Interleukin-1 (IL-1) has been implicated in the pathogenesis of sepsis. IL-1-receptor antagonist (IL-1ra) is a naturally occurring inhibitor of IL-1 activity that competes with IL-1 for occupancy of cell-surface receptors but possesses no agonist activity. We induced endotoxaemia in 9 healthy human volunteers by injection of Escherichia coliendotoxin, and measured plasma concentrations of IL-1 and IL-1ra by radioimmunoassay during the next 24 h. Peak plasma concentrations of IL-1ra were about a hundred-fold greater than those of IL-1β. No IL-1 or IL-1ra were detectable in the plasma of 4 volunteers injected with saline. Our results suggest that the predominant natural response to endotoxin in man is the production of antagonist rather than agonist.
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