Published online before print February 3, 2006
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,
,
* Departments of Tumor Immunology, Nijmegen Centre for Molecular Life Sciences,
Gastroenterology and Hepatology, and
Medicine,
Nijmegen University Centre for Infectious Diseases, Radboud University Nijmegen Medical Centre, The Netherlands
1Correspondence: Department of Tumor Immunology, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, Geert Grooteplein 28, 6525 GA, Nijmegen, The Netherlands. E-mail: g.adema{at}ncmls.ru.nl
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, interleukin (IL)-12, and IL-10 production, which is observed in control DC with intact NOD2. These data indicate that the NOD2fs mutation results in a loss-of-function phenotype in human myeloid DC and imply decreased immune regulation by IL-10 as a possible mechanism for this mutation in CD.
Key Words: human • cytokines • Toll-like receptor
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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NOD2 is a cytoplasmic protein that binds muramyl dipeptide (MDP), a motif common to peptidoglycan of Gram+ and Gram– bacteria, resulting in nuclear factor (NF)-
B activation and cytokine induction [3
]. Furthermore, NOD2 activation has been suggested to affect Toll-like receptor (TLR)-mediated responses [4
, 5
].
The mechanism by which NOD2fs contributes to CD remains largely unresolved. Recent data from several NOD2 mouse models have yielded surprisingly different conclusions. TLR2-induced interleukin (IL)-12 production by myeloid cells was found to be decreased after costimulation with MDP, an effect absent in NOD2–/– mice, implying that NOD2 is a negative regulator of TLR2-mediated T helper cell type 1 (Th1) responses [6
]. In line with this gain-of-function phenotype of knockout mice, NOD2fs knock-in mice showed enhanced NF-B activity and IL-1ß secretion in response to MDP as well as increased susceptibility to bacterial-induced intestinal inflammation [7
]. However, another mouse study demonstrated that NOD2 activation in wild-type mice enhanced TLR-mediated cytokine production by bone marrow-derived macrophages, and NOD2-deficient animals had decreased cryptdin expression in terminal ileum cells and impaired antibacterial responses after challenge with Listeria monocytogenes [8
], thus favoring a loss-of-function phenotype. Few studies have yet focused on the effect of NOD2fs in human dendritic cells (DC), which are the only antigen-presenting cells capable of activating naive T cells and the induction of immunity and tolerance [9
]. Also, in the gut, DC are crucial for the induction of tolerance to the resident intestinal flora [10
11
12
]. We therefore aimed to determine the consequence of NOD2fs for the responsiveness of DC to MDP, focusing on maturation and cytokine production. We specifically studied IL-12, tumor necrosis factor (TNF-), and IL-10, considering their importance in affecting inflammatory processes in general and the pathogenesis of CD in particular [13
14
15
16
].
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Isolation of mononuclear cells and generation of monocyte-derived DC (moDC)
After informed consent, 80 ml venous blood was drawn from the cubital vein of patients and healthy volunteers into 10 ml EDTA tubes (Monoject, s-Hertogenbosch, The Netherlands). Total blood was diluted 1/1 using phosphate-buffered saline (PBS) containing 0.45% sodium citrate (dilution solution), and mononuclear cells were isolated by density gradient centrifugation using Lymphoprep (1.077 g/ml, Axis Shield PoC AS, Oslo, Norway), according to the manufacturer’s instructions. Cells were washed once in dilution solution at 1800 rotations per minute (rpm) for 8 min to remove Lymphoprep remains and further washed (1500 rpm/5 min) using ice-cold dilution solution containing 1% fetal calf serum (FCS) until clear supernatant was obtained. After counting, cells were resuspended in RPMI containing 2% human serum (HS) at a density of 10–12.5 x 106 cells/ml and plated in T25 or T75 culture flasks (Costar, Corning, NY) at 37°C for a period of 1 h. Nonadherent cells were removed by washing 3x with PBS, and adherent cells were cultured in RPMI 1640 supplemented with 100 U/ml antibiotic-antimycotic (Invitrogen, Carlsbad, CA), 10 mM L-glutamine, and 10% FCS. To generate moDC, 400 U/ml IL-4 and 800 U/ml granulocyte macrophage-colony stimulating factor (GM-CSF; Schering-Plough, Kenilworth, NJ) were added to the culture medium, which was refreshed, and complete cytokines were added at Day 3. On Day 6, immature DC were harvested using cold PBS, and cells were stimulated as indicated below. An average yield of 2.3 x 106 (SD 0.7x106) immature DC was obtained per donor.
Stimulation of DC
For cytokine analysis, immature moDC (50x103) in 100 µl medium were added to round-bottom, 96-well plates (Costar) with 50 µl culture medium (negative control) or 50 µl medium containing the various stimuli, purified lipopolysaccharide (LPS; Escherichia coli, 100 ng/ml), synthetic Pam3 Cys-Ser-(Lys)4 .3HCl (Pam3Cys; 10 µg/ml, EMC Microcollections, Germany), synthetic polyionisicpolycytidylic acid [poly(I:C); 20 µg/ml, Sigma-Aldrich, St. Louis, MO] in the presence or absence of MDP (5 µg/ml, Sigma-Aldrich), interferon-
(IFN-; 400 U/ml), or a combination of both MDP and INF- for a period of 24 h. For flow cytometry, immature moDC (0.6x106) in a 1.5-ml vol were added to 12-well plates (Costar) and incubated with 20 µg/ml poly(I:C) or 10 µg/ml Pam3Cys for a period of 24 h, after which, the expression of costimulatory molecules was analyzed using flow cytometry.
Flow cytometric analysis of costimulatory molecule expression on DC
After 24 h incubation with indicated TLR ligands, cells were harvested and washed using ice-cold PBA (PBS containing bovine serum albumin and azide). Cells (50x103 cells/well) were added to a v-bottom, 96-well plate (Costar) and stained using CD80 or CD86-specific mouse anti-human immunoglobulin G1 (IgG1) antibodies or the appropriate isotype control (BD PharMingen, San Diego, CA) on ice for a period of 30 min. Cells were washed twice in ice-cold PBA and incubated with phycoerythrin-labeled goat anti-mouse Ig (BD PharMingen) on ice for a period of 30 min. After double washings, cells were incubated in 200 µl PBA, and the expression of CD80 and CD86 was analyzed via flow cytometry (FACSCalibur, Becton Dickinson, San Jose, CA). Analysis was done using WinMDI 2.8 software.
Cytokine measurements
After 24 h stimulation, supernatants were harvested and stored at –80°C until cytokine analysis was performed. IL-12 concentrations in supernatants were measured using an IL-12p70-specific sandwich enzyme-linked immunosorbent assay (Pierce-Endogen, Rockford, IL). TNF- and IL-10 levels were determined using commercially available kits (Bio-Rad Laboratories, Hercules, CA), according to the manufacturer’s instructions. Data analysis was done with Bio-Plex Manager software (Bio-Rad Laboratories).
Statistical analysis
Differences in the increase in mean fluorescence intensity (MFI) of CD80 and CD86 after 24 h stimulation with TLR ligands or MDP between individuals homozygous for NOD2fs (n=4) and those with intact NOD2 (four CD patients and five healthy controls) were analyzed using the Student’s t-test. Stimulation experiments for cytokine analysis were performed in duplo. Differences in cytokine production between cells from patients homozygous for the NOD2fs polymorphism (n=4) and cells from individuals bearing the wild-type allele (four CD patients and five healthy controls) were analyzed using the Student’s t-test.
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, and IL-10 after stimulation with TLR ligands in the presence or absence of IFN-, which is known to be present in increased amounts in the gut of CD patients and can enhance TLR and NOD2 responses. No significant difference in cytokine induction by LPS alone (IL12p70, P=0.31; TNF-, P=0.32; IL-10, P=0.18) or in combination with IFN- (IL12p70, P=0.23; TNF-, P=0.44; IL-10, P=0.16) between NOD2fs DC and control DC was observed (Fig. 1B)
. These findings indicate that DC maturation and cytokine production following TLR activation are not altered in DC from CD patients homozygous for NOD2fs. |
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Table 1. Overview of General Patient Characteristics, Relevant Clinical Information, and Prescribed Medication at the Time of Study
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Figure 1. TLR activation is not affected in NOD2fs DC. (A) DC were generated by culturing monocytes in the presence of IL-4 and GM-CSF for a period of 6 days. DC from healthy controls or NOD2fs patients were stimulated with synthetic TLR ligands Pam3Cys (10 µg/ml) or poly(I:C; 20 µg/ml) for 24 h. CD80 and CD86 expression on the cell surface was analyzed by flow cytometry. Maturation responses shown are representative of six healthy controls and four NOD2fs patients. Medium control and indicated TLR stimulation are represented by thin and thick lines, respectively. Filled histogram indicates isotype-matched, control monoclonal antibodies (mAb). (B) Production of IL-12, TNF-, and IL-10 by DC from healthy controls (n=5), NOD2+/+ CD patients (n=4), or homozygous NOD2fs CD patients (n=4). Cells were stimulated with LPS (E. coli, 100 ng/ml) alone or LPS in combination with 400 U/ml IFN- for a period of 24 h, after which, cytokine concentrations in culture supernatants were analyzed.
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and IL-10 responses [mean 1.7% (0–11%) and 0.7% (0–3%) of LPS response, respectively] were observed following MDP stimulation in a number of control DC but not NOD2fs DC (Fig. 2B)
. These results indicate that NOD2 triggering alone does not induce significant cytokine production in DC but does result in modest DC maturation, which is abrogated completely in DC homozygous for the NOD2fs mutation.
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Figure 2. NOD2fs DC show no maturation or cytokine production after stimulation with MDP. (A) Representative examples of the expression of CD80 and CD86 on DC from healthy controls (n=5), NOD2+/+ CD patients (n=4), or NOD2fs CD patients (n=4) after stimulation with 5 µg/ml N-acetylmuramyl-L-alanyl-D-isoglutamine hydrate (MDP) for a period of 24 h. Medium control and MDP stimulation are indicated by thin and thick lines, respectively. Filled histogram represents isotype-matched, control mAb. Increase in MFI of CD80 and CD86 after MDP stimulation was calculated. Differences between DCs from donors with intact NOD2 and NOD2fs DC were compared using Student’s t-test (*, P<0.05). (B) IL-12, TNF-, and IL-10 levels (pg/ml) in culture supernatant, comparing stimulation of cells with 100 ng/ml-purified LPS or 5 µg/ml MDP for a period of 24 h. No IL-12 could be detected after stimulation with MDP, whereas some, but not all, control DC responded with the production of low levels of TNF- or IL-10.
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. In contrast, TLR4 activation using LPS resulted in an appreciable amount of IL-12 (120 pg/ml), which was further enhanced by IFN-. In the presence and absence of IFN-, additional stimulation with MDP resulted in a significant increase in IL-12 as compared with LPS or LPS/IFN- alone. Thus, the reported synergy between TLRs and NOD2 for the production of cytokines also applies for IL-12 release by human DC.
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Figure 3. The NOD2fs mutation abrogates the synergy between TLR and NOD2 signals for release of cytokines. (A) IL-12 production by DC from healthy controls was measured after stimulation with 5 µg/ml MDP, 100 ng/ml purified LPS, or a combination of both in the presence or absence of 400 U/ml IFN-. Data shown are the mean + SD of triplicate measurements of one of four independent experiments. nd, Not detectable. (B) IL-12, TNF-, and IL-10 levels were measured following stimulation of DC from healthy controls (n=5), NOD2+/+ CD patients (n=4), or NOD2fs CD patients (n=4) with 100 ng purified LPS, 10 µg/ml Pam3Cys (PAM), or 20 µg/ml poly(I:C), alone or in combination with 5 µg/ml MDP for 24 h. Experiments were performed without (upper panel) or with (lower panel) additional IFN- stimulation. Displayed is the percentage increase in cytokine production as a result of the addition of MDP compared with TLR stimulation alone. Differences in the observed increases in cytokine levels between control DC and NOD2fs DC were analyzed using Student’s t-test (*, P<0.05, and **, P<0.01).
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, with or without additional stimulation with MDP. IL-12, TNF-, as well as IL-10 production was measured. Results are depicted as the percent increase in cytokine levels, comparing TLR activation alone with TLR activation combined with MDP (Fig. 3B)
. In control DC, stimulation with TLR ligands in the presence of MDP resulted in a significant increase in IL-12, IL-10, and TNF- levels compared with TLR activation alone, although this effect was not significant for all cytokines measured or all TLR ligands used. The synergistic effect of MDP stimulation on TLR-induced cytokine release was completely absent in DC from NODfs patients. In the presence of IFN-, there was a statistically significant difference for all cytokines measured after stimulation with the selected TLR ligands and MDP, indicating that in a proinflammatory Th1 environment, the effect of NOD2fs could become even more apparent. Together, these results demonstrate that the 3020insC mutation renders DC unable to mature in response to MDP and abrogates the synergy between NOD2 and TLRs for the production of pro- and anti-inflammatory cytokines.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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B-induced cytokines IL-12 and TNF-, and mAb against these cytokines are effective therapies for CD [18
19
20
]. It is striking that decreased NF-B activation and defective cytokine responses have been reported in human and mouse studies as a consequence of the CD-associated NOD2fs mutation, providing evidence for a loss-of-function phenotype [1
, 8
, 21
, 22
]. However, two recent studies in mice challenged this view [6
, 7
]. Watanabe and colleagues [6] suggested that NOD2 is a negative regulator of TLR2-induced Th1 responses, as measured by IL-12 production. Wild-type cells stimulated with the TLR2 ligand Pam3Cys plus MDP displayed lower IL-12 production than cells from NOD2–/– mice, which were stimulated similarly [6
]. In addition, Maeda et al. [7] developed a mouse model in which the NOD2fs variant was introduced into the mouse NOD2 locus and showed that mutant mice exhibited elevated NF-B activation and IL-1ß secretion following MDP stimulation, suggesting that the NOD2fs mutation would lead to a gain-of-function phenotype. This discrepancy between recent mouse and human data published necessitates further studies in, preferentially, human subjects. A lot of studies have used transfected human cell lines, but in these systems, NOD2 expression is well above physiological levels with unknown outcome. Also, the use of (patient-derived) peripheral blood mononuclear cells (PBMC) complicates identification of the effect of NOD2fs in specific cell types within this mixed population.
DC are present in the intestinal mucosa, where they sense the content of the intraluminal bacterial milieu, and they are crucial in the decision process between tolerance and immunity [12
23
]. We therefore decided to determine the consequence of the NOD2fs mutation in myeloid DC obtained from patients homozygous for this NOD2 polymorphism. Our results indicate that intact NOD2 is essential for the recognition of MDP by human DC and support the view that the NOD2fs mutation in CD patients results in a loss-of-function phenotype in these cells. To avoid the unwanted effect of possible contamination with, for instance, endotoxins, we used only synthetic or highly purified TLR and NOD2 ligands during our study. DC from CD patients bearing the NOD2fs mutation responded with a normal up-regulation of the costimulatory molecules CD80 and CD86 after TLR activation but failed to do so in response to MDP. The production of IL-12p70, TNF-, and IL-10 was not significantly different between DC from control and NOD2fs DC after TLR activation. MDP induced low cytokine responses in some but not all DC carrying intact NOD2, and NOD2fs DC did not produce any cytokines following MDP stimulation alone. Finally, in control DC, stimulation with TLR ligands plus MDP enhanced the production of IL-12, TNF-, and IL-10 compared with those levels obtained following TLR activation alone. This synergy between NOD2 and TLRs was completely absent in DC obtained from patients with the NOD2fs polymorphism. These results are in concordance with the recent findings by van Heel et al. [22
], who showed that PBMC from homozygous NOD2fs donors display significantly decreased TNF-ß and IL-1ß production following combined activation of TLRs and NOD2.
In the presence of IFN-, which is known to increase NOD2 and TLR expression and function [24
25
26
], the observed differences were even more significant. The absence of an increase in IL-12 production by simultaneous TLR2 and NOD2 activation in NOD2fs DC is at variance with findings reported in NOD2-deficient mice [6
]. The reason for this discrepancy is currently unknown but might be related to differences between the NOD2fs mutation and complete absence of NOD2 or (species-related) differences between human DC and mouse splenocytes. In addition, other mutations in NOD2 might have different consequences, for instance, in the case of Blau syndrome [27
].
The inflammatory phenotype found in CD patients is hard to explain by a decreased TNF- and IL-12 production by NOD2fs DC after combined TLR/NOD2 activation. However, we now demonstrate that NODfs DC also produce decreased amounts of the anti-inflammatory cytokine IL-10 under these conditions. IL-10 is crucially involved in preventing excessive immune responses, including down-regulation of IL-12 and TNF- production [28
]. We therefore postulate that deficient IL-10-mediated immune suppression is dominant over the reduction in TNF- and IL-12 levels, which is also observed after TLR/NOD2 stimulation in NOD2fs DC. As DC instruct the adaptive immune system via the release of specific cytokine combinations, a disturbed organization of this cytokine production could induce unwanted T cell responses. Indeed, studies using therapeutic IL-10 administration or IL-10-deficient mice have demonstrated the importance of this cytokine in preventing mucosal inflammation [29
, 30
]. Furthermore, IL-10 is a multifunctional cytokine that is also crucial for the development of suppressor T cells, which are involved intricately in controlling intestinal immune responses [31
32
33
]. NOD2fs-related reduction in IL-10 levels could thus result in a defective counter-regulation of the effect of proinflammatory cytokines with concomitant Th1 responses and thereby contribute to the perpetuation of chronic inflammation characteristic for CD.
Received August 30, 2005; revised October 30, 2005; accepted November 21, 2005.
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B activity and IL-1ß processing Science 307,734-738 (TNF-) antibodies] Rev. Med. Liege 55,827-832[Medline] overcomes low responsiveness of myeloid dendritic cells to CpG DNA Immunol. Cell Biol. 83,92-95[CrossRef][Medline] and IFN on the expression of pattern recognition receptors on the surface of mouse alveolar macrophages] Zhonghua Wai Ke Za Zhi 43,740-744[Medline] and IFN- regulate the expression of the NOD2 (CARD15) gene in human intestinal epithelial cells Gastroenterology 124,1001-1009[CrossRef][Medline]This article has been cited by other articles:
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