Endogenous Ceramide 24:1 Constrains Th17-Driven Neutrophilic Inflammation by Antagonizing EP2 Signaling.

Dysregulated chronic inflammation underlies a spectrum of severe asthma phenotypes, among which neutrophilic asthma (NA) represents a treatment-recalcitrant endotype characterized by Th17-driven airway inflammation and steroid resistance. Although lipid mediators are known to play dual roles in promoting and resolving inflammation, the lipid species governing the Th17-neutrophil axis in NA remain unknown. Here, through integrated lipidomic profiling of clinical samples (exhaled breath condensate, plasma, sputum) from an NA cohort and a murine model of Th17-driven airway inflammation, a deficiency in very-long-chain ceramides, notably Cer24:1, was identified. This reduction correlated with disease severity and neutrophilic inflammation. In vivo, Cer24:1 supplementation alleviated airway hyperresponsiveness and neutrophilic infiltration, while Smpd1 knockout mice-with impaired ceramide generation-displayed exacerbated Th17 pathology. Using structure-guided molecular docking, surface plasmon resonance, and functional assays, Cer24:1 was shown to directly target the prostaglandin E2 receptor EP2 on CD4+ T cells. This interaction suppressed JAK2-STAT3 signaling and RORγt-driven Th17 differentiation. Notably, PGE2 competitively reversed Cer24:1's protective effects, further supporting EP2-dependent modulation. Our results reveal Cer24:1 as an endogenous pro-resolving lipid that constrains neutrophilic inflammation via direct modulation of the EP2-STAT3 axis in Th17 cells, providing a new metabolic checkpoint and potential therapeutic strategy for severe neutrophilic asthma.