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.