What are antibodies and antigens?

 

An antigen is a molecule capable of stimulating an immune response. They may be proteins, polysaccharides, lipids or nucleic acids. Each antigen has distinct surface features that are recognized by the immune system.


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An antibody test reveals if a person has already been exposed to an infection, by detecting antibodies in their blood or serum. This can be done by a laboratory-based test such as an ELISA (enzyme-linked immunosorbent assay) or CIA (chemiluminescent immunoassay), or a point-of-care test based on lateral flow technology.
Antibody tests are not usually used to diagnose current infection as it takes the body some time to produce antibodies. During the period before the adaptive immune system kicks in, the fast-acting and non-specific innate immune response combats infection.
Data suggests that in the case of SARS-CoV-2, the IgM antibody response peaks around two weeks after infection, followed by the IgG antibody peak at three weeks.


What is an antibody test?


An antibody test reveals if a person has already been exposed to an infection, by detecting antibodies in their blood or serum. This can be done by a laboratory-based test such as an ELISA (enzyme-linked immunosorbent assay) or CIA (chemiluminescent immunoassay), or a point-of-care test based on lateral flow technology.
Antibody tests are not usually used to diagnose current infection as it takes the body some time to produce antibodies. During the period before the adaptive immune system kicks in, the fast-acting and non-specific innate immune response combats infection.
Data suggests that in the case of SARS-CoV-2, the IgM antibody response peaks around two weeks after infection, followed by the IgG antibody peak at three weeks.

What can antibody tests tell us


Antibody tests can help us to track the spread of disease, giving a more accurate representation of the COVID-19 pandemic. They can help to estimate how many people have already been infected with SARS-CoV-2, which can be important in assessing herd immunity.
A test which can distinguish between IgM and IgG could give information about the phase of infection, indicating how long ago the person was infected with SARS-CoV-2.
They could also help to identify those who should be prioritized for vaccinations when they become available, as well as potential donors for convalescent plasma therapy.