Kinetics of antibody-antigen interactions

Temperature-jump relaxation and the stopped-flow methods are suitable to follow the concentration changes over extremely short time intervals. Such studies have indicated that immune reaction kinetics resemble other biological systems in which ligands are bound to proteins (Weber, 1975) in that the binding strength of small molecules is largely dictated by the constant. The association rate constants ka, are very similar for various antibody-antigen systems, i.e., for 

Quantitative immunoelectrophoresis (Birkmeyer et al., 1981) and reverse quantitative immunoelectrophoresis (Birkmeyer et a)., 1982) allow the determination of average affinity of different antibody populations for an antigen. Plots of rocket area vs. the amount of antibody applied yield straight lines, the slope of which is indicative of affinity (steeper if the affinity is higher). Actual values of K are not obtained. Relative avidity indices can also be obtained with the test of Farr (1958) (Griswold and Nelson, 1984). 

In these methods (e.g., Ehrlich et al., 1982) antibody concentrations are, in contrast to the ranking method, kept constant (methods in Section 8.3). 

Influence of antibody affinity on determination of hapten concentration by a solid- 

Days after last boost Affinity constant ( x 10 - ) Standard Amplified ElA (/tg/ml) ElA (/ig/ml)  

---

In essence, this technique allows for the detection of surface binding interactions in real time without the use of labels. Immunosensors that rely on these principles are commercially available from Biacore AB (formerly Pharmacia Biosensor). These are based on the popular BIACORE 3000, BIACORE 2000 and BIACORE probe instruments in conjunction with disposable sensor chips, which may be purchased with affinity capture chemistries in place (e.g. SA5 Sensor Chips with streptavidin bearing surfaces for capture of biotinylated compounds) [92]. These devices incorporate micro-fluidic systems for delivery of reagents required for analysis and are capable of measuring affinities and kinetics of antibody-antigen interactions in addition to analyte concentrations, which can be determined to the picomolar range [93]. 

---