Genes and Immunity (2008) 9, 274–278 & 2008 Nature Publishing Group All rights reserved 1466-4879/08 $30.00 www.nature.com/gene SHORT COMMUNICATION The effect of NOD2 activation on TLR2-mediated cytokine responses is dependent on activation dose and NOD2 genotype MEA Borm1, AA van Bodegraven2, CJJ Mulder2, G Kraal1 and G Bouma1,2 1Department of Molecular Cell Biology and Immunology, Vrije Universiteit Medical Center, Amsterdam, The Netherlands and 2Department of Gastroenterology, Vrije Universiteit Medical Center, Amsterdam, The Netherlands The mechanism by which mutations in NOD2 predispose to Crohn’s disease (CD) is incompletely understood. In mice, NOD2 has been found to function as a negative regulator of Toll-like receptor 2 (TLR2) signaling. In contrast, studies in humans so far showed no negative regulatory interaction between NOD2 and TLR2, and in fact suggest a synergistic effect between the two. Here, we show that this interaction is dose dependent. Adding low doses of muramyl dipeptide (MDP) to TLR2 primed monocytes results in a significant increase in cytokine production, whereas adding higher doses of MDP led to a striking downregulation of the responses. This downregulation by high-dose MDP does not occur in monocytes from NOD2-deficient patients. The inhibitory role of NOD2 at high concentrations of MDP implicates a safety mechanism to prevent exaggerated antibacterial immune responses in the gut to high or perpetuating bacterial load. This regulatory mechanism is lost in NOD2- deficient CD patients. Genes and Immunity (2008) 9, 274–278; doi:10.1038/gene.2008.9; published online 13 March 2008 Keywords: Crohn’s disease; NOD2; TLRs; immune activation Mutations in the gene encoding nucleotide-binding peptidoglycan derivates).6 In mice, NOD2 has been oligomerization domain 2 (NOD2) are strongly asso- suggested to play a role as a negative regulator of ciated with an increased risk of developing Crohn’s TLR2 signaling, leading to excessive NF-kB dependent 1,2 disease (CD), a chronic inflammatory disorder of the IL-12 production associated with the strong Th1 response gastrointestinal tract. NOD2 is a member of the NOD- seen in murine colitis in NOD2 deficient mice.7,8 In leucine-rich repeat (LRR) protein family, which com- contrast, in human no indications for a negative prises of proteins that all consist of a C-terminal ligand regulatory interaction between NOD2 and TLR2 exist. recognition domain, a central NOD domain, and an Data in human on the simultaneous activation through N-terminal protein–protein interaction domain.3 Homozy- NOD2 and TLRs, including TLR2, show a positive gosity for mutations in the LRR of NOD2 results in a 20– synergistic effect, an effect that is lost in individuals 40 times higher risk of developing CD, whereas the risk bearing NOD2 mutations.9–12 This is accompanied by a of developing the disease is approximately four times loss of NF-kB signaling function leading to impaired higher in individuals that are heterozygotic.4 How the cytokine production after NOD2 stimulation, and to alterations in the NOD2 protein exert their effects on an impaired costimulatory effect of NOD2 signaling disease susceptibility is not completely clear, not in the on TLR-mediated cytokine production.9–12 This effect last place because this sensor of the bacterial peptido- appears contradictory to the elevated levels of NF-kB glycan component muramyl dipeptide (MDP) is ex- activation-dependent Th1 cytokines typically found in pressed in various cell types, including Paneth cells as the inflamed tissues from patients with CD.13,14 well as macrophages and dendritic cells. Furthermore, In the current study, we intended to bridge these activation of NOD2 results in activation of multiple seemingly contradictory findings. We hypothesized that pathways, including the nuclear factor (NF)-kB and the mode of interaction between NOD2 and TLR2 may mitogen-activated protein kinase pathways, leading to a be dose dependent and that part of the controversy may variety of responses.5,6 be related to differences in experimental design and Both NOD2 and Toll-like receptor 2 (TLR2) are stimulation dose. To test this hypothesis, we isolated activated by the same bacterial products (that is, monocytes from 5 healthy donors and 15 CD patients divided in three groups of 5 carrying 0, 1 or 2 mutant NOD2 alleles, respectively. All patients had inactive Correspondence: Dr G Bouma, Department of Gastroenterology, disease at the time of the study and were on minimum Vrije Universiteit Medical Center, De Boelelaan 1118, Amsterdam or no drug treatment. After isolation and an overnight 1081 HZ, The Netherlands. E-mail: [email protected] rest, cells were stimulated with low doses of either Received 21 January 2008; accepted 21 January 2008; published the synthetic TLR2 ligand Pam3CSK4 (Pam), or the online 13 March 2008 TLR4 ligand lipopolysaccharide (LPS). In addition, Effect of NOD2 on TLR2 responses in human monocytes MEA Borm et al 275 different concentrations of MDP (0, 1, 10, 25 Stimulation of cells with either LPS or Pam alone and 100 mgmlÀ1) were added and production of TNF-a, resulted in significant upregulation of cytokine produc- IL-6 and IL-12 was determined in the cell culture tion as compared to unstimulated cells. Stimulation of supernatant. cells with MDP alone resulted only in a small and Figure 1 TNF-a production in relation to NOD2 genotype in monocytes stimulated with different TLR ligands and different doses of MDP. Monocytes were isolated from 50 ml of heparinized peripheral blood by density gradient centrifugation. Cells were cultured in triplicate (105 cells per 100 ml culture medium) and allowed to rest overnight. They were then stimulated for 3 h with pure synthetic TLR2 ligand À1 À1 (Pam3CSK4;50pgml ) and different concentrations of MDP (0, 1, 10, 25 and 100 mgml ). TNF-a was determined by enzyme-linked immunosorbent assay (ELISA). (A) TNF-a secretion after stimulation with the TLR2 ligand Pam3CSK4. Each graph includes five different donors stimulated with three different MDP doses (0 mgmlÀ1 (open bars); 100 mgmlÀ1 (black bars), whereas the gray bars represents the low MDP dose in the 1–25 mgmlÀ1 range that resulted in optimal cytokine secretion for that individual). CD, Crohn’s disease. Table 1a represent the absolute values of TNF-a secretion. (B)TNF-a secretion after stimulation of cells with the TLR4 ligand LPS (10 ng mlÀ1) and the different doses of MDP (also see Table 1b). The individual genotypes of the heterozygous and NOD2-deficient patients are provided in Supplementary Table 1. Genes and Immunity Effect of NOD2 on TLR2 responses in human monocytes MEA Borm et al 276 Table 1a TNF-a responses in different groups of individuals according to NOD2 genotype in Pam3CSK4 stimulated monocytes in conjunction with different concentrations of MDP TNF-a (in pg mlÀ1) TNF-a (in pg mlÀ1) after stimulation TNF-a (in pg mlÀ1) after stimulation with high without MDP (range) with low dose MDP (range); P-value dose MDP (range); P-values (compared to 0 mgmlÀ1 (compared to 0 mgmlÀ1 MDP) MDP and low-dose MDP, respectively) NOD2 competent 865 (28–2761) 1556 (176–4073) 754 (85–1857) (at least one normal o0.0001 0.5/0.0002 allele; n ¼ 15) No mutations in 693 (28–2761) 1625 (176–4073) 666 (85–1857) NOD2 (n ¼ 10) 0.002 0.9/0.004 NOD2 heterozygous 1221 (428–1674) 1420 (513–2169) 932 (591–1349) (n ¼ 5) 0.06 0.3/0.3 NOD2 deficient 783 (351–1313) 914 (357–1991) 1029 (355–2104) (n ¼ 5) 0.6 0.2/0.4 Abbreviation: MDP, muramyl dipeptide; TNF-a, tumor necrosis factor-a. Bold values indicate statistically significant P-values. Table 1b TNF-a responses in different groups of individuals according to NOD2 genotype in LPS stimulated monocytes in conjunction with different concentrations of MDP TNF-a (in pg mlÀ1) TNF-a (in pg mlÀ1) after stimulation TNF-a (in pg/mlÀ1) after stimulation with without MDP (range) with low dose MDP (range); P-value high dose MDP (range); P-value (compared to 0 mgmlÀ1 (compared to 0 mgmlÀ1 MDP) MDP and low-dose MDP, respectively) NOD2 competent 1319 (43–3063) 1910 (161–5862) 1920 (260–5582) (at least one normal 0.0009 0.003/0.8 allele; n ¼ 15) No mutations in 997 (43–3063) 1679 (161–5862) 1703 (260–5582) NOD2 (n ¼ 10) 0.01 0.004/0.7 NOD2 heterozygous 1964 (931–2642) 2375 (920–3495) 2354 (1041–3731) (n ¼ 5) 0.1 0.3/1 NOD2 deficient 2789 (454–5083) 3340 (499–6275) 3412 (523–6693) (n ¼ 5) 0.6 0.6/0.6 Abbreviations: LPS, lipopolysaccharide; MDP, muramyl dipeptide; TNF-a, tumor necrosis factor-a. Bold values indicate statistically significant P-values. nonsignificant increase of cytokine expression in indivi- 100 mgmlÀ1 MDP resulted in a marked reduction of duals with at least one functional NOD2 allele. The TNF-a responses as compared to the low dose and magnitude of this response was 5–10 folds lower as at this concentration of MDP, TNF-a values returned compared to stimulation with the TLR ligands and to, or below the baseline level that was seen after independent of the dose (results not shown). As Pam stimulation alone (754 pg mlÀ1 (range 85–1857), expected, MDP stimulation of cells in NOD2-deficient P ¼ 0.0002 as compared with the low MDP dose). The individuals did not result in any upregulation of magnitude of this response was particularly evident in cytokine expression. individuals without any mutation in NOD2 and less Shown in Figure 1A and Table 1a is the TNF-a pronounced in heterozygous individuals, which is response of monocytes from different groups of CD indicative of a gene-dosage effect (Table 1a).