Plaque reduction assay in HEp-2 cells. RSV strain Long was assayed for its sensitivity to five compounds. Supernatants were harvested from test (25 μM) or control compound (35 μM) treated RSV-infected HEp-2 cells at a multiplicity of infection (MOI) of 0.1. Serial dilutions of the supernatants were added to monolayers of HEp-2 cells in 24-well plates. Cells were fixed after 6 days and stained with neutral red. Plaque reduction assays were performed in triplicate per compound. CC, uninfected cell control; VC, untreated virus-infected control. The concentration of DMSO in each assay well, including all control wells was 0.5%.