THE IMMUNOLOGICALLY REACTIVE PART OF IMMUNOPURIFIED CIRCULATING ANODIC ANTIGEN FROM SCHISTOSOMA-MANSONI IS A THREONINE-LINKED POLYSACCHARIDE CONSISTING OF -]6)-(BETA-D-GLCPA-(1-]3))-BETA-D-GALPNAC-(1-] REPEATING UNITS

The gut-associated excretory antigen CAA (circulating anodic antigen) from adult Schistosoma mansoni worms was isolated by immunoaffinity ch romatography. Amino acid analysis following alkaline borohydride treat ment indicated that CAA is a glycoprotein, O-glycosylated at Thr. The primary structure of the released O-glycan moiety was investigated by one- and two-dimensional, homo- and heteronuclear H-1 and C-13 NMR spe ctroscopy. It was found that the major carbohydrate chains have a nove l polysaccharide structure, consisting of a branched disaccharide repe ating unit containing 2-acetamido-2-deoxy-beta-D-galactopyranose (beta -D-Galp-NAc) and beta-D-glucopyranuronic acid (beta-D-GlcpA). [GRAPHIC S] The major antigenic character of CAA arises from this novel polysac charide, which was shown to be an absolutely specific diagnostic marke r in schistosomiasis. The cross-reactivity of CAA with anti-CCA (circu lating cathodic antigen) monoclonal antibodies is caused by the presen ce of a small amount of O-linked CCA-poly-Lewis x carbohydrate chains on the CAA protein chain.