Up-regulation of tumor necrosis factor alpha mRNA is associated with bovine-leukemia virus (BLV) elimination in the early phase of infection

Protective immune responses were analyzed in eight sheep vaccinated with BL V envelope peptides and experimentally infected with bovine-leukemia virus (BLV). Five of eight peptide-immunized sheep showed a high T-cell prolifera tive response to the BLV peptides and all of these were protected from the infection. The other three peptide-immunized sheep showed no T-cell prolife rative responses to any BLV antigens similar to control sheep, though they also exhibited resistance to BLV challenge. To investigate other mechanisms which suppress BLV expansion in these non-responding sheep, we measured th e levels of the cytokine expressions before, and after, BLV challenge using competitive reverse-transcriptase polymerase chain-reaction systems. It wa s revealed that the expression of tumor necrosis factor alpha (TNF alpha) w as higher in BLV-resistant sheep than in BLV-susceptible sheep. Thus, TNF a lpha expression rather than specific T-cell activity may play an important role in the protective mechanism against BLV infection, at least during the primary viremia phase. (C) 1999 Elsevier Science B.V. All rights reserved.