EFB Dengue Literature Review

CD27

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CD27

Overview

CD27 is a member of the TNF receptor superfamily expressed on the surface of B cells and T cells. On B cells, surface CD27 expression has long been used as a canonical marker of memory B cell identity — CD27⁺ B cells consistently carry somatic hypermutation, and CD27 expression is acquired during germinal centre reactions through cognate B–T cell interactions mediated by CD40–CD154. CD27 interacts with its ligand CD70 on activated helper T cells, facilitating memory B cell differentiation into plasma cells.

The discovery of IgD⁻CD27⁻ (double-negative) memory B cells — which carry somatic hypermutation and memory functional properties despite lacking CD27 — has qualified its status as a “universal” memory marker.

Key Points from Literature

  • CD27 expression was the dominant criterion for identifying human memory B cells prior to the characterisation of DN B cells (see Wei2007 - DN Memory B Cells in SLE, citing Klein et al. 1998).

  • CD27 is acquired by B cells following a GC reaction initiated by CD40–CD154-mediated B–T cell interactions; its absence in DN B cells is used as evidence for their GC-independent (extrafollicular) origin (see Wei2007 - DN Memory B Cells in SLE).

  • CD27–CD70 interactions regulate B cell activation by T cells and enhance plasma cell differentiation; impaired CD27 signalling in DN cells may limit their ability to receive sustained T cell help (see Wei2007 - DN Memory B Cells in SLE, citing Kobata et al. 1995, Jacquot et al. 1997).

  • CD27 expression is upregulated by the majority of proliferating DN cells after CpG DNA stimulation in vitro — suggesting CD27 negativity is not lineage-fixed and can be acquired upon TLR9-driven activation (see Wei2007 - DN Memory B Cells in SLE, in vitro proliferation assay).

  • In SLE, both CD27⁺ memory cells and DN cells tend toward the CD38^dull (early Bm5) phenotype, at the expense of the CD38⁻ (Bm5) fraction seen in healthy donors (see Wei2007 - DN Memory B Cells in SLE).

  • CD27^hi marks the ASC gate: Plasmablasts in peripheral blood are identified as CD19⁺IgD⁻CD27^hiCD38^hi. The CD27^hi criterion (substantially above conventional memory B cell CD27 levels) is a standard component of the Tipton2015/Sanz lab ASC gate, distinguishing ASCs from IgD⁻CD27^lo DN memory cells and from IgD⁺CD27⁺ unswitched memory cells (see Tipton2015 - ASC Diversity and Origin in SLE).

  • DN1/DN2 subdivision resolves the CD27⁻ memory puzzle: The DN1/DN2 subdivision within IgD⁻CD27⁻ cells reveals two distinct reasons for CD27 absence. DN1 cells (CXCR5⁺, CD21⁺, transcriptionally SWM-like with only 22 DEGs) likely represent early switched memory precursors that have not yet acquired CD27 via CD40–CD154 interactions — they are GC-associated. DN2 cells (CXCR5⁻, CD21⁻, CD11c⁺, T-bet⁺) are extrafollicular effector cells whose CD27 absence reflects genuine GC bypass via TLR7-dependent differentiation. CD40L stimulation inhibits DN2 generation but not DN1, consistent with DN1 acquiring CD27 through the conventional CD40 pathway (see Jenks2018 - DN2 B Cells and EF Pathway in SLE, RNA-seq + in vitro differentiation).

  • CD27 can be downregulated upon stimulation: CD27 expression is not lineage-fixed — it can be downregulated by CD70 on activated T cells, TLR ligands, and cytokines. Some CD27⁻ B cells may therefore represent cells that originally expressed CD27 and lost it upon stimulation, rather than cells that never entered GCs (see Sanz2025 - Human Atypical B Cells Overview, review citing Kang et al. 2024).

  • CD27 as sole memory marker is obsolete: Sanz (2025) argues that the prevailing model equating CD27⁺ with memory is now untenable. A substantial memory fraction normally resides in CD27⁻ populations, either because CD27 was never acquired or because it was downregulated. The term “atypical memory” — defined by CD27 absence — is therefore misleading (see Sanz2025 - Human Atypical B Cells Overview, invited review).

Contradictions & Debates

  • CD27 is not absent from all non-memory B cells; it can be transiently upregulated on activated naive B cells and on pre-plasmablasts, adding ambiguity to the memory gate in activated samples.

  • The use of CD27 alone to enumerate memory B cells in dengue cohort studies will miss DN/atypical B cell expansions — a systematic limitation to bear in mind when interpreting older literature.

  • CD27 modulation means that the same cell can appear CD27⁺ or CD27⁻ depending on its activation state and signalling environment — a fundamental challenge for phenotype-based classification (see Sanz2025 - Human Atypical B Cells Overview).

  • CD27^high as original dengue plasmablast criterion: Wrammert2012 used CD27^high combined with CD38^high (within CD19⁺CD3⁻CD20⁻/low) as the core plasmablast gate — the first application of this standard ASC gate to acute dengue. The use of CD27^high (not just CD27⁺) distinguishes plasmablasts from conventional CD27⁺ memory B cells, consistent with the Tipton2015/Sanz lab gate (see Wrammert2012 - Plasmablast Responses in Acute Dengue, 5-color conventional FCM).

  • CD27⁺CD21⁻ gate for plasmablast/activated memory in dengue: GarciaBates2013 used CD27⁺CD21⁻ as the first-tier gate for non-naive memory/effector B cells, then subdivided by CD20/CD38 into plasmablasts (CD20⁻CD38⁺) and activated memory (CD20⁺CD38⁻/lo). This confirms that CD27 upregulation is a consistent feature of dengue plasmablasts across cohorts (see GarciaBates2013 - Plasmablast Response and Dengue Severity, LSRII FCM, n=84 dengue).

  • CD27 as PB/MBC discriminator in dengue clonal analysis: Appanna2016 used CD27^hi (within CD19⁺CD20⁻CD38^hi) for PB sorting and CD27⁺ (within CD19⁺CD20⁺) for MBC sorting. The CD27⁺ MBC gate, which by definition excludes CD27⁻ DN memory B cells, may undercount the total DENV-specific memory compartment. This is acknowledged as a limitation — Singh2026 shows that CD27⁻CD21⁻ (atypical/DN) MBCs are a significant component of DENV-specific memory (see Appanna2016 - Plasmablasts as Subset of Memory B Cell Pool, FACSAria, n=12 dengue).

Double-Negative B Cell, DN2 B Cell, Memory B Cell, IgD, CD38, Germinal Center, Extrafollicular Response, Plasmablast

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