Interaction of immune and central nervous systems: contribution of anti-viral Thy-1+ cells to demyelination induced by coronavirus JHM.

The murine coronavirus JHM (JHMV or MHV-4) has been intensively studied as an experimental model of viral-induced demyelination; nonetheless, the degree to which demyelination results from direct viral cytolysis of oligodendroglia or immunological mechanisms remains controversial. To examine the contribution of immunity to the pathogenesis of JHMV in the central nervous system (CNS), mice were exposed to immunosuppressive doses of x-irradiation 3 days post infection and observed for clinical and pathological evidence of acute and subacute demyelination. Irradiated mice were found to have a nearly thousand-fold increase in central nervous system virus titer, as well as the presence of both abundant virus and viral antigen in white matter cells with the morphological characteristics of oligodendrocytes. Nonetheless, infected, irradiated mice had little or no evidence of demyelination or destruction of CNS cells. Adoptive transfers of spleen cells from syngeneic JHMV-immunized donors into irradiated JHMV-infected mice were carried out in order to determine the effect of immune reconstitution on pathogenesis. Splenocytes from JHMV-immune donors, but not naive donors or donors immunized with irrelevant antigen, completely restored demyelination in irradiated, JHMV-infected recipients. Depletion of Thy-1+ cells by treatment with monoclonal antibody and complement abolished the ability to transfer demyelination. We conclude that: 1) JHMV infection of the CNS does not result in acute or subacute demyelination in the absence of an intact immune response, and 2) viral-specific Thy-1+ cells are an essential element in the induction of demyelinating CNS lesions that result from JHMV infection.

The effect of mixed live vaccines of Newcastle disease and infectious bronchitis on the chicken respiratory tract.

The effect of mixed live vaccines of Newcastle disease (ND) and infectious bronchitis (IB) on specific pathogen-free chickens aged 7 days was investigated. The chickens were inoculated intranasally with mixed live vaccines with and without Escherichia coli, or with E. coli alone. "Vaccine 1" consisted of ND virus strain B1 and IB virus strain ON; "vaccine 2" consisted of ND virus strain B1 and IB virus strain H120. The tracheas of chickens inoculated with the vaccines and E. coli and with the vaccines alone showed multiplication of E. coli and histological lesions (loss of cilia, degeneration and hyperplasia in epithelial cells and cellular infiltration of subepithelial tissues). In the tracheas of chickens inoculated with vaccines and E. coli, multiplication of E. coli was greater than in chickens given vaccine alone. There were no histological lesions, and only mild, transient multiplication of E. coli in chickens inoculated with E. coli alone. The results suggest that these mixed live vaccines, especially vaccine 2, play a role in inducing or enhancing colibacillosis in the chicken.

Perspectives on the epizootiology of feline enteric coronavirus and the pathogenesis of feline infectious peritonitis.

This review presents some current thoughts regarding the epizootiology of the feline coronaviruses; feline infectious peritonitis virus (FIPV) and feline coronavirus (FECV) with primary emphasis on the pathogenesis of these viruses in nature. Although the mechanism(s) whereby FIPV causes disease are still incompletely understood, there have been significant contributions to the literature over the past decade which provide a framework upon which plausible explanations can be postulated. Two concepts are presented which attempt to clarify the pathogenesis of FIPV and at the same time may serve as an impetus for further research. The first involves the hypothesis, originally promulgated by Pedersen in 1981, that FIPV is derived from FECV during virus replication in the gastrointestinal tract. The second involves a unique mechanism of the mucosal immune system referred to as oral tolerance, which under normal conditions promotes the production of secretory immunity and suppresses the production of systemic immunity. In the case of FIPV infection, we propose that oral tolerance is important in the control of the virus at the gastrointestinal tract level. Once oral tolerance is disrupted, FIPV is capable of systemic spread resulting in immune-mediated vasculitis and death. Thus, it may be that clinical forms of FIP are due to a combination of two events, the first being the generation of FIPV from FECV, and the second being the capacity of FIPV to circumvent oral tolerance.

Psychological stress and susceptibility to the common cold.

BACKGROUND: It is not known whether psychological stress suppresses host resistance to infection. To investigate this issue, we prospectively studied the relation between psychological stress and the frequency of documented clinical colds among subjects intentionally exposed to respiratory viruses. METHODS: After completing questionnaires assessing degrees of psychological stress, 394 healthy subjects were given nasal drops containing one of five respiratory viruses (rhinovirus type 2, 9, or 14, respiratory syncytial virus, or coronavirus type 229E), and an additional 26 were given saline nasal drops. The subjects were then quarantined and monitored for the development of evidence of infection and symptoms. Clinical colds were defined as clinical symptoms in the presence of an infection verified by the isolation of virus or by an increase in the virus-specific antibody titer. RESULTS: The rates of both respiratory infection (P less than 0.005) and clinical colds (P less than 0.02) increased in a dose-response manner with increases in the degree of psychological stress. Infection rates ranged from approximately 74 percent to approximately 90 percent, according to levels of psychological stress, and the incidence of clinical colds ranged from approximately 27 percent to 47 percent. These effects were not altered when we controlled for age, sex, education, allergic status, weight, the season, the number of subjects housed together, the infectious status of subjects sharing the same housing, and virus-specific antibody status at base line (before challenge). Moreover, the associations observed were similar for all five challenge viruses. Several potential stress-illness mediators, including smoking, alcohol consumption, exercise, diet, quality of sleep, white-cell counts, and total immunoglobulin levels, did not explain the association between stress and illness. Similarly, controls for personality variables (self-esteem, personal control, and introversion-extraversion) failed to alter our findings. CONCLUSIONS: Psychological stress was associated in a dose-response manner with an increased risk of acute infectious respiratory illness, and this risk was attributable to increased rates of infection rather than to an increased frequency of symptoms after infection.

Canine coronavirus infection in the dog following oronasal inoculation.

The pathogenesis of canine coronavirus (CCV) infection in 10-week-old puppies was studied up to 14 days after oronasal inoculation. Mild diarrhoea was seen from three to 11 days after inoculation, approximately coincident with faecal virus shedding. Virus was initially isolated from the tonsils on day 3, and then from both small and large intestinal tissues up to 14 days after inoculation. Virus was also isolated from liver and lung. Histological changes were not seen in any tissues, but CCV antigen was detected, using a peroxidase antiperoxidase staining technique, mainly in epithelium overlying gut-associated lymphoid tissue. Virus neutralising antibody was first detected on day 10. Specific anti-CCV IgM was first detected in plasma three days after inoculation and IgG on days 4 to 7. Small amounts of anti-CCV IgG, IgM and IgA were detected in duodenal secretion, but none in bile.

Neurovirulence of six different murine coronavirus JHMV variants for rats.

Six variant viruses of the JHMV strain of murine coronavirus with large (cl-2, CNSV, DL and DS) or small (sp-4 and JHM-X) S proteins were compared in terms of their relative neurovirulence in weanling Lewis rats. Inoculation of various doses of the variants revealed that the cl-2 and CNSV were highly virulent and DL and DS were low-virulent, while sp-4 and JHM-X were avirulent. Pathological examination of rats infected with variants cl-2, DL and sp-4 showed that the cl-2 and DL induced severe and mild acute encephalomyelitis, respectively, while no lesions were observed in the central nervous system of rats infected with sp-4. Virus growth and distribution of antigen in rat brains correlated strongly with neurovirulence. These results suggest that S protein plays a role in neurovirulence in rats. In addition, these variant viruses were shown to be useful tools for further analysis of JHMV neurovirulence in animals as well as in cultured cells.

Light intensity-associated eye lesions of Fischer 344 rats in long-term studies.

Albino rats and mice are sensitive to light and the recommended illumination of animal rooms (75-125 ft-candles) is known to cause retinal damage. When a room is illuminated by ceiling lights, animals in the cages of the top row and, to some extent, in the side columns of cage racks will be exposed to higher light intensity than those in the other cages of the rack. In 2-yr chemical carcinogenicity studies of the National Toxicology Program (previously the Carcinogenicity Bioassay Program of the National Cancer Institute), Fischer 344 rats were group-housed in hanging drawer-type clear polycarbonate cages. During the course of the chronic studies, a number of rats developed opacity of the eye. Ocular examination indicated chronic uveitis, deep interstitial keratitis, cataract formation leading to panophthalmitis, and in severe cases, phthisis bulbi. Histologic examination showed cataract and retinal degeneration. Incidences of these lesions were highest (greater than 55%) in the rats of the top rows and lowest in those of the bottom rows (less than 10%) of cages with no relation to chemical treatment, indicating an association with light intensity. The incidence of these eye lesions was markedly decreased (less than 15%) by decreasing the light intensity of the animal room to less than 50 ft-candles at 5 ft from the floor and rotating the cages in each column of a rack from top to bottom when cages or racks were changed.

Experimental sialodacryoadenitis virus infection in severe combined immunodeficient mice.

Mice with a severe combined immunodeficiency in B and T lymphocytes and natural killer cells (SCID-beige) were inoculated intranasally with sialodacryoadenitis (SDA) virus, a coronavirus of rats. Animals were killed at designated intervals and tissues were examined for evidence of viral infection by light microscopy and immunofluorescence microscopy. Based on these criteria, there was no evidence that these immunodeficient mice were susceptible to infection with SDA virus.

Experimental Parker's coronavirus infection in Wistar rats.

Specific Pathogen Free (SPF) male Wistar rats were inoculated intranasally with Parker's rat coronavirus (PRC), then killed at various intervals post-inoculation (pi). PRC inoculated rats had transient respiratory signs. Intermandibular swelling was evident in some rats at 6-8 days pi. During the acute stages of the disease, inflammatory lesions were present in the respiratory tract and in the salivary and lacrimal glands. Regenerative lesions were observed in the salivary and lacrimal glands at 2 weeks pi. Inoculated rats seroconverted at 8-14 days pi, and significant coronaviral antibody titers were present in inoculated rats examined at 21 days pi with PRC. Changes in the respiratory tract and salivary and lacrimal glands were identical in incidence, distribution and nature to those observed in sialodacryoadenitis (SDA) virus inoculated Wistar rats. Thus, in the absence of viral isolation and characterization, "rat coronavirus infection" is a more appropriate term than either PRC infection or sialodacryoadenitis (SDA).

Pathogenesis of H13 nephropathogenic infectious bronchitis virus.

A nephropathogenic Massachusetts strain of infectious bronchitis virus (IBV) designated H13-IBV was isolated from the kidneys of commercial broilers. H13-IBV caused respiratory distress, depression, and diarrhea in specific-pathogen-free chickens. Gross renal lesions included pale coloration, swelling, and urate deposition. Histologic renal changes were interstitial mononuclear cell infiltration and degeneration and necrosis of tubular epithelial cells. Lesions in respiratory tissues included thickening and edema of the air sacs, congestion of the tracheal mucosa, and frothy serous exudate. Histologic tracheal lesions were deciliation, mucous gland distortion, inflammatory cell infiltration, and squamous metaplasia. Clinically, H13-IBV was highly pathogenic in birds infected at 1 day of age and mildly pathogenic in birds infected at 4 weeks of age. Kidney lesions were of marked severity only in birds infected at 1 day of age. Tracheal lesions were similar in severity in both age groups.

Persistence of sialodacryoadenitis virus in athymic rats.

To determine whether SDAV infection persists in athymic rats, weanling athymic rats and euthymic rats were inoculated intranasally with 10(4) TCID50 of SDAV and examined periodically for up to 90 days. Viral antigen and lesions characteristic of acute SDAV infection, including rhinotracheitis, bronchitis and sialodacryoadenitis, were detected in both groups of rats during the first week. In euthymic rats, tissues were under repair and viral antigen was undetectable by day 17, and tissues were histologically normal by day 31 except for mild focal dacryoadenitis. In athymic rats, viral antigen and chronic active inflammation of respiratory tract, salivary and lacrimal glands persisted through day 90. Inflammation and viral antigen also were observed in the transitional epithelium of the renal pelvis and urinary bladder as late as day 90. Virus was isolated from nasopharynx, lung, salivary gland and Harderian gland of athymic rats through day 90. All euthymic rats seroconverted to SDAV by day 6, whereas all athymic rats remained seronegative through day 31, and two of six were seropositive by day 90. As judged by seroconversion of contact sentinels, six of six athymic rats shed virus through 6 weeks, and five of six through 10 weeks. These results indicate that SDAV persists in athymic rats, and that normal T cell function is required for host defenses against SDAV.

[The frequency and pathogenesis of feline infectious peritonitis (FIP)]. / Untersuchungen zur Häufigkeit und zur Pathogenese der Felinen Infektiösen Peritonitis (FIP).

Between 1980 and 1987 about 10% of the cats which underwent a post mortem examination at the Institute of Veterinary Pathology of the Freie Universität Berlin were infected with feline infectious peritonitis (FIP). The exudative, granulomatous or mixed form of the FIP are all symptoms of the same disease whose clinical picture is dependent on the state of the cellular immunity. Statistically there is no significant relationship between the form of the FIP and the age of the cats. A breed or a sex disposition is also not apparent. 42 organs and/or tissue samples were taken from a total of 30 cats and were examined both histologically and immunohistochemically. The antigen is located, above all, in the mesothelium and the cells of the mononuclear phagocyte system, whereas the parenchymatous inflammation foci show little evidence of the FIP-virus-antigen. The antigen is, however, also found in the nerve cells. Within the framework of a second viraemia, occurring after infection of the mesothelium (polyserositis), a perivasculitis non purulenta generalisata occurs. Possible excretory organs of the antigen are the respiratory, digestive and urinary tract.

A model for persistent murine coronavirus infection involving maintenance via cytopathically infected cell centres.

The relatively cell impermeable hygromycin B was found to inhibit viral but not cellular protein synthesis when added to cultures of murine hepatitis virus (MHV)-infected or mock-infected mouse L-2 fibroblasts. Membrane permeability, as judged by influx of sodium ions, has previously been demonstrated to be an MHV E2 glycoprotein-mediated, cytopathic effect of MHV infection in L-2 cells. It is therefore likely that the selective effect of hygromycin B on viral protein synthesis is a reflection of an increased drug penetration into virus-infected cells. Using hygromycin B as a marker for MHV-induced cell membrane cytopathology, the effects of drug treatment on a persistent MHV infection in mouse LM-K fibroblasts were investigated. MHV persistence in LM-K cells, which normally involves a steady state infection of 0.1 to 1% of the cells in culture, was found to be cured by hygromycin B treatment, as measured by the elimination of infectious virus from the supernatant medium. Hygromycin B also resulted in the eradication of MHV-specific RNA from LM-K cells, arguing against the presence of a non-cytopathically or latently infected subpopulation of cells.

Molecular pathogenesis of virus infections.

Although a very wide range of viral diseases exists in vertebrates, certain generalizations can be made regarding pathogenetic pathways on the molecular level. The presentation will focus on interactions of virions and their components with target cells. Using coronaviruses as examples the changes in virulence have been traced back to single mutational events; recombination, however, is likely to be an alternative mechanism by which virus-host interactions (e.g. the cell-, organ- or animal species-spectrum) can dramatically change. Receptor molecules are essential for the early interactions during infection and some of these have been identified. Events in the target cell and the host organism are discussed, and wherever possible, aspects of virus evolution and cooperation between infectious agents are highlighted.

Epitope-specific antibody responses to virulent and avirulent feline infectious peritonitis virus isolates.

Feline infectious peritonitis virus (FIPV) has been isolated several times from infected cats. Some of these isolates vary markedly in their ability to cause disease. Specific-pathogen-free cats were inoculated with the avirulent FIPV-UCD-2 isolate or the extremely virulent FIPV-79-1146 isolate or both. After 1 month, cats which had received FIPV-79-1146 were either dead or showed clinical signs of FIP. All cats which received only FIPV-UCD-2 remained healthy up to 6 months after inoculation. Antibody-mediated immune enhancement of disease was not observed in cats which received FIPV-UCD-2 before inoculation with FIPV-79-1146. Monoclonal antibodies which recognized type-specific epitopes on each of the structural polypeptides of these two viruses were used in competitive-inhibition enzyme-linked immunosorbent assays to analyze the humoral immune responses of the cats. All cats produced antibodies to epitopes found on the homologous virus. In addition, cats inoculated with FIPV-79-1146 also produced antibodies which inhibited the binding of the anti-FIPV-UCD-2 E1 monoclonal antibody. One cat inoculated twice with FIPV-UCD-2 produced antibodies which inhibited the binding of the anti-FIPV-79-1146 N- and E1-specific monoclonal antibodies. Competitive enzyme-linked immunosorbent assays may prove useful in distinguishing cats which are infected with virulent FIPV isolates from cats infected with avirulent feline coronaviruses.

An outbreak of avian urolithiasis on a large commercial egg farm.

A significant outbreak of avian urolithiasis was observed on a large commercial egg farm. From the initial outbreak site (a single laying house), the incidence of urolithiasis slowly spread in the ensuing months to numerous other laying houses. Increasing mortality associated with urolithiasis commenced during late growout to early lay and then leveled off when egg production peaked. At the height of the outbreak, mortality was typically 0.5% per week; 75% of this mortality was due to urolithiasis. The clinical and pathologic features of this condition are described. Both infectious bronchitis virus (IBV) and fowl adenoviruses were isolated from organ homogenates of sampled birds. A clone of the IBV strain was found to induce nephritis in specific-pathogen-free white leghorns.

[Experimental coronavirus encephalomyelitis in mice]. / Eksperimental'nyi koronavirusnyi éntsefalomielit myshei.

A combined comparative virological, morphological, and immunological study of experimental coronavirus encephalomyelitis was carried out in mice in order to elucidate the pathogenetic mechanisms involved in the formation of the foci of lesions in acute and chronic forms of the disease. Intracerebral inoculation of C3H mice with the neurotropic JHM strain of murine hepatitis virus induces a disease with demyelinization foci in the CNS running acute, subacute, or chronic course. This model underlies a concept that demyelinating diseases are caused by viruses producing immunopathologic responses realized via certain histocompatibility loci. The long-term persistence of viral antigen in the CNS and liver may be explained by virus replication in hepatocytes and oligodendrocytes at low levels, and exacerbations of the disease are prevented by the immune system.