Factors present in the cystic bladder fluid of metacestodes of Taenia taeniaeformis and released by these parasites maintained in vitro were shown to interact with the C system in vitro and in vivo. This interaction resulted in the depletion of hemolytic C in normal sera of several species, the generation of anaphylatoxin-like activity in vitro, the conversion of C3, and the production of vascular permeability changes in vivo. The substances appeared to initiate C fixation nonimmunologically via both the alternative and classical pathways. Intravenous administration of parasite factors in rats led to profound depression of circulating C levels and the rats did not become refractory to this effect after repeated dosing over a 3-week period. Circulating levels of hemolytic C were not altered in infected rats over the first 8 weeks of infection. C-dependent inflammatory responses in the skin of rats were inhibited in animals given i.v. doses of parasite factors. The possibility is raised that local consumption of C around the metacestode in vivo could contribute to its successful evasion of inflammation and immune rejection during infection.

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