Complement depletion in rats infected with Fasciola hepatica: in vivo and in vitro studies.

The action of Fasciola hepatica on rat complement was evaluated by measuring the haemolytic activity. Extracts from metacercariae and eggs and the excretory and secretory products of adult flukes reduced the classical pathway of complement-mediated lysis by normal rat sera in a protein dose-dependent manner. Whole metacercariae produced the same effect. In vitro incubation of newly excysted juveniles and intact eggs with normal rat serum had no detectable effect on serum complement activity by either the alternative or classical pathway. During the course of rat fasciolosis a depletion in the classical pathway of complement-mediated lysis was demonstrated particularly 6-9 weeks post-infection; the alternative pathway of complement-mediated lysis was not affected.