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Ag-Ab reactions Tests for Ag-Ab reactions. Nature of Ag/Ab Reactions Lock and Key Concept Non-covalent Bonds – Hydrogen bonds – Electrostatic bonds –

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Presentation on theme: "Ag-Ab reactions Tests for Ag-Ab reactions. Nature of Ag/Ab Reactions Lock and Key Concept Non-covalent Bonds – Hydrogen bonds – Electrostatic bonds –"— Presentation transcript:

1 Ag-Ab reactions Tests for Ag-Ab reactions

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

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

4 Calculation of Affinity Ag + Ab Ag-Ab K eq = [Ag-Ab] [Ag] x [Ab] Applying the Law of Mass Action:

5 Avidity The overall strength of binding between an Ag with many determinants and multivalent Abs K eq = 10 4 Affinity 10 6 Avidity 10

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

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

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


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