Detection of carbohydrate terminals in the enteric parasite Enteromyxum scophthalmi (Myxozoa) and possible interactions with its fish host Psetta maxima

The existence and localisation of carbohydrate terminals in Enteromyxum scophthalmi stages was investigated at light (LM) and transmission electron microscopes (TEM) using lectin histochemistry techniques, with the aim of contributing to elucidate the participation of carbohydrate–lectin interactions in the parasite invasion and relationships with the fish host. The presence of abundant mannose and/or glucose residues was demonstrated by the intense staining by concanavalin A at both LM and TEM. The staining pattern obtained with soybean agglutinin and Bandeiraea simplicifolia I (BSI) indicated the abundance of N-acetyl-galactosamine and D-galactose at a lesser extent. The lectins wheat germ agglutinin, BSI and Ulex europaeus agglutinin produced weaker marks. Most lectins recognised structures present in both pre-sporogonic and sporogonic stages, though the glycosidic pattern and/or staining intensity varied between developmental stages. No staining was obtained with Sambucus nigra agglutinin. The TEM studies demonstrated glucose–mannose, N-acetyl-glucosamine, N-acetyl-galactosamine and α-D-galactose as dominant structures at the parasite membrane and host–parasite interface, suggesting a role in host–parasite interactions. All these terminals were also detected in the mitochondria of P cells and were scant in the S cells and nuclei. In turbot intestine, mannose–glucose terminals and N-acetyl-glucosamine were labelled on the epithelial brush border and in the mucous cells and rodlet cells. The relevance of these findings in relation to the host–parasite interaction is discussed.