1. Ag-Ab reactions Tests for Ag-Ab reactions

2. Nature of Ag/Ab Reactions
Source: Li, Y., Li, H., Smith-Gill, S. J., Mariuzza, R. A., Biochemistry 39, 6296, 2000
Lock and Key Concept
Non-covalent Bonds
Hydrogen bonds
Electrostatic bonds
Van der Waal forces
Hydrophobic bonds
Multiple Bonds
Reversible

3. Affinity =  attractive and repulsive forces
Strength of the reaction between a single antigenic determinant and a single Ab combining site Ab Ag
High Affinity Ab Ag
Low Affinity
Affinity =  attractive and repulsive forces

4. Calculation of Affinity
Ag + Ab  Ag-Ab
Applying the Law of Mass Action:
Keq =
[Ag-Ab]
[Ag] x [Ab]

5. Avidity
The overall strength of binding between an Ag with many determinants and multivalent Abs Y
Keq =
104
Affinity Y
106
Avidity Y
1010
Avidity

6. Specificity
The ability of an individual antibody combining site to react with only one antigenic determinant.
The ability of a population of antibody molecules to react with only one antigen.

7. Cross Reactivity Cross reactions
The ability of an individual Ab combining site to react with more than one antigenic determinant.
The ability of a population of Ab molecules to react with more than one Ag
Anti-A Ab
Ag C
Similar epitope
Cross reactions
Anti-A Ab
Ag A
Anti-A Ab
Ag B
Shared epitope

8. Factors Affecting Measurement of Ag/Ab Reactions
Ab excess
Ag excess
Affinity
Avidity
Equivalence – Lattice formation
Ag:Ab ratio
Physical form of Ag

9. Tests Based on Ag/Ab Reactions
All tests based on Ag/Ab reactions will have to depend on lattice formation or they will have to utilize ways to detect small immune complexes
All tests based on Ag/Ab reactions can be used to detect either Ag or Ab