Part of the immune system, antibodies are proteins produced by white blood cells that circulate in the blood looking for and attaching to foreign proteins and toxins to neutralize them.

Antibodies are a type of protein made by plasma cells (a type of white blood cell) in response to an antigen, or foreign substance. A single antibody can bind to only one specific antigen to help destroy the antigen. Antibodies can work in several ways, depending on the nature of the antigen. Some antibodies destroy antigens directly; others help white blood cells destroy the antigen.