Enzyme-linked immunosorbent assay is a molecular technique that utilizes an enzyme system to show specific combination of an antigen with its antibody. ELISA technique was first conceptualized and developed by Peter Perlmann and Eva Engvall at Stockholm University, Sweden.
Types of ELISA
There are different types of ELISAs available for the detection and quantitation of either the antigen or antibodies in serum and other body fluids. There are four types of ELISA tests:
- Direct ELISA: Antigen is attached to a polystyrene plate. Enzyme-labeled antibody is added that can react with the antigen and a substrate that can be measured.
- Indirect ELISA: Antigen is attached to a polystyrene plate. Addition of primary antibody followed by an enzyme-labeled antibody that can react with both the primary antibody and substrate.
- Sandwich ELISA: A capture antibody is attached to the polystyrene plate, then antigen is added that specifically attaches or captures the antigen. A second antibody, also specific for the antigen but not the same as the capture antibody is added and “sandwiches” the antigen. This second antibody is then followed by an enzyme-labeled antibody specific for the second antibody that can react with a substrate that can be measured.
- Competitive ELISA: This test is like the sandwich ELISA but involves the addition of competing antibodies or proteins when the second antibody is added. This results in a decrease in the substrate signal that is generated. This test is considered to give good, highly specific results.
- Presence of antigen or the presence of antibody in a sample can be evaluated.
- Determination of serum antibody concentrations in a virus test.
- Used in food industry when detecting potential food allergens.
- Applied in disease outbreaks- tracking the spread of disease e.g. HIV, bird flu, common, colds, cholera, STD etc.
- Used in toxicology as rapid presumptive screen for certain classes of drugs.
- Detection and quantification of substances such as peptides, antibodies, hormones, proteins etc.
Data Interpretation of ELISA
Enzyme assay yields data of different outputs and their interpretation is done as per data obtained.
- Quantative: The data obtained are interpreted in comparison to the standard curve (obtained by serial dilution of known purified antigen) to calculate the concentration/ quantity of antigen in various samples.
- Qualitative: It deals with indication of either presence or absence of particular antigen or antibody as per the color reaction compared to blank well containing no antigen or unrelated control antigen.
- Semi- quantitative: It relates to comparison of relative levels of antigen in samples depending upon the intensity which vary with antigen concentration.
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