[Immunoscreening of Schistosoma japonicum egg cDNA library and identification of positive clones]

To obtain promising antigens for diagnosis or therapeutic efficacy assessment of schistosomiasis japonica.

At an endemic area in Anqing of Anhui Provinces, Kato-Katz method (six slides from two consecutive stool samples) was used to examine schistosome eggs and serum samples of 10 egg-positive patients were collected. The EPG of the ten patients, aged 13 to 64, was among 4 to 172. The patients were then treated with praziquantel 60 mg kg for two days. Sera of the same patients were collected again at six months post treatment. The egg cDNA library was immunoscreening with the pre- and post-treatment serum samples, and the positive clones were classified according to different reactions. The inserted fragments of positive clones were sequenced and analyzed for their homology through BLAST program. The amino acid sequences of the proteins were deduced from the gene sequences, and their structures and functions were predicted by bioinformatics tools.

For the first round, 75 positive clones were screened from the egg cDNA library. Among them, 21 clones showed stronger reaction with the pre-treatment sera, and 8 clones showed stronger reaction with the post-treatment sera. According to the intensity of the reaction, types and the length of inserted fragments, 14 positive clones were selected for further study. Most of the clones belonged to miracidial antigen family, one clone was significantly homologous to the calcium-binding EF-hand, a domain-containing protein (score = 143), one was highly homologous to the cell wall integrity and stress response component 1 precursor (score = 487), and another four were homologous to the hypothetical protein.

Twenty nine positive clones screened from the egg cDNA library show different reactions with the sera of schistosome-infected patients, before and after praziquantel treatment.