Localization of carbohydrate determinants common to Biomphalaria glabrata as well as to sporocysts and miracidia of Schistosoma mansoni

The presence of antigenic carbohydrate epitopes shared by Biomphalaria glabrata as well as by the sporocysts and miracidia representing snail-pathogenic larval stages of Schistosoma mansoni was assayed by immunohistochemical staining of paraformaldehyde-fixed tissues. To this end, both polyclonal rabbit antiserum raised against soluble egg antigens (SEA) of S. mansoni and monoclonal antibodies recognizing the carbohydrate epitopes LDN [GalNAc(β1-4)GlcNAc(β1-)], F-LDN [Fuc(α1-3)GalNAc(β1-4)GlcNAc(β1-)], LDN-F [GalNAc(β1-4)[Fuc(α1-3)]GlcNAc(β1-)], LDN-DF [GalNAc(β1-4)[Fuc(α1-2)Fuc(α1-3)]GlcNAc(β1-)] and Lewis X [Gal(β1-4)[Fuc(α1-3)]GlcNAc(β1-)] were used. Intriguingly, anti-SEA serum as well as anti-F-LDN antibodies displayed significant binding in the foot region, anterior tissue and the hepatopancreas of uninfected snails, whereas the Lewis X epitope was only weakly detectable in the latter tissue. In contrast, increased binding of antibodies recognizing LDN, LDN-F and LDN-DF was observed in infected snail tissue, in particular in regions involved in sporocystogenesis, in addition to an enhanced binding of anti-SEA serum and antibodies reacting with F-LDN. A pronounced expression of most of these carbohydrate antigens was also observed at the surface of miracidia. Hence, the detection of shared carbohydrate determinants in uninfected snail tissue, sporocysts and miracidia may support the hypothesis of carbohydrate-based molecular mimicry as a survival strategy of S. mansoni.