Dose-dependent effects of hydatid fluid toxins from Echinococcus granulosus on mouse peritoneal macrophages.

Hydatid fluid (HF) from hydatid cysts of the cestode Echinococcus granulosus inhibited the phagocytosis of bacteria and yeast cells by host macrophages in vitro. Different assays were used to study the dose-dependent effect of partially purified HF toxins on peritoneal macrophages (PM phi) of the mouse. Trypan blue exclusion, as well as measuring the specific release of lactate dehydrogenase activity and 51Cr release of 51Cr-labelled PM phi, showed that incubation with HF toxins lead to the lysis of the target cells. By measuring the effect of the toxins on the reduction of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide by PM phi, and by experimental labelling using [3H]-uridine, a decrease in metabolic activity was seen. However, at non-lytic concentrations, the PM phi showed a peak of metabolic activity. The observations of the effects on macrophages by parasite-derived toxins may be related to a mechanism by which the parasite survives within an immunized host.