Antigens are large molecules of proteins, present on the surface of the pathogen, like bacteria, fungi viruses, and other foreign particles. When these harmful agents enter the body, it induces an immune reaction within the body for the assembly of antibodies.
For Example: When a standard cold virus enters the body, it causes the body to supply antibodies to stop from getting sick.
Properties of Antigens
The properties of antigens are as follows:
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The antigen should be a far off substance to induce an immune reaction .
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The antigens have a molecular mass of 14,000 – 6,00,000 Da.
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They are mainly proteins and polysaccharides.
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The more chemically complex they are, the more immunogenic they will be.
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Antigens are species-specific.
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Age influences immunogenicity. Very young and really old people exhibit very low immunogenicity.
Types of Antigens
On the Basis of Origin
There are different types of antigens on the idea of origin:
Exogenous Antigens
These are the antigens that have entered the body from outside, for example, inhalation, injection, etc. These are the foremost common sorts of antigens and include pollens and food that cause allergies.
Endogenous Antigens
Endogenous antigens are people who are generated within the traditional cells thanks to viral or intracellular bacterial infections.
Autoantigens
Autoantigens are normal proteins or a posh of proteins or macromolecules that’s attacked by a system causing autoimmune diseases.
Tumour Antigens
It is an antigenic substance produced in tumour cells that induces an immune reaction within the host. These are presented by MHC-I and MHC-II on the surface of tumour cells.
Native Antigens
A native antigen is the one that’s not processed by an antigen-presenting cell.
On the Basis of Immune Response
On the idea of the immune reaction , antigens are often classified as:
Immunogen
These could also be proteins or polysaccharides and may generate an immune reaction on their own.
Hapten
These are non-protein, foreign substances that need a carrier molecule to induce an immune reaction .
Antibodies aren’t found at an area intrinsically, but whenever our system encounters antigen of a pathogen, B cells get activated immediately releasing antibodies into the bloodstream. These immunoglobulins undergo mitosis leading to cellular division and continuously produce antibodies as a result of producing more cells. These antibodies remain within the blood for a few times but B cells remember these antigens and repeat an equivalent course of action whenever they reappear in our body.
What are Antibodies?
Antibody (Ab) is also known as an immunoglobulin(Ig). These are big in size, Y-shaped blood proteins produced by plasma cells. They bind to foreign particles and invade them. Antigens are foreign pathogens that invade the body and have the potential to offer rise to a response from our immunity system either by grouping up with a bigger molecule or alone after binding with antibodies for a specific immune reaction. Hence, antigens stimulate the assembly of antibodies by the system.
Antibody Structure
An antibody structure consists of a Y-shaped molecule composed of 4 polypeptide subunits. The N-terminus of the heavy chains associates with one of the light chains and forms two antigen binding domains. These form the arms of the “Y” shape and are referred to as fragment antigen binding (Fab) domains. It helps within the antibody’s interaction with the effector cells.
All four polypeptide subunits are held together by disulfide and non-covalent bonds.
The large chains of the antibodies contain a variable region and three constant regions. Each antibody has two identical antigen-binding sites and they differ within the antibodies.
Difference Between Antigen and Antibody
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Antigen |
Antibody |
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Also called Immunogens |
Also called Immunoglobulins |
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Antigens are usually lipids. However, they can also be proteins, carbohydrates, and nucleic acids |
All antibodies are proteins |
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Antigens cause allergic reactions or even illnesses |
Protects against the effects of the antigen either by lysis or immobilization of the particle |
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Epitopes are regions of the antigen where interacts with the antibodies |
Paratopes are variable regions of an antibody that binds to an epitope. |
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Antigens have origins outside the body |
Antibodies always originate within the body |