What term is used for any foreign particle that invades the body?

The term that is used for any foreign particle that invades the body is "antigen." Antigens are substances that the immune system recognizes as foreign and can provoke an immune response. They can be found on the surfaces of pathogens such as bacteria and viruses, but they can also include toxins, foreign proteins, and other molecules that do not originate within the body.

Antigens serve a critical role in the immune response by triggering the production of antibodies, which are proteins that specifically target and neutralize those foreign invaders. This interaction is fundamental to how the immune system identifies and eliminates threats to the body's health.

Understanding antigens is essential for grasping broader concepts in immunology, such as vaccination, where a harmless form of an antigen is introduced to the body to help it develop immunity against a disease. This knowledge also informs medical practices and approaches to treating infections and autoimmune diseases, as understanding how antigens interact with the immune system is vital for developing effective treatments.