The most common classifications are A1 and A2. These account for over 99% of group A bloods. Of this 99%, A1 compromises approximately 80%. Commercial anti-A typing serum does not differentiate between A1 and A2 cells. A1 cells contain “A” antigen and “A1” antigen. A2 is not really a unique antigen. It is thought to be simply “A” antigen with no “A1” antigen. Several preparations are available that will react with A1 cells, but not other subgroups of A. An extract of the seeds of the plant, Dolichos biflorus has specific anti-A1 activity. “Absorbed anti-A” serum can also be prepared. To do this, the anti-A from group B people is absorbed with A2 cells. Anti-A is removed and a second antibody that reacts only with A1 cells remains. Anti-A1 can also be found as a separate antibody in the sera of A2 and A2B individuals.
