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More than 200 million people worldwide are infected with parasitic helminths from the genus Schistosoma, and an additional 400 million are at risk. Although several currently available drugs, particularly Praziquantel, could effectively cure infections, concerns have been raised over the continued efficacy of these agents, as drug-resistant schistosomes have been reported. In addition, chemotherapy is ultimately undesirable since cured individuals are not necessarily protected against reinfection. A preventive strategy, such as the development of a vaccine against schistosomiasis, is a more attractive means of defense against schistosomes. Recently, an S. mansoni glycoprotein, Sm25, was identified in our laboratory as a putative vaccine antigen by its unique immunoreactivity with a protective rat serum (F2x) but not with a nonprotective rat antiserum (W2x). Sm25 is encoded by the GP22 gene, which has an open reading frame (ORF) of 182 amino acids (Barker et al. 1985; El-Sherbini et al. 1990, 1991; Mark et al. 1991). The 140-amino-acid carboxyl terminus (codons 43-182) was cloned and expressed as a fusion product in the pET15b bacterial vector system (PK Suri et al., in prep.).

In these studies, we characterized the humoral and cell-mediated immune responses against Sm25 in three strains of inbred mice. Two models of antigen presentation were examined. In one, mice were subcutaneously immunized with the recombinant product of Sm25, called r140, in an emulsion with aluminum hydroxide (alum), an adjuvant approved for clinical use. In the other, mice were presented with the native Sm25 in the context of an S. mansoni infection …