Blood Group Antigens(BGA) , ABO(H) -System & Rhesus System Flashcards Preview

Immunology > Blood Group Antigens(BGA) , ABO(H) -System & Rhesus System > Flashcards

Flashcards in Blood Group Antigens(BGA) , ABO(H) -System & Rhesus System Deck (10):
1

Blood group antigens (BGA)

- can be glycolipids or glycoproteins (the carbohydrate portion is responsible for feature of antigen, it is binded to proteins by enzymes)

- H-substance (oligosaccharid) is the the basic fragment, consist of 5sugars

- gene product of H-allel is located on 19. Chrmsm and is responsible for attachment of 5th sugar of H-substance (Fuctose)
-> only in presence of fuctose, the both other blood group alleles can be effective

- BGA are located on erythrocyte membrane -> the antibodies A and B are in blood serum

- BG-genes/alleles A, B and 0 are located on 19.Chrmsm and code for glycosyltransferase enzymes (responsible for synthesis of Ags)

2

Biosynthesis of BGA

- Precursor chain (Gen H, located on 19.Chrmsm) : L-fucose is added to -> encodes Fucosyltransferase wh produces the H-antigen

- In blood group A (Allel A) : N-Acetylgalactosamine is added at H-substance/-antigen by enzyme acetylgalactoseamine-transferase wh expresses antigen A

- In blood group B (Allel B) : D-Galactose is added at H-substance/-Ag by enzyme galactosyltransferase wh expresses antigen B

- In blood group 0 (Allel 0): no add sugar is added, no antigens are expressed
(->Allel 0 codes for a defective Glycosyltransferase so that H-substance is not modificated)

- Bombay-phenotype (blood group 0, genotype hh sese): glcyosyltransferase is missed for fucose, cannot express H-substance/H-antigen

3

Inheritance of blood group antigens/ alleluia interactions

- A is dominant over 0 and codominant to B
- B is dominant over 0 and codominant to A
-> 0 is recessive against A and B

4

Inheritance of blood groups

- Group A: have antigen A and antibodies B
- Group B: have antigen B and antibodies A
- Group 0: have no antigens but antibodies A and B
- Group AB: have antigens A and B but no antibodies
- body produces antibodies against antigens of blood groups also without contact with their associated erythrocyte
- but all lymphocytes, wh produce antibodies against the endogenous/body’s own antigens, are eliminated -> reason why only antibodies are present wh are against the absent blood group antigen
- every human possesses H-substance/antigen, therefore the body does not produce antibodies against it
(except Bombay-phenotype -> has no H-antigen -> body produces antibodies against H-antigen)

5

Additional information about Antibodies

- body produces antibodies against antigens of blood groups also without contact with their associated erythrocyte
- but all lymphocytes, wh produce antibodies against the endogenous/body’s own antigens, are eliminated -> reason why only antibodies are present wh are against the absent blood group antigen
- every human possesses H-substance/-antigen, therefore the body does not produce antibodies against it
(except Bombay-phenotype -> has no H-antigen ->body produces antibodies against H-antigen)
- the produced Abs belongs to IgM-class -> they are very big, so they cannot pass through the placenta (-> protect embryo from the Anti-B Abs of the mother with blood group 0 if he inherits blood group B from his father)

6

Biological functions of BGA

1. Markers of cell proliferation and differentiation
2. Tumor markers
3. Molecules of intercellular communications
4. Phylogenetic and ontogenic markers
5. Receptors of parasites, bacteria and viruses
6. Immunogen (=Ag wh can trigger an immune response bc of its immunogenity) — transfusions, transplantations, infertility
7. Markers associated with predisposition to diseases

7

Secretory status
(Add. Blood group system)

- says that persons possesses blood group antigens (BGA) not only on surface of erythrocytes, but also in body fluids
- Secretors: person with BGAs on blood cell and in body fluids
- Non-Secretor: person with BGAs only on surfaces of erythrocytes
- Secretor-Gene (located on 19.Chrmsm) is dominant and inherited independently of genes AB0 and H
- phenotype of Secretors: SeSe, Sese
- phenotype of Non-Secretors: sese

8

Rhesus- System
(Add. blood group system)

- Rhesus-Factor (abbr. Rh or D) is inherited dominant
- two homologous closely linked genes — RhD and RhCE, located on 1.Chrmsm
- Gene RhD codes for 1 antigen: RhD
- Gene RhCE codes for 2 antigens: RhC and RhE
- C- and E-AGs are homologous and products of the same gene (CE) as a result of alternating splicing
- D/Rh (+) individuals: have two Rh-genes (RhD and RhCE) and three Rh-antigens (D, C and E)
- D/Rh (-) individuals: have one Rh-gene (RhCE) and two antigens (C and E)

10

Hemolytic disease of newborn (Rhesus-system)

- normally they aren’t found in the serum of healthy people
- people with Rh-negative can produce antibodies against Rh-factor but only after their comes in contact with corresponding blood
- AntiRh-antibodies belong to IgG-type wh are very small and can passes through the placenta (they are always immune!)


Conditions/Steps for occurrence of this disease:
1. Mother D/Rh(-) (rhrh) and father D/Rh (+) (RhRh,Rhrh)
2. Fetus has D/Rh (+)
3. During pregnancy Fetus erythrocytes(Er) reach mother’s blood circulation where antibodies against Rh-factor/ Fetus Er’s are produced
4. At the 2nd pregnancy these Anti-Rh Abs can passage through placenta and agglutinate with the Er of the Rh-(+) Fetus (=hemolysis)

Prevention:
- High dose of Rh-antibodies is injected in mother (Rh(-)) just before and after first childbirth
-> they disguise the antigens of the fetus, thus they provide elimination of those Er in blood circulation

11

Agglutination (Def, principles)

- Def. It’s a antigen-antibody reaction in which the Ag and Ab clump together

- Direct Agglt.: Ag is a neutral component of blood corpuscle wh is agglutinated by Ab

- Indirect Agglt.: soluble Ag is attached to a carrier-particle ( when carrier is an Er, the test is known as passive hemagglutination)