PLEIOTROPIC EFFECT OF INTERLEUKIN-1 ON ENDOTHELIAL CELLS

Inflammatory processes are often associated with pathological alteration of the vessel wall and sometimes with local or disseminated thrombotic phenomena. Interleukin-1 (IL-1), a monokine produced by activated cells of the monocyte/macrophage lineage and responsible of most of the changes associated with the inflammatory acute phase response, appears to dramatically' modify several endothelial cell (EC) functions. Some groups including ours (for review 1) have shown that IL-1 stimulates prostacyclin (PGI2), platelet activating factor (PAF), plasminogen activator inhibitor (PAi), thromboplastin (PCA) synthesis by cultured human EC in vitro. In addition IL-1 can act directly on EC to increase neuthophil and other leukocyte adhesion on their surface (2). All these effects, in contrast to previously described inducers, require a long time of interaction (30 min to 4 hours) of IL-1 with EC to be apparent and then last for several hours (4 to 12 hours). The IL-1 effects are concentration dependent (minimal active concentration being about 1 unit/ml) and require protein and RNA synthesis. To better define the structural requirement for IL-1 induced modification of EC functions we compared the activity of different IL-1 molecular species. Our approach is based on the observation that IL-1 is indeed a family of polypeptides biochemically different(3). At least two dissimilar gene products have been cloned with very limited homology (denominated α and β). These molecules, though biochemically different, share common activities and possibly the same receptor in different cell types. On EC we investigated whether the αand β IL-1 forms have similar biological activities (4). All the IL-1 preparations used were active on thymocyte costimulatory assay and comparison was made on the basis of the concentrations of these agents equally active on this assay.Human recombinant IL- αandβ (hr IL-1 α and hr IL-1 β) were both active in stimulating PGI2, PCA, PAi production and in increasing neutrophil adhesion to EC. In contrast PAF synthesis was Stimulated by hr IL-1 α but not by hr IL-1 β. Murine recombinant IL-1 (mr IL-1 α highly homologous with hr IL-1 < α, at concentrations able to maximally activate thymocytes was inactive on PGI2, PCA and in increasing neutrophil adhesion to EC. In contrast, mr IL-1 α was equally effective on PAF production as hr IL-1 α. A short peptide fragment of hr IL-1β (fragment 167-171) was synthesized on the basis of its predicted exposure on the surface of the molecule (5). This peptide is also located in a region (150-186) of high homology between hr IL-1α and β sequences. While the peptide showed high thymocyte activation capacity it was inactive on EC activities. Overall these results indicate that the α and β forms of human IL-1 elicit largely but not completely overlapping patterns of response in EC. In addition they suggest that the structural requirement for activation by IL-1 is not identical for thymocytes and EC. These results might provide some clues to novel strategies for modulation of IL-1 vascular and immunological activities.1. Mantovani A. and E. Dejana (1987) Biochem. Pharm. 36:301.2. Bevilacqua M. et al. (1985) J. Clin. Invest. 76:20033. Dinarello C.A. (1985) J. Clin. Immunol. 5:287.4. Dejana E. et al. (1987) Blood 69:695.5. Antoni G. et al. (1987) J. Immunol, (in press).