IL-25-ILC2-IL-13 axis improves traumatic brain injury by mediating CXCL-10-dependent regulation of blood brain barrier integrity.

BACKGROUND: Traumatic brain injury (TBI) causes severe disruption of the blood-brain barrier (BBB), a key event that contributes to secondary neurological damage. Interleukin-25 (IL-25) has recently emerged as an important regulator of neuroinflammation, yet its role in BBB repair after TBI remains unclear. This study investigated the protective effects of IL-25 on BBB integrity and neurological function in mice following TBI and explored the underlying mechanisms. METHODS: IL-25 expression in mouse serum and cortical tissue after TBI was quantified using enzyme-linked immunosorbent assays, and its cellular sources were identified via immunofluorescence staining. The impact of exogenous IL-25 on BBB integrity was evaluated by measuring, tight junction proteins (ZO-1, occludin, and claudin-5), Evans Blue extravasation, and cerebral edema on magnetic resonance imaging. Mechanistic, investigations using flow cytometry and in vitro oxygen glucose deprivation/reoxygenation models assessed whether IL-25 acted directly on brain microvascular endothelial cells (BMECs) or indirectly through immune pathways. Cytokine array and Western blot analyses were used to identify downstream mediators, and single-cell RNA sequencing was performed to characterize IL-25-induced transcriptional changes. Neurological function was assessed using the modified Neurological Severity Score, rotarod test, and Morris water maze. RESULTS: IL-25 levels increased significantly in the cortex and serum after TBI, peaking at day 3, with neurons and BMECs identified as the main sources. Exogenous IL-25 administration alleviated BBB dysfunction, restored tight junction protein expression, reduced Evans Blue leakage, and diminished cerebral edema. Mechanistically, IL-25 acted indirectly by activating brain-resident group 2 innate lymphoid cells to secrete interleukin-13 (IL-13), rather than acting directly on BMECs. IL-13 preserved BBB integrity by suppressing C-X-C motif chemokine ligand 10 (CXCL-10) expression and inhibiting endothelial pyroptosis. Single-cell RNA sequencing confirmed upregulation of BBB-protective genes such as Tiam1, Hsp90aa1, and Hes1, along with activation of tight junction and transforming growth factor-β signaling pathways. IL-25 treatment improved both motor coordination and cognitive performance after TBI. CONCLUSIONS: IL-25 promotes BBB repair and enhances neurological recovery following TBI by inducing ILC2-derived IL-13, which suppresses CXCL-10 and endothelial pyroptosis. These findings identify IL-25 as a potential therapeutic target for mitigating BBB damage and improving outcomes after TBI.