Immunoglobulin D

The immunoglobulin D (IgD) was first described in 1965 and later determined on the lymphocyte surface.
The molecule is about 180 kDa and has a serum half-life of 3 days. It has been suggested that IgD play a role in immunological memory and in immune regulation.
Serum immunoglobulin D concentration is usually low in healthy individuals compared to other immunoglobulin classes.  The results of studies on serum IgD showed that IgD gradually increases with age in childhood as other immunoglobulin classes but later declines. Immunoglobulin D is therefore of interest in children when the immune system evolves.  These findings can be noteworthy in revealing the function of IgD in the immune system and their involvement in the development of pathologies, such as hyper-IgD syndrome.
Immunoglobulin D can be expressed as membrane IgD (mIgD) or secreted IgD (sIgD). Membrane IgD is an important B-cell marker, as it is co-expressed with IgM on most mature B-cells.
Dysregulated expression of IgD has been detected in the biopsy specimens of patients with some malignant lymphomas. Moreover, immunoglobulin D multiple myeloma (MM) is a rare variant of plasma cell dyscrasia.
It usually affects a younger population and has been characterized by an aggressive clinical course, with a higher incidence of Bence Jones proteinuria, renal failure, and an inferior outcome compared to other MM subtypes.
Since the secretion of intact IgD by the myeloma cells usually occurs at very low levels, and because serum immunofixation (IFE) with antisera to IgD is not established as a standard diagnostic procedure, this rare form of monoclonal gammopathy may easily be confused with a light-chain MM in clinical routine. Furthermore, immunoglobulin D levels can be elevated in patients with autoimmune diseases.
In general, serum level changes of IgD can be useful for monitoring the disease course and treatment outcome.(1)

Reference

• Serum ImmunoglobulinD in Infants and Children A’ HARALDSSON, C. M. R. WEEMAES, et Scand. J. Immunol. 51, 415±418, 2000.

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