β2-Adrenergic agonists bias TLR-2 and NOD2 activated dendritic cells towards inducing an IL-17 immune response
Highlights
► Salbutamol (β2-AR agonist) enhanced IL-6 production following NOD2 activation of DCs. ► Salbutamol inhibited IL-12 expression in TLR-2-activated DCs. ► Thus, β2-AR signaling alters DC cytokine expression to favor Th17 cell development. ► An enhanced Th17 response induced by β2-AR stimulation was observed in vivo.
Introduction
Dendritic cells (DCs) are professional antigen presenting cells (APCs) involved in the initiation and polarization of the adaptive immune response. The priming of Th cell subsets is orchestrated by cytokines produced by DCs that sense pathogen-associated molecular patterns (PAMPs) and local microenvironmental factors. Th17 cells are a recently discovered lineage of effector CD4+ T cells characterized by the production of IL-17, IL-21 and IL-22 [1]. Th17 cells provide defense against extracellular bacteria but are also implicated in autoimmune disorders. In mice, the development of a Th17 immune response depends on the presence of the proinflammatory cytokines IL-6 and TGF-β1 and is suppressed by the Th1-type cytokines IFN-γ and IL-12 and by the Th2-type cytokine IL-4 [2]. Furthermore, IL-23 was shown to be important for Th17 expansion [3]. Previous studies have demonstrated that adrenergic receptors may modulate cytokine production in DCs and affect their Th cell priming ability [4]. In particular, activation of β2-adrenergic receptors (β2-ARs) in DCs stimulated by Toll-like receptor (TLR) agonists hampered IL-12 and stimulated IL-10 production resulting in reduced migration and Th1 priming [5], [6]. More recently, we demonstrated that β-ARs in mouse skin may modulate the innate and adaptive immune response to certain, but not all, PAMPs suggesting that the physiological role of the skin adrenergic system might be that of limiting the immune response to specific pathogens [7]. We observed that inhibition of β-ARs in the skin increased the inflammatory cytokine response to peptidoglycan (PGN). When a protein antigen was injected after PGN administration and β-AR blockade, the consequent adaptive memory response was shifted toward the Th1-type. This was validated by increased interferon-γ (IFN-γ) production in cell suspensions from draining lymph nodes and by the delayed-type hypersensitivity response to a protein antigen [7]. However, the increased production of IFN-γ was not associated with a corresponding decrease of the Th2 cytokine IL-4, indicating that the Th1 shift did not depend on polarization of naïve Th cells toward the Th2-type. As IFN-γ may suppress Th17 cell formation [2], we hypothesized that the increased Th1 priming observed after β-ARs blocking was at the expense of Th17 cells. In our murine model, β-ARs in the skin could influence the response to the TLR-2 agonist PGN but not to the TLR-4 agonist lipopolysaccharide (LPS). Unlike LPS that signals only via TLR-4 [8], there are numerous PGN recognition molecules that are distinct from TLR2. These include CD14, the nucleotide oligomerization domain (NOD)-containing proteins, a family of peptidoglycan recognition proteins and PGN-lytic enzymes [9]. NOD2 is a cytosolic receptor, which induces innate immune responses by recognizing the PGN derivative muramyl dipeptide (MDP). It has been observed that TLR-2 and NOD2 co-stimulation was associated with a dose-dependent inhibition of IL-12 expression and stimulation of IL-6 and IL-10 resulting in negative regulation of the TLR-2-mediated Th1 response [10]. Moreover, it has been recently shown that NOD2 is involved in human Th17 differentiation [11].
In the present study, we investigated whether β-AR activation could influence NOD2 signaling along with its cross-talk with TLR-2 and the resulting Th cell priming ability by murine DCs. We found that the β2-AR agonist salbutamol modulates cytokine production in DCs stimulated with MDP or simultaneously by both TLR-2 and NOD2 ligands, resulting in a cytokine pattern suggestive for Th17 priming. Indeed, in mice immunized with antigen-pulsed DCs stimulated by MDP or by the TLR-2 ligand Pam3CysSK4 (PAM) + MDP in the presence of salbutamol, the resulting IL-17/IFN-γ production ratio was increased. These results were confirmed by the examination of cytokine production ratios by draining lymph node cells after direct injection in mice of the β-AR agonist norepinephrine (NE) along with PAM + MDP. Thus, β2-ARs represent an important mechanism by which the adaptive immune response to certain pathogens is regulated. Remarkably, β2-ARs might be involved in the defense against extracellular bacteria and in the pathogenesis of inflammatory diseases by modulating Th17 polarization.
Section snippets
Mice
C57BL/6 inbred mice were purchased from Harlan, Udine, Italy. All the mice used in these experiments were female, 2–3 months old and were maintained under a standard 12 h photoperiod, at 21 ± 1 °C, with food and water ad libitum. All the experiments performed were authorized by the local veterinary committee.
Bone marrow-derived DCs
Bone marrow cells from C57BL/6 mice were cultured in 10 cm petri dishes at a concentration of 2.5 × 106 cells/10 ml at 37 °C, 5% CO2 in complete medium: RPMI 1640 (Gibco, Karlsruhe, Germany)
β-Adrenergic effect on cytokine production in DCs
We examined the effect of salbutamol, a specific β2-AR agonist, on IL-6, IL-12 and IL-23 production by DCs stimulated by TLR-2 and/or NOD2 ligands. These cytokines are known to be implicated in the Th1/Th17 cell polarization. We used the lipopeptide PAM as a TLR-2 agonist and the NOD2 ligand MDP. Cytokine concentrations were measured in the supernatants after 6 h of culture. Salbutamol significantly increased IL-6 production when DCs were activated by MDP suggesting a possible involvement of
Discussion
In this study we show that β2-AR activation may modulate Th cell priming in favor of an IL-17 immune response. We found that the β2-AR agonist salbutamol enhanced IL-6 protein and gene expression in murine DCs stimulated with the NOD2 agonist MDP. IL-12 mRNA and protein were inhibited by salbutamol in PAM and PAM + MDP treated cells. This result confirms the ability of β2-AR agonists to inhibit IL-12 production in DCs stimulated by various PAMPs as previously reported by us and others [5], [12],
Acknowledgments
The authors thank Mrs. Elisabeth Hertens and Mrs. Paola Galli for excellent technical assistance. The Swiss National Science Foundation Grant No. 310000-107524/1 and NIH Grant 5R01 AR042429 supported this study.
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