Polymorphism and expression of the tumour necrosis factor-alpha (TNF-alpha) gene in non-infected cows and in cows naturally infected with the bovine leukaemia virus (BLV)

The objective of this study was to determine the influence of TNF-alpha gene polymorphism at position -824 A > G on TNF-alpha gene expression in BLV-positive animals with aleukaemic (AL) and persistent lymphocytosis (PL) forms of enzootic bovine leukosis (EBL) and in BLV-negative cows. Polymorphism of the TNF-alpha gene at position -824 A > G had a complex influence on TNF-alpha gene expression in cows infected with BLV. In animals with various TNF-alpha genotypes, mRNA levels were stable and similar, but significant differences were noted in the percentages of PBMCs expressing membrane TNF-alpha (mTNF-alpha) protein (PBMCs that were positive for mTNF-alpha). In healthy cows, significant differences in TNF-alpha gene expression were not noted at any of the analysed levels. BLV infection and EBL progression resulted in differential TNF-alpha gene expression at both mRNA and protein levels, but the differences in the amount of the transcript and the percentages of mTNF-alpha+ cells exhibited a reverse trend. The lowest mRNA levels and the highest percentage of PBMCs expressing mTNF-alpha protein were determined in BLV-positive cows. These complex results regarding TNF-alpha gene expression in BLV-positive cows could be attributed to the presence of virus or viral protein/proteins modifying the expression of the TNF-alpha gene.