Interaction between Taenia taeniaeformis and the complement system.

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.