Bovine lymphosarcoma: expression of BLV-related proteins in cultured cells

Bovine leukaemia virus (BLV) is known to be the aetiological agent of enzootic bovine lymphosarcoma. As the mechanism of tumour induction is unknown, we analysed the viral proteins expressed in cultured bovine cells of different origin, i.e. from enzootic or sporadic tumourous tissues, normal cells infected or not with BLV, and the reference FLK-BLV cells. We also investigated BLVs of different origins. As well as the previously described BLV polyproteins in FLK-BLV cells (pr70 and pr45) we have also found two additional polyproteins, p52 and p27. In these four proteins we observed the combined antigenicities of p24, p15 and p12. We observed an additional polyprotein in p42, with the antigenicities of the p24 and the p15 in cells derived from tumour tissue or infected in vitro with naturally occurring BLV isolates. None of these BLV-coded proteins, nor others with cross-reacting antigenicities, were encountered in non-BLV-producing cultured cells from enzootic or sporadic tumours. The use of autologous sera did not permit the detection of any proteins in addition to the above gag-coded and env-coded proteins. Thus, there is no evidence for the existence of a gag-x fusion protein which could play a role in BLV-induced tumourigenicity.