On the interactions between macrophages and developmental stages of Schistosoma mansoni: The cytotoxic mechanisms involved in macrophage-mediated killing of schistosomula in vitro

In an in vitro cytotoxicity assay, mouse adherent peritoneal exudate macrophages (APEM), harvested 8-10 weeks post Schistosoma mansoni infection caused sizable (> 90 %) specific killing of schistosomula.This cidal effect was not diminished by the addition of scavengers of oxidative burst products to the cytotoxicity assay, albeit macrophages from schistosomeinfected mice produced more H202 than did macrophages from non-infected mice.Of inhibitors of lysosomal enzyme function and release added to the cytotoxicity assay, trypan blue (1 mg/ml) fully abolished the schistosomulicidal effect; hydrocortisone (100 μg/ml) was partly effective, and gold salts (1 mg/ml) were ineffective.A cidal effect was not apparent in the absence of L-arginine nor in the presence of excess (> 400 μg/ml) L-arginine, L-lysine or Lornithine.Arginase (5 U/ml) totally abrogated the schistosomulicidal effect.The findings suggest that a macrophage protein of a lysosomal origin, dependent on arginine for its reaction and/or production, may be involved in the in vitro killing of schistosomula by macrophages from S.mansoni-infected mice.