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Ag-Ab reactions Tests for Ag-Ab reactions
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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
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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
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Calculation of Affinity
Ag + Ab Ag-Ab Applying the Law of Mass Action: Keq = [Ag-Ab] [Ag] x [Ab]
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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
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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.
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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
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Factors Affecting Measurement of Ag/Ab Reactions
Ab excess Ag excess Affinity Avidity Equivalence – Lattice formation Ag:Ab ratio Physical form of Ag
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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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