Mimicry of snail host antigens by miracidia and primary sporocysts of Schistosoma mansoni.

Polyvalent antisera generated in rabbits to soluble haemolymph components from Schistosoma mansoni-susceptible (PR albino 'M line') and S. mansoni-resistant (10-R2) stocks of the snail Biomphalaria glabrata were employed as membrane probes to determine if antigens related to snail haemolymph were produced by the early larval stages of S. mansoni (PR-1 strain). Using immunofluorescence and immunoelectron microscopical methods we have demonstrated that antibodies to susceptible (anti-Suscept) and resistant (anti-Resist) snail haemolymph (Hg-depleted fraction) crossreact with miracidial epidermal and ciliary membranes as well as the surface membranes of intercellular ridges. Primary sporocysts, both transformed in vitro and maintained in culture for various time intervals in the absence of snail-derived factors, retain haemolymph-like antigens on their surface tegument although at reduced levels in comparison to miracidial stages. Furthermore prolonged cultivation of sporocysts (48 h) has little effect on the density of crossreacting tegumental antigens suggesting that as sporocysts mature these antigenic components are continually being expressed at the surface membrane. Since miracidia and sporocysts were derived in media devoid of snail host materials, shared antigens on larval surfaces are believed to be of parasite origin and constitute true molecular mimicry as defined by Damian (1979). The occurrence of crossreacting antibodies in both anti-Suscept and anti-Resist antisera further suggests that mimicked haemolymph-like antigens include at least some which are common to both snail stocks.