Immunoglobulin G (IgG) ELISA test

Context:

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

About:

• 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.
• 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 the 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?

• 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.

Why serosurveys?

According to ICMR, serosurveys help to understand the proportion of the population which has been exposed to the SARS-CoV-2 infection including the asymptomatic individuals.