Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
6th lesson Medical students Medical Biology Blood group system ABO system ABO, the most important blood group system from the clinical blood transfusion perspective, was discovered in 1900 by Landsteiner, the discovery that first made blood transfusion feasible. At its basic level, there are two ABO antigens, A and B, giving rise to four phenotypes, A, B, AB and O. In the O phenotype, neither A nor B is produced . Group A people generally have anti-B in their plasma, group B people have anti-A, group AB people have neither antibody, and group O people have anti-A,B. These are predominantly agglutinating immunoglobulin (IgM) antibodies. Anti-A,B will agglutinate group A or B cells. In transfusion medicine it is imperative that donor red cells that are agglutinated by the patient’s plasma are not transfused. "Natural" antibodies called isoagglutinins exist in an individual's serum, directed against whichever of the A and B antigens is not present on that person's red cells. The presence of ABO antigens and antibodies (isoagglutinins) in the four blood types is summarized below: The success of blood transfusions depends on ensuring the compatibility of the blood types between donor and recipient. If the recipient has antibodies to the infused red cells, these red cells will be rapidly destroyed, resulting in a potentially lethal transfusion reaction. Type A blood given to a type B recipient, for instance, can result in such a reaction, since the recipient's serum contains anti-A antibodies. Structure of ABO antigens; "natural antibodies" Why are there so-called "natural" antibodies to A and B blood group antigens? A description of the nature and distribution of these antigens will help answer this question. The blood group substances A and B represent two modified forms of a "stem" carbohydrate present on red blood cells and other tissues. Their structures are 1 shown below (where GLU is glucosamine, GAL is galactose or galactosamine, FUC is fucose, and NAc represents an N acetyl group): These same carbohydrates are also a common component of many foods we eat and many microorganisms in our intestinal tract. The immune system is therefore constantly exposed to these antigens, and responds by making an effective humoral response. Since the immune system does not in general respond to antigens which are a normal part of "self", a type B individual does not make antibodies to the B blood group substance, although the response to the type A antigens is robust. The net result is the production of antibodies, mostly of the IgM class, to whichever of these substances is not present on an individual’s red blood cells. It is important to remember that the A and B blood group substances are present not only on red blood cells, but also in virtually every other tissue. They are therefore important transplantation antigens and must be taken into account together with HLA tissuetyping, when organ transplantation is performed. Genetics of ABO The presence of A and B carbohydrates in our tissues is determined by three alleles at a single genetic locus. One allele encodes an enzyme which produces the A substance, another the B substance; and when both of these alleles are present in a heterozygote both carbohydrates are made. The third allele, O, behaves essentially as a "null" allele, producing neither A nor B substance. Only a single genotype can produce the phenotype AB, namely the heterozygous state A/B. Likewise, type O individuals must be homozygous O/O. However, type A or type B individuals can be either homozygous or heterozygous, the O allele being effectively recessive since it does not contribute either of the two antigens. The inheritance of the ABO blood groups follows simple Mendelian rules. For instance, a homozygous type A mother and a type AB father can yield only two kinds of offspring, type A (genotype A/A) or 2 type AB (genotype A/B). A heterozygous type A and a heterozygous type B, on the other hand , can yield four genotypes and four corresponding phenotypes. The ABO gene is autosomal (the gene is not on either sex chromosomes). The ABO gene locus is located on the chromosome 9. A and B blood groups are dominant over the O blood group. A and B group genes are co-dominant. This meant that if a person inherited one A group gene and one B group gene their red cells would possess both the A and B blood group antigens. These alleles were termed A (which produced the A antigen), B (which produced the B antigen) and O (which was "non functional" and produced no A or B antigen). Group A Group AB Group B Approximately 10% of the population is group B. No A antigens present. These individuals form potent anti-A antibodies which circulate in the blood plasma at all times. Approximately 40% of the population is group A. No B antigens present. These individuals form potent anti-B antibodies which circulate in the blood plasma at all times. Approximately 5% of the population is group AB. Both A and B antigens present. These individuals possess no ABO antibodies. NOTE: This slide is in error as it only illustrates presence of one antigen not 2. 3 Hemolysis If an individual is transfused with an incompatible blood group destruction of the red blood cells will occur. This may result in the death of the recipient. Charts show the possible blood type results for offspring Mother's type Blood Type O A B AB O O O, A O, B A, B A O, A O, A O, A, B, AB A, B, AB B O, B O, A, B, AB O, B A, B, AB AB A, B A, B, AB A, B, AB A, B, AB Fathers' type 4 Rh system Rh is the most complex of the human blood group systems, with 45 well defined antigens. The most immunogenic and clinically important antigen of the Rh system is D. The other main polymorphisms of the Rh system are C/c and E/e, two pairs of allelic antigens. Before the 1970s, anti-D was the most common cause of haemolytic disease of the newborn (HDN). Injection of D negative women with antiD immunoglobulin within 72 hours of giving birth to a D-positive baby prevents the mothers from producing the anti-D that could damage their subsequent babies. This prophylactic procedure has made HDN due to anti-D relatively rare. The antigens of the Rh system are encoded by two genes, RHCE and RHD. These genes are highly homologous and closely linked on chromosome 1. Mother's Type Rh Factor Rh +(R) Rh –(r) Rh +(R) Rh + Rh +(Rr) Rh + Rh –(Rr) Rh –(r) Rh + Rh –(Rr) Rh –(rr) Father's Type !أنت حر مالم تضر:الدعوة للحرية ليس معناها دعوة لإلنفالت والفوضى والهمجيةالحرية قيمة عظيمة ولكن القاعدة Edited by :Mohammed J AlRawi 5