Anionic site behavior in Leishmania and its role in the parasite-macrophage interaction.

The behavior of cationized ferritin (CF) binding sites on the surface of Leishmania mexicana amazonensis (amastigotes, infective and non-infective promastigotes) and their participation in the interaction with macrophages were evaluated. Glutaral-dehyde-fixed parasites treated with CF present a uniform labelling over the whole cell surface. However, living parasites displayed CF patches and caps. Capping was usually seen towards the anterior (flagellated) portion of the cells, where shedding phenomena took place. These processes were inhibited by sodium azide but not by low temperature (4 degrees C). CF treatment of non-infective promastigotes led to an increase in their uptake by macrophages, whereas the uptake of amastigotes or infective promastigotes was not significantly altered. The effect of CF on the parasite surface charge was analyzed by whole-cell microelectrophoresis. The mean electrophoretic mobility (EPM) of non-infective promastigotes was decreased by 26%, while once again the other parasite forms were not significantly affected. Transmission electron microscopy of mouse peritoneal macrophage cultures, fixed after interaction with CF-labelled parasites, revealed that both amastigotes and infective promastigotes quickly removed bound CF. Therefore CF was seen neither in parasite-macrophage attachment areas nor in parasitophorous vacuoles. On the contrary, non-infective promastigote-macrophage attachment areas were remarkably large and preferentially comprised CF-labelled membranes. These results strongly suggest an important participation of cell surface anionic sites in the L. mexicana amazonensis-macrophage interaction.