1. ABO Blood Group System

2. History: Karl Landsteiner
Discovered the ABO Blood Group System in 1901
He and his five co-workers began mixing each others red cells and serum together and inadvertently performed the first forward and reverse ABO groupings

3. Why is it important?
ABO compatibility between donor cell and patient serum is the essential foundation of pretransfusion testing
It is the only system with expected antibodies
Whether they are IgG or IgM, ABO antibodies can activate complement readily
This means that incompatibilities can cause life threatening situations (transfusion reactions)

4. Biochemical & Genetic Considerations
ABO antigens:
Biochemical & Genetic Considerations

5. ABO and H Antigen Genetics
Genes at three separate loci control the occurrence and location of ABO antigens
The presence or absence of the A, B, and H antigens is controlled by the H and ABO genes

6. The presence or absence of the ABH antigens on the red blood cell membrane is controlled by the H gene
The presence or absence of the ABH antigens in secretions is indirectly controlled by the Se gene

7. ABO Antigen Genetics H gene – H and h alleles (h is an amorph)
Se gene – Se and se alleles (se is an amorph)
ABO genes – A, B and O alleles

8. H Antigen
The H gene codes for an enzyme that adds the sugar fucose to the terminal sugar of a precursor substance (PS)
The precursor substance (proteins and lipids) is formed on an oligosaccharide chain (the basic structure)

9. RBC Precursor Structure
Glucose
Galactose
Precursor Substance (stays the same)
N-acetylglucosamine
Galactose

10. Formation of the H antigen
RBC
Glucose
H antigen
Galactose
H enzyme is fucosyltransferase
N-acetylglucosamine
Galactose
Fucose

11. H antigen
The H antigen is the foundation upon which A and B antigens are built
A and B genes code for enzymes that add a sugar to the H antigen
Immunodominant sugars are present at the terminal ends of the chains and confer the ABO antigen specificity

12. A and B Antigen
The “A” gene codes for an enzyme (transferase) that adds N-acetylgalactosamine to the terminal sugar of the H antigen
N-acetylgalactosaminyltransferase
The “B” gene codes for an enzyme that adds D-galactose to the terminal sugar of the H antigen
D-galactosyltransferase

13. Formation of the A antigen
RBC
Glucose
Galactose
N-acetylglucosamine
Galactose
N-acetylgalactosamine
Fucose

14. Formation of the B antigen
RBC
Glucose
Galactose
N-acetylglucosamine
Galactose
Galactose
Fucose

16. Genetics
The H antigen is found on the RBC when you have the Hh or HH genotype, but NOT from the hh genotype
The A antigen is found on the RBC when you have the Hh, HH, and A/A, A/O, or A/B genotypes
The B antigen is found on the RBC when you have the Hh, HH, and B/B, B/O, or A/B genotypes

17. O>A2>B>A2B>A1>A1B
H antigen
Certain blood types possess more H antigen than others:
O>A2>B>A2B>A1>A1B
Greatest amount of H
Least amount of H

18. The O allele
Why do Group O individuals have more H antigen than the other groups?
The O gene is a silent allele. It does not alter the structure of the H substance….that means more H antigen sites

19. A A A A
Group O
Group A A
Many H antigen sites
Fewer H antigen sites
Most of the H antigen sites in a Group A individual have been converted to the A antigen

20. ABO Antigens in Secretions
Secretions include body fluids like plasma, saliva, synovial fluid, etc
Blood Group Substances are soluble antigens (A, B, and H) that can be found in the secretions.
This is controlled by the H and Se genes

21. Secretor Status The secretor gene consists of 2 alleles (Se and se)
The Se gene is responsible for the expression of the H antigen on glycoprotein structures located in body secretions
If the Se allele is inherited as SeSe or Sese, the person is called a “secretor”
80% of the population are secretors

22. Secretors
Secretors express soluble forms of the H antigen in secretions that can then be converted to A or B antigens (by the transferases)
Individuals who inherit the sese gene are called “nonsecretors”
The se allele is an amorph (nothing expressed)
sese individuals do not convert antigen precursors to H antigen and has neither soluble H antigen nor soluble A or B antigens in body fluids
Secretions include saliva, urine, tears, bile, amniotic fluid, breast milk, exudate, and digestive fluids.

23. Secretor Status Summary
The Se gene codes for the presence of the H antigen in secretions, therefore the presence of A and/or B antigens in the secretions is contingent on the inheritance of the Se gene and the H gene
A antigen
Se gene (SeSe or Sese)
H antigen in secretions
and/or
B antigen
No antigens secreted in saliva or other body fluids
se gene (sese)

24. Secretors (SeSe or Sese): Non-secretors (sese):
ABO Group
ABH
Substances
Secretors (SeSe or Sese): A B H
+++ + O AB
Non-secretors (sese):
A, B, O, and AB
Sese + h/h (no H antigen)  no antigens in secretions

26. Type I and Type II Precursors
There are two potential precursors substances for ABH antigens Type I and Type II
Both are comprised of identical sugars but the linkage of the terminal sugars differs in the two types
Type I precursor has a terminal galactose linked to a subterminal N-acetylgluosamine in a 1-3 linkage
These same sugars combine in a 1-4 linkage in type II precursor

28. Type II H
After fucose is added to Type II chains, the structure is termed Type II H
Four kinds of Type II H have been identified
H1, H2 are simple straight chain glycolipids
Whereas H3 & H4 have branched chains

29. ABH Ags on red cells are derived from Type II chains whereas the ABH Ags in plasma are made from both types I & II precursors

30. ABO Subgroups
ABO subgroups differ in the amount of antigen present on the red blood cell membrane
Subgroups have less antigen
Subgroups are the result of less effective enzymes.
They are not as efficient in converting H antigens to A or B antigens (fewer antigens are present on the RBC)
Subgroups of A are more common than subgroups of B

31. Subgroups of A The 2 principle subgroups of A are: A1 and A2
Both react strongly with reagent anti-A
To distinguish A1 from A2 red cells, the lectin Dolichos biflorus is used (anti-A1)
80% of group A or AB individuals are subgroup A1
20% are A2 and A2B

32. A2 Phenotype Why is the A2 phenotype important?
A2 and A2B individuals may produce an anti-A1
This may cause discrepancies when a crossmatch is done (incompatibility)
What’s the difference between the A1 and A2 antigen?
It’s quantitative
The A2 gene doesn’t convert the H3 & H4 to A very well
The result is fewer A2 antigen sites compared to the many A1 antigen sites

33. A1 and A2 Subgroups A1 A2 4+ Anti-B 900 x103 3+ Anti-B & anti-A1
Anti-A antisera
Anti-A1 antisera
Anti-H lectin
ABO antibodies in serum
# of antigen sites per RBC A1 4+
Anti-B
900 x103 A2 3+
Anti-B & anti-A1
250 x103

34. Other A subgroups There are other additional subgroups of A
Aint (intermediate), A3, Ax, Am, Aend, Ael, Abantu
A3 red cells cause mixed field agglutination when polyclonal anti-A or anti-A,B is used
Mixed field agglutination appears as small agglutinates with a background of unagglutinated RBCs
They may contain anti-A1

35. B Subgroups B subgroups occur less than A subgroups
B subgroups are differentiated by the type of reaction with anti-B, anti-A,B, and anti-H
B3, Bx, Bm, and Bel

36. Other ABO conditions Bombay Phenotype (Oh) Inheritance of hh
The h gene is an amorph and results in little or no production of L-fucosyltransferase
Originally found in Bombay (now Mumbai)
Very rare

37. Bombay Phenotype

38. Bombay The hh causes NO H antigen to be produced
Results in RBCs with no H, A, or B antigen (patient types as O)
Bombay RBCs are NOT agglutinated with anti-A, anti-B, or anti-H (no antigens present)
Bombay serum has strong anti-A, anti-B and anti-H, agglutinating ALL ABO blood groups
What blood ABO blood group would you use to transfuse this patient??

39. ANSWER: Another Bombay
Group O RBCs cannot be given because they still have the H antigen
You have to transfuse the patient with blood that contains NO H antigen

40. Important Issue ‼

41. ABO Blood Group
ABO Antibodies

42. Landsteiner’s Rule:
Normal, Healthy individuals possess ABO antibodies to the ABO antigen absent from their RBCs

43. ABO Blood Group System
The ABO Blood Group System was the first to be identified and is the most significant for transfusion practice
It is the ONLY system that the reciprocal antibodies are consistently and predictably present in the sera of people who have had no exposure to human red cells

44. Blood Group Systems
Most blood group systems (ABO and others) are made up of:
An antigen on a red cell and the absence of it’s corresponding antibody in the serum (if you’re A, you don’t have anti-A)
If you do NOT have a particular antigen on your red cells then it is possible (when exposed to foreign RBCs) to illicit an immune response that results in the production of the antibody specific for the missing antigen

45. ABO
Remember:
The ABO Blood Group System does NOT require the presence of a foreign red blood cell for the production of ABO antibodies
ABO antibodies are “non-red blood cell stimulated” probably from environmental exposure and are referred to as “expected antibodies”
Titer of ABO Abs is often reduced in elderly and in patients with hypogammaglobulinemia
Infants do not produce Abs until 3-6 months of age

46. ABO antibodies RBC Phenotype Frequency (%) Serum Ab A 43 Anti-B B 9
Anti-A AB 4 O 44
Anti-A,B

47. Clinically Significant Transfusion Reactions
Anti-A1
Anti-A1
Clinically Significant
Sometimes
Abs class
IgM
Thermal range
4 - 22
HDNB No
Transfusion Reactions
Extravascular
Intravascular
Rare
Group O and B individuals contain anti-A in their serum
However, the anti-A can be separated into different components: anti-A and anti-A1
Anti-A1 only agglutinates the A1 antigen, not the A2 antigen
There is no anti-A2.

48. Anti-A,B Found in the serum of group O individuals
Reacts with A, B, and AB cells
Predominately IgG, with small portions being IgM
Anti-A,B is one antibody, it is not a mixture of anti-A and anti-B antibodies

49. ABO antibodies
IgM is the predominant antibody in Group A and Group B individuals
Anti-A
Anti-B
IgG (with some IgM) is the predominant antibody in Group O individuals
Anti-A,B (with some anti-A and anti-B)

50. Clinically Significant Transfusion Reactions
ABO antibody facts
Complement can be activated with ABO antibodies (mostly IgM, some IgG)
High titer: react strongly (4+)
Anti-A, Anti-B, Anti-A,B
Clinically Significant
Yes
Abs class
IgM, less IgG
Thermal range
4 - 37
HDNB
Transfusion Reactions
Extravascular
Intravascular

51. ABO Antibodies Usually present within the first 3-6 months of life
Stable by ages 5-6 years
Decline in older age & in hypogammaglobulinemia
Newborns may passively acquire maternal antibodies (IgG crosses placenta)
Remember: most ABO antibodies are IgM, but some are IgG. Mothers can pass those IgG antibodies through placenta to fetus

52. Nature of antibodies Non-red blood cell stimulated ABO antibodies
Antibodies formed as a result of transfusion, etc
Usually IgG
Active at 37°C
Can occur in group O (may occur in group A or B)
These antibodies also occur in the other Blood Group Systems

53. Anti-H Auto-Anti-H Clinically Significant No Abs class IgM
Thermal range
4 - 15
HDNB
Transfusion Reactions
Extravascular
Intravascular
Allo-Anti-H
Clinically Significant
Yes
Abs class
IgM, IgG
Thermal range
4 - 37
HDNB
Transfusion Reactions
Extravascular
Intravascular