Platelets Orchestrate a Neuroimmune Axis Driving Cutaneous Inflammation and Itch

Platelets are traditionally recognized for their roles in hemostasis, but their involvement as active immune modulators in cutaneous neuroimmune signaling remains poorly understood. In this study, we integrated multi-modal genetic and pharmacological strategies to investigate the functional contribution of platelets to skin inflammation and chronic itch. Optogenetic activation of platelets was sufficient to elicit localized skin inflammation, erythema, and robust pruritus, with transcriptomic profiling of lesions showing strong concordance with the clinical signatures of atopic dermatitis (AD). In experimental AD models, platelet depletion markedly reduced scratching behavior, inflammatory cell infiltration, and C-fiber excitability, whereas platelet activation exacerbated these phenotypes. Mechanistically, activated platelets release serotonin [5-hydroxytryptamine (5-HT)], which compromises vascular integrity and facilitates platelet extravasation into the dermis. This "neuroimmune hub" promotes macrophage recruitment and sensitizes TRPV1⁺ pruriceptors. Transcriptomic analysis revealed that platelet-derived 5-HT drives these processes via HTR2B and HTR7 signaling. Specifically, genetic ablation of HTR2B in TRPV1⁺ neurons selectively impaired itch transmission. Furthermore, re-analysis of clinical datasets confirmed the enrichment of HTR2B and HTR7 in skin macrophage populations during inflammation. Systemic administration of HTR antagonists or the anti-platelet agent clopidogrel markedly attenuated both inflammation and pruritus across multiple models. Our findings identify the platelet-immune-neuron axis as a key driver of cutaneous dysfunction and a promising therapeutic target for chronic inflammatory skin disorders.