Cloning, expression, and characterization of Schistosoma japonicum tegument protein phosphodiesterase-5

The tegument proteins of schistosomes are regarded as potential vaccine candidates and drug targets to control schistosomiasis. Nucleotide pyrophosphatase/phosphodiesterase-5 (NPP-5), which belongs to a multigene family of nucleotide pyrophosphatase/phosphodiesterases (NPPs), is important in the hydrolysis of pyrophosphate or phosphodiester bonds in nucleotides and their derivatives. In the present study, SjNPP-5, identified as one of the tegument proteins of Schistosoma japonicum in our previous proteomic studies, was cloned on a fragment of 1,371 bp and expressed as a recombinant protein of 69 kDa. Real-time RT-PCR analysis showed that SjNPP-5 was up-regulated at 21-42 days, and the expression level in 42-day-old male worms was almost nine times higher than that in females. Western blot analysis revealed that rSjNPP-5 had good antigenicity. Immunofluorescence analysis found that SjNPP-5 was a membrane-associated antigen mainly distributed on the surface of the male adult worm of S. japonicum. BALB/c mice vaccinated with rSjNPP-5 three times showed a 29.90% worm reduction (P < 0.05) and a 26.21% egg count reduction (P > 0.05). Immunization with rSjNPP-5 induced a mixed Th1/Th2 response in which Th1 was dominant. The response was characterized by a reduced IgG1/IgG2a ratio and elevated production of cytokines IFN-γ and IL-4. This study suggested that SjNPP-5 may be important in schistosome development, and further investigations are required to fully understand the function of this molecule.