Blood groups

• An antigen is a molecule that triggers a specific immune response against itself when it enters the body, while an antibody is a protein produced by the immune system that is capable of binding with high specificity to an antigen
• The ABO blood group system was discovered by Austrian immunologist Karl Landsteiner in 1901
• The A and B antigens are inherited from both parents, dividing individuals into four major blood types
• The ABO blood group antigens (agglutinogens) are attached to oligosaccharide chains that project above the RBC surface, with blood type O being the most common worldwide
• The A and B antigens are the most important of the more than 100 different blood group antigens identified
• Two groups of antigens can cause transfusion reactions more than others: ABO and Rh systems of antigens
• Agglutinins, the antibodies, are gamma globulins, with most of them being IgM and IgG immunoglobulin molecules
• High levels of agglutinins are found in the plasma of people who have never been exposed to a different type of blood, considered naturally occurring antibodies
• If a recipient with blood group A is transfused with group B RBCs, the anti-B antibodies in the recipient's serum bind to the corresponding antigens on the transfused RBCs, causing rapid intravascular hemolysis
• Mismatched transfusions can lead to acute kidney failure due to the release of large amounts of hemoglobin from ruptured donor erythrocytes
• The Rh blood group system has over 50 antigens, with D being the most antigenic component, significantly more antigenic than the other Rh antigens
• The D antigen is the most immunogenic, making it most likely to cause a transfusion reaction in the recipient
• In the Rh system, the presence or absence of the D antigen is designated as Rh-positive or Rh-negative, respectively
• In the A-B-O system, plasma agglutinins cause transfusion reactions spontaneously, while in the Rh system, spontaneous agglutinins almost never occur
• To develop enough agglutinins in the Rh system to cause a significant transfusion reaction, a person must first be massively exposed to an Rh antigen, such as through a blood transfusion containing the Rh antigen
• When red blood cells (RBCs) containing the Rh factor are injected into an Rh-negative person, anti-Rh agglutinins develop slowly, reaching maximum concentration about 2 to 4 months later
• With multiple exposures to the Rh factor, an Rh-negative person eventually becomes strongly "sensitized" to the Rh factor, leading to enhanced and potentially severe transfusion reactions with subsequent transfusions of Rh-positive blood
• Erythroblastosis fetalis, also known as "Hemolytic Disease of the Newborn," is a disease characterized by agglutination and phagocytosis of the fetus's red blood cells, particularly significant when an Rh-negative mother carries an Rh-positive fetus
• In Erythroblastosis fetalis, maternal anti-Rh antibodies can cause agglutination of the fetus's blood, leading to hemolysis, jaundice in the baby, and potential damage to other cells in the body
• Erythroblastosis fetalis results in severe anemia at birth, with the destruction of red blood cells by maternal anti-Rh agglutinins potentially causing permanent mental impairment or damage to motor areas of the brain in surviving infants
• Prevention of sensitization to the D antigen in Rh-negative women who deliver Rh-positive babies is achieved through the administration of the anti-D antibody (RhoGAM) to prevent the development of large amounts of D antibodies during subsequent pregnancies
• An antigen is a molecule that triggers a specific immune response against itself when it enters the body, while an antibody is a protein produced by the immune system that is capable of binding with high specificity to an antigen
• The ABO blood group system was discovered by Austrian immunologist Karl Landsteiner in 1901
• The ABO blood group antigens (agglutinogens) are attached to oligosaccharide chains that project above the RBC surface
• The A and B antigens are inherited from both parents, dividing individuals into four major blood types
• The A and B antigens are the most important of the more than 100 different blood group antigens identified
• Two groups of antigens can cause transfusion reactions more than others: ABO and Rh systems of antigens
• Agglutinins, the antibodies, are gamma globulins, with most being IgM and IgG immunoglobulin molecules
• Agglutinins have two binding sites (IgG type) or 10 binding sites (IgM type), causing cells to clump together by the process of "agglutination"
• High levels of agglutinins are found in the plasma of people who have never been exposed to a different type of blood, considered naturally occurring antibodies
• Mismatched transfusions can lead to acute kidney failure due to the release of large amounts of hemoglobin from ruptured donor erythrocytes
• The Rh blood group system has over 50 antigens, with D being the most antigenic component
• The D antigen is the most immunogenic, making it most likely to cause a transfusion reaction in the recipient
• 85% of Caucasians are D-positive in the Rh system
• In the A-B-O system, plasma agglutinins cause transfusion reactions spontaneously, while in the Rh system, spontaneous agglutinins almost never occur
• For significant transfusion reactions to develop in the Rh system, a person must first be massively exposed to an Rh antigen, such as by transfusion of blood containing the Rh antigen
• When red blood cells (RBCs) containing Rh factor are injected into an Rh-negative person, anti-Rh agglutinins develop slowly, reaching maximum concentration about 2 to 4 months later
• With multiple exposures to the Rh factor, an Rh-negative person eventually becomes strongly "sensitized" to Rh factor, leading to enhanced and potentially severe transfusion reactions with subsequent transfusions of Rh-positive blood
• Erythroblastosis fetalis, also known as "Hemolytic Disease of the Newborn," is characterized by agglutination and phagocytosis of the fetus’s red blood cells, particularly significant when an Rh-negative mother carries an Rh-positive fetus
• In Erythroblastosis fetalis, maternal anti-Rh antibodies can cause agglutination of the fetus’s blood, leading to hemolysis, jaundice in the baby, and potential damage to other cells of the body