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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.