Antigenic relationship between five isolates of murine gammaherpesvirus analysed with monoclonal antibodies.

A panel of six monoclonal antibodies (mAbs) specific for murine gammaherpesvirus (MHV) was used for analysis of the antigenic relationship between five MHV-isolates (MHV 68, MHV 72, MHV 76, MHV 78, MHV S). Two mAbs raised against MHV 72 and four raised against MHV S were used in the study. Antibody-virus interactions were tested using immunochemical (ELISA, Western blot, immunofluorescence) and biological (virus-neutralization) assays. Immunoanalysis by ELISA showed a close antigenic relationship between the five viruses, nevertheless, some antigenic individuality of the isolate MHV S was observed. This isolate originated from a geographically distinct area in Czechia relative to the other four isolates from Slovakia. In Western blot analysis, antibodies to MHV 72 recognized viral antigens with the relative molecular mass about 116,000. Of four mAbs against MHV S, only two reacted with denatured viral antigen in Western blot and showed specificity for the 50-55,000 protein. These findings suggested that both isolates, besides of minor antigenic variability, could differ also in immunodominant proteins. Mabs to MHV S exhibited much stronger virus-neutralizing potency than mAbs to MHV 72, indicating thus that the 50-55,000 antigen might be more relevant for the infectivity of MHV-virus. Immunofluorescence with mAbs allowed specific localization of antigens in virus-infected VERO cells.

Immunophenotyping of leukocytes in peripheral blood of BALB/c mice infected with mouse herpesvirus isolate 72.

We characterized leukocytes in peripheral blood of BALB/c mice infected with mouse herpesvirus isolate 72 (MHV-72) representing an isolate of mouse herpesvirus strain 68 (MHV-68, species Murid herpesvirus 4, genus Rhadinovirus, subfamily Gammaherpesvirinae, family Herpesviridae) (van Regenmortel et al., 2000). In acute infection (up to day 30 post infection (p.i.)) the number of CD8+ T cells increased, reaching a maximum at day 11 p.i. This increase correlated with that of CD4+ T, activated CD 19+ B and natural killer (NK) cells. At day 30 p.i. the numbers of CD4+, CD8+, CD14+ and CD19+ cells decreased to normal values. A similar increase in the number of these cells was observed at day 730 p. i. In the course of persistent infection (after day 30 p.i.) some of the mice developed a leukemia-like syndrome characterized by an increase in the number of leukocytes and appearance of atypical, blastic immature forms of leukocytes. The latter forms of leukocytes were characteristic by an increased amount of argyrophilic proteins. These results show further similarities between MHV-72 (another isolate of MHV-68) and EBV infections and justify the use of MHV-68 or MHV-72 as an appropriate mouse model for the study of EBV infection of humans.

Pathogenetic characterization of a mouse herpesvirus isolate Sumava.

BALB/c mice inoculated intranasally (i.n.) with the mouse herpesvirus isolate Sumava (MHV-Sumava) did not show apparent symptoms of illness. However, they showed an increase in the number of leukocytes and appearance of atypical leukocytes in peripheral blood. The infiltration of spleen with atypical cells resulted in splenomegaly. In the course of the infection the virus persisted in lungs, spleen, thymus, bone marrow, mammary glands, peritoneal macrophages and liver. We regard MHV-Sumava as one of the eight isolates of MHV-68 (a virus and species Murid herpesvirus 4, genus Rhadinovirus, subfamily Gammaherpesvirinae, family Herpesviridae (van Regenmortel et al., 2000)) so far obtained. MHV-Sumava differs from MHV-68, MHV-72 and MHV-76 in some virological and pathogenetical features.

[New findings on the ecology and epidemiology of murine herpes virus isolated in Slovakia]. / Nové poznatky o ekológii a epidemiológii mysieho herpetického vírusu izolovaného na Slovensku.

Rodents are important reservoir animals of many human microbial pathogens. Of small rodents, trapped on Slovakia territory, were several strains of murine herpes virus (MHV) isolated. Our purpose was to complete the existing knowledge about circulation of MHV in rodents and to find out, whether also other animal species including man are MHV sensitive or not. The presence of antibodies against MHV in serum of the tested animals and men was followed by virus neutralization test (VNT) and ELISA. Pathological changes in differential white blood cell count of the trapped rodents, were also observed because it is known, that MHV induces them in laboratory mice. A total of 627 small terrestrial mammals of nine species were collected in four localities of western and eastern Slovakia during 1984-1988. Neutralizing antibodies to MHV were detected in five species of rodents in 130 cases (20.7%). Antibodies were most frequently detected in Apodemus flavicollis (34.9%). Pathological changes in differential white blood cell count of trapped rodents were detected in 37% (34/92). Neutralizing antibodies were found also in serum of fallow deers (Dama dama), wild boars (Sus scrofa), deers (Cervus elaphus) and sheep but not in serum of pheasants (Phasianus colchicus) and muflons (Ovis musimon). ELISA and VNT tests were used to investigate 20 serums of employees of the Institute of Virology, Slovak Academy of Sciences and Faculty of Natural Sciences of Comenius University. There were eight samples positive (40%). The titers of antibodies were 4-32 in VNT and 1000 in ELISA.

A murine gammaherpesvirus.

In 1976, within a project on isolation of herpesviruses from small rodents in former Czechoslovakia, the mouse herpesvirus strain 68 (MHV-68) was isolated (Blaskovic et al., 1980). This virus was accepted by The International Committee on Taxonomy of Viruses (ICTV) as a new, so far unassigned species (member) of the Gammaherpesvirinae subfamily of the Herpesviridae family (Murphy et al., 1995). Besides MHV-68, four more isolates (MHV-60, MHV-72, MHV-76, and MHV-78) similar to MHV-68 were obtained in that field experiment in Slovakia. Later, three more isolates (MHV-Sumava from Bohemia and MHV-4556 and MHV-5682 from Slovakia) were obtained in other field experiments. All these isolates are in some properties similar but in others different from each other. Nevertheless, as their comparative genome sequence analysis is not yet available, we propose at present to regard all the abovementioned isolates as different isolates of the same virus and strain, i.e. MHV-68. It is not excluded that a more detailed characterization of these isolates in the future will lead to proposals of designating some of these isolates as new strains of the virus of concern. This review summarizes the up to date knowledge of various biological and physico-chemical properties of MHV-68. At least three isolates, MHV-68, MHV-72 and MHV-Sumava seem to be involved in malignant neoplasm development in mice. It should be stressed that the pathogenesis of the induced lymphoproliferative disease in mice is similar to that caused by Epstein-Barr virus (EBV) in humans.

Increased neoplasm development due to immunosuppressive treatment with FK-506 in BALB/C mice persistently infected with the mouse herpesvirus (MHV-72).

BALB/c mice were infected with the lymphotropic mouse gammaherpesvirus (MHV-72). At late (7-12 months) post-infection intervals the latent virus was detected in the cells of lymphatic system (peripheral blood, lymphocytes and macrophages, thymocytes, lymph nodes, bone marrow, and peritoneal macrophages,) and in the spleen, lungs, liver, and kidney by cocultivation as well as by explantation. The MHV-72 infected mice, in which latency had been established, were treated with the immunosuppressive (IS) drug FK-506 (2 mg/kg/mouse for 30 days). This treatment increased the probability of virus reactivation by over two-fold. During the post-treatment observation period of 19 months, the incidence of lymphomas and the development of MHV-related lymphoproliferative and hemoblastic disorders raised to nearly five-fold in the drug treated mice as compared to untreated animals.

Detection of abnormal lymphocytes in the blood of Balb/c mice infected with murine gammaherpesvirus strain 72: the analogy with Epstein-Barr virus infection.

We have followed the effect of murine gammaherpesvirus strain 72 (MHV-72) infection and immunosuppression on the differential white blood cell count of Balb/c mice. In both the acute and chronic phase of infection, abnormal lymphocytes resembling human B lymphocytes infected with Epstein-Barr virus (EBV) were detected. Immunosuppression had no significant effect on the haematological changes during the infection. Some of mice, which had developed tumours as a consequence of infection, showed splenomegaly, lymphadenopathy, leukocytosis and high percentage of immature blastic forms of leukocytes.

Chronic infection of Balb/c mice with murine herpesvirus 72 is associated with neoplasm development.

One hundred Balb/c mice were infected with murine herpesvirus strain 72 (MHV-72) and observed for 2.5 years for neoplasm development and virus presence in tumour as well as non-tumour tissues. Out of 13 neoplasm-bearing mice the virus was recovered from solid tumours (one lymphoma, two non-differentiated lymphoblastomas and two fibrosarcomas) of five mice and from the spleen of one mouse with lymphatic leukemia. The virus persisted frequently also in various organs of the neoplasm-bearing mice.