ABOsystem
-
Upload
hari-haran -
Category
Documents
-
view
36 -
download
1
Transcript of ABOsystem
ABO Blood Group System
Renee Newman Wilkins, PhD, MLS(ASCP)cm
CLS 325/435
School of Health Related Professions
University of Mississippi Medical Center
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 http://www.nobelpreis.org/castellano/medizin/images/landsteiner.jpg
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)
ABO antigens:
Biochemical & Genetic Considerations
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
Location
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
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
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)
RBC Precursor Structure
Glucose
Galactose
N-acetylglucosamine
Galactose
Precursor Substance (stays the
same)
RBC
Formation of the H antigen
Glucose
Galactose
N-acetylglucosamine
Galactose
H antigen
RBC
Fucose
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 an immunodominant sugar to the H antigen Immunodominant sugars are present at the
terminal ends of the chains and confer the ABO antigen specificity
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
Formation of the A antigen
Glucose
Galactose
N-acetylglucosamine
Galactose
RBC
FucoseN-acetylgalactosamine
Formation of the B antigen
Glucose
Galactose
N-acetylglucosamine
Galactose
RBC
FucoseGalactose
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
H antigen
Certain blood types possess more H antigen than others:
O>A2>B>A2B>A1>A1BGreatest
amount of HLeast
amount of H
Why do Group O individuals have more H antigen than the other groups?
Group O individuals have no A or B genes to convert the H antigen to A or B antigens….that means more H antigen sites
Group O Group A
Many H antigen sites
Fewer H antigen
sites
A
A A
AA
Most of the H antigen sites in a Group A individual have been
converted to the A antigen
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
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
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
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
Se gene (SeSe or Sese)
H antigen in secretions
A antigen
B antigen
se gene (sese)
No antigens secreted in saliva or other
body fluids
and/or
ABO GroupABH
Substances
Secretors (SeSe or Sese): A B H
A +++ 0 +
B 0 +++ +
O 0 0 +++
AB +++ +++ +
Non-secretors (sese):
A, B, O, and AB 0 0 0
Sese + h/h (no H antigen) no antigens in secretions
Lewis (Le)
The Lewis Blood Group System is mentioned here because it is related to secretor status
Lewis antigens are plasma antigens formed by tissues and are released into plasma where they adsorb onto the RBCs (they are not an integral part of the RBC membrane)
Consists of 2 antigens Lea
Leb
Lewis
Lea and Leb are a single gene (Le) and its amorph (le) Lea is a precursor to Leb
The Le gene codes for a transferase, which attaches L-fucose to the precursor chain to form the Lea antigen (designated Le(a+b-)
If the H and Se genes are inherited, the Lea is converted to Leb and is designated Le(a-b+)
In childhood, both may be on the RBC, Le(a+b+) If a person is lele, they will have no Lewis
antigens in plasma or on red blood cells
Frequency of Lewis phenotypes*
Phenotype Whites Blacks
Le(a+b-) 22% 23%
Le(a-b+) 72% 55%
Le(a-b-) 6% 22%
lele
*Adapted from Flynn, J. (1998). Essentials of Immunohematology
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
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
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 H to A very well The result is fewer A2 antigen sites compared to
the many A1 antigen sites
A1 and A2 Subgroups*
Anti-A antisera
Anti-A1 antisera
Anti-H lectin
ABO antibodies in serum
# of antigen sites per
RBC
A14+ 4+ 0 Anti-B 900 x103
A24+ 0 3+ Anti-B &
anti-A1
250 x103
*Adapted from Flynn, J. (1998). Essentials of Immunohematology
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
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
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 (130 worldwide)
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??
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
ABO Blood Group:
ABO Antibodies
Landsteiner’s Rule:
Normal, Healthy individuals possess ABO antibodies to the ABO antigen absent from their RBCs
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
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
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”
ABO antibodies
group A serum contains anti-B group B serum contains anti-A group AB serum contains no antibodies group O serum contains anti-A, anti-B, and
anti-A,B
Anti-A1
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.
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
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)
ABO antibody facts
Reactions phase: Room temperature Complement can be activated with ABO
antibodies (mostly IgM, some IgG) High titer: react strongly (4+)
ABO Antibodies
Usually present within the first 3-6 months of life
Stable by ages 5-6 years Decline in older age Newborns may passively acquire maternal
antibodies (IgG crosses placenta) Reverse grouping (with serum) should not be
performed on newborns or cord blood
Nature of antibodies
Non-red blood cell stimulated (previously discussed) ABO antibodies
Red blood cell stimulated 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
Laboratory Testing:
ABO typing
ABO Blood Groups
ABO Group
Antigen Present
Antigen Missing
Antibody Present
A A B anti-B
B B A anti-A
O None A and B anti-A, anti-B, anti-A,B
AB A and B None None
Forward Grouping
Reaction of patient red blood cells tested with Reagent anti-A and anti-B antisera
Reverse Grouping
Reaction of patient serum with reagent Group A and Group B cells
Forward & Reverse Typing
anti-A anti-B A cells
B cells
ABO group
% US white pop.
% US black pop.
1 0 0 + + O 45 49
2 + 0 0 + A 40 27
3 0 + + 0 B 11 20
4 + + 0 0 AB 4 4
Reaction of cells tested with:
Reaction of serum tested with: