RH BLOOD GROUP SYSTEM (MID1)- PART 2

174,000

BIOCHEMISTRY OF RH ANTIGENS

• Non-glycosylated proteins- This are pure proteins

• Integral part of RBC membrane- RHAG

• MW _____________ Daltons

Functions:

• Cation transporters (sodium and potassium)

• Maintain the stability of RBC membrane

Weak D/Du variant

• D antigen is present but in small amount/ D antigen with missing parts or fragment

• Testing must be carried through the antiglobulin phase of testing to demonstrate the presence of the D antigen.

• It has D antigen but there are few numbers of the antigen

• It cannot produce lattice formation

• Sensitization only

Rh-positive

Weak D/Du variant

• RBCs carrying the weaker D antigen have historically been referred to as having the “Du” type.

• They are referred to as expressing weak D and are considered __________

• It is safe to transfuse Rh- blood to a weak D patient rather than Rh+, to avoid Alloimmunization.

Rh+, Rh-

Weak D/Du variant

• If you have weak D and you are the donor, you are ___

• But if you are the recipient, you are ____

3X

RH BLOOD GROUPING PROCEDURE (INDIRECT ANTIGLOBULIN TESTING (AHG))

• Incubate cells with anti-D at 37C, coating of D antigens will occur if present.

• Wash ___ add AHG

• AHG will bind to anti-D coating cells if present.

• If negative, individual is D negative

• If positive, individual is D positive

Genetic Weak D

Causes/Mechanisms

• D antigen is appear to be complete but few in number therefore it is weakly expressed

• Rh genes variants

Du

Causes/Mechanisms (GENETIC WEAK D)

• _____→ a red cell carrying the D Ag which is detectable only by indirect Coomb’s test and regarded as the weak form of D antigen

• Rarely found in Caucasians, more common on blacks and is more often part of the cDe (Ro) haplotype

• Most common Rh gene

C-trans

Causes/Mechanisms

• Position effect, Steric suppression, gene-interaction effect

• Occur when genes are present on different chromosome or trans to one another. In this mechanism, weakened D occurs when the C-antigen is inherited trans to the D-antigen.

• r’ (dCe) is paired with either R1(DCe) or R0 (Dce)

• The occurrence of DCse (R1) gene is less than 2%

• The locus of the D and the C are on separate chromosome.

Mosaic/ Partial D/ D variant / Categories of D

Causes/Mechanisms

• Structure of D antigen is in _____ structure, composed of 4 fragments

• Weakly expressed if one fragment is missing

• Qualitative defect

alloantibody

Causes/Mechanisms (Mosaic/ Partial D/ D variant / Categories of D)

• The remaining portion of the antigen will stimulate production of an ______________

Causes/Mechanisms

• Very rare caused by mutated D gene

• Produces lesser Antigen → individuals inherit Rh gene complex lacking alleles

• Present in 10-30% Of Asian population

• Written as D -- or - D -

• Agglutinated by Anti-D

D antigen

RH ANTIBODIES

• Most Rh antibodies are IgG and reacts optimally at 37°C or after antiglobulin testing

• Immune antibodies→ produced following exposure to foreign RBCs.

• Through either transfusion or pregnancy.

• ________ is the most immunogenic

Extravascular

RH ANTIBODIES

• Do not bind complement→ two IgG immunoglobulins must attach to an RBC in close proximity.

• RBC destruction is __________________→when an Rh antibody coats the RBCs, intravascular, complement mediated hemolysis does not occur.

  • RBC destruction resulting from Rh antibodies is primarily __________

120, 2-7

RH ANTIBODIES

• Causes HDFN (Hemolytic Disease of the Fetus/Newborn)

• Produced _____ days after primary exposure

• Produced ______ days after secondary exposure

Transfusion Reactions

Clinical Considerations

• Rh antigens are highly immunogenic.

• The D antigen is the most immunogenic antigen outside the ABO system

Rh-mediated hemolytic transfusion reactions

Clinical Considerations

• Extravascular hemolysis

HDN

Clinical Considerations

• Rh negative female

• Rh positive father

• Rh positive infants