What is the role of an 'antigen' in the immune system?

An antigen plays a crucial role in the immune system as a substance that induces the formation of antibodies. When the body detects an antigen, which can be a part of a pathogen like bacteria or viruses, it triggers the immune response. This response involves the activation of B cells, which are responsible for producing antibodies specifically designed to bind to that antigen. This binding action helps neutralize the pathogen, mark it for destruction by other immune cells, and provide long-term immunity by creating memory cells that "remember" the antigen for future infections.

Other terms in the choices can refer to relevant concepts in immunology or health care, but they do not define the specific function of an antigen as effectively. Immune cells are responsible for responding to antigens, medications for infections do not have the role of inducing antibodies, and methods of disease prevention include vaccination, which introduces antigens to stimulate an immune response. The specific function of an antigen as the initiator of antibody production is essential for understanding how the immune system protects the body from harmful invaders.