Antibody
An antibody (Ab), or immunoglobulin (Ig), is a large protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as those that exist on bacteria and virus cells, including those that cause disease. Each individual antibody recognizes one or more specific antigens, and antigens (a portmanteau of "antibody generator") of virtually any size and chemical composition can be recognized.