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

A method is described for selecting a single trypanosome so that it can be studied under phase contrast and then by electron microscopy in serial section. Illustrations are given of 18 serial sections through a short-stumpy trypanosome. Ribosomal particles which lie free in the cytoplasm of the long-thin form aggregate into polyribosomes; analogy with other cell types indicates active synthesis of intracellular protein. Larger ribosomal particles are attached to the outer surface of the endoplasmic reticulum. Similar analogy indicates the synthesis of protein for secretion. In the short-stumpy form the endoplasmic reticulum is distended with amorphous material. Similar material is present in “vacuoles” in the cytoplasm which we have shown to 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 pinocytotic activity) which may consist of vesicles or distended tubules. We discuss these differences in the ultrastructure of T. brucei in relation to its cycle of development in the blood and to the excretion of exo-antigen.