Hypothesis

We propose that chronic activation of the NLRP3 inflammasome drives a parallel decline in pain sensitivity and adaptive immune function, making heat pain threshold a readable proxy for inflammasome-mediated biological age.

Mechanistic rationale

• NLRP3 activation in myeloid cells releases IL-1β and IL-18, which promote systemic low-grade inflammation and sustain NF-κB signaling in lymphoid tissues.
• Persistent NF-κB signaling upregulates inhibitory receptors (PD-1, KLRG1, TIM-3) on CD8+ T cells, pushing them toward an exhausted/senescent phenotype.
• IL-1β also acts on sensory neurons and spinal glia, lowering the threshold for heat pain via TRPV1 sensitization and enhancing microglial reactivity, thus reducing pain tolerance.
• Consequently, individuals with high NLRP3 activity exhibit both low heat pain thresholds and elevated exhausted T-cell frequencies, linking sensory perception to immune aging.

Testable predictions

1. In aged mice, pharmacological inhibition of NLRP3 (e.g., MCC950) will increase heat pain threshold (longer latency to withdrawal) and decrease the proportion of PD-1+KLRG1+ CD8+ T cells in blood and spleen.
2. Adoptive transfer of NLRP3-deficient myeloid cells into wild-type aged recipients will rescue both pain tolerance and T-cell phenotypes without altering baseline inflammasome genetics in lymphocytes.
3. Cross-sectional human data will show that individuals in the lowest quartile of heat pain threshold have significantly higher plasma IL-1β and a greater CD8+ PD-1+ fraction than those in the highest quartile, independent of chronological age.
4. Longitudinally, a ten-minute quantitative sensory testing (QST) session predicting baseline NLRP3 activity (measured via monocyte caspase-1 cleavage) will forecast changes in epigenetic age acceleration (GrimAge) over 12 months better than standard frailty indices.

Experimental approach (murine)

• Use 20-month-old C57BL/6 mice; treat half with MCC950 (20 mg/kg i.p. thrice weekly) for 8 weeks, controls receive vehicle.
• Assess heat pain threshold via Hargreaves test (latency to hind-paw withdrawal).
• Flow cytometry of splenic CD8+ T cells for PD-1, KLRG1, TIM-3, and intracellular caspase-1 activity as a readout of NLRP3 signaling.
• ELISA for plasma IL-1β, IL-18.
• Statistical comparison using two-way ANOVA with post-hoc Tukey.

Human validation

• Recruit 120 adults aged 40-80; stratify by sex and BMI.
• Perform QST: heat pain threshold (median of five trials).
• Collect peripheral blood for plasma cytokines (IL-1β, IL-18) and flow cytometry for exhausted CD8+ markers.
• Compute GrimAge from DNA methylation.
• Use linear regression to test whether pain threshold predicts GrimAge after adjusting for age, sex, BMI, and smoking.

Falsifiability

If NLRP3 inhibition fails to improve pain threshold or does not reduce exhausted T-cell frequencies, or if pain threshold shows no association with inflammasome biomarkers or epigenetic age acceleration, the hypothesis would be refuted. Likewise, demonstrating that pain sensitivity changes occur independently of NLRP3 activity (e.g., in NLRP3-sufficient mice with sensory-specific TRPV1 overexpression) would challenge the proposed mechanistic link.

Broader impact

Confirming this link would position a simple, inexpensive sensory test as a functional readout of inflammasome-driven immunosenescence, offering a rapid screening tool for interventions targeting inflammasome components (e.g., NLRP3 inhibitors, colchicine) in aging populations.