Expression profile, localization of an 8-kDa calcium-binding protein from Schistosoma japonicum (SjCa8), and vaccine potential of recombinant SjCa8 (rSjCa8) against infections in mice.

Researches on genes expressed in a cercarial stage-specific manner may help us understand the molecular events and functions during schistosome invasion of skin. A genomic clone encoding 8-kDa calcium-binding protein (SjCa8) specifically expressed in cercariae and skin-stage schistosomulum (transformed within 3 h) was obtained from cercariae. Recombinant protein was expressed in vector pET32a (+) and purified using a Ni-NTA purification system. The target protein SjCa8 was determined by matrix-assisted laser desorption/ionization time-of-flight (TOF)/TOF mass spectrometer after thrombin digestion and dialysis. Reverse transcriptase polymerase chain reaction and Western blot revealed SjCa8 can be detected in cercaria and skin-stage schistosomulum but not lung-stage schistosomulum, adult, or egg and was localized to head gland, penetration gland tubes, and penetration glands where Ca(2+) was abundant, and the cercarial tegument (but not tegument of tail) and body-tail junction. Furthermore, SjCa8 was interestingly detected in cercarial secretions. The characterization of SjCa8 indicated that it may undergo structural and physiological modifications, including repair of the surface membrane, changes in permeability that account for the loss of water tolerance, activities of calcium-depending enzymes, and immune signaling, etc. Furthermore, vaccination with rSjCa8 plus adjuvant induced protective effect with 50.39% worm reduction rate and significantly high hepatic and intestine egg reduction rates (54.16%, 50.63%, respectively), which is possibly mediated through an apparent induction of Th1-type immune response for strikingly high level of IgG2a and IgG2b developed in immunized C57BL/6 mice.