We’ve been hearing this word a lot in this pandemic. So, what is an Antibody and why it has so much importance?. Antibodies are nothing but the warriors inside our body which protect us from the intruders (Bacteria and viruses). They have a crucial importance. Antibodies are also known as immunoglobulin. Antibodies can be defined as “A protein produced by white blood cells to provide immunity against bacteria, viruses and toxins by neutralizing them.”
Structure of Antibody
So, antibodies are Y-shaped protein and they are produced by the white blood cell called “B Cell” or “B lymphocyte”. Size of antibody molecule is 10 nm. These cells are used by our immune system to neutralize virus and bacteria. It consists of four polypeptides, two heavy chains and 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 epitope. Epitope is also known as antigenic determinant. Basically there are two types of epitopes, continuous and discontinuous. The paratope and the epitope bind with precision. This binding mechanism helps the antibody to neutralize the target.
The antibodies are classified into five types they are as follows;
IgG (Immunoglobulin G), it is the most common type of the 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 light chain by disulfide bonds. It binds and neutralizes the toxins to protect our body 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 antibody is monomeric with two identical heavy chains of epsilon class and two light chains. It is associated with hypersensitivity reaction of type 1.
IgD (Immunoglobulin D), it is found in the secreted form in the blood serum in small amount 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 which appears in the response. It has pentameric structure and they are linked by disulfide linkage using J chain fragments.
IgA (Immunoglobulin A), it plays crucial importance in the immune function. It is secreted in the intestinal lumen and it represents about 15% of total Ig. It can be produced as monomeric and dimeric. IgA has two subclasses IgA1 and IgA2.
Antibodies play a very important role, they are like first line of defense, as we all know they are the warriors which protect us from the viruses and bacteria. They also provide immunity to the developing fetus. They also facilitate the process of phagocytosis and also offer protection against the pathogens. Ig also participate 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 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 is also called as “Serology Test”. This 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 wide spread of the corona virus, 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 active patient of covid. Hence, the antibody tests are carried out which give accurate results.