Mohammed Laqqan The Rhesus (Rh) Blood Group system.

Mohammed Laqqan

The Rhesus (Rh) Blood Group systemThe Rhesus (Rh) Blood Group system

Mohammed Laqqan

The Rh(D) AntigenThe Rh(D) Antigen

Rh is the most complex system, with over 45 antigens. The complexity of the Rh blood group Ags is due to the

highly polymorphic genes that encode them. Discovered in 1940 after work on Rhesus monkeys. The 2nd most important after ABO in the crossmatch test. Only the most clinically significant Ags will be discussed.

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Rh GeneticsRh Genetics

The genes that control the system are autosomal codominant located on the short arm of chromosome 1.

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Rh blood group antigens are proteinsRh blood group antigens are proteins

The antigens of the Rh blood group are proteins. The RhD gene encodes the D antigen, which is a large

protein on the red blood cell membrane, & the most important.

RHD gene RHCE gene

Chromosome 1

Proteins

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Rh Antigen Frequency

D antigen – 85% d antigen – 15% C antigen – 70% c antigen – 80% E antigen – 30% e antigen – 98%

The presence or absence of D Ag determines if the person is Rh+ or Rh-

Rh PositiveRh Positive

Rh NegativeRh Negative

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3 Different nomenclatures:1- Fisher-Race2- Weiner3- Rosenfield Nomenclature

Nomenclature of the RH systemNomenclature of the RH system

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Fisher-Race TheoryFisher-Race Theory

Rh inheritance is controlled by 3 closely linked loci on each chromosome of a homologous pair

Each locus has its own set of alleles which are: Dd , Cc , and Ee .

The D gene is dominant to the d gene, but Cc and Ee are co-dominant co-dominant.

The 3 loci are so closely linked that crossing over does NOT occur, and the 3 genes on one chromosome are always inherited together.

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Fisher-RaceFisher-Race

Dd

Cc

Ee

3 close

ly linke

d genes

“d” antigen not produced

Produces D antigen

Produces C/c antigen

Produces E/e antigen

Dd

Cc

Ee

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Fisher-RaceFisher-Race

There are 8 gene complexes at the Rh locus

Fisher-Race uses DCE as the order

Others alphabetize the genes as CDE

DCe dCe

DcE dCE

Dce dcE

DCE dce

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Fisher-Race NomenclatureFisher-Race Nomenclature

Gene Combination Antigens

Dce D, c, e

DCe D, C, e

DcE D, c, E

DCE D, C, E

dce c,e

dCe C,e

dcE c,E

dCE C,E

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Fisher-Race ExampleFisher-Race Example::

DCe/DCe individual is homozygous for D, C, and e genes

DCe/dcE individual is heterozygous for D, C, e, d, c, and E genes

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Fisher-Race: Genetics/TerminologyFisher-Race: Genetics/Terminology

Rh phenotype is designated by the presence or absence of Rh antigens: D, C, c, E, e– little d: Indicates the ABSENCE of the D antigen and

nothing more. – There is NO little d antigen or allele. – Many blood bankers today are leaving the ‘d’ out the the

nomenclature entirely.

– Phenotype example: R1 phenotype is D, C, e

Rh genes are codominant.

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In the Fish-Race theory the D gene codes for the D antigen. The C gene codes for the C antigen, etc.

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Wiener TheoryWiener Theory

Good for describing phenotype There is one Rh locus at which occurs one Rh gene, but

this gene has multiple alleles. For example, one gene R1 produces one agglutinogen

(antigen) Rh1 which is composed of three "factors" The three factors are analogous to C, D, and e respectively The main difference between the Fisher-Race and Wiener

theories is that the: – Fisher-Race theory has three closely linked loci, – the Wiener theory has only one gene locus at which multiple

alleles occur.

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Wiener TheoryWiener Theory

Single gene at Rh locus

R’

r’

R0

r”

R”

Produces D antigen on RBC

Produces C antigen on RBC

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WienerWiener

Wiener further theorized that 8 major genes led to different combinations of antigens (D, C, E, c, e):– R0, R1, R2, Rz

– r, r′, r″, ry

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22 - -Weiner NomenclatureWeiner Nomenclature

Nomenclature expressed by the use of a single letter.

R D present

r D absent

Prime ′ or 1 C

Double ″ or 2 E

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Conversion of Wiener to Fisher-RaceConversion of Wiener to Fisher-Race

R in Wiener = D in Fisher-Race r is absence of D (d) 0 or no symbol implies c and e 1 or ′ implies C and e 2 or ″ implies c and E z or y implies C and E

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Fisher-Race and Wiener NomenclatureFisher-Race and Wiener Nomenclature

Fisher-Race Antigens (Weiner Gene)

Dce D, c, e R0

DCe D, C, e R1

DcE D, c, E R2

DCE D, C, E Rz

dce c,e r

dCe C,e r′

dcE c,E r″

dCE C,E ry

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Converting Wiener into Fisher-Race or vice versaConverting Wiener into Fisher-Race or vice versa

R D

r no D

1 and ′ C

2 and ″ E

Example: DcE R2

r″ dcE

Written in shorthand

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Rosenfield NomenclatureRosenfield Nomenclature

Each antigen assigned a number Rh 1 = D Rh 2 = C Rh 3 = E Rh 4 = c Rh 5 = e In writing the phenotype, the prefix “Rh” is followed by colon, then number

(if negative, number is preceded by -) e.g. D+, C+, E-, c+, e+ is written as

Rh:1,2,-3,4,5

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SignificanceSignificance

After ABO, the Rh system is the second most important system. This is because:

The D antigen is extremely immunogenic. It causes the production of anti-D in 50 - 70% of Rh(D)

negative people who are exposed to the D antigen. Moreover, anti-D is the most common cause of severe

HDN and can cause in Utero death. Because of this, in blood transfusion, the patient and

donor are matched for Rh(D) type as well as ABO groups. The C and E Ags are not as immunogenic as D, routine

typing for these Ags is not performed

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Rh DeletedRh Deleted

Red cells that express no Ags at the C & E loci ( D )

Number of D Ags greatly increase Anti-D IgG Abs can agglutinate these cells

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RH null: individual that appears to have no Rh antigens ( , , ) RBC has fragile membrane- short lived Must use autologous blood products

– No D, C, c, E, e antigens present on the RBC membrane Demonstrate mild hemolytic anemia (Rh antigens are integral part of

RBC membrane and absence results in loss of membrane integrity)– Stomatocytosis.

When transfusion is necessary ONLY Rh Null blood can be used to transfuse.

Rh nullRh null

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Rh antibodiesRh antibodies

Result from the exposure to Rh antigens

• IgG form• Bind at 37°C• Form agglutination in IAT

phase

Rh AbsClinically

Significant

Yes

Abs class

IgG

Thermal range

4 - 37

HDNB

Yes

Transfusion Reactions

Extravascular Intravascular

Yes No

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• Related to Hemolytic transfusion reactions• Re-exposure to antigen cause rapid secondary

response• Always check patients history for previous

transfusion or pregnancy to avoid re-exposure.

Clinical Significance of Rh antibodiesClinical Significance of Rh antibodies

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Usually related to D antigen exposure and the formation of anti-D

Usually results from D negative female and D positive male producing and offspring.

– The baby will probably be D positive. 1st pregnancy not effected, the 2nd pregnancy and on will be

effected-results in still birth, severe jaundice, anemia related to HDN.

To prevent this occurrence the female is administered RH-IG.

Hemolytic disease of the Newborn (HDN)Hemolytic disease of the Newborn (HDN)

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Rh factor can cause complications in some pregnancies.

Mother is exposed to Rh antigens at the birth of her Rh+ baby.

First pregnancy

PlacentaRh+ antigens

Rh factorRh factor

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Anti-Rh+ antibodies

Possible subsequent pregnancies

Mother makes anti-Rh+ antibodies.

During the mother’s next pregnancy, Rh antibodies can cross the placenta and endanger the fetus.

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Weak D PhenotypeWeak 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, some D-positive rbc’s DO NOT react (do NOT agglutinate) at Immediate Spin using Reagent Anti-D.

These require further testing (37oC and/or AHG) to determine the D status of the patient.

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• Weak expression of the Rh system on the RBC, )Du(

• Du red cells can be classified into three categories according to the mechanism that account for the Weak D antigen

Variants of DVariants of D

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Categories of DCategories of Duu red cells red cells

1- Acquired Du (Position Effect)

2- Du Variant (Partial D)

3- Hereditary Du (Genetically Transmissible)

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11 - -Acquired DAcquired Du u (Position Effect)(Position Effect)

C allele in trans position to D allele– Example: Dce/dCe, DcE/dCE

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: DCe/dce

Can safely transfuse D positive blood components.

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22 - -DDuu Variant (Partial D) Variant (Partial D)

The D- Ag consists of at least 4 parts Missing one or more PARTS (epitopes) of the D

antigen remaining Ag is weakly expressed Alloantibodies are produced to the missing parts Du variants should receive Rh –ve blood when

transfused

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

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..

A.

B. Patient B lacks one D epitope.

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33 - -Hereditary DHereditary Duu (Genetically Transmissible) (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.