IgDcontaining

IgD-containing refers to B lymphocytes that express surface immunoglobulin D as part of their B cell receptor. In humans, most mature naive B cells coexpress IgM and IgD on their surface, produced through alternative splicing of immunoglobulin heavy chain transcripts from the IGHD and IGHM genes. This coexpression allows a versatile initial antigen receptor before class-switching.

Development: During B cell maturation in the bone marrow, heavy chain rearrangement yields transcripts that can be translated as membrane-bound IgM or IgD; immature B cells then exit to peripheral lymphoid tissues, where many retain the IgM/IgD combination as naive B cells. Upon activation and class-switching, some B cells switch to other isotypes, reducing IgD expression on their surface.

Function: The exact role of IgD in B cell biology remains incompletely understood. IgD is thought to contribute to clonal diversity and help set activation thresholds, supporting the maintenance of a responsive naive B cell repertoire while limiting inappropriate activation. Some evidence suggests IgD may participate in mucosal immunity and in maintaining self-tolerance, but the mechanisms are not fully resolved.

Clinical relevance: Abnormal IgD levels occur in conditions such as hyper-IgD syndrome (mevalonate kinase deficiency), where serum IgD is markedly elevated and patients experience periodic fever and inflammation. IgD can also be involved in monoclonal gammopathies when produced by malignant plasma cells, though such instances are rare.

Research: Ongoing studies explore IgD signaling, its receptors, and its contribution to B cell homeostasis, including interactions with other immune cells and responses to pathogens.