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Journal of Virology, July 2005, p. 8164-8170, Vol. 79, No. 13
0022-538X/05/$08.00+0     doi:10.1128/JVI.79.13.8164-8170.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Isolation of a Bovine Plasma Fibronectin-Containing Complex Which Inhibits the Expression of Bovine Leukemia Virus p24

Department of Pediatrics, University of Western Ontario, London, Ontario, Canada,¹ Department of Pathobiology, University of Guelph, Guelph, Ontario, Canada²

Received 27 November 2004/ Accepted 10 March 2005

Bovine leukemia virus (BLV) is a deltaretrovirus that infects cattle worldwide. In agriculturally intensive regions, approximately 30% of dairy cows are BLV infected. Like the human T-cell leukemia virus (HTLV), there is a lengthy period of viral quiescence after initial infection with BLV. Unlike HTLV, BLV resides predominantly in B cells. Lymphoma is observed in less than 10% of BLV-infected adult cattle. Although viremia is undetectable in vivo, BLV-infected peripheral blood mononuclear cells readily become productive when cultured in vitro. Productivity is markedly diminished when cultures are supplemented with bovine plasma. This inhibitory activity of bovine plasma has been attributed to the "plasma blocking factor" (PBF). Here, we describe the purification of a PBF whose activity was resistant to heating to 65°C for 10 min and was attributable to a fibronectin-containing complex of approximately 320 kDa under nonreducing conditions. By use of two-dimensional polyacrylamide gel electrophoresis and matrix-assisted laser desorption ionization-time of flight (mass spectrometry), a protein with a size of 220 kDa and a pI of 5.4 was identified as a member of the fibronectin group of molecules. Both the purified protein and the commercially available bovine fibronectin inhibited BLV production in naturally infected peripheral blood mononuclear cells, although the fibronectin was less biologically active.