Bacterial lipopolysaccharide contamination of commercial collagen preparations may mediate dendritic cell maturation in culture

Protein Concentration Affects the Food Allergen γ-Conglutin Uptake and Bacteria-Induced Cytokine Production in Dendritic Cells

γ-Conglutin (γ-C) from lupin seeds has been identified as a potent allergen with cross reactivity to peanuts. Here, we investigated how γ-C affected the response in bone marrow-derived dendritic cells (DCs) to bacterial stimuli. γ-C enhanced L. acidophilus NCFM (LaNCFM)-induced IL-12, IL-10, and IL-23 dose-dependently. In contrast, together with E. coli Nissle or LPS, γ-C reduced the production of IL-12 but not of IL-23 and IL-10. Enzyme-hydrolyzed γ-C also enhanced LaNCFM-induced IL-12 and IL-23 production. All preparations induced ROS production in the DCs. The mannose receptor ligands mannan and dextran and the clathrin inhibitor monodansylcadaverine partly inhibited the endocytosis of γ-C. Kunitz trypsin inhibitor and the scavenger receptor ligand polyG also enhanced LaNCFM-induced IL-12, indicating the involvement of receptors other than C-type lectin receptors. The endocytosis of labeled γ-C increased dose-dependently by addition of unlabeled γ-C, which coincided with γ-C's tendency to aggregate. Taken together, γ-C aggregation affects endocytosis and affects the cytokine production induced by gram-positive and gram-negative bacteria differently. We suggest that γ-C is taken up by the same mechanism as other food proteins but due to aggregation is present in higher concentration in the DCs. This could influence the resulting T-cell response in a microbial stimuli-dependent way.

Strategies to Obtain Designer Polymers Based on Cyanobacterial Extracellular Polymeric Substances (EPS)

Biopolymers derived from polysaccharides are a sustainable and environmentally friendly alternative to the synthetic counterparts available in the market. Due to their distinctive properties, the cyanobacterial extracellular polymeric substances (EPS), mainly composed of heteropolysaccharides, emerge as a valid alternative to address several biotechnological and biomedical challenges. Nevertheless, biotechnological/biomedical applications based on cyanobacterial EPS have only recently started to emerge. For the successful exploitation of cyanobacterial EPS, it is important to strategically design the polymers, either by genetic engineering of the producing strains or by chemical modification of the polymers. This requires a better understanding of the EPS biosynthetic pathways and their relationship with central metabolism, as well as to exploit the available polymer functionalization chemistries. Considering all this, we provide an overview of the characteristics and biological activities of cyanobacterial EPS, discuss the challenges and opportunities to improve the amount and/or characteristics of the polymers, and report the most relevant advances on the use of cyanobacterial EPS as scaffolds, coatings, and vehicles for drug delivery.

Endotoxins-the invisible companion in biomaterials research

Metal implants and polymeric devices for the application in the clinical treatment of orthopedic tissue injuries are increasingly coated with bioactive biomaterials derived from natural substances to induce desirable biological effects. Many metals and polymers used in biomaterials research show high affinity for endotoxins, which are abundant in the environment. Endotoxin contamination is indicated in the pathology of periodontitis and aseptic implant loosening, but may also affect the evaluation of a biomaterial's bioactivity by inducing strong inflammatory reactions. In this review, we discuss the high affinity of three commonly used implant biomaterials for endotoxins and how the contamination can affect the outcome of the orthopedic fixation. The chemical nature of bacterial endotoxins and some of the clinical health implications are described, as this knowledge is critically important to tackle the issues associated with the measurement and removal of endotoxins from medical devices. Commonly used methods for endotoxin testing and removal from natural substances are examined and the lack of standard guidelines for the in vitro evaluation of biomaterials is discussed.

Collagen I enhances functional activities of human monocyte-derived dendritic cells via discoidin domain receptor 2

We evaluated the involvement of collagen and their discoidin domain receptors (DDRs), DDR1 and DDR2, on the activation of human monocyte-derived dendritic cells (hDCs). DDR2 was markedly expressed on mature hDCs in comparison to immature ones. Collagen I enhanced the release of IL-12p40, TNF-α and IFN-γ by hDCs. Additionally, hDCs exhibited enhanced expression of costimulatory molecules, and potent functional activities which, in turn, has therapeutic value. Interestingly, DDR2 depletion showed decrease in capacity of hDCs to stimulate T cells proliferation, whereas DDR1 silencing had no significant affect. These data demonstrate that DDR2 enhances hDCs activation and contributes to their functional activities. In addition, application of collagen I treated dendritic cells (DCs) vaccine reduced tumor burden giving longer survival in melanoma mice. Our study suggests that collagen I may enhance functional activities of DCs in immune response.

Persistent activation of dendritic cells after resolution of allergic airway inflammation breaks tolerance to inhaled allergens in mice

RATIONALE

Polysensitization of patients who are allergic is a common feature. The underlying immunologic mechanism is not clear. The maturation status of dendritic cells (DCs) is considered to be important for priming naive T cells in the draining lymph nodes. We hypothesized that chronic airway inflammation can induce an enhanced maturation of airway DCs and facilitate subsequent priming to neoallergens.

OBJECTIVES

To investigate whether chronic airway inflammation could induce an altered activation of airway DCs in mice and whether this influences the development of allergic sensitization.

METHODS

Balb/c mice were repeatedly challenged with DCs to induce a chronic airway inflammation. We evaluated (1) the induction of the main characteristic features of human asthma including persistent remodeling, (2) the maturation status of airway DCs 1 month after inflammation resolved, (3) whether this influences tolerance to inhaled neoallergen, and (4) what type of T helper response would be induced by DCs.

MEASUREMENTS AND MAIN RESULTS

Airway DCs displayed a mature phenotype after complete resolution of airway eosinophilia. Inhalation of a neoallergen without any adjuvant was able to induce airway inflammation in postinflammation lungs but not in control lungs. One month after inflammation, airway DCs were able to induce Th2 polarization in naive T cells consistent with the up-regulation of the Th2 skewing molecules Ym1/2 and OX-40L compared with DCs of control airways.

CONCLUSIONS

This study provides evidence that sustained maturation of DCs after resolution of Th2-mediated inflammation can contribute to polysensitization.

CD25 as an immune regulatory molecule expressed on myeloid dendritic cells

CD25 (alpha-chain of IL-2 receptor) on dendritic cells (DC) has been previously regarded as an activation marker. DC that concomitantly express surface CD25 and co-stimulatory molecules were considered to be fully mature. While both murine and human DC can express CD25, they do not express the beta-chain of the IL-2 receptor, which is indispensable for the execution of IL-2 signaling. The biological function of CD25 during the DC maturation therefore still remains undefined. In this review we focus on recent findings, describing CD25 expression and secretion by human myeloid regulatory DC. These DC co-express CD25 and the immunoregulatory enzyme indoleamine 2,3-dioxygenase (IDO) and inhibit T-cell function. CD25, expressed and secreted by such DC may capture IL-2 and thereby suppress T-cell proliferation, by this means providing an accessory mechanism of DC-mediated immune suppression. We also discuss the implication of DC-derived CD25 for human disease in both cancer and chronic infection.

Cytokine induction by pyrogens: comparison of whole blood, mononuclear cells, and TLR-transfectants

Given the shortcomings in the measurement of pyrogenic contamination of pharmaceuticals and/or test substances by means of the rabbit pyrogen test and the Limulus amoebocyte lysate (LAL) test, several in vitro pyrogen tests have been developed based on the measurement of cytokine production by monocytes. In this study we measured cytokine production (IL-6, IL-8, IL-1beta, and TNF) in diluted whole blood (WB), mononuclear cells (MNC), and HEK cells stably transfected with CD14 and Toll-like Receptor-2 (TLR2) or TLR4, after stimulation with both standard pyrogens and contaminated substances. Our study demonstrated that in MNC, IL-6 production was more sensitive to pyrogen stimulation than IL-1beta and TNF production. The sensitivity of WB IL-8 production for pyrogens was comparable with that of MNC IL-6 production, but higher than WB IL-6 production. MNC IL-8 production as readout for pyrogenic stimulation was not useful due to high background IL-8 production. Surprisingly, contaminated culture media potently stimulated WB IL-8 production, but not MNC IL-6 production. Finally, the value of TLR-transfected HEK cells in the detection of pyrogenic contamination as well as the role of IL-10 in interindividual differences in cytokine production, is discussed. To summarize, the results presented herein together with literature data indicate that the measurement of WB IL-8 production may represent an advantageous alternative to the measurement of MNC IL-6 production, for the detection of pyrogenic contamination of pharmaceuticals.

Enhanced T-cell activation and T-cell-dependent IL-2 production by CD83+, CD25high, CD43high human monocyte-derived dendritic cells

Although standardized protocols are widely used for the generation of monocyte-derived immunostimulatory dendritic cells (DC(ims)), the inducibility of Th1 cells by DC(ims) may considerably differ. As a measure for the quality of DC(ims) generated from an individual donor at a certain time point, CD83 is used in combination with HLA-DR and CD86 to assess DC maturation. When phenotypically analyzing DC(ims), we identified a subpopulation ( approximately 60%) of CD83+, CD86+, and HLA-DR+ DC(ims) that co-expressed CD25. DC within a given DC(ims) preparation identified by lower expression of CD83 and by selective expression of CD14, however, did not co-express CD25. In order to establish CD25 as an additional maturation marker of DC(ims), we studied the DC phenotype of these cells as well as the DC-dependent T-cell proliferation and T-cell cytokine production profile after co-incubation with sorted CD25(high) and CD25(low) subpopulations of CD83+, HLA-DR+, CD86+ DC(ims). CD25(high) DC(ims) showed significant up-regulation of the DC activation molecule CD43 and induced increased levels of IL-2 secretion in allogeneic T-cells (170.7+/-86.7pg/mL) as compared to T-cells coincubated with CD25(low) DC(ims) (86.6+/-37.6pg/mL) [p=0.0224]. This was reflected by a significantly lower T-cell stimulatory capacity of CD25(low) DC(ims) (84.0% of CD25(high) DC(ims), 1:10 ratio; p=0.014) whereas the T-cell stimulatory capacity of CD25(low) DC(ims) was much higher when compared to IL-10 induced regulatory DC (55.3% of CD25(high) DC(ims); 1:10 ratio). With regard to cancer vaccination protocols, we propose to use CD25 and CD43 as additional markers for DC quality control, assessment of maturational status, and positive selection.

Discoidin domain receptor 2 is involved in the activation of bone marrow-derived dendritic cells caused by type I collagen

Discoidin domain receptors (DDRs), DDR1 and DDR2, are non-integrin receptor tyrosine kinases for collagen in many cell types. In this study, we investigated the contributions of DDRs to the activation of mouse bone marrow-derived dendritic cells (DCs) by type I collagen (ColI). Our data showed that transcript and protein of DDR2 were expressed constitutively in immature DCs and upregulated in TNF-alpha-stimulated mature DCs. ColI treatment induced DDR2 phosphorylation and subsequently induced the upregulation of IL-12 production, CD86 expression, and antigen uptake activity by immature DCs. Depletion of DDR2 by specific siRNA attenuated significantly an increase in expression of IL-12 and CD86 in ColI-treated DCs. Additionally, DDR2-ColI interaction upregulated the ability of mature DCs to activate allogeneic T cells. These findings suggest that DDR2 is a critical collagen receptor for DC activation and that DDR2-collagen interaction plays an important role in the functional capacity of DCs regulating immune responses.

Discoidin domain receptor 1: a new class of receptor regulating leukocyte-collagen interaction

Previous studies demonstrated that type I collagen, a major component of the extracellular matrix, could influence the differentiation and function of leukocytes; however, it is not clear whether those effects of collagen were based on its interaction with the classic collagen receptors, alpha1beta1 and alpha2beta1 integrins. We recently detected significant upregulation of discoidin domain receptor 1 (DDR1), a new class of collagen receptor, in human leukocytes, including neutrophils, monocytes, and lymphocytes, in vitro, leading to the hypothesis that the leukocyte-activating effects of collagen might be owing to its interaction with DDR1. In this review, we summarize our recent findings demonstrating that DDR1-collagen interaction facilitates the adhesion, migration, differentiation/maturation, and cytokine/chemokine production of leukocytes. We also describe the intracellular signaling pathways activated by DDR1 interaction with collagen.

Endotoxin: The uninvited guest

In the laboratory environment where biomaterials are synthesized and their biocompatibility assessed, we find that endotoxin contamination is hard to avoid and must not be ignored. In those relatively few cases where endotoxin was known to be present, it has been clearly shown that endotoxin can significantly affect the biological response observed and hence confound any effect of the material. This short review explains what endotoxin is, how to test for it and remove it and what its effect on the biological response to biomaterials is. We advocate routine testing of endotoxin on biomaterials and of reagents used in experimental evaluation of biomaterials and this should be the responsibility of every scientist to ensure the validity of any biomaterial study.

Involvement of discoidin domain receptor 1 in the deterioration of pulmonary sarcoidosis

The prognosis of sarcoidosis with pulmonary infiltrates differs in each case, and several cytokines are reported to contribute to its deterioration. However, the detailed mechanism has not been fully elucidated. Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase activated by collagen and associated with cytokine production from inflammatory cells. We previously reported the functional expression of DDR1 on CD14-positive bronchoalveolar lavage fluid (BALF) cells in vivo. In this study, we hypothesized that DDR1 might be associated with the deterioration of pulmonary sarcoidosis (PS), and investigated 33 patients with sarcoidosis with pulmonary infiltrates, prospectively. We found that patients with deteriorated PS showed significantly higher DDR1 expression in CD14-positive BALF cells predominant with DDR1b isoforms. Activation of DDR1 induced monocyte chemoattractant protein-1 (MCP-1) and matrix metalloproteinase-9 (MMP-9) production in a p38 mitogen-activated protein kinase-dependent manner from CD14-positive BALF cells of patients with deteriorated sarcoidosis. DDR1 activation also induced NF-kappaB nuclear translocation in CD14-positive BALF cells of patients with deteriorated PS. The inhibitor of NF-kappaB inhibited the production of MCP-1 and MMP-9. We propose that DDR1 is associated with the deterioration of pulmonary sarcoidosis.

Endotoxin contamination contributes to the in vitro cytokine-inducing activity of osteopontin preparations

Recently, both native and recombinant preparations of human osteopontin (OPN) have been shown to be able to induce the production of several proinflammatory cytokines in human peripheral blood mononuclear cells (PBMCs) or purified monocytes. In the present study, we found that commercially available native and recombinant OPNs contain variable amounts of endotoxin (LPS) and that removal of endotoxin by polymyxin B-agarose column abrogated their cytokine-inducing activity. These results suggest the questionable evidence of the ability of OPN to induce several cytokines in human PBMCs and draw attention to the exquisite sensitivity of PBMCs/monocytes to endotoxin contaminants.

Activation of Discoidin Domain Receptor 1 on CD14-Positive Bronchoalveolar Lavage Fluid Cells Induces Chemokine Production in Idiopathic Pulmonary Fibrosis

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase activated by collagen. We previously reported the functional expression of DDR1 on human monocyte-derived macrophages in vitro; however, information regarding its role in diseases is limited. Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease, and the lesions contain an abundance of collagen. In this study, we examined DDR1 expression on bronchoalveolar lavage fluid (BALF) cells and investigated its functionality using samples obtained from 28 IPF patients, 13 chronic obstructive pulmonary disease patients, and 14 healthy volunteers. The DDR1 expression level in CD14-positive BALF cells was higher in IPF patients than in chronic obstructive pulmonary disease patients or healthy volunteers. The predominant isoform was DDR1b in the IPF group, while DDR1a was predominant in the other two groups. Using immunohistochemical analysis, we also detected DDR1 expression on infiltrating inflammatory cells in the IPF lesion. In IPF patients, DDR1 activation induced the production of MCP-1, IL-8, MIP-1 alpha, and matrix metalloproteinase-9 (MMP-9) from CD14-positive BALF cells in a p38 MAPK-dependent manner. In contrast, DDR1 activation of CD14-positive BALF cells in the other groups did not induce the production of these chemokines or MMP-9. These chemokines and MMP-9 contribute to the development of IPF and, therefore, we suggest that DDR1 might be associated with the pathogenesis of IPF in the tissue microenvironment.

Analysis of the activation profile of dendritic cells derived from the bone marrow of interleukin-12/interleukin-23-deficient mice

We have previously shown that macrophages from interleukin (IL)-12p40 gene knockout (IL-12/IL-23-/-) mice have a bias towards the M2 activation profile, spontaneously secreting large quantities of transforming growth factor-beta1 (TGF-beta1) and producing low levels of nitric oxide (NO) in response to lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma). To verify whether the activation profile of dendritic cells (DCs) is also influenced by the absence of IL-12/IL-23, bone marrow-derived DCs from IL-12/IL-23-/- and C57BL/6 mice were evaluated. At first we noticed that approximately 50% of the C57BL/6 DCs were dead after LPS-induced maturation, whereas the mortality of IL-12/IL-23-/- DCs was < 10%, a protective effect that diminished when recombinant IL-12 (rIL-12) was added during maturation. Similarly to macrophages, mature IL-12/IL-23-/- DCs (mDCs) produced higher levels of TGF-beta1 and lower levels of NO than C57BL/6 mDCs. NO release was IFN-gamma-dependent, as evidenced by the poor response of IFN-gamma-/- and IL-12/IL-23-/-IFN-gamma-/- mDCs. Nevertheless, IFN-gamma deficiency was not the sole reason for the weak NO response observed in the absence of IL-12/IL-23. The high level of TGF-beta1 secretion by IL-12/IL-23-/- mDCs could explain why exogenous IFN-gamma partially restored the NO production of IFN-gamma-/- mDCs, while IL-12/IL-23-/- IFN-gamma-/- mDCs remained unresponsive. We also showed that CD4+ T-cell proliferation was inhibited by C57BL/6 mDCs, but not by IL-12/IL-23-/- mDCs. IFN-gamma and NO appear to mediate this antiproliferative effect because this effect was not observed in the presence of mDCs from IFN-gamma-/- or IL-12/IL-23-/- IFN-gamma-/- mice and it was attenuated by aminoguanidine. We conclude that the presence of IL-12/IL-23 during LPS-induced maturation influences the activation profile of DCs by a mechanism that is, only in part, IFN-gamma dependent.

Lipopolysaccharide contamination of beta-lactoglobulin affects the immune response against intraperitoneally and orally administered antigen

BACKGROUND

Microbial components in the environment are potent activators of the immune system with capacity to shift the active immune response towards priming of Th1 and/or Th2 cells. Lipopolysaccharide (LPS), a cell-wall component of Gram-negative bacteria, is extensively present in food products like cow's milk. It is not well established, however, how this presence of LPS affects oral tolerance induction.

METHODS

We studied the effect of LPS contamination in a commercial preparation of the cow milk protein beta-lactoglobulin (beta-LG) on antigen-specific immune responses. IgG1/IgG2a production upon intraperitoneal immunization without adjuvant was measured, and oral tolerance induction against beta-LG after administration of either an aqueous solution or water-in-oil (w/o) emulsion of beta-LG was evaluated.

RESULTS

LPS contamination of beta-LG provoked a beta-LG-specific IgG2a response, as well as an enhanced beta-LG-specific IgG1 response upon intraperitoneal immunization. Oral tolerance induction to beta-LG was induced by aqueous solutions of beta-LG with and without LPS administration. Conversely, oral administration of w/o-emulsified beta-LG prevented oral tolerance to beta-LG only when the beta-LG was contaminated with LPS.

CONCLUSIONS

LPS contamination of an aqueous protein solution does not affect oral tolerance induction, whereas LPS present in emulsion prevents oral tolerance induction towards the food protein.

Immunostimulatory potential of beta-lactoglobulin preparations: effects caused by endotoxin contamination

BACKGROUND

The immunomodulating potential residing in cow's milk proteins is currently receiving increasing attention because of growing interest in functional foods and the complex problem of cow's milk allergy. One of the major cow's milk allergens, whey protein beta-lactoglobulin, has previously been shown to mediate cellular activation in both human and murine immune cells.

OBJECTIVE

We examined the response to different beta-lactoglobulin preparations in naive immune cells.

METHODS

Splenocytes and cells from mesenteric lymph nodes derived from BALB/c mice bred and maintained on a milk-free diet were cultured in vitro with different beta-lactoglobulin preparations. Cell proliferation, cytokine production, and increases in intracellular glutathione were used as cellular activation markers. Moreover, the effect of beta-lactoglobulin on cytokine production in murine bone-marrow-derived dendritic cells was examined.

RESULTS

We observed that some commercial beta-lactoglobulin preparations induced pronounced proliferation of both spleen cells and cells from mesenteric lymph nodes; production of TNF-alpha, IL-6, IL-1beta, and IL-10; and an increased level of intracellular glutathione in spleen cell cultures. Furthermore, TNF-alpha, IL-6, IL-1beta, and IL-10 production was induced in murine bone-marrow-derived dendritic cells. Purification of beta-lactoglobulin from raw milk using nondenaturating conditions, however, revealed that the beta-lactoglobulin per se did not possess the immunomodulatory activity. Eventually, the immunostimulatory effect was found to be caused by endotoxin contamination.

CONCLUSION

These results identify endotoxin as the main immunostimulatory component present in some commercial beta-lactoglobulin preparations. Moreover, the present study makes it evident that immunomodulatory effects attributed to beta-lactoglobulin need to be reassessed.

Activation of Discoidin Domain Receptor 1 Facilitates the Maturation of Human Monocyte-Derived Dendritic Cells Through the TNF Receptor Associated Factor 6/TGF-β-Activated Protein Kinase 1 Binding Protein 1β/p38α Mitogen-Activated Protein Kinase Signaling Cascade

Maturation of dendritic cells (DCs) is critical for their ability to stimulate resting naive T cells in primary immune responses. Previous studies demonstrated that collagen, such as type I collagen, could facilitate DC maturation; however, the basis of collagen-mediated DC maturation remains unclear. Discoidin domain receptor 1 (DDR1) is a nonintegrin collagen receptor constitutively expressed in a variety of epithelial cells, including tumor cells, and is inducible in leukocytes. In this study, we evaluated the role of DDR1 in DC maturation using human monocyte-derived DCs. Two DDR1 isoforms, DDR1a and DDR1b, were expressed in both immature and mature DCs. Activation of DDR1 on immature DCs resulted in their partial maturation; however, DDR1 activation markedly amplified TNF-alpha- and LPS-induced phenotypic and functional maturation of DCs through activation of p38 mitogen-activated protein kinase (MAPK), suggesting the involvement of DDR1b in this process. Activation of DDR1b on differentiated DDR1b-overexpressing THP-1 cells or DDR1 on mature DCs induced the formation of TNFR associated factor 6 (TRAF6)/TGF-beta-activated kinase 1 binding protein 1beta/p38alpha MAPK complex and p38alpha autophosphorylation. Transfection of differentiated DDR1b-overexpressing THP-1 cells with dominant negative TRAF6 completely abrogated DDR1b-mediated p38 MAPK phosphorylation, indicating a critical role of TRAF6 in DDR1b-mediated p38 MAPK activation. Taken together, our data suggest that DDR1b-collagen interaction augments the maturation of DCs in a tissue microenvironment through a unique TRAF6/TGF-beta-activated kinase 1 binding protein 1beta/p38alpha MAPK signaling cascade and contributes to the development of adaptive immune responses.

CD40 ligand is essential for generation of specific cytotoxic T cell responses in RNA-pulsed dendritic cell immunotherapy

BACKGROUND

Dendritic cell (DC)-based immunotherapy is a promising form of adjuvant therapy for high-risk tumors. DCs transfected with tumor-associated antigens are capable of stimulating antigen-specific T cells, but cytolytic responses have been disappointing. Activation of DC surface CD40 influences DC cytokine production, particularly that of interleukin (IL)-12, which favors a Th1 (cytotoxic) helper T cell response. This study evaluated the effects of exogenous soluble CD40 ligand (sCD40L) on RNA-transfected DC preparations and their subsequent ability to generate antimelanoma cytolytic T cells.

METHODS

Human monocyte-derived DCs were cultured and transfected with mRNA encoding full-length melanoma-associated antigen, Mart-1, and matured with and without sCD40L. DC IL-12 secretion and the ability to stimulate naïve T cells were assessed by enzyme-linked immunosorbent assay (ELISA), tetramer analysis, Elispot, and (51)Cr release assay.

RESULTS

Mature DCs stimulated with sCD40L secreted higher levels of IL-12 compared with immature DCs and DCs matured without sCD40L (P <.001). DCs treated with sCD40L generated a greater number of antigen-specific T cells (P <.05) by tetramer and Elispot analyses, and yielded specific T cells with significant cytotoxicity against HLA-matched melanoma cell lines.

CONCLUSIONS

CD40L augments DC IL-12 secretion and is essential to potentiate specific antimelanoma cytolytic responses stimulated by the Mart-1 antigen. sCD40L should be considered a crucial adjuvant in DC preparations for RNA-based DC vaccine therapies.

Interaction of discoidin domain receptor 1 isoform b (DDR1b) with collagen activates p38 mitogen-activated protein kinase and promotes differentiation of macrophages

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase activated by collagen. DDR1 is constitutively expressed in a variety of normal and transformed epithelial cells and plays a role in cell migration and differentiation through as yet unidentified signaling pathways. We previously reported inducible expression of DDR1 in human leukocytes and suggested a role for the DDR1a isoform in leukocyte migration through extracellular matrix. Here, we evaluated the contribution of DDR1 in the differentiation of the human monocytic THP-1 cells overexpressing these isoforms and of primary macrophages. Interestingly, collagen activation of DDR1b, but not DDR1a, further promoted phorbol ester-induced differentiation of THP-1 cells as determined by reduced cell proliferation and up-regulated expression of HLA-DR, CD11c, CD14, and CD40. Collagen activation of DDR1b also induced the recruitment and phosphorylation of Shc and subsequent phosphorylation of p38 mitogen-activated protein (MAP) kinase and its substrate ATF2. A p38 MAP kinase inhibitor, SB203580, completely inhibited DDR1b-mediated HLA-DR expression. Activation of DDR1 endogenously expressed on macrophages also up-regulated their HLA-DR expression in a p38 MAP kinase-dependent manner. Thus, DDR1b in response to collagen transduces signals that promote maturation/differentiation of HLA-DR-positive antigen-presenting cells and contributes to the development of adaptive immunity in a tissue microenvironment.

The role of lipopolysaccharide in T-cell responses following DNA vaccination

Bacterial products, including lipopolysaccharide (LPS), are potential impurities in plasmid DNA vaccines. LPS has immunostimulatory properties even at exceedingly low concentrations through activation of Toll-like receptor 4 (TLR4). The potency of T-cell responses after vaccination was tested with DNA containing high LPS or depleted of LPS in TLR4-competent and TLR4-deficient mice. CD8(+) T-cell responses were readily induced in TLR4-deficient mice immunized with DNA depleted of LPS. LPS in DNA vaccines is not required for CD8(+) T-cell responses.

Evaluation of dendritic cell immunogenicity after activation and chemical fixation: a mixed lymphocyte reaction model

Dendritic cells (DC) are central to the control of adaptive immunity. Their ability to activate antigen-specific T cells depends on their maturation state. Many microbial and inflammatory products have stimulated DC maturation. This in vitro study used assays of phenotype and function to examine the potential of bacillus Calmette-Guerin, muramyl dipeptide, and CpG-rich oligodeoxynucleotides to stimulate DC maturation. A chemical fixation method was developed to reliably assess the functional potential of stimulated DC within a mixed lymphocyte reaction model. Using this method, it was shown that bacillus Calmette-Guerin provides a maturation signal as effective as the prototype DC stimulant interleukin-1beta. Furthermore, weaker stimuli such as muramyl dipeptide and CpG-rich oligodeoxynucleotides also are able to induce functional maturation of DC. Using chemical fixation, it was possible to generate stable DC in an immature or a mature state. These observations have importance for our understanding of the regulation of adaptive immunity and for the design of DC-based immunotherapeutic strategies.

Infection of dendritic cells by murine cytomegalovirus induces functional paralysis

Cytomegalovirus (CMV), measles and HIV are the main human pathogens known to induce immunosuppression. Unlike measles and HIV, and despite the availability of a well studied animal model, little is known about the mechanisms that control CMV-induced immunosuppression. We hypothesized that dendritic cells (DCs), which are crucial in generating and maintaining immune responses, represent a target for CMV and that the transient, but profound, immunosuppression that accompanies CMV infection results from viral interference with DC functions. Here we show that DCs were permissive to murine CMV infection. In addition, DC infection prevented delivery of the signals required for T cell activation. Thus, CMV-mediated impairment of DC function may be crucial for virally induced immunosuppression and interleukin 2 is implicated as a key factor.

Antigen presentation of Type II collagen in rats

Collagen-induced arthritis (CIA) is a T-cell dependent disease of rats which follows immunization with bovine type II collagen (bCII). Susceptibility to CIA is linked to the genes encoding the major histocompatibility complex (MHC), suggesting that antigen presentation is important in disease pathogenesis. Antigen-presenting cells (APC) (macrophages, dendritic cells (DC) and B cells) were prepared from WA/KIR/KCL rats and presentation of antigen, in the form of native protein (bCII) or synthetic peptide (bCII:184-198), was assessed in T-cell proliferation assays. Whilst macrophages inhibited proliferative responses to bCII, splenic or thymic low density cells, enriched for DC, presented both bCII and bCII(184-198) peptide. However, bone marrow-derived DC, which stimulated T-cell responses to OVA, failed to present bCII, suggesting differences in processing of these two antigens. B-cell depletion from lymph node cells abrogated the proliferative response to bCII and reconstitution of a T-cell population with B cells restored the proliferative response, indicating that B cells are important for stimulating T-cell responses to bCII. B cells play a critical role in CIA by producing pathogenic anti-bCII antibodies, and we propose that B cells are also important APC which present bCII to CD4+ T cells.

A subset of human monocyte-derived dendritic cells expresses high levels of interleukin-12 in response to combined CD40 ligand and interferon-γ treatment

Dendritic cells (DCs) may arise from multiple lineages and progress through a series of intermediate stages until fully mature, at which time they are capable of optimal antigen presentation and T-cell activation. High cell surface expression of CD83 is presumed to correlate with full maturation of DCs, and a number of agents have been shown to increase CD83 expression on DCs. We hypothesized that interleukin 12 (IL-12) expression would be a more accurate marker of functionally mature DCs capable of activating antigen-specific T cells. We used combinations of signaling through CD40, using CD40 ligand trimer (CD40L), and interferon gamma to demonstrate that CD83 expression is necessary but not sufficient for optimal production of IL-12 by DCs. Phenotypically mature DCs could be induced to produce high levels of IL-12 p70 only when provided 2 simultaneous stimulatory signals. By intracellular cytokine detection, we determined that only a subset of cells that express high levels of CD80 and CD83 generate large amounts of IL-12. DCs matured with both signals are superior to DCs stimulated with the individual agents in activating antigen-specific T cell in vitro. These findings have important implications regarding the identification, characterization, and clinical application of functionally mature DCs.

A subset of human monocyte-derived dendritic cells expresses high levels of interleukin-12 in response to combined CD40 ligand and interferon-γ treatment

Dendritic cells (DCs) may arise from multiple lineages and progress through a series of intermediate stages until fully mature, at which time they are capable of optimal antigen presentation and T-cell activation. High cell surface expression of CD83 is presumed to correlate with full maturation of DCs, and a number of agents have been shown to increase CD83 expression on DCs. We hypothesized that interleukin 12 (IL-12) expression would be a more accurate marker of functionally mature DCs capable of activating antigen-specific T cells. We used combinations of signaling through CD40, using CD40 ligand trimer (CD40L), and interferon gamma to demonstrate that CD83 expression is necessary but not sufficient for optimal production of IL-12 by DCs. Phenotypically mature DCs could be induced to produce high levels of IL-12 p70 only when provided 2 simultaneous stimulatory signals. By intracellular cytokine detection, we determined that only a subset of cells that express high levels of CD80 and CD83 generate large amounts of IL-12. DCs matured with both signals are superior to DCs stimulated with the individual agents in activating antigen-specific T cell in vitro. These findings have important implications regarding the identification, characterization, and clinical application of functionally mature DCs.

Distinct subsets of dendritic cells resembling dermal DCs can be generated in vitro from monocytes, in the presence of different serum supplements

We recently demonstrated that dendritic cells (DCs) can be generated from monocytes in the presence of high concentrations of human serum (HS), provided the extra-cellular pH is maintained at plasma values. Because monocyte-derived DCs (Mo-DCs) can also be generated in the presence of fetal calf serum (FCS) or serum-free medium, we have investigated whether these different culture supplements influence DC generation. With this aim, purified monocytes were cultured with GM-CSF plus IL-4 for 6 days and were further exposed to TNF-alpha for 2 additional days, in the presence of HS, autologous plasma (AP), FCS, or X-VIVO 20, a serum-free medium. Our results show that good yields of functionally mature DCs can reproducibly be obtained in the presence of HS or AP, as assessed by CD83 and CD86 up-regulation, dextran-FITC uptake, allogeneic MLR assays and the induction of an autologous response. Interestingly, the effect of serum on DC generation was probably not only quantitative, but also qualitative, since (i) the majority of HS- or AP-cultured DCs expressed CD83 with very weak levels of CD1a, whereas CD83+ DCs cultured in FCS or X-VIVO were mostly CD1a++; (ii) HS- and AP-cultured DCs were much more granular and heterogeneous than FCS- or X-VIVO-cultured DCs, and (iii) the presence of Birbeck-like granules was preferentially observed in HS- or AP-cultured DCs, as assessed by electron microscopy. That these different cells resemble dermal DCs (DDCs) was further supported by the observations that most of the cells displayed intracytoplasmic FXIIIa in the absence of Lag antigen, and expressed E-cadherin at very low levels. Altogether, our results indicate that starting from the same monocytic population, different subsets of DCs can be generated, depending on the culture conditions. Thus, HS or AP favors the generation of fully mature DCs that resemble activated dermal DCs, whereas FCS, or X-VIVO preferentially leads to the generation of less mature CD1a++ dermal-like DCs.

Dendritic cells genetically engineered to express Fas ligand induce donor-specific hyporesponsiveness and prolong allograft survival

Polarization of an immune response toward tolerance or immunity is dictated by the interactions between T cells and dendritic cells (DC), which in turn are modulated by the expression of distinct cell surface molecules, and the cytokine milieu in which these interactions are taking place. Genetic modification of DC with genes coding for specific immunoregulatory cell surface molecules and cytokines offers the potential of inhibiting immune responses by selectively targeting Ag-specific T cells. In this study, the immunomodulatory effects of transfecting murine bone marrow-derived DC with Fas ligand (FasL) were investigated. In this study, we show that FasL transfection of DC markedly augmented their capacity to induce apoptosis of Fas+ cells. FasL-transfected DC inhibited allogeneic MLR in vitro, and induced hyporesponsiveness to alloantigen in vivo. The induction of hyporesponsiveness was Ag specific and was dependent on the interaction between FasL on DC and Fas on T cells. Finally, we show that transfusion of FasL-DC significantly prolonged the survival of fully MHC-mismatched vascularized cardiac allografts. Our findings suggest that DC transduced with FasL may facilitate the development of Ag-specific unresponsiveness for the prevention of organ rejection. Moreover, they highlight the potential of genetically engineering DC to express other genes that affect immune responses.

Allergen-specific immune deviation from a TH2 to a TH1 response induced by dendritic cells and collagen type I

BACKGROUND

Atopy and IgE production are associated with enhanced allergen-specific T(H)2 responses. Therefore a causative treatment may result from the deviation of this T(H)2-dominated immune response toward a T(H)1 response.

OBJECTIVE

This study was carried out to analyze whether dendritic cells, the most potent antigen-presenting cells that are also known to induce antigen-specific T(H)1 responses, are suitable for therapy of atopic diseases by shifting the allergen-specific T(H)2 response toward a T(H)1 response.

METHODS

Monocyte-derived dendritic cells were used to present allergens in vitro to autologous CD4(+) T cells of allergic persons. Because collagen type I activates dendritic cells and enhances the secretion of IL-12, we performed allergen presentation assays also in the presence of collagen type I.

RESULTS

After stimulation with allergen-pulsed dendritic cells the production of IFN-gamma as well as that of IL-4 and IL-5 by CD4(+) T cells was enhanced. In the presence of collagen type I, however, a significant shift toward a T(H)1 response with increased production of IFN-gamma and a decreased production of IL-5 could be observed. When T cells were stimulated directly with anti-CD3 and anti-CD28 in the absence of antigen-presenting cells, it was demonstrated that collagen type I also exerted a direct effect on T cells, increasing their IFN-gamma production.

CONCLUSION

These data indicate that collagen type I influences dendritic cells as well as T cells in a way that a shift in cytokine production results in a T(H)1 response even in already-sensitized atopic individuals.

CD40-deficient dendritic cells producing interleukin-10, but not interleukin-12, induce T-cell hyporesponsiveness in vitro and prevent acute allograft rejection

The induction of an immune response or tolerance is mediated by corresponding subsets of dendritic cells (DC). However, the property of tolerogenic DC is not clear. Recently, we have characterized a population of CD11c+ splenic DC derived from long-term mixed leucocyte culture (LT-MLC), which are able to proliferate upon stimulation and have a strong primary mixed leucocyte reaction (MLR)-stimulating activity in conventional MLR. In this study, we show that, in contrast to the irradiated ones, non-irradiated LT-MLC-derived DC induce polyclonal antigen-specific T-cell hyporesponsiveness when cocultured with allogeneic splenocytes for 3-11 days. The degree of the hyporesponsiveness increased with the length of coculture. Although these DC expressed major histocompatibility complex class II and B7 costimulatory molecules, which are down-regulated during coculture, they expressed very low or undetectable CD40 before and after coculture, respectively. The CD40-deficient DC spontaneously produce interleukin-10 (IL-10), but not IL-12. The skewed balance between IL-10 and IL-12 is associated with their capability to induce T-cell hyporesponsiveness, because a neutralizing antibody to IL-10, exogenous recombinant IL-12 or lipopolysaccharide (LPS) significantly blocked the hyporesponsiveness. Accordingly, infusion of a small number of non-irradiated LT-MLC-derived DC (5x105) significantly prolonged the survival of a vascularized heterotopic murine heart transplant, whereas irradiated DC accelerated graft rejection. These data suggest that CD40-deficient DC producing IL-10, but not IL-12 can induce T-cell hyporesponsiveness in vitro and in vivo.

Analysis of Adjuvant Function by Direct Visualization of Antigen Presentation In Vivo: Endotoxin Promotes Accumulation of Antigen-Bearing Dendritic Cells in the T Cell Areas of Lymphoid Tissue

T cell activation requires exposure to processed Ag and signaling by cytokines and costimulatory ligands. Adjuvants are thought to enhance immunity primarily through up-regulation of the latter signals. Here, we explore the effect of the bacterial adjuvant, endotoxin, on Ag presentation by B cells and dendritic cells (DC). Using an mAb (C4H3) specific for the hen egg lysozyme (HEL) 46-61 determinant bound to I-Ak, we analyze processed Ag expression and the tissue distribution of presenting cells following systemic administration of soluble HEL to mice. In both LPS-responsive and -hyporesponsive mice given endotoxin-containing HEL, B cells rapidly display surface 46-61/I-Ak complexes. In marked contrast, in LPS-hyporesponsive mice, splenic DC show little gain in C4H3 staining. In LPS-responsive animals, interdigitating DC in T cell areas show no staining above background at early times after HEL administration, but C4H3+ DC rapidly accumulate in the outer periarteriolar lymphoid sheaths (PALS) and in follicular areas. Within a few hours, C4H3+ DC appear in the T cell areas, concomitant with a decline in C4H3+ cells in the outer PALS, suggesting migration between these two sites. Endotoxin enhancement of C4H3 staining is seen for both CD8α− and CD8α+ DC subsets. These data suggest that a major effect of adjuvants is to promote mobilization of Ag-bearing DC to the T areas of lymphoid tissue, and possibly also to enhance Ag processing by these DC. Thus, microbial products promote T cell immunity not only through DC activation for cosignaling, but through improvement in signal 1 delivery.

Maturation of immune responses at the beginning of asthma

The prevalence of childhood asthma appears to be increasing worldwide. A critical element in the development of childhood asthma is maturation of the child's immune system. Most asthmatic children have a history of recurrent lower respiratory tract illnesses associated with airway obstruction during the first year of life. Most infants and young children who will go on to have persistent wheezing and asthma show high IgE production and eosinophilic immune responses at the time of their first viral lower respiratory tract illness. Understanding the genetic and environmental factors that regulate the maturation of the immune response during early life will greatly enhance the development of strategies for the primary and secondary prevention of asthma.