We’ve been hearing this word a lot, would rather say more than a lot in this pandemic. So, what is an Antibody, and why the importance of Antibodies is more?. Antibodies are nothing but the warriors inside our body that protect us from intruders (Bacteria and viruses). They have crucial importance. Antibodies are also known as immunoglobulin. In basic terms, Antibodies can be defined as “A protein which is produced by white blood cells to provide immunity against bacteria, viruses, and toxins by neutralizing them.”
Structure of Antibody
So, antibodies are Y-shaped proteins and they are produced by the white blood cell called “B Cell” or “B lymphocyte”. The size of the antibody molecule is 10 nm. These cells are used by our immune system to neutralize viruses and bacteria. It consists of four polypeptides, 1)two heavy chains, and 2)two light chains. Each tip of the antibody has a paratope, in the above diagram you can see paratope a.k.a antigen binding site. The paratope binds to the antigen at the epitope. The epitope is generally an antigenic determinant. Mainly, there are two types of epitopes, one is continuous and the other one is discontinuous. The paratope and the epitope bind with precision. This binding mechanism helps the antibody to negate the target.
The antibodies are classified into five types they are as follows;
IgG (Immunoglobulin G), it is the most common type of antibody. It has two binding sites. IgG molecules are produced by the white blood cells. It represents 75% of serum antibodies in humans and is made of four peptide chains and has a weight of 150 kDa. It has two heavy chains of 50 kDa and two light chains of 25 kDa. The two heavy chains are linked to each other and each heavy chain is linked to the light chain by disulfide bonds. It binds and neutralizes the toxins to protect our bodies from infections. It is also associated with hypersensitivity reactions of type 2 and type 3.
IgE (Immunoglobulin E), this type of antibody is found in mammals. It is incorporated by the plasma cells. IgE levels in the normal individual are 0.05% of Ig concentration. The structure of the antibody is monomeric with two identical heavy chains of epsilon class and two light chains. It is associated with the hypersensitivity reaction of type 1.
IgD (Immunoglobulin D), it is found in the secreted form in the blood serum in a small amount of about 0.25% of total Ig. The structure of the antibody is monomeric with two identical heavy chains of delta class and two light chains. The function of IgD is a mystery since its discovery. In white blood cells, the function of IgD is to activate the B cells so that they can take part in the defense mechanism.
IgM (Immunoglobulin M), this is one of several antibody produce by the vertebrates. It is the largest antibody and it is the first antibody that appears in the response. It has a pentameric structure and they are linked by disulfide linkage using J chain fragments.
IgA (Immunoglobulin A), it plays crucial importance in immune function. It is secreted in the intestinal lumen and represents about 15% of total Ig. It can be produced as dimeric and monomeric. IgA has two subclasses IgA1 and IgA2.
Antibodies play a very important role, they are like the first line of defense, as we all know they are the warriors which protect us from viruses and bacteria. They also provide immunity to the developing fetus. They also facilitate the process of phagocytosis and also offer protection against pathogens. Ig also participates in the immune response. They also play a vital role in hypersensitivity reactions.
How antibody test work?
The check for protein is done through the blood samples, if the protein is present in the blood sample then the specific person was exposed to the virus and the body has developed antibodies against the virus. This test of finding protein in the blood samples is also known as the “Serology Test”. These tests are basically carried out by taking a bit of blood through a finger prick, and later they look for IgM and IgG. During this pandemic as there is a widespread of the coronavirus, It is not possible to detect if the person is suffering from the covid as in some it may show the symptoms and in some, it may not. Hence, it becomes impossible to determine if the person is an active patient of covid. Hence, the antibody tests are carried out and they give accurate results.