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Immunoglobulin D (IgD) – Function and Significance

Immunoglobulin D (IgD) is an antibody class of the human immune system, found mainly on the surface of B lymphocytes, where it plays a key role in immune regulation and early immune responses.

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Things worth knowing about "Immunoglobulin D"

Immunoglobulin D (IgD) is an antibody class of the human immune system, found mainly on the surface of B lymphocytes, where it plays a key role in immune regulation and early immune responses.

What is Immunoglobulin D?

Immunoglobulin D (IgD) is one of five major classes of antibodies produced by the human immune system, alongside IgA, IgE, IgG, and IgM. It is present in human blood in very small amounts, accounting for less than 1% of all circulating immunoglobulins. Although its precise biological function is not yet fully understood, IgD is considered an important component of the early immune response.

Structure of Immunoglobulin D

Like all antibodies, IgD has a Y-shaped molecular structure consisting of two heavy chains (delta chains) and two light chains linked by disulfide bonds. Its molecular weight is approximately 185 kDa. IgD is particularly susceptible to proteolytic degradation, which explains why it is found only at very low concentrations in the bloodstream.

Location and Function

IgD is primarily expressed on the surface of naive B lymphocytes (immature, antigen-inexperienced B cells), where it serves as an antigen receptor alongside IgM. Its key roles include:

Activation and maturation of B cells upon first contact with an antigen
Regulation of immune tolerance, helping the immune system avoid attacking the body's own tissues
Signal transduction within the B cell receptor complex
Potentially contributing to defense against respiratory infections by binding to basophils and mast cells

IgD in Blood Serum

The normal reference range for IgD in adult serum is between 0 and 100 IU/mL (international units per milliliter), with most healthy individuals showing very low values. Elevated IgD levels can occur in the following conditions:

IgD myeloma: A rare form of multiple myeloma in which plasma cells uncontrollably produce IgD
Hyperimmunoglobulinemia D with periodic fever syndrome (HIDS): A rare autoinflammatory disease characterized by recurrent fever episodes, lymph node swelling, and elevated IgD levels
Chronic infections and inflammatory diseases

Clinical Relevance and Diagnostics

Measuring serum IgD is less common in routine clinical practice than measuring other immunoglobulins. However, it is specifically used in the following situations:

Suspected IgD myeloma
Evaluation of periodic fever syndromes, particularly HIDS
Immunological research investigations

Measurement is typically performed using nephelometry or ELISA (enzyme-linked immunosorbent assay) from a blood sample.

IgD Myeloma

IgD myeloma is a rare but clinically significant condition, representing only about 1–2% of all myelomas. It is often diagnosed later than other myeloma subtypes because serum IgD concentrations may not be markedly elevated. Typical symptoms include bone pain, kidney dysfunction, anemia, and increased susceptibility to infections.

References

Vladutiu AO. - Immunoglobulin D: properties, measurement, and clinical relevance. - Clinical and Diagnostic Laboratory Immunology, 2000.
Hammarstrom L, Vorechovsky I, Webster D. - Selective IgA deficiency (SIgAD) and common variable immunodeficiency (CVID). - Clinical and Experimental Immunology, 2000.
World Health Organization (WHO) - International Classification of Diseases and clinical immunology references, 2023.

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