delphinid species. They also suggest a complex interplay between viral and host's immune factors, thereby contributing to gain valuable insights into similarities, and differences of CeMV infection's immunopathogenesis in relation to body tissues, CeMV strains, and cetacean hosts.

Morbillivirus Experimental Animal Models: Measles Virus Pathogenesis Insights from Canine Distemper Virus

Morbilliviruses share considerable structural and functional similarities. Even though disease severity varies among the respective host species, the underlying pathogenesis and the clinical signs are comparable. Thus, insights gained with one morbillivirus often apply to the other members of the genus. Since the Canine distemper virus (CDV) causes severe and often lethal disease in dogs and ferrets, it is an attractive model to characterize morbillivirus pathogenesis mechanisms and to evaluate the efficacy of new prophylactic and therapeutic approaches. This review compares the cellular tropism, pathogenesis, mechanisms of persistence and immunosuppression of the Measles virus (MeV) and CDV. It then summarizes the contributions made by studies on the CDV in dogs and ferrets to our understanding of MeV pathogenesis and to vaccine and drugs development.

Diversified Anchoring Features the Peptide Presentation of DLA-88*50801: First Structural Insight into Domestic Dog MHC Class I

Canines represent a crucial animal model for studying human diseases and organ transplantation, as well as the evolution of domestic animals. MHCs, with a central role in cellular immunity, are commonly used in the study of dog population genetics and genome evolution. However, the molecular basis for the peptide presentation of dog MHC remains largely unknown. In this study, peptide presentation by canine MHC class I DLA-88*50801 was structurally determined, revealing diversified anchoring modes of the binding peptides. Flexible and large pockets composed of both hydrophobic and hydrophilic residues can accommodate pathogen-derived peptides with diverse anchor residues, as confirmed by thermostability measurements. Furthermore, DLA-88*50801 contains an unusual α2 helix with a large coil in the TCR contact region. These results further our understanding of canine T cell immunity through peptide presentation of MHC class I and shed light on the molecular basis for vaccine development for canine infectious diseases, for example, canine distemper virus.

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.

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”.

Dynamic changes of Foxp3(+) regulatory T cells in spleen and brain of canine distemper virus-infected dogs

Canine distemper virus (CDV) infection causes immunosuppression and demyelinating leukoencephalitis in dogs. In viral diseases, an ambiguous function of regulatory T cells (Treg), with both beneficial effects by reducing immunopathology and detrimental effects by inhibiting antiviral immunity, has been described. However, the role of Treg in the pathogenesis of canine distemper remains unknown. In order to determine the effect of CDV upon immune homeostasis, the amount of Foxp3(+) Treg in spleen and brain of naturally infected dogs has been determined by immunohistochemistry. In addition, splenic cytokine expression has been quantified by reverse transcriptase polymerase chain reaction. Splenic depletion of Foxp3(+) Treg was associated with an increased mRNA-expression of tumor necrosis factor and decreased transcription of interleukin-2 in the acute disease phase, indicative of disturbed immunological counter regulation in peripheral lymphoid organs. In the brain, a lack of Foxp3(+) Treg in predemyelinating and early demyelinating lesions and significantly increased infiltrations of Foxp3(+) Treg in chronic demyelinating lesions were observed. In conclusion, disturbed peripheral and CNS immune regulation associated with a reduction of Treg represents a potential prerequisite for excessive neuroinflammation and early lesion development in canine distemper leukoencephalitis.

Zymographic patterns of MMP-2 and MMP-9 in the CSF and cerebellum of dogs with subacute distemper leukoencephalitis

Distemper leukoencephalitis is a disease caused by the canine distemper virus (CDV) infection. It is a demyelinating disease affecting mainly the white matter of the cerebellum and areas adjacent to the fourth ventricle; the enzymes of the matrix metalloproteinases (MMPs) group, especially MMP-2 and MMP-9 have a key role in the myelin basic protein fragmentation and in demyelination, as well as in leukocyte traffic into the nervous milieu. To evaluate the involvement of MMPs during subacute distemper leukoencephalitis, we measured the levels of MMP-2 and MMP-9 by zymography in the cerebrospinal fluid (CSF) and in the cerebellum of 14 dogs naturally infected with CDV and 10 uninfected dogs. The infected dogs presented high levels of pro-MMP-2 in the CSF and elevated levels of pro-MMP-2 and pro-MMP-9 in the cerebellar tissue. Active MMP-2 was detected in the CSF of some infected dogs. As active MMP-2 and MMP-9 are required for cellular migration across the blood-brain barrier and any interference between MMPs and their inhibitors may result in an amplification of demyelination, this study gives additional support to the involvement of MMPs during subacute distemper leukoencephalitis and suggests that MMP-2 and MMP-9 may take part in the brain inflammatory changes of this disease.

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.

The role of pro- and anti-inflammatory cytokines in the pathogenesis of spontaneous canine CNS diseases

Dogs are comparatively frequently affected by various spontaneously occurring inflammatory and degenerative central nervous system (CNS) conditions, and immunopathological processes are a hallmark of the associated neuropathology. Due to the low regenerative capacity of the CNS a sophisticated understanding of the underlying molecular basis for disease initiation, progression and remission in canine CNS diseases represents a prerequisite for the development of novel therapeutical approaches. In addition, as many spontaneous canine CNS diseases share striking similarities with their human counterpart, knowledge about the immune pathogenesis may in part be translated for a better understanding of certain human diseases. In addition to cytokine-driven differentiation of peripheral leukocytes including different subsets of T cells recent research suggests a pivotal role of these mediators also in phenotype polarization of resident glial cells. Cytokines thus represent the key mediators of the local and systemic immune response in CNS diseases and their orchestration significantly decides on either lesion progression or remission. The aim of the present review is to summarize the growing number of data focusing on the molecular basis of the immune response during spontaneous canine CNS diseases and to detail the effect of cytokines on the immune pathogenesis of selected idiopathic, infectious, and traumatic canine CNS diseases. Steroid-responsive meningitis arteritis (SRMA) represents a unique idiopathic disease of leptomeningeal blood vessels characterized by excessive IgA secretion into the cerebrospinal fluid. Recent reports have given sophisticated insights into the cytokine-driven, immune-mediated pathogenesis of SRMA that is characterized by a biased T helper 2 cell response. Canine distemper associated leukoencephalitis represents an important spontaneously occurring disease that allows investigations on the basic pathogenesis of immune-mediated myelin loss. It is characterized by an early virus-induced up-regulation of pro-inflammatory cytokines with chronic bystander immune-mediated demyelinating processes. Lastly, canine spinal cord injury (SCI) shares many similarities with the human counterpart and most commonly results from intervertebral disk disease. The knowledge of its pathogenesis is largely restricted to experimental studies in rodents, and the impact of immune processes that accompany secondary injury is discussed controversially. Recent investigations on canine SCI highlight the pivotal role of pro-inflammatory cytokine expression that is paralleled by a dominating reaction of microglia/macrophages potentially indicating a polarization of these immune cells into a neurotoxic and harmful phenotype. This report will review the role of cytokines in the immune processes of the mentioned representative canine CNS diseases and highlight the importance of cytokine/cytokine interaction as a useful therapeutic target in canine CNS diseases.

Increased p75 neurotrophin receptor expression in the canine distemper virus model of multiple sclerosis identifies aldynoglial Schwann cells that emerge in response to axonal damage

Gliogenesis under pathophysiological conditions is of particular clinical relevance since it may provide regeneration-promoting cells recruitable for therapeutic purposes. There is accumulating evidence that aldynoglial cells with Schwann cell-like growth-promoting properties emerge in the lesioned CNS. However, the characterization of these cells and the signals triggering their in situ generation have remained enigmatic. In the present study, we used the p75 neurotrophin receptor (p75(NTR) ) as a marker for Schwann cells to study gliogenesis in the well-defined canine distemper virus (CDV)-induced demyelination model. White matter lesions of CDV-infected dogs contained bi- to multipolar, p75(NTR) -expressing cells that neither expressed MBP, GFAP, BS-1, or P0 identifying oligodendroglia, astrocytes, microglia, and myelinating Schwann cells nor CDV antigen. Interestingly, p75(NTR) -expression became apparent prior to the onset of demyelination in parallel to the expression of β-amyloid precursor protein (β-APP), nonphosphorylated neurofilament (n-NF), BS-1, and CD3, and peaked in subacute lesions with inflammation. To study the role of infiltrating immune cells during differentiation of Schwann cell-like glia, organotypic slice cultures from the normal olfactory bulb were established. Despite the absence of infiltrating lymphocytes and macrophages, a massive appearance of p75(NTR) -positive Schwann-like cells and BS-1-positive microglia was noticed at 10 days in vitro. It is concluded that axonal damage as an early signal triggers the differentiation of tissue-resident precursor cells into p75(NTR) -expressing aldynoglial Schwann cells that retain an immature pre-myelin state. Further studies have to address the role of microglia during this process and the regenerative potential of aldynoglial cells in CDV infection and other demyelinating diseases.

Immunohistochemical characterization of selected cell markers for the detection of hematopoietic cells in formalin-fixed, paraffin wax-embedded lymphoid tissues of harbor seals (Phoca vitulina) and walruses (Odobenus rosmarus rosmarus)

To facilitate a detailed investigation of pinniped lymphoid organs, 30 monoclonal antibodies (mAb) as well as eight polyclonal antibodies (pAb) of different species specificities directed against cell antigens of the hematopoietic system were tested for immunohistochemical cross-reactivity on formalin-fixed, paraffin wax-embedded tissues of harbor seals (Phoca vitulina) and a walrus (Odobenus rosmarus rosmarus). Six monoclonal and eight polyclonal antibodies showed specific immunoreactivities. Lymphocytes were immunolabeled by an anti-CD3 pAb, anti-Foxp3 mAb and anti-CD79 alpha mAb, while plasma cell subpopulations were recognized by anti-IgA pAb, anti-IgG pAb and anti-IgM pAb as well as by anti-kappa- and anti-lambda light chain pAb. Cells of the histiocytic lineage were recognized by lysozyme-, myeloid/histiocyte antigen-, and CD68-specific markers. Furthermore, dendritic cell-like cells were detected by an anti-S100 protein pAb. The MHC class II antigen was labeled on the majority of immune cells of the harbor seal and walrus using a bovine mAb. Mast cells were stained by an anti-mast cell tryptase mAb. Thus, using these antibodies from various species, it is now possible to determine phenotypical changes in lymphoid organs and detect different leukocyte subsets involved in inflammatory responses in archived tissue samples of these pinniped species.

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.

Acute canine distemper encephalitis is associated with rapid neuronal loss and local immune activation

For most virus infections of the central nervous system (CNS), immune-mediated damage, the route of inoculation and death of infected cells all contribute to the pathology observed. To investigate the role of these factors in early canine distemper neuropathogenesis, we infected ferrets either intranasally or intraperitoneally with the neurovirulent canine distemper virus strain Snyder Hill. Regardless of the route of inoculation, the virus primarily targeted the olfactory bulb, brainstem, hippocampus and cerebellum, whereas only occasional foci were detected in the cortex. The infection led to widespread neuronal loss, which correlated with the clinical signs observed. Increased numbers of activated microglia, reactive gliosis and different pro-inflammatory cytokines were detected in the infected areas, suggesting that the presence and ultimate death of infected cells at early times after infection trigger strong local immune activation, despite the observed systemic immunosuppression.

Axonal pathology and loss precede demyelination and accompany chronic lesions in a spontaneously occurring animal model of multiple sclerosis

Axonal damage has been highlighted recently as a cause of neurological disability in various demyelinating diseases, including multiple sclerosis, either as a primary pathological change or secondary due to myelin loss. To characterize and quantify axonal damage and loss in canine distemper demyelinating leukoencephalomyelitis (DL), formalin-fixed paraffin-embedded cerebella were investigated histochemically and immunohistochemically using the modified Bielschowsky's silver stain as well as antibodies against nonphosphorylated (n-NF), phosphorylated neurofilament (p-NF) and beta-amyloid precursor protein (beta-APP). Injured axons characterized by immunoreactivity against n-NF and beta-APP were detected in early distemper lesions without demyelination. In subacute and chronic demyelinating lesions the number of injured axons increased. Moreover, a significant decrease in axonal density was observed within lesions and in the normal appearing white matter in DL as determined by morphometric analyses using Bielschowsky's silver stain and p-NF immunohistochemistry. Summarized, the observed findings indicate that axonal damage (i) occurs early in DL; (ii) can be detected before myelin loss; and (iii) represents a pivotal feature in advanced lesions. It must be postulated that axonal damage plays an important role in the initial phase as a primary event and during progression of nervous distemper as a result of demyelination.

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.

In vitro characterization and preferential infection by canine distemper virus of glial precursors with Schwann cell characteristics from adult canine brain

AIMS

Canine distemper virus (CDV)-induced demyelinating leukoencephalomyelitis is a naturally occurring model for multiple sclerosis. The aim of this study was to establish primary glial cell cultures from adult canine brain for the analysis of CDV spread and cell tropism.

METHODS

Cultures were inoculated with the CDV-R252 and a CDV-Onderstepoort strain expressing the green fluorescent protein (CDV-OndeGFP). CDV antigen expression was studied using cell type-specific antibodies at different days post infection. Glial cells expressing p75(NTR) were purified using antibody-based techniques and characterized with regard to antigen expression and proliferation.

RESULTS

Three weeks after seeding, cultures contained spindle-shaped cells expressing p75(NTR), oligodendrocytic cells, astrocytes, microglia and fibroblasts. Both CDV strains induced a mild to moderate cytopathic effect that consisted of single necrotic and few syncytial giant cells, but displayed in part a differential cell tropism. Whereas CDV-OndeGFP expression in microglia and astrocytes did not exceed 1% and 50%, respectively, CDV-R252 infected 100% and 80% of both cell types, respectively. The cells most early infected by both CDV strains expressed p75(NTR) and may correlate to cells previously identified as aldynoglia. Treatment of p75(NTR+) cells with Schwann cell mitogens and serum deprivation increased proliferation and A2B5 expression, respectively, indicating common properties compared with Schwann cells and oligodendrocyte precursors.

CONCLUSIONS

Infection of adult canine astrocytes and microglia revealed CDV strain-specific cell tropism. Moreover, this is the first identification of a glial cell type with Schwann cell-like properties in adult canine brain and, more importantly, these cells displayed a high susceptibility to CDV infection.

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.

Vimentin-positive astrocytes in canine distemper: a target for canine distemper virus especially in chronic demyelinating lesions?

In canine distemper demyelinating leukoencephalitis (DL), caused by canine distemper virus (CDV), astrocytes represent the main virus target. In these cells, glial fibrillary acidic protein (GFAP) is the main intermediate filament, whereas vimentin occurs early in the astrocytic lineage and is replaced gradually by GFAP. To further characterize the role of astrocytic infection in dogs with DL, an animal model for multiple sclerosis, formalin-fixed paraffin-embedded cerebella were investigated immunohistochemically and by immunofluorescence. The expression and morphological alterations of these intermediate filaments were also determined by immunofluorescence studies of CDV-infected canine mixed brain cell cultures. In acute distemper lesions, the astrocytic response was mainly composed of GFAP- and CDV-positive cells. In contrast, vimentin-positive astrocyte-like cells were present in advanced lesions, which represented the main cell type harboring the pathogen, indicating a change in cell tropism and/or susceptibility of glial cells during lesion progression in CDV encephalomyelitis. Canine cell cultures were composed of GFAP-positive astrocytes, vimentin-positive cells and other glial cells. Following infection with the CDV-R252 strain, GFAP-positive astrocytes, especially multinucleated syncytial giant cells, displayed a disrupted cytoskeleton, whereas vimentin-positive cells though more frequently infected did not show any alteration in the filament network. This indicates increased vulnerability of mature GFAP-positive astrocytes compared to immature, vimentin-positive astrocytes. The latter, however, exhibited increased susceptibility to CDV. To conclude, the present findings indicate a change in cell tropism of CDV and/or the occurrence of less differentiated astrocytes representing a permanent source for virus infection and spread in advanced lesions of DL.

Induction of activator protein-1 and nuclear factor-kappaB as a prerequisite for disease development in susceptible SJL/J mice after theiler murine encephalomyelitis

Theiler murine encephalomyelitis (TME) represents an important mouse model of multiple sclerosis. Activator protein and nuclear factor-kappaB proteins are interacting transcription factors controlling the expression of cytokines involved in the demyelination process. However, specific expression patterns of these transcription factors in susceptible and resistant mouse strains and their relationship to demyelination remains to be determined. The expression of activator protein-1 (c-fos and c-jun) and nuclear factor-kappaB (p50 and p65) genes, TME virus, tumor necrosis factor-alpha, and interferon-gamma was investigated in the spinal cord of TME virus (BeAn strain)-infected SJL/J and C57BL/6 mice until 196 days postinfection (dpi) using reverse transcription-quantitative polymerase chain reaction. Additionally, c-fos, c-jun, and p50 expression was examined by applying immunohistochemistry. In susceptible SJL/J mice, in contrast to resistant C57BL/6 mice, all investigated mRNA transcripts were upregulated in the early (0-7 days dpi) and late phases (28-196 days dpi) of TME. In addition, white matter lesions of SL/J mice were characterized by c-jun-positive astrocytes and p50-positive mononuclear immune cells. Upregulation of activator protein-1 and nuclear factor-kappaB in resident glial cells in the early phase followed by strong downstream tumor necrosis factor-alpha production might account for disease development in susceptible SJL/J mice. In the late phase, the formation of JUN/JUN homodimers in intralesional astrocytes might contribute to the sustained release of proinflammatory cytokines, thereby promoting disease progression.

Simultaneous canine distemper virus, canine adenovirus type 2, and Mycoplasma cynos infection in a dog with pneumonia

The present case is the first description of a triple infection with canine distemper virus (CDV), canine adenovirus (CAV) type 2, and Mycoplasma cynos in a dog. The 5-month-old female Miniature Pinscher was euthanized because of dyspnea, croaking lung sounds, weight loss, and lymphopenia. Pathologic examination revealed a fibrinous necrotizing pneumonia with large amphophilic intranuclear and acidophilic intracytoplasmatic inclusion bodies in different lung cells. Immunohistochemically, CDV antigen was present in lung and many other organs. In situ hybridization for detection of CAV nucleic acid showed positive signals in the lung only. Polymerase chain reaction of lung tissue and consecutive sequencing of the amplification product identified CAV type 2. Bacteriologic examination of lung tissue yielded large amounts of M cynos. This infection was confirmed by immunohistochemistry detecting abundant positive signals in the lung tissue.

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.

Ets-1 represents a pivotal transcription factor for viral clearance, inflammation, and demyelination in a mouse model of multiple sclerosis

Demyelination of Theiler's murine encephalomyelitis (TME) depends on viral persistence and on the mouse genotype. Ets-1 expression, a transcription factor involved in T cell activation and cytokine expression, was investigated in the spinal cord during TME using RT-qPCR and immunohistochemistry. Resistant C57BL/6 mice lacking virus persistence and demyelination demonstrated a stronger upregulation of Ets-1 mRNA transcripts in the early phase of TME compared to susceptible SJL/J mice probably linked to viral clearance. Though strong Ets-1 expression in resident glial cells such as astrocytes might inhibit lesion development, delayed Ets-1 activation in inflammatory cells seemed to promote demyelination in the late phase of TME in SJL/J mice.

Non-suppurative meningoencephalitis of unknown origin in cats and dogs: an immunohistochemical study

Non-suppurative meningoencephalitis of unknown cause is a frequent finding in dogs and cats. Fifty-three dogs and 33 cats with non-suppurative meningoencephalitis of unknown aetiology were examined immunohistochemically for 18 different infectious agents, including viruses, bacteria and prion protein^Sc. In 14 (26%) of the dogs and 13 (39%) of the cats a causative agent was identified in the central nervous system (CNS), two dogs and one cat giving positive results for two infectious agents simultaneously. The study revealed infections with known causative agents (porcine herpes virus 1, feline infectious peritonitis virus, Escherichia coli) and a new disease pattern of parvovirus infection in the CNS of dogs and cats. Infection of the CNS with feline leukaemia virus was found in a cat. Five dogs and four cats gave positive results for West Nile virus (WNV) antigen. In one dog, canine parainfluenza virus antigen was detected in the brain. Four dogs and four cats gave positive results for encephalomyocarditis virus (EMCV). The significance of the detection of WNV and EMCV antigen requires further study. The aetiology remained undetermined in 39 dogs (74%) and 20 cats (61%). Although it is possible that non-infectious causes play a more important role than previously thought, infections with hitherto unrecognized agents cannot be ruled out.

Canine distemper virus uses both the anterograde and the hematogenous pathway for neuroinvasion

Canine distemper virus (CDV), a member of the Morbillivirus genus that also includes measles virus, frequently causes neurologic complications, but the routes and timing of CDV invasion of the central nervous system (CNS) are poorly understood. To characterize these events, we cloned and sequenced the genome of a neurovirulent CDV (strain A75/17) and produced an infectious cDNA that expresses the green fluorescent protein. This virus fully retained its virulence in ferrets: the course and signs of disease were equivalent to those of the parental isolate. We observed CNS invasion through two distinct pathways: anterogradely via the olfactory nerve and hematogenously through the choroid plexus and cerebral blood vessels. CNS invasion only occurred after massive infection of the lymphatic system and spread to the epithelial cells throughout the body. While at early time points, mostly immune and endothelial cells were infected, the virus later spread to glial cells and neurons. Together, the results suggest similarities in the timing, target cells, and CNS invasion routes of CDV, members of the Morbillivirus genus, and even other neurovirulent paramyxoviruses like Nipah and mumps viruses.

The regression of a canine Langerhans cell tumour is associated with increased expression of IL-2, TNF-alpha, IFN-gamma and iNOS mRNA

Canine cutaneous histiocytoma is a benign epidermal neoplasm of Langerhans cell origin, which usually displays spontaneous regression. Based on the degree of lymphocytic infiltration, 30 histiocytomas were classified into four groups representing different stages of tumour regression. To elucidate further the mechanisms of the antitumour immune response CD3+, CD21+, CD4+, CD8+ and myeloid/histiocyte antigen+ inflammatory cells were differentiated by immunohistochemistry and quantified. In addition, the number of apoptotic cells was detected using the TdT-mediated biotin-dUTP nick-end labelling (TUNEL) method. Furthermore, the expression of interleukin- (IL-2), IL-12(p40), tumour necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), IL-10 and transforming growth factor-beta (TGF-beta) as well as inducible nitric oxid synthase (iNOS) mRNA was determined by reverse transcription-polymerase chain reaction (RT-PCR). Phenotyping of inflammatory cells revealed a significantly increased infiltration of all lymphocyte subsets and myeloid/histiocytic cells with the onset of tumour regression. The latter was significantly correlated to up-regulation of IL-2, TNF-alpha, IFN-gamma and iNOS mRNA expression. Expression of remaining cytokines and percentage of apoptotic cells showed no group-specific changes. The results indicate an initial infiltration of CD4+ T cells followed by increased expression of Th1 cytokines and recruitment of antitumour effector cells as the principal mechanism for tumour regression. Canine cutaneous histiocytoma is a unique example for an effective immune response in a naturally occurring neoplasm derived from epidermal Langerhans cells and might represent a valuable animal model to investigate tumour immunity.

Up-regulation of mRNA for matrix metalloproteinases-9 and -14 in advanced lesions of demyelinating canine distemper leukoencephalitis

Matrix metalloproteinases (MMPs) comprise a family of proteolytic zinc- and calcium-dependent enzymes that are capable of disrupting the blood-brain barrier and mediating the destruction of extracellular matrix and myelin components. MMPs are also involved in facilitating leukocyte migration into inflammatory sites of the central nervous system. To determine the cellular localization and the amount of mRNA for MMP-9, MMP-14 and a tissue inhibitor of metalloproteinases (TIMP-1) in dogs with spontaneous demyelinating distemper encephalitis, formalin-fixed paraffin-embedded cerebella were investigated by in situ hybridization using specific digoxigenin-labeled RNA probes. Additionally, immunohistochemistry was performed to characterize the different types of plaques of demyelinating leukoencephalitis. Furthermore, virus antigen and mRNA were detected by immunohistochemistry and in situ hybridization. Healthy control dogs revealed a weak signal for mRNA for MMP-9, MMP-14, and TIMP-1 in various numbers of neurons, astrocytes, microglial cells and oligodendrocytes. In the cerebella of dogs with distemper, a strong increase of both number and staining intensity of MMP-9, MMP-14, and TIMP-1 mRNA-expressing cells, mainly in subacute inflammatory lesions and chronic plaques, was observed. The number of cells expressing mRNA for MMP-9 and MMP-14 increased about two- to threefold compared to TIMP-1 mRNA-expressing cells, whereas staining intensity of individual cells was similar. In early lesions, especially astrocytes and activated macrophages/microglial cells displayed a positive signal for MMPs and TIMP-1, whereas in older lesions activated microglia/macrophages and infiltrating lymphocytes represented the main source for MMP-9, MMP-14, and TIMP-1 mRNA synthesis as revealed by double-labeling techniques. In summary, the proportionally higher increase of MMP mRNA-expressing cells might indicate an MMP/TIMP imbalance as a cause for lesion initiation and progression in demyelinating canine distemper leukoencephalitis.

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.

Immunohistochemical Detection of CD4-, CD8- and MHC II-Expressing Immune Cells and Endoglin in the Canine Corpus Luteum at Different Stages of Dioestrus

Specific immunohistochemical methods were applied to detect the presence of CD4-, CD8- and major histocompatibility complex II (MHC II)-expressing immune cells and of endoglin in the canine corpus luteum between days 15 and 75, after ovulation. Corpora lutea were obtained from groups of three clinically healthy beagle bitches, ovariohysterectomized at the respective days. For all four parameters, the effect of time was highly significant. Quantitative evaluation yielded high values on day 15, followed by a decrease on day 30 (CD4, CD8 and endoglin) and day 45 (MHC II). While there were no further changes for cells staining positive for CD4 and endoglin, CD8-positive immune cells increased from day 45 to day 60 to drop again on day 75; MHC II-positive staining increased from day 45 to days 60-75. These data suggest an involvement of the immune system in control of luteal function also in the dog that may have both stimulatory and inhibiting effects.

Large granular lymphocytosis, lymphocyte subset inversion, thrombocytopenia, dysproteinemia, and positive Ehrlichia serology in a dog

A 7-year-old, mixed-breed dog was presented for evaluation of a possible lymphocytic leukemia. Results of laboratory testing included thrombocytopenia, large granular lymphocytosis, inverted CD4:CD8 ratio, hyperglobulinemia, and hypoalbuminemia. Results of a tick-borne disease panel indicated a positive immunoglobulin G serum titer (1:2,048) to Ehrlichia canis, supporting exposure to this organism. The dog responded to a combination treatment of doxycycline and prednisone. A review of the literature and novel diagnostic methods that aided in the diagnosis of this case are discussed.

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.

Immunohistochemical investigation of the cross-reactivity of selected cell markers from various species for characterization of lymphatic tissues in the harbour porpoise (Phocoena phocoena)

To facilitate a detailed investigation of cetacean lymphoid organs, 13 canine-, six bovine-, one equine-, one human- and four killer whale-specific monoclonal antibodies (mAbs) directed against cell surface antigens of the haematopoietic system (including CD2, CD4, CD8, CD45R, MHC class II, granulocyte, thrombocyte, pan-T cell and B-cell antigen), as well as a mAb and a polyclonal antibody (pAb) directed against the -peptide of the human CD3 complex, were tested for immunohistochemical cross-reactivity on frozen or formalin-fixed, paraffin wax-embedded lymphatic tissues of harbour porpoises. Eight of 26 mAbs and the pAb showed a specific reaction with harbour porpoise cells. Lymphocytes in T-cell compartments were labelled by the mAb and the pAb directed against the CD3 complex and by two killer whale mAbs specific for CD2 antigen. CD45R, labelled by a killer whale-specific mAb, was strongly expressed on B and weakly on T cells. MHC class II antigen, recognized by killer whale- and bovine-specific mAbs, was expressed on B and T cells. A canine MHC class II-specific mAb recognized an epitope on the surface of antigen-presenting cells and B lymphocytes. An anti-equine-pan-leucocyte marker labelled the majority of cells in B- and T-cell compartments. Thus, with leucocyte antigen markers from various species, it is now possible to determine the phenotype of lymphocytes in normal and diseased lymphoid organs of harbour porpoises.

Disappearance of beta2-adrenergic receptors on astrocytes in canine distemper encephalitis: possible implications for the pathogenesis of multiple sclerosis

It has been reported that astrocytes in the white matter of patients with multiple sclerosis (MS) lack beta2-adrenergic receptors. This abnormality might explain why astrocytes in active MS plaques aberrantly express major histocompatibility (MHC) class II molecules, which play an important role in the immunological cascade leading to myelin destruction. Canine distemper (CD) virus primarily infects astrocytes and causes a demyelinating disease in dogs that closely resembles MS. In control dogs, including three dogs with another inflammatory disease, beta2-adrenergic receptor immunoreactivity was observed on both neurons and astrocytes. In dogs with CD encephalitis, beta2-adrenergic receptors were present on neurons, but were absent on astrocytes in acute lesions, demyelinated lesions, and normal-appearing white matter. Similar to MS, several astrocytes in demyelinated lesions expressed MHC class II. These findings suggest that MS and the demyelinating stages of CD encephalitis have a common pathogenetic factor, and that the loss of astrocytic beta2-adrenergic receptors in MS might be induced by a viral infection of astrocytes.

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.

Phenotypical characterization of T and B cell areas in lymphoid tissues of dogs with spontaneous distemper

CD3, CD4, CD5, and CD8 antigen expression of T cells and IgG expression of B cells and canine distemper virus (CDV) antigen distribution were immunohistochemically examined in lymphoid tissues (lymph node, spleen, thymus, and tonsil) of control dogs and animals with spontaneous canine distemper. In addition, CNS tissue of all animals was studied for neuropathological changes and CDV antigen distribution. Based on the degree of depletion distemper dogs were classified into two groups. Group I represented animals with moderate to marked lymphoid depletion, while group II dogs displayed mild or no depletion. CDV antigen was mainly found in lymphocytes and macrophages of group I dogs, whereas CDV expression was most prominent in dendritic cells of group II animals. In group I dogs, a marked loss of CD3, CD4, CD5, CD8, and IgG expression was noticed, hereby loss of CD4+ cells was more prominent than depletion of CD8+ cells. In the lymphoid tissues of group II animals, a significant increase in the number of T and B cells was observed compared to group I dogs. The number of CD3+, CD4+, and CD8+ cells in group II dogs was similar to the findings in controls, however, CD5 and IgG expression was mildly reduced in T and B cell areas, respectively. Additionally, in groups I and II dogs, CD3+ and CD5- T cells were detected in T cell areas. Whether this cell population represents a cell type with autoimmune reactive potential remains to be determined. Surprisingly in group II animals, viral antigen was found predominantly in dendritic cells indicating a change in the cell tropism of CDV during chronic infection and a possible mechanism of viral persistence. The two patterns of lymphoid depletions correlated to two different types of canine distemper encephalitis (CDE). Group I dogs displayed acute non-inflammatory CDE, whereas group II dogs suffered from chronic inflammatory demyelinating CDE, indicating a pathogenic relationship between lymphocytic depletion and inflammatory brain lesions in distemper.

Dominating interleukin-10 mRNA expression induction in cerebrospinal fluid cells of dogs with natural canine distemper virus induced demyelinating and non-demyelinating CNS lesions

Canine distemper virus (CDV) infection in dogs is commonly associated with demyelinating leukoencephalitis (DL). Although the mechanism of primary demyelination in distemper remains undetermined recent studies showed a direct virus-induced cytolysis in early non-inflammatory and immune-mediated mechanisms in inflammatory lesions. To further investigate the pathogenesis of this morbillivirus-induced demyelination the expression of a variety of cytokine mRNA species (interleukin (IL)-1beta, IL-2, IL-6, IL-10, IL-12, tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta1, and interferon (IFN)-gamma in cerebrospinal fluid cells of 12 dogs with CDV encephalitis was investigated employing reverse transcription-polymerase chain reaction (RT-PCR) and these findings were correlated to the type of CNS lesions. Neuropathology revealed the whole spectrum of distemper DL lesions from acute to chronic alterations, however, most plaques lacked active demyelination. Three control animals were devoid of any cytokine expression, whereas in distemper animals IL-10 transcripts were found in nine dogs with acute and chronic lesions. IL-6, TNF, and TGF mRNA was found in six, four, and three animals, respectively. IL-12 and IFN-gamma, suggestive of a TH1-like dominated immune response, were detected only in one animal with chronic lesions. Summarized, TNF and IL-6, associated with disease exacerbation, and IL-10 and TGF, indicative of remission, were often observed simultaneously in distemper DL and could not be assigned to a specific disease stage. However IL-10 mRNA remained the most frequently detected cytokine indicating a stage of inactivity in most animals investigated.