Which statement accurately defines an antigen?

An antigen is accurately defined as a foreign macromolecule that elicits an immune response. Antigens are typically substances that are recognized as non-self by the immune system, triggering the production of antibodies and the activation of immune cells. These foreign macromolecules can include proteins, polysaccharides, lipids, or nucleic acids that are present on the surface of pathogens, such as bacteria and viruses, or other foreign substances.

When the immune system detects an antigen, it responds by producing specific antibodies, which are proteins that can bind to the antigen, marking it for destruction or neutralization. This process is fundamental to the body's defense mechanisms, as it helps identify and eliminate potential threats to health.

In contrast, other options mention different components of the immune system: cells that produce antibodies, types of immune cells, and proteins found within lymph, none of which accurately capture the definition of an antigen. Understanding the role of antigens is essential for comprehending how the immune system operates and responds to infections.