INTERLEUKIN-1 INDUCES INTERLEUKIN-8 SECRETION FROM ENDOTHELIAL-CELLS BY A JUXTACRINE MECHANISM

Inflammation is characterized by migration of neutrophils through the endothelium, and the chemokine interleukin-l (IL-8) appears to be involved. We asked whether adherence of cells bearing a membrane-form of interleukin 1 (IL-1) induces IL-8 secretion from human umbilical vein endothelial cells (HUVEC) and fibroblasts. Human peripheral blood mononuclear cells (PBMC) were stimulated with endotoxin for 12 hours and then fixed for 4 hours with paraformaldehyde. When these cells were added to HUVEC or fibroblasts, IL-8 production was induced. This stimulation by fixed PBMC was attributed to IL-l, because pretreatment of HUVEC or fibroblasts with IL-l receptor antagonist (1L-1Ra) reduced the induction by 95% and 80%, respectively, P < .005. Using anti-ll-l alpha monoclonal antibodies, reduction was complete, whereas anti-IL-l beta had no effect. IL-1 alpha was shown on the surface of monocytes by fluorescence-activated cell sorter (FAGS) analysis. Blockade of IL-l receptors on PBMC did not affect the activity of membrane-associated IL-1 alpha, indicating that IL-l is not anchored to the membrane through its receptors. However, PBMC treated with D-mannose before fixation resulted in a loss of activity; this loss of activity was associated with release of IL-l1 alpha, not IL-1 beta, into the supernatant. Thus, anchoring of IL-1 alpha to the membrane may be via a lectin or mannose receptor-like interaction. Blockade of membrane IL-1 alpha required a 30-fold and fivefold excess of IL-1Ra compared with the amount required to block soluble IL-1 beta and IL-1 alpha, respectively. We conclude that the fixed PBMC IL-8 inducing activity is almost entirely caused by IL-l, that this represents lL-1 alpha bound to a surface lectin or mannose receptor on the monocyte, and that it functions in inflammation via juxtacrine interactions. (C) 1994 by The American Society of Hematology.