Antigen: it is a toxin or foreign substance which induces an immune response in the body, especially the production of antibodies. Antigens are substances (usually proteins) on the surface of cells, viruses, fungi, or bacteria. Nonliving substances such as toxins, chemicals, drugs, and foreign particles can also be antigens.The immune system recognizes and destroys, or tries to destroy, substances that contain antigens. There are three types of antigens present in our body: macrophages, dendritic cells and В cells. The antigen and antibody Interaction is called specific chemical interaction. It produced by white blood cells and antigens during immune reaction.