Migration of Schistosoma mansoni in normal and passively immunized laboratory rats

Normal and passively immunized Fischer rats were infected with 75Se-selenomethionine-labeled cercariae of Schistosoma mansoni. Migration of the parasites from skin to lungs to liver was monitored by autoradiographic analyses of these sites. Labeled parasites migrated from skin to lungs with high efficiency in normal and immune rats; disappearance of labeled parasites from the lungs was slower in immune rats. Labeled parasites accumulated in the liver, reaching maximal values by 11 days post-infection in both groups and remaining constant through day 21. Half the number of labeled parasites were detected in the liver of immune rats. The total number of labeled parasites detected in the skin, lungs, and liver was constant through day 5, then declined to about 60% of this value by day 11 in both groups. Over the next 10 days, the rate of decline decreased significantly in normal rats but did not change in immune rats. By day 21 post-infection, nearly 50% fewer labeled parasites were detectable in immune rats. We conclude that a subpopulation of parasites in the lungs is the target of protective antibody in the serum used for passive immunization. Target parasites, retained longer in the lungs, were probably prevented from migrating successfully to the liver. Another parasite subpopulation migrated to the liver with normal kinetics. Lung schistosomula isolated from normal and passively immunized rats were transferred by intravenous injection into recipient rats and their continued migration from lungs to liver compared. No differences in portal perfusion worm yields were detected in normal recipients; equally reduced yields were detected in passively immunized recipients. We conclude that the effects of antibodies during week 1 post-infection were insignificant or reversible.