Uptake of fluorochrome-labelled exotoxins by different cell types in culture

The uptake of diphtheria toxin and of Staphylococcus alpha-toxin by two different human cell types cultured in vitro (the HEp-2 continuous cell line and human adult hepatocytes) was studied by fluorescence microscopy and phase-contrast microscopy. The behavior of these two bacterial exotoxins was quite different. Diphtheria toxin was incorporated into cells by pinocytosis, whereas alpha-hemolysin penetrated into the cytoplasm probably through lesions in the cell membrane. In addition, the penetration of diphtheria toxin into the cells was not inhibited by specific antiserum, whereas anti-alpha-haemolysin inhibited the penetration of alpha-tpxin through the cell membrane. The significance of these findings is discussed.