Antigens

Antigens are molecules or molecular structures that are recognized by the immune system and can trigger an immune response. They are typically found on the surface of pathogens such as bacteria, viruses, fungi, and parasites, but can also be present on allergens, toxins, and even cancer cells.

Types of Antigens

Antigens can be classified into several types based on their origin and the immune response they elicit:

• Exogenous antigens: These are antigens that enter the body from the outside, such as through inhalation, ingestion, or injection. Examples include pollen, food allergens, and vaccines.
• Endogenous antigens: These are antigens that are generated within the body, often as a result of normal cellular processes or infections. Examples include tumor antigens and viral antigens.
• Autoantigens: These are normal proteins or complexes of proteins that are mistakenly targeted by the immune system, leading to autoimmune diseases.

Antigen Presentation

The process by which antigens are presented to the immune system is known as antigen presentation. This involves the processing of antigens by antigen-presenting cells (APCs) such as macrophages, dendritic cells, and B cells. These cells display fragments of the antigen on their surface using major histocompatibility complex (MHC) molecules, which are then recognized by T cells.

Antigen-Antibody Interaction

Antigens are specifically recognized by antibodies, which are produced by B cells. The binding of an antibody to an antigen can neutralize the pathogen, mark it for destruction by other immune cells, or activate the complement system.

Applications

Antigens have several important applications in medicine and research:

• Vaccines: Vaccines often contain antigens that stimulate the immune system to develop immunity against specific pathogens.
• Diagnostic tests: Antigens are used in various diagnostic tests to detect the presence of pathogens or antibodies in a sample.
• Therapeutics: Monoclonal antibodies targeting specific antigens are used in the treatment of diseases such as cancer and autoimmune disorders.

See Also

• Immune system
• Antibody
• Pathogen
• Vaccine
• Autoimmune disease
• Major histocompatibility complex
• Antigen-presenting cell