EFB Dengue Literature Review

IgD

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IgD

Overview

IgD (Immunoglobulin D) is a surface immunoglobulin isotype co-expressed with IgM on mature naive B cells. Surface IgD expression is used in B cell subset classification as a marker of naivety and non-switching: naive B cells are IgD⁺CD27⁻, unswitched memory B cells are IgD⁺CD27⁺ (or IgD⁺IgM⁺), and cells that have undergone class switch recombination are IgD⁻. Loss of IgD therefore marks B cells that have either undergone isotype switching (to IgG, IgA, or IgE) or, in the case of IgM-only memory cells, have downregulated IgD without switching.

Key Points from Literature

  • IgD/CD27 dual staining defines the four canonical PBL B cell compartments: naive (IgD⁺CD27⁻), nonswitched memory (IgD⁺CD27⁺), switched memory (IgD⁻CD27⁺), and double-negative/DN (IgD⁻CD27⁻) (see Wei2007 - DN Memory B Cells in SLE).

  • DN B cells are IgD⁻ and contain both isotype-switched (~44% IgG⁺) and IgM⁺ cells; critically, the IgM⁺ fraction of DN cells lacks IgD co-expression, distinguishing it from the IgM⁺IgD⁺ fraction of conventional unswitched CD27⁺ memory cells (see Wei2007 - DN Memory B Cells in SLE).

  • Bm1–Bm5 classification uses IgD (combined with CD38) as an axis: Bm1 (IgD⁺CD38⁻), Bm2 (IgD⁺CD38^dull), Bm2ʹ (IgD⁺CD38⁺ pre-GC), Bm3–4 (IgD⁻CD38⁺ GC), early Bm5 (IgD⁻CD38^dull), Bm5 (IgD⁻CD38⁻) (see Wei2007 - DN Memory B Cells in SLE).

  • IgD⁺ retained on acN cells: Activated naive (acN) B cells remain IgD⁺ (and CD27⁻), placing them within the naive compartment gate even though they are functionally distinct from resting naive B cells. IgD expression is not lost until class switch recombination or differentiation into ASCs (IgD⁻CD27^hiCD38^hi). This means IgD staining alone cannot distinguish resting from activated naive B cells — the MTG + CD24 combination or CD19^hi + CD21⁻ markers are required to resolve acN cells within the IgD⁺CD27⁻ gate (see Tipton2015 - ASC Diversity and Origin in SLE).

  • IgD marks the aNAV→DN2 transition point in EF differentiation: In the EF pathway (rNAV → aNAV → DN2 → plasmablast), IgD expression is retained at the aNAV stage (IgD⁺CD27⁻) but lost at the DN2 stage (IgD⁻CD27⁻). This IgD loss marks the transition from an activated naive cell to a committed EF effector. RNA-seq confirms IgD downregulation at the transcriptional level in DN2 cells, concurrent with class switch recombination. The IgD⁺/IgD⁻ distinction between aNAV and DN2 is critical for flow cytometry gating: both populations share CD19^hi, CD21⁻, CD11c⁺, MTG⁺, and CD24⁻, but IgD separates them (see Jenks2018 - DN2 B Cells and EF Pathway in SLE, flow cytometry + RNA-seq).

Contradictions & Debates

None documented in current wiki sources.

Double-Negative B Cell, DN2 B Cell, Activated Naive B Cell, CD27, Memory B Cell, Class Switch Recombination, Conventional Flow Cytometry

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