blood transfusion in abo blood group system

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ABO - The First Discovered Multiple Allelic Blood Group System in Man • ABO blood group system was discovered by Karl Landsteiner in 1901. ABO system has • four different phenotypes which are distinct from each other on the basis of specfic • antigens on the surface of RBC. A person having antigen A has blood group A; a person • having antigen B has blood group B; a person having both the antigens A and B has • blood group AB; but a person having neither antigen A nor B would have blood group • O. • Bernstein explained the genetic basis of ABO system in 1925. This blood group system • is encoded by a single polymorphic gene I on chromosome 9. It has three multiple • alleles IA, IB, and i. • Allele IA specifies production of antigen A, and allele IB specifies production of antigen • B, but allele i does not specify any antigen. Their dominance relations are interesting • too. Alleles IA and IB are codominant to each other, because each expresses equally • in IA IB heterozygote to produce AB phenotype. But allele i is recessive to both IA and • IB. Therefore IA IA or IAi genotypes will produce phenotype A. Similarly IB IB or IBi • produces phenotype B. The homozygous ii will produce phenotype O • The blood group alleles start their expression at early embryonic stage and keep on • expressing themselves till death. Therefore the blood group phenotype of a person • never changes throughout life. • Anti-A and anti-B antibodies appear in plasma during the first few months after birth. • They are naturally occuring in the absence of corresponding antigen. The blood serum • of A phenotype contains anti-B antibodies. They will agglutinate7or clump any RBC • which have B antigens on them. B phenotype contains anti-A antibodies in the serum • and agglutinate any RBC with antigen A. Phenotype AB has neither anti-A nor anti-B • antibodies in the serum. The serum of O blood type contains both anti-A and anti-B • antibodies. The blood serum containing anti-bodies is called antiserum. • Any blood transfusion is ideally safe if it does not cause agglutination in the recipient. • Agglutination leads to serious results because clumped cells cannot pass through fine • capillaries. The blood samples of the donor and the recipient are cross matched for • compatibility before giving transfusion. If incompatible blood is transfused, dangerous • hemolytic reaction occurs. Either the antibodies of the recipient destroy the RBC of • donor or the antibodies of the donor hemolyze the RBC of the recipient. • Blood group A can be transfused only into A and AB recipients because they do • not have anti - A antibodies. Blood group B can be transfused only into B and AB • recipients as they do not have anti - B antibodies. AB blood can be transfused only into • AB recipients because they have neither anti - A, nor anti B antibodies. O blood has • neither A nor B antigen, but it does have anti - A and anti-B antibodies. An O recipient • can only be given tranfusion from a donor O. Phenotype O can also be used as donor • for small transfusions to A, B and AB recipients because donor’s antibodies are quickly • absorbed by other tissues or greatly diluted in the recipient’s blood stream. O blood • group individuals are called universal donors. AB blood group individuals are called • universal recipients because they can receive transfusions of blood from any of the • four blood groups. • A and B antigens can also be present in saliva and other body fluids of some persons • called secretors. Secretors have dominant secretor gene “Se” on chromosome 19 • Genetic analysis on the basis of blood groups helps in solving cases of disputed • parentage. It can only be used to prove that an individual is not the parent of a particular • child, e.g. a child of AB phenotype (IA IB) can not be the child of a parent of phenotype • O (ii). Similarly a man of B phenotype cannot be father of a blood type A child, whose • mother is of phenotype O. His father could either be A or AB phenotype. • #visiblescience • #alevelbiology • #federalboard

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