What are antibodies & how they fight the diseases?

Antibodies, also known as immunoglobulins, play a key role in the immune system. They are involved in the process of getting rid of the invaders that may cause harm or infection.

Defining antibodies

It is a Y-shaped structure which consists of four polypeptides — two heavy chains and two light chains. This structure allows antibody molecules to carry out their dual functions: antigen binding and biological activity mediation. When an intruder enters the body, the immune system springs into action. These invaders, which are called antigens, can be viruses, bacteria, or other chemicals. When an antigen is found in the body, the immune system will create antibodies to mark the antigen for the body to destroy. In this article, 3MEDS, the best online chemist shop, discusses on how antibodies work and the different kinds of antibodies.

Function of Antibodies

The antibodies are like the immune system's scouts. Each antibody is made for one and only one antigen, and it's fitted with special receptors that will only bind to that antigen. It’s done by finding an antigen, stick to them, and identify for the immune system the exact type of antigen, leading to its destruction.

In other words, when an antigen tries to enter the body, the immune system is triggered. Chemical signals are sent to alert all the different parts of the immune system into action.

First, the virus is met by a type of cell called B cells. The B cells are responsible for creating antibodies to match the antigen. Remember, each type of antibody matches to only one antigen. After the B cells have created their antibodies, the antibodies stick to the virus, marking it for the next round of attack. T cells are then ordered to attack the antigen that the antibodies have marked for it.

After the antigen has been destroyed, the clean-up crew comes along. A wave of phagocytes, large cells that can consume foreign matter, eats the remains of the infection.

Structure of Antibodies

Different parts of the antibody are fragment antigen-binding (Fab fragment) and fragment crystallisable region (Fc region), which carry out specific functions.

Fab fragment is a region on an antibody that binds to antigens. It is composed of one constant and one variable domain of each of the heavy and the light chain. These domains shape the paratope — the antigen-binding site — at the amino terminal end of the monomer.

Fc region is the tail region of an antibody that interacts with cell surface receptors called Fc receptors and some proteins of the complement system. This property allows antibodies to activate the immune system. The Fc regions of immunoglobulin Gs bear a highly conserved N-glycosylation site.

Types of Antibodies

IgG, IgM, IgA, IgE and IgD, are five immunoglobulin classes of antibody molecules found in serum. They are distinguished by the type of heavy chain they contain. 3MEDS, the best online pharmacy store in India, explains further the structure and function of the different antibodies.

1.      IgG antibody

Immunoglobulin G (IgG) antibodies are large globular proteins with a molecular weight of about 150 kDa made of four peptide chains. It provides long term protection because it persists for months and years after the presence of the antigen that has triggered their production. Also, protects against bacteria, viruses, neutralises bacterial toxins, triggers complement protein systems and binds antigens to enhance the effectiveness of phagocytosis.

2.      IgM antibody

Immunoglobulin M (IgM) antibodies are constructed of five or six units, which are each comprised of two heavy-chains (μ-chains) and two light chains, bound together by disulfide bonds and a so-called J-chain. It is involved in the ABO blood group antigens on the surface of RBCs. Also, enhances ingestions of cells by phagocytosis.

3.      IgA antibody

Immunoglobulin A (IgA) antibodies consist of heavy (H) and light (L) chains. Iy,s main function is to bind antigens on microbes before they invade tissues. And, it aggregates the antigens and keeps them in the secretions so when the secretion is expelled, so is the antigen. IgA is also first defence for mucosal surfaces such as the intestines, nose, and lungs.

4.      IgE antibody

Immunoglobulin E (IgE) antibodies have only been found in mammals and are synthesised by plasma cells. Monomers of IgE consist of two heavy chains (ε chain) and two light chains. It binds to mast cells and basophils which participate in the immune response.

5.      IgD antibody structure and function

Immunoglobulin D (IgD) antibodies are expressed in the plasma membranes of immature B-lymphocytes. It is also produced in a secreted form that is found in small amounts in blood serum. And, plays a role in the induction of antibody production too.

Ending note

Antibody is a protective protein present in the immune system, when a foreign substance called an antigen invades the body. As a response, antibodies function to destroy invaders, be it bacteria, virus or any microbial matter.