Molecular characterization of Schistosoma japonicum tegument protein tetraspanin-2: Sequence variation and possible implications for immune evasion

Members of tetraspanin family expressed on the tegument of Schistosoma mansoni have been regarded as potential protective antigens. In this work, we were surprised to identify seven tetraspanin-2 (TSP-2) homologs of the protective antigen Sm-TSP-2 in Schistosoma japonicum and found that the transcription profiles of Sj-tsp-2 subclasses were highly variable in individual adult worms. RT-PCR revealed that Sj-tsp-2 genes were transcribed in cercariae, schistosomula, adult worms, and eggs; however, Western blot analysis indicated that the Sj-TSP-2 proteins were not expressed in eggs. Immunolocalization assays showed that the Sj-TSP-2 proteins localized on the tegument of schistosomula and adult worms, but exposed only on the surface of adult worms. Mice immunized with the recombinant protein of a single TSP-2 subclass showed no protection, while immunized with a mixture of seven recombinant TSP-2 subclasses provided a moderate protection. Those data implicate that the tegument protein Sj-TSP-2 is involved in immune evasion and the high polymorphism of this molecule must affect its potential as a vaccine candidate.