Publisher Summary Chagas' disease-like all really great and important discoveries-has its own and very peculiar history, called by Magalhaes , a “tragicomedy, which embittered and destroyed the life of one of our greatest compatriots”. In this history it is useful to distinguish the following six periods. Chagas in 1908 discovered in the intestine of the blood-sucking triatomas that were common in the primitive huts of the Brazilian hinterland, an unknown trypanosome, which was named by “Schizotrypanum cruzi.” The presence of this parasite in bugs suggested to him the possible existence of an infectious disease in animals and man. Soon afterwards Chagas also found the parasites in the blood of domestic animals (dogs and cats) and in the blood of a sick child with a high temperature. The discovery of American trypanosomiasis by Carlos Chagas represents one of the most fascinating events in the history of medicine. It is almost incredible that such severe pathological manifestations, which represent the “causa mortis” of one third of our autopsy material, would have been overlooked or unknown before Chagas' unique discovery. American trypanosomiasis shows a very peculiar pathology of homeostasis of the human organism, and represents even today a new realm in pathology, which becomes understandable through Cannon's law of denervation.

Chagas' disease and Chagas' syndromes: the pathology of American trypanosomiasis.

The mode of entry and intracellular fate of epimastigotes and trypomastigotes of Trypanosoma cruzi in cultured cells was studied. Electron microscopic observations indicated the uptake by phagocytosis of both forms into mouse peritoneal macrophages and of trypomastigotes and transition forms into other cultured cell types. In each instance the organisms were initially surrounded by a plasma membrane-derived phagosome. Trypsin and chymotrypsin treatment of the macrophages completely abolished attachment and ingestion of both forms, indicating that protease-sensitive structures on the macrophage plasma membrane mediate ingestion. The macrophage Fc or C3b receptors were not essential for uptake of T. cruzi in the conditions used. Cytochalasin B inhibited ingestion but not the attachment of both forms by macrophages. Epimastigotes were not taken up by HeLa, L cells, and calf embryo fibroblasts. In macrophages, epimastigotes were killed and digested within phagolysosomes. In contrast, trypomastigotes and transition forms escaped from the phagocytic vacuole and then multiplied in the cytoplasmic matrix. Amastigotes released from infected cells exhibited properties similar to those of trypomastigotes and were able to enter all cell types studied and multiply intracellularly.

https://rupress.org/jem/article-pdf/143/6/1402/1087768/1402.pdf

Trypanosoma cruzi: mechanism of entry and intracellular fate in mammalian cells.

Publisher Summary Among the protozoa of the Trypanosomatidae family, a large number of species represent agents of diseases, such as Chagas' disease. This chapter reviews some aspects of the cell biology of Trypanosoma cruzi, giving emphasis to those aspects related to the ultrastructure of pathogenic protozoa. Protozoa of the Trypanosomatidae family show, during their, life cycle, several forms which can be easily identified by light microscopy in Giemsa-stained preparations. The chapter also explains the life cycle of T. cruzi. In the life cycle of T. cruzi, there are forms which are able to divide. There is one form, considered to be highly differentiated and responsible for the infectivity of these protozoa, which does not divide. It is highlighted that the trypomastigote form can transform into a rounded form which possesses a free flagellum. This form, which appears in the stomach, is able to transform into either short epimastigotes that start a process of multiplication in the intestinum or into long epimastigotes which move to the more posterior region of the digestive tract of the bug. Cell surface is also emphasized in the chapter.

Cell Biology of Trypanosoma cruzi

SYNOPSIS. With the technique of preselecting pure suspensions of trypanosomes for subsequent electron microscopy and with epoxy resin embedding after glutaraldehyde fixation, we have re-examined the ultrastructure of Trypanosoma lewisi with particular reference to the flagellum and pellicle. The peripheral flagellar tubules exhibit clockwise asymmetry; however, sub-tubule B of the peripheral tubules is divided into a doublet by a diagonally running anti-clockwise arm that originates from the median diaphragm. Projections which seem to be continuous with the counter-clockwise arms extend into a “basket shaped” intra-flagellar structure. This structure, originating distal to the flagellar pocket and running anteriorly within the flagellar membrane, may play a role in maintaining the rigidity of the flagellum.

The central flagellar tubules have a double helical substructure and dense cross-striae (diameter 50 A), and are regularly arranged at distances of approximately 250 A. The central tubules arise from separate kinetosomal plates that lie at two different elevations. One central flagellar tubule originates from a flattened kinetosomal plate which makes contact with the peripheral tubules. The other central tubule passes through the flattened plate to fuse with an underlying “disc-like” plate.

The primary kinetosome exhibits the uniform triplet pattern of tubules at its most proximal region. A pair of tubules closely associated with one of the triplets represents two of the four subpellicular tubules which penetrate the cytoplasm in the region of the flagellar pocket. Sub-pellicular tubules of dimensions similar to the flagellar tubules form a uniform cytoskeleton in all regions of the cell except in the area of the flagellar pocket.

A desmosome-like structure maintains continual cell membrane contact with the flagellum and the pellicle. This structure is designated the attachment zone. The fine structure of the kinetoplast is demonstrated. The dense intra-mitochondrial elements (presumably containing DNA) are actually tubules, embedded in a moderately dense matrix. Morphological observations indicate that this organelle is probably primarily concerned with the ontogenesis of mitochondria, and several mitochondria extend from it into the cytoplasm of the cell.

Ultrastructure of Trypanosoma lewisi: Flagellum, Microtubules, and the Kinetoplast

Summary: Acute Trypanosoma cruzi infections can be asymptomatic, but chronically infected individuals can die of Chagas' disease. The transfer of the parasite mitochondrial kinetoplast DNA (kDNA) minicircle to the genome of chagasic patients can explain the pathogenesis of the disease; in cases of Chagas' disease with evident cardiomyopathy, the kDNA minicircles integrate mainly into retrotransposons at several chromosomes, but the minicircles are also detected in coding regions of genes that regulate cell growth, differentiation, and immune responses. An accurate evaluation of the role played by the genotype alterations in the autoimmune rejection of self-tissues in Chagas' disease is achieved with the cross-kingdom chicken model system, which is refractory to T. cruzi infections. The inoculation of T. cruzi into embryonated eggs prior to incubation generates parasite-free chicks, which retain the kDNA minicircle sequence mainly in the macrochromosome coding genes. Crossbreeding transfers the kDNA mutations to the chicken progeny. The kDNA-mutated chickens develop severe cardiomyopathy in adult life and die of heart failure. The phenotyping of the lesions revealed that cytotoxic CD45, CD8+ γδ, and CD8α+ T lymphocytes carry out the rejection of the chicken heart. These results suggest that the inflammatory cardiomyopathy of Chagas' disease is a genetically driven autoimmune disease.

Pathogenesis of Chagas' Disease: Parasite Persistence and Autoimmunity

Thin sections of Trypanosoma cruzi in tissue cultures and from blood agar medium have been examined with the electron microscope.In the leishmania and crithidia forms of the parasite a neat separation of kinetonucleus and blepharoplast has been obtained and these structures are described. The blepharoplast is the row of basal corpuscles which give origin to the axial fibres of the flagellum.Division of the parasite seems to begin in the basal corpuscles; it is followed by binary division of the kinetonucleus and only later by fission of nucleus and cytoplasm.During the development of the leishmania into the crithidia form, the kinetonucleus and basal bodies are dislocated towards the posterior half of the trypanosome. The migration of these two structures and the consequent lengthening of the flagellum causes the surface membrane of the flagellum to be pushed inwards to form a deep invagination, so that the flagellum comes to the surface of the body and is separated from it along its whole length by its own sheath.In the adult form of the parasite a great vacuole is formed near the posterior tip of the trypanosome. It has no definite structure in the electron microscope, is transparent and seems to be filled with a liquid content. The basal corpuscles are situated in this region near the wall of the vacuole. The typical structure of the kinetonucleus could not be identified with certainty in these forms; it seems to be altered by the formation of the vacuole.The vacuole is crossed by a fibre system which comes from the body of the trypanosome and is often dislodged by the size of the vacuole. This fibre system ends in a sharply pointed process of varying length.The cost of reproduction of figures was defrayed by the Instituto de Biofisica da Universidade do Brasil.

M. de Oliveira Musacchio

Papers

Electron microscopic study of Trypanosoma cruzi in thin sections of infected tissue cultures and of blood-agar forms.