History of enzyme immunoassays

EIA were developed in the mid-sixties for the identification and localization of antigens in histological preparations, analogous to immunofluorescence methods, and for the identification of precipitation lines obtained by immunodiffusion and immunoelectrophoresis (Na-kane and Pierce, 1966, 1967 Avrameas and Uriel, 1966). These enzyme immunohistochemistry (EIH) methods were recognized as very useful in other fields (Tijssen and Kurstak, 1974 Kurstak et al, 1975, 1977 Sternberger, 1979 Farr and Nakane, 1981 Polak and Van Noorden, 1983). 

The observation that antigens or antibodies can be immobilized on solid phases made it possible to apply similar methods for the quantitative detection of immunoreactants in test tubes (Engvall and Perlmann, 1971 Van Weemen and Schuurs, 1971), not only enlarging enormously the number of haptens, antigens or antibodies 

Rubenstein et al. (1972), subsequently, developed a homogeneous system in which the enzyme is labeled, generally with a hapten, without seriously affecting its activity. This method is applicable if the antibody reacting with the hapten either reduces or increases enzyme activity. The presence of free hapten in the added sample lowers the fraction of antibody able to react with enzyme-hapten conjugate and thus lowers the effect of the antibody on the enzyme. 

The development of methods to produce monoclonal antibodies (Kohler and Milstein, 1975 Section 5.4) not only enhanced the possibility of a more stringent standardization of EIA with higher specificity and sensitivity, but also contributed to new assay designs. 

In addition to the detection of antigens and antibodies, EIA will, undoubtedly, play an increasingly important role in molecular biology. For example, the bio-blot method (Leary et al., 1983) for the detection of DNA-DNA or DNA-RNA duplexes on nitrocellulose membranes offers important advantages over conventional procedures in which radioactive probes are used and autoradiographic detection. In this method, biotinylated DNA probes are prepared by nick translation (Rigby et al., 1977) in the presence of biotinylated analogs and hybridized with the DNA or RNA on filters. Biotin is then detected by avidin-labeled enzyme (Section 3.1). 

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