Abstract
This study focused on products of the bovine Mx1 gene as specific markers for acute viral infections. The rationale for this is the fact that viral infections are commonly paralleled by the synthesis, release, and remote action of alpha/beta interferons (IFN-alpha/beta). Released IFN-alpha/beta act through specific receptors present on nucleated cells to transduce signals for the transcription of numerous IFN-regulated genes, such as the ones for double-stranded-RNA-dependent protein kinase, 2'-5'-oligoadenylate synthetase, or the Mx proteins. In this study, cultured MDBK cells and bovine white blood cells (WBC) were treated with recombinant IFN-alpha or infected with either bovine herpesvirus 1 (BHV-1) or bovine rotavirus (BRV). Treatment of cultured cells with IFN-alpha was followed within 4 h by a time- and dose-dependent accumulation of intracytoplasmic Mx protein as revealed by immunostaining and Western blot immunoassay. This was preceded by a distinct rise of Mx mRNA in similarly treated cells, as revealed by a newly established quantitative TaqMan PCR technique. The two viruses displayed a cell-dependent in vitro ability to induce Mx proteins, which was limited to bovine WBC with BHV-1 and to MDBK cells with BRV. The established methods were successfully used to show that infection of calves with a noncytopathic strain of bovine viral diarrhea virus, a pestivirus, was followed within 2 days postinfection by strong expression of both Mx mRNA and Mx proteins in WBC.