What is Covid-19 Antigen & Antibody

Antigens are molecules capable of stimulating an immune response. Each antigen has distinct surface features, or epitopes, resulting in specific responses.

Antibodies (immunoglobins) are Y-shaped proteins produced by B cells of the immune system in response to exposure to antigens. Each antibody contains a paratope that recognizes a specific epitope on an antigen. Therefore it acts like a lock and key-binding mechanism.  This binding helps to eliminate antigens from the body, by direct neutralization or by ‘tagging’ for other arms of the immune system.

	Antigen	Antibody
Overview	Substances that can induce an immune response	Proteins that recognize and bind to antigens
Molecule Type	Proteins, may also be polysaccharides, lipids, or nucleic acids	Proteins
Origin	Within the body or externally	Within the body
Specific binding site	Epitope	Paratope

Purpose of Covid-19 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 combat infection. A negative test result may occur if the test is taken too soon after infection before antibodies have been produced by the body. False positive test results could also occur due to cross-reactivity.

Antibody tests are useful to help track the spread of a disease, identify those who should be prioritized for vaccinations, and highlight potential donors for convalescent plasma therapy.

Purpose of Covid-19 Antigen Test

An antigen test reveals if a person is currently infected with a pathogen. Once the infection has gone, the antigen disappears.

Unlike nucleic acid-based tests such as PCR, which detect the presence of genetic material, antigen tests detect proteins, such as those found on the surface of a virus. Accuracy can be a problem, with antigen tests typically having a much lower sensitivity than PCR.

However, they usually provide test results rapidly, are relatively cheap, and can be more amenable to point-of-care use, which could make them more suitable for testing in the community and in remote regions.

Why a Covid-19 Antibody Test

Antibody tests play an important role throughout the patient care pathway and are vital for the management and surveillance of the virus. They are critical in determining the full scope of the disease, combating the pandemic, and rebuilding public confidence. Antibody tests can be used for the following:

• As an adjunct to PCR tests to aid in clinical assessment
• To help determine prior exposure to the virus, by detecting antibodies that may neutralize the virus
• To identify potential donors of convalescent plasma
• For epidemiological purposes including establishing the prevalence of disease in populations
• May help verify the effectiveness of vaccines as they become available

Specificity in Covid-19 Testing

When an individual is infected with the SARS-CoV-2 virus, unique antibodies will develop at different stages of the infection.

Invitroal Biotech’s Covid-19 Antibody Self-test Kit detects both antibodies (IgM and IgG) that are present during current infection or early during the immune response. SARS-CoV-2 IgG antibody tests specifically detect IgG antibodies that persist and are the basis for an individual’s longer-term immune response.

A robust portfolio of reliable antibody tests to detect neutralizing antibodies

We offer the SARS-CoV-2 RBD Protein IgG Detection Kit (Colloidal Gold-Based) and the Covid-19 Antibody Self-test Kit(Colloidal God-Based) for the qualitative and quantitative detection of neutralizing antibodies to the SARS-CoV-2 virus. This allows clinicians to be able to assess and track patients’ neutralizing antibody levels. The detection of neutralizing antibodies is critical for potential convalescent donor identification as well as determining vaccine efficacy and monitoring post vaccination antibody titers in the future. 

Comparison of numerical results will help determine how the immune response develops in an individual and persists over time. The combination of these assays provides a more complete picture of a patient’s serological status for the most accurate results throughout his or her continuum of care.

Neutralizing Antibodies: Why the Spike Protein?

We selected the receptor-binding domain (RBD) of the S1 spike antigen to detect antibodies that block the virus entry into the cells. This selection is aligned with the multiple vaccines that target or include the SARS-CoV-2 S1 RBD, with the goal of producing protective antibody.

Our SARS-CoV-2 RBD Protein IgG Detection Kit detects antibodies to the S1 RBD antigen. S1 RBD antibodies are relevant to vaccines incorporating this immunodominant region with the goal to elicit neutralizing (and therefore likely protective) antibodies in vaccinated subjects. The spike protein and particularly the RBD are the most common target of vaccine designs.