Difference Between Antigen and Antibody

Introduction

Immunity is the response system in the body needed to be prepared to fight against diseases. The body faces various symptoms when the immunity system breaks down. Antigens act as foreign elements in the body that binds with antigens to proceed with the immune response. Antigens and antibodies acts in the body with opposite natures. Sometimes antibodies fail to fight against antigens. As a result, various diseases occur in the body.

What are Antigens?

Antigens are large molecular protein structures located on the surface parts of different pathogens. These pathogens include - viruses, fungi, bacteria, and particles of some other foreign agents. The body’s immune response gets increased with the formation of antibodies while these foreign agents enter the body. If a cold virus enters the body, the immune system generates antibodies to prevent the virus attack. Antigens become more immunogenic if their chemical complexity gets higher. Antigens present themselves to the body as far-off substances. Antigens vary specifically in different species. The main substances in antigens are polysaccharides and proteins.

Information about antibodies

Antibodies are a type of immunoglobulin. They are Y-shaped, big size blood proteins. Plasma cells produce these protein substances. Antibodies bind with the foreign agents named antigens to eliminate them. Each antibody is composed of four subunits of polypeptides.

Antibody, public domain, via Wikimedia Commons

Antigen binding domains are formed by the association of N terminus heavy chains with onelight chain. The formed Y-shaped arms are known as fragment antigen binding domains or FAB domains. The immune reaction occurs while antibodies associate with antigens by binding and grouping process. A couple of antigen-binding sites in identical patterns are present in antibodies.

Classification of antigens

Antigens are classified into different types based on their source.

• Endogenous antigens − Bacterial and viral infection and cellular metabolism can cause the formation of Endogenous antigens inside the body.

• Exogenous antigens − These external antigens make their entry into the body from outside. Aerosols, pollen, and allergen are some types of external antigens.

• Tumour antigens − These antigens are located in tumour cell surfaces. They are antigenic substances. The host’s immune response gets induced by them. A mechanism is developed by tumours for evading the body’s immune system.

• Autoantigens − These are self nucleic acids or proteins with attachment to their own immune systems. This is caused to environmental or genetic alterations resulting in autoimmune diseases.

• Native Antigens − some antigens remain unprocessed by antigen-presenting cells. These are native antigens.

Antigen-antibody binding sites, Creative Commons Attribution-Share Alike 4.0, via Wikimedia Commons Immunogen and hapten are two classes of antigens based on immune response. Immunogens are polysaccharides or proteins. They can self-generate immune response.

Haptens are foreign substances. The immune response of these non-proteins are induced by carrier molecules

Antibody types and their functions

Different types of antibodies and their functions are discussed below.

Type of antibody	Function
IgD	They are found in B cell surfaces. Its functions are not clear exactly. Some experts say B cell activation and maturation is supported by IgD.
IgA	IgA gives protection against inhaled and ingested pathogens. It is found in breast milk, mucus, saliva, intestinal fluid, and tears.
IgG	IgG, the most common antibody covers 70 to 75% of immunoglobulins. It can be found in tissue fluids and blood. It prevents the body from infections caused by viruses and bacteria.
IgE	Mucus membranes, skin and lungs are the main locations of IgE. Histamine and some other chemicals are released in blood by mast cells with the help of IgE antibodies.
IgM	It is found in the lymph system and blood. IgM is a first-line defence providing antibody. It helps in immune regulation.

Antigen and antibody - differences

The main differences between antigens and antibodies are as follows.

Antigens	Antibodies
The body's immune response is triggered by substances called antigens.	Blood proteins that are produced against antigens are known as antibodies (Suurs etal. 2019).
The substance can be nucleic acids, proteins, lipids or carbohydrates.	They are glycoproteins.
These are immunogens.	These are immunoglobulins.
The epitope is their interacting domain with antibodies.	The epitope can be bound by variable sites.
Diseases and allergic reactions are caused by antigens.	They give protection to the body by lysing pathogens and immobilizing antigens.
Main antigen types include endogenous antigens, exogenous antigens, neoantigens, and autoantigens.	The main antibody types are - IgE, IgA, IgG, IgM, and IgD.

Summary

Immune reactions occur in the body by binding two factors. One stays in the body and fights against the others and they are known as antibodies. The factors that try to break the immune system of the body are called antigens. There are significant differences between antigens and antibodies. IgD, IgA, IgG, IgE, and IgM are the main types of antibodies. Endogenous antigens are formed inside the body whereas exogenous antigens make their entry from outside the body. Different allergic reactions and diseases are caused by antigens. Antibody immobilizes antigens to protect the body against diseases.

Frequently Asked Questions (FAQs)

Q1. What is immunity?

Ans. Immunity is a special ability of the body that makes prevention of pathogenic invasion. Pathogens means foreign substances that cause disease. Pathogens like viruses, bacteria, and fungi try to attack the body to destroy the immune system.

Q2. What are the two types of immunity?

Ans. Immunity is of two types - Innate immunity and Acquired immunity. Innate immunity is naturally acquired immunity. This type of immunity transfers genetically and gives lifelong protection. Acquired immunity is the immunity that can be acquired through adaptation. Immunization, antibiotics, vaccination, and other methods are used to initiate body immunity, as the immunity is not inborn.

Q3. What is immunoglobulin?

Ans. Antibodies are generally known as immunoglobulin. White blood cells or plasma cells produce molecules of glycoprotein to form antibodies. They have a critical role in the body's immune response system. They recognize and bind with specific antigens like viruses and bacteria.