Single-cell transcriptomic profiling reveals aberrant CD4⁺ naive T cell differentiation driving immune activation in Behçet's uveitis.

BACKGROUND: Behçet's uveitis (BU) is a severe inflammatory ocular manifestation of Behçet's disease, characterized by dysregulated T cell responses. However, the precise mechanisms underlying T cell dysfunction and local immune activation in BU remain poorly understood. METHODS: We performed single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs) from BU patients and healthy controls (HCs). These data were integrated with publicly available single-cell transcriptomes of aqueous humor (AH) samples from BU patients. Key findings were validated using qPCR, flow cytometry, and functional assays. RESULTS: We observed a significant depletion of naive CD4⁺ T cells in BU, accompanied by their differentiation toward terminal effector states characterized by IL-32 and CXCR4 upregulation. IL-32 was identified as a central regulator promoting Th1 and Th17 polarization. Pseudotime trajectory analysis revealed a progressive differentiation process from circulating CD4⁺ T cells to Th17-like inflammatory cells within the AH, enriched for NF-κB and JAK-STAT signaling pathways. CXCR4 expression was associated with T cell chemotaxis into the ocular microenvironment. Cell-cell interaction analyses further highlighted active crosstalk between macrophages and CD4⁺ T cells via the MIF-(CD74(+)CXCR4/CD44) signaling axis. CONCLUSION: Our study reveals a coordinated mechanism linking systemic T cell dysregulation to localized ocular inflammation in BU. Targeting IL-32 and CXCR4 may represent promising strategies for restoring immune balance and preventing tissue damage in BU.