Transfusion Medicine 2 Notes PDF

Transfusion Medicine 2 ‫ادلكتـور هـــيمث أمحـــد الربيـــعي‬ Professor of Hematopathology MBChB (1985) FICMS - Hematopathology (1998) DEPARTMENT OF PATHOLOGY AND FORENSIC MEDICINE COLLEGE OF MEDICINE – UNIVERSITY OF BAGHDAD Learning Objectives: At the end of this lectur...

Transfusion Medicine 2 ‫ادلكتـور هـــيمث أمحـــد الربيـــعي‬ Professor of Hematopathology MBChB (1985) FICMS - Hematopathology (1998) DEPARTMENT OF PATHOLOGY AND FORENSIC MEDICINE COLLEGE OF MEDICINE – UNIVERSITY OF BAGHDAD Learning Objectives: At the end of this lecture, the student will be able to: Identify the Red cell antigens (ABO and Rh systems) and blood group antibodies. Define the clinical significance of blood groups antigens in blood transfusion Characterize the naturally-occurring and immune- occurring antibodies ABO system Red cell antigens & Blood Group antibodies How many blood group antigens are there on a red blood cell membrane? More than 400 RBC GROUP ANTIGENS (Ags) have been described. What is the clinical significance of blood groups (Ags) in blood transfusion? Individuals who lack a particular blood group Ag may produce Abs reacting with that Ag which may lead to a transfusion reaction. Different blood group Ags vary greatly in their clinical significance with the ABO and Rh groups being the most important. Some other systems are present.  BLOOD GROUP ANTIBODIES: A. Naturally-occurring antibodies (Abs): These antibodies occur in the plasma of subjects who: Lack the corresponding antigen. Have not been transfused. Have not been pregnant. These antibodies are: Usually IgM React optimally at cold temperature (4°C) Although reactive at 37°C, are called cold antibodies The most important are anti-A and anti-B Others: Abs to Hh, Ii, Lewis, MN, and P blood group systems. Although anti-A (from blood group B individuals) and anti-B (from blood group A individuals) contains predominantly IgM antibody, there may be small quantities of IgG present. Naturally occurring antibodies to A and/or B antigens are found in the plasma of subjects whose red cells lack the corresponding antigen. B. Immune antibodies: develop in response to: 1. Blood Transfusion 2. Transplacental passage during pregnancy of fetal red cells possessing Ags that the mother lacks. These antibodies are: Commonly IgG. Immune Abs react optimally at 37°C (warm Abs). Although some IgM Abs may also develop usually in the early phase of an immune response. Only IgG Abs are capable of transplacental passage from mother to fetus. The most important immune Ab is the Rh Ab (anti-D). Why the Performance of serum grouping is unique to the ABO blood group system? The ABO is the only blood group system in which individuals have regularly antibodies in their serum to antigens that are absent from their RBCs. Blood group O is the most frequent ABO phenotype in all ethnic groups followed by A then B then AB. Blood group B is found twice as frequently in blacks and Asians as in whites. Sub-group A2 is rarely found in Asians. The ABO Phenotype Frequencies of Ethnic Groups in the United States Iraq (%) Phenotype White Black Hispanic Asian (n=341) 2020; (n=888) 2005 O 45 50 56 40 ~ (32.3-35.7) A 40 26 31 28 ~ (26.2-31.7) B 11 20 10 25 ~ (20.2-28.3) AB 4 4 3 7 ~ (9.8-15.8)  The ABO blood group system Phenotype Genotype Antigens Naturally-occurring Abs O OO H Anti-A , anti-B, anti-A,B Anti-B A AA or AO A (anti-H is very rare) B BB or BO B Anti-A AB AB AB None IS IT POSSIBLE TO DETERMINE THE GENOTYPE FROM THE PHENOTYPE IN ABO SYSTEM? Although there are six possible genotypes (AA, AO, BB, BO, OO, AB) the absence of a specific anti-O prevents the serological recognition of more than four phenotypes. Serologically it is not possible to determine the genotype from the phenotype in all ABO system. But the phenotype and genotype are the same in an AB individual because of the inheritance of both the A and B gene. The ABO system consists of three allelic genes: A, B, and O. The A and B genes control the synthesis of specific (transferase) enzymes responsible for the addition of single carbohydrate residues on H substance. The O gene is amorph and does not transform the H substance. 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 RC membrane. The H antigen of the O blood group has a terminal L-fucose (fuc). The A antigen has an additional N-acetyl galactosamine (galnac), and the B antigen has an additional D-galactose (gal). glu, glucose; gnac, N-acetyl glucosamine  H gene elicits the production of an enzyme called α-2-L-fucosyltransferase, which transfers the sugar L-fucose to an oligosaccharide chain on the terminal galactose of type 2 chains. H antigen on RBC is composed of Ceramide – glucose – D-galactose – N-acetylglucosamine – D-galactose – Fucose. Type 2 precursor chain on RBC is composed of Ceramide – glucose – D-galactose – N-acetylglucosamine – D-galactose. A type 2 precursor substance of ABO on RBC refers to a beta 1 ---> 4 linkage between galactose and N- acetylglucosamine.  Individuals who are blood group O inherit at least one H gene (genotype HH or Hh) and two O genes. The H antigen expression in A blood group is less than in B blood group individuals. As many as 810,000 to 1,170,000 antigen sites exist on an A1 adult RBC in response to inherited A genes. More than 1,320,000 H antigen sites are present on an RBC Anywhere from 610,000 to 830,000 antigen sites exist on a B adult RBC in response to conversion of the H antigen by the enzyme produced by the B gene. When BOTH A and B genes are inherited, the B enzyme (α-3-D-galactosyltransferase) seems to compete more efficiently for the H substance than the A enzyme (α-3-N-acetylgalactosaminyl- transferase). Therefore, the average number of A antigens on an AB adult cell is approximately 600,000 sites, compared with an average of 720,000 B antigen sites. On an AB adult cell, the average number of A antigen sites is less than B antigen sites.  The ABH ANTIGENS develop early in fetal life but do not increase much in strength during the gestational period. The RBC of the newborn have been estimated to carry anywhere from 25% to 50% of the number of antigenic sites found on the adult RBC. The expression of A and B antigens on the RBCs is fully developed by 2 to 4 years of age. The phenotypic expression of ABH antigens may vary with age, race, genetic interaction, and disease states. Is it logical to perform only forward grouping on cord blood from newborn infant? Most antibodies found in cord blood serum are IgG of maternal origin. The production of ABO Abs is initiated at birth, but titers are generally too low for detection until the individual is 3 to 6 months of age. Ab production peaks when an individual is between 5 and 10 years of age and declines later in life. Do you recommend the use of anti-A,B reagents in routine testing of RBCs? Anti-A,B reagent was more effective at detecting weakly expressed A and B Ags than reagents anti-A and anti-B. The production and use of monoclonal antisera have made anti-A and anti-B much more sensitive, to the point where weak A and B Ags can be detected routinely. Anti-A,B reagent is routinely used when performing ABO confirmation of blood donors, because it is more economical to use one reagent (anti-A,B) to verify group O donor unit. Therefore, Anti-A,B reagent is not usually used in routine ABO red cell testing on patient samples. The formation of ABH antigens results from the interaction of ABO, Hh, and Se genes. The H antigen is a precursor structure on which A and B antigens are made. Inheritance of the H gene results in the formation of H antigen. H and Se genes are closely linked and located on chromosome 19, in contrast to ABO genes which are located on chromosome 9. Between 1% to 8% of A2 individuals produce anti-A1 in their serum. Between 22% to 35% of A2B individuals produce anti-A1. Anti-A1 is unlikely to cause a transfusion reaction because it usually reacts only at temperatures well below 37°C.  Differentiation of A1 and A2 phenotypes can be determined by using anti-A1 lectin (from Dolichos biflorus). Anti-A1 lectin does not agglutinate A2 (or A2B cells) Bandeiraea simplicifolia agglutinates B cells and does not agglutinate B subgroups. The inheritance of an A2 gene, results in the production of only 240,000 to 290,000 antigen sites on an adult A2 RBC. The immunodominant sugar on both A1 and A2 RBCs is N-acetyl-D-galactosamine (in A2 it is less amount and less efficient). The differences between blood group A1 and A2 are: Quantitative Qualitative Decrease number of Differences in the antigen sites precursor oligosaccharide chains Decrease amount of Subtle differences in transferase enzyme transferase enzymes (A2 enzyme is less efficient) Decrease amount of Formation of anti-A1, in a branching of H antigen percentage of some subgroups  The A, B and H antigens are present on most body cells including white blood cells and platelets. In the 80% of the population who have secretor genes, these antigens are also found in soluble form in secretions and body fluids (e.g. plasma, saliva, semen and sweat).  The H antigen on A1 and A1B RBCs may be hidden and therefore may not be available to react with anti- H antisera. Anti-H is occasionally found in the serum of A1 and A1B blood group individuals. Anti-H is a naturally occurring IgM cold agglutinin that reacts best below room temperature (RT). High-titered anti-H may react at RT and present a problem in: Antibody screening procedures, (because reagent screening cells are group O). Compatibility testing. Anti-H is an insignificant antibody in term of transfusion purposes, because it has no reactivity at body temperature (37°C). What are the types of clinically significant naturally occurring antibodies present in the serum of blood group O individuals? Serum from group O individuals contains not only anti- A and anti-B but also anti-A,B. Anti-A,B antibody activity is not a mixture of anti-A and anti-B, (if group O serum is adsorbed with A or B cells, the antibody eluted will react with both A and B cells). Anti-A,B antibody is a separate “cross-reacting” antibody that is usually IgG in nature. What is the clinical significance of ABO Abs? Knowing the amount of IgG anti-A, anti-B, or anti- A,B in: A woman’s serum sometimes allows prediction or diagnosis of HDFN caused by ABO incompatibility. Often cord blood samples from babies of group O mothers are examined for possible ABO HDFN. Both Ig (IgM & IgG) classes of ABO antibodies react preferentially at RT (20°C to 24°C) or below and efficiently activate complement at 37°C. What is paragloboside or glycan (type 2 chain)? It is a basic precursor material from which the A, B, and H antigens are formed, to which sugars are attached in response to specific enzyme transferase elicited by an inherited gene. It is immediate precursor for the H and P antigens of the RBC. Define the immunodominant sugars. These are sugars that occupy the terminal positions of type 2 precursor chain and confer blood group specificity. Why the H antigen expression in A blood group is less than B blood group individuals? The A gene tends to elicit higher concentrations of transferase than the B gene. This leads to the conversion of practically all of the H antigen on the RBC to A antigen sites. Arrange the blood groups from the greatest to the least according to their reactivity with anti-H lectin. Greatest Least > > > > > amount amount of H of H Arrange the blood groups from the greatest to the least according to their reactivity with anti-H lectin. Greatest Least O > A 2 > B > A2 B > A1 > A1 B amount amount of H of H