[Epstein-Barr Virus LMP1 oncogene variants in cell lines of different origin].

It is well known that the Epstein-Barr virus (EBV) is a widespread infection in the human population. Typically, infection occurs in early childhood without serious consequences for infected people. At the same time, a secondary infection with an additional EBV strain occurs quite often. During the in vitro cultivation of peripheral blood lymphocytes from persons infected with multiple strains of the virus, only one of these strains with higher transforming potential becomes dominant, while the others are eliminated. Under certain conditions, such a highly transforming EBV strain apparently is able to be the etiologic agent of EBVassociated diseases. To find out the range of highly transforming EBV strains prevalent among Russians, cell lines from patients with EBV-associated and non-associated tumors, as well as healthy individuals, were established. The structural analysis of the latent membrane protein 1 gene (LMP1), a key oncogene of the virus, isolated from established cell lines and peripheral blood lymphocytes of blood donors was carried out, and data obtained were compared with the respective data for LMP1 isolates, amplified from cell lines established from African and Japanese patients with Burkitt's lymphoma. The data obtained show a genetic relationship between Russian LMP1 isolates regardless the fact whether they come from patients with tumors or healthy individuals and differ significantly from LMP1 isolates from Burkitt's lymphoma patients. Thus, the results of the study suggest that in nonendemic region for EBV-associated pathology, Russia, any strain of EBV with any structure of LMP1 with concomitant effect of additional factors may become an etiologic agent for EBV-associated neoplasia.

Notes on the mechanism of postvaccination immunity in Marek's disease.

The investigated 16th and 45th in vitro passages of non-pathogenic variant 83 of the Kekava strain Marek's disease virus have led in chickens to resistance to Marek's disease by introduction of the above-mentioned virus 14 days before application of pathogenic variant 55 of the Kekava strain Marek's disease virus. Simultaneous administration of both variants of the Kekava strains Marek's disease virus did not protect chickens from the disease. Presence in those variants of the Kekava strain Marek's disease virus of genetic markers manifesting themselves on passaging the virus in chicken fibroblast cultures created the possibility to investigate interrelations between them in the organism of chickens, utilizing in isolation of the virus the method of infecting cultures with chicken fibroblasts. The results of isolation of the virus from the blood cells of vaccinated chickens have shown that in their organism there is interference between those virus variants since the frequency of isolation of the pathogenic virus variant was 3-times lower than that of the apathogenic Kekava strain Marek's disease virus, and both virus variants persisted in various cells. After simultaneous administration of both virus variants to chickens equal amounts of the pathogenic and of the apathogenic Kekava strain Marek's disease virus were isolated from their blood cells. In that case also persistance of both virus variants in one cell may occur.

Attempts ot activate endogenous virus expression with Marek's disease virus DNA.

Several DNAs derived from Marek's disease virus-infected cells and tissues were tested for in vitro infectivity and for the ability to activate avian endogenous type C virus. The DNA isolated from tumour tissue, peripheral blood buffy coat cells, MDV-infected tissue cultures, lymphoblastoid cell lines and feather follicle epithelium cells from MDV-infected birds elicited a negative response in transfection assays. The MDV DNAs isolated did not activate the endogenous type C virus from cell cultures derived from the C, I and M chicken lines. Activation was observed only in one experiment in the early period after transfection with MDV DNA. The treatment with DNase destroyed this MDV DNA activity, and lambda phage DNA and cell DNAs did not activate the endogenous viruses. Repeated experiments failed to confirm the early activation of endogenous viruses.

Marek's disease virus (Kekava strain) replication in chickens, chick embryos and cell cultures.

In the course of 12 passages of Marek's disease virus (MDV) strain Kekava (MDV-Kekava) in chickens, the morbidity varied greatly (from 23 to 50 percent). MDV-Kekava produced plaques in cultures of chick embryo kidney and adult chicken kidney cells and chick embryo fibroblasts (CEF). The virus adaptation to the cultures was very slow. MDV-Kekava induced the formation of pocks on the chorioallantoic membranes (CAM) of chick embryos but the proportion of embryos with CAM lesions did not exceed 24 percent. Serial passaging of the virus in chick embryos beyond the 5th passage was unsuccessful. The results of virus isolation in chickens, cell cultures and chick embryos indicate the possibility of a long-term latent virus carrier state in chickens without development of tumours.