Interleukin-6 is a mediator of therapeutic efficacy in acute lung injury.

Summary

Using individual patient data from five RCTs, this mediation analysis shows that reductions in IL-6 partially mediate the survival benefit of imatinib, anakinra, and low tidal volume ventilation, whereas higher PEEP and simvastatin do not influence IL-6 trajectories. Elevated IL-6 consistently associates with increased 28-day mortality across studies.

Key Findings

• IL-6 mediated the mortality benefit of imatinib, anakinra, and low tidal volume ventilation.
• Higher PEEP and simvastatin did not change IL-6 trajectories.
• Across trials, higher IL-6 levels were strongly associated with increased 28-day mortality (pooled HR per log10 increase 4.83, 95% CI 3.50–6.66).
• Other inflammatory markers (IL-8, TNFR1, CRP) were analyzed, but IL-6 emerged as the key mediator.

Clinical Implications

IL-6 trajectory monitoring may inform response-adaptive strategies and trial enrichment, and supports targeting inflammation resolution. Interventions not altering IL-6 (e.g., higher PEEP, simvastatin) may act via non-IL-6 pathways or be ineffective on inflammatory resolution.

Limitations

• Secondary mediation analysis not randomized for the mediator; potential residual confounding
• Heterogeneity in assay timing and platforms across trials may affect IL-6 comparability

Future Directions

Prospective IL-6-guided stratification and response-adaptive trials; interventional studies testing IL-6 reduction as a surrogate endpoint and integrating multi-analyte inflammatory panels.