Antigen Definition, Structure, 4 Types, Function, and Test

Below, we will explain about Antigen Definition, Structure, 4 Types, Function, Test, and the difference in antigen and antibodies.

Antigen Definition

The antigen is a substance that stimulates the immune response, especially in generating antibodies. The antigen is usually a protein or polysaccharide, but it can also be other molecules, including small molecules (hapten) that combine a protein-carrier or carrier.

The antigen is considered a dangerous foreign object, so the body creates antibodies that will then protect the body.

Antigenic Structure

After knowing the antigen definition, the following is the antigen structure.

Immunogen

This immunogen is a large molecule of an antigen that has the properties of a carrier molecule because it transports a small molecule (hapten) of an antigen. The immunogen can be or can be called by antibodies and also promotes the formation of antibodies (immunogenic)

Hapten

This hapten is a small molecule that has an antigenic content (a carrier molecule) that is tied to a large molecule (Immunogen). But the hapten can not or can spur the production of antibodies when not binds with large molecules so it is called as a non-immunogenic molecule.

Antigen types

Types of antigenic based on determinants

• Univalent determinant is a type of the epitope
• Unideterminan multivalent of the type of one epitope and more than one number,
• Univalent multi-determinants are more than one type of the epitope and one is sum,
• A multivalent multi-determinant is a type of epitope of more than one and its meaning is more than one.

Antigen types based on its specificity

• Heteroantigen, an antigen owned by many species,
• Xenoantigen is an antigen belonging to a certain species,
• Alloantigen which is an antigen owned by one species,
• Antigen specific organs that are antigen owned with a particular organ,
• Autoantigen is an antigen derived from its own body.

Types of Antigen based on its chemical ingredients

• Carbohydrates are immunogenic antigen
• Lipid is an antigen that is not immunogenic but Hapten
• Nucleic acids are not immunogenic antigen
• Proteins are immunogenic antigen.

Antigen types based on dependence on T cells

• Dependent T is an antigen that requires an introduction to T cells and B cell to stimulate antibodies,
• Independent T is an antigen that can stimulate B cell without having to know the T cell first.

Antigen function

• Antigen function is to be used to describe a molecule that can be utilized in spurring process of the immune response is generally known as Immunogen.
• Then used as a way to be able to show a molecule can perform reactions with antibodies or also T cells that have gone through the process of sensitization.
• This epitope is known as determinant is a part of an antigen that has a function to introduce into the process of forming antibodies.
• Paratope which is a part of an antibody that can help to bind to the epitope.

Antigen Test

Antigen tests are tests conducted to detect the presence of antigen in the body. This test can help in the diagnosis of infections or certain other conditions.

Antigen tests can detect antigen from the surface of bacteria or other types of germs. Examples include the feces examination for detecting Helicobacter pylori. These bacteria can cause infections of the stomach and duodenal that cause gastric ulcer or duodenal ulcer.

Antigen and Antibodies

Many people are confused about the difference in antigen and antibodies, because both are indeed closely related.

As already mentioned, antigens are substances that are considered to be foreign or dangerous objects from the body. The presence of this antigen then triggers the response of the body immune system that then produces antibodies.

In general, antigens are distinguished in two, i.e. Foreign antigen or Heteroantigen and Autoantigen. Foreign antigen comes from outside the body, while the Autoantigen is derived from the body.

Examples of foreign antigen are such as viruses, bacteria, toxins, certain proteins from food, and components of serum and red blood cells derived from other individuals. Examples of Autoantigen are thyroglobulin, DNA, corneal tissue, etc.

Antigen induces an immune response, which stimulates lymphocytes to produce antibodies or directly attack antigens that called Immunogen. Immunogen is generally a protein, but it can also be polysaccharides, nucleic acids, or also lipids.

The presence of antigen is not always threatening health, because the body has its own protective system that we call the body immune system. Applying a healthy lifestyle can help maintain the body’s immune system to work properly and protect the body from the antigen.

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