blood transfusion in abo blood group system

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