Host serum proteins in Echinococcus multilocularis: complement activation via the classical pathway

The presence of host serum proteins, including IgG and IgM, within the cyst membranes and on the surface of protoscoleces of Echinococcus multilocularis was demonstrated by the use of HRPO-conjugated purified antisera. Viable protoscoleces incubated either in EDTA- or EGTA-fresh human sera were not lysed; the addition of calcium restored the protoscolecidal activity of the EGTA serum. It is concluded that the complement-mediated lysis of this metazoan organism proceeds via the classical pathway of complement activation. The results are discussed in relation to the ability of this parasite to survive in the immunologically hostile environment of the host.