A monoclonal antibody blocking the Schistosoma mansoni 28-kDa glutathione S-transferase activity reduces female worm fecundity and egg viability

The protective effects of two different monoclonal antibodies (mAb) raised against the Schistosoma mansoni 28-kDa glutathione S-transferase (Sm 28 GST) were investigated. Two mAb of the same isotype (IgM) have been selected according to the blocking effect on Sm 28 GST enzymatic activity (S13) or the lack of blockade (H12). When passively transferred into Fischer rats, both S13 and H12 significantly reduced the worm burden. In BALB/c mice clear effects on female worm fecundity and egg viability were observed when the S13 mAb was transferred; these effects included significantly reduced loads of intestinal eggs, reduced egg hatching rates and an increased proportion of non-living eggs. No effect on egg production and egg hatching was observed in H12-treated mice. In addition, worm pairs recovered from S13-but not H12-treated mice laid significantly fewer eggs in vitro, and normal worm pairs incubated in vitro with the S13 mAb produced significantly fewer eggs than those incubated with H12 mAb. The impairment of egg hatching ability was also reproduced in vitro by the S13 mAb. These data suggest the existence of two different effector mechanisms induced by immunization with Sm 28 GST. The effect on the schistosome worm burden appears to be independent of GST activity whereas the effect on S. mansoni female fecundity and egg viability seems to be significantly linked to the inactivation of the enzymatic site.