Schistosoma mansoni: Radioisotope uptake and retention by cercariae and developing schistosomules

Biomphalaria glabrata snails which had been previously infected with Schistosoma mansoni were cultivated for extended periods of time in water containing one of three radioisotopes: [ 3H]thymidine, l-[ 3H]amino acids, or [ 14C]formate. The growth and development of both snails and schistosomules were not affected by the presence of isotopes. Substantial radiolabeling of cercariae was obtained from 6 to 20 days following the isotope introduction. The most heavily labeled cercariae were those derived from snails incubated with l-[ 3H]amino acids. The processes of membrane penetration resulted in a 50% reduction of isotope during the conversion from cercariae to schistosomules. Worms derived from the same cercarial pool and perfused from rat groups at different intervals demonstrated a rapid loss of isotope. After 15 to 19 days of development within the vertebrate host, labeled schistosomules were no longer detectable by liquid scintillation criteria; however, they could still be distinguished by autoradiography. A portion of the radioactivity could be recovered from host serum in the form of circulating immune complexes composed of worm antigen and host immunoglobulin. The described research opens the way for potential applications of subpopulation analysis of worm development and in vitro analyses of the products of these subpopulations.