Author(s): Escoll P, del Fresno C, Garca L, Valls G, Lendnez MJ,
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Abstract The exposure of human monocytes to the gram-negative endotoxin LPS provokes them to enter a transient state in which they are refractory to further stimulation by LPS. This phenomenon is known as 'endotoxin tolerance' (ET) and it is characterized by a decrease in leukocyte proinflammatory cytokine production in response to LPS. In the present study, we have analyzed the expression of IRAK-M mRNA and protein in a human model of ET using human monocytes isolated from peripheral blood. In these monocyte cultures, IRAK-M mRNA was expressed 6h after stimulation with different doses of LPS. However, endotoxin pretreatment induced a more immediate up-regulation of IRAK-M gene expression, transcripts appearing only one hour after a second LPS-challenge, and the production of high levels of IRAK-M protein in these tolerant monocytes. We also analyzed the response of monocytes isolated from septic patients within a temporal tolerance timeframe when stimulated ex vivo with LPS. In contrast to monocytes from healthy volunteers and patients outside of the tolerance timeframe, monocytes from septic patients rapidly expressed IRAK-M mRNA when stimulated with LPS ex vivo. Moreover, the expression of IRAK-M mRNA was more rapidly induced in the presence of a PI3K inhibitor, suggesting a connection between these two kinases. Thus, our data indicate that IRAK-M could play a pivotal role in the process of ET in human monocytes and provide evidence that PI3K is involved in regulating its expression.
This article was published in Biochem Biophys Res Commun
and referenced in Journal of Clinical & Cellular Immunology