ABO-incompatible kidney transplantation (A2 to O). Qualitative and semiquantitative studies of the humoral immune response against different blood group A antigens.

The humoral immune response against blood group A antigens with different core saccharide structures has been investigated in four blood group O recipients transplanted with kidneys from two blood group A2 donors. Radioimmunoassay and thin-layer chromatogram binding assay studies showed that different individuals responded differently to the same antigenic stimulus. Antibodies were produced in the recipient that bound to the terminal trisaccharide of the blood group A antigens. In some cases antibodies that bound to a larger antigen epitope, including the fourth and fifth sugar in the polysaccharide core chain, also occurred. Immunoglobulin class-specific, as well as subclass specific, responses were seen. The antibody response in the blood group O recipients receiving an A2 graft seem to be dependent on the antigenic expression in the transplanted kidney. In view of the recent findings of individuality of A antigen expression in kidneys within the A1 and A2 subgroups, an extended typing of A2 donors may be important. The humoral immune response in the recipient may also be dependent on earlier contacts with ABO incompatible pregnancies, vaccinations, or infections. A possible correlation between pre- and posttransplant findings was noted in one case and deserves further notice.