TLR-9 Plays a Role in Mycobacterium leprae-Induced Innate Immune Activation of A549 Alveolar Epithelial Cells.

The respiratory tract is considered the main port of entry of Mycobacterium leprae, the causative agent of leprosy. However, the great majority of individuals exposed to the leprosy bacillus will never manifest the disease due to their capacity to develop protective immunity. Besides acting as a physical barrier, airway epithelium cells are recognized as key players by initiating a local innate immune response that orchestrates subsequent adaptive immunity to control airborne infections. However, to date, studies exploring the interaction of M. leprae with the respiratory epithelium have been scarce. In this work, the capacity of M. leprae to immune activate human alveolar epithelial cells was investigated, demonstrating that M. leprae-infected A549 cells secrete significantly increased IL-8 that is dependent on NF-κB activation. M. leprae was also able to induce IL-8 production in human primary nasal epithelial cells. M. leprae-treated A549 cells also showed higher expression levels of human ß-defensin-2 (hßD-2), MCP-1, MHC-II and the co-stimulatory molecule CD80. Furthermore, the TLR-9 antagonist inhibited both the secretion of IL-8 and NF-κB activation in response to M. leprae, indicating that bacterial DNA sensing by this Toll-like receptor constitutes an important innate immune pathway activated by the pathogen. Finally, evidence is presented suggesting that extracellular DNA molecules anchored to Hlp, a histone-like protein present on the M. leprae surface, constitute major TLR-9 ligands triggering this pathway. The ability of M. leprae to immune activate respiratory epithelial cells herein demonstrated may represent a very early event during infection that could possibly be essential to the generation of a protective response.

Discovery of 4 exonic and 1 intergenic novel susceptibility loci for leprosy.

Seven new risk coding variants have been identified through an exome-wide association study (EWAS), which studied the contributions of protein-coding variants to leprosy susceptibility. But some potential susceptibility loci were not studied in the previous EWAS study because of the project consideration. Seventeen unstudied potential susceptibility loci of the previous EWAS were validated in 3169 cases and 9814 controls in this study. Four disease-associated exonic loci were identified: rs671 in ALDH2 (P = 2.0 × 10-20 , odds ratio [OR] = 1.35), rs13259978 in SLC7A2 (P = 1.74 × 10-8 , OR = 1.28), rs925368 in GIT2 (P = 9.18 × 10-17 , OR = 1.44), and rs75680863 in TCN2 (P = 8.37 × 10-21 , OR = 0.74). Potentially implicating ZFP36L1 as a new susceptibility gene, 1 intergenic single nucleotide polymorphism (SNP), rs1465788 (P = 7.81 × 10-6 , OR = 0.88), was also suggested to be associated with leprosy. A luciferase reporter assay showed that the rs1465788 risk allele notably decreased the transcription activity of the flanking sequence. These findings suggest the possible involvement of lipid metabolism, NF-κB homeostasis and macrophage antimicrobial pathways in leprosy pathogenesis.

A pathway-based association analysis identified FMNL1-MAP3K14 as susceptibility genes for leprosy.

The nuclear transcription factor-κB (NF-κB) plays a pivotal role in controlling both innate and adaptive immunity and regulates the expressions of many immunological mediators. Abundant evidences have showed the importance of NF-κB pathway in the host immune responses against Mycobacterium leprae in the development of leprosy. However, no particular association study between leprosy and NF-κB pathway-related gene polymorphisms was reported. Here, we performed a large-scale and two-stage candidate association study to investigate the association between 94 NF-κB pathway-related genes and leprosy. Our results showed that rs58744688 was significantly associated with leprosy (P = 7.57 × 10-7 , OR = 1.12) by combining the previous genomewide association data sets and four independent validation sample series, consisting of a total of 4631 leprosy cases and 6413 healthy controls. This founding implicated that MAP3K14 and FMNL1 were susceptibility genes for leprosy, which suggested the involvement of macrophage targeting and NF-κB pathway in the development of leprosy.

NFκB transcription factor (p65) immunohistochemistry in leprosy dermal microvasculature.

Leprosy caused by Mycobacterium leprae is characterized by a spectrum of clinical manifestations that are determined by the predominant immunological profile of the host. The recruitment of leukocytes to the sites of injury can influence the development of these profiles. Cell adhesion molecules such as ICAM-1, VCAM-1 and CD62E participate in this process and their expression is regulated by transcriptions factors such as NFκB. To correlate the expression of cell adhesion molecules and NFκB (p65) in leprosy lesions, 30 skin biopsies of patients with leprosy [16 with the tuberculoid (TT) or borderline tuberculoid (BT) forms and 14 with the lepromatous (LL) or borderline lepromatous (BL) forms] were analyzed by immunohistochemistry. A larger mean number of cells expressing VCAM-1 (BT/TT: 18.28 ± 1.4; BL/LL: 10.67 ± 1.2; p = 0.0002), ICAM-1 (BT/TT: 9.92 ± 1.1; BL/LL: 5.87 ± 1.0; p = 0.0084) and CD62E (BT/TT: 13.0 ± 1.5; BL/LL: 2.58 ± 0.3; p = 0.0001) were observed in BT and TT lesions. The mean number of cells expressing NFκB was similar in the two clinical forms (BT/TT: 2.21 ± 2.7; BL/LL: 2.35 ± 3.1;p = 0.9285). No significant correlation was observed between expression of the transcription factor and adhesion molecules analyzed. The synthesis of ICAM-1, VCAM-1 and CD62E depends on the activation of NFκB, which acts synergistically with other transcription factors. Adequate activation of intracellular signaling pathways results in the production of endothelial adhesion molecules, contributing to the recruitment of cells to the site of injury and thus eliciting an effective inflammatory response in the elimination of the bacillus.

Trisaccharides of Phenolic Glycolipids Confer Advantages to Pathogenic Mycobacteria through Manipulation of Host-Cell Pattern-Recognition Receptors.

Despite mycobacterial pathogens continue to be a threat to public health, the mechanisms that allow them to persist by modulating the host immune response are poorly understood. Among the factors suspected to play a role are phenolic glycolipids (PGLs), produced notably by the major pathogenic species such as Mycobacterium tuberculosis and Mycobacterium leprae. Here, we report an original strategy combining genetic reprogramming of the PGL pathway in Mycobacterium bovis BCG and chemical synthesis to examine whether sugar variations in the species-specific PGLs have an impact on pattern recognition receptors (PRRs) and the overall response of infected cells. We identified two distinct properties associated with the trisaccharide domains found in the PGLs from M. leprae and M. tuberculosis. First, the sugar moiety of PGL-1 from M. leprae is unique in its capacity to bind the lectin domain of complement receptor 3 (CR3) for efficient invasion of human macrophages. Second, the trisaccharide domain of the PGLs from M. tuberculosis and M. leprae share the capacity to inhibit Toll-like receptor 2 (TLR2)-triggered NF-κB activation, and thus the production of inflammatory cytokines. Consistently, PGL-1 was found to also bind isolated TLR2. By contrast, the simpler sugar domains of PGLs from M. bovis and Mycobacterium ulcerans did not exhibit such activities. In conclusion, the production of extended saccharide domains on PGLs dictates their recognition by host PRRs to enhance mycobacterial infectivity and subvert the host immune response.

Phagocytosed Clofazimine Biocrystals Can Modulate Innate Immune Signaling by Inhibiting TNFα and Boosting IL-1RA Secretion.

Clofazimine (CFZ) is an FDA-approved leprostatic and anti-inflammatory drug that massively accumulates in macrophages, forming insoluble, intracellular crystal-like drug inclusions (CLDIs) during long-term oral dosing. Interestingly, when added to cells in vitro, soluble CFZ is cytotoxic because it depolarizes mitochondria and induces apoptosis. Accordingly, we hypothesized that, in vivo, macrophages detoxify CFZ by sequestering it in CLDIs. To test this hypothesis, CLDIs of CFZ-treated mice were biochemically isolated and then incubated with macrophages in vitro. The cell biological effects of phagocytosed CLDIs were compared to those of soluble CFZ. Unlike soluble CFZ, phagocytosis of CLDIs did not lead to mitochondrial destabilization or apoptosis. Rather, CLDIs altered immune signaling response pathways downstream of Toll-like receptor (TLR) ligation, leading to enhanced interleukin-1 receptor antagonist (IL-1RA) production, dampened NF-κB activation and tissue necrosis factor alpha (TNFα) production, and ultimately decreased TLR expression levels. In aggregate, our results constitute evidence that macrophages detoxify soluble CFZ by sequestering it in a biocompatible, insoluble form. The altered cellular response to TLR ligation suggests that CLDI formation may also underlie CFZ's anti-inflammatory activity.

Immunohistochemical analysis of the expression of cellular transcription NFκB (p65), AP-1 (c-Fos and c-Jun), and JAK/STAT in leprosy.

Leprosy is a disease whose clinical spectrum depends on the cytokine patterns produced during the early stages of the immune response. The main objective of this study was to describe the activation pattern of cellular transcription factors and to correlate these factors with the clinical forms of leprosy. Skin samples were obtained from 16 patients with the tuberculoid (TT) form and 14 with the lepromatous (LL) form. The histologic sections were immunostained with anti-c-Fos and anti-c-Jun monoclonal antibodies for investigation of AP-1, anti-NFκB p65 for the study of NFκB, and anti-JAK2, STAT1, STAT3, and STAT4 for investigation of the JAK/STAT pathway. Cells expressing STAT1 were more frequent in the TT form than in LL lesions (P = .0096), in agreement with the protective immunity provided by IFN-γ. STAT4 was also more highly expressed in the TT form than in the LL form (P = .0098). This transcription factor is essential for the development of a Th1 response because it is associated with interleukin-12. NFκB (p65) and STAT4 expression in the TT form showed a strong and significant correlation (r = 0.7556 and P = .0007). A moderate and significant correlation was observed between JAK2 and STAT4 in the TT form (r = 0.6637 and P = .0051), with these factors responding to interleukin-12 in Th1 profiles. The results suggest that STAT1, JAK2, and NFκB, together with STAT4, contribute to the development of cell-mediated immunity, which is able to contain the proliferation of Mycobacterium leprae.

A TNFSF15 disease-risk polymorphism increases pattern-recognition receptor-induced signaling through caspase-8-induced IL-1.

Inflammatory diseases are characterized by dysregulated cytokine production. Altered functions for most risk loci, including the inflammatory bowel disease and leprosy-associated tumor necrosis factor ligand superfamily member 15 (TNFSF15) region, are unclear. Regulation of pattern-recognition-receptor (PRR)-induced signaling and cytokines is crucial for immune homeostasis; TNFSF15:death receptor 3 (DR3) contributions to PRR responses have not been described. We found that human macrophages expressed DR3 and that TNFSF15:DR3 interactions were critical for amplifying PRR-initiated MAPK/NF-κB/PI3K signaling and cytokine secretion in macrophages. Mechanisms mediating TNFSF15:DR3 contributions to PRR outcomes included TACE-induced TNFSF15 cleavage to soluble TNFSF15; soluble TNFSF15 then led to TRADD/FADD/MALT-1- and caspase-8-mediated autocrine IL-1 secretion. Notably, TNFSF15 treatment also induced cytokine secretion through a caspase-8-dependent pathway in intestinal myeloid cells. Importantly, rs6478108 A disease risk-carrier macrophages demonstrated increased TNFSF15 expression and PRR-induced signaling and cytokines. Taken together, TNFSF15:DR3 interactions amplify PRR-induced signaling and cytokines, and the rs6478108 TNFSF15 disease-risk polymorphism results in a gain of function.

Haplotype structure and positive selection at TLR1.

Toll-like receptor 1, when dimerized with Toll-like receptor 2, is a cell surface receptor that, upon recognition of bacterial lipoproteins, activates the innate immune system. Variants in TLR1 associate with the risk of a variety of medical conditions and diseases, including sepsis, leprosy, tuberculosis, and others. The foremost of these is rs5743618 c.2079T>G(p.(Ile602Ser)), the derived allele of which is associated with reduced risk of sepsis, leprosy, and other diseases. Interestingly, 602Ser, which shows signatures of selection, inhibits TLR1 surface trafficking and subsequent activation of NFκB upon recognition of a ligand. This suggests that reduced TLR1 activity may be beneficial for human health. To better understand TLR1 variation and its link to human health, we have typed all 7 high-frequency missense variants (>5% in at least one population) along with 17 other variants in and around TLR1 in 2548 individuals from 56 populations from around the globe. We have also found additional signatures of selection on missense variants not associated with rs5743618, suggesting that there may be multiple functional alleles under positive selection in this gene.

IL-10 production from dendritic cells is associated with DC SIGN in human leprosy.

The defective antigen presenting ability of antigen presenting cells (APCs) modulates host cytokines and co-stimulatory signals that may lead to severity of leprosy. In the present study, we sought to evaluate the phenotypic features of APCs along with whether DC SIGN (DC-specific intercellular adhesion molecule-grabbing nonintegrin) influences IL-10 production while moving from tuberculoid (BT/TT) to lepromatous (BL/LL) pole in leprosy pathogenesis. The study revealed an increased expression of DC SIGN on CD11c⁺ cells from BL/LL patients and an impaired form of CD83 (∼50 kDa). However, the cells after treatment with GM-CSF+IL-4+ManLAM showed an increased expression of similar form of CD83 on DCs. Upon treatment with ManLAM, DCs were found to show increased nuclear presence of NF-κB, thus leading to higher IL-10 production. High IL-10 production from ManLAM treated PBMCs further suggested the role of DC SIGN in subverting the DCs function towards BL/LL pole of leprosy. Anti-DC SIGN treatment resulting in restricted nuclear ingression of NF-κB as well as its acetylation along with enhanced T cell proliferation validated our findings. In conclusion, Mycobacterium leprae component triggers DC SIGN on DCs to induce production of IL-10 by modulating intracellular signalling pathway at the level of transcription factor NF-κB towards BL/LL pole of disease.

Mycobacterium indicus pranii mediates macrophage activation through TLR2 and NOD2 in a MyD88 dependent manner.

Mycobacterium indicus pranii (MIP) is a non-pathogenic strain of mycobacterium and has been used as a vaccine against tuberculosis and leprosy. Here, we investigated the role of different pattern recognition receptors in the recognition of heat-killed MIP by macrophages. Treatment of macrophages with MIP caused upregulation of pro-inflammatory cytokines (like TNFα and IL-1ß) which was mediated through both TLR2 and NOD2, as revealed by our knockdown and/or knockout studies. Mechanistically, MIP-induced macrophage activation was shown to result in NF-κB activation and drastically abrogated by MyD88 deficiency, suggesting its regulation via an MyD88-dependent, NF-κB pathway. Interestingly, the IFN-inducible cytokine, CXCL10, which is known target of the TRIF-dependent TLR pathway was found to be upregulated in response to MIP but, in an MyD88-dependent manner. Collectively, these results demonstrate macrophages to recognize and respond to MIP through a TLR2, NOD2 and an MyD88-dependent pathway. However, further studies should clarify whether additional TLR-dependent or -independent pathways also exist in regulating the full spectrum of MIP action on macrophage activation.

Identification of a novel gene product that promotes survival of Mycobacterium smegmatis in macrophages.

BACKGROUND: Bacteria of the suborder Corynebacterineae include significant human pathogens such as Mycobacterium tuberculosis and M. leprae. Drug resistance in mycobacteria is increasingly common making identification of new antimicrobials a priority. Mycobacteria replicate intracellularly, most commonly within the phagosomes of macrophages, and bacterial proteins essential for intracellular survival and persistence are particularly attractive targets for intervention with new generations of anti-mycobacterial drugs. METHODOLOGY/PRINCIPAL FINDINGS: We have identified a novel gene that, when inactivated, leads to accelerated death of M. smegmatis within a macrophage cell line in the first eight hours following infection. Complementation of the mutant with an intact copy of the gene restored survival to near wild type levels. Gene disruption did not affect growth compared to wild type M. smegmatis in axenic culture or in the presence of low pH or reactive oxygen intermediates, suggesting the growth defect is not related to increased susceptibility to these stresses. The disrupted gene, MSMEG_5817, is conserved in all mycobacteria for which genome sequence information is available, and designated Rv0807 in M. tuberculosis. Although homology searches suggest that MSMEG_5817 is similar to the serine:pyruvate aminotransferase of Brevibacterium linens suggesting a possible role in glyoxylate metabolism, enzymatic assays comparing activity in wild type and mutant strains demonstrated no differences in the capacity to metabolize glyoxylate. CONCLUSIONS/SIGNIFICANCE: MSMEG_5817 is a previously uncharacterized gene that facilitates intracellular survival of mycobacteria. Interference with the function of MSMEG_5817 may provide a novel therapeutic approach for control of mycobacterial pathogens by assisting the host immune system in clearance of persistent intracellular bacteria.

Thalidomide modulates Mycobacterium leprae-induced NF-κB pathway and lower cytokine response.

It is widely accepted that tumor necrosis factor alpha (TNF-α) plays a critical role in the development of tissue and nerve damage in leprosy and during the reactional episodes of acute inflammation. Thalidomide (N-α-phthalimidoglutarimide), a drug used to treat leprosy reaction, modulates immune response, inhibits inflammation and NF-κB activity. Here we investigated whether thalidomide inhibits NF-κB activation induced by Mycobacterium leprae, p38 and ERK1/2 MAPK activation. EMSA and supershift assays were performed to investigate NF-κB activation in response to M. leprae and its modulation following in vitro treatment with thalidomide. Luciferase assay was assayed in transfected THP-1 cells to determine NF-κB transcriptional activity. Flow cytometry and immunofluorescence were used to investigate p65 accumulation in the nucleus. Immunoblotting was used to investigate p38 and ERK1/2 phosphorylation. Following activation of PBMC and monocytes with M. leprae, the formation and nuclear localization of NF-κB complexes composed mainly of p65/p50 and p50/p50 dimers was observed. Induction of NF-κB activation and DNA binding activity was inhibited by thalidomide. The drug also reduced M. leprae-induced TNF-α production and inhibited p38 and ERK1/2 activation. Definition of the activation mechanisms in cells stimulated with M. leprae can lead to the development of new therapy applications to modulate NF-κB activation and to control the inflammatory manifestations due to enhanced TNF-α response as observed in leprosy and in leprosy reactions.

[Thalidomide as immunomodulatory drug: pharmacological actions and its indications].

Thalidomide was developed in the 1950s as a sedative drug and withdrawn in 1961 because of its teratogenic effects, but has been rediscovered as an immuno-modulatory drug. It has been administered successfully for the treatment of erythema nodosum leprosum, aphthous ulceration and cachexia in HIV disease, inflammatory bowel diseases, and several malignant diseases. The suppressive effect of thalidomide on the activation of the nuclear transcription factor NF-κB may explain these effects of thalidomide. NF-κB is retained in the cytoplasm with IκBα, and is activated by a wide variety of inflammatory stimuli including TNF, IL-1 and endotoxin followed by its translocation to the nucleus. Angiogenesis and organogenesis also require gene transcription and signal translocation. The findings shed new light on the anti-inflammatory properties of thalidomide and suggest pharmaceutical actions of thalidomide via interference of transcription mechanism. I reviewed the effects of thalidomide on auto-inflammatory diseases of childhood.

Therapeutic role of rifaximin in inflammatory bowel disease: clinical implication of human pregnane X receptor activation.

Human pregnane X receptor (PXR) has been implicated in the pathogenesis of inflammatory bowel disease (IBD). Rifaximin, a human PXR activator, is in clinical trials for treatment of IBD and has demonstrated efficacy in Crohn's disease and active ulcerative colitis. In the current study, the protective and therapeutic role of rifaximin in IBD and its respective mechanism were investigated. PXR-humanized (hPXR), wild-type, and Pxr-null mice were treated with rifaximin in the dextran sulfate sodium (DSS)-induced and trinitrobenzene sulfonic acid (TNBS)-induced IBD models to determine the protective function of human PXR activation in IBD. The therapeutic role of rifaximin was further evaluated in DSS-treated hPXR and Pxr-null mice. Results demonstrated that preadministration of rifaximin ameliorated the clinical hallmarks of colitis in DSS- and TNBS-treated hPXR mice as determined by body weight loss and assessment of diarrhea, rectal bleeding, colon length, and histology. In addition, higher survival rates and recovery from colitis symptoms were observed in hPXR mice, but not in Pxr-null mice, when rifaximin was administered after the onset of symptoms. Nuclear factor κB (NF-κB) target genes were markedly down-regulated in hPXR mice by rifaximin treatment. In vitro NF-κB reporter assays demonstrated inhibition of NF-κB activity after rifaximin treatment in colon-derived cell lines expressing hPXR. These findings demonstrated the preventive and therapeutic role of rifaximin on IBD through human PXR-mediated inhibition of the NF-κB signaling cascade, thus suggesting that human PXR may be an effective target for the treatment of IBD.

SNP 668C (-44) alters a NF-kappaB1 putative binding site in non-coding strand of human beta-defensin 1 (DEFB1) and is associated with lepromatous leprosy.

UNLABELLED: Leprosy is an infectious disease caused by Mycobacterium leprae. The peptide human beta-defensin 1 is an antimicrobial effector of innate epithelial immunity. A study was done on the association of three single nucleotide polymorphisms (SNPs) in the beta-defensin 1 gene (DEFB1) - 668 C/G (-44 C/G or rs1800972; in 5' UTR), 692 A/G (-20 A/G or rs11362; in 5' UTR) and A1836G (rs1800971; in 3' UTR) - with leprosy susceptibility per se and clinical leprosy variants. The SNPs were genotyped by real-time polymerase chain reaction (rt-PCR) and PCR-restriction fragment length polymorphisms. Subjects were of Mexican mestizo ethnicity from Sinaloa state, México. Analysis was done on borderline leprosy, lepromatous leprosy (L-lep) and indeterminate leprosy subgroups compared with healthy controls. RESULTS: The genotypes associated with L-lep and no other leprosy subgroup after Bonferroni correction were those that contain 668C in a dominant model (OR=3.06, 95% CI 1.47-6.4, p=0.024). Estimated haplotype CGA is over-represented in L-lep (p=0.009; OR=2.25, 1.23-4.03). Five NF-kappaB1 putative binding sites (NPBSs) were identified with JASPAR software in non-coding strand spanning the 5' UTR and intron 1 of DEFB1, including one which is altered when SNP 668C is present. SNP 668C probably abrogates NF-kappaB-dependent DEFB1 upregulation leading to L-lep variant.

Tryptophan aspartate-containing coat protein (CORO1A) suppresses Toll-like receptor signalling in Mycobacterium leprae infection.

Mycobacterium leprae is an intracellular pathogen that survives within the phagosome of host macrophages. Several host factors are involved in producing tolerance, while others are responsible for killing the mycobacterium. Tryptophan aspartate-containing coat protein (TACO; also known as CORO1A or coronin-1) inhibits the phagosome maturation that allows intracellular parasitization. In addition, the Toll-like receptor (TLR) activates the innate immune response. Both CORO1A and TLR-2 co-localize on the phagosomal membrane in the dermal lesions of patients with lepromatous leprosy. Therefore, we hypothesized that CORO1A and TLR-2 might interact functionally. This hypothesis was tested by investigating the effect of CORO1A in TLR-2-mediated signalling and, inversely, the effect of TLR-2-mediated signalling on CORO1A expression. We found that CORO1A suppresses TLR-mediated signal activation in human macrophages, and that TLR2-mediated activation of the innate immune response resulted in suppression of CORO1A expression. However, M. leprae infection inhibited the TLR-2-mediated CORO1A suppression and nuclear factor-kappaB activation. These results suggest that the balance between TLR-2-mediated signalling and CORO1A expression will be key in determining the fate of M. leprae following infection.

[Action mechanism of thalidomide in treatment of multiple myeloma].

Thalidomide, N-phtalidoglutamide, is a well-known teratogenic agent when given to pregnant women. It was first synthesized by CIBA in 1953, but put on market in Germany as a sedative, but Dr. Rentz reported first the relation with the teratogenicity. However, its clinical activity to erythema nodosum leprosum was accidentally found. In 1997, thalidomide was found active to multiple myeloma, but its clinical use is not authorized yet in Japan. The mechanisms which so far reported are as follows. 1) The inhibitory activity of angiogenesis 2) NF-kappaB suppression 3) Suppression of GVHD, and other activity to immunity (suppression or augmentation), suppression of TNFa 4) Suppression of intracellular adhesion molecule 5) Binding to DNA From these reports, the teratogenicity or the clinical activities have been somewhat understood. Recently clinical studies of the analogue, Lenalidomide, have been reported.

C-type lectin DC-SIGN modulates Toll-like receptor signaling via Raf-1 kinase-dependent acetylation of transcription factor NF-kappaB.

Adaptive immune responses by dendritic cells (DCs) are critically controlled by Toll-like receptor (TLR) function. Little is known about modulation of TLR-specific signaling by other pathogen receptors. Here, we have identified a molecular signaling pathway induced by the C-type lectin DC-SIGN that modulates TLR signaling at the level of the transcription factor NF-kappaB. We demonstrated that pathogens trigger DC-SIGN on human DCs to activate the serine and threonine kinase Raf-1, which subsequently leads to acetylation of the NF-kappaB subunit p65, but only after TLR-induced activation of NF-kappaB. Acetylation of p65 both prolonged and increased IL10 transcription to enhance anti-inflammatory cytokine responses. We demonstrated that different pathogens such as Mycobacterium tuberculosis, M. leprae, Candida albicans, measles virus, and human immunodeficiency virus-1 interacted with DC-SIGN to activate the Raf-1-acetylation-dependent signaling pathway to modulate signaling by different TLRs. Thus, this pathway is involved in regulation of adaptive immunity by DCs to bacterial, fungal, and viral pathogens.