Histological examination of the cellular reactions around schistosomula of Schistosoma mansoni in the lungs of sublethally irradiated and unirradiated, immune and control rats.

Histopathological data on the cellular reactions (foci) around Schistosoma mansoni schistosomula in the lungs of both irradiated (750 rad) and unirradiated, passively immunized and normal rats were consistent with the idea that a significant proportion of immune-mediated attrition in passively immunized rats occurs in the lungs. In unirradiated rats, immune serum elicited an enhanced (i.e. larger) and accelerated (i.e. more rapidly developing) inflammatory cellular infiltration around lung-stage parasites when administered 5 days post-infection, when the parasites were already in the lungs. This demonstrated the antigenicity of lung-stage schistosomula and their potential as targets for immune attack. In irradiated rats, innate immunity was decreased as judged by an increase in the number of worms recovered by portal perfusion, and was accompanied by an overall decreased percentage of trapped parasites compared with unirradiated controls, suggesting that trapping in the lungs is involved in innate, as well as acquired immunity. In contrast to the results in unirradiated rats, passive transfer of immune serum into irradiated recipients did not result in larger lung foci than in the NRS-recipients. However, there was evidence of an accelerated response resulting in an essentially similar ratio of trapped parasites (VRS- compared with NRS-recipients) in irradiated rats, as compared with unirradiated rats, reflecting the similar levels of resistance manifested in both groups of rats. This also lent credence to the notion that it was the speed of immune recognition of the migrating schistosomula and the establishment of trapping foci that were of greater importance rather than the size of the enveloping granulomata.(ABSTRACT TRUNCATED AT 250 WORDS)