RT assay for the detection of replication competent virus. PEC and spleen cells were obtained 24 and 48 hours after thioglycollate injection and cocultured with either 3T3 cells or LPS-stimulated spleen cells. Supernatants were obtained every 24 hours for 7 days and added to fresh 3T3 cells. Two samples of supernatants harvested at day 3 of the first and second cultures were checked for the presence of RT (columns 3 through 10). Columns 1 and 2 represent control supernatants taken from cultures of N2 producer line, spleen cells, PEC, and media control, as marked in the figure.