The endocytic pathway in Entamoeba histolytica

We studied the endocytic pathway of Ent-amoeba histolytica using (a) confoc al laser scanning microscopy to observe living cells labeled with fluoresce nt probes and (b) transmission electron microscopy of cells incubated in th e presence of gold-labeled proteins or in a cytochemical medium designed fo r the localization of acid phosphatase activity. Images of acridine-orange- labeled cells showed that most of the intracellular vacuoles were acidic an d were also labeled with Lucifer yellow, a fluorescent dye widely used for labeling of compartments of the endocytic pathway. A similar labeling patte rn was observed when the cells were incubated in the present of fluorescein -labeled bovine albumin. However, no labeling was observed when fluorescein -labeled transferrin was used. Gold-labeled proteins (albumin, transferrin, horseradish peroxidase, and lactoferrin) were used for further characteriz ation of the endocytic pathway. With the exception of transferrin, all the proteins bound to the protozoan surface and were subsequently internalized, appearing in small peripheral vesicles and some tubular structures. The in gested molecules accumulated in large vesicles located in the more central portion of the cell, which also presented acid phosphatase activity.