O blood group. Agglutinogens A and B are present in AB blood group and do not contain anti A and anti B in them. Distribution of antigens and antibodies in blood groups are shown in Table . .
A, B and O are major allelic genes in ABO systems. All agglutinogens contain sucrose, D-galactose, N-acetyl glucosamine and 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 transferase.
Table . Distribution of antigens and antibodies in different blood groups Blood group Agglutinogens (antigens) on the RBC Agglutinin (antibodies) in the plasma A A Anti B B B Anti A AB AB No antibodies O No antigens Anti A and Anti B Rh factor is a protein (D antigen) present on the surface of the red blood cells in majority ( %) of humans. This protein is similar to the protein present in Rhesus monkey, hence the term Rh. Individuals who carry the antigen D on the surface of the red blood cells are Rh (Rh positive) and the individuals who do not carry antigen D, are Rh (Rh negative).
Rh factor compatibility is also checked before blood transfusion. When a pregnant women is Rh and the foetus is Rh incompatibility (mismatch) is observed. During the first pregnancy, the Rh antigens of the foetus does not get exposed to the mother’s blood as both their blood are separated by placenta. However, small amount of the foetal antigen becomes exposed to the mother’s blood during the birth of the first child.
The mother’s blood starts to synthesize D antibodies. But during subsequent pregnancies the Rh antibodies from the mother (Rh ) enters the foetal circulation and destroys the foetal XI Std Biology-Zoology Chapter- RBCs. This becomes fatal to the foetus because the child suffers from anaemia and jaundice. This condition is called erythroblastosis foetalis .
This condition can be avoided by administration of anti D antibodies ( Rhocum ) to the mother immediately after the first