antigens and immunology - Overview, Structure, Properties & Uses

Antigen and Immunology: Definition, Properties, Types, Structure, Function

Edited By Irshad Anwar | Updated on Jul 23, 2024 06:00 PM IST

Antigen Definition

An antigen is a molecule that initiates the production of an antibody to help our immune system be prepared against invaders and causes an immune response.

What is an Antigen?

Antigens are the key players in the amazing world of immunology. In this article, we take in the nitty-gritty definition of antigens and move further to uncover how critical their role is in the immune system and how extensively antigen triggers an immune response. Learn how antigens were first identified and gain a synopsis of what will be covered in this piece.

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Antigen Definition
What is an Antigen?
Properties of Antigens
Types of Antigens based on Origin
Type of Antigen on the Basis of Immune Response
Structure of Antigens
How Antigens Work
Functions of Antigens
Antigens and the Immune System
Antigens in Diseases
Recommended Video On Antigen
Applications of Antigens
Conclusion

Antigen and Immunology: Definition, Properties, Types, Structure, Function

Ranging from historical background to how antigens work with antibodies, this article has you covered. Be it an experienced immunology fanatic or a beginner, this article will offer you real insights into the massive world of antigens and their role in our immune systems.

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Properties of Antigens

Antigens are substances that are so important because they help our immune system be prepared against invaders.

Property	Description
Immunogenicity	The property of an antigen by which it can stimulate an immune response.
Antigenicity	The ability of an antigen to combine specifically with the products of the immune response (for example, antibodies or T-cell receptors).
Molecular Size	Larger molecules are, in general, more immunogenic than smaller ones.
Complexity	More complex molecules, such as proteins, are more likely to be antigenic than simpler ones.
Degradability	The immunogenicity of an antigen reflects its capacity to be processed by the immune system and affects how well it can be presented to the immune cells.

Immunogenicity is one of the most remarkable properties of antigens, which cause an immune response. Thus, upon entry of antigens into the host, immune cells are activated to produce antibodies or are triggered by the T-cell receptor, leading to subsequent reactions that eventually kill the invader.
Another important characteristic of antigens is antigenicity, which is the ability of an antigen to combine specifically with the binding products of the immune response. This characteristic of antigens gives them the ability to specifically bond with antibodies or T-cell receptors to enable specific targeting. This leads to the need for such specificity, and it also means that our immune system will not attack our cell types.
The immunogenicity of an antigen is also determined by its degree of foreignness. Antigens that differ from our native molecules to a greater extent are more likely to induce a strong immune response.
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Generally, the molecular size and complexity of antigens also have a bearing on their immunogenicity. Usually, large molecules are more immunogenic since they provide a bigger surface area for the interaction with immune cells. Similarly, complex structures, such as proteins, are more likely to be antigenic and elicit a robust immune response.
The final property, which is very important for immune recognition of antigens, is their degradability. In most cases, antigens ought to be processed so that they can be presented to other immune cells, especially T-cells. This is important because it stimulates a coordinated immune response against the antigen.

Types of Antigens based on Origin

Antigens have diverse types, depending on their sources, each possessing very unique characteristics.

Exogenous Antigens

These antigens are those which originate outside of the body and can be found in things such as bacteria, viruses, and allergens. They enter our bodies through different means such as inhalation and ingestion. Examples of exogenous antigens are pollen, dust mites, and the flu virus. As soon as these antigens enter the system, our immune system reacts and eliminates them, as these foreign substances seem to be unknown and may harm our system.

Endogenous Antigens

These are antigens that are produced within the body's cells. Derived from normal cellular proteins, they will be changed or degraded due to infection or cellular damage. The immune system will become aware of the changed protein as a foreign one and immune responses will be activated to get rid of infected cells that contain the modified protein. For example, a classic example of an endogenous antigen is a viral protein expressed on the surface of infected cells, but alternatively, a cancer cell can display its abnormal protein as antigen in a way that elicits an immune response.

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Autoantigens

These are normal cellular protein antigens derived from normal cellular proteins that our immune system identifies as foreign and mounts an immune response against, for some reason. These may be causing autoimmune disease responses, where the immune system of one's body attacks its tissues and organs. Examples of autoantigens include insulin in Type 1 diabetes and thyroid-stimulating hormone receptors in Graves' disease.

Neoantigens

These are newly formed antigens formed because of genetic changes or mutations. In most cases, those antigens are common among cancer cells and, therefore, may serve as therapeutic targets. These antigens can only be found in an individual's tumour and can be identified by the immune system as foreign targets in the specific destruction of the cancer cells.

Type of Antigen on the Basis of Immune Response

Antigens possess this unique quality of triggering an immune response, so they initiate the production of antibodies, which protect our body from harmful invaders. Depending on the type of immune response elicited, there are different categories of antigens.

Complete Antigen

They are also known as immunogens. It can induce an immune response. These antigens can be found in pathogen-associated molecules, such as the proteins in bacteria or viruses.

Incomplete Antigens

They are also known as haptens. The antigens are too small to carry an immune response by themselves and need to be conjugated with a carrier protein to be able to carry an immune response. Incomplete antigens are usually small molecules, such as penicillin. When it enters our body, it has to bind to a carrier protein to be recognised by our immune system.

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Structure of Antigens

Epitopes, also known as antigenic determinants, are antigen components. Every antigen contains several epitopes.

Molecular Structure

Normally, antigens are proteins, polysaccharides, lipids, or nucleic acids. Their complex molecular architecture allows them to be recognised as non-self.

Epitope Explanation

An epitope, otherwise known as an antigenic determinant, is the portion of an antigen that binds to a particular antibody. An antigen possesses more than one epitope, which presents a diversified type of immune response.

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How Antigens Work

The interaction of antigen with immune system are explain below in detail:

Interaction with the Immune System

The antigens interact with the immune system by binding to its specific receptors on the immune cells, and that binding would trigger a cascade of immune responses in regards to a pathogen's neutralisation.

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Role in Triggering Immune Responses

Whenever there is contact with an antigen, the immune system activates lymphocytes. B-cells produce antibodies, while T-cells attack infected cells by orchestrating combined defence.

Antigen-Antibody Interaction

The competition for antigen binding is also a major feature of the humoral responses. This is where antibodies produced exclusively by B-cells bind to antigens, neutralising them with high specificity and marking them to be destroyed by other immune cells.

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Functions of Antigens

Inducing Immune Responses

The antigen is important in the induction of both innate and adaptive immune responses, protecting the host from infection.

Vaccine Development

Vaccines use inactivated or weakened antigens to stimulate the immune system with the help of immunity, not causing disease.

Role in Hypersensitivity Reactions

At times, antigens cause hypersensitivity reactions, such as allergies and autoimmune diseases, wherein the immune system reacts too much.

Antigens and the Immune System

Role in Innate Immunity

It is just in innate immunity that antigens are seen as a result of this recognition by PRRs on the surface of immune cells, and an immediate but non-specific response is induced.

Role in Adaptive Immunity

Adaptive immunity is the specific recognition of antigens by B-cells and T-cells, which results in a targeted and long-lasting immune response.

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Antigens in Diseases

Role in Autoimmune Diseases

It is characterised by the immune system attacking self-antigens. This causes damage to tissues.

Role in Infections

Antigens from pathogens such as bacteria and viruses trigger immune responses to fight infections.

Tumour Antigens in Cancer

Tumour antigens are abnormal proteins expressed by cancer cells, and they can be targeted by the immune system for cancer therapy.

Examples of Diseases Involving Antigens

HIV/AIDS: The virus contains antigens that are targeted by the immune system.
Rheumatoid Arthritis: Autoantigens trigger immune responses against joint tissues.

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Applications of Antigens

Diagnostic Tools

Antigens find application/purpose in diagnostic tests such as the ELISA test to check for the presence of antibodies against a given sample.

Therapeutic Applications

Antigen-based therapies include vaccines and monoclonal antibodies for the treatment of infections and cancer.

Use in Research and Biotechnology

Antigens find wide application in research labs in studies of the immune response and construction of new treatments.

Example: ELISA Test

The ELISA test detects specific antigens or antibodies in a sample; it is the assay widely used for diagnosing diseases like HIV and COVID-19.

Conclusion

The understanding of antigens and their structure, activity, and position in the immune system will pave the way for the development of medical science. In other words, improved knowledge and awareness of antigens would lead to disease prevention, diagnosis, and better treatment.

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Frequently Asked Questions (FAQs)

1. What are antigens, and what is their importance?

Antigens are molecules that can trigger an immune response, which is important for the body to recognize pathogens and initiate defence.

2. What is Immunization?

The process of immunizing a person involves triggering their immune system, usually through the administration of a vaccine. This procedure aids in a person's defense against a subsequent infection or terrible disease.

3. What is Immunology?

Biology's field of immunology focuses on the study of the immune system in humans, including the different types of immune systems, their functions, and how the body defends itself from infectious diseases brought on by microorganisms and other infectious agents.

4. What substances constitute antigens?

Antigens typically contain proteins, peptides, and polysaccharides.

5. What size does an antigen have?

Vaccines against viral or protein subunit antigens are the smallest (10 nm).

6. What antigen is the most significant?

RhD is the most significant Rh antigen. when RhD is visible on the surface of red cells

7. What is the difference between endogenous and exogenous antigens?

Those antigens that are formed within the body are endogenous antigens. In contrast, those antigens that enter the body from the external environment through infection or some other means are called exogenous antigens.

8. How do antigens contribute to the occurrence of autoimmune diseases?

Autoantigens are normally body proteins that are mistakenly identified by the immune system, which identifies them as if they were foreign antigens, thus leading to the production of any autoimmune response.

9. What is the role of antigens in vaccination?

Antigens present in the vaccines trigger an immune response in the host, whereby the host produces antibodies to the disease and develops immunity to that particular disease.

10. Are antigens useful in cancer therapy?

Yes, tumour antigens are being increasingly recognised and used in immunotherapy for the immune system to kill the cancer cells expressing these antigens.