The ultrastructure of toxoplasma gondii

This chapter reviews the electron microscopic data on Toxoplasma gondii and its life-cycle stages. There are four invasive forms of T. gondii: the tachyzoite, bradyzoite, merozoite, and sporozoite. Tachyzoites and bradyzoites are associated with the intermediate host, and merozoites and sporozoites with the definitive host. Tachyzoites and merozoites are responsible for the expansion of the population within a host, while the bradyzoites and sporozoites are capable of environmental transmission to new hosts. All of the infectious stages have the same basic morphology, with only minor variations. The standard features are described in this chapter, and are based mainly on observations of tachyzoites. They are comprised of a unique cytoskeleton, secretory organelles, endosymbiontic derived organelles, eukaryotic universal organelles, and specific structures, all enclosed by a complex membranous structure termed the pellicle. The pellicle is a distinctive membrane complex that encloses the infectious stages. Immunoelectron microscopy has played an important role in the understanding of the functions of these organelles. With the development of antibodies to specific proteins, it is possible to begin to identify proteins specifically located in the different organelles. It has also been possible to identify proteins (MIC proteins) that are only present in the micronemes or proteins located in the dense granules (GRA proteins). © 2007 Copyright © 2007 Elsevier Ltd. All rights reserved..