ABO Antibodies

Transcript ABO Antibodies

ABO/Rh Blood Group System A . Amirzargar

Carl Landsteiner:

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

Landsteiners Rule: If an antigen is patients red blood cells the corresponding antibody will NOT be present in the patients plasma, under ‘normal conditions’.

present on a

Blood group systems

 Each system represents either a single gene or a cluster of two or three closely linked homologous genes

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 (antithetical) antibodies are consistently and predictably present in the sera of people who have had no exposure to human red cells.

Major ABO Blood Groups

ABO Group A B O

Antigen Present A B None

A and B

Antigen Missing B A A and B Antibody Present Anti-B Anti-A Anti-A,B

None None

Definition:

Forward Grouping

Determination of ABO antigens found on patient red blood cells using reagent antisera.

Patient

1 2 3 4

Patient Red Cells Tested With: Anti-A Anti-B Interpretation

0 4+ 0 4+ 0 0 4+ 4+ O A B AB

Definition:

Reverse Grouping

Determination of ABO antibodies found in patient serum using reagent red blood cells.

Patient

1 2 3 4 Patient Serum Tested With:

A 1 Cells

4+ 0 4+ 0

B Cells

4+ 4+ 0 0

Interpretation

O A B AB

Reaction of Cells Tested With:

Anti-A 0 + 0 + Anti-B 0 0 + +

Reaction of Serum Tested Against: ABO Group

A Cells B Cells + 0 + 0 + + 0 0 O A B AB % US White Pop.

45 40 11 4 % US Black Pop.

49 27 20 4

H Antigen

The

gene on ch. 19 near the Se gene, codes for an enzyme (fucosylytranferase) that adds a Fucose to the terminal sugar of a Precursor Substance (PS*).

The biochemical structure below constitutes the

H Antigen

(

gene is an amorph.)

H gene

acts on a Precursor substance(PS)* by adding

Fucose

*PS = oligosaccharide chain attached to either glycosphingo lipid, Type 2 chain (on RBC) or glycoprotein, Type 1 chain (in secretions)

H antigen

is the

foundation

upon which A and B antigens are built.

and

genes code for enzymes that add an immunodominant sugar to the

H antigen

.

Formation of the A Antigen

The

A gene

codes for an enzyme that adds GalNAc (N-Acetyl-D galactosamine) to the terminal sugar of the H Antigen.

This biochemical structure constitutes the A antigen .

Formation of the B Antigen

gene codes for an enzyme that adds D-Galactose to the terminal sugar of the H Antigen. This biochemical structure constitutes the B Antigen

The

H antigen

is found on the rbc when you have the

genotypes but

NOT

with the

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.

ABO Genetics



– – Genes at three separate loci control the OCCURRENCE antigens and LOCATION of A and B

genes

– H

and

alleles

allele codes for a fucos yltransferase enzyme that adds a fucose on Type 2 chains (primarily) to form the H antigen onto which A and B antigens are built on red blood cells .

allele is a silent allele (amorph)

• A, B and H antigens are built on oligosaccharide chains of 4 types. The most common forms are Type 1 and Type 2. Type 1: #1 carbon of Gal is attached to the #3 carbon of GlcNAc.

Type 2:

#1 carbon of Gal is attached to the #4 carbon of GlcNAc.

ABO Genetics

2. Se

genes

– Se

and

alleles –

allele codes for a fucos yltransferase enzyme that adds fuscos onto Type 1 chains (primarily) in secretory glands. Controls expression of H antigens in secretions (i.e. saliva, body fluids, etc.) –

allele is an amorph

3. ABO

genes

– A

and

alleles – –

and

alleles code for glycosyltransferase enzymes that add a sugar onto H antigens to produce A and B antigens

allele does not code a functional enzyme

H Ag concentration in ABO

Amount of H Antigen According to Blood Group

• Blood Group O people have red blood cells rich in H antigen. Why?

Neither the A or B genes have converted the H antigens to A or B antigens - just a whole bunch of H!

Greatest

Amount of H

O > A

> B > A

B > A

> A

B

Least

Amount of H

Bombay (O

) Phenotype

    Homozygous inheritance of the the A or B antigens.

gene (

) results in the inability to form the H antigen and subsequently This is referred as the Bombay or O the location of its discovery.

h phenotype due to This phenotype has no H, A or B antigens on the red blood cell membrane, only an abundant amount of precursor substance.

They also have anti-H, anti-A and Anti-B. What blood type can we safely transfuse?

ABO Antigens in Secretions

 

Secretions:

– Body fluids including plasma, saliva, synovial fluid, etc.

Blood Group Substance: Soluble antigen – Soluble antigen found in the secretions not bound to a membrane such as a rbc or epithelial cell.

Soluble blood group substances (A, B and H) can be found in the secretions. This is controlled by the

and

genes.

FORMATION OF ABO ANTIGENS IN

SECRETIONS

PS 1 Se/se genes PS 2 H/H genes A/O H Ag A ,

Ag genes From left to right is the gene interactions necessary for the production of ABH antigens in secretions. Must have Se gene (78% of population) for ABO Ag’s to be in secretions.

FORMATION OF ABO ANTIGENS IN

SECRETIONS

PS 1 Se/se genes PS 2 H/H genes O/O H Ag H Ag genes

Inheritance of the

O/O

genotype results in the presence of only H antigen in the secretions.

LACK OF ABO ANTIGENS IN

SECRETIONS

e/se

PS 1 genes PS 2 h/h genes PS 2 A/O genes PS 2

Two mechanisms exist that account for a

LACK

of ABO antigens in secretions: Either se/se or

h/h

genotypes.

LACK OF ABO ANTIGENS IN

SECRETIONS

e/se

PS 1 genes PS 1 H/h genes PS 1 A/O genes PS 1

Two mechanisms exist that account for a

LACK

of ABO antigens in secretions: Either se/se or

h/h

genotypes.

ABO Antibodies

 Generally IgM class antibodies

.

 ABO Antibody Development: Hypothesis – Immune response following exposure to environmental antigens (such as bacterial cell walls) similar to A and B antigens during infancy results in production of ABO antibodies. Remember, babies have a tendency to put EVERYTHING into their mouths …

ABO Antibodies

 For Group A and Group B persons the predominant antibody class is IgM  For Group O people the dominant antibody class is IgG (with some IgM)  React best at room temperature (22-24 o C) or below

in vitro

 Activates complement to completion at 37 o C – Can cause acute hemolytic transfusion reactions  RBC Immune form : Predominantly IgG

Which ABO blood group presents a higher risk for Hemolytic Disease of the Newborn? Why?

  Group O - because the dominant immunoglobulin class is IgG , which crosses the placenta. Group A and B can but only the immune form. Which means that only after exposure to foreign ABO antigens will the mother make immune anti-A or anti B that is predominantly IgG.

ABO Antibodies

  Time of appearance: Generally present within first 4-6 months of life – Do we perform a reverse grouping on newborns (<4-6 months of age) and cord blood?

– If there are anti-A or anti-B antibodies in newborn serum where did they most likely originate? What source?

ABO antibody titers with age: – Reach adult level at 5-10 years of age – – Level off through adult life Begin to decrease in later years: >65 years of age

ABO Antibodies

Group O Phenotype

 Anti-A,B Antibody – Inseparable anti-A and anti-B antibody. If we add A cells to anti-A,B serum all of the antibody activity is removed, not just anti-A!!

 RBC immune Anti-A,B – When exposed to Group A or B antigens (or both) Group O persons will have an immune response that results in the production of separate immune anti-A and/or anti-B antibodies. This could be seen in a fetomaternal bleed of a Group O mom with a Group A baby. (Hemolytic Disease of the Newborn)

ABO Antibodies

Group B or O phenotype

 Have both anti-A and Anti-A 1 antibodies    Anti-A Reacts with both A 1 and A 2 red blood cell antigens Reacts only with A 1 Anti-A

antigens on red blood cells A 2 and A 2 B phenotypes can make anti-A 1 antibodies. What is clinical significance? Thermal range is up to 25 o C - not usually clinically significant. Can cause an ABO discrepancy.

ABO Antibodies

 Is there a reagent anti-A 1 

NO!!

antisera?

  But there is

Dolichos biflorus,

that has anti-A 1 a plant lectin activity when diluted properly.

This is not an antibody, but a chemical that acts like an antibody in that it specifically agglutinates A 1 red blood cells.

ABO Subgroups

 ABO Phenotypes that differ in the amount of antigen carried on red cell and saliva, for secretors: There are fewer Ag sites!

 Subgroups are the results of less effective glycosyltransferase enzymes – just not as good at attaching the immunodominant sugar to the H antigen.

 Subgroups of A are more common than Subgroups of B.

ABO Subgroups

 80% of all Group A ’s are A 1 are A 2 .

– A 1 ’s have 4-6 times the # of antigen sites on the RBC surface than A 2 ’s.

– and about 19% Both react strongly with reagent Anti-A but …  – Only A 1

biflorus

cells are agglutinated with

Dolichos

plant lectin and not A 2 cells. The remainder of the Subgroups of A have even weaker expression of A antigen.

Rh Blood Group System

 Currently – 5 common antigen – three nomenclatures – two theories of inheritance

Rh antigen

Rh antigene

Antigens

     Rh o ( D ) rh’ ( C ) hr’ ( c ) rh’’ ( E ) hr’’ ( e )

Rh

(D) antigen

 A very potent antigen (50% may form antibody to exposure)  85% positive - Rh positive  15% negative - Rh negative  no allele found

Inheritance

 Fisher - Race – Rh antigens produced under the control of three sets of allelic genes at closely linked locus – Nomenclature is C, D, E, c, e – Certain combinations of the antigens that are inherited more often than others

Fisher-Race

 There are 8 gene complexes at the Rh locus  Fisher-Race uses

DCE

as the order  It is often written alphabetically as

CDE

DCe DcE Dce DCE dCe dCE dcE dce

** Sometimes “d” is written just to indicate that D is absent

Weak D Phenotype

 Most D positive rbc’s react macroscopically with Reagent anti-D at immediate spin – – These patients are referred to as Rh positive Reacting from 1+ to 3+ or greater  HOWEVER, (do

NOT

some D positive rbc’s

DO NOT

react agglutinate) at Immediate Spin using Reagent Anti-D. These require further testing (37 o C and/or AHG) determine the D status of the patient.

Weakened Antigens

 The Rh-Hr system has a number of antigens that are suppressed by other antigens or only a weakened form of the antigens are present  Weakened D antigen – – often does not react with initial spin may require 37 o incubation or antiglobulin test to detect sensitization – two forms - inherited or suppression by C antigen in the trans position

Weak D Mechanism ’s

There are three mechanisms that account for the Weak D antigen.

Genetically Transmissible Position Effect Partial D (D Mosaic)

Genetically Transmissible

 The

RHD

gene codes for weakened expression of D antigen in this mechanism.

– – D antigen is complete, there are just fewer D Ag sites on the rbc. Quantitative!

Common in Black population (usually Dce haplotype). Very rare in White population.

 Agglutinate weakly or not at all at immediate spin phase.

 Agglutinate strongly at AHG phase.

 Can safely transfuse D positive blood components.

Position Effect (Gene interaction effect)

 C allele in trans position to D allele – Example:

ce/d

e, D cE/d C E In both of these cases the C allele is in the trans position in relation to the D allele.

 D antigen is normal, C antigen appears to be crowding the D antigen. (Steric hindrance)  Does

NOT

happen when C is in

cis

position  – Example: DC e/dce Can safely transfuse D positive blood components.

Position Effect

C in trans position to D:

D c e / d C e

Weak D C in cis position to D:

D C e / d c e

NO weak D

Partial D (D Mosaic)

 Missing one or more PARTS of the D antigen – D antigen comprises many epitopes  PROBLEM – Person types D positive but forms alloanti-D that reacts with all D positive RBCs except their OWN .

Partial D : Multiple epitopes make up D antigen. Each color represents a different epitope of the D antigen.

A.

B.

Patient B lacks one D epitope.

The difference between

Patient A

and

Patient B

is a single epitope of the D antigen. The problem is that

Patient B

can make an antibody to

Patient A

even though both appear to have the entire D antigen present on their red blood cell’s using routine anti D typing reagents..

D Mosaic/Partial D

 If the patient is transfused with D positive red cells, they may develop an

anti-D alloantibody

* to the part of the antigen (epitope) that is missing Missing portion

RBC RBC 51

*alloantibody- antibody produced with specificity other than self

Weak-D Determination: Donor Blood

 When testing Donor Blood testing is required through for the D antigen,

all phases.

– Weak-D testing is

REQUIRED

 We need to know the D Status of all Donor Blood. Why? – Main problem is Rh Negative women of child bearing age and pediatric patients.

 Donor RBCs are labelled Rh positive if any part of the D antigen is present on the red blood cell membrane.

Unusual Phenotypes

D-Deletion Rh null



D-Deletion

No reaction when RBCs are tested with anti-E, anti-e, anti-C or anti-c

 Requires transfusion of other D-deletion red cells, because these individuals may produce antibodies with single or separate specificities( anti-Hr 0 or anti-Rh17)  Red cells that lack C/c or E/e antigens may demonstrate stronger D antigen activity  Written as

D- -

-D-

Rh Null

 Lack all Rh antigens   The lack of antigens causes the red cell membrane abnormalities Immunized idividuals have anti Rh29( “Total Rh” or Rh29)  2 Rh null phenotypes: – Regulatory type – gene inherited(Xºr) (X¹r is a normal regulator gene) the Rh gene are inherited but not expressed.

– Amorph type –Result from the r amorph gene

RHD

gene is absent, lack of expression of the

RHCE

gene

Rh Antibodies

 Most antibodies react at 37 o and require a coombs procedure to demonstrate the reaction.  Some react at saline and room temperature  Most are IgG  None fix Complement  All are important in HDN and HTR

Rh System Antibodies

React optimally 1.

37 o C and AHG Phases 2.

RBC Immune 2.

Transfusion or pregnancy, IgG, HDN, HTR, etc.

Clinically Significant 3.

Will result in shortened red cell survival - need to transfuse antigen negative blood

Rh typing

  Normal typing for Rh antigens only includes typing for Rh o (D).

The result of this typing determines the Rh status of the cells (Rh - positive or Rh negative). Other antigens are identified for genotyping  Some Rh typing sera is diluted in high protein solutions and may require a negative control.

HEMOLYTIC DISEASE OF THE NEWBORN

HDN: THE DISEASE

     Caused by blood group system or HLA maternal/fetal incompatibility (mother has IgG1 or IgG3 Abs to Ag on baby RBCs) With Rh HDN, previous matherno-fetal bleeds usually the stimulus for Ab production; with other HDNs, stimulus may be unclear Begins in utero Range of severity from asymptomatic --> mild anemia --> kernicterus --> stillborn ABO, Rh, and Kell groups most commonly involved

Categories of HDN

Rh System Antibodies 1.

• • Most severe form of HDN. Anti-D Less common due to RhIg 2.

Other Blood Group Antibodies 1.

ABO Antibodies Anti-K, -Fy a , -s, etc. Least severe. Group O mom with A or B fetus. Most common form of HDN.

ABO

vs.

Rh

HDN

Mother Infant Occurrence in first born Stillbirth and or hydrops Severe Anemia DAT Spherocytes Exchange Transfusion Phototherapy Rh Negative Positive 5% Frequent Frequent Positive None Frequent Adjunct to exchange ABO Group O A or B (AB) 40-50% Rare Rare Pos or Negative Present Infrequent Often only treatment

 Risk is also increased in pregnancies complicated by :   placental abruption spontaneous or therapeutic abortion       Toxemia after cesarean delivery ectopic pregnancy Amniocentesis chorionic villus sampling cordocentesis

 After sensitization, maternal anti-D antibodies cross the placenta into fetal circulation and attach to Rh antigen on fetal RBCs, which form rosettes on macrophages in the reticuloendothelial system, especially in the spleen.

 These antibody-coated RBCs are lysed by lysosomal enzymes released by macrophages and natural killer lymphocytes, and they are independent of the activation of the complement system

Rh HDN

   Most severe form of HDN (Usually*) affects only 2nd or subsequent pregnancies (mother allo-immunized at delivery of 1st pregnancy; has pre-formed Abs during subsequent pregnancies) Usually Ab directed to D Ag but Abs to C, c, and E also seen

BEFORE BIRTH

 Antibodies cause destruction of the red cells  Anemia  heart failure  fetal death

Metabolism of bilirubin:

    Before delivery : Fetal bilirubin produced by the breakdown of sensitized RBCs in fetal spleen is sefely metabolized by the maternal liver.

After delivery : Newborn’s liver doesn’t produce glucuronyl transferase and cannot convert bilirubin to an excretable form.as a result,it collects in tissues and causes brain damage.

Metabilim of bilirubin:

HDN: SIGNS & SYMPTOMS

    Anemia (Hb < 16 mg/dL) - begins in utero Increased bilirubin - begins after birth – Baby ’s liver does not conjugate bilirubin efficiently; unconjugated (toxic) bilirubin increases as RBCs continue to be destroyed – If > 18 mg/dL, may have to exchange transfuse Jaundice Hepato- and splenomegaly

AFTER BIRTH

      Antibodies cause destruction of the red cells Anemia Heart failure Build up of bilirubin Kernicterus Severe retardation

PROBLEMS FOR BABY

   Anemia – heart failure – erythroblastosis General edema -Called hydrops fetalis and erythroblastosis fetalis Kernicterus ( a condition with severe neural symptoms, associated with high level of bilirubin in the blood) – severe retardation

  Bilirubin has been postulated to cause neurotoxicity via 4 distinct mechanisms: (1) interruption of normal neurotransmission (inhibits phosphorylation of enzymes critical in release of neurotransmitters) (2) mitochondrial dysfunction  (3) cellular and intracellular membrane impairment (bilirubin acid affects membrane ion channels and precipitates on phospholipid membranes of mitochondria  (4) interference with enzyme activity (binds to specific bilirubin receptor sites on enzymes).

 PREVENTION   Before birth – Work up mother for risk and evaluation of complications After birth – Rh immune globulin - IgG anti-D given to prevent primary immunization

 Before birth workup – Identify women at risk – – ABO - Rh -(Du) - Antibody screen  based on results continue testing (Handout) IgM antibodies are insignificant – IgG antibodies - titer - freeze and store retiter with a second sample - looking for a 1:32 rise or change in titer

 Before birth workup – titer identifies mothers who need amniocentesis – titer every 4 week until 24th week - then every 2 weeks – amniocentesis is performed after 21st week on high titer - high mortality

PRENATAL TESTING

 Test father to see if he is Ag positive (if he is negative, not a concern)  If Ab is significant and father is positive for Ag, perform Ab titers (> 32 significant) on mother’s serum  If serum Ab titer high, test amniocytes for presence of Ag

PRENATAL TESTING

   ABO/Rh type (including D w ) & Ab screen at 1st visit If Ab screen neg., repeat at 24 weeks; if Ab screen pos., perform Ab ID If Ab is to IgM or IgG, – – determine if IgM or IgG by treating serum with DTT (DTT destroys IgMs) Repeat Ab ID (using treated serum) for detection of IgGs that the IgMs may be masking (IgMs are not a HDN concern)



Amniocentesis

Intrauterine transfusions   Bilirubin Hb is below 11 g/dL – Usually O and compatible with mother ’s antibody – CMV, Hb S, and leukocyte negative – immediate correction of anemia and resolution of fetal hydrops, reduced rate of hemolysis and subsequent hyperinsulinemia, and acceleration of fetal growth for nonhydropic fetuses who often are growth retarded

 Post Natal Laboratory Studies  Mother – ABO - Rh - Du (micro) - Antibody screen Antibody identification if necessary  Baby – ABO - Rh - Du - DAT for IgG antibodies - elute DAT positive and identify antibody – – CBC Imaging studies

 TREATMENT  Exchange transfusion  Phototherapy

 After birth  Rh Immune Globulin – – – Give antenatal 28 -32 weeks also after amniocentesis - IUT - abortion - ectopic pregnancy - miscarriage Each vial contains 300 ugm and will prevent sensitization by 15 ml RBC or 30 ml whole blood

Rh (D) HDN: PREVENTION

     Rh Immune Globulin is a potent solution of Anti-D Anti-D covers D epitopes in baby RBCs in maternal circulation Coated cells removed by splenic macrophages D-bearing RBCs destroyed before mother can mount immune response Very effective preventative treatment

Rh (D) HDN: PREVENTION

 Rh Immune Globulin given to mother at 28 weeks gestation and within 72 hours of delivery of infant if: – Baby is Rh positive – – Rh type of fetus is unknown, and Mother is known to be negative for Anti-D  Dosage calculated using results of the Kleihauer-Betke test

  1 Rh Immune Globulin dose protects against 30 mL fetal whole blood Kleihauer-Betke test – sample from mother treated with acid then stained; fetal cells resistant to acid, maternal cells become ghost cells – determine # fetal cells in first 2000 maternal cells counted – % fetal x 50 = Whole blood bleed

 It should be considered if the total serum bilirubin level is approaching 20 mg/dL and continues to rise despite intense in-hospital phototherapy.

Selection of blood for exchange transfusion:

       Group o(or ABO-compatible) Fresh(less than 7 days old)RBCs resuspended in fresh frozen plasma CMV negative Irradiate blood HbS negative Blood lack of Ag corresponding to maternal Ab Compatible crossmatch with maternal serum

 Exchange Transfusions Objectives – decrease serum bilirubin and prevent kernicterus – provide compatible red cells to provide oxygen carrying capacity – decrease amount of incompatible antibody – remove fetal antibody coated red cells

 The following are requirements for exchange transfusion :  Severe anemia (Hb <10 g/dL)  Rate of bilirubin rises more than 0.5 mg/dL despite optimal phototherapy  Hyperbilirubinemia  DAT



Potential complications of exchange transfusion include the following:

– – – – – – Cardiac - Arrhythmia, volume overload, congestive failure, and arrest Hematologic - Overheparinization, neutropenia, thrombocytopenia, and graft versus host disease Infectious malarial - Bacterial, viral (CMV, HIV, hepatitis), and Metabolic - Acidosis, hypocalcemia, hypoglycemia, hyperkalemia, and hypernatremia Vascular - Embolization, thrombosis, necrotizing enterocolitis, and perforation of umbilical vessel Systemic - Hypothermia

Phototherapy



Phototherapy

– The efficacy of phototherapy depends on the spectrum of light delivered , the blue-green region of visible light being the most effective; irradiance (mW/cm2/nm); and surface area of the infant exposed.

– Nonpolar bilirubin is converted into 2 types of water-soluble photoisomers as a result of phototherapy. The initial and most rapidly formed configurational isomer 4z, 15e bilirubin accounts for 20% of total serum bilirubin level in newborns undergoing phototherapy and is produced maximally at conventional levels of irradiance (6-9 mW/cm2/nm).



Phototherapy

 The structural isomer lumirubin is formed slowly irradiance of phototherapy on skin. , and its formation is irreversible and is directly proportional to the  Lumirubin is the predominant isomer formed during high intensity phototherapy. stool. Decrease in bilirubin is mainly the result of excretion of these photoproducts in bile and removal via  In the absence of conjugation, these photoisomers can be reabsorbed by way of the enterohepatic circulation and diminish the effectiveness of phototherapy

ABO HDN

      Most common form of HDN Mother is “O” with IgG form of Anti-A,B Baby is “A” or “B” May occur with 1st or subsequent pregnancies Usually less severe than Rh HDN (babies’ A and B Ags not fully developed) Most cases treated only with phototherapy



ABO incompatibility

 ABO incompatibility is limited to type O mothers with fetuses who have type A or B blood  in type O mothers, the antibodies are predominantly IgG in nature  Because A and B antigens are widely expressed in a variety of tissues besides RBCs , only small portion of antibodies crossing the placenta is available to bind to fetal RBCs. In addition, fetal RBCs appear to have less surface expression of A or B antigen, resulting in few reactive sites —hence the low incidence of significant hemolysis in affected neonates.

ABO HDN: PREVENTION AND TREATMENT

 Not preventable as with Rh (D) HDN  Usually treatable using only phototherapy  If exchange transfusion required, use type “O” cells and “AB” plasma  ABO HDN sometimes protects babies from the more severe forms of Rh HDN