The present study was designed to clarify (1) the effects of cytokines on intercellular adhesion molecule-1 (ICAM-1) expression on human endothelial cells (EC) and soluble ICAM-1 (sICAM-1) production by these cells and (2) the effects of purified sICAM-1 on leukocyte-EC adhesion. IL-1 beta and TNF-alpha induced a parallel increase of both the ICAM-1 expression on EC and sICAM-1 production by EC, while IFN-gamma induced only the dose dependent enhancement of ICAM-1 expression, but not the production of sICAM-1, IL-4 and IL-6 did not show any effects on the ICAM-1 expression nor on the sICAM-1 production. IL-4 and IL-6 abolished the expression enhancing effect by IL-1 beta, while TNF-alpha showed a synergism with IL-1 beta to promote ICAM-1 expression on EC. The sICAM-1 continued to accumulate in the culture supernatant even at 48 h after stimulation of EC by IL-1 beta, whereas the ICAM-1 expression on EC reached the maximum at 40 h and declined thereafter under the stimulation by IL-1 beta. IL-1 beta treatment of EC resulted in an increase in adhesion of leukocytes to the EC. The sICAM-1, purified from the cell-free supernatant obtained after a 48 h culture of EC in IL-1 beta by affinity column chromatography using monoclonal ICAM-1 antibody coupled to Sepharose beads, significantly inhibited leukocyte-EC adhesion.(ABSTRACT TRUNCATED AT 250 WORDS)