Drop Titration Protocol
Concept
Instead of a single bolus liberator addition, add liberator incrementally at controlled intervals. Each drop incrementally increases stimulus. Time-to-signal reflects the reactivity threshold of the captured cell population.
- Signal at drop 3 = extremely reactive
- Signal at drop 8 = moderately reactive
- No signal by drop 20 = normal reactivity or poor cell capture (check nuclear control)
This turns a semi-quantitative measurement problem into a timing/counting problem. No reader device required — patients count drops.
Why This Works
More cells at normal reactivity = faster response than fewer cells at normal reactivity. But a non-reactive cell population won’t fire regardless of cell number. The nuclear control vial (see below) confirms cells are present and viable, so if that fires but titration takes many drops, you’re seeing normal reactivity rather than low cell count.
The two confounds (cell count vs. reactivity) are partially disentangled by having both the drop number (threshold) and the endpoint signal intensity (total burden) as outputs.
The Vial System
Vial A — Nuclear control: Maximally potent liberator cocktail (compound 48/80 at saturation + calcium ionophore or similar). Any viable mast cell fires regardless of reactivity level. Confirms:
- Cells were captured on swab
- Cells were viable at time of testing
- Detection chemistry is working
If nuclear control doesn’t fire → invalid test, bad collection or dead cells.
Vial B — Titration vial: Sub-threshold liberator concentration per drop. Each drop incrementally increases stimulus. Contains tryptase-cleavable fluorescent substrate for real-time signal detection.
Vial C — Blank control: Liberator buffer without cells. Confirms liberator alone doesn’t produce false signal. Also establishes baseline fluorescence.
Titration Procedure
- Complete collection and wash protocol (see Feasibility Experiment)
- Split resuspended pellet: portion to nuclear control vial A, portion to titration vial B, buffer only to blank vial C
- Observe vial A — should produce signal within 5-10 minutes. If not, collection failed.
- Add one drop of liberator solution to vial B every 3 seconds
- Observe for fluorescence signal under UV (included keychain UV light)
- Record drop number at first signal — this is the reactivity score
- Continue adding drops to full protocol duration regardless of when signal appears
- At endpoint, apply all three vials to lateral flow strips
- Strip intensity from vial B = total activation burden
- Strip intensity from vial C = background (should be near zero)
Detection Chemistry Options
Primary (Product Target): Tryptase fluorescent substrate
Tryptase-cleavable fluorescent probe — tryptase cleaves substrate, fluorescence appears. Visible under UV.
- Highly specific to mast cell tryptase
- Real-time readout during titration
- Research compounds exist, not yet consumer-available
- This is the novel development work required
Interim (Feasibility/Home): Histamine colorimetric
Post-wash baseline histamine is near zero. Released histamine accumulates in vial. OPA-based colorimetric detection (brewing test kit chemistry).
- Less specific than Tryptase
- Detection chemistry mature and accessible
- Good enough to prove concept
- May be sufficient for product depending on validation data
Visual (Microscope): Toluidine blue cell counting
Direct observation of degranulated vs intact cells. Most definitive but requires microscope. Vision model automates counting. See Vision Model.
The Stabilizer Variant (Treatment Monitoring Mode)
Standard protocol uses cromolyn spray pre-collection as collection stabilizer (suppresses handling stress degranulation). This becomes part of the assay definition — drop number always means “reactivity above the cromolyn floor.”
For treatment monitoring: run same protocol periodically. Is your drop number shifting? That’s objective treatment response data.
For treatment comparison: run without stabilizer spray occasionally to get raw reactivity baseline. Delta between stabilized and unstabilized score reflects how much of your reactivity is coming from baseline activation state vs intrinsic threshold.
Notes on Lateral Flow Application
The titration happens in the vial, not on the strip. The strip is a single-bolus confirmatory/quantitative read applied at endpoint — standard lateral flow geometry is preserved. Drop titration doesn’t break lateral flow assumptions because the assay is decoupled: titration in solution phase, detection on strip at endpoint.
Dropper standardizes volume applied to strip — critical for semi-quantitative line intensity comparison.