Abstract: 　AIM:To study the gene structure encoding some antigenic polypeptides of plerocercoid of Spirometra erinaceieuropaei (SEP). METHODS:A cDNA library constructed from SEP was immunoscreened using mouse anti SEP polyclonal antibody.The gene structure was analyzed by computer after the insert of positive clone was subcloned and the nucleotide sequences of the insert were determined.The length of mRNA hybridized with cDNA was detected by Northern blotting. RESULTS:A cDNA clone of 1 084 bp encoding an antigenic polypeptide was isolated. The clone contained one open reading frame composed of 828 bp encoding 276 amino acids.The open reading frame contained tandem repeating unit of 123 bp which appeared 5 times in this clone.The 41 amino acids deduced from 123 bp repeating unit consisted of 53 7% of hydrophobic amino acid residues.In Northern blot assay of poly (A) +RNA,a strong band of about 1 1 kb and a weak band of about 1 7 kb were found in the plerocercoids but no band was found in the adult worms. CONCLUSION:The repeating element derived from the plerocercoids may be associated with the migration of the plerocercoids in the host tissue.The polypeptides with repeating element may act as evasive antigens of the parasite to escape from the destruction of host immune reactions.

Key words: Spirometra erinaceieuropaei, plerocercoid, cDNA, repeating unit.