In vitro activity of Acanthamoeba castellanii on human platelets and erythrocytes

The effect of Acanthamoeba on human platelets and erythrocytes has not been fully elucidated. This paper
reports that cell-free supernatants prepared from A. castellanii can activate human platelets, causing both a
significant increase in the cytosolic free-calcium concentration and platelet aggregation. In addition, we
demonstrated that platelet activation depends on the activity of ADP constitutively secreted into the medium
by trophozoites. This study also showed that A. castellanii can affect human red blood cells, causing hemolysis,
and provided evidence that hemolysis occurs in both contact-dependent and contact-independent ways; there
are differences in kinetics, hemolytic activity, and calcium dependency between the contact-dependent and
contact-independent mechanisms. Partial characterization of contact-independent hemolysis indicated that
ADP does not affect the plasma membrane permeability of erythrocytes and that heat treatment of amoebic
cell-free supernatant abolishes its hemolytic activity. These findings suggest that some heat-labile molecules
released by A. castellanii trophozoites are involved in this phenomenon. Finally, our data suggest that human
platelets and erythrocytes may be potential cell targets during Acanthamoeba infection.