Antibody response in an ABO-incompatible blood transfusion. Antigen specificity and immunoglobulin class.

The anti-A response in a group B patient accidentally given 1 unit transfusion of A1 blood is described. The antibody response is characterized both with conventional agglutination techniques and with radioimmunoassay using pure group A antigens with different core saccharide structures (type 1, 2, and 4 chains) and class-specific second antibodies. The anti-A titer rose to a maximum Days 11 to 14 after the incompatible transfusion. The antibodies involved were mainly of the IgG and IgA types, while the IgM response was moderate. The IgA antibodies seemed to be nonselective with respect to group A antigen type, while the IgG antibodies showed a specificity against type 2 chain group A antigens.