blood group serology Flashcards
define blood group antigens
substances present on the surface of red cells
are normally glycolipids or glycoproteins
genetically determined
glycoprotein determinants vs glycolipid determinants
protein determinants
- genes for the antigenic determinant itself
- e.g. Rh, Kell, duffy, Kidd systems
glycolipid determinants
- gene codes for productions of enzymes that add/remove carbohydrate or lipid structures
- e.g. ABO, lewis group system
blood group antibodies
blood group antigen systems important as they stimulate antibody production
- antibodies recognise foreign antigens
- may be IgM, IgG, sometimes IgA
- may be naturally occurring or immune stimulated
describe naturally occurring antibodies vs immune stimulated antibodies
naturally occurring
- no exposure to foreign red cells but exposure to bacteria containing for example, A-like antigen
- therefore anti-A produced
- related to glycolipid antigens
- IgM component to AB
- can activate complement
immune
- exposure to foreign red cells (for example Rh+)
- by transfusion
- or pregnancy (Rh+ fetes)
- anti-Rh produced
- related to glycoprotein antigen
- IgG component to AB
immune requires red cells, natural doesn’t
incompatible transfusion
leads to complement activation
- red cells from donor carry antigen to AB in patient plasma
can cause:
- intravascular haemolysis
- renal failure
- disseminated intravascular coagulation (DIC)
ABO
antigens widely distributed e.g. bloods cells, epithelial cells, body fluids
- all express H antigen
- vary depending on presence or absence of terminal sugar
- antibodies get formed in the first 3-6months when theres an absence of an antigen present
e.g. phenotype = AA, AO genotype = A AB present = anti-B donor = A, O
Rh blood group system
- 2nd most important system
- Protein determinant
- Expression only on RBCs
- Antibodies produced following immune stimulation
- Highly immunogenic, particularly Rh (D)
define agglutination
when antigen and antibody complexes come together they form a red cell clump
Rh(D) and transfusion
- 90% of Rh(D) negative transfuse with Rh(D) positive cells will produce anti-D antibodies
anti-D is IgG and is unable to bind complement. Red cell destruction is extravascular
never transfuse Rh(D) positive cells to an Rh(D) negative female of child bearing age
Rh(D) negative genotype
must have dd
cannot have any D genotype
define zeta potential
Red cells are negatively charged, prevents them coming in contact with each other (no cross-linking and therefore no agglutination)
IgM agglutination vs IgG
IgM > zeta potential
- cross-linking and agglutination forms
IgG < zeta potential
- no agglutination
- needs potentiator = anti-human globulin
describe haemolytic disease of the newborn
- occurs when maternal AB crosses placenta leading to fatal red cell destruction
- involves IgG (as this crosses placenta)
- most frequently caused by anti-D
- reduced greatly by immunoprophylaxis
mechanism of HDNB
Rh(D) -ve mother is exposed to Rh(D) +ve red foetal cells, most frequently following transplacental haemorrhage at delivery. This causes Rh(D) +ve cells to enter the maternal circulation and cause anti-D to form. Subsequent pregnancies, anti-D crosses the placenta and causes damage to foetal red cells
consequences of HDNB
Foetal anaemia, develops cardiac failure –> congestive cardiac failure
More commonly survives pregnancy, baby jaundiced (bilirubin removed via maternal circulation) bilirubin crosses BBB and causes brain damage
