OBJECTIVETo express and purify Schistosoma japonicum ribosomal protein S4(SjRPS4) in Escherichia coli, and assess its value in immunodiagnosis of Schistosomiasis japonica.

METHODSGene fragment of SjRPS4 was amplified by screening the cercaria cDNA library of Schistosoma japonicum. The target gene was cloned into the expressive vector pQE30 and transformed into E. coli M15. The recombinant protein expression was induced by isopropylthio-β-D-galactoside (IPTG). This fusion protein was purified by Ni(2+)-NTA chromatography and identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Western blot and ELISA.

RESULTSThe plasmid pQE30/SjRPS4 was constructed successfully and expressed a SjRPS4 fusion protein in E. coli as showing a single special band on SDS-PAGE gel at Mr 30 × 10(3) position. It reached a purity of above 90% after purification. The Western blot result confirmed that the recombinant protein could specifically react with the serum samples from patients of schistosomiasis. Detecting the serum of Schistosomiasis japonica patients by ELISA, the sensitivity and specificity of the ELISA method were 90.91% (70/77) and 92.59% (25/27), the positive rate of recombinant protein expression was 67.30% (70/104). There was no cross-reaction with paragonimiasis patients' serum.

CONCLUSIONProtein SjRPS4 was successfully cloned and expressed, and it was confirmed that SjRPS4 antibodies were valuable in the diagnosis of Schistosomiasis japonica.