What is an antigen?

An antigen is defined as a substance that stimulates an immune response in the body. When introduced into the system, antigens can be recognized by the immune system as foreign or harmful, triggering the production of specific antibodies and the activation of other immune cells to target and eliminate the perceived threat.

This is critical in various biological processes, including the functioning of vaccines, which often contain antigens to prepare the immune system for future encounters with the actual pathogen. Understanding the role of antigens is essential in immunology and helps in developing treatments and preventive measures against diseases.

The other options describe different biological components or functions. Antibodies, minerals, and hormones each have distinct roles in the body but do not define the concept of an antigen. Thus, the correct answer captures the fundamental role of antigens in initiating immune responses.