Cerebral vessels express interleukin 1beta after focal cerebral ischemia

Rapid and marked increased levels of expression of interleukin 1beta (IL-1beta) mRNA have been detected in animal models of cerebral ischemia. However, the protein production of IL-1beta and the cellular sources of IL-1beta are largely undefined after cerebral ischemia. In the present study, we have measured the cellular localization of IL-1beta protein in brain tissue from non-ischemic and ischemic mice using immunohistochemistry. Male C57B/6J (n=45) mice were subjected to middle cerebral artery (MCA) occlusion by a clot or a suture. The mice were sacrificed at time points spanning the period from 15 min to 24 h after onset of the MCA occlusion. Non-operated and sham-operated mice were used as control groups. A monoclonal anti-IL-1beta antibody was used to detect IL-1beta. In the non-operated and sham-operated mice, a few IL-1beta immunoreactive cells were detected scattered throughout both hemispheres. IL-1beta immunoreactive cells increased in the ischemic lesion as early as 15 min and peaked at 1 h to 2 h after MCA occlusion. IL-1beta immunoreactivity was detected in the cortex of the contralateral hemisphere 1 h after ischemia. By 24 h after onset of ischemia, IL-1beta immunoreactivity was mainly present adjacent to the ischemic lesion and in the non-ischemic cortex. IL-1beta immunoreactivity was found on endothelial cells and microglia. This study demonstrates an early bilateral expression of IL-1beta on endothelium after MCA occlusion in mice.