INDUCTION OF SYNCYTIA BY BOVINE C-TYPE LEUKEMIA-VIRUS

Abstract

Bovine buffy coat cells infected with the bovine leukemia virus (BLV) induce syncytia formation in human diploid embryonic lung cells and in monolayer cell cultures of bovine, simian, ovine, bat and caprine origin, but not in mouse fibroblast cells, normal rat kidney cells, or Rous sarcoma virus-transformed rat [xc] cells. Syncytia were not observed in diploid embryonic lung cells inoculated with bovine buffy coat cells free of BLV. The syncytia-induction effect is associated with the synthesis of complete BLV by the buffy coat cells and is independent of cell viability, disruption, normality or malignancy. Cell-free preparations of BLV and density gradient-purified virus also induce syncytia when added directly to diploid embryonic lung cells and to bovine, bat and caprine monolayer cell cultures. Ether treatment, UV irradiation, heating, freezing and thawing destroy the syncytia-inducing activity of BLV. This activity is also neutralized when the virus is incubated with [bovine] sera containing BLV antibodies, but not when incubated with sera free of these antibodies or reference serum for the foamy-like bovine syncytial virus. The possibility that this virus or other bovine viruses are responsible for the syncytia-inducing phenomenon was ruled out. BLV antigen was consistently detected by immunofluorescence in the syncytia-positive monolayer indicator cultures. Syncytia formation was not necessarily associated with BLV production by the indicator cells. The ability to induce syncytia in monolayer cultures of nontransformed cells distinguishes BLV from all the known C-type leukemia viruses.