EFB Dengue Literature Review

Conventional Flow Cytometry

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Conventional Flow Cytometry

Overview

Conventional flow cytometry uses laser excitation and fluorescence detection to measure multiple surface and intracellular markers simultaneously on single cells. In the context of B cell immunology, it is the primary tool for classifying peripheral blood B cell subsets by surface phenotype. “Conventional” here refers to standard multi-laser instruments (e.g., BD FACSCalibur, FACSCanto, LSRFortessa) running panels of up to ~10–14 colours, as distinct from spectral flow cytometry (which can run 28+ colour panels by full spectral unmixing).

In dengue and related infection studies, conventional flow cytometry has been used to quantify plasmablasts, memory B cell subsets, and atypical/DN B cells during acute and convalescent phases.

Key Points from Literature

  • Wei2007 panel (8–9 color, FACSCalibur): CD19, IgD, CD27, CD38, plus one of: IgG, IgM, IgA, B220, CD10; 9-color protocol adds CD24, CD138, CD3; FcRH4 detected with biotinylated anti-FcRH4 + streptavidin. Standard IgD vs. CD27 dot plot used to define four quadrant populations: naive (IgD⁺CD27⁻), nonswitched memory (IgD⁺CD27⁺), switched memory (IgD⁻CD27⁺), and DN/double-negative (IgD⁻CD27⁻) (see Wei2007 - DN Memory B Cells in SLE).

  • Bm1–Bm5 classification: An alternative IgD/CD38-based gating strategy that identifies B cell subsets from naive (Bm1: IgD⁺CD38⁻) through GC (Bm3–4: IgD⁻CD38⁺) to memory (Bm5: IgD⁻CD38⁻/dull). The Bm5 gate substantially overlaps with classical memory cells but contains both CD27⁺ and CD27⁻ fractions; used as an orthogonal check on IgD/CD27 gating (see Wei2007 - DN Memory B Cells in SLE).

  • Limitation of limited panels: 8-color conventional panels cannot simultaneously resolve all relevant B cell subsets. Classification schemes based on IgD, CD27, and/or CD38 have acknowledged limitations: naive Bm1/Bm2 fractions contain non-switched CD27⁺ memory cells; Bm2ʹ pre-GC cells overlap with transitional B cells (see Wei2007 - DN Memory B Cells in SLE). Newer spectral panels adding T-bet, CD11c, CXCR5, FcRL5 provide finer resolution.

  • Fluorescence-minus-one (FMO) controls used to define positive/negative boundaries; Simply Cellular compensation beads used for spectral compensation (see Wei2007 - DN Memory B Cells in SLE).

  • Anolik2004 panel (≤5 color, FACSCalibur): CD19, CD20, CD27, IgD, CD38 — used in three gating configurations: (1) IgD vs. CD27 four-quadrant plot for naive/memory/DN/plasmablast classification; (2) CD38 vs. CD19 for plasmablast identification (CD38^high CD19^low gate with CD20 overlay); (3) CD38 vs. IgD Bm1–Bm5 scheme for developmental staging. 9G4 antiidiotype added separately for VH4.34 B cell tracking. Cells isolated by Ficoll-Hypaque from heparinized blood; B cells enriched by CD19 magnetic selection for residual cell analysis at maximal depletion timepoints (see Anolik2004 - Rituximab and B Cell Abnormalities in SLE).

  • Combining IgD/CD27 and CD38/IgD axes: Using both gating strategies simultaneously (by adding CD27 to the CD38/IgD plot) resolves the ambiguity between DN memory B cells and Bm5 cells, since DN cells (IgD⁻CD38⁻CD27⁻) and CD27⁺ memory cells (IgD⁻CD38⁻CD27⁺) are indistinguishable on CD38/IgD alone. The recommended practice is to combine both axes; 5-color panels can do this with CD19, IgD, CD27, CD38, and one additional marker (see Bm Classification).

  • Tipton2015 panel (multi-color, FACSAria II): IgD (FITC), IgM (PE-Cy5), CD38 (Pacific Blue), CD23 (PE-Cy7), CD21 (PE-Cy5), CD27 (PE), CD19 (APC-Cy7), CD3/CD14 (Pacific Orange, exclusion dump channel), CD24 (PE-Alexa Fluor 610), IgD (APC, second clone), CD138 (APC), Ki67, and MitoTracker Green (MTG). Ficoll density-gradient PBMC isolation; ~10⁴–3×10⁵ cells sorted per population on FACSAria II (BD Biosciences). Key gating logic: (1) ASC gate: CD19⁺IgD⁻CD27^hiCD38^hi, further subdivided by CD138⁻/CD138⁺; (2) naive compartment: CD19⁺IgD⁺CD27⁻, subdivided by MTG vs. CD24 into resting (MTG⁻CD24⁺), transitional (MTG⁺CD24⁺), and activated naive/acN (MTG⁺CD24⁻) fractions; (3) IgD⁻ memory gate: CD19⁺IgD⁻CD27⁺ (see Tipton2015 - ASC Diversity and Origin in SLE).

  • MitoTracker Green (MTG) as activation discriminator: MTG is a mitochondrial membrane potential dye retained by activated and transitional B cells but not by resting naive B cells. Combined with CD24 staining, MTG distinguishes three populations within the IgD⁺CD27⁻ naive compartment: MTG⁻CD24⁺ (resting naive), MTG⁺CD24⁺ (transitional), and MTG⁺CD24⁻ (acN/activated naive). This is a non-standard reagent not captured by antibody-based panels; it was validated by concordance with activated B cell surface markers (CD19^hi, CD21⁻, CD23⁻) and with disease activity (see Tipton2015 - ASC Diversity and Origin in SLE).

  • Jenks2018 DN1/DN2 resolution panel (multi-color, LSRFortessa + FACSAria II): Panel includes: CD19, IgD, CD27, CD38, CXCR5, CD21, CD11c, CD24, MTG, T-bet (intracellular), BLIMP-1 (intracellular), Ki67 (intracellular), with additional markers in extended panels: FCRL4, FCRL5, CD62L, CD32b, CD22, CD69, HLA-DR, CD86. The critical gating logic for DN1/DN2 subdivision: within IgD⁻CD27⁻CD19⁺ (DN gate), DN1 = CXCR5⁺CD21⁺ and DN2 = CXCR5⁻CD21⁻CD11c⁺CD19^hi. This panel also resolves aNAV cells within IgD⁺CD27⁻ as CXCR5⁻CD19^hiCD21⁻MTG⁺CD24⁻. T-bet intracellular staining confirms highest expression in DN2 and aNAV. Phospho-flow (pERK, pMAPKp38) after R848 stimulation used separately for TLR7 responsiveness (see Jenks2018 - DN2 B Cells and EF Pathway in SLE).

  • Minimum markers for DN2 identification: CXCR5 is the single most discriminating marker between DN1 and DN2 within the DN gate; adding CD11c and CD21 provides redundancy. A practical 8-color panel for DN2 screening would require: CD19, IgD, CD27, CXCR5, CD21, CD11c + two additional channels (e.g., CD38 for plasmablast exclusion, viability dye). This is achievable on conventional instruments (see Jenks2018 - DN2 B Cells and EF Pathway in SLE).

  • Sanz2025 recommended classification scheme (Table 1, Figure 2): The definitive gating strategy for human B cell subsets uses IgD vs. CD27 for the four parental populations (naive, USM, SM+PB, DN), then CD21 vs. CD11c (or equivalently CXCR5 vs. CD11c, or CXCR5 vs. T-bet) within each parental gate to resolve subsets: resting naive (rN: CD21⁺CD11c⁻), activated naive (aNAV: CD21loCD11c⁺); resting memory (rMem: CD21⁺CD11c⁻), ABC memory (CD21⁺CD11c⁺ resting; CD21loCD11c⁺ activated); DN1 (CD21⁺CD11c⁻), DN2 (CD21loCD11c⁺⁺), DN3 (CD21loCD11c⁻). CXCR5 can substitute for CD21, and T-bet or FcRL5 for CD11c, with each alternative identifying similar populations (see Sanz2025 - Human Atypical B Cells Overview, review, Table 1 + Figure 2).

  • Classification inconsistency is the root problem in cross-study comparison: Different studies define AtB/ABC using different subsets of CD27⁻, CD21lo, CD11c⁺, T-bet⁺, FcRL5⁺ — often without IgD measurement. This makes it impossible to compare AtB/ABC frequencies across diseases or to assign function from phenotype alone. Sanz (2025) recommends comprehensive phenotyping with at least IgD, CD27, and one of {CD21/CXCR5} × {CD11c/T-bet/FcRL5} to resolve subsets properly (see Sanz2025 - Human Atypical B Cells Overview, review).

  • Ansari2025 panel — first dengue EF B cell panel with CD21/CD11c resolution: Two multi-color panels used on acute dengue PBMCs: (1) T cell panel: CXCR5, PD-1, CD38, HLA-DR, CD4, CD8, CD45RA — resolves Tph (CXCR5⁻PD-1⁺) vs. cTfh (CXCR5⁺PD-1⁺) within CD38⁺HLA-DR⁺ activated CD4⁺ T cells. (2) B cell panel: IgD, CD27, CD21, CD11c, CD38, CD20, Ki67, CD71, CXCR3 — resolves DN gate (IgD⁻CD27⁻) with CD21 vs. CD11c for EF phenotype (CD21⁻CD11c⁺ ≈ DN2) and defines plasmablasts as CD20⁻CD38⁺⁺CD27⁺Ki67⁺CD71⁺CXCR3⁺. Includes IgD (passes Sanz2025 audit). Lacks CXCR5 in the B cell panel — cannot formally subdivide DN1/DN2 by CXCR5; uses CD21/CD11c as equivalent (per Woodruff2020). Lacks intracellular T-bet — cannot confirm T-bet expression on EF B cells (see Ansari2025 - Peripheral T Helper Subset Drives B Cell Response in Dengue, n=170 acute dengue).

  • Woodruff2020 Table 1 — complete standardised B cell population definitions: The most comprehensive published lookup table for B cell gating, defining 5 primary and 14 secondary populations with precise marker criteria. Primary: Tr (CD19⁺CD27⁻CD38^intCD24⁺), N (CD19⁺CD27⁻CD38⁻CD24⁻IgD⁺), DN (CD19⁺CD27⁻CD38⁻CD24⁻IgD⁻), M (CD19⁺CD27⁺CD38⁻/lo), ASC (CD19⁺CD27⁺CD38^hi). Secondary: Tr→CD21lo/CD21hi; N→aN(CD11c⁺)/rN(CD11c⁻); DN→DN1(CD11c⁻CD21⁺)/DN2(CD11c⁺CD21⁻)/DN3(CD11c⁻CD21⁻); M→sM/usM/mM/dM by IgM/IgD; ASC→CD138⁻/CD138⁺. This table is the reference standard for designing dengue EF pathway panels (see Woodruff2020 - EF B Cell Responses in COVID-19, Table 1; see also Spectral Flow Cytometry for the 24-marker spectral implementation).

  • Intracellular T-bet staining integrated with surface phenotyping: True-Nuclear Transcription Factor Buffer Set (BioLegend) used for intracellular T-bet staining combined with the spectral surface panel. This validated the T-bet hierarchy (aN > DN2 > DN1 > rN) in an infection context (see Woodruff2020 - EF B Cell Responses in COVID-19).

  • Wrammert2012 panel (5-color, whole blood) — simplest dengue plasmablast panel: CD19-FITC (555412, Pharmingen), CD38-PE (555460, Pharmingen), CD3-PerCP (340663, Pharmingen), CD20-PerCP (347674, Pharmingen), CD27-APC (17-0279-73, eBiosciences). Whole blood staining with erythrocyte lysis (BD FACS lysing solution) and 2% phosphonoformic acid fixation. Gating: CD19⁺CD3⁻ → CD20⁻/low → CD27^high CD38^high on extended lymphocyte gate (to include blasting cells). Absolute counts by BD Trucount bead system. This is the minimum viable dengue plasmablast panel — 5 markers identify PBs but cannot resolve memory subsets (no IgD), EF populations (no CD21, CD11c, CXCR5), or proliferation/apoptosis (no Ki-67, caspase-3). Every subsequent dengue panel in this wiki adds markers beyond this foundation (see Wrammert2012 - Plasmablast Responses in Acute Dengue, n=46 dengue + controls).

  • GarciaBates2013 panel (multi-color, LSRII) — earliest dengue B cell subset panel with severity stratification: Markers: CD19 (HIB19), CD20 (2H7), CD10 (HI10a), CD27 (M-T271), CD69 (L78), CD95 (DX-2), CD3 (SP34-2), CD21 (B-ly4), CD38 (AT-1, Stem Cell Technologies), Ki-67 (B56, intracellular), active caspase-3 (C92-605, intracellular), LIVE/DEAD (Invitrogen). Gating: (1) Live cells → CD19⁺CD3⁻ → CD10⁻ (mature B cells); (2) CD27 vs. CD21 defines naive (CD27⁻CD21⁺), resting memory (CD27⁺CD21⁺), atypical memory (CD27⁻CD21⁻); (3) CD27⁺CD21⁻ fraction further resolved by CD20 vs. CD38 into plasmablasts (CD20⁻CD38⁺) and activated memory (CD20⁺CD38⁻/lo). Lacks IgD (fails Sanz2025 IgD audit — cannot confirm naive vs. unswitched memory within CD27⁻ gate). Lacks CD11c, CXCR5, T-bet (cannot resolve DN1/DN2). Includes Ki-67 and active caspase-3 for proliferation/apoptosis — unique among dengue panels in this wiki (see GarciaBates2013 - Plasmablast Response and Dengue Severity, LSRII, n=84 dengue + controls).

  • Scharer2019 intracellular TF staining — PD-1 and ATF3 validated by flow: Beyond subset sorting, Scharer2019 used conventional flow cytometry for protein-level validation of two novel EF markers: (1) PD-1 surface staining on sorted subsets (mean ~60% PD-1⁺ on DN2 vs. ~10% rN, ~20% aN, ~15% SM; n=4 SLE); (2) ATF3 intracellular staining (significantly elevated MFI in rN, aN, SM, and DN2 in SLE vs. HC; P=0.034, 0.034, 0.033, 0.048 by Wilcoxon rank-sum). These represent practical flow cytometry readouts for EF pathway activation that could be added to dengue panels (see Scharer2019 - Epigenetic Programming in SLE B Cells).

  • Appanna2016 panel (5-marker sort panel + antigen-specific probes, FACSAria) — first dengue panel with CD138 and live virus antigen probes: Markers: CD19, CD20, CD27, CD38, CD138 for B cell subset sorting; Alexa Fluor-labelled live DENV-1, -2, -3 virions for antigen-specific MBC identification. Gating: (1) Plasmablasts: CD19⁺CD20⁻CD27^hiCD38^hi (acute phase, days 3–7); (2) DENV-specific MBCs: CD19⁺CD20⁺CD27⁺, gated by binding to fluorescent live DENV particles (convalescence, days 16–166). Includes CD138 — first dengue study to incorporate this marker in sorting, though used only to refine subset boundaries rather than CD138⁺/CD138⁻ ASC subdivision (cf. Tipton2015, Woodruff2020). Lacks IgD (fails Sanz2025 audit — cannot distinguish naive from unswitched memory within CD27⁻). Lacks CD21, CD11c, CXCR5, T-bet (cannot resolve DN subsets or EF populations). The live virus antigen probe approach enables direct identification of DENV-binding B cells without recombinant protein; however, it selects for surface-accessible epitopes on intact virions and cannot resolve specificity for individual viral proteins (E vs. prM vs. NS1) by flow cytometry alone (see Appanna2016 - Plasmablasts as Subset of Memory B Cell Pool, FACSAria, n=12 dengue).

  • Singh2026 panel (12-color, BD LSRFortessa) — first dengue MBC subset panel with antigen-specific detection: Dump: CD3-V500, CD14-V500, CD16-V500. Viability: Aqua L/D. B cell: CD19-APC-Cy7. Subset: CD20-PerCP-Cy5.5, IgD-V450, IgM-BV605, IgG-BV786, CD21-PE-CF594, CD27-PE-Cy7, CD38-PE. Antigen probes: AF488-DENV (1+2+3), AF647-DENV (1+2+3) — 6-antigen cocktail using whole virions grown on Vero-furin cells, dual-labelled for double-positive gating. DENV-specific B cells defined as AF488+/AF647+ double-positive. Defines 9 B cell subsets: naive (CD20+/IgD+), IgD+/IgM+ naive, class-switched MBC (CD20+/IgD⁻), activated MBC (CD20+/IgD⁻/CD27+/CD21⁻), resting MBC (CD20+/IgD⁻/CD27+/CD21+), atypical MBC (CD20+/IgD⁻/CD27⁻/CD21⁻), IgG+ MBC (CD20+/IgD⁻/IgG+), IgM+ MBC (CD20+/IgD⁻/IgM+), IgD⁻/IgM⁻/IgG⁻ MBC. FMO for CD21 and CD27; no-antigen control for DENV-specific threshold. Includes IgD (passes Sanz2025 audit); lacks CXCR5 and CD11c (cannot resolve DN1/DN2/DN3) (see Singh2026 - DENV-Specific Memory B Cell Subsets).

  • Sutton2021 validation panel (multi-color) — flow cytometry validation of transcriptomic clusters: A conventional flow cytometry panel including CD19, CD20, CD21, CD27, CD11c, IgD, IgG was applied to 18 donors (11 malaria-exposed, 7 non-exposed) to validate the transcriptomically-defined alternative lineage from scRNA-seq/CITE-seq. This confirmed that CD11c⁺ cells are present in non-exposed donors and that the alternative lineage is a substantial (~20%) component of the B cell repertoire. The panel was designed to test the CITE-seq prediction that CD11c outperforms CD21⁻CD27⁻ as a gating marker (see Sutton2021 - Alternative Lineage B Cells in Vaccination and Infection, n=18 donors).

  • CITE-seq reveals CD21⁻CD27⁻ gating captures only ~45% of transcriptomic atBCs: This finding (see CITE-seq for details) has direct implications for all flow cytometry studies using CD21⁻CD27⁻ or IgD⁻CD27⁻ gates — including every dengue panel in this wiki. Studies using these gates have likely underestimated the true size of the atypical/alternative lineage B cell population (see Sutton2021 - Alternative Lineage B Cells in Vaccination and Infection).

  • ★ Surface phenotype cannot assign memory B cell origin — a general limit on flow-based subsetting. Benchmarked against GC-specific genetic fate mapping, the surrogate criteria used to infer germinal-center vs GC-independent origin — cell-surface markers, class-switch status, and SHM load — are each “insufficient to definitively distinguish” the two populations. Their phenotypes overlap substantially and their transcriptomes differ only subtly (see Glaros2025 - Multilayered Identity of B Cell Memory, review, no original data, mouse). Flow cytometry remains the right tool for enumerating subsets; it cannot certify their developmental provenance.

  • The CD80/PD-L2 axis, and its naming collision with this wiki’s DN gate. Memory B cells are widely resolved by flow into DP (CD80⁺PD-L2⁺), SP (CD80⁻PD-L2⁺), and DN (CD80⁻PD-L2⁻) — an origin-enriching, not origin-defining, partition. ⚠ That “DN” is CD80⁻PD-L2⁻, not IgD⁻CD27⁻; see the false-friend note on Atypical B Cell. Neither marker is in the curator’s current 11-color or Panel-4 designs.

  • ⚠ Marker-set caution for atypical B cell gating. The review’s human ABC definition is CD27⁻CD21⁻ with T-bet, CD11c, CXCR3, FCRL4, and FCRL5 — a CD27/CD21-based definition that does not map one-to-one onto this wiki’s IgD⁻CD27⁻ DN gate, and which includes FCRL4 even though DN2 is defined as FCRL4⁻. Papers using this definition enumerate a partly different population. Separately, T-bet is not strictly required for CD11c⁺ ABC formation, so a T-bet-gated definition is a lower bound — see T-bet Contradictions and B Cell Panel Variant 1.

  • ★ The Hao/Rubtsov divergence is a genuine methods lesson in single-axis gating. The two founding murine ABC definitions used entirely different marker sets — Hao et al. (loss of CD21, CD23, CD95, CD43) versus Rubtsov et al. (gain of CD11c) — on the same B220⁺CD19⁺ splenocyte population, yielding “largely overlapping” but non-identical populations both called “ABC.” Compounding this, within the CD21⁻CD23⁻ gate only ~2/3 of cells are T-bet⁺, and only about half of those are CD11c⁺ — at least three populations sit inside a single-axis ABC gate. Together these are a direct caution against relying on any one marker axis to define this cell population, in flow panels of any species (see Cancro2020 - Age-Associated B Cells, review — no original data; mouse).

  • Purity verification for a non-B-cell isolate. Human Plasmacytoid Dendritic Cells enriched by BDCA-4 magnetic positive selection were confirmed >85% pure by lineage⁻CD123⁺HLA-DR⁺ staining before use — a reminder that magnetic enrichment yields are routinely checked by flow, and that an “isolated” primary population in a mechanistic paper commonly carries a ~15% contaminating fraction (see Wang2006 - Flavivirus Activation of pDCs and TLR7 Signaling, in vitro).

  • ★ Across ~25 diseases, “DN B cells” are defined by mutually incompatible gates — published frequencies are not comparable. A 2023 review’s disease-by-disease table records the phenotype used by each study. The parent gate alone varies across CD19⁺, CD19^low / CD19^int / CD19^hi, CD20⁺, and CD20^low; the DN gate is variously IgD⁻CD27⁻, CD27⁻CD21^-/low (with no IgD at all), CD27⁻CD38^low CD21^low, CD19⁺CD10⁻CD27⁻CD21^-/lo, CD19⁺CD5⁺CD27⁻CD21^-/low, CD20⁺CD27⁻IgG⁺, and (CD21^low/⁻)IgM⁻CD27⁻. Methodological consequence: an “increased DN B cells” row in one disease and the same row in another may refer to overlapping but non-identical populations, and no cross-disease frequency comparison in that table is quantitative (see Beckers2023 - Origins and Functions of DN B Cells, review, Table 1).

  • The review’s Table 1 records direction of change but no effect sizes. Alterations are recorded as “Increased in PB” or “Decreased in PB” — without n, percentages, confidence intervals, or p-values anywhere in the table. It is a map of where to look, not a source of comparative magnitudes; any number wanted from it must be traced to the primary (see Beckers2023 - Origins and Functions of DN B Cells, review, Table 1).

  • Panels omitting IgD cannot report DN cells at all. Several rows define the population as CD27⁻CD21^-/low with no IgD parameter, which cannot exclude IgD⁺ naive and unswitched cells from the gate. This is the same audit criterion the wiki applies from Sanz2025 - Human Atypical B Cells Overview, now visible as a majority-of-the-field problem rather than an occasional lapse (see Beckers2023 - Origins and Functions of DN B Cells, review, Table 1).

  • ⚠ A CD11c-gated DN2 panel may be blind to a plasmablast-like DN subset. Szelinski 2022’s DN^low (CD19^low IgD⁻CD27⁻CXCR5⁻ — see the typo note on Atypical B Cell) is reported to lack CD11c while sharing the plasmablast transcriptome. Such cells fall into the DN3 bin under the standard CXCR5/CD21/CD11c scheme, so a panel that treats DN3 as a residual category rather than an effector one will not measure them. Unvalidated, and in tension with the CITE-seq finding that CD11c is the best single alternative-lineage marker (Sutton2021 - Alternative Lineage B Cells in Vaccination and Infection) — both open (see Beckers2023 - Origins and Functions of DN B Cells, review, citing Szelinski 2022; see Atypical B Cell, DN2 Panel - Staining, Compensation, and Gating Protocol).

  • ★ The hardest methodological limit stated in the wiki: no flow cytometry panel, of any size, can identify an extrafollicular B cell response. “Currently there are no flow cytometry-based means alone that can distinguish EF B cells nor their progeny from activated cells in earlier phases. Few if any markers exist that define EF B cells in the absence of tissue imaging of antigen-specific B cell proliferation outside of a follicle.” The reason is categorical rather than technical — EF names a location and a process, and “EF refers only to the nature and site of the response, not the precursor B cell that initiated it.” EF responses can be seeded by naive follicular, marginal zone, B-1, or memory B cells, all of which enter with different phenotypes. Adding colours does not address this; spectral panels are subject to the same limit (see Eisenbarth2025 - A Roadmap for Defining Extrafollicular B Cell Responses, consensus Perspective, 12 authors, no primary data).

  • Individually non-definitive markers, named. Absence of CXCR5, low SHM, low BCR affinity, and IgM isotype “are all not definitive markers of an EF B cell, as they can be observed in B cells that have participated in a GC response.” Separately, CD21^lo, CXCR5⁻, CD11c⁺ and CD71⁺ may indicate recent B cell activation rather than a permanent state — so a single acute-timepoint panel cannot distinguish a differentiation state from an activation state (see Eisenbarth2025 - A Roadmap for Defining Extrafollicular B Cell Responses, consensus Perspective, 12 authors, no primary data).

  • What a panel can license. Marker combinations, transcription factor expression, proliferation status (Ki67), ASC potential, and mutational load remain “defining characteristics of different B cell states that can help define stages and pathways of B cell activation” — the recommendation is to state the criteria used rather than to abandon the method. The reportable claim from blood is GC-independence (probabilistically, from converging evidence), not extrafollicular location. See GC-Independent Response (see Eisenbarth2025 - A Roadmap for Defining Extrafollicular B Cell Responses, consensus Perspective, 12 authors, no primary data).

  • ★ [2026-08-27] STAINING PEARL — a conformation-dependent CXCR5 clone requires 37 °C, and requires being stained first. The protocol stained CXCR5 (clone J252D4) alone, first, at 37 °C, “as the clone highly depends on its target protein’s 3D conformation,” then stained the remaining twelve markers separately at 4 °C — a two-step surface stain of 30 min each. Brilliant Stain Buffer (50 µL) was included to suppress polymer-dye interactions in a panel carrying multiple BD Horizon dyes. This corroborates and explains the 37 °C pre-fix instruction already specified for CXCR5 in B Cell Panel Variant 1 (see Allard-Chamard2023 - DN3 B Cells Infiltrate Inflamed Tissues, methods).

  • [2026-08-27] Batch-consistency and compensation practice in a 13-colour B cell panel. Rainbow 8-peak calibration beads were run to ensure consistent signals across flow batches; compensation used VersaComp antibody-capture beads (Beckman Coulter). Viability: SYTOX AADvanced for live sorting, LIVE/DEAD Fixable Blue (1:1000, 30 min) with 4% PFA fixation for analysis-only runs. Acquisition on a BD Symphony, sorting on an Aria II SORP, analysis in FlowJo v10. Fresh PBMCs (stained within 2 h of isolation) for sorting; cryopreserved PBMCs for analysis — a split the wiki has not previously recorded (see Allard-Chamard2023 - DN3 B Cells Infiltrate Inflamed Tissues, methods).

  • [2026-08-27] The panel that produced the DN1–DN4 scheme, in full: CD3, CD19, CD27, IgD, CD38, CD20, IgG, IgM, IgA, FcRL4, SLAMF7, CD11c, CXCR5. No CD21, no T-bet, no CD24, no CD71. The four-way DN split therefore rests on CXCR5 × CD11c alone — worth knowing when comparing to CD21-based gating (see Allard-Chamard2023 - DN3 B Cells Infiltrate Inflamed Tissues, n=38). See DN3 B Cell Contradictions.

  • [2026-08-27] High-dimensional reduction before simplification. Twenty-five distinct B cell subpopulations were resolved in IgG4-RD blood by tSNE + PhenoGraph (Levine 2015) before the authors deliberately collapsed to the four-marker DN classification “to simplify further analyses and to be consistent with” the Sanz scheme. A useful precedent for the workflow of unsupervised discovery followed by supervised, comparable gating (see Allard-Chamard2023 - DN3 B Cells Infiltrate Inflamed Tissues, n=38).

  • ★ The seven-marker core panel — the field’s most-cited minimum recommendation for human B cell phenotyping. Sanz2019 holds that proper analysis of the major canonical human B cell subsets “requires the analysis of 7-markers combined with proper exclusion of dead cells and cellular doublets”: (1) a non-B dump (CD3, CD14); (2) CD19; (3) IgD; (4) CD27; (5) CD38; (6) CD24; (7) CD21. This combination supports both widely used schemes at once — IgD vs CD27 and IgD vs CD38 (Bm1–Bm5) — and CD21 is argued in specifically because it flags activated cells inside every parental population. ⚠ The paper is inconsistent about its own core: the Table 1 footnote reads “Core Markers: CD19, IgM, IgD, CD27, CD38, CD24, CD21”, substituting IgM for the dump and listing IgM among the additional markers as well (see Sanz2019 - Consistent Classification of Human B Cell Populations, review — no original data). See Bm Classification, DN2 Gating Strategy.

  • [2026-08-29] A 207-patient clinical stratification obtained from an 8-marker conventional panel — and a caution about what was published with it. Cryopreserved PBMC (BD Vacutainer CPT, banked in liquid nitrogen), stained 30 min at 4 °C in PBS + 2% FBS, viability by Fixable Viability Dye eFluor506, fixed in 0.5% formaldehyde, acquired on a BD LSRII, analysed in FlowJo. Markers recoverable from the text and figures are CD19, CD3, IgD, CD27, CD38, CD24, CD21, CD11c — the full conjugate list sits in an online supplemental table that is not part of the deposited manuscript, so the panel cannot be reproduced from the paper alone (see Jenks2021 - B Cell Subset Composition in Cutaneous Lupus, n=207 + 46 healthy controls, cross-sectional).

  • ⚠ [2026-08-29] Two comparability caveats when quoting frequencies from this study. (i) Cryopreserved/thawed PBMC, not fresh or fixed whole blood — CD21 and CD11c are the two markers doing all the subsetting work here, and both are the kind of surface marker whose recovery is sensitive to freeze-thaw. (ii) Significance is reported as colour-coded bands (p<0.05 green, p<0.01 blue, p<0.001 red, p<0.0001 dark purple) rather than numeric p-values, so exact p-values for subset comparisons are not extractable from the published text (see Jenks2021 - B Cell Subset Composition in Cutaneous Lupus).

  • Intracellular transcription-factor staining protocol for T-bet/IRF4/BLIMP1, with the permeabilisation detail spelled out. Surface stain → fix in neutral-buffered 10% formalin → permeabilise in 0.1% IGEPAL in the presence of the antibodies (or, alternatively, eBioscience transcription-factor and phospho-TF staining buffer sets). FcR blocked with 2% human serum or Miltenyi human FcR blocking reagent; 7AAD or LIVE/DEAD Fixable Dead Cell Stain for viability; acquisition on a FACSCanto II, analysis in FlowJo v9.9.3/v10.2 (see Zumaquero2019 - IFN-gamma Programs T-bet-hi B Cells for ASC Differentiation, human, n=20 HD + n=40 SLE + in vitro reconstruction). Directly reusable for any panel adding intracellular T-bet to a surface DN gate — the wiki’s most-wanted validation.

  • Whole-blood staining with CBC-anchored absolute counts, applied across a human cohort, an NHP model and an in vitro assay. Human: 100–200 µl of CPT-collected whole blood stained with the antibody cocktail, washed in PBS + 5% FBS, red cells lysed with BD FACS lysis buffer, fixed in Cytofix, acquired on a BD FACSAria used as an analyser; absolute counts were calculated from the paired complete blood count, not from counting beads (contrast the BD Trucount approach of Wrammert2012 - Plasmablast Responses in Acute Dengue). NHP PBMC and lymph-node cells were processed separately; the in vitro coculture was read on a BD LSRII (see Kwissa2014 - Monocytes Drive Plasmablast Differentiation in Dengue, n=28 acute dengue + 19 convalescent + 9 controls; NHP n=5; in vitro n=4 donors).

  • Two design points worth carrying from it. (i) The study reports proportion and absolute number separately for every innate subset, and the two dissociate — monocyte frequency rose in high-VL patients while absolute monocyte number did not, whereas BDCA-1⁺ mDC-1 fell on both measures. A frequency-only readout would have reported a monocyte expansion the absolute count does not support. (ii) In tissue, the activation readout is CD163 and CD169 mean fluorescence intensity rather than a positivity gate, because all resident lymph-node monocytes were already CD163⁺ at baseline (see Kwissa2014 - Monocytes Drive Plasmablast Differentiation in Dengue, NHP model, n=5). ⚠ The gating tree is supplementary Figure S3A and the antibody list sits in the Supplemental Information — neither is in the wiki’s PDF, so no panel composition is recorded here.

  • ★ The i.v. anti-CD45 labelling trick — a flow readout for anatomical position. Song2022 injected 6 µg of PE-conjugated anti-CD45 retro-orbitally 5 minutes before euthanasia, labelling only cells in compartments open to the circulation (including the marginal zone) and thereby converting a location question into a flow parameter: T-bet⁺CD11c⁺ cells were 40.3% labelled at day 12 and 60.5% at day 15, against naive follicular 16.8%/23.3% and GC 2.24%/3.47%. The rest of the panel is conventional: LSRII or Fortessa X-20; surface staining 35 minutes at room temperature; intracellular T-bet and Ki67 via the Foxp3/Transcription Factor kit; antigen-specific cells detected with recombinant HA on streptavidin-APC and streptavidin-PE used together, because single-probe frequencies were too low to be reliable (see Song2022 - Tfh Outside Germinal Centers Drive T-bet CD11c B Cells, mouse, LCMV-Armstrong + influenza PR8).

  • Dual-fluorophore antigen probes make antigen specificity a flow readout without any sorting step. Recombinant SARS-CoV-2 RBD was labelled separately with APC and with PE, and only cells staining with both were counted as authentic RBD-specific B cells — the double-label requirement is what suppresses the single-probe background, and the same logic appears independently in Song2022’s paired streptavidin-APC/streptavidin-PE HA probes above. The B cell panel itself is 13-colour (CD3, CD56, CD19, CD27, IgD, CD38, CD10, CD45RB, CD21, CD73, CD138, CD11c, CXCR5) on a BD Symphony (see Kaneko2020 - GC Loss and TFH Block in COVID-19, n=10 convalescent + n=4 severe for the RBD panel — blood arm of a post-mortem tissue study). ⚠ No cell sorting anywhere in this paper — the RBD populations were identified, never isolated; this page holds the content that the source page previously mis-filed under FACS Sorting.

Contradictions & Debates

  • Conventional panels with limited colour capacity may undercount DN B cells or conflate them with transitional B cells if CD10 or CD24 are not included. The Wei2007 data (Fig. 2B) show that DN cells are CD10⁻, which resolves this ambiguity — but earlier studies using 4- or 5-color panels may have misclassified these cells.
  • The DN1/DN2 distinction requires CXCR5 staining, which was not included in any of the prior Sanz lab panels (Wei2007, Anolik2004, Tipton2015). Studies using IgD/CD27 gating alone capture both DN1 and DN2 without discrimination — this affects interpretation of all prior DN frequency data.
  • Lack of IgD is a common omission: Many studies defining AtB/ABC do not include IgD in the panel, which means they cannot distinguish naïve-derived aNAV (IgD⁺) from DN2 (IgD⁻) among CD11c⁺ T-bet⁺ cells. This conflation is a major source of confusion in the literature (see Sanz2025 - Human Atypical B Cells Overview).

Bm Classification, FACS Sorting, Double-Negative B Cell, DN2 B Cell, Activated Naive B Cell, Memory B Cell, Plasmablast, CD27, IgD, CD38, CD19, CD20, CXCR5, CD11c, T-bet, PD-1, ATF3, Early Memory B Cell, Tissue-Resident Memory B Cell, Atypical B Cell, Plasmacytoid Dendritic Cell, GC-Independent Response, DN3 B Cell, Spectral Flow Cytometry

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