Antigen definition
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Understanding Antigens: Definition and Immune Response
What is an Antigen?
An antigen is a molecule that can be recognized by the immune system, particularly by antibodies. These molecules can be proteins, polysaccharides, pesticides, antibiotics, toxins, and hormones, among others . However, not all antigens can stimulate the immune system to generate antibodies. Those that do are specifically termed immunogens .
Antigenic Properties and Immune Response
To induce an immune response, an antigen must be perceived as foreign by the immune system of the organism. This foreignness is a fundamental concept in immunology, as the immune system typically does not react against the body's own substances . When an antigen provokes a specific immune response, it is called an immunogen. The immune response involves the production of antibodies or the activation of antigen-reactive cells .
Types of Antigens
Antigens can be classified based on their origin and the type of immune response they elicit:
- Proteins and Polysaccharides: These are the most common natural macromolecules investigated as antigens. They include glycoproteins, nucleoproteins, lipoproteins, peptidoglycans, and glycolipids .
- Haptens: These are small molecules that are not immunogenic by themselves but can become immunogenic when attached to larger carrier molecules .
- Superantigens: These are a group of microbial antigens that can cause an extensive immune response by interacting with a large number of T-cells. Examples include certain bacterial, mycoplasmal, and viral proteins .
Antigen-Antibody Interaction
The interaction between an antigen and an antibody is a specific chemical reaction that forms the basis of the immune response. This interaction is highly specific, with antibodies binding to particular structures on the antigen known as epitopes . The antigen-antibody complex is then transported to cellular systems where it can be destroyed or deactivated, protecting the body from foreign molecules such as pathogens and their toxins .
Role in Vaccine Development
Antigens play a crucial role in vaccine development. Protective antigens are those that can invoke a specific and enhanced adaptive immune response upon subsequent exposure to the pathogen. Identifying these antigens is essential for creating effective vaccines . Modern techniques like Reverse Vaccinology use computational methods to predict protective antigens, making the process more efficient and less reliant on traditional laboratory experiments .
Conclusion
Antigens are vital components of the immune system's ability to recognize and respond to foreign substances. They can be proteins, polysaccharides, or other molecules that, when recognized as foreign, trigger an immune response. Understanding the nature and function of antigens is essential for advancements in immunology, vaccine development, and therapeutic interventions.
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