Kinetics and polarization of the membrane expression of cytokine-induced ICAM-1 on rat brain endothelial cells.

ICAM-1 is a major cellular adhesion molecule by which lymphocytes attach to vascular endothelial cells. Rat brain endothelial cells (RBEC) in culture show very low levels of ICAM-1. However, after exposure to IL-1beta and IFN-gamma, the ICAM-1 expression increases up to 20-fold (as judged by FACS analysis). We used immunogold electron microscopy to examine the kinetics in distribution of cytokine-induced ICAM-1 on the surfaces of tight-junction RBEC (grown on matrigel-coated transwells) when exposed to cytokines from either the luminal (upper well) or the abluminal (lower well) surface. Luminal stimulation produced an early upregulation of ICAM-1 not only on the luminal surface of the endothelial cells but also on the lateral surface below the tight junctions and on the abluminal surface. Peak expression on the abluminal surface of the monolayer occurred at the time of maximal "trapping" of lymphocytes seen during an in vitro migration assay. This suggests that the in vitro trapping, as well as the in vivo trapping described by others, may have its basis in a receptor-ligand interaction. We also demonstrate that when the monolayer is stimulated with cytokine from the abluminal surface there is a delayed but preferential upregulation of ICAM-1 on the luminal surface.