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-1 beta and IF N-gamma, the ICAM-1 expression increases up to 20-fold (as judged by FACS a nalysis). 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 e ither the luminal (upper well) or the abluminal (lower well) surface. Lumin al stimulation produced an early upregulation of ICAM-1 not only on the lum inal surface of the endothelial cells but also on the lateral surface below the tight junctions and on the abluminal surface. Peak expression on the a bluminal surface of the monolayer occurred at the time of maximal "trapping " of lymphocytes seen during an in vitro migration assay. This suggests tha t the in vitro trapping, as well as the in vivo trapping described by other s, may have its basis in a receptor-ligand interaction. We also demonstrate that when the monolayer is stimulated with cytokine from the abluminal sur face there is a delayed but preferential upregulation of ICAM-1 on the lumi nal surface.