A disaccharide hapten from streptococcal group C carbohydrate that cross-reacts with the Forssman glycolipid.

A disaccharide hapten was isolated in approximately 20% yield from an acid hydrolysate of the streptococcal Group C carbohydrate. This disaccharide was assigned the structure 3-0-alpha-N-acetylgalactosaminosyl-N-acetylgalactosamine on the basis of chemical and immunochemical data. The ability of the hapten to inhibit completely the binding between Group C carbohydrate and most Group C antibodies indicated that this disaccharide is the immunodominant feature of the Group C carbohydrate. Fractionation of antisera on an alpha-N-acetylgalactosamine immunoadsorbent column yielded several populations of anti-Group C antibodies. The reaction between labeled Group C carbohydrate and antibodies which strongly bound the immunoadsorbent column was 50% inhibitable by the disaccharide hapten when the hapten was added in approximately 15-fold excess (w/w) of the labeled antigen. On the other hand, the binding of those antibodies which did not bind to the immunoadsorbent column was poorly inhibited under these conditions. The Forssman glycosphingolipid, which has a common terminal digalactosamine unit, was shown to likewise inhibit Group C carbohydrate binding reactions.