TLR4 Activation Assay with NETs and Anti-CarP Antibodies

Protocol: TLR4 Activation Assay with Neutrophil Extracellular Traps (NETs) and Anti-Carbamylated Protein (Anti-CarP) Antibodies

Study Design

In vitro assay examining whether NETs containing carbamylated proteins activate TLR4 signaling in HEK293-TLR4 reporter cells, and whether anti-CarP antibodies modulate this activation.

Components

NETosis induction:

• Neutrophils isolated from healthy donor peripheral blood (Ficoll gradient)
• Activate with PMA (100 nM) or ionomycin (1 µM) for 4 hours
• Collect NETs in supernatant, verify by DNA quantification (PicoGreen) and neutrophil elastase activity

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Protocol: TLR4 Activation Assay with Neutrophil Extracellular Traps (NETs) and Anti-Carbamylated Protein (Anti-CarP) Antibodies

Study Design

In vitro assay examining whether NETs containing carbamylated proteins activate TLR4 signaling in HEK293-TLR4 reporter cells, and whether anti-CarP antibodies modulate this activation.

Components

NETosis induction:

• Neutrophils isolated from healthy donor peripheral blood (Ficoll gradient)
• Activate with PMA (100 nM) or ionomycin (1 µM) for 4 hours
• Collect NETs in supernatant, verify by DNA quantification (PicoGreen) and neutrophil elastase activity

Anti-CarP antibodies:

• Use commercial anti-CarP antibody (e.g., from rheumatoid arthritis patient serum or monoclonal)
• Confirm specificity: ELISA with carbamylated vs non-modified BSA

HEK293-TLR4 reporter cells:

• HEK-Blue-hTLR4 cells (Invivogen) or stable transfected HEK293 with NF-κB-luciferase reporter + hTLR4
• Maintain in DMEM + 10% FBS + blasticidin (for selection maintenance)

Co-treatment Experiment

Seed HEK293-TLR4 cells (50,000 cells/well in 96-well)

Stimulate with:

• NETs alone (various concentrations: 1, 5, 10 µg/mL DNA content)
• Anti-CarP antibody alone (1, 5, 10 µg/mL)
• NETs + anti-CarP antibody (pre-incubated 30 min at RT)
• LPS (100 ng/mL) as positive control
• Ultrapure LPS (E. coli) for TLR4 specificity

3. Incubate 6-24 hours

Readouts

NF-κB activation:

• SEAP reporter (HEK-Blue detection medium, read at 650 nm)
• OR luciferase reporter (One-Glo assay)

2. TLR4 specificity:

• Include HEK293 cells without TLR4 as negative control
• Use TLR4 antagonist (TAK-242, 1 µM) to block responses

3. Signaling pathways:

• Western blot: pIKK, pIκBα, p65 phosphorylation
• Cytokine release: ELISA for IL-8, TNF-α in supernatant

Controls

• Negative control: Untreated cells, isotype antibody control
• Positive control: LPS (100 ng/mL) or PAM3CSK4 (TLR2/1 agonist)
• Specificity control: TAK-242 (TLR4 inhibitor) + stimulus
• NET controls: Neutrophil lysate (non-NET components), DNase-treated NETs

Expected Outcomes

NETs activate TLR4 in dose-dependent manner (DNA and protein components)

Anti-CarP antibodies enhance NET-TLR4 activation (crosslinking/triggering)

TAK-242 blocks NET-induced activation (confirms TLR4 specificity)

DNase treatment reduces but may not abolish activation (protein component)

Success Criteria

• [ ] NETs verified: DNA content > 500 ng/mL, elastase activity > baseline
• [ ] Anti-CarP antibody: specific binding to carbamylated proteins confirmed
• [ ] TLR4 activation: ≥3-fold increase in NF-κB reporter over baseline
• [ ] Dose-response relationship: EC50 for NETs and antibody enhancement
• [ ] TAK-242 inhibition: ≥80% reduction in NET-induced activation
• [ ] Cytokine confirmation: IL-8 or TNF-α release in supernatant
• [ ] ≥3 biological replicates (independent neutrophil donors)

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