Taenia solium: Germinal cell precursors in tapeworms grown in hamster intestine

Background. In a previous study, it was shown that growth of evaginated met acestodes occurs in the germinative tissue of the neck by duplication of so matic stem cells. In these specimens, it was not possible to find the mitot ic figures required to demonstrate duplication of germ cell lines. Methods. Taenia solium strobilae were collected from the intestinal lumen o f outbred hamsters infected orally with 10 metacestodes dissected from natu rally infected pigs, Animals were anesthetized 1-10 days postinfection, the small intestine excised, submerged in PBS, and cut open longitudinally. Li ve Taenias were incubated for 6-8 h in medium containing colchicine or H-3- thymidine, washed, and embedded for electron microscopy. For light microsco py and autoradiography, longitudinal sections were cut from whole blocks an d mounted on glass slides. A population of large cells without nuclear memb ranes and containing discrete aggregates of chromatin were observed apposed to myofibrils in the germinative tissue of the neck. These cells were conf irmed by electron microscopy as metaphase mitotic figures, with chromosomes attached to a microtubular spindle, embedded in cytoplasm, without a nucle ar membrane, and with characteristic centrioles. Results. Only tapeworms in which H-3-thymidine was injected directly into t he worm tissue by microsyringe were positive by autoradiography, demonstrat ing that in contrast to evaginated metacestodes, intestinal worms do not: t ransport thymidine across the tegument. Conclusions. The results show that differentiating T. solium worms have a s ubset of stem cells that require passage through a mammalian host to go int o mitosis, and that tapeworms grown in an experimental animal do not take u p H-3-thymidine in vitro. (C) 2001 IMSS. Published by Elsevier Science Inc.