EFB Dengue Literature Review

Germinal Center

11 min read

Germinal Center

Overview

Germinal centres (GCs) are specialised microanatomical structures within secondary lymphoid organs (lymph nodes, spleen, tonsils, Peyer’s patches) where antigen-activated B cells undergo rapid proliferation, somatic hypermutation (SHM) of immunoglobulin variable genes, affinity-based selection, and class switch recombination (CSR). GC reactions generate high-affinity isotype-switched memory B cells (which acquire CD27) and long-lived plasma cells. They are the canonical route for production of durable, high-quality humoral immunity.

In the context of this wiki, the germinal centre response is the primary counterpoint to extrafollicular B cell responses — understanding which populations are GC-derived vs. EF-derived is central to interpreting B cell dynamics in dengue infection.

Key Points from Literature

  • GC reactions are initiated by cognate B–T cell interactions mediated by CD40–CD154 (CD40 ligand); this interaction is required for normal GC formation and for CD27 acquisition by B cells (see Wei2007 - DN Memory B Cells in SLE, citing Maclennan 1994 and Grewal & Flavell 1998).

  • CD27 is acquired by B cells as a result of CD40–CD154-mediated signalling in GCs; absence of CD27 on DN memory B cells therefore suggests these cells bypassed or aborted GC entry (see Wei2007 - DN Memory B Cells in SLE).

  • In SLE, GC reactions appear dysregulated: germinal centre exclusion of autoreactive B cells is defective (cited as Cappione et al. 2005 in Wei2007 - DN Memory B Cells in SLE), and anti-CD154 blockade failed to reduce DN cell frequency — consistent with DN cells arising outside GC reactions.

  • Murine evidence for SHM outside GCs: William et al. (2002, Science) demonstrated that somatic hypermutation can occur in extrafollicular reactions (cited in Wei2007 - DN Memory B Cells in SLE). This is a critical precedent for the EF origin model of DN cells.

  • T cell-independent GC reactions produce low-level SHM compared with T cell-dependent GCs (cited as Toellner et al. 2002 in Wei2007 - DN Memory B Cells in SLE), supporting the idea that the lower mutation rate in DN cells is consistent with GC-independent or abortive-GC origin.

  • Circulating pre-GC (Bm2ʹ) cells in SLE: A subset of SLE patients have expanded circulating IgD⁺CD38^high CD20⁺CD10⁺ cells — putative GC founder cells. In a clinical cohort, 3 of 15 patients had marked pre-GC expansion (mean 9 ± 11.9% across cohort vs. 4.7 ± 2.8% in controls). These cells are phenotypically distinct from plasmablasts (they retain CD20 and CD19^bright expression) (see Anolik2004 - Rituximab and B Cell Abnormalities in SLE; see also Bm Classification).

  • Pre-GC cells may resist rituximab despite being CD20⁺: All three patients with marked pre-GC expansion had incomplete or transient B cell depletion, and pre-GC frequency increased rather than decreased after rituximab in two. This suggests either intrinsic resistance or continuous replenishment from ongoing antigen-driven GC reactions. GC-biased SLE may thus represent a mechanistically distinct disease subset (see Anolik2004 - Rituximab and B Cell Abnormalities in SLE).

  • Defective GC censoring of autoreactive B cells in SLE: VH4.34 autoreactive memory B cells are elevated 12-fold in SLE vs. healthy donors (16.2 ± 11.9% vs. 1.3 ± 0.3%; P=0.03), consistent with a GC checkpoint failure. After rituximab treatment, autoreactive memory B cell frequencies normalised (1.92 ± 0.7%), interpreted as restored GC censoring upon immune reconstitution (see Anolik2004 - Rituximab and B Cell Abnormalities in SLE).

  • acN cells can enter both EF and GC pathways: Phylogenetic clone trees in Tipton2015 show complex clones in which acN cells with 0% SHM co-exist with CD138⁻ and CD138⁺ ASCs carrying up to 21.5% VH mutation. The aggregate data are most consistent with a model of sustained and asymmetric differentiation of acN cells through both extrafollicular pathways and GC reactions — both pathways are simultaneously active rather than mutually exclusive (see Tipton2015 - ASC Diversity and Origin in SLE).

  • IgM⁺ memory B cells as GC-independent first memory layer: The high frequency of IgM sequences in the IgD⁻CD27⁺ memory compartment in SLE patients (20.9–68.1%) vs. vaccinated controls (1.5–37.5%), together with the prominent naive-cell connectivity to ASCs, is consistent with IgD⁻IgM⁺ memory cells representing the first GC-independent memory layer generated from newly activated naive cells (see Tipton2015 - ASC Diversity and Origin in SLE, citing Dogan et al. 2009).

  • SM and DN2 have divergent epigenetic programmes despite similar methylation levels: DNA methylation phylogenetics place both SM and DN2 closest to ASCs, yet their chromatin accessibility landscapes are sharply distinct. SM chromatin is enriched for NF-κB, EBF, and OCT2 motifs — transcription factors associated with GC transit and canonical memory identity. DN2 chromatin is enriched for T-BET, AP-1, and EGR motifs. This epigenetic bifurcation provides the strongest evidence that SM and DN2 represent genuine alternative differentiation endpoints (GC vs. EF), not different stages of a single pathway (see Scharer2019 - Epigenetic Programming in SLE B Cells, RRBS + ATAC-seq, n=9 SLE + 12 HC).

  • DN1 cells are transcriptionally GC-derived: DN1 cells (CXCR5⁺, CD21⁺, within the IgD⁻CD27⁻ compartment) share a near-identical transcriptome with switched memory cells (only 22 DEGs by RNA-seq). They express TCF7 (the central memory TF), CXCR5 (the follicle-homing receptor), and BACH2 — all hallmarks of GC-transit. DN1 likely represent early switched memory precursors that have not yet acquired CD27 through CD40–CD154 interactions, placing them in a GC-associated differentiation pathway. CD40L stimulation does not inhibit DN1 generation in vitro (unlike DN2), consistent with their GC compatibility (see Jenks2018 - DN2 B Cells and EF Pathway in SLE, RNA-seq + in vitro differentiation).

  • CD40L actively inhibits EF pathway — antagonistic regulation between GC and EF: CD40L stimulation inhibits rNAV differentiation into aNAV and DN2 cells. IL-4 (the canonical GC-associated Th2 cytokine) also inhibits aNAV/DN2/PC generation when substituted for IFN-γ. These inhibitory effects demonstrate that GC and EF pathways are not merely parallel — they are antagonistically regulated. Conditions that promote GC entry (CD40L, IL-4) suppress EF differentiation (TLR7, IFN-γ, IL-21) and vice versa (see Jenks2018 - DN2 B Cells and EF Pathway in SLE, in vitro differentiation).

  • ZEB2 represses GC differentiation: Zeb2, the primary TF driving ABC/DN2 formation, represses Mef2b — a TF required for GC differentiation. This provides the first direct molecular mechanism linking EF commitment to GC exclusion: cells expressing high ZEB2 are actively prevented from entering GC reactions (see Sanz2025 - Human Atypical B Cells Overview, review citing Dai et al. 2024, Gao et al. 2024).

  • GC-independent autoimmunity is confirmed by monogenic evidence: TLR7 gain-of-function mutations cause human SLE with expanded ABC/DN2. In mice, the orthologous mutation causes autoimmunity that is GC-independent — ABC expansion and pathology proceed normally even when GC reactions are blocked (see Sanz2025 - Human Atypical B Cells Overview, review citing Brown et al. 2022).

  • ABC sustain GC responses in chronic infection: Paradoxically, Zeb2-driven CD11c⁺ B cells may sustain GC responses in chronic infections by functioning as APCs for GC TFH induction. Excessive ABC activity leading to abnormal TFH regulation has been proposed as a mechanism of defective antigen-specific GC responses (see Sanz2025 - Human Atypical B Cells Overview, review citing Gao et al. 2024, Zhang et al. 2019).

  • GC loss confirmed histopathologically in fatal COVID-19: Kaneko et al. (2020) demonstrated loss of Bcl-6⁺ Tfh cells and germinal centers in spleens and lymph nodes of patients who died of COVID-19. This provides the histopathological evidence for the peripheral EF dominance observed by Woodruff2020 — in severe COVID-19, the GC pathway is suppressed rather than merely outcompeted. TNF-α was implicated as a mediator of GC disruption (see Woodruff2020 - EF B Cell Responses in COVID-19, citing Kaneko et al. 2020, Cell).

  • EF dominance in severe COVID-19 is not due to sampling timing: CoV-A (EF-high) and CoV-B (EF-low) clusters had similar sampling times post-symptom onset, ruling out the possibility that EF dominance simply reflects early kinetics before GCs have had time to form (see Woodruff2020 - EF B Cell Responses in COVID-19).

  • Concurrent GC activity alongside dominant EF pathway in acute dengue: Despite ~75% of activated CD4⁺ T cells being CXCR5⁻PD-1⁺ Tph (extrafollicular), plasma CXCL13 — the canonical Tfh/GC biomarker — is elevated in acute dengue. This suggests GC reactions are simultaneously active, not suppressed as in fatal COVID-19 (Kaneko et al. 2020). The EF/GC relationship in dengue may therefore be concurrent rather than antagonistic, consistent with the Sanz2025 endotype concept where patients can have mixed EF+GC responses (see Ansari2025 - Peripheral T Helper Subset Drives B Cell Response in Dengue, n=170 acute dengue, plasma CXCL13 ELISA).

  • Convergent CDR3 mutation levels compatible with prior GC transit: In the first BCR repertoire analysis of acute dengue, convergent CDR3-bearing B cells carried 4.4–6.9% V gene mutation — within the range expected for GC-experienced memory B cells. The convergent CDR3s were more prevalent in secondary dengue, consistent with recall of previously GC-matured memory clones. However, the intermediate mutation level does not exclude contributions from EF maturation, as EF SHM is now documented (see Parameswaran2013 - Convergent Antibody Signatures in Dengue, 454 pyrosequencing, n=60 dengue patients — unsorted PBMCs, not cell-type resolved).

  • Delayed DENV-specific MBC peaks suggest prolonged GC reactions in 2° dengue: Peak frequency of several DENV-specific MBC subsets (IgD+/IgM+, IgD⁻ MBC, IgG+, atypical) occurred >3 months post-infection in 2° but not 1° dengue immunity (p<0.05 for 3 subsets). The authors cite Turner et al. (2021) demonstration of GC reactions persisting ~8 months post-SARS-CoV-2 vaccination as precedent. An uptick from 12–18M in 2° cases further suggests either ongoing GC output, tissue redistribution, or subclinical boosting in an endemic setting (see Singh2026 - DENV-Specific Memory B Cell Subsets, n=4/group — small sample).

  • Comparable VH mutation in dengue PBs and MBCs — consistent with both populations having GC history: Appanna2016 found that PB- and MBC-derived antibodies had comparable VH nucleotide mutation rates. The authors initially hypothesised MBCs would show higher SHM (consistent with more extensive GC maturation), but neither population showed significantly more mutation than the other. This is consistent with both populations deriving from memory B cells that had undergone similar prior GC experience, then being activated through different pathways during reinfection — one (E-specific IgG) feeding the PB wave, the other (prM/complex epitope) emerging at convalescence. The similar mutation levels do not resolve whether PBs transit through GCs during the acute response but are compatible with the Ansari2025 model of EF recall of pre-matured memory cells (see Appanna2016 - Plasmablasts as Subset of Memory B Cell Pool, n=12 dengue, IMGT analysis).

  • Low SHM in acute dengue IgG B cells argues against dominant GC origin of the plasmablast wave: GodoyLozano2016 found paradoxically low global SHM during acute dengue, lower in DWS+ than DWS−, and lower in secondary than primary infections — the opposite of what GC-dependent memory recall would predict (increased SHM with antigen re-exposure). Influenza vaccination produced the expected GC pattern (SHM increase at day 7). The authors propose that a rapid GC-independent pathway operating concurrently with the GC pathway is responsible, consistent with the concurrent Tph + CXCL13 activity in Ansari2025 (see GodoyLozano2016 - Lower IgG SHM Rates in Acute Dengue, n=19 acute dengue + 10 TIV controls, 454 pyrosequencing).

  • High SHM in sorted secondary dengue PBs argues FOR GC-experienced memory origin: Priyamvada2016 found mean 18.1 VH mutations per plasmablast (range 5–39), significantly higher than IgG⁺ GC B cells (p<0.005) and comparable to influenza recall responses. CDR R:S ratios >2.9 confirmed antigenic selection. This SHM level is best explained by prior GC transit of the memory B cells that gave rise to these PBs — contrasting with GodoyLozano2016’s low-SHM finding in bulk IgG and suggesting two concurrent populations: GC-experienced memory recall (high SHM) and de novo EF differentiation (low SHM) (see Priyamvada2016 - Cross-Reactive Memory Plasmablasts in Secondary Dengue, n=4 secondary DHF, single-cell BCR sequencing).

Contradictions & Debates

  • The DN1/DN2 subdivision resolves much of the original debate: DN2 cells are EF-derived (TLR7-dependent, CD40L-inhibited), while DN1 cells are GC-associated (SWM-like transcriptome, CD40L-tolerant). The remaining question is whether DN1 cells complete full GC reactions or represent early GC emigrants.
  • ABC can be both GC-sustaining and GC-excluded: Sanz2025 reveals a paradox — Zeb2-driven ABC/DN2 cells are molecularly excluded from entering GCs (Zeb2 represses Mef2b), yet ABC can sustain GC responses as APCs. These functions need not be contradictory if ABC provide TFH support from extrafollicular positions without themselves entering GCs.

Extrafollicular Response, Somatic Hypermutation, Class Switch Recombination, Memory B Cell, Double-Negative B Cell, DN2 B Cell, CD27, Plasmablast

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