An antibody is a protein produced by the body's immune system when it detects harmful substances, called antigens. Examples of antigens include microorganisms (bacteria, fungi, parasites, and viruses) and chemicals.

Antibodies may be produced when the immune system mistakenly considers healthy tissue a harmful substance. This is called an autoimmune disorder.

Each type of antibody is unique and defends the body against one specific type of antigen.


Antigens are large molecules (usually proteins) on the surface of cells, viruses, fungi, bacteria, and some non-living substances such as toxins, chemicals, drugs, and foreign particles. The immune system recognizes antigens and produces antibodies that destroy substances containing antigens.