LPS tolerance in macrophages

Among the multiple mechanisms that control the intensity and duration of macrophage activation, the development of a state of refractoriness to a second stimulation in cells treated with LPS has long been recognized. Release of inhibitory cytokines and alterations in intracellular signaling pathways may be involved in the development of LPS tolerance. Although a number of molecules have been implicated, a detailed picture of the molecular changes in LPS tolerance is still missing. We have used a genome-wide gene expression analysis approach to (i) define which fraction of LPS target genes are subject to tolerance induction and (ii) identify genes that are expressed at high levels in tolerant macrophages. Our data show that in LPS tolerant macrophages the vast majority of LPS-induced gene expression is abrogated. The extent of tolerance induction varies for individual genes, and a small subset appears to be excepted. Compared to other negative control mechanisms of macrophages, e.g. IL-10-induced deactivation, LPS-tolerance inhibits a much wider range of transcriptional targets. Some previously described negative regulators of TLR-signaling (e.g. IRAK-M) were confirmed as expressed at higher levels in LPS-tolerant macrophages. In addition, we discuss other potential players in LPS tolerance identified in this group of genes. Keywords: pre and restimulation with LPS, tolerance induction Cells were either prestimulated (1_X) or not (0_X) for 18h with 100 ng/ml LPS. Media was exchanged and after 2h rest, cells either restimulated (X_1) or not (X_0) with again 100 ng/ml LPS. This resulted in 4 experimental conditions: 0_0, 0_1, 1_0 and 1_1. There were 3 biological replicates done, resulting in 12 arrays altogether.