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Modulation of lipopolysaccharide-induced cytokine gene expression in mouse bone marrow-derived macrophages by muramyl
C Le Contel1, N Temime, D J Charron
1Laboratoire d'Immunopharmacologie Experimentale, CNRS UPR 405, Paris, France.
Abstract:
Previous studies have shown that an i.v. injection of muramyl dipeptide (MDP) before a LPS challenge strongly potentiated serum TNF and IL-6 release in mice. Therefore the direct action of MDP was examined on TNF-producing cells, namely in macrophages stimulated or not by LPS. The level of TNF-alpha, IL-1 alpha, and IL-6 mRNA was determined in bone marrow-derived macrophages (BMM). A marked TNF-alpha mRNA accumulation was found between 1 and 6 h after stimulation with MDP or LPS. LPS-induced IL-1 alpha mRNA transcript was delayed (3 h) than those after MDP induction (1 h). Conversely, kinetic induction of the IL-6 mRNA transcript was delayed in MDP-treated BMM as compared with LPS-stimulated cells. MDP pretreatment of BMM for 3 h not only enhanced the total level of LPS-induced TNF-alpha, IL-1 alpha, and IL-6 mRNA (respectively 2.9-, 1.6-, and 2.4-fold increase), but it also delayed the kinetics of IL-1 alpha and IL-6 species accumulation. The enhancement induced by MDP pretreatment at the level of cytokine mRNA accumulation was correlated with an increase in LPS-induced TNF and IL-6 biologic activity production in supernatant fluids. In addition, in BMM from C3H/Hej mice MDP pretreatment enhanced the weak effect of LPS on TNF mRNA transcript accumulation and was required to produce LPS-induced TNF bioactivity. Our results suggest that MDP and LPS could act through distinct pathway(s) to induce cytokine gene expression. Moreover, the priming effect displayed by MDP could result in modulation of the LPS-induced cytokine gene expression at the transcriptional and/or post-transcriptional level.
Insights
Muramyl dipeptide (MDP) primes macrophages, enhancing lipopolysaccharide (LPS)-induced cytokine release. MDP pretreatment modulates cytokine gene expression, suggesting distinct pathways for MDP and LPS signaling.
Area of Science:
- Immunology
- Molecular Biology
Background:
- Muramyl dipeptide (MDP) is known to potentiate serum TNF and IL-6 release following LPS challenge.
- The direct action of MDP on TNF-producing cells, specifically macrophages, requires further investigation.
Purpose of the Study:
- To examine the direct action of MDP on TNF-producing macrophages.
- To investigate the effect of MDP on cytokine mRNA expression (TNF-alpha, IL-1 alpha, IL-6) in macrophages stimulated with LPS.
Main Methods:
- Bone marrow-derived macrophages (BMM) were stimulated with MDP and/or LPS.
- Quantitative analysis of TNF-alpha, IL-1 alpha, and IL-6 mRNA accumulation was performed.
- Bioactivity of TNF and IL-6 in supernatant fluids was assessed.
Main Results:
- MDP and LPS induced TNF-alpha mRNA accumulation in BMM.
- MDP pretreatment enhanced LPS-induced TNF-alpha, IL-1 alpha, and IL-6 mRNA levels and altered their kinetic accumulation.
- MDP pretreatment increased the biologic activity of LPS-induced TNF and IL-6.
- MDP enhanced LPS effects on TNF mRNA in C3H/Hej mice macrophages.
Conclusions:
- MDP and LPS may utilize distinct pathways to induce cytokine gene expression.
- MDP exhibits a priming effect on macrophages, modulating LPS-induced cytokine gene expression at transcriptional and/or post-transcriptional levels.