Interleukin 1 (IL-1) alters several potentially pathogenic endothelial cell (EC) functions. The authors report here that recombinant human IL-1 (rIL-1) alpha (0.1 to 10 ng/ml) or IL-1-beta (1 to 100 ng/ml) induce concentration- and time-dependent increases in IL-1-beta mRNA levels in EC derived from adult human saphenous vein. rIL-1 induced IL-1-alpha mRNA only in EC treated concomitantly with cycloheximide (2 micrograms/ml). IL-1-beta mRNA production began within 1 hr of exposure to rIL-1, peaked after 24 hr, and declined thereafter. Actinomycin D prevented the appearance of IL-1 mRNA in rIL-1-treated EC. rIL-1 also induced the release of biologically active IL-1 from EC, which was inhibited by cycloheximide (1 microgram/ml). When compared on the basis of their activity in the thymocyte costimulation assay, rIL-1-alpha and rIL-1-beta were equipotent as inducers of IL-1 production by EC. EC stimulated with rIL-1 produced prostaglandin E2, which inhibits IL-1 production by other cell types and also decreases the responsiveness of thymocytes to IL-1. When EC were exposed to rIL-1 in the presence of indomethacin (1 microgram/ml), which blocked prostaglandin E2 production, greater amounts of rIL-1-induced IL-1 release were detected, although the inhibitor did not affect IL-1-beta mRNA levels. IL-1-induced IL-1 production was unlikely to be caused by endotoxin contamination of tissue culture media or IL-1 preparations, because the lipopolysaccharide (LPS) antagonist polymyxin B (10 micrograms/ml) blocked LPS-induced IL-1 production by EC but did not affect IL-1 release in response to rIL-1-beta (100 ng/ml). The IL-1-inducing property of rIL-1-beta was heat-labile, whereas heated LPS stimulated EC IL-1 production. The source of IL-1 in our cultures was not monocyte/macrophages, as treatment of EC with monoclonal antibody to the monocyte antigen Mo2 under conditions that lysed adherent peripheral blood monocytes did not affect production of IL-1 by EC in response to LPS (1 microgram/ml) or rIL-1-beta (100 ng/ml). IL-1 elicits a coordinated program of altered endothelial function that increases adhesiveness for leukocytes and coagulability. IL-1-induced IL-1 gene expression in human adult EC could thus provide a positive feedback mechanism in the pathogenesis of vascular disease including atherosclerosis, vasculitis, and allograft rejection.