CLINICALLY LESS SIGNIFICANT BLOOD GROUP SYSTEMS,

CLINICALLY LESS SIGNIFICANT BLOOD GROUP SYSTEMS

• Lutheran Blood Group System
• LW Blood Group System
• Kidd Blood Group System
• Duffy Blood Group System
• Kell Blood Group System
• MNSs Blood Group Systems
• P Blood Group System
• Lewis Blood Group System (Le)

CLINICALLY LESS SIGNIFICANT BLOOD GROUP SYSTEMS

Besides the ABO and Rh systems, there are a large number of other antigens detectable on a human red cell. Some of these antigens have been identified to form distinct systems similar to ABO and Rh systems, but they are clinically much less sig. nificant. Some of such blood group systems most commonly encountered in clinical situations are described below.

Lewis Blood Group System (Le)

The Lewis blood group is determined by the productive allele, called Le. A silent Le may be present at the same lo, cus in the absence of Le. There are two main Le antigens, Le and Le', with phenotypes Le (a+b-), Le (a-b+) and Le (a-b-). Le (a-b-) individuals have no Le gene, but theyproduce antigens which are similar to a and b. These are called Leand Leb). Another Le antigen Le (x) is present on all adult cells which are Le (a+b-) or Lea-b+). Antigens Le(a) and Le(e) are found in non-secretors and Le(b) and Le(d) are found in secretor individuals.

Usually, anti-Le(a) and anti-Le(b) are produced by Le-5-) individuals i.e those lacking both the antigens a and b. Occasionally, Le (a+b-) individual may produce anti-Le(b), but Le (a-b+) individuals never produce anti-Le(a). Lewis antibodies are IgM in nature and therefore, do not cross through the placenta. They react better at lower temperatures. However, transfusions with a Lewis incompatible blood group rarely results in a severe transfusion reaction.

P Blood Group System                                  

Most of the red cells have two closely related antigens on their surfaces, P and Pk. Occasionally some lack P and have only Pk antigen. Approximately 80-90% individuals also have on their red cells an antigen called PI. The red cells lacking PIare called P2. Anti-Pl occurs very commonly in the sera of P2 individuals, and is detectable at low temperature. 

The p phenotype results from the absence of P antigen.'pi individuals therefore lack P, Pl and Pk antigens. They contain an anti-P,P1,Pk antibody. The serum of Pk individuals contains anti-P antibody. These two antibodies can produce haemolysis. The biphasic haemolysis in paroxysmal cold haemoglobinuria (PCH) is often found to be due to anti-P antibodies.

MNSs Blood Group Systems

This system contains two sets of antigens, MN and Ss. Both the genes responsible for their production are closely linked and are inherited together as a complex. Anti-M and Anti-N occur in human serum as natural antibodies if the respective antigen is absent on red cells. 

They are IgM in nature and are active below 37°C. Anti-S and anti-s are often of an immune origin and can be detected by antihuman globulin serum. Antibodies of this system are destroyed by enzymes and therefore can not be detected by the enzyme technique.

Kell Blood Group System

This system includes at least 22 antigens such as K1, K2, K3, etc. There are other less frequent antigens also found to belong to this group. The K antigen is considered to be next in immunogenicity to the D antigen of the Rh system, but it is relatively much less frequent. There is a rare Ko group which does not possess any of the K antigens, but is rich in their precursor Kx.

Kell antibodies are capable of mediating immune haemolysis. They have high titres and high affinity for their antigens. Most Kell antibodies are IgG and can be detected by anti human globulin serum.

Duffy Blood Group System

This system consists of at least three allelic genes Fya and Fyb, which produce antigens Fya and Fyb respectively. The third gene Fy does not produce

either Fya or Fyb. An antibody, anti-Fy3 was first detected in the serum of an individual of the phenotype Fy(a-b-). Anti-Fy3 is directed against the cells other than Fy(a-b-) phenotype.

Anti-Fya and anti-Fyb are present in serum invariably as a result of immune response. They can be detected by the antihuman globulin test. They are inactivated by proteolytic enzymes, and cannot be detected by the enzyme method.

Kidd Blood Group System

Two antigens have been detected which belong to this system and are called Jka and Jkb. A phenotype Jk (a--b-) has an antibody which reacts with both Jka and Jkb antigens. A peculiar property of Jk (ab-) phenotype is that these red cells resist lysis by 2M urea solution. This can be used as a screening method for the detection of Jk (a-b-) phenotype.

Anti-Jka and anti-Jkb can be detected by the antihuman globulin test. They react better with the antihuman globulin reagent with anti-complement component (polyspecific reagent). However, the antibodies are lost quickly on storage. They can cause delayed haemolytic transfusion reactions.

LW Blood Group System

Both Rh-D positive and Rh-D negative red cells carry LW antigen, but it is present in much lesser amounts on Rh-D negative cells. The LW blood group has two alleles, LWa and LWb. The LW negative individuals lack the antigen LWa. Some LW positive persons are known to produce autoantibodies to the LW antigen.

Lutheran Blood Group System

The Lutheran system has two allelic genes producing Lu and Luoantigens. An Lu(a-b-) phenotype exists due to an inhibitor gene, InLu. This inhibitor gene is also known to suppress some other antigen such as the i, and Pl. The Lutheran system has about 15 antigens, but the antibodies are not clinically important. They can be detected by the antihuman globulin serum.