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Importance of the other blood group systems
9. Importance of the other blood group systemsBlood samples are routinely grouped for ABO & Rh only. However all individuals carry antigens from other blood group systems also and they may also develop antibodies if transfused blood containing antigens absent on their own RBCs.
All patient samples are subjected to an antibody screen prior to a transfusion to detect such unexpected antibodies. If the antibody screen is positive, it is necessary to identify the antibody and transfuse blood lacking the corresponding antigen.
Lewis blood group system
Lewis antigens (Lea and Leh) derived from precursor and H substances involved in synthesis of A and B antigens are absorbed by red cells from plasma. Le gene is present on chromosome 19 and is inherited independent of ABO, hh and Sese genes. The phenotypic expression of Le gene depends on individual’s Se/se and H/h status. All Le (a-b+) are secretors and all Le(a+b-) are non-secretors. Le (ab-) individuals can be secretors or non-secretors.
Lewis antibodies are usually naturally acquired IgM type. They fix compliment and may cause haemolysis generally below room temperature. Anti-Lea antibodies commonly occur in Le (a-b-) individuals and rarely in Le (a-b+) individuals. Both anti-Lea and -Leh can cause decreased red cell survival and HTR. In pregnancy, Lewis antibodies (IgM) are found however, these do not cause HDNB.
MNSs blood group system
Two groups of antigens MN and Ss U are situated on glycophorin A and glycophorin B respectively. Two pairs of codominant genes M&N, S and s located on chromosome 4, control the expression of these antigens.
Red cells express M,N or both antigens in addition to “N-like” antigen on M cells.
The homozygous individuals show stronger agglutination than heterozygotes thus showing a dosage effect. The actively of the antigens depends on presence and composition of attached sialic acid residue. Therefore, the activity of these antigens is destroyed after treatment with proteolytic enzymes.
Ss antigen are located on sialoglycoprotein, glycophorin B and U antigen is related to all genes involved in the synthesis of Ss gene products.
Anti-M is a naturally occurring antibody and is found more commonly than anti-N. MN antibodies do not usually cause transfusion-induced reactions as MN antigens are weak immunogens. Anti-Mantibodies usually are IgG which behave as “complete” antibodies because of increased density of antigenic sites on red cells. These are cold antibodies.
Anti-N antibody, although uncommon is also a cold antibody of IgM type.
Anti-M and anti-N are not usually clinically significant but HDN and HTR are known to occur.
Anti-S and anti-s are clinically significant antibodies. These are formed in response to prior blood transfusion and may be either IgM or IgG type. Anti-s is less frequently encountered antibody than antiS. Anti-U antibodies are found in S-s-U- individuals and may cause HTR.
Kell blood group system
Kell antigens are highly immunogenic and known to cause HTR and HDN. Two antigens K (Ki) and K (1(2) have been identified. Incidence of Kell antigen (K) in India is reported to be 0.3-0.7%, where as cellano (k) is a high frequency antigen (>99% incidence). Kpa (K3), Kph (1(4), Jsa (K6) and Jsb (1(7) are other antigens of this system consisting of 23 KelI antigens. In Ko (Kell null), all Kell system antigens are absent.
As the Kell system consists of numerous antigens, it has become very complex and now a numerical nomenclature has been introduced.
Kell antigens are expressed weakly in this X-lkinked syndrome consisting of mild haemolytic anaemia, acanthocytosis, neuomuscular abnormalities with elevated cratine phosphokinase (CPK) enzyme.
Individuals with Mcleod phenotype may have chronic granulomatous disease (CGD), or a high level of CPK.
Anti-K are formed in response to transfusion and are usually IgG type. Alloimmunization in mother can occur due to foetomaternal haemorrhage. Anti-K can cause immediate and delayed haemolytic reactions. Anti-k (anti-cellano) is less common and only KK homozygotes produce this antibody after blood transfusion.
These antibodies are best detected by the indirect antiglobulin test. Some examples do bind complement also.
The in-vitro characteristics of anti-Kell antibody
Duffy antigen system
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