Blood Banking ABO System Lecture PDF

ABO SYSTEM Mohamed Dafallah  introduction ◼ Landsteiner's discovery in 1901 that human blood groups existed ◼ After that, 25 blood group systems have been described ◼ Each system is a series of red cell antigens, determined either by a single genetic l...

ABO SYSTEM Mohamed Dafallah  introduction ◼ Landsteiner's discovery in 1901 that human blood groups existed ◼ After that, 25 blood group systems have been described ◼ Each system is a series of red cell antigens, determined either by a single genetic locus or very closely linked loci.  Blood Cell Antigens ◼ Red cell antigen or blood group factors. ◼ Human leukocyte antigen, HLA-A, HLA-B, HLA-C and HLA-D. ◼ granulocytic specific antigen N1 , N2 ◼ Platelet specific antigen. PlA1 , PlA2 , PlE1 PlE2 , Koa , Kob  Blood group Antigens  Refers to the red cell antigens, more than 400 red cell antigens identified and determined the blood group some of them clinically important (major blood group), others less important (minor blood group).  They were inherited from parents and existed in early fetal life, and found as cells bound or soluble antigens in body fluids of the secretor and detected by serological reactions tests.  Blood groups may be protein, glycoprotein or glycolipids in nature.  Blood group Terminology In some systems blood group antigens indicated by a capital  letters ( A,B,M,N) Or by a capital letter and a numerical or alphabetical subscript  ( A1,A2,Ax,Am). Other systems use capital and lower case letters for antigens  produced by allels ( K&k, S&s, I&i). Others indicated by a capital and a lower case letter followed  by a an alphabetical superscript ( Jka, Jkb, Fya, Fyb)  Blood group Terminology ◼ Others use letter/s as specific name ( K for kell, k for Cellano, Fy for duffy Le for lewis) ◼ Genes usually written in italics( A,B O), and antigens in bold (A,B,O) ◼ Antibodies indicated by the term anti-plus blood group antigen designation( anti-Fya). ◼ Former names agglutinogens for antigens, and agglutinins for antibodies foud to be not appropriate. Clinical Importance of Blood groups 1) Blood group systems and antibodies form the basis for pre-transfusion testing. 2) Pre-transfusion testing focuses on ABO and Rh antigen testing, as well as screening for antibodies in the plasma 3) Antigens and antibodies are the etiologies of hemolytic disease of the fetus and newborn and hemolytic transfusion reactions. 4) Some antigens play a primary role in transplant therapy. Classification and nomenclature ◼ Historically, all blood group antigens have been assigned a name and an abbreviation. ◼ The International Society of Blood Transfusion (ISBT) examined this identification system, and a committee was developed in 1980 to standardize blood group terminology ◼ The committee’s criteria for assigning an antigen to blood group system are: - Genetic studies (genotype) - Serologic testing (Phenotype) Major&minor blood group Systems ◼ ABO system. ◼ Rhesus system. ◼ Kell system. ◼ Kidd system. ◼ Duffy system. ◼ MNSs system. ◼ Major blood group system associated with production of immune warmed active antibodies caused hemolytic transfusion reactions. The ABO Blood Group System History of ABO system: ◼ Karl Landsteiner discovered the ABO blood group system in 1901. His experiments led him to discover three of the four ABO groups: A, B, and O. ◼ Shortly after Landsteiner’s initial discovery, his associates, Alfred and Adriano, discovered the fourth blood group, AB. ◼ Felix Bernstein discovered the group inheritance pattern of multiple alleles at one locus in 1924. ◼ In 1930, O. Thompson proposed the four allelic genes: A1, A2, B, and O. ABO Antigens ◼ Antigens of the ABO system are A, B and H. ◼ ABO antigens are also present on lymphocytes, platelets, organs, endothelial cells, and epithelial cells. ◼ They are detectable at 5 to 6 weeks of gestation. ◼ Newborns and infants have fewer antigen sites on their red cells. but ABO antigens are fully developed by two to four years of age. Inheritance of A, B, and H Antigens ◼ As Bernstein discovered, ABO antigens are inherited in a simple Mendelian fashion from an individual’s parents. ◼ Each individual possesses a pair of genes. Each gene occupies an identical locus on chromosome 9. ◼ There are three possible genes that can be inherited. The three genes are: A, B, and O. ◼ A and B genes produce a detectable product while the O gene does not produce a detectable product. ◼ The expression of the A and B genes is codominant. ◼ The H antigen is required to produce A and/or B antigens. The H gene is also inherited in Mendelian fashion and occupies a locus on chromosome 19. ◼ Each parent contributes one gene, either H or h. The possible genetic combinations are HH, Hh, or hh. Individuals who are genetically either HH or Hh will produce the H antigen, and it can be detected on their red cells. ◼ The frequency of occurrence of the H antigen in the Caucasian population is greater than 99.99%. ◼ Individuals inheriting an hh genotype do not produce the H antigen and have the Bombay phenotype, Oh. ◼ The plasma of an individual with a Bombay phenotype frequently demonstrates an anti-H. Biochemical and Structural Development of A, B, and H Antigens ◼ Expression of A, B, and H genes does not result in the direct production of antigens. Rather, each gene codes for the production of an enzyme known as a transferase ◼ Each transferase catalyzes the transfer of a carbohydrate molecule to an oligosaccharide chain. The attached carbohydrate provides antigenic specificity. ◼ The O gene codes for an enzymatically inactive protein and, hence, no antigen is produced. Development of H Antigen ◼ The H allele codes for the transferase, L- fucosyltransferase. ◼ This enzyme catalyzes the formation of the H antigen by transfer of L-fucose to oligosaccharide chains. ◼ The L-fucose is the immunodominant sugar for the H antigen. It is the sugar that confers antigenic specificity to the H antigen. ◼ The H antigen serves as a precursor for A and B antigens. ◼ The h allele is an amorph (silent) and does not produce a detectable product. Development of A and B Antigens ◼ The H antigen oligosaccharide chain serves as a precursor for both the A and B antigens. ◼ The A and B alleles each code for a transferase that attaches a sugar molecule to the terminal end of the H antigen oligosaccharide chain, which forms either the A or B antigen. ◼ The A allele codes for N-acetylgalactosamine transferase. This transferase attaches N- acetyl-D-galactosamine to the H antigen forming the A antigen. ◼ The B allele codes for D-galactosyltransferase. This transferase attaches D-galactose to the H antigen forming the B antigen. ◼ The product of the O allele is an enzymatically inactive protein. Hence, this allele produces no detectable antigen. ◼ Structure of ABO blood group antigens. Each consists of a chain of sugars attached to lipids or proteins which are an integral part of the cell membrane. The H antigen of the O blood group has a terminal fucose (fuc). The A antigen has an additional N-acetyl galactosamine (galnac), and the B antigen has an additional galactose (gal). Secretor Status ◼ Soluble forms of A, B, and H antigens may be found in body secretions. ◼ The ability of a person to secrete water- soluble substances is controlled by independently inherited genes. The secretor gene is on chromosome 19. ◼ At least one Se gene is required for the secretory property to be expressed. ◼ Persons with soluble A,B or H antigen (SeSe or Sese) in their secretions are secretors. ◼ While those with no A or B antigens in secretions (sese) are nonsecretors. ◼ Approximately 78% of the population possesses at least one Se gene. ◼ An individual that possesses a Se gene will secrete A, B, and/or H antigen(s) dependent on possession of the corresponding ABH gene(s). A1 and A2 Subgroups ◼ Group A antigens can be differentiated into multiple subgroups. The two major subgroups are - A1, 80% of Group A individuals, and - A2, 20% of group A individuals. ◼ Persons typing as AB can be divided into the same percentages of A antigen presentation. - A1B make up approximately 80% and - A2B are 20% of all AB individuals. ◼ The A1 gene produces a transferase that has a greater ability to convert H antigen to A antigen than the A2 gene Applications of ABO Grouping ◼ Pre-transfusion Testing ◼ Donor Testing ◼ Prenatal Testing ◼ Paternity Determination ◼ Transplant Matching ◼ Used by police in forensic science  ABO & susceptibility to disease ◼ Despite their obvious clinical importance, the physiological functions of ABO blood group antigens remain a mystery. ◼ Numerous associations have been made between particular ABO phenotypes and an increased susceptibility to disease. For example, the ABO phenotype has been linked with: - stomach ulcers (more common in group O individuals) and - gastric cancer (more common in group A individuals). - individuals with blood type O have lower levels of vWF The ABO Blood Group System Secretor Status ◼ 78% of people Soluble A, B, and H antigens found in their body fluid secretions. ◼ The ability of a person to secrete water-soluble antigens depend on the presence of Se gene ◼ At least one Se gene is required for the secretory property to be expressed. A1 and A2 Subgroups ◼ Group A antigens can be differentiated into multiple subgroups. The two major subgroups are - A1, 80% of Group A individuals, and - A2, 20% of group A individuals. ◼ The A1 gene produces a transferase that has a greater ability to convert H antigen to A antigen than the A2 gene ◼ A2 antigens are composed mainly of linear oligosaccharide chains while the A1 cells have a greater number of branched chains ◼ A2 individuals can develop antibodies to the A1 antigens. ◼ The typical reaction pattern of reverse grouping in a group A individual is no agglutination with the A cells (no anti-A) and agglutination with B cells (anti-B present) ◼ In A2 persons with an anti-A1, the A cells will also be agglutinated in the reverse grouping.  ABO Antibodies ◼ “Antibodies directed against ABO antigens are the most important antibodies in transfusion medicine ◼ The ABO antibodies were originally thought to be natural antibodies formed with no apparent antigenic stimulus. ◼ However there are stimulants (Secretions) (suggestion) ◼ Newborns have no ABO antibodies. When newborns are tested, only a forward group is performed. ◼ Newborns may exhibit passive ABO antibodies that have crossed the placental barrier. ◼ Reverse grouping of a newborn or umbilical cord serum indicates the blood group of the mother. ◼ The child will begin antibody production, and have a detectable titer, at three to six months of age. ◼ ABO antibody production peaks at age five to ten years of age and continues in immuno-competent individuals throughout life ◼ Conditions with decreased levels of ABO antibodies are: - Young infants - Elderly - Immuno-deficient persons - Immuno-suppressed patients Immunoglobulin Class ◼ ABO antibodies are cold and agglutinins (They are saline agglutinins with optimal reactivity at 4°C) ◼ These naturally occurring antibodies are mostly IgM isotype ◼ but IgG and IgA classes of ABO antibodies have been detected. ◼ The development of IgG antibodies occurs via transfusion of incompatible red cells or fetal maternal incompatibility. ◼ Group O individuals do not have A or B antigens on their cells. Consequently, they produce anti-A, anti-B, and anti-A,B. Anti- A,B is an antibody that has cross- reactivity with A and B cells. ◼ Group B individuals produce anti-A ◼ Group A individuals produce anti-B ◼ group B and O individuals produce anti-A. ◼ This anti-A can be separated into anti-A and anti-A1. ◼ The anti-A1 antibody reacts specifically with A1 cells and not with A2 cells ◼ Like other ABO antibodies, this antibody reacts optimally at room temperature or colder. Clinical Significance of ABO Antibodies ◼ ABO antibodies are capable of causing both : - Hemolytic Disease of the Fetus and Newborn (HDFN) and - Hemolytic Transfusion Reactions (HTR). ◼ These issues explain the clinical significance of “naturally occurring” antibodies.  Forward and Reverse Grouping ABO Forward Grouping ◼ The forward grouping is a test performed for antigens using known antisera with patient’s cells that may contain unknown antigens. ◼ Test methods for forward grouping include - Tube typing, - Gel technology, - Automation, - Solid phase technology ◼ ABO forward grouping with tube typing uses a saline suspension of 3 to 5% (up to 10%) washed patient red cells. ◼ These cells are combined in a 1:1 ratio with commercial antisera. ◼ These cells are applied to the anti-A and anti-B tubes then, centrifugation is applied and results interpreted Reverse Grouping ◼ ABO reverse grouping uses patient plasma (or serum) combined in a 2:1 ratio with commercially prepared cells. The cells are packaged in sets of three (A, B and O) or four (A1, A2, B and O). ◼ The cells are used to detect unknown antibodies in the plasma. The result is evaluated by examining the tubes for hemolysis and agglutination. ABO Reverse Grouping, tube method Any Questions?