The Rhesus (Rh) Blood Group system

1. The Rhesus (Rh) Blood Group system

2. The 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

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

4. Rh 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. Proteins RHD gene RHCE gene Chromosome 1

5. Rh Antigen Frequency Rh Positive • 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 Negative

7. Nomenclature of the RH system 3 Different nomenclatures: 1- Fisher-Race 2- Weiner 3- Rosenfield Nomenclature

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

9. D D Produces D antigen d d “d” antigen not produced C C 3 closely linked genes Produces C/c antigen c c E E Produces E/e antigen e e Fisher-Race

11. Fisher-Race • There are 8 gene complexes at the Rh locus • Fisher-Race uses DCE as the order • Others alphabetize the genes as CDE

12. Fisher-Race Nomenclature

13. 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

14. Fisher-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.

15. In the Fish-Race theory theD genecodes for theD antigen. TheC genecodes for theC antigen, etc.

16. Wiener 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.

17. Wiener Theory Produces D antigen on RBC r” R0 R” R’ Produces C antigen on RBC r’ Single gene at Rh locus

18. Wiener • 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

19. 2- Weiner Nomenclature Nomenclature expressed by the use of a single letter.

20. Conversion 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

21. Fisher-Race and Wiener Nomenclature

23. Converting 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

24. Rosenfield 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

25. Significance • 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

26. 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, 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.

27. Variants of D • 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

28. Categories of Du red cells 1- Acquired Du (Position Effect) 2- Du Variant (Partial D) 3- Hereditary Du (Genetically Transmissible)

29. 1- Acquired Du (Position Effect) • C allele in transpositionto 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 cisposition • Example: DCe/dce • Can safely transfuse D positive blood components.

31. 2- Du 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

32. Partial D: Multiple epitopes make up D antigen. Each color represents a different epitope of the D antigen. A. Patient B lacks one D epitope. B. 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..

34. 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.

36. Rh 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

37. Rh null • 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 • Demonstratemild 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.

39. Rh antibodies • Result from the exposure to Rh antigens • IgG form • Bind at 37°C • Form agglutination in IAT phase

41. Clinical Significance of Rh antibodies • 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.

42. Hemolytic disease of the Newborn (HDN) • 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 RHIG.

43. Rh factor First pregnancy • Rh factor can cause complications in some pregnancies. Placenta Rh+ antigens • Mother is exposed to Rh antigens at the birth of her Rh+ baby.

44. Mother makes anti-Rh+ antibodies. Possible subsequent pregnancies Anti-Rh+ antibodies • During the mother’s next pregnancy, Rh antibodies can cross the placenta and endanger the fetus.