OA together with GA abolished the inhibitory effect of GA. (A) Dissecting the stages of fusion affected by the presence of GA. Bar 1, control: GA was not present. Bar 2: GA was maintained throughout the experiments. Bar 3: Effector and target cells were incubated for 30 min. in the presence of 10 µM GA. The neutral pH bathing solution was then replaced by a pH 5.7 solution, which did not contain GA, and this was maintained for 10 min. The low pH bathing solution was replaced by one at neutral pH, also without GA, and fusion was measured. Bar 4: The same protocol was followed as for experiments of bar 3, but prior to acidification, the GA-containing neutral pH solution was replaced by a GA-free neutral pH solution that was maintained for 10 min to allow GA in the membranes to dissociate into the aqueous solution. This almost restored the extent of fusion to that of control. Bar 5: The same protocol as for experiments of bar 3 was used, but GA was maintained through acidification. The subsequent neutral pH wash solution did not contain GA. EBOV GP was the fusion protein for these experiments. (n = 3). (B) The inhibition of cell-cell fusion by GA is reversed by the presence of oleic acid (OA). Upper panels: Massive dye mixing was observed for control (left image), but none was observed in the presence of 10 µM GA (middle image). Addition of 250 µM OA along with GA (right image), resulted in the same degree of fusion as for the control. Extent of fusion is quantified in the bar graphs. (n = 3).