FIG 8.

Human polyclonal antibodies fail to efficiently block gB/VSV-G-mediated fusion. Purified IgGs from plasma samples derived from 40 individual HCMV-positive elite neutralizers were tested in the cell fusion assay for their ability to prevent gB/VSV-G-induced syncytium formation. Lentivirally transduced HEK293 cells in 96-well plates were treated with 100 ng/ml of doxycycline to induce expression of fluorescently tagged gB/VSV-G-EGFP. In parallel, 25 μg of 1G2 and 800 μg/ml of either the individual elite neutralizer IgG preparations or the HCMV HIG Cytotect were added to the medium. Untreated cells (no antibody) served as the mock control. Images were recorded 24 h after addition of the IgG preparations by a Fluorospot reader, and syncytium counts were measured as specified in Materials and Methods using ImmunoSpot, version 6.0.0.2, software. Values were derived from biological triplicates. Syncytium counts were calculated relative to the level of the mock control (no antibody), which was set to 100%.