What is an Antigen?
“An antigen is a molecule that initiates the production of an antibody and causes an immune response.”
Antigens are large molecules of proteins, present on the surface of the pathogen- such as bacteria, fungi viruses, and other foreign particles. When these harmful agents enter the body, it induces an immune response in the body for the production of antibodies.
For example: When a common cold virus enters the body, it causes the body to produce antibodies to prevent from getting sick.
Also Read: Difference between B cells and T cells
Properties of Antigens
The properties of antigens are as follows:
- The antigen should be a foreign substance to induce an immune response.
- The antigens have a molecular mass of 14,000 to 6,00,000 Da.
- They are mainly proteins and polysaccharides.
- The more chemically complex they are, the more immunogenic they will be.
- Antigens are species-specific.
- The age influences the immunogenicity. Very young and very old people exhibit very low immunogenicity.
Also Read: Role of Antibodies
Types of Antigens
On the basis of Origin
There are different types of antigens on the basis of origin:
Exogenous antigens are the antigens that have entered the body from outside, for eg., inhalation, injection, etc. These are the most common kinds of antigens and include pollens and food that cause allergies.
Endogenous antigens are those that have been generated within the normal cells due to viral or intracellular bacterial infections.
Autoantigens are normal proteins or a complex of proteins or nucleic acid that is attacked by an immune system causing autoimmune diseases.
It is an antigenic substance produced in tumour cells that induces an immune response in the host. These are presented by MHC-I and MHC-II on the surface of tumour cells.
A native antigen is the one that is not processed by an antigen-presenting cell.
On the Basis of Immune Response
On the basis of the immune response, antigens can be classified as:
These may be proteins or polysaccharides and can generate an immune response on their own.
These are non-protein, foreign substances that require a carrier molecule to induce an immune response.
Also Read: Immunity
Structure of Antigens
The epitopes or antigenic determinants are the components of antigen. Every antigen has several epitopes. An antibody has atleast two binding sites that can bind to specific epitopes on antigens.
The antigens combine with the antibody according to the lock and key mechanism.
The ability of the body to act against the disease-causing agents and antigens by the immune system is termed as the immunity. This immunity may be either inborn or acquired from vaccinations.
Also Read: Human Diseases
Let us explore more about antigens, its definition, types, structure and properties by referring to the BYJU’S website.
Frequently Asked Questions
What are antigens?
Antigens are molecules that trigger the production of antibodies by inducing an immune response.
What is Immunization?
Immunization is the process of activating the person’s immune system, typically by the administration of a vaccine. This process helps an individual to protect against subsequent infection or dreadful disease.
What is Immunology?
Immunology is a branch of biology, which mainly deals with the study about the human immune system, types of the immune system, its functions and how our body protects itself against infectious diseases caused by microorganisms and infectious agents.
What are the different types of Immunity?
There are two major types of immunity:
- Innate immunity — It is also called as the natural immunity, as it is inherited from the parents to their young ones and protects from birth throughout life.
- Acquired immunity– It is also called as the adaptive immunity, as it is acquired after the birth in the form of vaccination, antibiotics, Immunization, etc.