Preparation of A2 reverse grouping cells from A2B red blood cells by alpha-galactosidase.

Correct typing of donors’ and recipients’ blood group is of paramount importance in transfusion services. There are two distinct parts in ABO typing, forward and reverse typing, both of which are routinely carried out1. Reverse typing is obligatory, because it can help to reveal mistyping, weak A subgroups with anti-A1 and unexpected IgM antibodies. Any discrepancy between the results of the tests with serum or plasma and red cells should be investigated. Reverse grouping cells, including A, B, O and A2 type red blood cells (RBC), are important to resolve ABO discrepancies. Anti-A and/or anti-B antibodies can be easily detected by red blood cells with A and/or B blood group antigens. The presence of an anti-A1 should be confirmed by testing serum against A1, A2, and O red cells. This method necessitates A2 reverse grouping cells. Very few people in China have the A2 blood group. In the Xi’an area (north-western China) only about 0.0006% of the population have A2 RBC, while about 0.003% of the population have the A2B group are. The ratio of the prevalence of A2B:A2 is 5 (unpublished data). In the Shanghai area (eastern China), this same ratio is about 2.5. Thus, there are more people with A2B group RBC than there are with A2 RBC2,3. As it is known that α-galactosidase, a kind of exoglycosidase, can remove the reducing end α-galactose residues of group B antigen by hydrolysis and based on the characteristics of the group B epitopes and α-galactosidase hydrolysis reaction, α-galactosidase has been used in B to O RBC conversion study since the 1980s4. Our group has been researching in this area for more than 10 years5,6 and we recently obtained a novel α-galactosidase from B. fragilis (which belong to CAZy GH110) with highly specific activity, greatly restricted substrate specificity and a neutral pH optimum7,8. Our research showed that this novel α-galactosidase can convert B RBC to O RBC with high substrate specificity and at low cost7,8. We, therefore, started to study the A2B to A2 conversion using α-galactosidase in order to broaden the source of A2 RBC.