RESUMO
BACKGROUND: In a previous study, it was shown that growth of evaginated metacestodes occurs in the germinative tissue of the neck by duplication of somatic stem cells. In these specimens, it was not possible to find the mitotic figures required to demonstrate duplication of germ cell lines. METHODS: Taenia solium strobilae were collected from the intestinal lumen of outbred hamsters infected orally with 10 metacestodes dissected from naturally infected pigs. Animals were anesthetized 1-10 days postinfection, the small intestine excised, submerged in PBS, and cut open longitudinally. Live Taenias were incubated for 6-8 h in medium containing colchicine or 3H-thymidine, washed, and embedded for electron microscopy. For light microscopy and autoradiography, longitudinal sections were cut from whole blocks and mounted on glass slides. A population of large cells without nuclear membranes and containing discrete aggregates of chromatin were observed apposed to myofibrils in the germinative tissue of the neck. These cells were confirmed by electron microscopy as metaphase mitotic figures, with chromosomes attached to a microtubular spindle, embedded in cytoplasm, without a nuclear membrane, and with characteristic centrioles. RESULTS: Only tapeworms in which 3H-thymidine was injected directly into the worm tissue by microsyringe were positive by autoradiography, demonstrating that in contrast to evaginated metacestodes, intestinal worms do not transport thymidine across the tegument. CONCLUSIONS: The results show that differentiating T. solium worms have a subset of stem cells that require passage through a mammalian host to go into mitosis, and that tapeworms grown in an experimental animal do not take up 3H-thymidine in vitro.
Assuntos
Intestinos/parasitologia , Teníase/patologia , Animais , Autorradiografia , Cricetinae , Intestinos/patologia , Mesocricetus , Microscopia Eletrônica , Taenia/crescimento & desenvolvimento , Taenia/ultraestruturaRESUMO
Platyhelminths, like many other organisms, are capable of producing mineral concretions. In cestodes these are referred to as calcareous corpuscles. Studies on these concretions in different cestodes both in vivo and in vitro have resulted in a number of hypotheses on their origin, formation, and structure. Calcareous corpuscles are believed to be of cellular origin, although the kind of cell involved and the mechanisms of mineralization remain under discussion. In the present paper we show that formation of calcareous corpuscles in cysticerci of Taenia solium is not of intracellular origin, as described for other cestodes, but occurs extracellularly in the lumen of protonephridial ducts in a way similar to that proposed for trematodes. This finding enhances the function of the protonephridial ducts, at least in the larvae of T. solium, to the roles formerly ascribed to the calcareous corpuscles.
Assuntos
Cysticercus/fisiologia , Cysticercus/ultraestrutura , Animais , Cisticercose/parasitologia , Cisticercose/veterinária , Cysticercus/isolamento & purificação , Microscopia Eletrônica , Músculo Esquelético/parasitologia , Suínos , Doenças dos Suínos/parasitologia , Vacúolos/fisiologia , Vacúolos/ultraestruturaRESUMO
Crystals of virus-like particles (VLP) are described as occurring in the nuclei of damaged tegumentary cytons from carcasses of Taenia solium metacestodes that had been stripped of their teguments. The VLP are grouped as parallel lines of round particles in an hexagonal packaging of spheroids forming small or large crystals. The individual particles have an external diameter of 36-37 nm and a wall of 5-6 nm thick, which surround a cavity of lower electron density. As identical crystals were also observed in normal tissues of T. solium and of T. crassiceps, it is suggested that both species of cysticerci are normal carriers of a similar species of virus. The possible biological implications of this condition are discussed.