Antibodies antigen affinity

NHH Heegaard. Determination of antigen—antibody affinity by immuno-cap-illary electrophoresis. J Chromatogr A 680 405-412, 1994. 

Scheme 13 Electronic and optical transduction of the formation of antigen-antibody affinity complexes on transducers (A) ampero-metric transduction at an electrode (R+/Ris a redox label in the electrolyte solution), (B)...

Affinity chromatography (12) has become an important tool in the isolation of purified fractions of such substances as enzymes. Advantage is taken of specific interactions such as antigen-antibody interactions. One substance of the pair (e.g. antigen) is bonded to a support. When a mixture is passed through the column, the specific interaction retains the corresponding antibody relative to other substances. A change of mobile phase conditions then elutes the pure antibody. This method has a real potential for analysis of specific proteins in body fluids. 

Pedersen, M.K., Sorensen, N.S., Heegaard, P.M., Beyer, N.H., and Bruun, L. (2006) Effect of different hapten-carrier conjugation ratios and molecular orientations on antibody affinity against a peptide antigen./. Immunol. Meth. 311(1-2), 198-206. 

Antibody affinity from the Latin, affinis = connected with, having things in common. In immunohistochemistry, antibody affinity determines the strength of binding of a monovalent antibody, such as Fab fragment, to one epitope, i.e., how tightly an antibody binds to its particular antigen. 

Antibody avidity is commonly applied to antigen-antibody interaction, where multiple, weak, noncovalent bonds form between antigen and antibody. Avidity is distinct from affinity, which is a term used to describe the strength of a single bond. As such, avidity is the combined synergistic strength of bond affinities rather than the sum of bonds. 

Nielsen et al. used this method to separate antigen-antibody complexes of recombinant hGH with monoclonal antibody specific to hGH (12). The complexes were well resolved from the free antibody and antigen in solution. The strong binding affinity of the antibody for hGH results in strong, stable antibody-antigen complexes that form very rapidly in solution two complexes (IgG-hGH, IgG-(hGH)2) have been observed. 

The examples mentioned up to now utilized strong Ag-Ab interactions using the equilibrium-mixture mode of ACE. But the quantitation of weak antigen-antibody interaction is also possible by ACE, if the mobility-shift approach, sometimes also called dynamic equilibrium affinity electrophoresis, is applied. 

B5. Boder, E. T, Midelfort, K. S., and Wittrup, K. D., Directed evolution of antibody fragments with monovalent femtomolar antigen-binding affinity. Proc. Natl. Acad. Set U.S.A. 97, 10701-10705 (2000). 

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