A quantitative assay for measuring human foamy virus using an established indicator cell line

In order to improve the accuracy for detecting human foamy virus (HFV), an indicator cell line was established by co-transfecting baby hamster kidney- 21 cells with two plasmids: one containing a G418 antibiotic resistance mar ker and the other including the luc gene which was placed downstream of the inducible HFV long terminal repeat promoter (from -533 to +20). Among II i ndependent subclones, IdB14 was found to be stable with a low basal level o f luciferase activity. Although the changes in luciferase activity in infec ted clones showed time-dependency and peaked at day 8, it is possible to di fferentiate infected and uninfected cells on day 2. The sensitivity of the foamy virus activated luciferase (FAL) assay was 400 times higher than the end-point syncytium formation by TCID50. The HFV LTR promoter in the IdB14 cell line was specific for this virus. Moreover, a linear relationship was found between the MOI and the activated intensity of luciferase expression. These findings suggest that the FAL assay using the IdB14 indicator cell l ine is a simple and useful technique for rapid diagnosis and quantitation o f active HFV infection. (C) 2001 Elsevier Science B.V. All rights reserved.