Schistosoma mansoni cercariae experience influx of macromolecules during skin penetration

SUMMARY We have observed that when cercariae penetrate the skin of mice, there is influx into their tissues of Lucifer Yellow andcertain labelled molecules of up to 20 kDa molecular weight. This observation was made using a variety of fluorescentmembrane-impermeant compounds injected into the skin before the application of cercariae. This unexpected phenom-enon was investigated further by transforming cercariae in vitro in the presence ofthe membrane-impermeant compoundsand examining the distribution by microscopy. In schistosomula derived from this procedure, the nephridiopore andsurfacemembranewerelabelledwhilethepre-andpost-acetabularglandswerenotlabelled.Theregionassociatedwiththeoesophagus within the pharyngeal muscle clearly contained the fluorescent molecules, as did the region adjacent to theexcretory tubules and the germinal mass. We used cercariae stained with carmine to aid identification of regions labelledwith Lucifer Yellow. Although the mechanism of this influx is unclear, the observation is significant. From it, we cansuggest an hypothesis that,during skin penetration, exposure of internal tissues of the parasite toexternal macromoleculesrepresents a novel host-parasite interface.Key words: cercaria, fluorescent dextrans, in vitro transformation, Lucifer Yellow, propidium iodide, schistosomulum,skin penetration.