Objective: To find out the candidate antigen for immunoreagent, which could be used to diagnose Schistosoma japonicum infection early in mice.
Methods: The mice were infected with cereariae of S. japonicum Chinese mainland strain. The sera of mice before and after infection at different time were collected. The recombinant fusion protein (GST-HD) of the large hydrophilic domain (HD) of 23 kDa membrane protein of S. japonicum with the Glutathione-S-transferase (GST) of S. japonicum, soluble eggs antigen (SEA), TSP2 hydrophilic domain of S. japonicum (TSP2HD), IL4-inducing principle of S. mansoni eggs (IPSE), fusion protein GST-SjMP10 (SjMP-10), and recombinant S. japonicum (Chinese strain) signaling protein 14-3-3 (Sj14-3-3) were used as diagnostic antigens, the specific IgG and IgM antibodies were measured respectively by enzyme linked immunosorbent assay (ELISA). The antigens with the value of diagnosing schistosomiasis early were screened by analyzing the changes of the levels of specific IgG (or IgM) antibodies and the positive rates of specific antibodies in the sera of mice before and post infection at different time. Moreover, the antigen's value of early diagnosis was further validated by Immunoblot.
Results: On the 18th, 21st and 28th day post infection, the positive rates of specific antibody IgM against GST-HD were 60%, 70% and 100%, respectively; the positive rates of specific antibody IgG against GST-HD were 40%, 60% and 90%, respectively. The positive rates of antibody IgM against SEA were 50%, 60% and 90%, respectively; the positive rates of antibody IgG against SEA were 20%, 50% and 70%, respectively. The positive rates of IgM against TSP2HD were 30%, 40% and 50%, respectively; the rates of IgG against TSP2HD were 20%, 30% and 70%, respectively. The positive rates of IgM against IPSE were 20%, 30% and 50%, respectively; the positive rates of IgG against IPSE were 20%, 30% and 60%, respectively. The positive rates of IgM against SjMP-10 were 10%, 20% and 20%, respectively; the rates of IgG against SjMP-10 were 10%, 20% and 30%, respectively. The positive rates of IgM against Sj14-3-3 were 0, 10% and 20%, respectively; the rates of IgG against Sj14-3-3 were 0, 10% and 30%, respectively. The sensitivities of GST-HD and SEA for diagnosing schistosome infection early in mice were significantly higher than those of Sj14-3-3, IPSE, TSP, and MP-10. The sensitivity of IgM was higher than that of IgG. In Western blotting, the about 73 kDa protein band of SEA was recognized by sera of mice one week post infection and showed stronger reaction as the infected time went on. Moreover, the bands (33 kDa) of GST-HD were earliest recognized by the mouse sera on the 10th day post-infection, the bands showed strong reaction with the mouse sera of 5-week post-infection.
Conclusions: The GST-HD fusion protein and the protein of which molecular weight is about 73 kDa of SEA have the early diagnostic value for schistosomiasis, and the sensitivity of Immunoblot is higher than that of ELISA.