Human dendritic cells respond to Helicobacter pylori, promoting NK cell and Th1-effector responses in vitro

Helicobacter pylori infection leads to chronic gastric inflammation. The current study determined the response of human APCs, NK cells, and T cells toward the bacteria in vitro. Human monocyte-derived dendritic cells (DC) were incubated with bacteria for 48 h. Intact H. pylori at a multitude of infection 5 stimulated the expression of MHC class II (4- to 7-fold), CD80, and CD86 B7 molecules (10- to 12-fold) and the CD83 costimulatory molecule (>30-fold) as well as IL-12 secretion (>50-fold) in DCs, and thereby, strongly induced their maturation and activation. CD56(+)/CD4(-) NK cells, as well as CD4(+)/CD45RA(+) naive T cells, were isolated and incubated with DCs pulsed with intact bacteria or different cellular fractions. Coculture of H. pylori-pulsed DCs with NK cells strongly potentiated the secretion of TNF-alpha and IFN-gamma. Coculture of naive T cells with H. pylori-pulsed DCs significantly enhanced TNF-alpha, IFN-gamma, and IL-2 secretion as well as T-bet mRNA levels, while GATA-3 mRNA was lowered. However, the effect appeared attenuated compared with coculture with Escherichia coli. A greater stimulation was seen with naive T cells and DCs pulsed with H. pylori membrane preparations. Intact H. pylori potently induced the maturation and activation of human monocyte-derived DC and thereby promote NK and Th1 effector responses. The strong activation of NK cells may be important for the innate immune response. Th1-polarized T cells were induced especially by incubation with membrane preparations of H. pylori, suggesting that membrane proteins may account for the specific adaptive immune response.     

Helicobacter pylori stimulates a mixed adaptive immune response with a strong T-regulatory component in human gastric mucosa

BACKGROUND: Host factors play an important role in the pathophysiology of Helicobacter pylori infection and development of gastritis and related disease. The established opinion is that the T-cell-mediated immune response to H. pylori infection is of Th1 type. Our earlier immune cell phenotype studies indicate a mixed Th1-Th2 profile of the effector cells. Therefore, an extensive adaptive and regulatory cytokine gene expression profile was conducted by quantitative real-time polymerase chain reaction (qPCR). MATERIALS AND METHODS: Biopsies from gastric mucosa of 91 patients diagnosed as H. pylori negative, H. pylori positive with gastritis, or H. pylori positive with peptic ulcer were obtained by endoscopy. Gene expressions of nine cytokines and CagA status were measured by qPCR. RESULTS: All cytokine genes showed higher expression levels in the presence of H. pylori when compared to H. pylori-negative samples (fold increase: IL8: x 11.2; IL12A: x 2.4; TNF-alpha: x 5.2; IFN-gamma: x 4.3; IL4: x 3.6; IL6: x 14.7; and IL10: x 6.7). Patients infected with CagA-positive strains had higher expression of IL1-beta and IL18 compared to patients infected with CagA-negative strains (x 1.6 for IL1-beta and x 2.0 for IL18). Patients with duodenal ulcer had a lower antral Th1/Th2 ratio than other H. pylori-positive patients. CONCLUSIONS: The cytokine profile of H. pylori-infected gastric mucosa shows a mixed Th1-Th2 profile. Furthermore, a high IL10 expression may indicate that also regulatory T cells play a role in the chronic phase of H. pylori infection.     

Innate Responses Induced by Whole Inactivated Virus or Subunit Influenza Vaccines in Cultured Dendritic Cells Correlate with Immune Responses In Vivo

Vaccine development involves time-consuming and expensive evaluation of candidate vaccines in animal models. As mediators of both innate and adaptive immune responses dendritic cells (DCs) are considered to be highly important for vaccine performance. Here we evaluated how far the response of DCs to a vaccine in vitro is in line with the immune response the vaccine evokes in vivo. To this end, we investigated the response of murine bone marrow-derived DCs to whole inactivated virus (WIV) and subunit (SU) influenza vaccine preparations. These vaccine preparations were chosen because they differ in the immune response they evoke in mice with WIV being superior to SU vaccine through induction of higher virus-neutralizing antibody titers and a more favorable Th1-skewed response phenotype. Stimulation of DCs with WIV, but not SU vaccine, resulted in a cytokine response that was comparable to that of DCs stimulated with live virus. Similarly, the gene expression profiles of DCs treated with WIV or live virus were similar and differed from that of SU vaccine-treated DCs. More specifically, exposure of DCs to WIV resulted in differential expression of genes in known antiviral pathways, whereas SU vaccine did not. The stronger antiviral and more Th1-related response of DCs to WIV as compared to SU vaccine correlates well with the superior immune response found in mice. These results indicate that in vitro stimulation of DCs with novel vaccine candidates combined with the assessment of multiple parameters, including gene signatures, may be a valuable tool for the selection of vaccine candidates.     

β2-Adrenergic agonists bias TLR-2 and NOD2 activated dendritic cells towards inducing an IL-17 immune response

This study tested the hypothesis that activation of β2-adrenoceptors on DCs influences NOD2 signaling along with its cross-talk with Toll-like receptor-2 resulting in altered Th cell priming ability. Th17 cells are a newly discovered lineage of CD4(+) T cells involved in defense against extracellular bacteria and also implicated in autoimmune disorders. Initiation and polarization of the adaptive immune response is controlled by innate immune recognition mediated by DCs. Previous studies demonstrated that adrenergic receptors modulate cytokine production by DCs and affect their Th cell priming ability. We show that the β2-adrenoceptor agonist salbutamol enhanced IL-6 production in murine bone marrow-derived DCs stimulated with the nucleotide-binding oligomerization domain 2 ligand muramyl dipeptide. However, when the Toll-like receptor-2 ligand Pam3CysSK4 was added, salbutamol inhibited IL-12 but did not alter IL-6 and IL-23 expression. Gene expression analysis showed that salbutamol inhibited the p40 subunit as well as IL-12p35, while IL-23p19 and IL-6 were stimulated. Therefore, β2-adrenoceptors modulated cytokine production resulting in a Th17 cell priming cytokine pattern. Indeed, when antigen-pulsed DCs stimulated by muramyl dipeptide or Pam3CysSK4+muramyl dipeptide in the presence of salbutamol were used for in vivo immunization, the resulting Th17/Th1 cell ratio was increased as evaluated by IL-17 and IFN-γ production. In addition, intradermal injection of norepinephrine along with Pam3CysSK4+muramyl dipeptide increased the Th17 response to an immunogenic protein and this effect was reversed by a β2-adrenoceptor antagonist. Thus, β2-adrenoceptors may be involved in the regulation of defense against extracellular bacteria and the pathogenesis of inflammatory diseases.     

Shaping immune responses through the activation of dendritic cells–P2 receptors

Dendritic cells (DCs) activate and shape the adaptive immune response by capturing antigens, migrating to peripheral lymphoid organs where naïve T cells reside, expressing high levels of MHC and costimulatory molecules and secreting cytokines and chemokines. DCs are endowed with a high degree of functional plasticity and their functions are tightly regulated. Besides initiating adaptive immune responses, DCs play a key role in maintaining peripheral tolerance toward self-antigens. On the basis of the information gathered from the tissue where they reside, DCs adjust their functional activity to ensure that protective immunity is favoured while unwanted or exaggerated immune responses are prevented. A wide variety of signals from neighbouring cells affecting DC functional activity have been described. Here we will discuss the complex role of extracellular nucleotides in the regulation of DC function and the role of P2 receptors as possible tools to manipulate immune responses.     

IFN-alpha skews monocyte differentiation into Toll-like receptor 7-expressing dendritic cells with potent functional activities

IFN-alpha is an important cytokine for the generation of a protective T cell-mediated immune response to viruses. In this study, we asked whether IFN-alpha can regulate the functional properties of dendritic cells (DCs). We show that monocytes cultured in the presence of GM-CSF and IFN-alpha can differentiate into DCs (IFN-alpha-derived DCs (IFN-DCs)). When compared with DCs generated in the presence of GM-CSF and IL-4 (IL-4-derived DCs), IFN-DCs exhibited a typical DC morphology and expressed, in addition to DC markers CD1a and blood DC Ag 4, a similar level of costimulatory and class II MHC molecules, but a significantly higher level of MHC class I molecules. After maturation with CD40 ligand, IFN-DCs up-regulated costimulatory, class I and II MHC molecules and expressed mature DC markers such as CD83 and DC-lysosome-associated membrane protein. IFN-DCs were endowed with potent functional activities. IFN-DCs secreted large amounts of the inflammatory cytokines IL-6, IL-10, TNF-alpha, IL-1beta, and IL-18, and promoted a Th1 response that was independent of IL-12p70 and IL-18, but substantially inhibited by IFN-alpha neutralization. Furthermore, immature IFN-DCs induced a potent autologous Ag-specific immune response, as evaluated by IFN-gamma secretion and expansion of CD8(+) T cells specific for CMV. Also, IFN-DCs expressed a large number of Toll-like receptors (TLRs), including acquisition of TLR7, which is classically found on the natural type I IFN-producing plasmacytoid DCs. Like plasmacytoid DCs, IFN-DCs could secrete IFN-alpha following viral stimulation or TLR7-specific stimulation. Taken together, these results illustrate the critical role of IFN-alpha at the early steps of immune response to pathogens or in autoimmune diseases.     

Host response to Helicobacter pylori infection before initiation of the adaptive immune response

Helicobacter pylori persistently colonizes the human stomach. In this study, immune responses to H. pylori that occur in the early stages of infection were investigated. Within the first 2 days after orogastric infection of mice with H. pylori, there was a transient infiltration of macrophages and neutrophils into the glandular stomach. By day 10 postinfection, the numbers of macrophages and neutrophils decreased to baseline levels. By 3 weeks postinfection, an adaptive immune response was detected, marked by gastric infiltration of T lymphocytes, macrophages, and neutrophils, as well as increased numbers of H. pylori-specific T cells, macrophages, and dendritic cells in paragastric lymph nodes. Neutrophil-attracting and macrophage-attracting chemokines were expressed at higher levels in the stomachs of H. pylori-infected mice than in the stomachs of uninfected mice. Increased expression of TNFalpha and IFNgamma (Th1-type inflammatory cytokines) and IL-17 (a Th17-type cytokine) was detected in the stomachs of H. pylori-infected mice, but increased expression of IL-4 (a Th2-type cytokine) was not detected. These data indicate that a transient gastric inflammatory response to H. pylori occurs within the first few days after infection, before the priming of T cells and initiation of an adaptive immune response. It is speculated that inappropriate waning of the innate immune response during early stages of infection may be a factor that contributes to H. pylori persistence.     

Helicobacter pylori-pulsed dendritic cells induce H. pylori-specific immunity in mice

Background: The growing concern over the emergence of antibiotic‐resistant Helicobacter pylori infection is propelling the development of an efficacious vaccine to control this highly adaptive organism. Aim: We studied the use of a dendritic cell (DC)‐based vaccine against H. pylori infection in mice. Methods: The cellular immune responses to murine bone marrow‐derived DCs pulsed with phosphate‐buffered saline (PBS‐DC) or live H. pylori SS1 (HP‐DC) were assessed in vitro and in vivo. The protective immunity against H. pylori SS1 oral challenge was compared between HP‐DC or PBS‐DC immunized mice. The effect of regulatory T‐cell (Treg) depletion by anti‐CD25 antibody on HP‐DC vaccine efficacy was also evaluated. Results: HP‐DC induced a Th1‐dominant response in vitro. In vivo, HP‐DC immunized mice were characterized by a mixed Th1/Th2 peripheral immune response. However, in the stomach, HP‐DC immunized mice expressed a higher level of IFN‐γ compared to PBS‐DC immunized mice; no difference was found for interleukin‐5 expressions in the stomach. A lower bacterial colonization post‐H. pylori challenge was observed in HP‐DC immunized mice compared to PBS‐DC immunized mice with no significant difference in gastritis severity. H. pylori‐specific Th1 response and protective immunity were further enhanced in vivo by depletion of Treg with anti‐CD25 antibody. Conclusion: DC‐based anti‐H. pylori vaccine induced H. pylori‐specific helper T‐cell responses capable of limiting bacterial colonization. Our data support the critical role of effector cellular immune response in the development of H. pylori vaccine.     

Dendritic cell-tumor fusion vaccine prevents tumor growth in vivo

Dendritic cells (DCs) are potent antigen presenting cells that are uniquely effective in generating primary immune responses. DCs that are manipulated to present tumor antigens induce antitumor immunity in animal models and preclinical human studies. A myriad of strategies have been developed to load tumor antigen effectively onto DCs. DC-tumor fusion presents a spectrum of tumor-associated antigens to helper T- and cytotoxic T-cell populations in the context of DC-mediated costimulatory signals. In this study, fusion cells (FCs) were generated with MCA-102 fibrosarcoma cells and murine bone marrow-derived myeloid DCs. The FCs coexpressed the DC-derived MHC class II and costimulatory molecules. The FCs also retained the functional properties of DCs and stimulated syngeneic T cell proliferation and interferon-gamma (IFN-gamma) production. Significantly, the results show that syngeneic T cells are primed by FCs to induce MHC class I-dependent lysis of MCA-102 fibrosarcoma. These findings indicate that fusions of tumor cells and DCs activate T-cell responses against syngeneic tumors.     

Deconstructing tick saliva: non-protein molecules with potent immunomodulatory properties

Dendritic cells (DCs) are powerful initiators of innate and adaptive immune responses. Ticks are blood-sucking ectoparasite arthropods that suppress host immunity by secreting immunomodulatory molecules in their saliva. Here, compounds present in Rhipicephalus sanguineus tick saliva with immunomodulatory effects on DC differentiation, cytokine production, and costimulatory molecule expression were identified. R. sanguineus tick saliva inhibited IL-12p40 and TNF-α while potentiating IL-10 cytokine production by bone marrow-derived DCs stimulated by Toll-like receptor-2, -4, and -9 agonists. To identify the molecules responsible for these effects, we fractionated the saliva through microcon filtration and reversed-phase HPLC and tested each fraction for DC maturation. Fractions with proven effects were analyzed by micro-HPLC tandem mass spectrometry or competition ELISA. Thus, we identified for the first time in tick saliva the purine nucleoside adenosine (concentration of ～110 pmol/μl) as a potent anti-inflammatory salivary inhibitor of DC cytokine production. We also found prostaglandin E(2) (PGE(2) ～100 nM) with comparable effects in modulating cytokine production by DCs. Both Ado and PGE(2) inhibited cytokine production by inducing cAMP-PKA signaling in DCs. Additionally, both Ado and PGE(2) were able to inhibit expression of CD40 in mature DCs. Finally, flow cytometry analysis revealed that PGE(2), but not Ado, is the differentiation inhibitor of bone marrow-derived DCs. The presence of non-protein molecules adenosine and PGE(2) in tick saliva indicates an important evolutionary mechanism used by ticks to subvert host immune cells and allow them to successfully complete their blood meal and life cycle.     

A mouse model for immunization with ex vivo virus-infected dendritic cells

Dendritic cells (DCs) have been demonstrated to be an important if not essential inducer of cellular immune responses. The ability to grow these cells in vitro may open up new avenues for protective immunizations. In this study we have analyzed the virus-specific memory response generated following immunization with ex vivo-infected bone marrow-derived dendritic cells. We demonstrate that mouse DCs are efficiently infected with influenza virus but do not release infectious progeny virus. Ex vivo-infected DCs secrete interleukin-12 (IL-12) and induce a potent T helper (Th)1-like immune response when injected into mice. This was demonstrated by the generation of cytotoxic T lymphocytes, the production of high levels of gamma-interferon, and undetectable levels of IL-4 upon in vitro restimulation of splenocytes from immunized animals. In addition, the virus-specific antibody response is primarily of the IgG2a isotype, consistent with the expansion of Th1 cells. Animals immunized with DCs infected with X-31 influenza virus and challenged with PR8 influenza virus cleared the infection faster than animals not vaccinated. Thus, infected DCs efficiently activate the cellular immune response and induce heterosubtypic immunity in mice.     

Cloning and Characterization of a 22 kDa Outer-Membrane Protein (Omp22) from Helicobacter pylori

Helicobacter pylori is a causative agent of gastritis and peptic ulceration in humans. As the first step towards development of a vaccine against H. pylori infection, we have attempted to identify protective antigens. A potential target of vaccine development would be a H. pylori specific protein, which is surface-exposed and highly antigenic. We identified a 22 kDa outer-membrane protein (Omp22) from H. pylori, which was highly immunoreactive. By screening a H. pylori genomic DNA library with rabbit anti-H. pylori outer-membrane protein antibodies, the omp22 gene was cloned and 1.4 kb of the nucleotide sequence was determined. One open reading frame, encoding a 179-residue polypeptide, was identified and the amino acid sequence deduced showed homology with peptidoglycan-associated lipoproteins. The sequence was conserved among other H. pylori strains. Omp22 protein is expressed as a precursor polypeptide of 179 residues and undergoes lipid modification and cleavage of an 18 amino acid signal peptide to yield a mature protein. Omp22 protein in H. pylori as well as recombinant Omp22 protein expressed in E. coli was localized into the outer membrane and exposed on the cell surface. Omp22 may have the potential as a target antigen for the development of a H. pylori vaccine.     

IgG subclass responses in childhood Helicobacter pylori duodenal ulcer: evidence of T-helper cell type 2 responses

BACKGROUND: Duodenal ulcer in adults chronically infected with Helicobacter pylori is associated with a polarized T-helper cell type 1 (Th1) mucosal immune response, with a predominantly immunoglobulin G2 (IgG2) systemic specific response. It has been suggested that children colonized by H. pylori also produce a mucosal Th1 response, but there are few studies that have measured IgG subclass responses in children with duodenal ulcer. MATERIALS AND METHODS: Seven children with endoscopically proven duodenal ulcer and H. pylori infection and 18 children with biopsy proven H. pylori infection but no duodenal ulcer had relative concentrations of IgG subclass responses (IgGsc) against H. pylori antigens measured by ELISA. Eighteen IgG seropositive adults acted as controls. The range of antigens recognised by IgG1 and IgG2 subclass responses were investigated by Western blots. RESULTS: There were no differences in mean IgGsc responses between children with or without duodenal ulcer. Adults produced an IgG2 predominant response. Western blots showed no qualitative differences in antigens recognised by IgG1 or IgG2. CONCLUSION: Children with duodenal ulcer, in contrast to adults, produce an IgGsc response consistent with a mucosal Th2 response to H. pylori regardless of the presence of duodenal ulceration. This suggests that disease causation amongst children with H. pylori associated duodenal ulceration may not be dependant upon a mucosal Th1 biased response.     

Ox40 costimulation enhances the development of T cell responses induced by dendritic cells in vivo.

Dendritic cells (DCs) are bone marrow-derived APCs that display unique properties aimed at stimulating naive T cells. Several members of the TNF/TNFR families have been implicated in T cell functions. In this study, we examined the role that Ox40 costimulation might play on the ability of DCs to regulate CD4(+) and CD8(+) T cell responses in vivo. Administration of anti-mouse Ox40 mAb enhanced the Th response induced by immunization with Ag-pulsed DCs, and introduced a bias toward a Th1 immune response. However, anti-Ox40 treatment enhanced the production of Th2 cytokines in IFN-gamma(-/-) mice after immunization with Ag-pulsed DCs, suggesting that the production of IFN-gamma during the immune response could interfere with the development of Th2 lymphocytes induced by DCs. Coadministration of anti-Ox40 with DCs during Ag rechallenge enhanced both Th1 and Th2 responses induced during a primary immunization with DCs, and did not reverse an existing Th2 response. This suggests that Ox40 costimulation amplifies an ongoing immune response, regardless of Th differentiation potential. In an OVA-TCR class II-restricted adoptive transfer system, anti-Ox40 treatment greatly enhanced the level of cytokine secretion per Ag-specific CD4(+) T cell induced by immunization with DCs. In an OVA-TCR class I-restricted adoptive transfer system, administration of anti-Ox40 strongly enhanced expansion, IFN-gamma secretion, and cytotoxic activity of Ag-specific CD8(+) T cells induced by immunization with DCs. Thus, by enhancing immune responses induced by DCs in vivo, the Ox40 pathway might be a target for immune intervention in therapeutic settings that use DCs as Ag-delivery vehicles.     

B lymphocyte stimulator regulates adaptive immune responses by directly promoting dendritic cell maturation

B lymphocyte stimulator (BLyS) is a well-known direct costimulator of adaptive immune cells, particularly B lineage cells. However, we have reported recently that BLyS is also able to activate monocytes. Other innate immune cells, such as dendritic cells (DCs), play a key role in the initiation of adaptive immune responses and the purpose of the current study was to assess whether there is a direct role for BLyS in modulating human DC functions. In this study, we show that BLyS induces DC activation and maturation. Thus, BLyS strongly induced up-regulation of surface costimulatory molecule expression and secretion of specific cytokines and chemokines in DCs. BLyS-stimulated DCs (BLyS-DCs) were also able to augment allogeneic CD4 T cell proliferation to a greater extent than control DCs. BLyS-DCs secreted elevated levels of the major Th1-polarizing cytokine, IL-12p70, and they promoted naive CD4 T cell differentiation into Th1 T cells. Regarding BLyS receptor expression, DCs primarily express cytoplasmic transmembrane activator and CAML interactor; however, low levels of cell surface transmembrane activator and CAML interactor are expressed as well. Collectively, our data suggest that BLyS may modulate adaptive immune cells indirectly by inducing DC maturation.     

Salmonella enterica Serovar Typhi Plasmid Impairs Dendritic Cell Responses to Infection

Salmonella enterica serovar Typhi (S. typhi) evades from innate immunity by expression of a variety of pathogenic factors. The "pR(ST98)" plasmid of S. typhi is involved in multidrug-resistant and virulence of S. typhi. However, its exact effect on host cell function remains elusive. Dendritic cells (DCs) play an important role in shaping immune response against Salmonella. For the purpose of investigation whether pR(ST98) might target DCs involved in adaptive immune response, murine DCs were infected with S. typhi wild type and mutant strains. S. typhi stimulation resulted in up-regulation of costimulatory molecules on DCs. S. typhi wild type resulted in decreased up-regulation of CD40, CD80, and CD86 expression. Experiments with S. typhi pR(ST98) mutant (S. typhi-Δ-pR(ST98)) and S. typhi-Δ-pR(ST98) with a complemented plasmid encoding pR(ST98) (S. typhi-c-pR(ST98)) revealed that pR(ST98) accounts for inhibition of surface molecule expression and functional maturity. S. typhi-Δ-pR(ST98) gave maximal levels of IL-12 and IFN-γ release compared with wild type S. typhi or the complemented strains. In contrast to IL-12 and IFN-γ, IL-10 secretion by S. typhi-Δ-pR(ST98)-infected DCs was significantly lower than induction by S. typhi wild type. This indicates that immunity in response to pR(ST98) is skewed away from a protective Th1 response. Moreover, infection with S. typhi-Δ-pR(ST98) induced autophagy in DCs. We herein demonstrate S. typhi pR(ST98) plays essential roles in modulating DCs maturation, activation, inflammatory responses, and autophagy. Together, these data prove that pR(ST98) targets functions of DCs that are required for T-cell activation. This might contribute to evasion of adaptive immune responses by S. typhi.     

Helicobacter pylori-secreted factors inhibit dendritic cell IL-12 secretion: a mechanism of ineffective host defense

Helicobacter pylori evades host immune defenses and causes chronic gastritis. Immunity against intestinal pathogens is largely mediated by dendritic cells, yet the role of dendritic cells in acute H. pylori infection is largely unknown. We observed the recruitment of dendritic cells to the gastric mucosa of H. pylori-infected mice. Bone marrow-derived dendritic cells from mice responded to live H. pylori by upregulating the expression of proinflammatory cytokine mRNA (i.e., IL-1alpha, IL-1beta, and IL-6). The supernatant from dendritic cells stimulated with H. pylori for 18 h contained twofold higher levels of IL-12p70 than IL-10 and induced the proliferation of syngeneic splenocytes and type 1 T helper cell cytokine release (IFN-gamma and TNF-alpha). These responses were significantly lower compared with those induced by Acinetobacter lwoffi, another gastritis-causing pathogen more susceptible to host defenses. Analysis of whole H. pylori sonicate revealed the presence of a heat-stable factor secreted from H. pylori that specifically inhibited IL-12 but not IL-10 release from dendritic cells activated by A. lwoffi. Our findings suggest that dendritic cells participate in the host immune response against H. pylori and that their suppression by H. pylori may explain why infected hosts fail to prevent bacterial colonization.     

Saturated and polyunsaturated fatty acids reciprocally modulate dendritic cell functions mediated through TLR4

TLRs provide critical signals to induce innate immune responses in APCs such as dendritic cells (DCs) that in turn link to adaptive immune responses. Results from our previous studies demonstrated that saturated fatty acids activate TLRs, whereas n-3 polyunsaturated fatty acids inhibit agonist-induced TLR activation. These results raise a significant question as to whether fatty acids differentially modulate immune responses mediated through TLR activation. The results presented in this study demonstrate that the saturated fatty acid, lauric acid, up-regulates the expression of costimulatory molecules (CD40, CD80, and CD86), MHC class II, and cytokines (IL-12p70 and IL-6) in bone marrow-derived DCs. The dominant negative mutant of TLR4 or its downstream signaling components inhibits lauric acid-induced expression of a CD86 promoter-reporter gene. In contrast, an n-3 polyunsaturated fatty acid, docosahexaenoic acid, inhibits TLR4 agonist (LPS)-induced up-regulation of the costimulatory molecules, MHC class II, and cytokine production. Similarly, DCs treated with lauric acid show increased T cell activation capacity, whereas docosahexaenoic acid inhibits T cell activation induced by LPS-treated DCs. Together, our results demonstrate that the reciprocal modulation of both innate and adaptive immune responses by saturated fatty acid and n-3 polyunsaturated fatty acid is mediated at least in part through TLRs. These results imply that TLRs are involved in sterile inflammation and immune responses induced by nonmicrobial endogenous molecules. These results shed new light in understanding how types of dietary fatty acids differentially modulate immune responses that could alter the risk of many chronic diseases.