The demonstration by Burmester, Prickett and Belding( 1 ) that a cell-free extract of the Olson ( 2 ) transplantable lymphoid tumor could transmit avian visceral lymphomatosis, firmly established the fact that an agent or agents other than cells could induce the disease. Further studies(3) have shown that filterable agents are present in other rapidly growing lymphoid tumor strains. Because propagation of viruses in various cell-medium systems is now common, it was thought that a system might be found in which the agent of avian visceral lymphoma tosis would mu1 tiply and show its presence by induction of cytological damage. Previous attempts to do this have been only partially successful. Doljanski and Pikovski (4) have reviewed previous work and reported that they were able to propagate the agent of fowl leucosis in cultures of common mesenchyme cells but were unable to produce cytopathological changes.The present communication is a preliminary report on successful propagation from avian lymphomatosis liver filtrates of an agent producing focal lesions in tissue culture, serial passage of the agent, infection of embryos and chicks with the cultured agent, and recovery of the agent from the diseased embryos and chicks.Materials and methods. Virus. The virus was contained in a filtrate of lymphomatous liver obtained from Dr. B. R. Burmester, Regional Poultry Research Laboratory, East Lansing, Mich. The filtrate was designated KPL-12-L28 and represented the 16th serial filtrate passage in White Leghorn chicks. Tissue culture. Chick embryo liver cultures were prepared as follows: Sixteen-day-old chick embryo livers were minced and mildly agitated with 0.85 % trypsin solution. Gross particles that settled rapidly were discarded. The remaining cells were then sedimented by lowspeed cenitrifugation and washed with balanced salt solution. Tubes were seeded with approximately 500,000 cells in 1 ml of medium consisting of 30% horse serum and 70% medium 199(5), and incubated 2 days a t 37°C. The medium was then replaced with 100% medium 199, after which the tubes were inoculated with tissue filtrates or infective tissue culture fluid. Cultures of whole chick embryo were prepared in a similar manner from 10-to 12-day-old embryos. A slightly modified Eagle( 6) medium containing 10% horse serum was used. After 24 hours' incubation at 37"C, the medium was changed to 100% 199, and the tubes were inoculated. Neutralization tests. Serum neutralization tests in tissue culture were done by inoculating tubes with 0.1 ml of serum-virus mixture. A constant amount of virus (1,000 to 10,000 tissue culture infectious doses) was mixed with serial 2-fold dilutions of serum, and the mixture remained a t room temperature for a t least 2 hours. The neutralization titer of the serum was the highest dilution of serum in the incubated inoculum which prevented cellular destruction for 7 days.Results. Tissue culture. Chick embryo liver cells grew on glass as discrete islands of hepatic cells surrounded by large strands of fibroblasts. On low powe...

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