What does the term "antigens" refer to in the context of the immune response?

In the context of the immune response, "antigens" refer specifically to foreign substances that provoke an immune response. These substances can include a range of materials, such as bacteria, viruses, toxins, or any other agents that the body identifies as non-self. When the immune system encounters these antigens, it initiates a response to neutralize or eliminate them, often through the action of specialized cells and antibodies.

Understanding the role of antigens is crucial in immunology, as they are the targets of the immune system that elicit a defensive reaction. The recognition of antigens by immune cells leads to the activation of various immune pathways, which can include the production of antibodies and the mobilization of immune cells to attack and destroy the foreign invaders.

The other choices describe elements that are related to the immune system or body responses but do not accurately represent what an antigen is. Proteins produced by the body are not classified as antigens unless they are part of a response to a foreign substance. Cells that repair tissue damage pertain to healing mechanisms rather than the immune response itself. Lastly, chemicals released during inflammation are part of the immune response but are not considered antigens.