Blood group A1 and A2 revisited: an immunochemical analysis

Background and Objective  The basis of blood group A₁ and A₂ phenotypes has been debated for many decades, and still the chemical basis is unresolved. The literature generally identifies the glycolipid chemical differences between blood group A₁ and A₂ phenotypes as being poor or no expression of A type 3 and A type 4 structures on A₂ red cells, although this assertion is not unanimous.
Materials and Methods  Using purified glycolipids and specific monoclonal antibodies, we revisited the glycolipid basis of the A₁ and A₂ phenotypes. Purified glycolipids were extracted from four individual A₁ and four individual A₂ blood units. One blood unit from an A weak subgroup was also included. Monoclonal anti-A reagents including those originally used to define the basis of A₁ and A₂ phenotypes were used in a thin layer chromatography – enzyme immunoassay to identify the presence of specific glycolipids.
Results  A type 3 glycolipid structures were found to be present in large amounts in all phenotypes. In contrast, the A type 4 glycolipid structure was virtually undetectable in the A₂ phenotype, but was present in the A₁ and A subgroup samples.
Conclusion  The major glycolipid difference between the A₁ and A₂ phenotypes is the dominance of A type 4 glycolipids in the A₁ phenotype.