Plaque assay for some strains of avian leukosis virus

Abstract

Some strains of avian leukosis virus were found to produce plaques at 41 ° in cultures of chick embryo cells which had been fully infected with a temperature-sensitive mutant of Rous sarcoma virus (RSV) which fails to induce morphological transformation at the elevated temperature. The leukosis viruses caused no discernible lesion in normal chick embryo cultures. Macroscopically visible plaques appeared within 4 days after infection in the mutant-infected cultures, and by 7 to 10 days the plaques became nonstainable by neutral red. The titer of plaque-forming units of these virus preparations was comparable to the titer of virus-infectivity estimated by the interference assay. Avian leukosis viruses of subgroups B and D thus far tested produced plaques under these conditions, while viruses of subgroups A, C, and E did not. Some preparations of avian sarcoma virus, subgroups B and D, also induced plaques, but whether or not the sarcoma virus itself can induce plaques has not been clearly determined. Conditions required for plaque formation, and possible mechanisms are discussed.