Partial characterization and isolation of 130 kDa antigenic protein of Dicrocoelium dendriticum adults

The study focused on characterizing and isolating Dicrocoelium dendriticum antigens or their fractions that could be used for the immunological diagnosis of dicrocoeliosis. Somatic (SoAg) and excretory-secretory antigens (ESAg) were analyzed by SDS-PAGE and their specificity was evaluated by Western blot with homologous and heterologous sera. The antigens were partially purified by chromatographic techniques of gel-filtration (Sephacryl S-300) and ion exchange (Hitrap-DEAE-Sepharose). Western blot analysis using sera of ovine infected with D. dendriticum revealed eight main antigenic polypeptides ranging from 24 to 205 kDa for SoAg and seven for ESAg with apparent molecular mass in the range of 26-205 kDa. We detected a specific parasite protein with an approximate molecular weight of 130 kDa in SDS-PAGE gels, arranged as a 450 kDa tetramer in native conditions. It also showed strong immunoreactivity by Western blot against ovine sera experimentally infected with D. dendriticum. Gel filtration chromatography (Sephacryl S-300) also showed other specific proteins, one of about 24 kDa in SoAg and another of about 42 kDa in ESAg. The elution conditions of 450 kDa protein (130 kDa monomer) by DEAE chromatography were similar to those from the somatic antigen (pH 7.2, 0.1M NaCl, in 29-34 ml fractions) and from the excretion-secretion antigen (pH 8.0, 0.1M NaCl, in 29-35 ml fractions). The suitability of 130 kDa polypeptide for D. dendriticum infection diagnosis was confirmed by Western blot using a pool of sera as well as individual serum samples from experimentally infected sheep. The sequence of amino termini of 130 kDa polypeptide from both fractions was the same and identical to that reported for a peptide from D. dendriticum described as a globin. This sequence also revealed an appreciable similarity with the amino end of globins from some phylogenetically related worms.