Sensory neuroimmune signaling in the pathogenesis of Stevens-Johnson syndrome and toxic epidermal necrolysis.

Background: Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are life-threatening cutaneous reactions often triggered by medications. While the involvement of CD8⁺ T cells causing keratinocyte death is well recognized, the contribution of neural elements to the persistent skin inflammation has been largely overlooked.

Objective: We investigated the potential neuroimmune regulation in SJS/TEN.

Methods: Unbiased single-cell RNA sequencing and flow cytometry were performed using circulating CD8⁺ T cells from healthy controls and patients with SJS/TEN. ELISA and LEGENDplex assays were respectively used to detect neuropeptides and inflammatory mediators. Skin tissues were examined by immunofluorescence staining for neuropeptide-associated nerves and cytokine receptors. Calcium imaging, Smart-seq, and a 3-D skin model were used for cultured human CD8⁺ T cells.

Results: Unbiased RNA sequencing revealed an upregulation of the receptor for neuropeptide calcitonin gene-related peptide (CGRP), known as RAMP1, in effector CD8⁺ T cells in SJS/TEN. Increased CGRP⁺ nerve fibers and CGRP levels, along with upregulated IL-15R and IL-18R on CD8⁺ T cells, were displayed in the affected skin of SJS/TEN. The CGRP-RAMP1 axis was necessary and sufficient to enhance receptors for IL-15 and IL-18 and cytotoxic activities in CD8⁺ T cells, ultimately resulting in keratinocyte apoptosis. Calcium influx was detected in CGRP-stimulated CD8⁺ T cells. HCN2, a hyperpolarization-activated cation channel, was required for this process and the subsequent cytotoxic effects.

Conclusions: Our study highlights the role of neural elements in regulating CD8⁺ T-cell-mediated inflammatory responses and provides new potential translational targets to improve the outcomes of severe cutaneous drug reactions.