A1 Erythrocytes Express Protein Structures with Blood Group A Antigenic Determinants that are not Detected on A2 Erythrocytes

Abstract

Background and objectives: There is considerable disagreement in the literature regarding the nature of differences underlying subgroups of blood group A. The purpose of this study is to further investigate possible qualitative and quantitative variations between A1 and A2 erythrocytes. Materials and methods: Erythrocytes from type A blood donors were tested for hemagglutination with A and B monoclonal antibodies and the A1 lectin, Dolichos biflorus. A2 subgroup was assigned to those A erythrocytes that did not react with Dolichos biflorus but did react strongly with A antibody. Once A1 and A2 cells were thus identified, variation in A antigen expression was assessed by flow cytometry and western blot. Results: Flow cytometry revealed that A2 cells express less A antigen than A1 cells, but the extent of the difference was less than expected and decreased as the dilution of the A antibody increased. However, when A1 and A2 erythrocytes were studied by western blot, A1 erythrocytes yielded dramatic protein bands, which A2 erythrocytes failed to demonstrate. Conclusion: Only A1 erythrocytes expressed antigen identified by western blot. This dramatic qualitative difference between A1 and A2 cells seems to be more substantial than the small quantitative differences detected by flow cytometry.