Effect of platelet-derived factor on expression of bovine leukemia virus genome.

Plasma of cattle infected with bovine leukemia virus (BLV) contains a factor, plasma blocking factor (PBF), that inhibits the expression of viral genome in cultured lymphocytes from BLV infected cattle. When platelet lysate was added to this culture, BLV antigen became detectable in the culture and there are some factors (PDF) in platelet lysate which have inhibitory activity against PBF. The PDF was present in platelet from BLV-free cattle as well as BLV-infected cattle at relatively high titer. The effect of platelet lysate against PBF on the expression of BLV genome seemed to be irreversible.