What is the difference between an antigen and an antibody?

An antigen is a particle that is foreign to the body’s immune system. Most often, antigens come from the outside – these are particles of bacteria, viruses, fungi. But there may also be antigens formed inside – for example, in autoimmune diseases (rheumatoid arthritis, lupus). Antigens are tiny molecules, they “turn on” immunity, make lymphocytes create antibodies. The antibody for each type of antigen is its own. Antibodies bind to antigens, transforming them from dangerous molecules into harmless complexes. Such a complex is either destroyed or excreted from the body.