Introduction
There are more than 30 blood grouping system in use in the world to day; the most popular and of great use to medical applications and related researches is ABO grouping system. This blood grouping was discovered by an Australian by the name Karl Landsteiner in early 20th century. Works of Landsteiner that led to this noble prize winning development were observations that Red Blood Cells of some individuals were agglutinated by serums of some other individuals. This agglutination whose literal meaning is clumping together of blood cells; He associated with antigens on the Red Blood Cells and Antibodies in the serum (Yamamoto, 1995, p.5). Antigens are distinct macromolecules on the Red Blood Cells surface that trigger formation of antibodies; an immunogenic response to presence of foreign matter in blood compartment.
Main body
Antigens In broader sense are in themselves foreign to the body cells, but are introduced for the purpose of antibody formation to protect the body from future invasion by disease causing organisms ; a classical example being vaccination with attenuated life vaccine. Landsteiner’s works involved separation of these antigens and classifying them as either B or A, depending on the kind of antibody response they elicited. This reaction formed the bases of ABO blood grouping system (Hisao et al, 2000, p. 4).
There are four antigens to the ABO blood group that is A, B, AB and A1; there is a sequence of oligosaccharides (a form of stored body sugars) that determines whether the antigen is A, B, or A1. The antigens attach themselves on oligosaccharides protruding above the red blood cells surface (Olsson and Chester, 1996, p.30). At a molecular level the ABO gene indirectly encodes the blood group antigen through ABO locus which present three allelic forms of A, B and O. A and B alleles separately encode an enzyme called glycosyltransferase that catalyses in finality synthesis of A and B antigen. “The A and B polymorphism is as result of several base changes on the DNA strand of the ABO gene resulting into A and B transferases distinct by four amino acids. O allele encodes an inactive glycosyltransferase that leaves the ABO antigen precursor unchanged” (Lung-Chih et al, 2000, p. 6). Blood group ABO antigens have antibodies produced against them; antibody A is present in people with blood groups O and B. Antibody B is found in people with blood group O and A.
In an event of introduction of contra antigen in the serum through transfusion, respective antibodies bind to Red Blood Cells and activate the compliment cascade which breaks down red blood cells in circulation leading to intravascular hemolysis. This is the main cause of death resulting from ABO incompatible blood transfusion (Lung-Chih et al, 2000, p. 6). Another medical condition arising from such incompatibilities is the Hemolytic Disease of The new born, where a mother possessing blood group O gets more than one pregnancy with a child possessing either A, B or AB blood groups. Bearing in mind that mother’s blood does not mix with the fetus’, she is able to bear the first pregnancy to delivery; during which traces of child’s blood antigen gets introduced to mother’s through blood contacts (Kobata et al, 1968, p. 272). These elicit formation of respective antibodies in the mother’s serum which later come to haunt subsequent pregnancies leading to spontaneous abortions.
Despite the fact that the ABO blood group antigens exist in a variety of human tissues they mostly prevail in the blood tissues as well as the endothelial and epithelial cells. A single red blood cell exhibit about two million ABO antigens. Other blood cells exhibit less ABO antigens and are mainly taken up from the serum. “A soluble form of ABO blood group antigen is found in all bodily fluids except the cerebrospinal fluid” (Lung-Chih et al, 2000, p. 6).
Person’s ABO phenotype can be changed by a number of causes, of most importance being diseases. Bacteria in a necrotizing infection produce an enzyme which change A1 antigen into B-like antigen. In this time of necrotizing infection, patients who receive blood products with antigen B will risk suffering from intravascular hemolysis. Patient’s blood group turns back to normal on healing. “Another cause of alteration in expression of ABO blood group system is diseases that increase demand of red blood cells, and cancers that lend use of A and B antigens as tumor markers of acute leukemia and in other blood disorders like myelodysplasia and myeloproliferative disorders” (Nakamura et al, 2003, p. 926). Individuals lacking ABO blood group antigens are healthy, portraying that ABO antigens are not beneficial to the body.
ABO antibodies may not have great benefits to the human body but are significant clinically due to the fact that they are very reactive and occur naturally. “In blood transfusions, reactions can be prevented in cross matching blood products” (Nakamura et al, 2003, p. 926). Hemolytic disease of the newborn is possible to prevent with advent of modern technologies where immune-suppressors are applied during the course of pregnancy. ABO blood group antigens are encoded to by one genetic locus with three allelic forms A, B and O (Trepicchio and Krontiris, 1992, 2430). An offspring receives one of the three alleles from each parent making possible six genotypes and four phenotypes as illustrated below.
An individual’s immune systems form antibodies against antigens absent from his red blood cells. Phenotype A will exhibit antibodies B, phenotype B will exhibit antibodies A, phenotype AB will have no antibodies will phenol type O will have both A and B antibodies as illustrated below.
Formation of ABO antibodies is triggered by absence of ABO blood group antigens in foods (certain sugars) or in micro organisms inhabiting the body e.g. the bacterial E-coli. Formation of these antibodies takes place at an early age because babies start feeding on carbohydrates identical ABO blood group antigens early in life. “ABO locus with its three allelic forms encodes a glycosyltransferase, i.e. an enzyme that produces the antigen A, an N-acetylgalactosamine immunodominant sugar while the B allele encodes same enzyme creating antigen B which is D-galactose immunodominant sugar” (Yamamoto, 1995, p.5).
Conclusion
ABO grouping system finds great application in modern medicine, in medical sciences and in their related researches.
Reference List
Hisao, T. Oshihiko, K. and Ichiro S. (2000). Progress in the study of Al30 blood group System. Department of Legal Medicine, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Toyama 930-01 94, Japan.
Lung-Chih Yu. Ching-Yi Chang, Yuh-Ching Twu, and Marie Lin. (2000). Human Histo- blood Group ABO Glycosyltransferase Genes: Different Enhancer Structures with Different Transcriptional Activities. Web.
Kobata A, Grollman E, and Ginsburg V. (1968). An enzymatic basis for blood type B in humans. Biochem Biophys Res Comm.
Nakamura, S. Matsushita, H. Nagai, T. Sugie, H. Furukawa, M. and Kurihara, K. (2003). DNA analysis of ABO blood group system detected by single-base nucleotide substitutions in a paternity case. International Congress Series.
Olsson, M. and Chester, M. (1996) Frequent occurrence of a variant O1 gene at the blood group ABO locus. Vox Sang.
Trepicchio, W. and Krontiris, T. (1992) Members of therel/NF-kB family of transcriptional regulatory proteins bind the HRAS1 minisatellite DNA sequence. Nucleic Acids Res.
Yamamoto F. (1995). Molecular genetics of the ABO histblood group system. VOX Sang 69.