Efficiency and duration of transduction of immortalized feline fibroblasts by vGFP and vEnv-GFP. A: GFP expression by the fibroblasts of uninfected cat BO 2 days post-transduction with vGFP (50 TU/cell), as determined by flow cytometry. Left panel, percent GFP positive cells; middle panel, intensity of GFP expression; right panel, mock-transduced cells. B: Susceptibility of fibroblasts from 3 FIV chronically infected cats and 1 uninfected cat to transduction by vEnv-GFP at 100 TU/cell. Percent GFP positive cells (upper panel) and extent of Env expression (lower panel) were evaluated 2 days post-transduction by flow cytometry and western blot, respectively. C: GFP expression (upper panel) and Env expression (lower panel) by fibroblasts of one infected cat (BS) transduced with vEnv-GFP at 50 TU/cell, evaluated at the indicated times by flow cytometry and western blot, respectively. The arrows in panels B and C indicate the Env precursor (135 Kd) and surface (95 Kd) glycoproteins. Bars represent SD calculated from 3 independent experiments. FL-4: Env expressed by the chronically FIV infected cell line FL-4.