Granules and tubules in the cytoplasm of the sleeping sickness trypanosome: An electron microscope study

Abstract

Electron and phase contrast microscopic studies of serial sections of T. brucei reveal ribosomal particles which lie free in the cytoplasm of the long-thin form and aggregate into polyribosomes; analogy with other cell types indicates active synthesis of intracellular protein. Larger ribosomal particles are attached to the outer suface of the endoplasmic reticulum; similar analogy indicates the synthesis of protein for secretion. In short-stumpy form the endoplasmic reticulum is distended with amorphous material. Similar material is present in cytoplasmic vacuoles which correspond to the Type II (phase positive) granules, the appearance of which precedes a crisis in the infection. Type I (volutin) granules which stain with Giemsa have been demonstrated, and have the appearance of lysosomes. The short-stumpy form carries a variable structure between the nucleus and the basal vacuole (an area associated with plnocytotic activity) which may consist of vesicles of distended tubules. These differences in the ultrastructure of T. brucei are discussed in relation to its cycle of development in the blood and to the excretion of exo-antigen.