1. Definition
Antigen is a molecule that triggers an immune response by causing the body to produce antibodies against the epitope, often in response to pathogens such as bacteria or viruses.
2. Classification
- Exogenous antigens: Enter the body from outside (e.g., bacteria, viruses, pollen).
- Endogenous antigens: Produced within cells (e.g., virus-infected cells).
- Autoantigens: Normal body components that are mistakenly attacked by the immune system (in autoimmune diseases).
3. Reactions
Antigens bind to immune cells, resulting in the activation of B cells and T cells.
- B cells produce specific antibodies to neutralize the antigen.
- T cells destroy infected or abnormal cells, orchestrating an immune response.