The Rhesus (Rh) Blood Group system

The Rh(D) AntigenRh is the most complex system, with over 45 antigensThe complexity of the Rh blood group Ags is due to the highly polymorphic genes that encode them.Discovered in 1940 after work on Rhesus monkeysThe 2nd most important after ABO in the crossmatch test Only the most clinically significant Ags will be discussed

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

Rh blood group antigens are proteinsThe 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 geneChromosome 1Proteins

Rh Antigen FrequencyD 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 Negative

Nomenclature of the RH system3 Different nomenclatures:1- Fisher-Race2- Weiner3- Rosenfield Nomenclature

Fisher-Race TheoryRh inheritance is controlled by 3 closely linked loci on each chromosome of a homologous pairEach 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.The 3 loci are so closely linked that crossing over does NOT occur, and the 3 genes on one chromosome are always inherited together.

Fisher-Race

Fisher-RaceThere are 8 gene complexes at the Rh locusFisher-Race uses DCE as the orderOthers alphabetize the genes as CDE

Fisher-Race Nomenclature

Fisher-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

Fisher-Race: Genetics/TerminologyRh phenotype is designated by the presence or absence of Rh antigens: D, C, c, E, elittle 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, eRh genes are codominant.

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

Wiener TheoryGood for describing phenotypeThere 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 respectivelyThe 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.

Wiener TheorySingle gene at Rh locusRrR0rRProduces D antigen on RBCProduces C antigen on RBC

WienerWiener further theorized that 8 major genes led to different combinations of antigens (D, C, E, c, e):R0, R1, R2, Rzr, r, r, ry

2- Weiner NomenclatureNomenclature expressed by the use of a single letter.

Conversion of Wiener to Fisher-RaceR in Wiener = D in Fisher-Racer is absence of D (d)0 or no symbol implies c and e1 or implies C and e2 or implies c and Ez or y implies C and E

Fisher-Race and Wiener Nomenclature

Converting Wiener into Fisher-Race or vice versaR Dr no D1 and C2 and E

Example: DcE R2 r dcEWritten in shorthand

Rosenfield Nomenclature Each antigen assigned a number Rh 1 = D Rh 2 = C Rh 3 = E Rh 4 = c Rh 5 = eIn 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

SignificanceAfter 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

Weak D PhenotypeMost D positive rbcs react macroscopically with Reagent anti-D at immediate spinThese patients are referred to as Rh positiveReacting from 1+ to 3+ or greater

HOWEVER, some D-positive rbcs 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.

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 antigenVariants of D

Categories of Du red cells1- Acquired Du (Position Effect)2- Du Variant (Partial D)3- Hereditary Du (Genetically Transmissible)

1- Acquired Du (Position Effect) C allele in trans position to D alleleExample: 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 positionExample: DCe/dceCan safely transfuse D positive blood components.

2- Du Variant (Partial D)The D- Ag consists of at least 4 partsMissing one or more PARTS (epitopes) of the D antigen remaining Ag is weakly expressedAlloantibodies are produced to the missing partsDu variants should receive Rh ve blood when transfused

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 cells using routine anti-D typing reagents..A.B.Patient B lacks one D epitope.

3- Hereditary Du (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.

Rh DeletedRed cells that express no Ags at the C & E loci ( D ) Number of D Ags greatly increaseAnti-D IgG Abs can agglutinate these cells

Rh nullRH null: individual that appears to have no Rh antigens ( , , )RBC has fragile membrane- short livedMust use autologous blood productsNo 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 antibodiesResult from the exposure to Rh antigensIgG formBind at 37CForm agglutination in IAT phase

Clinical Significance of Rh antibodiesRelated to Hemolytic transfusion reactionsRe-exposure to antigen cause rapid secondary responseAlways check patients history for previous transfusion or pregnancy to avoid re-exposure.

Hemolytic disease of the Newborn (HDN)Usually related to D antigen exposure and the formation of anti-DUsually 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 RHIG.

Rh factorRh factor can cause complications in some pregnancies.Mother is exposed to Rh antigens at the birth of her Rh+ baby.First pregnancyPlacentaRh+ antigens

Anti-Rh+ antibodiesPossible subsequent pregnanciesMother makes anti-Rh+ antibodies.During the mothers next pregnancy, Rh antibodies can cross the placenta and endanger the fetus.

It received its name in 1940, when Landsteiner and Wiener immunized rabbits with red blood cells from rhesus monkeys and found that the rabbit antirhesus antibody agglutinated approximately 85 percent of human red blood cells tested. They gave the name "Rh" to this determinant present on all rhesus monkey cells and apparently present on 85 percent of human red blood cells.Capable of inducing an immune response; antigenic