What is an antigen?

An antigen is defined as a substance that triggers an immune response. This usually occurs when the body recognizes the antigen as foreign or potentially harmful. Antigens can be parts of pathogens like bacteria, viruses, or other substances such as pollen, pet dander, or even transplanted organs. When an antigen enters the body, it prompts the immune system to produce antibodies to combat the invader. This process is essential for the immune system to protect the body against infections and diseases. Understanding the role of antigens is crucial for topics like vaccinations, where a harmless form of an antigen is introduced to help the body learn to recognize and fight off actual infectious agents in the future.