INHIBITION OF PLATELET ENDOTHELIAL-CELL ADHESION MOLECULE-1 SYNTHESISAND LEUKOCYTE TRANSMIGRATION IN ENDOTHELIAL-CELLS BY THE COMBINED ACTION OF TNF-ALPHA AND IFN-GAMMA

Endothelial cell (EC) junctions regulate circulating leukocyte extrava sation and infiltration at inflammatory sites. Several lines of eviden ce show that platelet endothelial cell adhesion molecule-1 (PECAM-1), a specific component of EC junctions, is required for leukocyte transm igration through EC monolayers. In this paper, we examined the effects of two inflammatory cytokines, TNF-alpha and IFN-gamma, on PECAM-1 an d vascular endothelial-cadherin/catenin organization. We found that th e addition of inflammatory cytokines (TNF-alpha plus IFN-gamma in comb ination, for greater than or equal to 24 h) caused PECAM-1 to disappea r from EC intercellular contacts. Confocal microscopy indicated that a fter treatment with the cytokines, PECAM-1 was rapidly internalized, I n addition, a strong inhibition of PECAM-1 synthesis and a decrease in PECAM-1 mRNA were observed. This phenomenon was only found when TNF-a lpha plus IFN-gamma were used in combination. Adhesion of polymorphonu clear cells to doubly treated EC was increased compared with control c ells or cells incubated with TNF-alpha or IFN-gamma separately. This w as correlated with an increased expression of intercellular adhesion m olecule-1. However, the disappearance of PECAM-1 from cell junctions a fter treatment with TNF-alpha plus IFN-gamma was accompanied by a mark ed reduction of leukocyte migration through EC monolayers, The correla tion between PECAM-1 level and leukocyte transmigration was supported by transmigration inhibition assays using blocking anti-PECAM-1 mAb. T hese data indicate that PECAM-1 is a specific target of inflammatory c ytokines and suggest that changes in its synthesis and organization mi ght negatively modulate leukocyte recruitment.