Immunosuppression by canine distemper virus: modulation of in vitro immunoglobulin synthesis, interleukin release and prostaglandin E2 production

Insights into the mechanism of Morbillivirus induced immune suppression

Viruses enter the host cell, and various strategies are employed to evade the host immune system. These include overcoming the various components of the immune system, including modulation of the physical and chemical barriers, non-specific innate response and specific adaptive immune response. Morbilliviruses impose immune modulation by utilizing various approaches including hindering antigen presentation to T-Helper (TH) cells, hematopoiesis and suppression of effector molecule activities. These viruses can also impede the early stages of T cell activation. Despite the availability of effective vaccines, morbilliviruses are still a significant threat to mankind. After infection, they also induce a state of immune suppression in the host. The molecular mechanisms employed by morbilliviruses to induce the state of immune suppression in the infected host are still being investigated. This review is an attempt to summarize insights into some of the strategies adopted by morbilliviruses to mediate immune modulation in the host.

Meningoencephalitis caused by concurrent infection with canine distemper virus and a unique Sarcocystis sp. in a gray fox

A deceased 9-wk-old male gray fox (Urocyon cinereoargenteus) with a history of decreased ambulation and diarrhea was submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory. No significant gross findings were evident on postmortem examination. Histologically, the cerebrum and brainstem had mild necrotizing meningoencephalitis with protozoal schizonts and merozoites. Additionally, glial cells contained intracytoplasmic and intranuclear viral inclusion bodies. Sections of the cerebrum were positive for canine distemper virus (CDV) and negative for Sarcocystis neurona on immunohistochemistry. Bayesian analysis revealed that this Sarcocystis sp. clustered most closely with a clade of unnamed Sarcocystis sp. found in viperid snakes, with a posterior probability of 99%. CDV likely played a significant role in the expression of clinical sarcocystosis in this gray fox.

Canine distemper virus infection leads to an inhibitory phenotype of monocyte-derived dendritic cells in vitro with reduced expression of co-stimulatory molecules and increased interleukin-10 transcription

Canine distemper virus (CDV) exhibits a profound lymphotropism that causes immunosuppression and increased susceptibility of affected dogs to opportunistic infections. Similar to human measles virus, CDV is supposed to inhibit terminal differentiation of dendritic cells (DCs), responsible for disturbed repopulation of lymphoid tissues and diminished antigen presenting function in dogs. In order to testify the hypothesis that CDV-infection leads to an impairment of professional antigen presenting cells, canine DCs have been generated from peripheral blood monocytes in vitro and infected with CDV. Virus infection was confirmed and quantified by transmission electron microscopy, CDV-specific immunofluorescence, and virus titration. Flow cytometric analyses revealed a significant down-regulation of the major histocompatibility complex class II and co-stimulatory molecules CD80 and CD86 in CDV-infected DCs, indicative of disturbed antigen presenting capacity. Molecular analyses revealed an increased expression of the immune inhibitory cytokine interleukin-10 in DCs following infection. Results of the present study demonstrate that CDV causes phenotypical changes and altered cytokine expression of DCs, which represent potential mechanisms to evade host immune responses and might contribute to immune dysfunction and virus persistence in canine distemper.

Cyclooxygenase-2-prostaglandin E2-eicosanoid receptor inflammatory axis: a key player in Kaposi's sarcoma-associated herpes virus associated malignancies

The role of cyclooxygenase-2 (COX-2), its lipid metabolite prostaglandin E2 (PGE2), and Eicosanoid (EP) receptors (EP; 1-4) underlying the proinflammatory mechanistic aspects of Burkitt's lymphoma, nasopharyngeal carcinoma, cervical cancer, prostate cancer, colon cancer, and Kaposi's sarcoma (KS) is an active area of investigation. The tumorigenic potential of COX-2 and PGE2 through EP receptors forms the mechanistic context underlying the chemotherapeutic potential of nonsteroidal anti-inflammatory drugs (NSAIDs). Although role of the COX-2 is described in several viral associated malignancies, the biological significance of the COX-2/PGE2/EP receptor inflammatory axis is extensively studied only in Kaposi's sarcoma-associated herpes virus (KSHV/HHV-8) associated malignancies such as KS, a multifocal endothelial cell tumor and primary effusion lymphoma (PEL), a B cell-proliferative disorder. The purpose of this review is to summarize the salient findings delineating the molecular mechanisms downstream of COX-2 involving PGE2 secretion and its autocrine and paracrine interactions with EP receptors (EP1-4), COX-2/PGE2/EP receptor signaling regulating KSHV pathogenesis and latency. KSHV infection induces COX-2, PGE2 secretion, and EP receptor activation. The resulting signal cascades modulate the expression of KSHV latency genes (latency associated nuclear antigen-1 [LANA-1] and viral-Fas (TNFRSF6)-associated via death domain like interferon converting enzyme-like- inhibitory protein [vFLIP]). vFLIP was also shown to be crucial for the maintenance of COX-2 activation. The mutually interdependent interactions between viral proteins (LANA-1/vFLIP) and COX-2/PGE2/EP receptors was shown to play key roles in the biological mechanisms involved in KS and PEL pathogenesis such as blockage of apoptosis, cell cycle regulation, transformation, proliferation, angiogenesis, adhesion, invasion, and immune-suppression. Understanding the COX-2/PGE2/EP axis is very important to develop new safer and specific therapeutic modalities for KS and PEL. In addition to COX-2 being a therapeutic target, EP receptors represent ideal targets for pharmacologic agents as PGE2 analogues and their blockers/antagonists possess antineoplastic activity, without the reported gastrointestinal and cardiovascular toxicity observed with few a NSAIDs.

Morbillivirus and Toxoplasma exposure and association with hematological parameters for southern Beaufort Sea polar bears: potential response to infectious agents in a sentinel species

Arctic temperatures are increasing in response to greenhouse gas forcing and polar bears have already responded to changing conditions. Declines in body stature and vital rates have been linked to warming-induced loss of sea-ice. As food webs change and human activities respond to a milder Arctic, exposure of polar bears and other arctic marine organisms to infectious agents may increase. Because of the polar bear's status as arctic ecosystem sentinel, polar bear health could provide an index of changing pathogen occurrence throughout the Arctic, however, exposure and monitoring protocols have yet to be established. We examine prevalence of antibodies to Toxoplasma gondii, and four morbilliviruses (canine distemper [CDV], phocine distemper [PDV], dolphin morbillivirus [DMV], porpoise morbillivirus [PMV]) including risk factors for exposure. We also examine the relationships between antibody levels and hematologic values established in the previous companion article. Antibodies to Toxoplasma gondii and morbilliviruses were found in both sample years. We found a significant inverse relationship between CDV titer and total leukocytes, neutrophils, monocytes, and eosinophils, and a significant positive relationship between eosinophils and Toxoplasma gondii antibodies. Morbilliviral prevalence varied significantly among age cohorts, with 1-2 year olds least likely to be seropositive and bears aged 5-7 most likely. Data suggest that the presence of CDV and Toxoplasma gondii antibodies is associated with polar bear hematologic values. We conclude that exposure to CDV-like antigen is not randomly distributed among age classes and suggest that differing behaviors among life history stages may drive probability of specific antibody presence.

Ferrets as a model for morbillivirus pathogenesis, complications, and vaccines

The ferret is a standard laboratory animal that can be accommodated in most animal facilities. While not susceptible to measles, ferrets are a natural host of canine distemper virus (CDV), the closely related carnivore morbillivirus. CDV infection in ferrets reproduces all clinical signs associated with measles in humans, including the typical rash, fever, general immunosuppression, gastrointestinal and respiratory involvement, and neurological complications. Due to this similarity, experimental CDV infection of ferrets is frequently used to assess the efficacy of novel vaccines, and to characterize pathogenesis mechanisms. In addition, direct intracranial inoculation of measles isolates from subacute sclerosing panencephalitis (SSPE) patients results in an SSPE-like disease in animals that survive the acute phase. Since the advent of reverse genetics systems that allow the targeted manipulation of viral genomes, the model has been used to evaluate the contribution of the accessory proteins C and V, and signalling lymphocyte activation molecule (SLAM)-binding to immunosuppression and overall pathogenesis. Similarly produced green fluorescent protein-expressing derivatives that maintain parental virulence have been instrumental in the direct visualization of systemic dissemination and neuroinvasion. As more immunological tools become available for this model, its contribution to our understanding of morbillivirus-host interactions is expected to increase.

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.

Morphometric analysis of the thymus of puppies infected with the Snyder Hill Strain of canine distemper virus

The thymic morphometry analysis was used for determining apoptosis and atrophy of the thymus of eight puppies inoculated with canine distemper virus (CDV). Three healthy dogs were used as negative controls. Sections, 5µm thick, were stained by HE and Shorr, and the latter were evaluated by morphometry. CDV nucleoprotein was detected by immunohistochemistry. Morphometric results confirmed lymphoid hypotrophy in CDV inoculated dog thymuses, more stroma, less parenchyma and higher apoptotic index/field than negative control (not inoculated) puppies. Apoptosis plays a role in the mechanism of thymus atrophy that develops in canine distemper.

Dietary antioxidants and behavioral enrichment enhance neutrophil phagocytosis in geriatric Beagles

The study objective was to determine the effects of feeding food enriched in antioxidants and a program of environmental/cognitive enrichment on selected ex vivo assays of inflammatory and immune cells in healthy geriatric Beagle dogs (n=21). Four groups of dogs were tested using a 2 x 2 factorial design. The 2-year longitudinal study included both nutritional (control food or antioxidant-fortified food) and behavioral (normal level or cognitive enrichment) interventions. Behavior enrichment included increased exercise, environmental enrichment, and a series of learning tasks. Phagocytosis of opsonized latex-coated beads by peripheral blood neutrophils was measured by flow cytometry and found to be significantly increased in dogs receiving both dietary antioxidants and cognitive enrichment. Simultaneous stimulation of cells with Con A and suppression with Dex resulted in decreased lymphocyte proliferation in dogs receiving both dietary antioxidants and cognitive enrichment, compared to dogs receiving dietary antioxidants or cognitive enrichment alone. There were no significant differences between the groups of dogs for percentages of CD4 and CD8 T-lymphocyte subpopulations before or after lymphocyte stimulation with Con A. These results support our hypothesis that both dietary antioxidants and behavioral enrichment enhance host defense mechanisms.

The role and regulation of COX-2 during viral infection

Prostaglandins are lipid mediators, generated by cyclooxygenase (COX), that have been shown to participate in the regulation of virus replication and the modulation of inflammatory responses following infection. A number of studies support a role for PGE2 in the modulation of virus replication and virulence in a cell type and virus selective manner. Virus infection also stimulates the expression of a number of proinflammatory gene products, including COX-2, inducible nitric oxide synthase (iNOS) as well as proinflammatory cytokines. This review will focus on the mechanisms by which proinflammatory prostaglandin production regulates virus replication and virulence. In addition, the signaling pathways that are activated during a virus infection, and that regulate proinflammatory gene expression in macrophages will be reviewed. Specific attention will be placed on the ability of virus infection to activate multiple signaling cascades (such as PKR, MAPK, iPLA2, NF-kappaB) and how these pathways are integrated in the regulation of individual target gene expression.

Effects of dietary n-6 and n-3 fatty acids and vitamin E on the immune response of healthy geriatric dogs

OBJECTIVE

To determine the effect of dietary n-6 to n-3 fatty acid ratios and alpha-tocopheryl acetate concentration on immune functions andT cell subpopulations in healthy dogs.

ANIMALS

Thirty-two 7- to 10-year old female Beagles.

PROCEDURE

For 17 weeks, dogs were fed food that contained low (1.4:1) or high (40:1) ratios of n-6 to n-3 fatty acids in combination with 3 concentrations of all rac-alpha-tocopheryl acetate (low, 17 mg/kg of food; medium, 101 mg/kg; high, 447 mg/kg). Dogs were inoculated twice with a keyhole limpet hemocyanin suspension at 13 and 15 weeks.

RESULTS

After 12 weeks, dogs consuming low concentrations of alpha-tocopheryl acetate had lower percentages of CD8+ T cells, compared with dogs consuming medium or high alpha-tocopheryl acetate concentrations. Also, dogs consuming low alpha-tocopheryl acetate concentrations had higher CD4+ to CD8+ T cell ratios. On day 4 of week 15, the percentage of CD8+ T cells was highest in dogs fed medium concentrations of alpha-tocopheryl acetate, compared with other dogs; however, the CD4+ to CD8+ T cell ratio was higher only in dogs fed low concentrations of alpha-tocopheryl acetate with high concentrations of n-3 fatty acids. Dogs consuming low concentrations of n-3 fatty acids with medium concentrations of alpha-tocopheryl acetate had the largest delayed-type hypersensitivity (DTH) skin test response.

CONCLUSIONS AND CLINICAL RELEVANCE

An optimum amount of dietary alpha-tocopheryl acetate concentration, regardless of the dietary n-6 to n-3 fatty acid ratio, stimulates the CD8+ T cell population. Effects of an optimum amount of dietary alpha-tocopheryl acetate concentration on the DTH response are blunted by dietary n-3 fatty acids.

An outbreak of toxoplasmosis in farmed mink (Mustela vison S.)

A large Wisconsin mink (Mustela vison) farm experienced an outbreak of toxoplasmosis in the spring of 1999 following an outbreak of canine distemper during the previous fall. Major clinical signs for pregnant females included reduced feed consumption, abortions, and stillborn kits; kits < or =3 weeks old experienced ataxia and mortality. Of 7,800 females, 1,976 (26%) lost their entire litter either from abortion or neonatal mortality. Kit mortality from 7 days to 3 weeks of age was 3,300, and overall kit mortality attributed to the toxoplasmosis outbreak was 10,408. Six neonatal mink kits, 12 3-week-old kits, and 2 adult female mink were submitted to the University of Minnesota Veterinary Diagnostic Laboratory for diagnostic workup. Gross postmortem lesions were limited to empty stomachs (12 of 12 kits) and pale livers (4 of 12 kits) for the 3-week-old kits. Major microscopic lesions included interstitial pneumonia, encephalitis, encephalomalacia, and myocarditis. Toxoplasmosis was diagnosed by microscopic lesions, microscopic lesion distribution, and the detection of Toxoplasma gondii tachyzoites by immunohistochemistry. This is the first detailed report of an outbreak of toxoplasmosis in mink in the United States.

Seroprevalence of canine distemper virus in cats

A seroepidemiological survey of canine distemper virus (CDV) infection in Asian felids revealed that the prevalence of antibodies varied depending on region and, in some cases, exposure to dogs. The serologic pattern in cats with antibodies indicated that they had likely been exposed to field strains rather than typical CDV vaccine strains.

Canine viral infections

The ophthalmic effects of viral infection are varied. With the added possibility for pathologic effects of attenuated vaccine viruses, the diagnosis of viral diseases can be a challenge. In many cases, ocular manifestations can provide added support to a presumptive diagnosis of viral disease, thereby underscoring the benefit of thorough ophthalmic examination of any animal with nonspecific signs of illness.

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.

Immunopathogenesis of classical swine fever: role of monocytic cells

Virulent classical swine fever (CSF) represents an immunomodulatory viral infection that perturbs immune functions. Circulatory and immunopathological disorders include leukopenia, immunosuppression and haemorrhage. Monocytic cells - targets for CSF virus (CSFV) infection - could play critical roles in the immunopathology, owing to their production of immunomodulatory and vasoactive factors. Monocytes and macrophages (Mphi) are susceptible to virus infection, as a consequence of which prostaglandin E2 (PGE2) production is enhanced. The presence of PGE2 in serum from CSFV-infected pigs correlated with elevated PGE2 productivity by the peripheral blood mononuclear cells from these same animals. It was noted that these PGE2-containing preparations did not inhibit, but actually enhanced, lymphocyte proliferation. The proinflammatory cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-6 were not involved, although elevated IL-1 production could relate to lymphocyte activation. Nevertheless, IL-1 was not the sole element: infected Mphi produced lympho-stimulatory activity but little IL-1. This release of immunomodulatory factors, following CSFV infection of monocytic cells, was compared with other characteristics of the disease. Therein, PGE2 and IL-1 production was noted to coincide with the onset of fever and the coagulation disorders typical of CSF. Consequently, these factors are of greater relevance to the haemorrhagic disturbances, such as petechia and infarction, rather than the leukopenia found in CSF.

Secondary immunodeficiency in dogs with enteric, dermatologic, infectious or parasitic diseases

A group of 238 dogs with various infectious and parasitic disease, in which suppressed activity of the immune system could e presumed, was examined using a set of immunological methods. The frequency and depth of immunosuppression and its association with certain infectious or parasitic disease were determined. Marked immunosuppression was found 62 (26%) of the dogs examined. Dogs with distemper, parvovirosis and German Shepherd dog pyoderma (GSP) were the most severely impaired. Dogs in acute phases of distemper or parvovirosis had decreased numbers and activity of lymphocytes and decreased immunoglobulin levels. Dogs with GSP had some of the following immunologic symptoms: inhibition of phagocytosis, reduced activity of lymphocytes, decreased levels of haemolytic complement and increased levels of immunoglobulin and lysozyme. A persistent immunosuppression was found in 12 dogs. These dogs were diagnosed with deep pyoderma, giardiasis, dermatophytosis or neoplasms. Although samples were not taken before the clinical diseases appeared, it can be presumed that some diseases caused immunosuppression (distemper or parvovirosis), and for other diseases immunosuppression was a predisposing factor (dermatophytosis, giardiasis and possibly GSP).

The ratio of dietary (n-6) to (n-3) fatty acids influences immune system function, eicosanoid metabolism, lipid peroxidation and vitamin E status in aged dogs

We studied the effects of feeding experimental diets containing (n-6) to (n-3) fatty acid ratios of 31:1, 5.4:1, and 1.4:1 to 20 healthy female geriatric Beagles (9.5-11.5 y) for 8-12 wk on various indices of the immune response. Compared with the 31:1 diet, consumption of the 5.4:1 and 1.4:1 diets significantly increased (n-3) fatty acids in plasma (2.17 +/- 0.64, 9.05 +/- 0.64, 17.46 +/- 0.64 g/100 g fatty acids, respectively, P < 0.0001). Although supplementation with (n-3) fatty acids did not significantly alter the humoral immune response to keyhole limpet hemocyanin (KLH), it significantly suppressed the cell-mediated immune response based on results of a delayed-type hypersensitivity (DTH) skin test. The DTH response after intradermal injection of KLH at 24 h was significantly lower in the group consuming the 1.4:1 diet compared with the group consuming the 5.4:1 (P = 0.02) or the 31:1 diets (P = 0.04), and remained significantly suppressed at 48 h in the group fed 1.4:1 relative to the group fed 31:1. After consumption of the 1.4:1 diet, stimulated mononuclear cells produced 52% less prostaglandin E2 (PGE2) than those from dogs fed the 31:1 diet (224 +/- 74 and 451 +/- 71 pmol/L, respectively, P = 0.04). Plasma concentration of alpha-tocopherol was 20% lower in dogs fed the 1.4:1 diet compared with those fed the 31:1 diet (P = 0.04), and lipid peroxidation was greater in both plasma (P = 0.03) and urine (P = 0.002). These data suggest that although a ratio of dietary (n-6) to (n-3) fatty acids of 1.4:1 depresses the cell-mediated immune response and PGE2 production, it increases lipid peroxidation and lowers vitamin E concentration.

Vaccination of racing greyhounds: effects on humoral and cellular immunity

Greyhound kennel owners frequently employ multiple vaccination schedules in an attempt to reduce financial losses incurred as a result of infectious diseases. In order to determine the effects of multiple vaccination schedules on the immune system of racing greyhounds, three litters of greyhound pups raised in laboratory conditions were divided into two groups and subjected to either a maximum or a minimum vaccination schedule. Blood samples were collected biweekly for 6 months beginning at 2 weeks of age and analyzed to establish 'baseline' values for the lymphatic system of greyhounds. Lymphocyte transformation, total and differential leukocyte counts, and flow cytometry were used to evaluate cellular immunity. Humoral immunity was evaluated using serum neutralization and hemagglutination inhibition tests. Proliferation of peripheral blood lymphocytes in response to the mitogen concanavalin A (Con A) was higher for the maximum vaccination groups. The frequency distribution of circulating CD4 and IgG labeled lymphocytes was higher in the minimum vaccination groups. A significant treatment by time interaction in CD4, IgG, and IgM labeled cells was observed, This interaction, however, was not significant at any point in time for CD4 and IgG labeled cells. The percentage of lymphocytes expressing surface IgM was significantly higher in the minimum vaccination groups at 10 and 14 weeks of age. No significant differences were detected in humoral immunity between the maximum and minimum groups of each litter. Results of this study indicate that maximum vaccination schedules do not appear to be more effective or more immunosuppressive than minimum vaccination schedules.

Leucocyte interleukin-1-like activity in the common seal (Phoca vitulina) and grey seal (Halichoerus grypus)

Interleukin-1 (IL-1) is an important cytokine with predominantly proinflammatory activities, which have been characterized in many mammals. This study showed the production of IL-1-like bioactivity by cultured seal leucocytes. Increasing concentrations of lipopolysaccharide (LPS) (0-1 micrograms/ml) stimulated an increase in measurable IL-1-like activity in cell culture supernates. This activity increased for the first 24 h after LPS stimulation and the substance responsible had an apparent molecular weight of 17 kDa on gel filtration, similar to that described for other species. Specificity of the bioassay used was confirmed by blocking the bioactivity with an IL-1 receptor antagonist (IL-1 ra).

In vitro characteristics of the microsporidian: Enterocytozoon salmonis

Enterocytozoon salmonis, as intranuclear microsporidian of salmonid fish, was propagated in vitro using chinook salmon mononuclear leukocytes. Characteristic morphology and infectivity of the cultured parasites were evaluated to determine the effect of in vitro maintenance and passage on the parasites. Cultured parasites developed through several stages from meronts to infectious spores. Parasites obtained from in vitro passages tested up to the 17th subculture, retained their morphological characteristics and pathogenicity for chinook salmon (Oncorhynchus tshawytscha). The disease induced by experimental infections with parasites from in vitro cultures was identical to that observed in naturally infected chinook salmon. An examination of supernatants obtained from the infected cultures revealed evidence of soluble factor(s) produced by E. salmonis-infected cells that stimulated uninfected target cells in vitro. This observation may explain in part the proliferative disease of hematopoietic tissues which characterizes the disease in infected chinook salmon.

Immunohistochemical studies of lymphoid tissues of rabbits infected with rinderpest virus

The pathogenesis of infection with the L-strain of rinderpest virus (RPV) in rabbits was investigated. Of several lymphoid tissues examined, those associated with the gut showed the most marked virus growth. The virus titres were maximal 4 days after inoculation but had declined at day 6. The distribution of viral antigen was examined immunohistochemically with the recently established anti-rabbit CD5 monoclonal antibody (MoAb), which is a pan-T-cell marker, and the anti-RPV-nucleoprotein MoAb. The virus antigen was localized in the CD5+ area at the initial stage of infection but spread to all areas of the lymphoid tissues at the later stages. By flow cytometric analysis with both rabbit CD5 and CD4 MoAbs, a decrease of the CD4+ and CD5+ subpopulations was observed in the spleen and mesenteric lymph nodes.

Immune mechanisms in the pathogenesis of viral diseases: a review

Three immunopathological mechanisms may determine the pathogenesis of viral diseases in animals. (1) A variety of viruses causes transient or prolonged immunosuppression by infecting lymphoreticular tissues and interacting with components of the immune system. (2) In persistent viral infections effective immune responses may result in tissue damage. The mechanisms involved are T-cell-mediated destruction of infected cells and delayed-type hypersensitivity. (3) In a number of viral diseases pathogenic immune complexes are formed when antibodies are produced and react with viral antigen molecules persisting in the host. The selected examples of immune dysfunction are the focus of this review.

Canine distemper virus increases procoagulant activity of macrophages

Inflammatory demyelination in canine distemper has been proposed to be due to a "bystander" mechanism, in which macrophages play an important role. In the present work we studied whether infection of macrophages by canine distemper virus (CDV) results in changes of macrophage functions, including Fc receptor-dependent and -independent phagocytosis, release of reactive oxygen species (ROS), and procoagulant activity (PCA). As a source of macrophages, dog bone marrow cells were seeded in teflon bags and grown for 1-2 weeks, at which time a marked enrichment of macrophages was noted. These cells were infected with the A75/17 strain of CDV. We could not detect any significant difference between uninfected and CDV-infected macrophages with respect to Fc receptor-dependent or -independent phagocytosis or with respect to the release of ROS. However, from Day 4 p.i. to the end of our observation period (10 days p.i.), PCA was up to 10-fold higher in CDV-infected unstimulated macrophage cultures than in uninfected unstimulated cultures of the same age. Increase in PCA was not due to the inoculation procedure by itself nor to components of the inoculum other than CDV; in particular, PCA was not due to contaminating endotoxin. Thus, several important macrophage functions do not appear to be impaired by CDV infection. The marked increase of macrophage PCA expression suggests that certain macrophage functions may even be enhanced as a result of infection. Such macrophage activation might contribute to the pathogenesis of the disease.

In vitro immunologic features of Weimaraner dogs with neutrophil abnormalities and recurrent infections

In vitro evaluation of cellular and humoral immunity in Weimaraner dogs with recurrent infections and abnormal neutrophil function revealed significantly lower serum immunoglobulin (Ig) G and M concentrations than control dogs. Lymphocyte blastogenesis in response to three different mitogens, interleukin-1 and -2 production, natural killer (NK) cell activity, and in vitro IgG and IgM production were similar to those of control dogs.

The effects of human interferon-alpha upon in vitro canine immune responses

The effects of varying amounts (100.0-0.01 units/ml) of human interferon (IFN) alpha upon in vitro canine immune responses were studied. Exogenous heterologous species IFN-alpha suppressed B-cell differentiation in a dose-dependent fashion and enhanced interleukin-2 production (P less than 0.05) by activated T-lymphocytes. Interferon enhanced natural killer (NK) cytotoxicity when tested against NK-resistant target cells (less than 0.05). One hundred units IFN/ml increased interleukin-1 production by canine monocytes, but this effect was not statistically significant. Exogenous IFN had no discernible effect upon lectin-induced lymphocyte blastogenesis. The results of this study demonstrate that human IFN-alpha does affect various canine lymphocyte functions and these effects depend upon the in vitro assay system employed.

In vitro and in vivo methods in immunotoxicology

One approach to assessment of the immunotoxic effects of drugs and chemicals upon the immune system is briefly described. Appropriate in vivo and in vitro methods and techniques are delineated. It is likely that programs implemented at individual institutions will be modified to specific circumstances.