Ultrastructural studies on the in vitro interaction of Trypanosoma cruzi bloodstream forms and mouse peritoneal macrophages.

Macrophages are normally host cells for T. cruzi in the vertebrate host. Since the process of interiorization of this parasite into those cells is still controversial, we decided to investigate by electron microscopy the in vitro uptake of T. cruzi bloodstream forms by mouse peritoneal macrophages. After 15 min of interaction with macrophages, parasites are interiorized by a process of phagocytosis in which both parasite and host cell seem to play a specific role. Sequential steps of the uptake process and the simultaneous ultrastructural alterations of the host cell morphology have been studied. A dense amorphous substance interposed between the parasite and the macrophage surface was regularly observed. Although its origin, significance and nature remain unknown, we discuss the possibility that it might be released extracellularly by the macrophage in response to the parasite stimulation.