The antibody/antiserum as an analytical reagent in quantitative immunoassays

Antibodies and antisera have been successfully employed as diagnostic tools for many years. However, there has always been a problem in reproducing the quality of an antiserum, once its usefulness in a diagnostic test has been established. After the introduction of monoclonal antibodies it was hoped that this problem could be circumvented and that more reliable reagents of higher specificity could be obtained. This assumption has proved basically right, although some pitfalls remain when using monoclonal antibodies. Whereas reactions with polyclonal antibodies or antisera are of statistical nature, monoclonal antibodies react with epitopes in a very defined and restricted manner. This makes the antibody-antigen reaction more susceptible to physical and chemical changes of the antigen and antibody structure and also to "environmental" influences. Association and dissociation kinetics are important features of antibody-antigen reactions, especially if tests are run in an non equilibrium mode. Alterations in cross-reactivity, dependent on reaction kinetics, are frequently more prominent with monoclonal than with polyclonal antibodies. When attempting to standardize immunoassays all this has to be kept in mind, and will finally lead to a demand for agreed reference methods. Singular reference materials cannot take care of the entire intricate network of variables in an immunoassay; they are only one step in the right direction.