2-NBDG Flow Cytometric Glucose-Uptake Assay in Activated Primary Human CD4+ T Cells

Primary CD4+ T cells isolated from healthy-donor PBMCs (≥3 donors as biological replicates). Per donor, run resting and activated arms in triplicate wells. Glucose-uptake measured after a 30 min 2-NBDG pulse in glucose-free medium. Each run includes: an unstained control, a 2-NBDG-only sample, a glucose-competition sample (20 mM unlabeled glucose), and a GLUT-inhibitor control (cytochalasin B or phloretin). Activation time course optional (24, 48, 72 h). Acquire ≥30,000 live CD4+ events per sample. Donor identity is the blocking factor; samples within a donor are processed identically and acquired in randomized order.

BSL-2 for primary human blood/PBMCs — treat all donor material as potentially infectious; work in a certified biosafety cabinet with appropriate PPE (gloves, lab coat, eye protection). Cytochalasin B and phloretin are toxic — handle in a hood and dispose as chemical waste. 2-NBDG and antibody-stained material plus cells go to biohazard waste; sharps to sharps containers. Follow institutional bloodborne-pathogen and IRB/consent requirements for human donor samples.

Unstained cells set autofluorescence/baseline. 2-NBDG-only (no antibody) confirms the FITC-channel signal. Negative specificity control: glucose competition (20 mM D-glucose) and a GLUT inhibitor (cytochalasin B/phloretin) should both reduce 2-NBDG gMFI, proving transporter-mediated uptake. Vehicle control: DMSO at matched concentration (<0.5%). Positive biological control: TCR/CD28-activated cells, which should show elevated uptake versus resting. Viability dye gates out dead cells (which accumulate dye nonspecifically). Single-color compensation controls if multi-fluorophore panel is used.

Activated CD4+ T cells typically show 2-5x higher 2-NBDG gMFI than resting cells. Glucose competition and cytochalasin B should reduce activated-cell signal back toward 30-60% of uncompeted, confirming specificity. Live-cell gating should retain >80% viability for healthy cultures. Histograms show a clear rightward shift for activated cells; CV across triplicates typically <15%. Unstained autofluorescence should be well below the 2-NBDG-loaded signal.

• Fresh human PBMCs (leukopak or Ficoll-isolated from donor blood)
• EasySep Human CD4+ T Cell Isolation Kit (STEMCELL 17952) or equivalent negative selection
• 2-NBDG (Thermo N13195), 10 mM stock in DMSO; working 100-200 µM
• Dynabeads Human T-Activator CD3/CD28 (Gibco 11131D) or plate-bound anti-CD3 (1 µg/mL) + soluble anti-CD28 (2 µg/mL)
• RPMI 1640 + 10% FBS + 1% pen/strep + 2 mM glutamine (culture); glucose-free RPMI (Gibco 11879) for the uptake pulse
• Recombinant human IL-2 (50 U/mL) for activated cultures
• Anti-CD4-APC, anti-CD3-PerCP antibodies; viability dye (Zombie Aqua, BioLegend 423102)
• Cytochalasin B (Sigma C6762, 10 µM) or phloretin (200 µM) as GLUT inhibitor
• FACS buffer: PBS + 2% FBS + 2 mM EDTA; round-bottom 96-well plates

To measure single-cell glucose uptake in primary human CD4+ T cells using the fluorescent deoxyglucose analog 2-NBDG (2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose) read on a flow cytometer. The assay reports the geometric mean fluorescence intensity (gMFI) of 2-NBDG in defined live CD4+ populations, comparing resting versus anti-CD3/anti-CD28-activated cells, with a glucose-competition control to confirm transporter-mediated specificity.

1. Isolate CD4+ T cells from PBMCs by negative selection; assess purity (>90%) by flow if needed. Rest 2 h in complete RPMI.
2. Activate one arm with CD3/CD28 Dynabeads (1:1 bead:cell) + IL-2; leave the resting arm in IL-2-containing medium. Culture 48 h at 37 °C/5% CO2.
3. Harvest cells, count, and aliquot 2-3 x 10^5 cells per well in round-bottom plates.
4. Wash twice in glucose-free RPMI (300 x g, 5 min) and starve 30 min at 37 °C to deplete intracellular glucose.
5. For competition/inhibitor controls, pre-incubate with 20 mM unlabeled glucose or 10 µM cytochalasin B for 15 min.
6. Pulse with 100-200 µM 2-NBDG in glucose-free medium, 30 min at 37 °C in the dark.
7. Stop uptake with ice-cold FACS buffer; wash twice at 4 °C to remove unincorporated dye.
8. Surface stain (anti-CD4, anti-CD3) + viability dye, 20 min on ice in the dark; wash.
9. Acquire immediately on a flow cytometer (2-NBDG read in the FITC/B530 channel), ≥30,000 live CD4+ events.

Independent variables: activation state (resting vs. activated), and presence of glucose competitor/GLUT inhibitor. Dependent variable: 2-NBDG geometric MFI in live CD4+ cells (and % 2-NBDG-high cells). Controlled variables: 2-NBDG concentration and pulse duration (30 min), glucose-free starvation time, cell number per well, temperature (37 °C), wash conditions, donor, and flow cytometer voltages/compensation.

We hypothesize that TCR/CD28 activation upregulates GLUT1 surface expression and increases 2-NBDG uptake by ≥2-fold (gMFI) relative to resting CD4+ T cells within 48-72 h of stimulation. Co-incubation with excess unlabeled D-glucose will competitively reduce 2-NBDG signal, confirming the uptake is transporter-dependent rather than passive dye accumulation.

Analyze FCS files in FlowJo or equivalent. Gate: singlets (FSC-H vs FSC-A) → lymphocytes (FSC/SSC) → live (viability-dye-negative) → CD3+CD4+ → 2-NBDG. Report geometric MFI of 2-NBDG and the percentage of 2-NBDG-high cells (gate set on the 2-NBDG-only/competition control). Normalize each sample's gMFI to the matched glucose-competition control or to the resting condition within a donor to compute fold-uptake. Subtract autofluorescence (unstained gMFI) before ratioing.

1. No difference between resting and activated: activation failed — verify CD25/CD69 upregulation and bead:cell ratio; ensure adequate culture time (48-72 h). 2. High background in all samples: insufficient washing of unincorporated 2-NBDG — add an extra cold wash and keep cells at 4 °C post-pulse. 3. Low viability: over-starvation or harsh handling — limit glucose-free starvation to 30 min and keep cells cold after the pulse. 4. No competition/inhibitor effect: dye accumulation is nonspecific or dead-cell driven — tighten the live-cell gate and confirm inhibitor potency. 5. Weak signal: increase 2-NBDG to 200 µM or extend pulse to 45 min, but keep constant across conditions.

Use donor as the experimental unit (n≥3). For resting vs. activated, apply a paired two-tailed t-test on per-donor mean gMFI (or fold-uptake). For multiple conditions (resting/activated/competition/inhibitor), use repeated-measures one-way ANOVA with Tukey or Dunnett (vs. activated) post-hoc. Set alpha = 0.05. Report mean ± SEM, exact p-values, and individual donor points. With expected effect size d>1.2, n=3-4 donors gives ~80% power.