Stabilizing effect of GP64 on HRSV lacking its homologous transmembrane glycoproteins. (A) Stability of virus having the GP64/F gene added to its genome (RSΔSH,G,F/GP64/F) and (B) stability of virus having the GP64/F protein provided by complementation from Vbac cells (RSΔSH,G,F). Stocks of viruses RSΔSH and RSΔSH,G,F/GP64/F were generated in Vero cells (A) and stocks of virus RSΔSH,G,F were prepared in Vbac cells (B), and then stored at 4°C , 22°C or 37°C. Titers were determined by TCID50 over different time intervals as indicated on the graphs and compared with the titers from the day of harvest. Infectivity was plotted as a percentage of the TCID50 at the start of the experiment (time 0). Error bars represent standard deviations from the mean of triplicate samples.