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The fibronectin isoform containing the alternatively spliced extra domain A (EDA+-FN) is normally absent from the circulation, but plasma levels of EDA+-FN can become markedly elevated in several human pathological conditions associated with inflammation including ischemic stroke. It remains unknown whether EDA+-FN contributes to stroke pathogenesis or is simply an associative marker. Several in vitro studies suggest that EDA+-FN can activate Toll-like receptor 4, an innate immune receptor that triggers proinflammatory responses. We undertook a genetic approach in mice to investigate the ability of EDA+-FN to mediate inflammatory brain damage in a focal cerebral ischemia/reperfusion injury model.We used genetically modified EDA+/+ mice, which constitutively express EDA+-FN. Extent of injury, neurological outcome, and inflammatory mechanisms were assessed after 1-hour cerebral ischemia/23-hour reperfusion injury and compared with wild-type mice.We found that EDA+/+ mice developed significantly larger infarcts and severe neurological deficits that were associated with significant increased neutrophil and macrophage infiltration as quantitated by immunohistochemistry. Additionally, we found upregulation of nuclear factor-κB, cyclo-oxygenase-2, and inflammatory cytokines tumor necrosis factor-α, interleukin-1β, and interleukin-6 in the EDA+/+ mice compared with wild-type mice. Interestingly, increased brain injury and neurological deficits were largely abrogated in EDA+/+ mice by treatment with a specific Toll-like receptor 4 inhibitor.These findings provide the first evidence that EDA+-FN promotes inflammatory brain injury after ischemic stroke and suggest that the elevated levels of plasma EDA+-FN observed in chronic inflammatory conditions could worsen injury and outcome in patients after acute stroke.