Investigations were made for further biological characterization of strain R avian leukosis virus, which is responsible primarily for erythroblastic leukemia as well as other growths in the chicken. An agent derived from the chicken revealed leukemogenic activity comparable with that previously observed by others. For chickens, infectious capacity as measured by viremia and antibody induction was approximately 1000-fold greater than that of leukemogenic activity. Infectivity for chick embryo cells measured by virus interference was 10-fold less than that which induced viremia and antibodies in chickens, but the titer requisite for morphological alteration of chick cells approximated that for leukemogenesis in chickens. The strain was observed to induce foci in chick embryo cell monolayers proportional to virus amount, thus providing a method for direct assay. Leukemogenic activity was diminished by passage of the virus in tissue culture. The agent induced infection in C/O and C/A chick embryo cells, but not in C/B or C/AB cells; interfered with infection with Rous sarcoma virus (Rous-associated virus-2); and was neutralized by anti-Rous-associated virus-2 immune serum, indicating that strain R is a member of the avian tumor virus Subgroup B. Evidence suggesting heterogeneity of strain R derived directly from the chick was observed in the results of interference tests with Rous sarcoma virus (Rous-associated virus-2), which revealed the activity of an agent capable of infecting but not morphologically altering chick embryo cells.

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©1970 American Association for Cancer Research.
1970
Cancer Research, Inc.