MN, ABO AND Rh BLOOD GROUPS

The MN blood group consists of two alleles which are codominantly expressed. It is used in paternity testing. The ABO blood group is the most important in terms of blood transfusions. It has three major alleles. The A allele produces A antigens on the surface of red blood cells and never have anti A antibodies in its serum. The Allele B produces B antigens on the surface of cells and never has anti B antibodies in its serum. Both A and B are inherited codominantly. Allele O does not produce a cell surface antigen and is recessive to both A and B.

In transfusions, blood cells expressing an antigen should be transfused only into persons who have the same antigen. For example AB blood must be transfused into people with group AB and not A, B or O. Blood cells lacking an antigen may be transfused into persons who have that antigen. For example O blood can be given to persons of group A, B or AB.

The Rh blood group for simplicity may be considered to contain an allele D that produces a major cell surface antigen. In reality, it has two more additional minor antigens called C and E. An individual carrying the D are referred to as Rh+ and those who do not carry are Rh -. When Rh - persons have their blood exposed to Rh+ cells, they are capable of manufacturing antibodies against the Rh+ cells that they have been exposed to. This sensitization usually occurs in a pregnancy of an Rh- mother with an Rh+ foetus or transfusion with Rh+ blood.

Haemolytic disease of the newborn or erythroblastosis foetalis is cause by a destruction of foetal red blood cells by the antibodies produced by the Rh - mother who was sensitized by some Rh + foetal cells that crossed the placenta to the maternal side. It could be prevented by avoiding transfusion of Rh - girls and women with Rh + blood and also by treatment of Rh - pregnant women with anti - Rh antibody (RhoGAM) injections.