Adolfo Martínez-Palomo

Morphological differences in cap formation were found when trophozoites of different free-living amoebae were treated with the lectin Concanavalin A, which resulted in a rapid redistribution of certain surface components to form small clusters and membrane-folded structures of diverse sizes. Acanthamoeba castellanii, Acanthamoba polyphaga and Naegleria lovaniensis exhibited characteristic caps, however, in A. castellanii this structure was larger and included several folds of the plasma membrane; furthermore, some of these caps had vacuoles containing a fi bro granular content. In contrast, the caps formed by A. polyphaga and N. lovaniensis lacked vacuoles. Regarding Naegleria fowleri, the trophozoites did not produce a defi ned cap, and only small patches of lectin-bound surface receptor complexes were observed at one pole of the cell body. In the free-living amoebae studied, it was not possible to correlate the shape and size of cap with pathogenicity.

Using ultrastructural cytochemical techniques we have found differences in the distribution of surface coat components between the invasive protozoan parasite Entamoeba histolytica and the non-invasive Entamoeba dispar. Carbohydrate-containing components and anionic sites in the cell surface of both species were detected by staining with ruthenium red and cationized ferritin, respectively. Ruthenium red staining revealed a thicker surface coat in E. histolytica trophozoites, whereas trophozoites of E. dispar showed a higher concentration of cationized ferritin particles on its surface. Mannose or glucose residues were found at the plasma membrane of both parasites treated with Concanavalin A (Con A)-peroxidase; the surface reaction product was more evident in E. dispar, compared with E. histolytica. Con A rapidly produced surface caps in E. histolytica trophozoites, whereas E. dispar showed a much less efficient mobilization of surface Con A receptors. Agglutination with Con A produced much larger clumps  in E. histolytica in comparison with E. dispar. In turn, biotinylation assays revealed striking differences in the composition of surface membrane proteins in both amebic species. Overall, these results further emphasize the phenotypic differences between these two  common parasites of the human intestinal tract, once considered to be the same protozoan.