An antigen may be a substance from the environment, such as chemicals, bacteria, viruses, or pollen. An antigen may also form inside the body.

Where are antigen found?

Blood group antigens are found on the surface of red blood cells and are ignored by the immune system. But antigens of another blood type will be seen as foreign, and attacked by antibodies. Antibodies are produced by white blood cells and used by the immune system to identify and attack foreign substances in the body.

Where are antigens found what are they made of?

In general, antigens are composed of proteins, peptides, and polysaccharides. Any portion of bacteria or viruses, such as surface protein, coat, capsule, toxins, and cell wall, can serve as antigens.