Endotoxin-macrophage interaction: post-translational regulation of tumor necrosis factor expression.

Abstract

Thioglycollate-elicited murine peritoneal macrophages produce significant quantities of TNF 2 to 4 h after induction with bacterial endotoxin, LPS. However, macrophages exposed to a second LPS stimulus are refractory and the amount of TNF detected in these supernatants is reduced 10- to 50-fold. The acquisition of the refractory state in vitro or in vivo requires the continued presence of LPS for a minimum of 6 to 8 h, is optimal by 20 h, and is reversible. Refractory macrophages incubated for an additional 48 h in the absence of LPS produce significant quantities of TNF after reexposure to endotoxin. Although LPS refractory macrophages do not release TNF in response to a secondary endotoxin challenge, riboprobe ribonuclease protection assays demonstrated amplification of TNF message, suggesting that post-transcriptional events are involved in the regulation of TNF production in endotoxin refractory macrophages. Immunoprecipitation studies revealed the accumulation of the 26-kDa TNF precursor in lysates of refractory macrophages, thus demonstrating a post-translational regulatory process. Although LPS refractory macrophages do not release TNF in response to a second LPS stimulus, ingestion of zymosan by these cells results in the release of significant quantities of TNF. Furthermore, LPS-refractory macrophages do not demonstrate a reduction in other effector functions including Fc-mediated erythrophagocytosis. Therefore, the LPS refractory state is a metabolically dependent post-translational regulatory process, which requires continuous LPS exposure, is specific in which macrophage effector functions are inhibited, and is reversible with further incubation or by non-LPS-related stimuli.

NF-κB1 (p50) Is Upregulated in Lipopolysaccharide Tolerance and Can Block Tumor Necrosis Factor Gene Expression

“…LPS tolerance may be regulated at the translational (20) and posttranslational (46) levels, but most studies have demonstrated a decrease in transcripts for TNF in tolerant cells (11,21,31). In the present study, we have confirmed that LPS tolerance in Mono Mac 6 cells accompanies a decreased level of TNF protein and mRNA.…”

Prolonged Inhibition of the MEK1/2-ERK Signaling Axis Primes Interleukin-1 Beta Expression through Histone 3 Lysine 9 Demethylation in Murine Macrophages

“…Several stimuli, including β-glucan, Bacillus Calmette-Guérin (BCG) vaccine, and oxidized low-density lipoprotein (oxLDL), render macrophages to a trained state that enhances inflammatory responses when cells are subsequently exposed 2 of 20 to microbial components such as lipopolysaccharide (LPS) [3,4]. Conversely, tolerance is demonstrated when macrophages that were pre-exposed to LPS become less responsive to the same or similar stimuli in producing inflammatory cytokines [5]. The first level of tolerance is a general dampening of activation and signaling through transient (lasting hours) negative feedback mechanisms including the downregulation of receptors [6], expressing negative signaling regulators, such as A20 [7] and interleukin-1 receptor-associated kinase-M (IRAK-M) [8], and inducing repressive transcription factors, such as B cell leukemia-3 and nuclear factor-κB (NF-κB) p50 [9].…”