Final answer:
An antigen is a foreign macromolecule that can provoke an immune system response by forming antibodies. Not all antigens cause a response, due to immune tolerance. Antigens contain epitopes that are specifically recognized by immune cells.
Step-by-step explanation:
An antigen is a molecule that the immune system identifies as either self or non-self. If identified as non-self, it may provoke the immune system to respond by forming antibodies. Antigens, also known as immunogens, are typically macromolecules like proteins or polysaccharides that can interact with immune components such as B cells and T cells. A key characteristic of an antigen is its epitopes, which are the specific parts of the antigen molecule that are recognized by immune cells.
Not all antigens will trigger an immune response due to a process called tolerance, which prevents the immune system from attacking the body's own cells or harmless substances. Furthermore, the immune system responds to antigens through two main approaches: the humoral immune response, which involves B cell production of antibodies, and the cellular immune response.
The ability of an antigen to elicit an immune response is influenced by several factors, including its molecular structure, size, and complexity.