Induced expression of adhesion molecules following focal brain ischemia

Central nervous system injuries such as focal brain ischemia and trauma are known to initiate inflammatory reactions. To demonstrate the involvement of adhesion molecules in these inflammatory responses, we have observed significant increases of ICAM-1 and ELAM-1 mRNA expression in the ischemic cortex of rats by means of Northern blot analysis and/or semiquantitative reverse transcription and polymerase chain reaction (RT-PCR). In the ischemic cortex, levels of ICAM-1 mRNA increased significantly at 3 h (2.6-fold, p < 0.05), peaked at 6 to 12 h (6.0-fold, p < 0.01), and remained elevated for up to 5 days (2.5-fold, p < 0.05) after permanent occlusion of the middle cerebral artery (PMCAO). The basal expression of ELAM-1 mRNA was extremely low (undetectable by Northern analysis). Following focal ischemia, however, ELAM-1 mRNA was markedly increased at 6 h in the ischemic cortex, peaked at 12 h (6.4-fold increase compared to sham samples, p < 0.01), and then returned to almost basal levels by 5 days post-PMCAO. Immunohistochemical stainings using anti-ICAM-1 antibodies demonstrated a marked increase of ICAM-1 in the ischemic cortex over the nonischemic cortex or the sham-operated samples. The immunoreactive ICAM-1 signal was localized to endothelial cells of intraparenchymal blood vessels in the ischemic cortex. Furthermore, time-course analysis demonstrated that the increased expression of ICAM-1 and ELAM-1 parallel those of chemokines such as KC and MCP-1, but are more delayed than those of inflammatory cytokines including TNF-alpha and IL-1 beta, which are known to induce expression of ICAM-1 and ELAM-1 on endothelial cells. The upregulation of the inflammatory genes and their products precedes leukocytes' adhesion to endothelial cells and their migration into the ischemic tissue, suggesting that these upregulated adhesion molecules on brain capillary endothelium play an important role in leukocyte migration into ischemic brain tissue.