The ELISA platform (enzyme-linked immunosorbent assay) has become a tool that is widely used in biological research and medical diagnosis since it was created in the 1970s. An ELISA test kit is a versatile and reliable platform for measuring the presence of many different antibodies in a sample. Since it was created, ELISA has been customized for various applications and improved upon over time.
One important development in the lifecycle of modern ELISA assays is the blocking reaction. When an ELISA assay uses a blocking reaction to help “filter” out unwanted materials and improve the quality of results, the assay is referred to as bELISA or “Blocking Elisa”.
BELISA vs. bELISA: Avoiding Confusion
The blocking ELISA is sometimes confused with a biomimetic enzyme-linked immunoassay, another specialized type of ELISA. This is because biomimetic ELISA is often referred to as BELISA. However, bELISA with a lower-case “b,” refers to an ELISA assay that employs the use of a blocking reaction to improve results:
- BELISA (with upper-case “B”), or biomimetic enzyme-linked immunoassay. A type of ELISA assay that is designed around the use of a biomimetic reaction that mimics natural biological function in some way.
- bELISA (with lower-case “b”), or blocking enzyme-linked immunoassay. An ELISA assay that has as an additional step — a reaction using a blocking buffer, which “filters” unwanted substances that could harm the accuracy and usability of test results.
How Does a Blocking Reaction Improve ELISA Results?
There are many different ways to set up an assay to test for antigens. Despite its broad applications, the standard mechanism of an ELISA is quite simple to follow.
When using a typical ELISA kit, the antigen-containing sample (e.g., blood or plasma) is mixed with a special compound and applied to absorbent test plates. An antibody that binds to the target antigen is then introduced to the test. This antibody is additionally linked to a reporting enzyme. When the antibody binds to the antigen in the blood sample, it carries this reporting enzyme with it. The reporting enzyme reacts to the prepared plates, thereby signaling the presence (or absence) of the target antigen.
A blocking ELISA, or bELISA, adds another step to this reaction-based testing. A “blocking buffer” substance is also added to the process to induce a reaction that will remove the influence of undesirable matter that could otherwise influence or degrade test results.
The particular blocking buffer used can depend on the purpose of the test and the other reagents being used. Each new type of ELISA test kit must be developed to meet its exact application (i.e., to detect a particular antigen), and blocking ELISA is no exception.
Blocking ELISA in Practice
Some recent examples of how blocking reactions have helped make ELISA more effective include:
- A highly sensitive and specific blocking ELISA was developed to help eliminate cross-reactivity when testing populations of rabbits infected with non-pathogenic rabbit calicivirus (RCV-A1). ELISA use for this application had previously been an issue due to antibodies also reacting with rabbit hemorrhagic disease virus (RHDV) in addition to detecting RCV-A1. When the blocking reaction was added, results indicated 100% sensitivity to RCV-A1 with no RHDV cross-reactivity.
- The development of a blocking ELISA test kit for the detection of avian hepatitis E virus has shown impressive results in China. In various tests of infected poultry populations, the blocking ELISA demonstrated sensitivities ranging from around 83% to 98%.
Developing ELISA test kits with advanced blocking functionality has the potential to improve ELISA results across many applications.