AUTORADIOGRAPHIC ANALYSIS OF THE GERMINATIVE TISSUE IN EVAGINATED TAENIA-SOLIUM METACESTODES

Evaginated Taenia solium metacestodes dissected from infected pork mea t were incubated in vitro in RPMI 1640 medium with tritiated thymidine , washed, and further incubated for various chase periods. Worms were fixed and embedded in Poly/Bed and sections were processed for autorad iography. Results showed that all longitudinal sections had a germinat ive region located 500-700 mm posterior to the apex of the scolex with tegumentary cytons arranged in staggered columns perpendicular to the tegument. After 6-hr pulse and 0-12-hr chase periods, a large number of labeled cells were found in the parenchyma and tegumentary wall, in cluded were myocytons, calcareous corpuscle cells, flame cells, osmore gulatory channel cells, and, in the medullary parenchyma, labeled undi fferentiated round cells with a large nucleus, prominent nucleolus, ab undant ribosomes, and no cytoplasmic organelles. These undifferentiate d cells were not labeled after 24-hr and 48-hr chase periods, an obser vation that strongly suggests these cells divide and migrate toward th e tegument in a pattern similar to that described for other cestodes. The morphology and localization of these cells support the view that t hey are stem cells that give rise to the various cell types of the teg umentary wall. The results indicate chat T. solium contains a germinat ive tissue similar to that described in other cestodes, in which stem cells proliferate continuously, differentiate, and migrate to the tegu ment, constituting the main process by which these worms develop from metacestode to the adult stage.