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Updated: Aug 17, 2026
Development and Functional Characterization of Murine Tolerogenic Dendritic Cells
Published on: May 18, 2018
Dendritic cell maturation induced by muramyl dipeptide (MDP) derivatives: monoacylated MDP confers TLR2/TLR4
Junji Uehori1, Koichi Fukase, Takashi Akazawa
1Department of Microbiology and Immunology, Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
Abstract:
6-O-acyl-muramyldipeptides (MDP) with various lengths of fatty acid chains were examined for their dendritic cell (DC) maturation activity expressed through TLRs. Judging from anti-TLR mAb/inhibitor-blocking analysis, MDP derivatives with a single octanoyl or stearoyl fatty acid chain were found to activate TLR2 and TLR4 on human DCs, although intact and diacylated MDP expressed no ability to activate TLRs. Human DC activation profiles by the monoacylated MDP were essentially similar to those by Calmette-Guerin (BCG)-cell wall skeleton (CWS) and BCG-peptidoglycan (PGN) based on their ability to up-regulate costimulators, HLA-DR, beta(2)-microglobulin, and allostimulatory MLR. Monoacylated MDP induced cytokines with similar profiles to BCG-CWS or -PGN, although their potency for induction of TNF-alpha, IL-12p40, and IL-6 was less than that of BCG-CWS or -PGN. The MDP derivatives initiated similar activation in normal mouse macrophages, but exhibited no effect on TLR2/4-deficient or MyD88-deficient mouse macrophages. Mutation of d-isoGln to l-isoGln in monoacylated MDP did not result in loss of the DC maturation activity, suggesting marginal participation of nucleotide-binding oligomerization domain 2, if any, in monoacyl MDP-dependent DC maturation. These results define the adjuvant activity of 6-O-acyl MDP compounds at the molecular level. They target TLR2/TLR4 and act through the MyD88-dependent pathway in DCs and macrophages. Hence, the unusual combined activation of TLR2 and TLR4 observed with Mycobacterium tuberculosis is in part reflected in the functional properties of monoacylated MDP compounds. These findings infer that the essential minimal requirement for TLR2/4-mediated adjuvancy of BCG lies within a modified MDP.
Insights
Monoacylated muramyldipeptides (MDP) activate Toll-like receptors 2 and 4 (TLR2/TLR4) on dendritic cells (DCs) and macrophages, mimicking Mycobacterium tuberculosis adjuvant properties. This activation occurs via the MyD88-dependent pathway, highlighting minimal requirements for TLR2/4-mediated adjuvancy.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Toll-like receptors (TLRs) are crucial for innate immunity, recognizing pathogen-associated molecular patterns.
- Muramyldipeptides (MDPs) are components of bacterial cell walls with known immunomodulatory activities.
- Dendritic cells (DCs) are key antigen-presenting cells that bridge innate and adaptive immunity.
Purpose of the Study:
- To investigate the dendritic cell (DC) maturation activity of 6-O-acyl-muramyldipeptides (MDP) derivatives.
- To elucidate the molecular mechanisms underlying MDP-induced DC activation, specifically the role of Toll-like receptors (TLRs).
- To define the minimal structural requirements for MDP-mediated adjuvancy.
Main Methods:
- Synthesis of 6-O-acyl-muramyldipeptides (MDP) with varying fatty acid chain lengths.
- Analysis of DC maturation using anti-TLR monoclonal antibodies (mAbs) and inhibitors.
- Assessment of DC activation markers (costimulators, HLA-DR, beta(2)-microglobulin) and cytokine induction (TNF-alpha, IL-12p40, IL-6).
- Evaluation of MDP activity in wild-type and TLR/MyD88-deficient mouse macrophages.
Main Results:
- Monoacylated MDPs (octanoyl or stearoyl) activated human DCs via TLR2 and TLR4, unlike intact or diacylated MDPs.
- Monoacylated MDPs induced DC maturation profiles similar to BCG-cell wall skeleton (CWS) and BCG-peptidoglycan (PGN).
- MDP derivatives activated macrophages through a MyD88-dependent pathway, highlighting TLR2/TLR4 involvement.
- Mutation of d-isoGln to l-isoGln in monoacylated MDP did not abolish DC maturation activity.
Conclusions:
- 6-O-acyl MDP compounds act as adjuvants by targeting TLR2 and TLR4 through the MyD88-dependent pathway in DCs and macrophages.
- The combined activation of TLR2 and TLR4 by monoacylated MDPs reflects the properties of Mycobacterium tuberculosis.
- A modified MDP structure represents the essential minimal requirement for TLR2/4-mediated adjuvancy of BCG.
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