Studies on the mechanism of lysis ofEchinococcus granulosusprotoscoleces incubated in normal serum

Abstract

ABSTRACTBrood capsules were obtained from freshly collected cysts of equine and ovine strains ofEchinococcus granulosus. Protoscoleces were freed from brood capsules either by mechanical disruption or pepsin-HCl digestion. Preparations of protoscoleces studied included: mechanically released protoscoleces without further treatment, or incubated either in HCl pH 2·0 or in evaginating solution (containing Na taurocholate) for 24 h; pepsin-HCl released protoscoleces without further treatment or incubated in evaginating solution for 24 h or 7 days. Half of each preparation of ovine protoscoleces was fixed in absolute methanol.All fresh preparations of protoscoleces lysed rapidly when incubated in normal human serum. Studies with a fluorescein isothiocyanate (FITC) labelled sheep anti-human C3antiserum revealed the presence of C3on the surface of lysing protoscoleces. Antibody could not be detected on the surface of any of the preparations of fresh or methanol-fixed protoscoleces using direct or indirect fluorescent antibody tests suggesting that the classical pathway of complement activation was not involved in the lytic process. Strong evidence for lysis by the alternate pathway of complement activation was the lysis of protoscoleces which had been treated with pepsin-HCl and lysis of protoscoleces in guinea-pig serum deficient in C4component of complement.