Fig. 4.

Effect of acidic pH on the temperature dependence of NDV F-promoted cell–cell fusion. RBCs were double--NDV vectors. At 24 h post-transfection, F0 precursor was activated with acetyl trypsin and cells were treated with pH 5.0- or pH 7.4-buffered PBS for 5 min at 37 °C. Then, cells were incubated with labeled RBC (0.2% hematocrit) at different temperatures for 1 h. After washing unbound RBC, the extent of dye transfer was analyzed and quantified as the percentage of red- (R18) or green- (calcein) stained cells out of the total number of cells. Data concerning R18 transfer are shown and are similar to those of calcein transfer (not shown). (A) Microphotographs from a representative experiment. (B) Results are means ± SD of three independent experiments. Statistical analyses were performed using the paired t test: * p < 0.05 statistically significant: ** p < 0.01 very significant.