A New Indicator Cell Line Established to Monitor Bovine Foamy Virus Infectio

In order to improve the accuracy for quantitating the bovine foamy virus （BFV） in vitro, we developed a baby hamster kidney cell （BHK）-21-derived indicator cell line containing a plasmid that encodes the firefly luciferase driven by the BFV long terminal repeat promoter （LTR, from -7 to 1012）. The BFV titer could be determined by detecting the luciferase expression since the viral trans-activator BTas protein activates the promoter activity of the LTR. One clone, designated BFVL, was selected from ten neomycin-resistant clones. BFVL showed a specific and inducible dose- and time-dependent luciferase activity in response to BFV infection. Although the changes in luciferase activity of BFVL peaked at 84 h post infection, it was possible to differentiate infected and uninfected cells at 48 h post infection. A linear relationship was established between the multiplicity of infection （MOI） of BFV and the activated ratio of luciferase expression in BFVL. Moreover, the sensitivity of the BFVL-based assay for detecting infectious BFV was 10,000 times higher than the conventional CPE-based assay at 48 h post infection. These findings suggest that the BFVL-based assay is rapid, easy, sensitive, quantitative and specific for detection of BFV infection.