ABO Blood Group System Overview

ABO Blood Group System

• Discovered by Karl Landsteiner
• Only blood group system where individuals predictably have antibodies in their serum against antigens absent from their red blood cells (RBCs).
• Antibody production occurs without exposure to RBCs via transfusion or pregnancy.
• Severe, fatal consequences if incompatible blood types are mixed (most immunogenic; causes most serious hemolytic transfusion reactions (HTR)).
• ABO forward and reverse grouping tests are required for all donors and patients.
• ABO forward and reverse grouping are reciprocal; one test serves as a check on the other.

Introduction

• Bacteria's antigens are chemically similar to A and B antigens.
• Exposure to these antigens stimulates the production of anti-A and anti-B antibodies.
• Frequency of blood types in whites and blacks:
  • O: 49% (whites), 45% (blacks)
  • A: 27% (whites), 40% (blacks)
  • B: 19% (whites), 11% (blacks)
  • AB: 4% (whites), 4% (blacks)
• ABO blood frequencies vary by ethnic group.
• (See Table 6-7 in the slides for detailed frequencies)

Nomenclature

• Landsteiner, Jansky, and Moss systems for classifying blood groups.
• Table displaying the different blood group classifications across these 3 systems.

Formation of A, B, & H Antigens

• ABH antigens' formation results from the interaction of genes at three separate loci (ABO, Hh, and Se).
• Precursor substance (paragloboside or glycan) is the starting material for all ABO blood group systems.
• H gene is necessary to create the H antigen.
• H and Se genes are closely linked and found in chromosome 19.
• ABO blood genes are found in chromosome 9.
• H antigen is the foundational antigenic material for A, B, and AB antigens.
• H gene must be inherited to form ABO antigens on red blood cells (RBCs).
• Se gene is required to form ABO antigens in secretions.
• A and B antigens fully develop between ages 2 and 4 and remain consistent throughout life.
• Phenotypic expression of ABH antigens varies with race, genetic interaction, and diseases.

Hh and ABO Genes

• L-fucose is responsible for H specificity.
• N-acetylgalactosamine is responsible for A specificity.
• D-galactose is responsible for B specificity.
• hh genotype, also called Bombay phenotype, lacks expression of ABH antigens.

Precursor Substance

• With H gene, precursor substance forms the H antigen.
• Without H gene, no H antigen forms.
• A antigens (A gene), B antigens (B gene), and O antigens (O gene) based on inheritance.

Enzymes Involved

• H gene: 1,2 fucosyl transferase
• A gene: 1,3 N-acetylgalactosaminyl transferase
• B gene: 1,3 galactosyl transferase

H Antigen

• Red blood cells (RBCs) have D-galactose
• Also have GlcNAc (N-acetylgalactosamine).
• D-galactose and L-fucose combine.

A Antigen

• Red blood cells (RBCs) have D-galactose
• Also have GlcNAc (N-acetylgalactosamine)
• D-galactose and L-fucose combine.

B Antigen

• Red blood cells (RBCs) have D-galactose
• Also have GlcNAc (N-acetylgalactosamine)
• D-galactose and L-fucose combine.

Formation of Soluble Antigens

• Found in body secretions (saliva, tears, urine, digestive juices, bile, milk, amniotic fluid).
• Dependent on ABO genes and secretor genes (Se).

Inheritance of Se Antigens

• Se gene codes for a transferase enzyme that modifies the type 1 precursor substance in secretions to generate the H substance.
• Se gene doesn't change A,B, or H antigen formation directly on RBCs.
• People who inherit the sese genotype are considered nonsecretors.

Fluids with A,B, and H Antigens

• These substances are secreted in various bodily fluids. (List of fluids provided)

Bombay Blood

• Absence of H, A, and B antigens; no agglutination with anti-A, anti-B, or anti-H lectin.
• Presence of anti-A, anti-B, anti-A,B, and a potent wide thermal range of anti-H in the serum
• Absence of a-2-L-fucosyltransferase.
• Presence of A or B enzymes in the serum, determined by the ABO genotype.
• Recessive form of inheritance.
• RBCs of the Bombay phenotype are compatible only with the serum from another Bombay individual.

Lectins Used in Blood Banking

• Dolichos biflorus agglutinates A₁ or A₁B
• Bandeiraea simplicifolia agglutinates B cells
• Ulex europaeus agglutinates O cells (H specificity)

Forward Grouping

• Unknown sample's antigens are determined.
• Known antibodies (anti-A, anti-B, anti-A,B ) are used.
• RBC suspension ( 2-5% ) is the specimen.
• Anti-A, Anti-B, and Anti-A,B are the reagents used for forward typing

Forward Grouping (Basis Table)

• Table detailing the basis, source, color, and dyes utilized in forward grouping tests for different blood types.

Reverse Grouping

• Unknown sample's antibodies are determined.
• Known antigens (A cells, B cells, O cells) are used.
• Serum is the specimen. (2-5% erythrocytes)

Reverse Grouping (Table)

• Table displaying the reactions observed in serum samples corresponding to the presence of A cells, B cells, and O cells.

ABO Blood Groups

• Table showing antigens on RBCs, antibodies, and extra notes for each blood type (A, B, AB, and O).

Donor/Recipient Chart

• Chart indicating which blood types can donate or receive red blood cells to each other (0, A, B, AB)

ABO Discrepancies

• Unexpected reactions in forward and/or reverse grouping tests.
• Divided into four categories based on suspected source of errors.
• Group 1: weakly reacting or missing antibodies
• Group 2: weakly reacting or missing antigens
• Group 3: rouleaux formation from abnormal proteins.
• Group 4: miscellaneous problems (presence of autoantibodies, antibodies other than ABO system antibodies, etc.)

Causes of ABO Discrepancies

• Inadequate identification, test tubes, or slides.
• Cell suspension (too heavy or too light).
• Mistakes in recording results (clerical errors).
• Samples being mixed up
• Hemolysis being missed
• Missing or incorrect reagents.
• Inadequate centrifuging.
• Contaminated reagents

Resolution for ABO Discrepancies

• Repeat testing using proper sample preparation.

Group 1 Discrepancies

• Occur in newborns, elderly patients with certain conditions, or those on immunosuppressives.
• These discrepancies are often due to weakly reacting or missing antibodies potentially due to the patient's medical conditions or recent transfusions.
• Resolution involves further tests, such as incubating the patient's serum at room temperature and at 4 degrees celsius.

Group 2 Discrepancies

• Unexpected reactions in the forward grouping due to weakly reacting or missing antigens
• May result in various underlying diseases, like leukemia, Hodgkin's disease, or conditions affecting the digestive tract.
• Resolution involves incubating at room temperature and at lower temperatures for further evaluation.

Group 3 Discrepancies

• Result from abnormal plasma components or proteins; lead to rouleau formation.
• Conditions causing elevated serum globulin levels including plasma expanders (such as dextran or polyvinylpyrrolidone) or serum samples containing Wharton's jelly could contribute to discrepancies.
• Resolution often involves flushing the RBCs with saline to dilute the abnormal components.

Group 4 Discrepancies

• Unexpected reactions due to various reasons, such as cold-reacting autoantibodies, multiple ABO groups in circulating RBCs from recent transfusions or bone marrow transplants, or other non-ABO antibodies.
• Resolution involves a variety of test methods dependent on the particular cause of the discrepancy.

ABO Antigens

• Present in diverse body tissues and secretions
• Detected in early fetal development.
• Found in multiple bodily locations and animal forms.

ABO Antibodies

• Predominantly IgM, react at room temperature, and activate complement.
• Produced after birth.
• Typically low in early months; rise in later life and decline again in older age.
• Predominant antibody in cord blood is maternal IgG.

Genotype

• The combination of genes inherited from both parents—father (50%) and mother (50%).
• Some genes are expressed as homozygous (identical from parents), whereas others are heterozygous (different types from parents.)
• Dominant genes always express while recessive genes may not.
• (A > B > O)

Phenotype

• The observed/tested expression of genes—resulting blood type.
• Phenotypes, rather than genotypes, are determined by tests.

Inheritance of ABO Blood Groups

• Based on Mendelian theory.
• One locus (position) on chromosome 9 dictates blood type.
• O is an amorph gene, while A and B are phenotypes

Codominant Blood Types

• Table demonstrating inheritance patterns for blood type A, B, O, and AB.

Explore the ABO blood group system and its significance in immunology. This quiz covers the discovery by Karl Landsteiner, the unique antigen-antibody interactions, and the implications of blood type compatibility. Test your knowledge on the grouping tests and demographic frequencies of blood types.