Analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot of nonspecific and specific viral proteins frequently detected in different antigen preparations of bovine leukemia virus

Bovine leukemia virus (BLV) infection in cattle is seldom manifested clinically, and is routinely diagnosed by serologic tests such as enzyme-linked immunosorbent assay or Western blot (WB). Because of the difficulty in interpreting WE results, the aim of the present study was to determine which of the bands observed in WE were specifically produced by BLV and which corresponded to nonspecific proteins, either derived from medium components or of a cellular nature. Five different BLV antigen preparations from 2 cell lines (FLK-BLV and BLV-bat(2)) frequently used for the production of BLV antigen were compared. The protein profiles of these antigen preparations were analyzed using sodium dodecyl sulfate polyacrylamide gel electrophoresis and WE. Fetal calf serum, required for cellular growth and important in induction of viral transcription in vitro, was identified as a source of irrelevant proteins. In this study, 15 nonspecific protein bands in the growth medium were observed. These bands interfered with the interpretation of results. A nonspecific protein (25 kD) that was highly reactive in cell lysate preparation from BLV-bat(2) was also detected. The unequivocal identification of protein bands, both specific and nonspecific, seen in WE is important not for understanding the protein profile of antigen preparations but also for determining if an animal is BLV positive or negative.