In this article, we are going to learn about the basic introduction of antibodies and antigen. We’ll read in detail about their types and other functions in the next articles.

what are antibodies?

Antibodies are proteins that are produced by our immune system against foreign substances (such as bacteria or viruses) known as an antigen. Antibodies are also known as Immunoglobulins. In our body B cell secrete antibodies with antigen-binding sites which are identical to the B-cell membrane antigen receptor. The immunoglobulin domain is generated when a polypeptide chain folds into an organized series of anti-parallel beta-pleated strands. In antibodies, most of the immunoglobulins contain approx. 110 amino acids and each of the Beta sheets contain three to five strands. Molecules of antibody form a ‘Y’ shape structure having two antigen-binding receptors. Each one of the antigen-binding region. Antibodies share a common structure of two light and two heavy chains.

Each light chain in an antibody is bounded to its partner heavy chain by a disulfide bond. There is a Fab region in an antibody known as the Fragment antigen-binding domain.

Every antibody has almost the same (Y shape) structure, but antibodies are classified into five categories: IgG, IgM, IgA, IgD,  IgE. The most common antibody is IgG.

Antigen :

An antigen is a foreign molecule that can stimulate an immune response in our body. An antigen binds to the receptors via covalent bonding interactions.

There are two types of antigens:

• Foreign which comes from outside in our body
• Autoantigen: in this situation, our body is unable to understand/differentiate between self or non-self (foreign particles). Also known as an autoimmune disease.

What is an immunogen?

An immunogen is a specific type of antigen that can provoke an immune response.  The ability of an antigen to provoke an immune response is known as immunogenicity.

Difference between an antigen and antibody

S.N	Antibody	Antigen
1.	Antibodies are proteins.	Antigens are also proteins, sometimes they can be lipids or nucleic acids.
2.	Recognizes the antigen.	Stimulates the immune response.
3.	Originated inside the body.	External factors, sometimes internal (in the case of autoimmune diseases).
4.	The specific binding site is known as a paratope.	The specific binding site is known as Epitope.
5.	Protects our body from different diseases (antigens).	Cause the disease in our body.