EXPRESSION OF A-ANTIGENS ON ERYTHROCYTES OF WEAK BLOOD-GROUP A SUBGROUPS

Scanning immune electron microscopy using a monoclonal anti-A antibody which reacts with all type A oligosaccharide chains revealed A antige ns on less than 5% of A(m) and A(el) cells, some of which showed extre mely strong labelling. This explains why A(m) and A(el) cells can abso rb significant amounts of anti-A without being agglutinated. A(3) may be a heterogenous subgroup, since A antigens were found on 82 and 58%, respectively, of the cells of 2 A(3) individuals. A antigens were fou nd on 75% or more of A(x) cells. In many weak A individuals A-positive cells are apparently best detected if an anti-A is used which reacts strongly with other A oligosaccharide chains than type 2. From hyperim mune pregnancy sera A(x), A(m) and A(el) erythrocytes absorbed antibod ies which seemed to have other fine specificities than those absorbed by A(2) cells. We conclude that weak subgroups of A may deviate from A (2) both by number of erythrocytes expressing A antigens and the bioch emical nature of the antigens.