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Serum ELISA is a reliable clinical test that detects biological substances in serum samples through the interaction between an antigen and an antibody. It is widely used for large-scale operations and is commercially available. It is also being studied for cytokine detection to assess disease states associated with chronic inflammation.
The serum enzymatic immunosorbent assay (serum ELISA) is a method used to determine the amount of a biological substance in a serum sample based on the specific interaction between an antigen and an antibody. Examples of biological substances of interest include an antibody produced in response to a viral infection, such as an antibody against human immunodeficiency virus (HIV), or a hormone that indicates pregnancy, such as human chorionic gonadotropin (hCG), or an autoimmune antibody produced in rheumatoid arthritis, such as rheumatoid factor. In general, there is a direct assay, which uses a specific antibody to detect the presence of antigen in a serum sample, and an indirect assay, which uses an antigen to determine the presence of antibody in a serum sample.
In direct serum ELISA, a sample containing an unknown amount of antigen is attached to an immobile surface, such as a reaction tube or microtiter plate, and is incubated with a specific antibody that is chemically bound to an enzyme. In contrast, in indirect serum ELISA, a known antigen is attached to an immobile surface and then incubated with the serum sample which contains an unknown amount of antibody. Antigen-specific antibody in the serum sample is expected to bind tightly to the immobilized antigen, while non-specific antibodies are removed in the following wash steps. Typically, the immobile surface is treated with a second antibody that recognizes the invariable region of all antibodies and is chemically linked to an enzyme. In both direct and indirect ELISA, the final step is the addition of a specific enzyme substrate, initiating a reaction that produces a measurable signal that is directly proportional to the amount of antigen or antibody present in the serum sample.
The serum ELISA is a widely used test for several reasons. Above all, it is considered a reliable clinical test due to the specificity of the antigen-antibody interaction and the sensitivity of this test allows for the detection of biological substances at extremely low concentrations in serum. It is designed for evaluating large numbers of samples simultaneously, so it is often used in large-scale operations, such as screening blood donor samples for the presence of HIV antibodies. Additionally, ELISA kits that measure commonly tested antibodies and antigens are commercially available for use in research or clinical settings and conveniently contain all the reagents needed to perform a complete experiment.
A growing area of study is in the application of serum ELISA technology in the area of cytokine detection. Cytokines are soluble protein molecules secreted by the immune system that are often involved in inflammatory processes; cytokine levels are therefore informative about disease states associated with chronic inflammation, such as heart disease, autoimmune disease, and digestive system disease. It is thought that the assessment of cytokine levels may be able to distinguish between inflammatory bowel diseases, such as Crohn’s disease and ulcerative colitis, and may possibly predict the outcome of heart disease and rheumatoid arthritis.
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