Salinas, G., Fernández, V., Fernández, C., and Selkirk, ME 1998. neither catalase nor GPx activity could be detected, either by spectro-Echinococcus granulosus: Cloning of a thioredoxin peroxidase. Experi- photometric methods (Aebi 1983; Paglia and Valentine 1967) or by mental Parasitology 90, 298–301. 1998 Academic Press assays applicable to polyacrylamide gels (Manchenko 1994). Despite Index Descriptors and Abbreviations: Echinococcus; cestode; perox- the apparent deficiency in these enzyme activities, protoscoleces of E. iredoxin; thioredoxin peroxidase; hydrogen peroxide metabolism; ROS, granulosus were observed to metabolize hydrogen peroxide (Fig. 1). reactive oxygen species; SOD, superoxide dismutase; GPx, glutathione peroxidase; TPx, thioredoxin peroxidase; TSA, thiol-specific antioxidant; PCR, polymerase chain reaction; RT-PCR, reverse transcriptionpolymerase chain reaction; PBS, phosphate-buffered saline; RACE, rapid amplification cDNA ends.

Helminth parasite antioxidant enzymes play a key role in protecting these organisms from the potentially damaging effects of reactive oxygen species (ROS) derived from normal aerobic metabolism (Halliwell and Gutteridge 1989) and host-activated leukocytes (Callahan et al. 1988). These organisms have adapted to oxidative stress by synthesizing high levels of antioxidant enzymes and, in many cases, expressing them at the host–parasite interface (Cookson et al. 1992; James 1994). Although nematode and trematode antioxidant enzymes have been extensively characterized, very few studies have been carried out in cestode parasites (Callahan et al. 1988; James 1994). We have initiated FIG. 1. Hydrogen peroxide consumption by Echinococcus granu-