ELISA (Enzyme-linked immunosorbent assay)

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ELISA (Enzyme-linked immunosorbent assay)

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A researcher is studying antibody production in response to a novel viral infection among a group of study participants. The researcher performs an enzyme-linked immunosorbent assay with the results detailed below. Which of the following participants has the strongest antibody titers against this particular virus?  


Enzyme-linked immunosorbent assay - or ELISA for short - is a laboratory technique or assay where antibodies or antigens in people’s samples are immobilized in a surface, and then detected by an antibody with an enzyme attached that causes a change of color.

So it’s useful to diagnose infections, such as HIV, hepatitis B, or malaria; and autoimmune diseases, like Graves’ disease, systemic lupus erythematosus, or rheumatoid arthritis, where the body reacts to its own proteins as if they were foreign antigens.

Immune response

We are constantly surrounded by harmful microorganisms called pathogens, that could cause a lot of damage if it wasn’t for the immune system.

These pathogens have unique parts called antigens.

Now, B lymphocytes are cells of the immune system that can detect those antigens and trigger an immune response by secreting lots and lots of antibodies.

These antibodies, also called immunoglobulins or Ig, are Y-shaped proteins that have two regions: the constant fragment region, also called Fc, that determines the antibody class - IgD, IgM, IgG, IgA, or IgE; and two fragment-antigen binding, or Fab regions, that recognize and bind to the antigen in order to inactivate it, preventing the pathogen from reaching its target cell and causing damage.

Principle of ELISA

Now, the basic idea with ELISA is to use that specific link between the antigen and antibody to help diagnose infections or autoimmune diseases.

More specifically, ELISA can be used to look for either the pathogen’s antigens or the antibodies our body secretes against them.


ELISA is a biochemical assay used in immunology to detect the presence of an antigen, antibody, or another protein. It takes its name from the enzyme-linked immunosorbent assay (ELISA).

The basic principle behind ELISA is that if an antigen or antibody is present in a sample, it will bind to a specific antibody or antigen attached to a solid support. The bound antigen or antibody can then be detected using an enzyme-linked secondary antibody that recognizes the primary antibody or antigen. The presence of this enzyme can be detected using various methods depending on the assay format, such as spectrophotometry, fluorimetry, or chemiluminescence. ELISA is a very sensitive assay that can detect minute levels of antigens or antibodies in a sample. It is often used to measure the concentration of proteins in body fluids, such as serum or urine.


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