2 Nature 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
3 Affinity = 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
4 Calculation of Affinity Ag + Ab Ag-AbApplying the Law of Mass Action:Keq =[Ag-Ab][Ag] x [Ab]
5 AvidityThe overall strength of binding between an Ag with many determinants and multivalent AbsYKeq =104AffinityY106AvidityY1010Avidity
6 SpecificityThe 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 AgAnti-A AbAg CSimilar epitopeCross reactionsAnti-A AbAg AAnti-A AbAg BShared epitope
8 Factors Affecting Measurement of Ag/Ab Reactions Ab excessAg excessAffinityAvidityEquivalence – Lattice formationAg:Ab ratioPhysical 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 complexesAll tests based on Ag/Ab reactions can be used to detect either Ag or Ab