Epidermal and Dermal T Cells Exhibit Distinct Proteomic Signatures.

T lymphocytes in human skin play essential roles in immune surveillance and tissue homeostasis, with distinct populations residing in the epidermal and dermal compartments. To characterize the molecular basis of their compartmentalized functional specialization, we performed proteomic analysis of total T cell populations isolated from healthy human skin, combining flow cytometry and liquid chromatography-tandem mass spectrometry. We quantified 5985 proteins across epidermal and dermal T cell populations, identifying 2177 significantly differentially expressed proteins (FDR < 0.05), including 1008 with >2-fold changes. Compared with dermal T cells, epidermal T cells showed elevated intensity of tissueresidency marker CD69, co-stimulatory protein CD27, complement components (C3, C4a, and Factors B and D), and proteins involved in oxidative phosphorylation and cholesterol metabolism. Epidermal T cells also exhibited higher levels of antimicrobial S100 proteins, chemokine receptor CCR6, IL-18, and MHC class I molecules, while, in contrast, dermal T cells showed increased expression of CXCR4, IL-16, and MHC class II-related proteins. While these distinct proteomic signatures suggest compartment-specific adaptations in metabolism, immune surveillance, and antigen presentation, the results should be interpreted as exploratory, given methodological limitations. Nonetheless, this study provides a valuable molecular resource for understanding the specialization of T cells within different skin layers and offers a basis for future investigations into skin immune biology and its potential implications in disease.