The protective mechanism of action of amines in diphtheria toxin treated Vero cells.

The mechanisms by which a number of alkylamines and ethylenediamine derivatives protect Vero cells from diphtheria toxin were studied. The protective alkylamines and ethylenediamine compounds blocked the cellular degradation of diphtheria toxin, but did not prevent bulk toxin uptake. Specific antibody neutralized the inhibitory effects of toxin on protein synthesis in amine-treated cells when added at 37 degrees C, but was ineffective when added at 4 degrees C. Analogous results were obtained when inositol hexaphosphate was used in the place of specific antibody. Both experiments suggested that, in the presence of the amine compounds studied, diphtheria toxin is sequestered intracellularly and is recycled to the surface for antibody or inositol hexaphosphate neutralization. Finally, it was shown that the protective amines markedly increased the intralysosomal pH of Vero cells and that when the pH of the culture medium was lowered to 4.5, the amine-mediated protective effect was bypassed. In general, the results suggest that the amines exert their protective effect at the level of some acidic intracellular vesicle population, possibly the lysosomes, and thus may indicate a crucial role for the lysosomes in the generation of cytotoxicity.