2Nature of Ag/Ab Reactions Source: Li, Y., Li, H., Smith-Gill, S. J., Mariuzza, R. A., Biochemistry 39, 6296, 2000Lock and Key ConceptNon-covalent BondsHydrogen bondsElectrostatic bondsVan der Waal forcesHydrophobic bondsMultiple BondsReversible
3Affinity = attractive and repulsive forces Strength of the reaction between a single antigenic determinant and a single Ab combining siteAbAgHigh AffinityAbAgLow AffinityAffinity = attractive and repulsive forces
4Calculation of Affinity Ag + Ab Ag-AbApplying the Law of Mass Action:Keq =[Ag-Ab][Ag] x [Ab]
5AvidityThe overall strength of binding between an Ag with many determinants and multivalent AbsYKeq =104AffinityY106AvidityY1010Avidity
6SpecificityThe 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.
7Cross 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 AgAnti-A AbAg CSimilar epitopeCross reactionsAnti-A AbAg AAnti-A AbAg BShared epitope
8Factors Affecting Measurement of Ag/Ab Reactions Ab excessAg excessAffinityAvidityEquivalence – Lattice formationAg:Ab ratioPhysical form of Ag
9Tests 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 complexesAll tests based on Ag/Ab reactions can be used to detect either Ag or Ab