blood types (gochin)

2. the Rh blood group system

- Rh (chr 1) is a transmembrane protein embedded in the erythrocyte cell membrane, responsible for ammonium transport - Rh associated glycoprotein (RhAG, cur 6) assists in localization - there are two linked Rh genes on cur 1, RHD and RHCE, which encode the proteins RhD and RhCE respectively - the antigens expressed are D, C/c, E/e - THUS, ONES RH ANTIGEN HAPLOTYPE COULD BE DCe for example - THE MOST IMMUNOGENIC OF THE PROTEINS IS RhD - a person who is RhD negative lacks RhD protein anti-Rh antibodies: - for the purposes of blood compatibility, the RhD antigen is important, because it is highly immunogenic - Rh positive = RhD positive 93-100% prevelance - Rh negative = RhD negative (typically lacking expression of RhD protein) - unlike the ABO system, individuals do not automatically develop anti-Rh antibodies if they are Rh negative - Rh antibodies, when they develop, are mainly IgG - universal acceptor is AB Rh D+ - universal donor is O RhD- II. THE RH SYSTEM The Rh antibody is a transmembrane protein embedded in the erythrocyte cell membrane. Missense mutations in exposed loops give rise to D, C/c and E/e antigens in two linked RhD and RhCE genes on chromosome 1. The antigenic epitope is complex, but the RhD haplotype is the most immunogenic, and defines Rh status. Most individuals are Rh positive. Rh negative Individuals do not automatically develop antibodies to RhD. These will develop if the individual is exposed to Rh -ve blood, and typically take several months to mature. Subsequent exposure will trigger a delayed hemolytic response. Rh antibodies are mainly IgG. Clinical correlation Rh IgG antibodies can cross the placenta and will cause hemolytic disease of the newborn (erythroblastosis fetalis) in an Rh +ve baby of an Rh sensitized Rh-ve mother. Sensitization occurs if there has been a previous pregnancy with an Rh +ve baby; fetal blood most likely enters the maternal blood stream during birth. RhoGAM is an anti-D antibody that is given to the mother to prevent development of anti-D IgG. RhoGAM is specific to RhD and does not address other Rh incompatibilities. Since ABO antibodies are mainly IgM, ABO incompatibility between fetus and mother does not typically cause HDN.

erythroblastosis fetalis - hemolytic disease of newborn (HDN)

- Rh(-) mother exposed at time of placental separation - antibody production begins. next or subsequent pregnancy at risk - maternal exposure to fetal red blood cells leads to development of anti-D agglutinins. this is called maternal alloimmunization onset of HDN: - anti-D IgG can diffuse back across the placenta and cause fetal red blood cell agglutination and hemolysis prevention of HDN: - HDN due to anti-D is prevented by Rh IMMUNE GLOBULIN, an anti-D antibody administered to the mother starting at 30-40 weeks gestation - IT IS ALSO GIVEN TO AN RH NEGATIVE MOTHER WHO DELIVERS AN RH POSITIVE BABY, TO PREVENT SENSITIZATION TO THE D ANTIGEN - RhoGAM: given to mother within 72 hours postpartum RhoGAM prevents HDN (erythroblastosis fetalis): - blood donor: Rh +ve --> recipient: Rh -ve (plasma contains no Rh antibodies) --> agglutination by RhoGAM (anti-D) and rapid degradation - secondary pregnancy --> NO anti-RH antibodies - RhoGAM is RhD specific, it does not protect against anti-C/c or anti-E/e

the bombay phenotype

- an individual lacking FUCOSYL TRANSFERASE (defect in FUT1 gene) is in the Bombay blood group which Ab will be present in the serum? all of them (anti A,B...) which blood type can be safely transfused into this individual? H blood only (only bombay)

Rh incompatibility induces a slow immunological response

- blood transfusion DONOR: (Rh +ve) - recipient: (not previously transfused or pregnant): Rh -ve, plasma contains no Rh antibodies - DONOR BLOOD DEGRADED BY MACROHPAGES, BUT ACT AS FOREIGN ANTIGENS --> formation of anti-Rh Ab is stimulated --> transfusion of Rh+ve blood months later --> agglutination and hemolysis - pregnancy with Rh + ve fetus --> anti-Rh IgG can cross placenta --> agglutination and hemolysis in the presence of anti-RhD antibodies, a delayed hemolytic reaction occurs, 1-14 days: - protein antigen - IgG antibodies, initially low titer: Fc binds to Fc-receptor on macrophages, IgG-C3b binding and association with C3b receptor on macrophages, facilitate phagocytosis - Agglutination - EXTRAVASCULAR LYSIS in splenic macrophages - jaundice, splenomegaly

1. the ABO blood groups

- the ABO blood groups are defined by the presence of immunodominant sugars on the surface of RBCs - these sugars are oligosaccharide components of glycosphingolipids or glycoproteins embedded in red blood cell (and other cell) membranes - the sugars extend into the extracellular space - they serve as cell recognition factors - the exact function of the ABO blood group oligosaccharides is unknown I. THE ABO SYSTEM ABO antigens on the surface of RBC's are sugar groups that extend from the membrane surface, attached to sphingolipids. The base antigenic component is H-antigen, Fuc-α1,2-Gal-β1-4-GlcNac -. The FUT1 gene encodes fucosyltransferase which incorporates the H-antigen. A and B antigens are built upon the H-antigen, A-antigen by an α1-3 linked GalNAc and B-antigen by an α1-3 linked Gal to the Gal sugar of H-antigen. These reactions are catalyzed by glycosyltransferases, products of the ABO gene. The ABO gene has three codominant alleles, O (null - inactive glycosyltransferase), A and B. Individuals lacking A or B antigen will develop anti-A or anti-B antibodies in their serum, most likely from exposure to gut microbes with similar antigens. There are no anti-O antibodies since all of the antigens contain the H-antigen (fucose). It is thought that antibody development occurs after birth upon exposure to environmental antigens in bacteria or plants. Antibodies can be IgG or IgM. Only IgG can cross the placenta, and only IgM activate the complement cascade. Clinical correlation Transfusion of ABO mismatched blood causes an acute hemolytic transfusion reaction, due to activation of the complement cascade by IgM-bound red blood cells. Intravascular hemolysis occurs accompanied by shock and kidney failure. IgG-bound RBC's are phagocytosed by spleen macrophages, in a process of extravascular hemolysis. Individuals with defective FUT1 cannot be transfused with O, A, B or AB blood.

testing for bound Ab by direct Coombs test

- the direct coombs test (direct anti globulin test, DAT) is used if autoimmune hemolytic anemia is suspected - it also is used to test babys cord blood if HDN is suspected - measure Ab bound to red blood cells of patient

gene loci encoding ABO blood type

- the gene FUT1 (chr 19) encodes FUCOSYLTRANSFERASE for making the H antigen on the surface of RBCs - the ABO gene (chr 9) encodes GLYCOSYLTRANSFERASES that catalyze the final step in the synthesis of the A or B antigen. there are three co dominant allelic variants, of which the O (null) variant encodes an inactive enzyme the relative frequencies of different blood types in a caucasian population: - type O: 47%, OO (ABO), HH, Hh (FUT1) - type A: 41%, AA or AO (ABO), HH, Hh (FUT1) - type B: 9%, BB or BO (ABO), HH, Hh - type AB: 3%, AB, HH, Hh

the ABO antigenic determinants

- the immunodominat sugar of H antigen is L fucose - this antigen gives rise to the O blood group A and B antigens are built upon the H antigen: - type A: N acetyl galactosamine - type B: galactose

antibody titer by the indirect coombs test

- the indirect coombs test: this is an ELISA test that screens the recipients serum and potential donor blood against a wide range of RBCs that exhibit a full range of surface antigens - it is used in antenatal testing to screen for IgG antibodies in maternal serum, and prior to blood transfusions - agglutination = positive = patient had antibodies to something in blood - measure Ab in serum of patient

3. other blood antigens of interest

- the third most immunogenic red blood cell antigen class: KELL - 68% of american blacks have null phenotype: DUFFY - DUFFY is a chemokine receptor

anti-A, B antibodies in blood serum

- when an individual lacks the A and/or B antigen on the red cells, the plasma will contain naturally-occurring Ab to the missing antigens. they generally appear in the blood by 4 to 6 months of age in structure to the A and B blood group antigens as the gut becomes colonized in early infancy alloantibodies (agglutinins) present in serum (IgM/IgG): - type A --> anti-B - type B --> anti-A - type O --> anti-A and anti-B - type AB --> none transfusion reactions are an iatrogenic type II hypersensitivity reaction

lab stuff

III. LABORATORY METHODS FOR BLOOD TYPING AND ANTIBODY TITERS a. A simple two minute test for blood typing uses anti-A, anti-B and anti-D antibodies to determine ABO blood type and Rh factor status from a few drops of blood. b. Antibody titers (levels) are determined using the Coombs test. • Indirect Coombs test for blood typing: Patient serum is reacted with red blood cells of known antigenic composition. After washing off unbound protein, anti- human Ig (Coombs reagent) is added. Agglutination indicates a positive test result. The titer is obtained by dose response measurement (serial dilution of the patient's serum) • Indirect Coombs test for blood matching: Patient serum is reacted with red blood cells from the potential donor. • Direct Coombs test. Here auto-antibodies against the patient's own blood cells are measured by adding the antiserum directly to the patient's blood sample.

5. blood typing and cross matching for transfusions

blood typing: - 1. drops of recipients blood in three depressions on a slide - 2. add: anti-A, anti-B, or anti-D - 3. read after 2 minutes look for coagulation, agglutination cross matching: - detection of unexpected antibodies in patients serum - 1. donor RBCs on a microscope slide - 2. add recipients serum - 3. read after 2 minutes - a positive test in cross matching indicates one of three past medical events: pregnancy, prior blood transfusion, prior transplantation

structure of glycosphingolipds

extracellular: - sugar membrane: - sphingosine

4. immune mediated hemolytic transufion reactions

extravascular lysis: - delayed hemolytic reaction - RBC --> phagocytosis by macrophage --> heme --> in liver --> UCB --> CB intravascular lysis: - acute hemolytic reaction (rare) - Hb (haptoglobin) bind to hemoglobin --> transport to liver ABO incompatibility in a transfusion - acute hemolytic reaction: - oligosaccharide antigens, densely expressed on RBCs - HIGH TITER OF IGM present - agglutination - complement mediated lysis of antibody bound RBCs - INTRAVASCULAR HEMOLYSIS - response is typically IMMEDIATE - decreased plasma haptoglobin - HEMOGLOBINUREA AND HEMOGLOBINEMIA - fever, kidney failure

erythroblastosis fetalis notes

what are some likely symptoms associated with hemolysis of fetal and infant blood cells by maternal anti-Rh agglutinins? anemia, juandice why is Rh compatibility more critical than ABO compatibility between mother and fetus? IgM can't cross the placenta (IgG of Rh can) in which case could an ABO incompatibility arise between mother and fetus? ABO HDN is restricted to group A and B infants of Group O mothers note that anti-c, anti-e, and anti-k (kell antibodies) make up the great majority of clinically significant HDN observed at present time

AB recipient given O blood but had reaction

what happened? - plasma of blood group O contained in the platelet transfusion can carry a very high titer of an anti A and anti B antibodies what was the immune reaction? naturally occurring anti A and anti B caused agglutination, complement fixing, causing rapid intravascular hemolysis and disseminated coagulation how could this be avoided? - check titer of anti A and anti B in blood group O platelets