Neutralizing antibody responses elicited in mice immunized with recombinant bacillus Calmette-Guérin producing the Schistosoma mansoni glutathione S-transferase.

Schistosomiasis is a group of severe parasitic diseases, in humans and domestic animals, that are especially of importance in the developing world. No efficacious vaccine is currently available. However, Ab-mediated immune responses against the 28-kDa glutathione S-transferase of Schistosoma mansoni (Sm28GST) appear to be involved in protection. This Ag was produced in recombinant Mycobacterium bovis bacillus Calmette-Guérin (BCG). The recombinant protein bound glutathione and expressed enzymatic activity, indicating that the active site of Sm28GST was folded properly. Single i.v., i.p., s.c., or intranasal immunizations with rBCG in BALB/c mice resulted in significant anti-SM28GST Ab responses, which were enhanced by a booster dose. The Ab responses remained high for at least 1 yr after immunization. Analyses of the isotype profiles indicated that i.v. immunized mice produced high titers of anti-Sm28GST IgG2a, and less IgG2b and IgG1. Mice immunized by the s.c. route initially also produced high levels of IgG2a and low titers of IgG1 and IgG2b, but the titers of the latter two isotypes increased gradually thereafter, tending toward a mixed profile. Intraperitoneal immunization provided a mixed profile directly after the first administration. High titers of anti-Sm28GST Abs also corresponded to high levels of neutralization of the enzymatic activity. These results indicate that rBCG induces strong IgG1, IgG2a, and IgG2b, and neutralizing Ab responses against Sm28GST, which has been found to correlate with protection against S. mansoni in humans.