Responses of Different Stocks of Chickens to Inoculation as Embryos and as Chicks with Strain RPL 12 and Field Isolates of Leukosis Virus

The RPL 12 strain of avian tumor virus has been used extensively in studies on viral oncology at this Laboratory. This strain of virus was isolated from a transplantable lymphoid tumor that came originally from a field case of visceral lymphomatosis in 1938 (3). The pattern of neoplastic disease induced by RPL 12 in line 15I chickens is quite similar to that occurring spontaneously among chickens in commercial populations, though with notable differences. High doses of RPL 12 cause high incidence of erythroblastosis, a disease rarely encountered in the field, whereas low to moderate doses induce visceral lymphomatosis, the commonly occurring neoplastic disease among commercially raised chickens (4,6,11). Also, mortality from visceral lymphomatosis induced by RPL 12 is rare until at least 120 days after inoculation, whereas many deaths from the natural disease may occur as early as 40 days after hatching in so-called acute leukosis (2,9). For these reasons it was thought desirable to compare the oncogenic potency and spectrum of strain RPL 12 virus with viruses isolated directly from field cases of visceral lymphomatosis. Most studies on RPL 12 virus have been done in line 151