Immunochemical studies on blood groups. LI. A comparative study of the reaction of A 1 and A 2 blood group glycoproteins with human anti-A.

The immunochemical properties of purified A(1) and A(2) glycoproteins have been compared to ascertain whether their antigenic determinants differ. Quantitative precipitin and complement-fixation studies using several anti-A sera as well as purified gammaG anti-A antibodies clearly showed a specificity difference. This was also supported by absorption studies: A(2) substance specifically removed antibodies reacting with A(2) substance leaving anti-A(1) activity. A(1) substance was more effective than A(2) substance in dissolving an A(1) anti-A(1)-specific precipitate. Purified gammaM anti-A hemolyzed A(1) cells more readily than A(2) cells. Inhibition studies using mono- and difucosyl type 2 A-active oligosaccharides showed that type 2 difucosyl receptors are present in A(2) substance. The structural basis for the specificity difference between A(1) and A(2) would appear to be that A(2) substances lack type 1 A determinants; this would account for the observed higher H and Le(b) activity in A(2) substances.