antigen antibody reactions Flashcards
What governs antigen-antibody reaction?
The law of mass action
What is the equation showing an antibody-antigen reaction?
[Ag] + [Ab] -> (k1 + k2) [AgAb]
What is an application of the antigen-antibody reaction?
It is used in vitro to test for antibodies & antigens
How is the antigen-antibody reaction visualised in transfusion science?
Haemagglutination & haemolysis of RBCs
How many stages are there in haemagglutination?
2
Explain the 1st stage of haemagglutination.
~Known as sensitisation, binding, association, or coating
~Antibodies attach to corresponding antigens
~Antibody combining sites (FAB region) - complimentary in shape & size to antigens - react specifically and form reversible bonds
~bonds in antibody binding include - ionic bonds, hydrogen bonds, hydrophobic bonds, van der Waals,
Explain the second stage of haemagglutination.
~Agglutination
~Intracellular bridges form - antibodies already bound to antigens on one RBC bind to the antigens of others RBCs
~Aggregating forces - surface tension change pulls RBCs together
~Repulsive forces - RBC surface - net - charge due to sialic acid & neuraminic acid - prevents RBCs from adhering to each other
What are Igs composed of?
~2 heavy chains, 2 light chains
~Variable region & constant region
~Heavy chains bound by disulphide bonds
~Y shaped
~2 Antigen combining bond sites on variable region
What is the zeta potential?
Net strength of forces that exist between cells suspended in saline
For direct agglutination to occur what distance must an antibody span & what causes it?
20nm cause by zeta potential
What is the maximum gap between binding sites for IgMs?
30nm - allows direct agglutination
What is the maximum gap between binding sites for IgGs?
14nm - can’t cause direct agglutination
What factors affect antigen-antibody reactions?
Temperature, pH, ionic strength, antigen & antibody conc.
How does temperature affect that antibody-antigen reaction?
React differently at different temperatures - ABO @ RT , Rh @ 37°
How does pH affect that antibody-antigen reaction?
Optimum 6.5-6.8
Little effect between 5.5-8.5