Gut microbiota mediates trafficking of intestinal T cells to the brain to exacerbate neuroinflammation after ischemic stroke

Ischemic stroke disrupts neuroimmune homeostasis, leading to pronounced neurological impairment, yet the cellular mechanisms remain incompletely defined. Here, we construct a high-resolution spatiotemporal immune atlas of infarcted brain regions from post-stroke patients using imaging mass cytometry, revealing a marked perivascular accumulation of PD-1⁺ T cells. Parallel investigations in a murine model of middle cerebral artery occlusion (MCAO) recapitulate this central enrichment, with PD-1⁺ T cell infiltration peaking at three days post-ischemia and persisting for up to fourteen days. Spatiotemporal fate mapping with Kaede photoconvertible reporter mice demonstrates that intestinal-derived PD-1⁺ T cells infiltrate the injured brain in a gut microbiota–dependent manner and engage directly with brain-resident PD-L1⁺ microglia. Both genetic and pharmacological disruption of the gut–brain PD-1/PD-L1 axis markedly reduces the infiltration of gut-derived T cells and ameliorates neurological deficits. Single-cell RNA sequencing of PD-L1⁺ microglia identifies Notch1-driven inflammatory signaling as a key mediator of neuroinflammation. Notably, acute stroke patients exhibit a significant increase in circulating PD-1⁺ T cells, serving as a diagnostic indicator of central nervous system injury. Together, these findings define a previously unrecognized gut–brain immune circuit that orchestrates post-stroke neuroinflammation and highlight circulating PD-1⁺ T cells as a potential biomarker of neurological damage.