Activation of complement by hydatid cyst fluid of Echinococcus granulosus.

Factors present in hydatid cyst fluid of Echinococcus granulosus were found to interact with complement from several species. This nonimmunologic fixation resulted in the depletion of hemolytically active complement from fresh guinea pig serum, the conversion of human C3 to an electrophoretically faster species and the genration of smooth muscle contracting substances, analogous to anaphylatoxins, in normal rat serum in vitro. Vascular permeability changes were produced in vivo in rats and humans after intradermal inoculation of complement interacting fractions of hydatid fluid. It is suggested that these factors may contribute to the pathogenesis of the shock syndrome which follows intravenous administration of hydatid fluid in normal animals, and to the nonspecificity of immunodiagnostic skin tests for hydatid infection in man and animals.