[Effect of the method of passage on the biological properties of attenuated alphavirus strains].

Experiments with attenuated clones of Venezuelan equine encephalomyelitis virus and Eastern equine encephalomyelitis virus were carried out to study the regularities in changes of biological properties of virus in "undiluted" passages and in passages by subcultivation of small doses. In the latter case the biological activity of the virus remained at the initial low level but in "undiluted" passages it increased, due to accumulation in the population of clones with altered plaque phenotype and increased reproductive potential. In a number of cases this virus had a higher level of residual virulence than the original one.

[Comparative study of variants of the Venezuelan equine encephalomyelitis virus isolated from chronically infected cells by transfection in different cells].

Comparative data with regard to the properties of Venezuelan equine encephalomyelitis (VEE) virus isolated from HeLa carrier cultures by transfection in different cell cultures have been obtained. Introduction of DNA extracted from the carrier cultures into BHK-21 cell cultures resulted in production of an actively multiplying medium-plaque virus, and parallel addition of the same DNA preparations in chick fibroblast or monkey kidney cultures led to production of small-plaque virus with a low reproduction potential. The virus produced by transfection of BHK-21 cells differed from that produced in chick fibroblast and monkey kidney cultures in electrophoretic mobility of virion envelope proteins.

[Interaction of Venezuelan equine encephalitis virus ts-mutants with cells].

An acute infection of HeLa cell cultures with a ts mutant of Venezuelan equine encephalomyelitis (VEE) virus may have different outcomes ranging from formation of a chronic virus-carrier state to complete elimination of virus from the culture. One of the possibilities is also a short-time carrier state (up to 10 passages) of the virus genome apparently existing in the form of DNA-provirus. The carrier state of virus genetic material in this case is indicated by the infectivity of cellular DNA and the presence in it of sequences homologous to those of virion RNA.

[Further study of the pathological process induced in monkeys by LPV oncornavirus].

Experiments were performed on pathogenicity of LPV oncornavirus and Mason-Pfizer-like virus for monkeys Macaca mulatta. The mixture of culture fluid and cell homogenate ultrafiltrates of virus-producing T-9 cell line was used as a source of LPV virus. The same materials derived from HEp-2 continuous cell line served as a source of Mason-Pfizer-like virus.