Figure 7. R70 and SyH7 promote the accumulation of ricin in Rab7 ⁺ vesicles when endosome acidification is inhibited.

Vero cells were treated at 4 °C with R70 or SyH7 and ricin-FITC, in the absence or presence of NH₄Cl to prevent lysosome acidification, and then shifted to 37 °C for 4.5 hr. Vero cells were then fixed and immunolabeled with Rab7 antibodies. (A) NH₄Cl treatment resulted in the accumulation of ricin-mAb containing vesicles that were positive for Rab7 (arrowheads within insets, middle and bottom right panels). Scale bar, 5 μm. (B) The frequency of ricin (in the presence of mAbs) colocalization with Rab7 in cells treated or not with NH₄Cl. Each bar represents the average of 25–30 cells (with SEM) per time point. ***p < 0.001, determined using a one-way ANOVA with Tukey’s post-test.