Characterization of a stage-specific M(r)16 000 schistosomular surface glycoprotein antigen of Schistosoma mansoni

A 16 kDa Schistosoma mansoni schistosomular surface antigen (Sm16) was orig inally described as the target of a passively protective mAb (B3A). It appe ared on the schistosomular surface after transformation of cercariae and wa s uniquely recognised by sera from animals exposed to attenuated cercariae. In this work sequential extractions of schistosomula with Triton X-114 and sodium dodecyl sulphate showed Sm16 to be an integral membrane structure w hich did not appear to be glycosylphosphatidylinositol-anchored as judged b y experiments using phosphatidyl inositol-specific phospholipase C. The ant igen was strongly reactive in Western blotting with rabbit irradiated vacci ne sera. Sm16 was demonstrated in the hepatopancreas of S. mansoni-infected snails and was equally abundant in cercariae and mechanically- transformed schistosomula but was undetected in liver stage worms or eggs. Immunoelect ron microscopy showed Sm16 to be localised, in cercariae, to what are belie ved to be subtegumental cell bodies packed with membraneous vesicles. Treat ment with proteases and with sodium metaperiodate showed Sm16 to be a glyco protein of which the epitope recognised by B3A was periodate sensitive. Two -dimensional electrophoresis gave a PI of 6. Neither the size or the recogn ition by B3A was affected by treatment with N-glycosidase F, endoglycosidas e F or endo-alpha-N-acetylgalactosaminidase. Western blotting using a wide range of biotinylated lectins showed recognition only by peanut agglutinin and Ricinus communis agglutinin II (ricin). Ir is concluded that Sm16 has a ntigenic surface-exposed O-linked complex oligosaccharides which lack manno se/glucose, GlcNAc, L-fucose and sialic acid but contain terminal Gal beta (1-3) GalNAc and/or galactose. (C) 1999 Elsevier Science B.V. All rights re served.