Blood–brain–barrier (BBB) breakdown and cerebral edema result from postischemic inflammation and contribute to mortality and morbidity after ischemic stroke. A functional role for the carcinoembryonic antigen–related cell adhesion molecule 1 (CEACAM1) in the regulation of reperfusion injury has not yet been demonstrated.

We sought to identify and characterize the relevance of CEACAM1-expressing inflammatory cells in BBB breakdown and outcome after ischemic stroke in Ceacam1^−/− and wild-type mice.

Focal ischemia was induced by temporary occlusion of the middle cerebral artery with a microfilament. Using MRI and Evans blue permeability assays, we observed increased stroke volumes, BBB breakdown and edema formation, reduction of cerebral perfusion, and brain atrophy in Ceacam1^−/− mice. This translated into poor performance in neurological scoring and high poststroke-associated mortality. Elevated neutrophil influx, hyperproduction, and release of neutrophil-related matrix metalloproteinase-9 in Ceacam1^−/− mice were confirmed by immune fluorescence, flow cytometry, zymography, and stimulation of neutrophils. Importantly, neutralization of matrix metalloproteinase-9 activity in Ceacam1^−/− mice was sufficient to alleviate stroke sizes and improve survival to the level of CEACAM1-competent animals. Immune histochemistry of murine and human poststroke autoptic brains congruently identified abundance of CEACAM1⁺matrix metalloproteinase-9⁺ neutrophils in the ischemic hemispheres.

CEACAM1 controls matrix metalloproteinase-9 secretion by neutrophils in postischemic inflammation at the BBB after stroke. We propose CEACAM1 as an important inhibitory regulator of neutrophil-mediated tissue damage and BBB breakdown in focal cerebral ischemia.