Depending on the presence or absence of surface antigens on the RBCs, blood group in individual belongs to four different types namely, A, B, AB and O. The plasma of A, B and O individuals have natural antibodies (agglutinins) in them.
Surface antigens are called agglutinogens. The antibodies (agglutinin) acting on agglutinogen A is called anti A and the agglutinin acting on agglutinogen B is called anti B.
Agglutinogens are absent in O blood group. Agglutinogens A and B are present in AB blood group and do not contain anti A and anti B in them. A, B and O are major allelic genes in ABO systems.
All agglutinogens contain sucrose, D-galactose, Nacetyl glucosamine and 11 terminal amino acids.
The attachments of the terminal amino acids are dependent on the gene products of A and B. The reaction is catalysed by glycosyl transferanse.
