Blood transfusion Medical Assignment Help

The cells and proteins in the blood express antigens which are controlled by polymorphic genes, i.e. a specific antigen may be present in some individuals but not others. A blood transfusion may immunize the recipient against donor antigens that the recipient lacks (alloimmunization); repeated transfusions increase the risk of the occurrence of alloimmunization. Similarly, the transplacental passage of fetal blood cells during pregnancy may alloimmunize the mother against fetal antigens inherited from the father. Antibodies stimulated by blood transfusion or pregnancy are termed immune antibodies, in contrast to naturally occurring antibodies, such as ABO antibodies, which are made in response to environmental antigens present in food and bacteria.

BLOOD GROUPS

The blood groups are determined by antigens on the surface of red cells; more than 400 blood groups have been found. The ABO and Rh systems are the two most important blood groups but incompatibilities involving many other blood groups (such as Kell, Duffy, Kidd) may cause haemolytic transfusion reactions and/or HDN.

ABO system

This is the most important blood group system because naturally occurring IgM anti-A and anti-B antibodies are capable of producing rapid and severe intravascular haemolysisof incompatible red cells.
The ABO system is under the control of a pair of allelic genes, Hand h, and also three allelic genes, A, Band 0, producing the genotypes and phenotypes shown . The A, Band H antigens are very similar in structure; differences in the terminal sugars determine their specificity. The H gene codes for enzyme H, which attaches fructose to the basic glycoprotein backbone to form H substance, which is the precursor for A and B antigens.
The A and B genes control specific enzymes responsible for the addition to H substance of N-acetylgalactosamine for Group A and D-galactose for Group B. The 0 gene is amorphic and does not transform H substance and therefore 0 is not antigenic. The A, B and H antigens are present on most body cells. These antigens are also found in soluble form in tissue fluids such as saliva and gastric juice in the 80% of the population who possess secretor genes.

Rh system

This is the second most clinically important blood group system because of the high frequency of development of The cells and proteins in the blood express antigens which are controlled by polymorphic genes, i.e. a specific antigen may be present in some individuals but not others. A blood transfusion may immunize the recipient against donor antigens that the recipient lacks (alloimmunization); repeated transfusions increase the risk of the occurrence of alloimmunization. Similarly, the transplacental passage of fetal blood cells during pregnancy may alloimmunize the mother against fetal antigens inherited from the father. Antibodies stimulated by blood transfusion or pregnancy are termed immune antibodies, in contrast to naturally occurring antibodies, such as ABO antibodies, which are made in response to environmental antigens present in food and bacteria.

BLOOD GROUPS

The blood groups are determined by antigens on the surface of red cells; more than 400 blood groups have been found. The ABO and Rh systems are the two most important blood groups but incompatibilities involving many other blood groups (such as Kell, Duffy, Kidd) may cause haemolytic transfusion reactions and/or HDN.

ABO system

This is the most important blood group system because naturally occurring IgM anti-A and anti-B antibodies are capable of producing rapid and severe intravascular haemolysis of incompatible red cells.
The ABO system is under the control of a pair of allelic genes, Hand h, and also three allelic genes, A, Band 0, producing the genotypes and phenotypes shown . The A, Band H antigens are very similar in structure; differences in the terminal sugars determine their specificity. The H gene codes for enzyme H, which attaches fructose to the basic glycoprotein backbone to form H substance, which is the precursor for A and B antigens.
The A and B genes control specific enzymes responsible for the addition to H substance of N-acetylgalactosamine for Group A and D-galactose for Group B. The 0 gene is amorphic and does not transform H substance and therefore 0 is not antigenic. The A, B and H antigens are present on most body cells. These antigens are also found in soluble form in tissue fluids such as saliva and gastric juice in the 80% of the population who possess secretor genes.
This is the second most clinically important blood group system because of the high frequency of development of IgG RhD antibodies in RhD-negative individuals after exposure to RhD-positive red cells following blood transfusions or during pregnancy. The antibodies formed are of major importance in causing HDN and haemolytic transfusion reactions.
This system is coded by allelic genes, C and c, E and e, D and no D, which is signified as d; they are inherited as triplets on each chromosome, one from each pair of genes, i.e. CDE/cde. The presence of the d antigen has not been demonstrated and the presence or absence of the D antigen determines whether an individual is characterized as RhD positive or negative.

Antigens and antibodies in the ABO system.

Antigens and antibodies in the ABO system.

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