Where is IgD primarily found?

Immunoglobulin D (IgD) is primarily found on the surface of B cells, where it functions as a receptor. It plays a critical role in the initiation and regulation of B cell activation and maturation. When antigens bind to IgD on the surface of B cells, it triggers a cascade of signaling events that lead to the activation of these immune cells, ultimately contributing to the adaptive immune response.

Although low levels of IgD can be detected in the bloodstream, its primary and significant role is associated with B cells. In contrast, it is not normally found on the surface of mast cells, which typically express other types of immunoglobulins, such as IgE. Additionally, while immunoglobulins can be distributed throughout the body, IgD's unique association with B cells underscores its critical function within the immune system rather than a widespread presence in all tissues.