Three-dimensional reconstruction of the feeding process of the malaria parasite.

The use of serial sectioning followed by three-dimensional (3D) reconstruction is a convenient way to study the spatial morphology of any structure (organ, cell, organelle). This method was applied to the study of the feeding mechanism of some strains of murine and human Plasmodium and enabled clarification of morphological features of this process. The feeding and digestive system of Plasmodium is polymorphic: in single sections, it shows rounded or elongated vesicles or vacuoles of very different sizes and content. The 3D reconstruction allowed us to describe the phenomenon both in space and in time. The contents of the host cell are taken up through the cytostome to form a sausage-shaped cytostomal tube. Individual digestive vesicles are either pinched off from the terminal portion of the tube or by the individualization of the different portions of the tube itself. The cytosomal system can be made of several tubes or vesicles always originating from cytostomes that can disappear when the tube is fully developed. A second feeding mechanism is also observed. Smaller vesicles are formed from the cytostomal vacuoles or tubes, or from the surface of the so-called "food vacuole, " or from the whole erythrocyte/parasite interface. Very few differences appear when the different strains are compared. In the chloroquine-resistant strain of P. berghei or in the P. falciparum FCR3 strain, there appears to be a large increase in the number of cytostomal vesicles, with several functional cytostomes in P. falciparum. The chronology of the appearance of the two systems is comparable between the different species except in P. falciparum, where the pigment vesicles fuse together very rapidly to form a large residual vacuole with which the subsequently formed and degraded digestive vacuoles fuse.