Ag-Ab reactions Tests for Ag-Ab reactions

1. Ag-Ab reactionsTests for Ag-Ab reactions

2. http://www.med.sc.edu:85/chime2/lyso-abfr.htm Source: Li, Y., Li, H., Smith-Gill, S. J., Mariuzza, R. A., Biochemistry 39, 6296, 2000 Nature of Ag/Ab Reactions • Lock and Key Concept • Non-covalent Bonds • Hydrogen bonds • Electrostatic bonds • Van der Waal forces • Hydrophobic bonds • Multiple Bonds • Reversible

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

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

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

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 reactions Anti-A Ab Anti-A Ab Anti-A Ab Ag B Ag C Shared epitope Similar epitope Ag A Cross Reactivity • 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

8. Ab excess Ag excess Equivalence – Lattice formation Factors Affecting Measurement of Ag/Ab Reactions • Affinity • Avidity • 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