Interleukin-1β inducesin vivotolerance to lipopolysaccharide in mice

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Abstract
Endotoxin or lipopolysaccharide (LPS) tolerance may be partially due to the secretion of potent anti-inflammatory cytokines following severe Gram-negative infections, or by low doses of LPS. In this work, we describe the effects of interleukin-1β (IL-1β) and tumour necrosis factor alpha (TNF-α), two early cytokines secreted after LPS exposure, in the induction of LPS tolerance. Our results demonstrate that mice treated with three daily doses of 100 ng of IL-1β were tolerant to LPS-induced shock. However, TNF-α was unable to induce an LPS refractory state. Given the fact that 100 ng of IL-1β increase the plasma levels of glucocorticoids, we evaluated whether a daily injection of dexamethasone (DEX) alone was able to reproduce the LPS-like tolerant state. However, no signs of LPS refractoriness were detected, except when DEX was administered concomitantly with a dose of IL-1β that does not induce corticosterone secretion (12 ng/mouse). This dose was found to induce in vitro up-regulation of the glucocorticoid receptors (GcR) of peritoneal macrophages following 24 h of treatment. In addition, we demonstrate that IL-1β is capable of inducing the down-regulation of Toll-like receptor 4 (TLR4), a crucial molecule in the signal transduction of LPS. Taken together, our results indicate that IL-1β can generate tolerance to LPS in vivo, and suggest that the regulation of mechanisms of the down-regulation of TLR4, as well as those involved in the expression of GcR and/or in the secretion of glucocorticoids, would be crucial for these effects.