PRODUCTION OF SCHISTOSOMA-MANSONI DAUGHTER SPOROCYSTS FROM MOTHER SPOROCYSTS MAINTAINED IN SYNXENIC CULTURE WITH BIOMPHALARIA-GLABRATA EMBRYONIC (BGE) CELLS

In vitro production of Schistosoma mansoni daughter sporocysts (DS) from miracidium-derived mother sporocysts (MS) was achieved by synxenic larval cultivation with cells of the Biomphalaria glabrata embryonic (Bge) cell line. The in vitro growth and viability of MS cocultured with Bge cells or in Bge cell-conditioned medium were significantly extended beyond that of larvae cultured in fresh medium alone. However, complete DS development and emergence from MS were achieved only in the presence of Bge cells. Introduction of either miracidia or previously transformed MS onto Bge cell monolayers resulted in an initial attachment of cultured cells to sporocysts, followed by a gradual encapsulation of larvae by multiple layers of Bge cells. Sporocysts and their encapsulating cells eventually formed large cellular aggregates, within which MS increased 4-fold in size during the first 20 days of cultivation. The timing of in vitro DS development was somewhat variable; however, in general, early embryo formation, i.e., germ cell aggregates with surrounding primitive epithelium, was first detected at 15-20 days of culture, whereas motile, intra-MS daughter stages were seen at 25-30 days and thereafter. Mature, first generation DS, measuring 136 +/- 46 mu m long by 22 +/- 6 mu m wide, emerged from MS starting at approximately 30-45 days of initial cultivation. Although the basic morphology and size of emergent, in vitro-derived DS were comparable to those propagated in vivo, there was a large reduction in the in vitro reproductive capacity of the MS and a delay in DS culture development. Bge cells provided an acceptable physiological and physical environment for in vitro MS-to-DS development, although conditions optimal for sporocyst growth and those permitting continued DS-to-cercarial stage formation have yet to be defined.