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Modulation of muramyl dipeptide stimulation of cytokine production by blood components
J H M van der Meer1, M G Netea, C A Dinarello
1Division of Infectious Diseases, University of Colorado Health Sciences Center, Denver, CO 80602, USA.
Abstract:
Muramyl dipeptide (MDP) is the minimal active fragment of peptidoglycan of the cell wall of Gram-positive bacteria, with potential beneficial effects as a vaccine adjuvant. Peptidoglycans and MDP are recognized by the intracellular receptor NOD2 (nucleotide-binding oligomerization domain 2), leading to production of proinflammatory cytokines. In the present study, it is shown that, despite stimulatory effects on isolated human mononuclear cells, MDP does not stimulate production of tumour necrosis factor-alpha, interleukin-1beta or interleukin-6 in a whole-blood assay. However, MDP retains synergistic effects on lipopolysaccharide-induced cytokines in whole blood. Screening tests of NOD2 function based on whole-blood stimulation should therefore employ strategies based on the synergistic effects of MDP on Toll-like receptor-induced cytokine production. Plasma was not responsible for the inhibition of MDP in whole blood. The inhibition of MDP stimulation was dependent upon cellular components, with erythrocyte-derived haemoglobin and neutrophils collaborating in the inhibition of MDP effects in whole blood.
Insights
Muramyl dipeptide (MDP) stimulates isolated cells but not whole blood, yet it enhances lipopolysaccharide-induced cytokine production. Cellular components, not plasma, inhibit MDP’s effects in whole blood assays.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Muramyl dipeptide (MDP) is a key fragment of bacterial peptidoglycan.
- MDP is recognized by the intracellular receptor NOD2, typically inducing proinflammatory cytokines.
- MDP has potential as a vaccine adjuvant.
Purpose of the Study:
- To investigate MDP's cytokine-inducing effects in a whole-blood assay.
- To determine the mechanism of MDP inhibition in whole blood.
- To propose strategies for NOD2 screening using whole-blood assays.
Main Methods:
- Whole-blood assay measuring cytokine production (TNF-α, IL-1β, IL-6).
- Assay assessing MDP's synergistic effects with lipopolysaccharide (LPS).
- Fractionation of blood components to identify inhibitory factors.
Main Results:
- MDP did not stimulate TNF-α, IL-1β, or IL-6 production in whole blood, unlike in isolated mononuclear cells.
- MDP showed synergistic effects on LPS-induced cytokine production in whole blood.
- Inhibition of MDP stimulation in whole blood was attributed to cellular components, specifically haemoglobin and neutrophils, not plasma.
Conclusions:
- Standard whole-blood assays may underestimate MDP's immune-stimulatory potential.
- NOD2 screening assays should leverage MDP's synergistic effects with Toll-like receptor agonists.
- Erythrocyte-derived haemoglobin and neutrophils play a critical role in inhibiting MDP's direct stimulatory effects in whole blood.
