Definition and mapping of epitopes recognized by specific monoclonal antibodies to Schistosoma bovis 28 kDa glutathione S-transferase: relation with anti-egg viability immunity

Monoclonal antibodies to the 28kDa glutathione S-transferase of Schistosoma bovis have been constructed in mice and used to characterize the epitope(s) potentially implied in the induction of anti-fecundity and anti-egg viability immune responses. Among the MoAbs produced three were particularly studied: Sb4-50 (IgG2a) and Sb4-56 (IgG1) which inhibited Sb28GST activity and Sb4-10 (IgG1) which did not. The use of overlapping peptides covering the entire amino acid sequence of Sb28GST, allowed us to define the linear epitopes recognized by these anti-Sb28GST MoAbs. Amino acid residues 202-211 were recognized by both MoAbs Sb4-50 and Sb4-56 and MoAb Sb4-10 recognized amino acid residues 58-67. Their capacity to inhibit GST activity suggested binding to the active site or to neighbouring regions, which include the C-terminal domain (a.a. 190-211) of the protein. When passively transferred into BALB/c mice MoAbs induced a significant reduction in egg hatching and an increase in immature eggs. Effects on worm burdens were, however, variable and no clear-cut association between the inhibition of enzyme activity and anti-fecundity or anti-viability activities was recorded. Our data indicate that beside the anti-fecundity and anti-viability immunity related to the impairment of GST activity, immune response to epitopes located in other regions of the molecule also contribute to the reduction of egg viability.