Immunoglobulin G (IgG) ELISA test

The Indian Council of Medical Research (ICMR) has advised states to conduct ‘sero survey’ to measure the coronavirus exposure in a population by using the Immunoglobulin G (IgG) ELISA test.

• Immunoglobulins, also known as antibodies, are glycoprotein molecules produced by plasma cells (white blood cells).
• They act as a critical part of the immune response by specifically recognizing and binding to particular antigens, such as bacteria or viruses, and aiding in their destruction.
• The body makes different antibodies, or immunoglobulins, to fight different things. For example, the antibody for chickenpoxisn't the same as the antibody for mononucleosis.
• Sometimes, the body may even mistakenly make antibodies against itself, treating healthy organs and tissues like foreign invaders. This is called an autoimmune disease.

The types of antibodies are:

• Immunoglobulin A (IgA):It is found in the linings of the respiratory tract and digestive system, as well as in saliva (spit), tears, and breast milk.
• Immunoglobulin G (IgG):This is the most common antibody. It's in blood and other body fluids, and protects against bacterial and viral infections. IgG can take time to form after an infection or immunization.
• Immunoglobulin M (IgM):Found mainly in blood and lymph fluid, this is the first antibody the body makes when it fights a new infection.
• Immunoglobulin E (IgE):Normally found in small amounts in the blood. There may be higher amounts when the body overreacts to allergens or is fighting an infection from a parasite.
• Immunoglobulin D (IgD):This is the least understood antibody, with only small amounts in the blood.

What is an ELISA test?

• Enzyme-Linked Immunosorbent Assays (ELISAs) are the most widely used type of assay. They have evolved from viral lysate tests to tests containing recombinant protein and synthetic peptide antigens
• ELISAs are designed specifically for screening large numbers of specimens at a time, making them suitable for use in surveillance and centralized blood transfusion services.
• It is an IgG Elisa-based test. This means that the test will be done to detect the Immunoglobulin G (IgG) antibody.
• The body produces Immunoglobulin M (IgM) and IgG antibodies to fight against a pathogen.
  • The IgM antibodies are produced in four-seven days after pathogens enter the body
  • The IgG antibodies are produced between 10-14 days of the pathogen's appearance.
• If the IgG antibody is detected, it can be concluded that the person was exposed to SARS-CoV-2.
• Those who test positive using these tests are usually tested with RT-PCR tests. RT-PCR tests are considered as the gold standard for confirming the presence of SARS-CoV-2.
• RT-PCR is a time consuming, lab-based test and involves the collection of throat and nasal swabs and is not a blood-based test.

Why sero-surveys?

• According to ICMR, sero-surveys help to understand the proportion of population which has been exposed to the SARS-CoV-2 infection including the asymptomatic individuals.
• Depending upon the level of sero-prevalence of infection, proper public health intervention steps can be implemented, which will lead to the prevention and control of the infection.
• Sero-surveys are conducted using IgG ELISA test. The purpose of the test is to detect the presence of IgG antibodies in an individual, which represents a possible exposure to the COVID-19 infection. The immune system of a human body starts developing IgG antibodies after getting exposed to SARS-CoV-2.