Enzyme-Linked Immunosorbent Assay – ELISA Test

There are many instances in the life sciences where detecting and quantifying antigens or antibodies in a sample in a rapid and cost-effective manner is important. From identifying immune responses in vaccinated or infected people, to detecting the expression of a protein you want to express on the surface of a cell, to performing quality control tests. Having a tool capable of making such assessments is essential.

The enzyme immunoassay (ELISA) is one such test that has proven to be invaluable as a research and diagnostic tool. In this article, we'll look at what an ELISA is, how it works, variations of the technique, and what it can tell you.

An ELISA test is an immunoassay commonly used to measure antibodies or antigens, including proteins or glycoproteins, in biological samples. Like other immunoassays, they rely on the binding of antibodies to their targets to facilitate detection.

Typically, ELISA tests are performed in 96-well plates, a format that makes them suitable for screening many samples at once. Serum, plasma, cell culture supernatants, cell lysates, saliva, tissue lysates, and urine are all common sample types used for these tests, but most liquid sample types could be used in theory. However, it is important to consider that some sample types may include inhibitory factors, such as buffer components that share similar antigenic epitopes1 or factors such as proteases2 that can damage the target or detection components, which can interfere with test performance.

There are several different assay formats, but all rely on binding the target itself or an antibody/antigen capable of capturing the target to the surface of the plate. A detection step involving a conjugated antigen, or more often an antibody, is then employed to allow detection and quantification of successful binding, most often by colorimetric detection.

ELISA was initially conceptualized, independently, in 1971 by Eva Engvall and Peter Perlman3 at Stockholm University in Sweden, and Anton Schuurs and Bauke van Weemen4 in the Netherlands. They sought an immunoassay method capable of detecting the presence of antigens or antibodies to replace the radioimmunoassay, which employed potentially dangerous radiolabeled antigens or antibodies, and thus devised an enzyme-based alternative.

There are now four main types of ELISA, direct, indirect, sandwich and competitive. The images below (Figure 1) illustrate the detection of antigens; however, the same principle applies for antibody detection essentially with the roles of antigen and primary antibody reversed.