Tumor necrosis factor α and its receptors in experimentally bovine leukemia virus-infected sheep

To examine whether tumor necrosis factor α (TNF α) contributes to the pathogenesis of bovine leukemia virus (BLV) infection, the mRNA expression patterns of TNF α and its receptors, type 1 (TNF R1) and type 2 (TNF R2) were investigated. Sheep inoculated with BLV were divided into two groups; one was BLV-positive and the other BLV-negative based on the detection in peripheral blood mononuclear cells (PBMC). Expression of TNF R1 mRNA was down-regulated in PBMC from the BLV-positive compared to BLV-negative sheep. No difference was shown in the expression levels of TNF R2 mRNA between the two groups. Furthermore, proliferative responses of PBMC in the presence of TNF α were observed from the BLV-positive, but not BLV-negative sheep. Membrane-bound TNF α (mTNF α) is thought to be one of the ligands, inducing B-cell activation. Flow cytometric analysis demonstrated that the number of PBMC, that were positive for mTNF α expression, was increased in the BLV-positive sheep. Thus, the expression of TNF α and its receptors may be closely associated with lymphocytosis induced by BLV.