Enzyme-linked immunosorbent assay.

Abstract

The acronym for enzyme-linked immunosorbent assay (ELISA) has become a standard abbreviation in many scientific journals. ELISAs are immunoassays in which one reactant is immobilized on a solid phase and the “signal generator” or “reporter,” is an enzyme. This definition includes enzyme immunoassay (EIA) which like classical radioimmunoassay (RIA), is competitive in design, but employs an enzyme reporter instead of a radionuclide. ELISAs and EIAs, which consist of both a solid and a fluid phase, are designated heterogeneous EIAs (HetEIA). Homogeneous enzyme immunoussuys (HomEIA) do not involve a solid phase and are often not included under the ELISA umbrella, although they will be briefly discussed in this chapter. The HetEIA is often treated under the category of solid-phase irnrnunoassuy (SPI) because assays done on a solid phase have more in common with each other than they do with assays that share a common reporter system (i.e., an enzyme). ELISA and SPI are performed on a variety of solid phases ranging from smooth polystyrene to membranous nitrocellulose (NC) and nylon. The term ELISA was coined by Engvall and Perlmann in 1971 for a noncompetitive HetEIA configuration, whereas EIA historically denoted a competitive one. These acronyms, as well as EM1 (enzymemediated immunoassay) and others, are often used interchangeably in the literature. Solid-phase immunoassays and ELISA have technically simplified antigen quantitation and antibody detection. They are the basis for most modern immunodiagnostic tests for acquired immunodeficiency syndrome (AIDS), hepatitis, allergies, and many other human and animal diseases. Before 1970, nearly all immunodiagnostic tests were based either on fluid phase or cellular interactions of antigens and antibodies (e.g., agglutination, precipitation, and complement fixation). Also before that time, immunological tests for quantifying the levels of small molecules used radioisotopes as reporters and involved tedious procedures for the separation of the bound and free reactants. The observation that proteins are spontaneously adsorbed to hydrophobic surfaces (Catt and Tregear, 1967), led to the development of contemporary SPI, which technically simplified immunoassays and permitted them to be easily automated. Add to this development the use of enzymes as alternatives to radioisotopes, and you describe “immunoassay for the common man” (i.e., ELISA).