Lipoteichoic acid and muramyl dipeptide synergistically induce maturation of human dendritic cells and concurrent expression of proinflammatory cytokines

Lipoproteins are key immunostimulatory components of Bacillus species for dendritic cell maturation and activation

Dendritic cells (DCs) play an important role in immunity by sensing and responding to invasive microbes. Bacillus species are rod-shaped sporulating bacteria that include the pathogenic Bacillus cereus and commensal Bacillus subtilis. Although the interaction between DC and these two Bacillus species has been studied, their key structural component that prompts DC activation is poorly understood. Here, we investigated the two Bacillus species in DC activation by whole cells and their representative microbe-associated molecular patterns (MAMPs). MAMPs including lipoteichoic acid (LTA), lipoprotein (LPP), and peptidoglycan (PGN) were purified from the two Bacillus species. Among the MAMPs, LPP from both species most potently induced the maturation and activation of DCs while PGN, but not LTA, moderately stimulated DCs. LPPs from both Bacillus species enhanced the expression of DC maturation markers including CCR7, CD40, CD80, CD83, CD86, CD205, MHC-I, and MHC-II. Among the MAMPs from B. cereus, PGN most considerably lowered the endocytic capacity of DCs implying DC maturation whereas PGN from B. subtilis lowered it to a similar degree to its LPP. Furthermore, DCs sensitized with LPPs from both Bacillus species and PGN from B. subtilis moderately induced TNF-α and IL-6 production. Notably, a combination of MAMPs did not show any synergistic effect on DC activation. Taken together, our results demonstrate that LPP is the key structural component in B. cereus and B. subtilis that leads to DC activation.

Multifaceted roles and regulation of nucleotide-binding oligomerization domain containing proteins

Nucleotide-binding oligomerization domain-containing proteins, NOD1 and NOD2, are cytosolic receptors that recognize dipeptides and tripeptides derived from the bacterial cell wall component peptidoglycan (PGN). During the past two decades, studies have revealed several roles for NODs beyond detecting PGN fragments, including activation of an innate immune anti-viral response, NOD-mediated autophagy, and ER stress induced inflammation. Recent studies have also clarified the dynamic regulation of NODs at cellular membranes to generate specific and balanced immune responses. This review will describe how NOD1 and NOD2 detect microbes and cellular stress and detail the molecular mechanisms that regulate activation and signaling while highlighting new evidence and the impact on inflammatory disease pathogenesis.

Lipoteichoic acid of Streptococcus gordonii as a negative regulator of human dendritic cell activation

Streptococcus gordonii, an opportunistic Gram-positive bacterium, causes an infective endocarditis that could be fatal to human health. Dendritic cells (DCs) are known to be involved in disease progression and immune responses in S. gordonii infection. Since lipoteichoic acid (LTA) is a representative virulence factor of S. gordonii, we here investigated its role in the activation of human DCs stimulated with LTA-deficient (ΔltaS) S. gordonii or S. gordonii LTA. DCs were differentiated from human blood-derived monocytes in the presence of GM-CSF and IL-4 for 6 days. DCs treated with heat-killed ΔltaS S. gordonii (ΔltaS HKSG) showed relatively higher binding and phagocytic activities than those treated with heat-killed wild-type S. gordonii (wild-type HKSG). Furthermore, ΔltaS HKSG was superior to wild-type HKSG in inducing phenotypic maturation markers including CD80, CD83, CD86, PD-L1, and PD-L2, antigen-presenting molecule MHC class II, and proinflammatory cytokines such as TNF-α and IL-6. Concomitantly, DCs treated with the ΔltaS HKSG induced better T cell activities, including proliferation and activation marker (CD25) expression, than those treated with the wild-type. LTA, but not lipoproteins, isolated from S. gordonii weakly activated TLR2 and barely affected the expression of phenotypic maturation markers or cytokines in DCs. Collectively, these results demonstrated that LTA is not a major immuno-stimulating agent of S. gordonii but rather it interferes with bacteria-induced DC maturation, suggesting its potential role in immune evasion.

"Just right" combinations of adjuvants with nanoscale carriers activate aged dendritic cells without overt inflammation

BACKGROUND

The loss in age-related immunological markers, known as immunosenescence, is caused by a combination of factors, one of which is inflammaging. Inflammaging is associated with the continuous basal generation of proinflammatory cytokines. Studies have demonstrated that inflammaging reduces the effectiveness of vaccines. Strategies aimed at modifying baseline inflammation are being developed to improve vaccination responses in older adults. Dendritic cells have attracted attention as an age-specific target because of their significance in immunization as antigen presenting cells that stimulate T lymphocytes.

RESULTS

In this study, bone marrow derived dendritic cells (BMDCs) were generated from aged mice and used to investigate the effects of combinations of adjuvants, including Toll-like receptor, NOD2, and STING agonists with polyanhydride nanoparticles and pentablock copolymer micelles under in vitro conditions. Cellular stimulation was characterized via expression of costimulatory molecules, T cell-activating cytokines, proinflammatory cytokines, and chemokines. Our results indicate that multiple TLR agonists substantially increase costimulatory molecule expression and cytokines associated with T cell activation and inflammation in culture. In contrast, NOD2 and STING agonists had only a moderate effect on BMDC activation, while nanoparticles and micelles had no effect by themselves. However, when nanoparticles and micelles were combined with a TLR9 agonist, a reduction in the production of proinflammatory cytokines was observed while maintaining increased production of T cell activating cytokines and enhancing cell surface marker expression. Additionally, combining nanoparticles and micelles with a STING agonist resulted in a synergistic impact on the upregulation of costimulatory molecules and an increase in cytokine secretion from BMDCs linked with T cell activation without excessive secretion of proinflammatory cytokines.

CONCLUSIONS

These studies provide new insights into rational adjuvant selection for vaccines for older adults. Combining appropriate adjuvants with nanoparticles and micelles may lead to balanced immune activation characterized by low inflammation, setting the stage for designing next generation vaccines that can induce mucosal immunity in older adults.

Harnessing self-assembling peptide nanofibers toprime robust tumor-specific CD8 T cell responses in mice

Induction of tumor-specific CD8 + T cell responses is known as a major challenge for cancer vaccine development; here we presented a strategy to improve peptide nanofibers-mounted antitumor immune responses. To this end, peptide nanofibers bearing class I (Kb)-restricted epitope (Epi-Nano) were formulated with polyethylene imine backbone (Epi-Nano-PEI), and characterized using morphological and physicochemicalcharacterizationtechniques. Nanofibers were studied in terms of their uptake by antigen-presenting cells (APCs), antigen cross-presentation capacity, and cytotoxic activity. Furthermore, nanofibers were assessed by their potency to induce NLRP3 inflammasome-related cytokines and factors. Finally, the ability of nanofibers to induce tumor-specific CD8 T cells and tumor protection were investigated in tumor-bearing mice. The formulation of Epi-Nano with PEI led to the formation of short strand nanofibers with a positive surface charge, a low critical aggregation concentration (CAC), and an increased resistancetoproteolytic degradation. Epi-Nano-PEI was significantly taken up more efficiently by antigen-presenting cells (APCs), and was more potent in cross-presentation when compared to Epi-Nano. Moreover, Epi-Nano-PEI, in comparison to Epi-Nano, efficiently up-regulated the expression of NLRP3, caspase-1, IL-1b, IL18 and IL-6. Cell viability analysis showed that formulation of PEI with Epi-Nano not only abolished its cytotoxic activity, but surprisingly induced macrophage proliferation. Furthermore, it demonstrated that Epi-Nano-PEI triggered robust antigen-specific CD8+ T cell responses, and induced maximum antitumor response (tumor growth inhibition and prolonged survival) in tumor-bearing mice that were significantly higher compared to Epi-Nano. Taken together, the formulation of Epi-Nano with PEI is suggested as a promising strategy to improve nanofibers-mounted antitumor immune response.

Tissue microenvironment initiates an immune response to structural components of Staphylococcus aureus

Cell-to-cell communication in skin participates to the maintenance of homeostatic responses to foreign substances. Certain strains of Staphylococcus (S) aureus are vicious pathogens that cause deleterious effects in host cells and tissues. Both secreted toxins and structural components of S. aureus trigger an immune response, though how S. aureus stimulates host immune responses is poorly understood. We explored here how keratinocytes and fibroblasts initiate the first steps of an immune response by activating dendritic cells (DCs) through recognition of structural components of S. aureus. We treated monocyte-derived Langerhans cells (moLCs) and monocyte-derived DCs (moDCs) with conditioned media from keratinocytes (K-CM) and fibroblasts (F-CM) treated with heat-killed S. aureus (HKSA) respectively, or directly with HKSA. Immune and inflammatory responses from keratinocytes, fibroblasts, moLCs and moDCs were assessed by analysis of cell surface markers and cytokine production using flow cytometry, real-time PCR and ELISA assays. K-CM and F-CM increased the expression of CD86 and HLA-DR on moLCs and moDCs, in association with a specific cytokine profile. K-CM upregulated TNFA, IL-1B and GM-CSF mRNA expression in moLCs, while F-CM upregulated IL-12 and downregulated TNFA and TGFB mRNA expression in moDCs. Additionally, F-CM attenuated the induction of an inflammatory profile in monocytes. The recognition of structural components from S. aureus by cutaneous microenvironment induces the activation and the expression of specific cytokines from LCs and DCs.

Synergistic interactions between NOD receptors and TLRs: Mechanisms and clinical implications

Interactions between pattern recognition receptors (PRRs) shape innate immune responses to particular classes of pathogens. Here, we review interactions between TLRs and nucleotide-binding oligomerization domain 1 and 2 (NOD1 and NOD2) receptors, two major groups of PRRs involved in innate recognition of bacteria. Most of experimental data both in vitro and in vivo suggest that NODs and TLRs synergize with each other at inducing the production of cytokines and antimicrobial peptides. Molecular mechanisms of this synergy remain poorly understood, although several scenarios can be proposed: (i) direct interactions of signaling pathways downstream of NODs and TLRs; (ii) mutual transcriptional regulation of unique components of NOD-dependent and TLR-dependent signaling pathways; and (iii) interactions at the post-transcriptional level. Potential practical implications of NOD-TLR synergy are dual. In sepsis, where synergistic effects probably contribute to excessive proinflammatory cytokine production, blockade of NOD1, and/or NOD2 in addition to TLR4 blockade may be required to achieve therapeutic benefit. On the other hand, synergistic combinations of relatively small doses of NOD and TLR agonists administered before infection could be used to boost innate resistance against bacterial pathogens.

Muramyl dipeptide potentiates a Bacillus anthracis poly-γ-d-glutamic acid capsule surrogate that induces maturation and activation of mouse dendritic cells

Poly-γ-d-glutamic acid (PGA) of anthrax is an important pathogenic factor due to its anti-phagocytic activity. Additionally, PGA has the ability to activate mouse macrophages for the secretion of cytokines through Toll-like receptor (TLR) 2. Peptidoglycan (PGN), a major bacterial cell-wall component, induces inflammatory responses in the host. We assessed whether PGA can induce maturation and cytokine expression in immature mouse dendritic cells (DCs) in the existence of muramyl dipeptide (MDP), the minimum motif of PGN with immunostimulatory activity. Stimulation of immature DCs with PGA or MDP alone augmented expression of costimulatory molecules and MHC class II proteins, which are all cell surface markers indicative of maturation. The observed effects were further enhanced by costimulation of PGA and MDP. PGA alone was sufficient to induce expression of TNF-α, IL-6, MCP-1, and MIP1-α, whereas MDP alone did not under the same conditions. Treatment with MDP enhanced PGA-induced expression of the tested inflammatory mediators; however, the synergistic effect found for PGA and MDP was not observed in TLR2- or nucleotide-binding oligomerization domain (NOD) 2-knockout DCs. Additionally, MDP augmented PGA-induced MAP kinases and NF-κB activation, which is crucial for expression of cytokines. Furthermore, MAP kinase and NF-κB inhibitors attenuated MDP enhancement of PGA-induced cytokine production. In addition, co-culture of splenocytes and PGA/MDP-matured DCs induced higher expression of IL-2 and IFN-γ compared to that of splenocytes and PGA-matured DCs. Collectively, our results suggest that PGA and MDP cooperatively induce inflammatory responses in mouse DCs through TLR2 and NOD2 via MAP kinase and NF-κB pathways, subsequently leading to lymphocyte activation.

Lack of Both Nucleotide-Binding Oligomerization Domain-Containing Proteins 1 and 2 Primes T Cells for Activation-Induced Cell Death

Nucleotide-binding oligomerization domain (Nod)-containing proteins Nod1 and Nod2 play important roles in the innate immune response to pathogenic microbes, but mounting data suggest these pattern recognition receptors might also play key roles in adaptive immune responses. Targeting Nod1 and Nod2 signaling pathways in T cells is likely to provide a new strategy to modify inflammation in a variety of disease states, particularly those that depend on Ag-induced T cell activation. To better understand how Nod1 and Nod2 proteins contribute to adaptive immunity, this study investigated their role in alloantigen-induced T cell activation and asked whether their absence might impact in vivo alloresponses using a severe acute graft versus host disease model. The study provided several important observations. We found that the simultaneous absence of Nod1 and Nod2 primed T cells for activation-induced cell death. T cells from Nod1 × 2^-/- mice rapidly underwent cell death upon exposure to alloantigen. The Nod1 × 2^-/- T cells had sustained p53 expression that was associated with downregulation of its negative regulator MDM2. In vivo, mice transplanted with an inoculum containing Nod1 × 2^-/- T cells were protected from severe graft versus host disease. The results show that the simultaneous absence of Nod1 and Nod2 is associated with accelerated T cell death upon alloantigen encounter, suggesting these proteins might provide new targets to ameliorate T cell responses in a variety of inflammatory states, including those associated with bone marrow or solid organ transplantation.

Wall teichoic acid is an essential component of Staphylococcus aureus for the induction of human dendritic cell maturation

Staphylococcus aureus is a Gram-positive pathogen that can cause chronic skin inflammation, pneumonia, and septic shock. The immunomodulatory functions of wall teichoic acid (WTA), a glycopolymer abundantly expressed on the Gram-positive bacterial cell wall, are poorly understood. Here, we investigated the role of WTA in the phenotypic and functional activation of human monocyte-derived dendritic cells (DCs) treated with ethanol-killed S. aureus. WTA-deficient S. aureus mutant (ΔtagO) exhibited attenuated binding and internalization to DCs compared to the wild-type. ΔtagO induced lower expression of maturation markers on and cytokines in DCs than the wild-type S. aureus. Furthermore, autologous human peripheral blood mononuclear cells cocultured with ΔtagO-treated DCs exhibited a marked reduction in T cell proliferative activity, the expression of activation markers, and the production of cytokines compared to the wild-type S. aureus-stimulated DCs. Collectively, these results suggest that WTA is an important cell wall component of S. aureus for the induction of DC maturation and activation.

Lipoteichoic acids as a major virulence factor causing inflammatory responses via Toll-like receptor 2

Lipoteichoic acid (LTA), a major cell wall component of Gram-positive bacteria, is associated with various inflammatory diseases ranging from minor skin diseases to severe sepsis. It is known that LTA is recognized by Toll-like receptor 2 (TLR2), leading to the initiation of innate immune responses and further development of adaptive immunity. However, excessive immune responses may result in the inflammatory sequelae that are involved in severe diseases such as sepsis. Although numerous studies have tried to identify the molecular basis for the pathophysiology of Gram-positive bacterial infection, the exact role of LTA during the infection has not been clearly elucidated. This review provides an overview of LTA structure and host recognition by TLR2 that leads to the activation of innate immune responses. Emphasis is placed on differential immunostimulating activities of LTAs of various Gram-positive bacteria at the molecular level.

A single bout of dynamic exercise by healthy adults enhances the generation of monocyte-derived-dendritic cells

The ex vivo generation of monocyte-derived-dendritic cells (mo-DCs) has facilitated the use of DCs in immunotherapy research. However, low blood monocyte numbers frequently limit the manufacture of sufficient numbers of mo-DCs for subsequent experimental and clinical procedures. Because exercise mobilizes monocytes to the blood, we tested if acute dynamic exercise by healthy adults would augment the generation of mo-DCs without compromising their differentiation or function. We compared mo-DC generation from before- and after-exercise blood over 8-days of culture. Function was assessed by FITC-dextran uptake and the stimulation of autologous cytomegalovirus (pp65)-specific-T-cells. Supporting the hypothesis, we found a near fourfold increase in number of mo-DCs generated after-exercise. Furthermore, relative FITC-dextran uptake, differentiation rate, and stimulation of pp65-specific-T-cells did not differ between before- and after-exercise mo-DCs. We conclude that exercise enhances the ex vivo generation of mo-DCs without compromising their function, and so may overcome some limitations associated with manufacturing these cells for immunotherapy.

Polyacrylate-based delivery system for self-adjuvanting anticancer peptide vaccine

Vaccination can provide a safe alternative to chemotherapy by using the body's natural defense mechanisms to create a potent immune response against tumor cells. Peptide-based therapeutic vaccines against human papillomavirus (HPV)-related cancers are usually designed to elicit cytotoxic T cell responses by targeting the HPV-16 E7 oncoprotein. However, peptides alone lack immunogenicity, and an additional adjuvant or external delivery system is required. In this study, we developed new polymer-peptide conjugates to create an efficient self-adjuvanting system for peptide-based therapeutic vaccines. These conjugates reduced tumor growth and eradicated E7-positive TC-1 tumors in mice after a "single shot" immunization, without the help from an external adjuvant. The new conjugates had a significantly higher anticancer efficacy than the antigen formulated with a commercial adjuvant. Furthermore, the polymer-peptide conjugates were promptly taken up by antigen presenting cells, including dendritic cells and macrophages, and efficiently activated CD4(+) T-helper cells and CD8(+) cytotoxic T lymphocyte cells.

Dendritic cells during Staphylococcus aureus infection: subsets and roles

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that play a crucial role in both innate and adaptive immune responses. DCs orient the immune responses by modulating the balance between protective immunity to pathogens and tolerance to self-antigens. Staphylococcus aureus (S. aureus) is a common member of human skin microbiota and can cause severe infections with significant morbidity and mortality. Protective immunity to pathogens by DCs is required for clearance of S. aureus. DCs sense the presence of the staphylococcal components using pattern recognition receptors (PRRs) and then orchestrate immune systems to resolve infections. This review summarizes the possible roles of DCs, in particular their Toll-like receptors (TLRs) involved in S. aureus infection and strategies by which the pathogen affects activation and function of DCs.

Dasatinib enhances migration of monocyte-derived dendritic cells by reducing phosphorylation of inhibitory immune receptors Siglec-9 and Siglec-3

The SRC family of kinases (SFKs) is crucial to malignant growth, but also important for signaling in immune cells such as dendritic cells (DCs). These specialized antigen-presenting cells are essential for inducing and boosting specific T-cell responses against pathogens and malignancies. Targeted therapy with SFK inhibitors holds great promise as a direct anti-cancer treatment, but potentially also as an indirect treatment via immunomodulation. Here, we investigated whether the BCR-ABL/SRC inhibitor dasatinib would modulate the major effector functions of DCs, especially their migration, a prerequisite to interaction with lymphocytes in secondary lymphoid organs. We report for the first time that dasatinib more than doubled the number of mature human monocyte-derived DCs (moDCs) migrating toward a CCL19 gradient despite unchanged CCR7 expression when used for pretreatment. These effects were caused by dephosphorylation of SFKs, as confirmed by the specific SFK inhibitor SRC inhibitor 1, leading to dephosphorylation of the inhibitory immunoreceptors Siglec-9 and Siglec-3. The specific blocking of the latter also enhanced migration and underlined the importance of these SFK-dependent receptor systems for migration of moDCs. Dasatinib hampered the secretion of interleukin-12 by moDCs at clinically relevant concentrations. In contrast, endocytosis or boosting of cytomegalovirus-specific CD8(+) T-cell responses remained unaltered when applying dasatinib-pretreated moDCs, in line with minor effects on the expression of co-stimulatory molecules essential for DC-T cell interaction. The induction of enhanced migration of moDCs may potentially be useful in chemo-immunotherapeutic applications. Thus, the use of dasatinib or blocking Siglec antibodies as adjuvants in this setting to induce stronger immune responses is worthy of further study.

Stimulation of platelet apoptosis by peptidoglycan from Staphylococcus aureus 113

Peptidoglycan (PGN), a component of bacterial cell wall and belonging to "Microbe-Associated Molecular Patterns" (MAMP) triggers host reactions contributing to the pathophysiology of infectious disease. Host cell responses to PGN exposure include apoptosis. Bacterial infections may result in activation of blood platelets and thrombocytopenia. The present study explored, whether HPLC-purified fractions of PGNs from Staphylococcus aureus 113 triggers apoptosis of platelets. To this end platelets were exposed to PGN fractions and annexin-V binding determined to depict cell membrane scrambling, DiOC6 fluorescence to estimate depolarization of mitochondrial potential, Fluo-3AM staining for intracellular Ca(2+) activity ([Ca(2+)](i)) and immunofluorescence to quantify protein abundance of active caspase-3. As a result, a 30 min exposure to monomeric fraction (mPGN) (≥50 ng/ml) was followed by annexin-V binding, paralleled by increase of [Ca(2+)](i), mitochondrial depolarization, caspase-3 activation and integrin α(IIb)β(3) upregulation. The annexin-V binding was significantly blunted by anti-TLR-2 antibodies, in absence of extracellular Ca(2+), and by pancaspase inhibitor zVAD-FMK (1 μM). In conclusion, PGN triggers apoptosis of platelets in activation-dependent manner, characterized by mitochondrial depolarization, caspase-3 activation and cell membrane scrambling.

NOD1 and NOD2 Signaling in Infection and Inflammation

Sensing intracellular pathogens is a process mediated by innate immune cells that is crucial for the induction of inflammatory processes and effective adaptive immune responses against pathogenic microbes. NOD-like receptors (NLRs) comprise a family of intracellular pattern recognition receptors that are important for the recognition of damage and microbial-associated molecular patterns. NOD1 and NOD2 are specialized NLRs that participate in the recognition of a subset of pathogenic microorganisms that are able to invade and multiply intracellularly. Once activated, these molecules trigger intracellular signaling pathways that lead to the activation of transcriptional responses culminating in the expression of a subset of inflammatory genes. In this review, we will focus on the role of NOD1 and NOD2 in the recognition and response to intracellular pathogens, including Gram-positive and Gram-negative bacteria, and on their ability to signal in response to non-peptidoglycan-containing pathogens, such as viruses and protozoan parasites.

TLR8 and NOD signaling synergistically induce the production of IL-1β and IL-23 in monocyte-derived DCs and enhance the expression of the feedback inhibitor SOCS2

Pattern recognition receptors (PRRs) like Toll-like receptors (TLRs) and NOD-like receptors (NLRs) are important sensors of microbial products. Although they are referred to as innate immune receptors, they make essential contributions to adaptive immune responses by activating dendritic cells (DCs). Simultaneous activation of DCs via different classes of PRRs provides a powerful tool for inducing strong immune responses. In the present study we investigate the interplay of the NLRs NOD1 and NOD2 and their crosstalk with TLR signaling in terms of DC-activation. We found strong synergistic effects upon treatment with NOD1 and NOD2 ligands combined with the TLR7/8 agonist R848. Simultaneous stimulation of monocyte-derived DCs resulted in highly increased production of IL-1β, IL-23 and SOCS2, a member of the suppressor of cytokine signaling (SOCS) family. Silencing of SOCS2 resulted in enhanced IL-23 expression, indicating that SOCS2 is involved in the regulation of TLR/NOD-dependent cytokine secretion. Finally, we demonstrate that TLR7/8-, NOD1- and NOD2-activated DCs promote CD4+ T cells to release increased amounts of IL-17. These results demonstrate that cooperative activation of DCs with NOD1 and NOD2 agonists and TLR7/8 ligands results in a synergistic release of pro-inflammatory mediators which promote the activation of IL-17-producing T cells.

Lactobacillus plantarum lipoteichoic acid alleviates TNF-α-induced inflammation in the HT-29 intestinal epithelial cell line

We recently observed that lipoteichoic acid (LTA) isolated from Lactobacillus plantarum inhibited endotoxin-mediated inflammation of the immune cells and septic shock in a mouse model. Here, we examined the inhibitory role of L. plantarum LTA (pLTA) on the inflammatory responses of intestinal epithelial cells (IEC). The human colon cell line, HT-29, increased interleukin (IL)-8 expression in response to recombinant human tumor necrosis factor (TNF)-alpha, but not in response to bacterial ligands and interferon (IFN)-gamma. TNF-α also increased the production of inducible nitric oxide synthase (iNOS), nitric oxide (NO), and intercellular adhesion molecule 1 (ICAM-1) through activation of p38 mitogen-activated protein kinase (MAPK) from HT-29 cells. However, the inflammatory response of HT-29 on TNF-α stimulation was significantly inhibited by pLTA treatment. This pLTA-mediated inhibition accompanied the inhibition of nuclear factor (NF)-kappa B and MAPKs. Our data suggest that pLTA regulates cytokine-mediated immune responses and may be a good candidate for maintaining intestinal homeostasis against excessive inflammation.

Systematic review of membrane components of gram-positive bacteria responsible as pyrogens for inducing human monocyte/macrophage cytokine release

Fifty years after the elucidation of lipopolysaccharides (LPS, endotoxin) as the principal structure of Gram-negative bacteria activating the human immune system, its Gram-positive counterpart is still under debate. Pyrogen tests based on the human monocyte activation have been validated for LPS detection as an alternative to the rabbit test and, increasingly, the limulus amebocyte lysate test. For full replacement, international validations with non-endotoxin pyrogens are in preparation. Following evidence-based medicine approaches, a systematic review of existing evidence as to the structural nature of the Gram-positive pyrogen was undertaken. For the three major constituents suggested, i.e., peptidoglycan, lipoteichoic acids (LTA), and bacterial lipoproteins (LP), the questions to be answered and a search strategy for relevant literature was developed, starting in MedLine. The evaluation was based on the Koch–Dale criteria for a mediator of an effect. A total of 380 articles for peptidoglycan, 391 for LP, and 285 for LTA were retrieved of which 12, 8, and 24, respectively, fulfilled inclusion criteria. The compiled data suggest that for peptidoglycan two Koch–Dale criteria are fulfilled, four for LTA, and two for bacterial LP. In conclusion, based on the best currently available evidence, LTA is the only substance that fulfills all criteria. LTA has been isolated from a large number of bacteria, results in cytokine release patterns inducible also with synthetic LTA. Reduction in bacterial cytokine induction with an inhibitor for LTA was shown. However, this systematic review cannot exclude the possibility that other stimulatory compounds complement or substitute for LTA in being the counterpart to LPS in some Gram-positive bacteria.

Effects of Indomethacin, Nimesulide, and Diclofenac on Human MG-63 Osteosarcoma Cell Line

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most widely prescribed drugs worldwide and serve as treatment of some degenerative inflammatory joint diseases. The aim of the present study was to investigate the influence of different concentrations of three NSAIDs on cell proliferation, differentiation, antigenic profile, and cell cycle in the human MG-63 osteosarcoma cell line, incubated for 24 hr. All NSAIDs had an inhibiting effect on osteoblastic proliferation. Treatments for 24 hr had small but significant effects on the antigenic profile. No treatment altered osteocalcin synthesis. Indomethacin and nimesulide treatments arrested the cell cycle at G0/G1. These results suggest that indomethacin, nimesulide, and diclofenac appear to have no effects on osteocalcin synthesis and a slight effect on the antigenic profile. They may delay bone regeneration due to their inhibiting effect on osteoblast growth. Therefore, these drugs should only be used in situations that do not require rapid bone healing.

Dendritic cells produce inflammatory cytokines in response to bacterial products from Staphylococcus aureus-infected atopic dermatitis lesions

Atopic Dermatitis (AD) patients often acquire secondary skin infections resulting in increased inflammation. The increased inflammation occurs through the activation of multiple cell types including dendritic cells (DC). In this study, we investigated the activity of soluble products present in infected AD lesions by measuring the ability of patients' wash fluids from a quantitative culture of lesions to activate DC. We found that wash fluid derived from AD lesions induced cytokine production by murine bone marrow-derived DC, including IL-1β, IL-6, ΙL-10, and tumor necrosis factor-α. The lipoprotein lipoteichoic acid (LTA) from Staphylococcusaureus was implicated as a potent stimulus in the wash fluids as only wash fluid samples that contained LTA exerted this activity, and exogenous LTA triggered similar DC cytokine activation. Wash fluid- and LTA-stimulated DC cytokine production required MyD88, but not the platelet-activating factor receptor (PAF-R), despite the ability of LTA to function through this receptor in keratinocytes. Thus, our results support a role for DC in the worsening of AD inflammation due to secondary bacteria infections.

Muramyl dipeptide synergizes with Staphylococcus aureus lipoteichoic acid to recruit neutrophils in the mammary gland and to stimulate mammary epithelial cells

Staphylococcus aureus, a major pathogen for the mammary gland of dairy ruminants, elicits the recruitment of neutrophils into milk during mastitis, but the mechanisms are incompletely understood. We investigated the response of the bovine mammary gland to muramyl dipeptide (MDP), an elementary constituent of the bacterial peptidoglycan, alone or in combination with lipoteichoic acid (LTA), another staphylococcal microbial-associated molecular pattern (MAMP). MDP induced a prompt and marked influx of neutrophils in milk, and its combination with LTA elicited a more intense and prolonged influx than the responses to either stimulus alone. The concentrations of several chemoattractants for neutrophils (CXCL1, CXCL2, CXCL3, CXCL8, and C5a) increased in milk after challenge, and the highest increases followed challenge with the combination of MDP and LTA. MDP and LTA were also synergistic in inducing in vitro chemokine production by bovine mammary epithelial cells (bMEpC). Nucleotide-binding oligomerization domain 2 (NOD2), a major sensor of MDP, was expressed (mRNA) in bovine mammary tissue and by bMEpC in culture. The production of interleukin-8 (IL-8) following the stimulation of bMEpC by LTA and MDP was dependent on the activation of NF-κB. LTA-induced IL-8 production did not depend on platelet-activating factor receptor (PAFR), as the PAFR antagonist WEB2086 was without effect. In contrast, bMEpC and mammary tissue are known to express Toll-like receptor 2 (TLR2) and to respond to TLR2 agonists. Although the levels of expression of the inflammatory cytokines tumor necrosis factor alpha (TNF-α) and IL-1β were increased by LTA and MDP at the mRNA level, no protein could be detected in the bMEpC culture supernatant. The level of induction of IL-6 was low at both the mRNA and protein levels. These results indicate that MDP and LTA exert synergistic effects to induce neutrophilic inflammation in the mammary gland. These results also show that bMEpC could contribute to the inflammatory response by recognizing LTA and MDP and secreting chemokines but not proinflammatory cytokines. Overall, this study indicates that the TLR2 and NOD2 pathways could cooperate to trigger an innate immune response to S. aureus mastitis.

Hyperforin is a modulator of inducible nitric oxide synthase and phagocytosis in microglia and macrophages

Upon activation, microglia, the immunocompetent cells in the brain, get highly phagocytic and release pro-inflammatory mediators like nitric oxide (NO). Excessive NO production is pivotal in neurodegenerative disorders, and there is evidence that abnormalities in NO production and inflammatory responses may at least support a range of neuropsychiatric disorders, including depression. Although extracts of St. John's wort (Hypericum perforatum L.) have been used for centuries in traditional medicine, notably for the treatment of depression, there is still considerable lack in scientific knowledge about the impact on microglia. We used N11 and BV2 mouse microglia, as well as RAW 264.7 macrophages to investigate the effects of St. John's wort extract and constituents thereof on NO production Moreover, flow cytometry and fluorescence microscopy were employed to analyze the influence on phagocytosis, transcription factor activation states, and cell motility. We found that extracts of St. John's wort efficiently suppress lipopolysaccharide-induced NO release and identified hyperforin as the responsible compound, being effective at concentrations between 0.25 and 0.75 microM. The reduced NO production was mediated by diminished inducible nitric oxide synthase expression on the mRNA and protein level. In addition, at similar concentrations, hyperforin reduced zymosan phygocytosis to 20-40% and putatively acted by downregulating the CD206 macrophage mannose receptor and modulation of cell motility. We found that the observed effects correlate with a suppression of the activated state of Nf-kappaB and phospho-CREB, while c-JUN, STAT1, and HIF-1alpha activity and cyclooxygenase-2 expression remained unaffected by hyperforin. These results reveal that hyperforin influences pro-inflammatory and immunological responses of microglia that are involved in the progression of neuropathologic disorders.

Taxifolin glycoside inhibits dendritic cell responses stimulated by lipopolysaccharide and lipoteichoic acid

Antigen-presenting dendritic cells may play an important role in the pathogenesis of atopic dermatitis. Taxifolin is demonstrated to have anti-inflammatory effects. The present study was designed to assess the effect of taxifolin glycoside against stimulated responses of dendritic cells isolated from mouse bone marrow and spleen. Dendritic cells exposed to lipopolysaccharide, lipoteichoic acid or interleukin (IL)-1β exhibited increased production of IL-12 p70 and tumour necrosis factor alpha, increased formation of reactive oxygen species (ROS) and nitric oxide (NO), and elevation of intracellular Ca2+ levels. Treatment with taxifolin glycoside inhibited responses stimulated by the microbial products or IL-1β in dendritic cells in a dose-dependent manner. Taxifolin glycoside had a significant inhibitory effect on the production of cytokines, formation of ROS and NO, and change in intracellular Ca2+ levels in dendritic cells of bone marrow and spleen. The results show that taxifolin glycoside seems to inhibit the dendritic cell responses stimulated by microbial products and IL-1β, suggesting that taxifolin glycoside may exert an inhibitory effect against dendritic-cell-mediated immune responses.

Muramyldipeptide augments the actions of lipopolysaccharide in mice by stimulating macrophages to produce pro-IL-1β and by down-regulation of the suppressor of cytokine signaling 1 (SOCS1)

Muramyldipeptide (MDP), the minimum essential structure responsible for the immuno-adjuvant activity of peptidoglycan, is recognized by intracellular nuclear-binding oligomerization domain 2 (NOD2). Muramyldipeptide enhances the activities of lipopolysaccharide (LPS), but the mechanism underlying this effect is unclear. Here, we obtained evidence that intravenously injected MDP augments LPS-induced hypothermia in wild-type mice, but not in mice deficient in interleukin (IL)-1α/β and/or tumor-necrosis factor (TNF)-α. Muramyldipeptide also: (i) increased pro-IL-1β in tissues, but did not increase IL-1β in serum (since caspase-1 was not activated by MDP); (ii) downregulated the expression of suppressor of cytokine signaling 1 (SOCS1; a negative-feedback regulator of LPS-induced signaling); and (iii) augmented the LPS-induced production of TNF-α, IL-12 p40, and interferon (IFN)-γ. Moreover, by performing in vivo and in vitro experiments, we obtained evidence that macrophages were involved in these effects of MDP. These results suggest that two different mechanisms may underlie the augmenting effect of MDP: namely, stimulation of pro-IL-1β production by, and down-regulation of SOCS1 in, macrophages. We consider that this work may help to elucidate the pathogenesis of mixed bacterial infections, including septic shock and multiple organ dysfunction syndrome (MODS).

Lipoprotein lipase and hydrofluoric acid deactivate both bacterial lipoproteins and lipoteichoic acids, but platelet-activating factor-acetylhydrolase degrades only lipoteichoic acids

To identify the Toll-like receptor 2 ligand critically involved in infections with gram-positive bacteria, lipoprotein lipase (LPL) or hydrogen peroxide (H(2)O(2)) is often used to selectively inactivate lipoproteins, and hydrofluoric acid (HF) or platelet-activating factor-acetylhydrolase (PAF-AH) is used to selectively inactivate lipoteichoic acid (LTA). However, the specificities of these chemical reactions are unknown. We investigated the reaction specificities by using two synthetic lipoproteins (Pam(3)CSK(4) and FSL-1) and LTAs from pneumococci and staphylococci. Changes in the structures of the two synthetic proteins and the LTAs were monitored by mass spectrometry, and biological activity changes were evaluated by measuring tumor necrosis factor alpha production by mouse macrophage cells (RAW 264.7) following stimulation. PAF-AH inactivated LTA without reducing the biological activities of Pam(3)CSK(4) and FSL-1. Mass spectroscopy confirmed that PAF-AH monodeacylated pneumococcal LTA but did not alter the structure of either Pam(3)CSK(4) or FSL-1. As expected, HF treatment reduced the biological activity of LTA by more than 80% and degraded LTA. HF treatment not only deacylated Pam(3)CSK(4) and FSL-1 but also reduced the activities of the lipoproteins by more than 60%. Treatment with LPL decreased the biological activities by more than 80%. LPL also removed an acyl chain from the LTA and reduced its activity. Our results indicate that treatment with 1% H(2)O(2) for 6 h at 37 degrees C inactivates Pam(3)CSK(4), FSL-1, and LTA by more than 80%. Although HF, LPL, and H(2)O(2) treatments degrade and inactivate both lipopeptides and LTA, PAF-AH selectively inactivated LTA with no effect on the biological and structural properties of the two lipopeptides. Also, the ability of PAF-AH to reduce the inflammatory activities of cell wall extracts from gram-positive bacteria suggests LTA to be essential in inflammatory responses to gram-positive bacteria.

Differential activation of dendritic cells by Toll-like receptor agonists isolated from the Gram-positive vaccine vector Streptococcus gordonii

The oral commensal bacterium Streptococcus gordonii has been gathering interest as a candidate live mucosal vaccine delivery vector. S. gordonii has been shown to be capable of activating antigen presenting immune cells in a manner which leads to their activation and maturation, yet the mechanism used by S. gordonii to do so is poorly understood. The aim of this work was to investigate the immunostimulatory components of S. gordonii in inducing murine dendritic cell (DC) activation and maturation. Lipoteichoic acid (LTA), lipoprotein (LP), peptidoglycan (PGN), and DNA were isolated from S. gordonii, and used to stimulate murine DC. Cytokine production and DC surface marker upregulation in response to the bacterial components was quantified by enzyme-linked immunosorbent assay and flow cytometry respectively. The results were contrasted against data obtained from DC derived from MyD88, TRIF [TIR(Toll/Interleukin-1 Receptor)-domain-containing adapter-inducing interferon-beta] or toll-like receptor-2 (TLR-2) knockout mice. The four S. gordonii bacterial components were found to differentially induce cytokine production and surface marker upregulation by murine DC. Activation of DC by both whole S. gordonii cells and the four bacterial components was abrogated in the absence of MyD88, but not in the absence of TRIF. LTA, LP and PGN, but not DNA and whole S. gordonii, required TLR-2 to induce a DC response. The results collectively indicate that S. gordonii activates DC predominantly through a MyD88-dependent and TRIF-independent pathway. This activation can be attributed to multiple immunostimulatory components present within S. gordonii bacterial cells.

Critical role of CD11b+ macrophages and VEGF in inflammatory lymphangiogenesis, antigen clearance, and inflammation resolution

Using a bacterial pathogen-induced acute inflammation model in the skin, we defined the roles of local lymphatic vessels and draining lymph nodes (DLNs) in antigen clearance and inflammation resolution. At the peak day of inflammation, robust expansion of lymphatic vessels and profound infiltration of CD11b+/Gr-1+ macrophages into the inflamed skin and DLN were observed. Moreover, lymph flow and inflammatory cell migration from the inflamed skin to DLNs were enhanced. Concomitantly, the expression of lymphangiogenic growth factors such as vascular endothelial growth factor C (VEGF-C), VEGF-D, and VEGF-A were significantly up-regulated in the inflamed skin, DLNs, and particularly in enriched CD11b+ macrophages from the DLNs. Depletion of macrophages, or blockade of VEGF-C/D or VEGF-A, largely attenuated these phenomena, and produced notably delayed antigen clearance and inflammation resolution. Conversely, keratin 14 (K14)-VEGF-C transgenic mice, which have dense and enlarged lymphatic vessels in the skin dermis, exhibited accelerated migration of inflammatory cells from the inflamed skin to the DLNs and faster antigen clearance and inflammation resolution. Taken together, these results indicate that VEGF-C, -D, and -A derived from the CD11b+/Gr-1+ macrophages and local inflamed tissues play a critical role in promoting antigen clearance and inflammation resolution.

Generation in vivo of peptide-specific cytotoxic T cells and presence of regulatory T cells during vaccination with hTERT (class I and II) peptide-pulsed DCs

Background

Optimal techniques for DC generation for immunotherapy in cancer are yet to be established. Study aims were to evaluate: (i) DC activation/maturation milieu (TNF-α +/- IFN-α) and its effects on CD8+ hTERT-specific T cell responses to class I epitopes (p540 or p865), (ii) CD8+ hTERT-specific T cell responses elicited by vaccination with class I alone or both class I and II epitope (p766 and p672)-pulsed DCs, prepared without IFN-α, (iii) association between circulating T regulatory cells (Tregs) and clinical responses.

Methods

Autologous DCs were generated from 10 patients (HLA-0201) with advanced cancer by culturing CD14+ blood monocytes in the presence of GM-CSF and IL-4 supplemented with TNF-α [DCT] or TNF-α and IFN-α [DCTI]. The capacity of the DCs to induce functional CD8+ T cell responses to hTERT HLA-0201 restricted nonapeptides was assessed by MHC tetramer binding and peptide-specific cytotoxicity. Each DC preparation (DCT or DCTI) was pulsed with only one type of hTERT peptide (p540 or p865) and both preparations were injected into separate lymph node draining regions every 2–3 weeks. This vaccination design enabled comparison of efficacy between DCT and DCTI in generating hTERT peptide specific CD8+ T cells and comparison of class I hTERT peptide (p540 or p865)-loaded DCT with or without class II cognate help (p766 and p672) in 6 patients. T regulatory cells were evaluated in 8 patients.

Results

(i) DCTIs and DCTs, pulsed with hTERT peptides, were comparable (p = 0.45, t-test) in inducing peptide-specific CD8+ T cell responses. (ii) Class II cognate help, significantly enhanced (p < 0.05, t-test) peptide-specific CD8+T cell responses, compared with class I pulsed DCs alone. (iii) Clinical responders had significantly lower (p < 0.05, Mann-Whitney U test) T regs, compared with non-responders. 4/16 patients experienced partial but transient clinical responses during vaccination. Vaccination was well tolerated with minimal toxicity.

Conclusion

Addition of IFN-α to ex vivo monocyte-derived DCs, did not significantly enhance peptide-specific T cell responses in vivo, compared with TNF-α alone. Class II cognate help significantly augments peptide-specific T cell responses. Clinically favourable responses were seen in patients with low levels of circulating T regs.

Immunomodulatory effect of resistin in human dendritic cells stimulated with lipoteichoic acid from Staphylococcus aureus

Resistin is an adipokine whose physiologic role in obesity, type II diabetes mellitus, and inflammatory diseases has been a subject of debate because while it is expressed in adipocytes and adipose tissue in mouse, it is expressed in leukocytes, such as macrophages, in human. In the present study, we attempt to define the effect of resistin on human dendritic cells (DCs) derived from CD14(+) monocytes. When DCs were stimulated with lipoteichoic acid (LTA) and treated with various concentrations of resistin, antigen-uptake process and the endocytic capacity of DCs were decreased. It is intriguing that resistin attenuated cytokine production in LTA-primed DCs. Consequently, T cell activity was reduced when lymphocytes were mixed with Staphylococcus aureus-primed autologous DCs treated with resistin compared to S. aureus-primed DCs without resistin. Our results suggest that resistin interferes with the efficacy of immune responses activated by Gram-positive bacterial infection in human DCs.

Armillariella mellea induces maturation of human dendritic cells without induction of cytokine expression

ETHNOPHARMACOLOGICAL RELEVANCE

Armillariella mellea, an edible and medicinal mushroom possessing immuno-modulating potential, has been frequently used for the treatment of infectious diseases or cancers.

AIM OF THE STUDY

In order to elucidate immune-regulatory mechanisms of Armillariella mellea, we investigated the effect of water-soluble components from Armillariella mellea (AME) on the regulation of human dendritic cell (DC) maturation and activation.

MATERIALS AND METHODS

Immature DCs (iDCs) were prepared by differentiating human peripheral blood CD14-positive cells with GM-CSF and IL-4. Then, iDCs were treated with AME at 2-20 microg/ml for 48 h and subjected to flow cytometry to analyze the expression of DC markers. Dextran-FITC uptake assay and enzyme-linked immunosorbent assay were performed to examine the endocytic capacity of AME-stimulated DC and their production of cytokines, respectively.

RESULTS

iDCs stimulated with AME showed representative features during DC maturation such as up-regulated expression of CD80, CD83, CD86, both MHC class I and II molecules, and CD205, with a simultaneous decrease in the expression of CD206 and the endocytic capacity. Interestingly, AME was not able to induce the production of TNF-alpha, IL-12p40, or IL-10, whereas lipopolysaccharides induced a substantial increase of all of the cytokines.

CONCLUSION

Armillariella mellea induces maturation of human DCs through a unique mechanism without inducing cytokine expression.

Receptor-mediated endocytosis of particles by peripheral dendritic cells

Human peripheral dendritic cells (DCs) are antigen-presenting cells with the ability to internalize antigen and present antigen-derived peptides to T cells. Human DCs express several receptors on the surface for endocytosis and other recognition receptors that bind to microbes or microbial products, which are internalized and processed. Here, we report the use of nanometer-size zeolite particles as a tool to study receptor-mediated endocytosis by the two subsets of immature DCs, myeloid (mDC) and plasmacytoid (pDC) dendritic cells. A major difference in receptor-mediated endocytosis was observed between the two populations of peripheral DCs. The pDC population demonstrated an almost complete lack of receptor-mediated endocytosis of zeolite particles, whereas the mDC population demonstrated a clear receptor-mediated endocytosis. Fc receptors are expressed by both peripheral DC populations and lipoteichoic acid (LTA) and lipopolysaccharide (LPS) are known ligands of the Toll-like receptor (TLR)-2 and TLR4, respectively, both TLRs expressed by human mDCs. An efficient receptor-mediated endocytosis of immunoglobulin G-, LTA-, and LPS-coated zeolite particles was observed by the mDC population and their endocytosing capacity depended strongly on the density of the ligand adsorbed onto the zeolite particles. In conclusion, an efficient receptor-mediated endocytosis was observed from the mDC population, whereas the pDCs demonstrated an almost complete lack of receptor-mediated endocytosis and nanometer-size dealuminated zeolite particles were a useful tool for studying receptor-mediated endocytosis in human peripheral DCs.