Immunoglobulin D, or IgD, is a type of antibody that is found in small amounts in the blood. Synonyms for this molecule include delta-class immunoglobulin, IGHD, and immunoglobulin delta heavy chain. IgD plays an important role in the immune system, helping to recognize and defend against invading pathogens. It is also thought to have a role in regulating the immune response and preventing excessive inflammation. While IgD is not as well-known as other antibodies such as IgG or IgE, it is still an essential component of the body's immune defenses and helps keep us healthy.