Oncogenicity and immunogenicity associated with membranes isolated from cell-free ascites fluid of lymphoma-bearing mice.

Membrane vesicles (AFM ) were isolated from cell-free ascites fluid of Moloney virus-induced lymphoma-bearing mice. Biochemical analysis has indicated that the AFM. fraction is highly enriched in the plasma membrane en zyme marker 5 -nucleotidase. Neither reduced nicotinamide adenine dinucleotide dehydrogenase nor succinic dehydrogenase could be detected in the AFM,, fractions, indicating their plasma membrane origin. A specific radioimmunoassay for the murine leukemia virus-protein with a molecular weight of 30,000 antigen has indicated that the specific activity of this antigen is 20-fold higher in the AFM,, fraction than in Moloney virus-induced lymphoma cell homogenate. Electron microscopy studies of the AFM,, fraction have shown that virus-like particles are associated with the plasma membrane vesicles. In vivo experiments carried out with the cell-free AFM,, fraction resulted in two different biological functions: (a) induction of immunity against viable Moloney virus-induced lymphoma cells; and (b) induction of tumors. The two activi ties were dissociated by an in vitro ultraviolet irradiation prior to the inoculation of the AFM,, fraction into A strain mice. High-speed centrifugation of the cell-free ascites fluid resulted in the pellet (AFM,,) that contained both activities and in a supernatant (ascites fluid membrane supernatant) that contained only the immune activity. On the basis of these observations, it is suggested that tumor cells growing as an ascites form shed plasma membrane vesicles with a high specific activity of tumor-specific surface antigens that are responsible for the increased immunity and a tumor promotor factor and virus-like par ticles that are responsible for the increased tumorigenicity. The possibility that shedding of plasma membrane vesi cles and virus-like particles is associated with the same mechanisms on the cell surface of the lymphoma cells is discussed.