Constitutive and inducible expression of interleukin-6 by Langerhans cells and lymph node dendritic cells

Anti-Inflammatory Effects of Extracellular Vesicles from Ecklonia cava on 12-O-Tetradecanoylphorbol-13-Acetate-Induced Skin Inflammation in Mice

Steroids, which are often used to treat the inflammation associated with various skin diseases, have several negative side effects. As Ecklonia cava extract has anti-inflammatory effects in various diseases, we evaluated the efficacy of Ecklonia cava-derived extracellular vesicles (EVEs) in decreasing 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation. We determined the effect of the EVEs on the TLR4/NF-κB/NLRP3 inflammasome in human keratinocytes and mouse ear skin. TPA-treated human keratinocytes showed an increased expression of TLR4 and its ligands HMGB1 and S100A8. TPA also increased the expression of (1) NF-κB; (2) the NLRP3 inflammasome components NLRP3, ASC, and caspase 1; and (3) the pyroptosis-related factors GSDMD-NT, IL-18, and IL-1β. However, the expression of these molecules decreased in the TPA-treated human keratinocytes after EVE treatment. Similar to the in vitro results, TPA increased the expression of these molecules in mouse ear skin, and EVE treatment decreased their expression. The TPA treatment of skin increased edema, redness, neutrophil infiltration, and epidermal thickness, and EVE reduced these symptoms of inflammation. In conclusion, the EVEs decreased TPA-induced skin inflammation, which was associated with a decrease in the TLR4/NF-κB/NLRP3 inflammasome.

Ovol1/2 loss-induced epidermal defects elicit skin immune activation and alter global metabolism

Skin epidermis constitutes the outer permeability barrier that protects the body from dehydration, heat loss, and myriad external assaults. Mechanisms that maintain barrier integrity in constantly challenged adult skin and how epidermal dysregulation shapes the local immune microenvironment and whole-body metabolism remain poorly understood. Here, we demonstrate that inducible and simultaneous ablation of transcription factor-encoding Ovol1 and Ovol2 in adult epidermis results in barrier dysregulation through impacting epithelial-mesenchymal plasticity and inflammatory gene expression. We find that aberrant skin immune activation then ensues, featuring Langerhans cell mobilization and T cell responses, and leading to elevated levels of secreted inflammatory factors in circulation. Finally, we identify failure to gain body weight and accumulate body fat as long-term consequences of epidermal-specific Ovol1/2 loss and show that these global metabolic changes along with the skin barrier/immune defects are partially rescued by immunosuppressant dexamethasone. Collectively, our study reveals key regulators of adult barrier maintenance and suggests a causal connection between epidermal dysregulation and whole-body metabolism that is in part mediated through aberrant immune activation.

Marking vertebrates langerhans cells, from fish to mammals

Langerhans cells (LCs) are specialized dendritic cells (DCs) that play a defense role in recognizing foreign antigens, in tissue where antigenic exposures occur, as in the skin and mucous membranes. LCs are able to continuously move within the tissues thanks to dendritic contraction and distension performing their surveillance and/or phagocytosis role. These cells are characterized by the presence of Birbeck granules in their cytoplasm, involved in endocytosis. LCs have been characterized in several classes of vertebrates, from fish to mammals using different histological and molecular techniques. The aim of the present review is to define the state of art and the need of information about immunohistochemical markers of LCs in different classes of vertebrates. The most used immunohistochemical (IHC) markers are Langerin/CD207, CD1a, S-100 and TLR. These IHC markers are described in relation to their finding in different vertebrate classes with phylogenetical considerations. Among the four markers, Langerin/CD207 and TLR have the widest spectrum of cross reactivity in LCs.

Human dendritic cells transfected with a human papilloma virus-18 construct display decreased mobility and upregulated cytokine production

The marked depletion of dendritic cells (DCs) in skin cancers, as well as preneoplastic and neoplastic cervical epithelium, suggests a central role for DCs in productive human papillomavirus (HPV) infection and cancer promotion. It has been suggested that HPV may facilitate tumor development by reducing DC density, contributing to a decrease in local immune surveillance. In this study, we have examined the response of human DCs transfected with a construct containing the HPV18 genome and their subsequent expression of papilloma virus proteins. Transfected cells expressed the L1 major capsid protein and upregulated E6 and E7 oncoprotein transcripts as detected by RT-PCR. Transfection of DCs also resulted in a significant increase in cytokine production. Finally, we observed that HPV18 transfection decreased the migratory activity of DCs. Our data indicate that HPV transfection of DCs leads to changes in migratory activity and cytokine production, which potentially can suppress or delay immune responses to viral antigens. Additionally, changes in cytokine production by HPV-transformed human fibroblasts and human cervical epithelial cells revealed that the migratory and antigen-presenting functions of DCs may be impaired by the suppressive effects of cytokines produced by HPV-infected epithelial and stromal cells.

Non-animal test methods for predicting skin sensitization potentials

Contact allergies are complex diseases, and it is estimated that 15-20 % of the general population suffers from contact allergy, with increasing prevalence. Evaluation of the sensitization potential of a substance is usually carried out in animal models. Nowadays, there is much interest in reducing and ultimately replacing current animal tests. Furthermore, as of 2013, the EU has posed a ban on animal testing of cosmetic ingredients that includes skin sensitization. Therefore, predictive and robust in vitro tests are urgently needed. In order to establish alternatives to animal testing, the in vitro tests must mimic the very complex interactions between the sensitizing chemical and the different parts of the immune system. This review article summarizes recent efforts to develop in vitro tests for predicting skin sensitizers. Cell-based assays, in chemico methods and, to a lesser extent, in silico methods are presented together with a discussion of their current status. With considerable progress having been achieved during the last years, the rationale today is that data from different non-animal test methods will have to be combined in order to obtain reliable hazard and potency information on potential skin sensitizers.

Topical application of marine briarane-type diterpenes effectively inhibits 12-O-tetradecanoylphorbol-13-acetate-induced inflammation and dermatitis in murine skin

Background

Skin is the largest organ in the body, and is directly exposed to extrinsic assaults. As such, the skin plays a central role in host defense and the cutaneous immune system is able to elicit specific local inflammatory and systemic immune responses against harmful stimuli. 12-O-tetradecanoylphorbol-13-acetate (TPA) can stimulate acute and chronic inflammation and tumor promotion in skin. TPA-induced dermatitis is thus a useful in vivo pharmacological platform for drug discovery. In this study, the inhibitory effect of briarane-type diterpenes (BrDs) from marine coral Briareum excavatum on TPA-induced dermatitis and dendritic cell (DC) function was explored.

Methods

Evans blue dye exudation was used to determine vascular permeability. H&E-stained skin section was used to determine the formation of edema in mouse abdominal skin. We also used immunohistochemistry staining and western blot assays to evaluate the activation of specific inflammation makers and key mediators of signaling pathway in the mouse skin. Furthermore, mouse bone marrow DCs were used to determine the relationship between the chemical structure of BrDs and their regulation of DC function.

Results

BrD1 remarkably suppressed TPA-induced vascular permeability and edema in skin. At the biochemical level, BrD1 inhibited TPA-induced expression of cyclooxygenase-2, inducible nitric oxide synthase and matrix metalloproteinase-9, the key indicators of cutaneous inflammation. This inhibition was apparently mediated by interference with the Akt/NF-κB-mediated signaling network. BrD1 also inhibited TNF-α and IL-6 expression in LPS-stimulated BMDCs. The 8, 17-epoxide of BrDs played a crucial role in the inhibition of IL-6 expression, and replacement of the C-12 hydroxyl group with longer esters in BrDs gradually decreased this inhibitory activity.

Conclusions

Our results suggest that BrDs warrant further investigation as natural immunomodulatory agents for control of inflammatory skin diseases.

Dendritic cells in chronic in vivo ethanol exposure models

Dendritic cells (DCs) play a key role in the initiation of effective immune responses against infectious agents because they are unique in their ability to provide antigen-specific activation of naïve T cells. To do this, they must acquire antigen and migrate to spleen or lymph node to present the antigen to T cells in association with costimulatory molecules and cytokines. Murine models of chronic EtOH exposure have been developed for dissecting the mechanisms by which EtOH alters immune cell functions. This chapter details methods for assessing DC functions in such models. Methods are presented for 1) the identification and isolation of various DC subsets from spleen, epidermis, and lung, 2) measurement of LC migration out of epidermis and DC migration into peripheral and peribronchial lymph nodes, and 3) measurement of alloantigen presentation in vitro as well as transgenic T-cell activation in vitro and in vivo.

Particle-based vaccines for transcutaneous vaccination

Immunization concepts evolve with increasing knowledge of how the immune system works and the development of new vaccination methods. Traditional vaccines are made of live, attenuated, killed or fragmented pathogens. New vaccine strategies can take advantage of particulate compounds--microspheres or nanoparticles--to target antigen-presenting cells better, which must subsequently reach the secondary lymphoid organs, which are the sites of the immune response. The use of the skin as a target organ for vaccine delivery stems from the fact that immature dendritic cells (DCs), which are professional antigen-presenting cells can be found at high density in the epidermis and dermis of human or animal skin. This has led to design various methods of dermal or transcutaneous vaccination. The quality and duration of the humoral and cellular responses to vaccination depend on the appropriate targeting of antigen-presenting cells, of the vaccine dose, route of administration and use of adjuvant. In this review, we will focus on the use of micro- and nano-particles to target the skin antigen-presenting cells and will discuss recent advances in the field of transcutaneous vaccination in animal models and humans.

Phenotypic alterations and cytokine production in THP-1 cells in response to allergens

In the induction phase of allergic contact hypersensitivity, dendritic cells (DCs), including Langerhans cells (LCs) present in epidermis, can trigger an efficient T cell response once they have matured in response to an allergen. Upon maturation, DCs have been shown to induce expression of several surface molecules and the up-regulation of cytokine production. We have previously shown that THP-1 cells, human acute monocytic leukemia cell line, can discriminate between allergens and irritants by measuring expression of surface markers, CD86 and CD54, following chemical exposure. At the same time, we have also reported that augmented expression of HLA and CD80, and production of IL-1beta were up-regulated in THP-1 cells when treated with an allergen, 2,4-dinitrochlorobenzene (DNCB). In the present study, we first evaluated whether THP-1 cells induced the phenotypic changes and the production of cytokines, which are observed in the process of DC maturation, when treated with two known allergens, DNCB and nickel sulfate (NiSO(4)), and one irritant (sodium lauryl sulfate (SLS)). Exposure to DNCB and NiSO(4) induced significant augmentation of CD40 and CD83 expression as well as CD86 and CD54. Also, TNF-alpha and IL-8 secretion were markedly induced by DNCB and NiSO(4) in a dose-dependent manner. In addition, DNCB and NiSO(4) augmented CD1a expression and production of IL-6, respectively. On the contrary, SLS did not change any of these markers. We then evaluated a series of chemicals, including six known allergens (e.g., hydroquinone (HQ)) and two non-allergens (e.g., methyl paraben (MP)), in order to investigate the potential increase of CD86, CD54, CD40, and CD83 expression on THP-1 cells, and production of TNF-alpha and IL-8. Indeed, all tested allergens, except eugenol (EU), caused significant increased changes in at least four of the analyzed six markers, while non-allergens did not induce any changes. EU significantly augmented CD86, CD54 and CD40 expression. These results revealed that the wide variety of responses to allergens in THP-1 cells may emulate allergen-induced maturation processes of DCs. It is suggested that THP-1 cells, which could develop several DC-like properties, are suitable for identifying sensitizing potential of chemicals.

The use of three-dimensional oral mucosa cell cultures to assess the toxicity of soldered and welded wires

The aim of the present study was to determine whether there is a difference in toxicity and loss of viability of three-dimensional (3D) reconstructed human oral epithelium (RHOE) cell cultures induced by point-welded (PW), laser-welded (LW), and silver-soldered (SiS) orthodontic wires. Three types of soldered stainless steel (SS) wires: PW, LW, and SiS were prepared (n = 3) and subjected to multiple end-point analysis (MEA). Six pieces were cut from each wire. Each piece was placed on the triplicate cell cultures (RHOE model based on TR 146 cells). After 24 hours of topical exposure, the cell cultures were cut and stained with haematoxylin/eosin. Toxicity was assessed by evaluating the morphological changes and classifying these as mild, moderate, or severe. The in vitro cell cultures were subjected to a 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) assay in order to quantify viability. Copper wires served as the control to determine severe toxicity and native cell cultures were used as a baseline. Untreated SS wire (0.9 mm) was included for comparison with the welded wires. Histological evaluation with respect to toxicity and measurement of viability in the 3D cell cultures showed no severe toxicity or loss of viability for any of the wires. The morphological ranking of the tested wires from mild to severe toxicity was: SS = PW = LW < SiS. MTT tests revealed the following mean viability values: native cell line (negative control) 98.1 per cent, SS 96.8 per cent, PW 95.5 per cent, LW 95.5 per cent, SiS 85.7 per cent, and copper wires (positive control) 51.2 per cent. Relative comparison between the different welding techniques tested on RHOE revealed, however, that LW and PW wires induced less toxicity/loss of viability compared with SiS wires.

Cellular and cytokine kinetics after epicutaneous allergen challenge (atopy patch testing) with house dust mites in high-IgE beagles

The cellular and cytokine dynamics of reactions triggered by atopy patch testing with house dust mites were studied in six high-IgE beagles. Sites were scored and biopsied at 6, 24, 48, and 96 h, and samples were processed for histopathology, immunohistochemistry, and polymerase chain reaction (PCR). All dogs developed positive reactions at some point in time. Mean clinical scores were significantly higher than baseline at 24, 48, and 96 h. Clinically, one of six dogs had a positive reaction at 6 h; two of six reacted at 24 and 48 h, and five of six at 96 h. Histologically, superficial perivascular mononuclear and granulocytic dermatitis developed (5/6) after 6 h, and progressed in severity at 24 h (6/6). Additionally, at 48 h epidermal spongiosis, hyperplasia and pustules developed (5/6), and were marked at 96 h (6/6). At and beyond 6 h, progressive CD1c-positive epidermal Langerhans cell hyperplasia with cluster formation and dermal dendritic cell infiltration was noted. Cutaneous infiltration of CD3-positive T lymphocytes with epidermal clusters developed over time. mRNA expression for the cytokines gamma-interferon (gamma-IFN), interleukin-6 (IL-6), IL-12p35, IL-13, IL-18, and thymus and activation regulated chemokine (TARC) exhibited significant increases during the challenge compared to baseline, but there was no appreciable alteration in expression for tumour necrosis factor-alpha (TNF-alpha), IL-12p40, IL-10, regulated on activation normal T-cell expressed and secreted (RANTES), IL-5, IL-2, IL-4, and IL-8. No correlation was detected between clinical scores and cytokines. It is concluded that IL-6 plays a role in early reactions followed by an increase of TARC and IL-13, while IL-18 progressively increases in later reactions.

Interleukin-6 promotes human epidermal keratinocyte proliferation and keratin cytoskeleton reorganization in culture

We have studied the effects of interleukin-6 (IL-6) on human epidermal keratinocytes by using serum-free culture conditions that allow the serial transfer, differentiation, and formation of well-organized multilayered epithelia. IL-6 at 2.5 ng/ml or higher concentrations promoted keratinocyte proliferation, with an ED(50) of about 15 ng/ml and a maximum effect at 50 ng/ml. IL-6 was 10-fold less potent than epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) and supported keratinocyte growth for up to eight cumulative cell generations. IL-6-treated keratinocytes formed highly stratified colonies with a narrower proliferative/migratory rim than those keratinocytes stimulated with EGF or TGF-alpha; confluent epithelial sheets treated with IL-6 also underwent an increase in the number of cell layers. We also examined the effect of IL-6 on the keratin cytoskeleton. Immunostaining with anti-K16 monoclonal antibodies showed that the keratin network was aggregated and reorganized around cell nucleus and that this was not attributable to changes in keratin levels. This is the first report concerning the induction of the reorganization of keratin intermediate filaments by IL-6 in human epidermal keratinocytes.

Early up-regulation of Th2 cytokines and late surge of Th1 cytokines in an atopic dermatitis model

We investigated cytokine profiles in interleukin (IL)-4 transgenic (Tg) mice with a skin inflammatory disease resembling human atopic dermatitis. cDNA microarray revealed that the mRNAs encoding IL-1beta, IL-2, IL-3, IL-4, IL-5, IL-6, IL-10, IL-12p40, IL-13, tumour necrosis factor (TNF)-alpha, TNF-beta and interferon (IFN)-gamma were up-regulated in the skin of late lesion Tg mice and to a lesser degree in non-lesion Tg mice when compared to those of non-Tg mice. Real time reverse transcription-polymerase chain reaction (RT-PCR) analyses indicated that the cDNA copy numbers of IL-1beta, IL-4, IL-6, IL-10, TNF-alpha and IFN-gamma from the skin of late, early and non-lesions increased significantly compared to non-Tg mice. IL-2 and IL-12p40 cDNA copy numbers were increased significantly in early, but not late, lesions. Interestingly, IL-1beta, IL-3, IL-4, IL-5, IL-6, IL-10, IL-13, TNF-alpha, and IFN-gamma cDNAs were increased significantly the skin of before-onset and/or non-lesion mice. Flow cytometry analyses demonstrated an increased percentage of keratinocytes producing IL-4 as the disease progressed. The percentage of IL-2, IL-4, IL-10 and IFN-gamma-producing T cells and IL-12-producing antigen-presenting cells in skin-draining lymph nodes and inflammatory skin also increased, particularly in mice with late lesion. These results suggest that disease induction is primarily triggered by Th2 cytokines and that Th1, Th2 and non-Th proinflammatory cytokines are all involved in the disease process.

Cytokine transcript profiling in CD34+-progenitor derived dendritic cells exposed to contact allergens and irritants

We here investigated wether genes encoding the interleukins IL-1beta, IL-6 and IL-8, and the chemokines CCL2, CCL3, CCL3L1 and CCL4 are useful markers for sensitization testing in CD34+-progenitor derived dendritic cells (CD34-DC). CD34-DC from at least three donors were exposed during 0.5 up to 24h to the chemical sensitizers nickel sulphate, oxazolone, 2,4-dinitrochlorobenzene (DNCB) and eugenol, and to the irritants sodium dodecyl sulphate (SDS) and benzalkonium sulphate (BC). mRNA expression was evaluated using real-time RT-PCR. We observed a large inter-individual variation in mRNA expression in CD34-DC exposed to the chemicals. No or limited effects on expression were observed for the irritant BC and the weak sensitizer eugenol. All other chemicals modulated the transcript levels of most cytokines that were investigated. Most of the time, no clear-cut distinctions could be made between the sensitizers and SDS. After 24 h, consistent upregulatory effects of all sensitizing compounds on transcript expression of CCL2, CCL3 and CCL4 were observed, whereas SDS (and BC) had no effect. Our findings suggest that the CCL2, CCL3 and CCL4 genes may be selective end-point markers in the CD34-DC model to discern chemical sensitizers from irritants.

Regulation of T helper cell differentiation in vivo by GP43 from Paracoccidioides brasiliensis provided by different antigen-presenting cells

Paracoccidioidomycosis, endemic in Latin America, is a progressive systemic mycosis caused by Paracoccidioides brasiliensis. The infection can evolve into different clinical forms that are associated with various degrees of suppressed cell-mediated immunity. Assuming that the effector immune response is a consequence of the preferential activation of either Th1 or Th2 subsets, in the present work we evaluated whether the nature of antigen-presenting cells (APCs) can influence the Th1/Th2 balance in vivo. It was observed that the injection of mature dendritic cells (DCs), macrophages and B cells primed the mice and induced a proliferation of T cells in vitro. It was seen that DCs from resistant mice stimulated predominantly interleukin-2 (IL-2) and interferon-gamma (IFN-gamma), whereas macrophages activated IL-10, IL-4 and IFN-gamma-secreting T cells and B cells IL-4 and IL-10 only. Results presented here clearly demonstrate that DC drives the development of cells secreting Th1-derived cytokines, whereas B cells induce the differentiation of a Th2 phenotype in vivo.

CD1a and CD1c cell sorting yields a homogeneous population of immature human Langerhans cells

There is increasing evidence that ex vivo generated Langerhans cells (LCs) cannot fully substitute for their physiological counterparts in normal epidermis when studying the immunobiology of this prototype of a tissue-residing immature dendritic cell (DC). Here, we present CD1-based magnetic-activated cell-sorting (MACS) protocols for the effective isolation of human epidermal LCs. CD1c selection yielded a homogeneous population of pure and viable HLA-DR(+)/CD1a(+) DCs, with the ultrastructural features, surface antigen expression and cytokine profile, characteristic of epidermis-resident immature LCs. The immature state and functional integrity were established by allogeneic mixed lymphocyte reactions showing a weak stimulatory capacity of freshly isolated cells and upregulation upon stimulation. Characterizing the cells in more detail, we could demonstrate for the first time that normal human LCs express CXCR4, CD40 ligand (CD40L), and Fas and Fas ligand (FasL). The observed constitutive transcription of TGF-beta suggests that the viability and immature state of epidermal LCs are maintained not only by the TGF-beta production from the microenvironment, but also in an autocrine or paracrine manner. LPS and IFN-omega stimulated the expression of the inflammatory cytokines TNF-alpha and IL-1beta, and there was secretion of IL-12p70 after CD40 ligation. Remarkably, the CD1-sorted LCs showed no loss of their Birbeck granules and CD1a expression upon culturing and no spontaneous phenotypic and functional maturation into potent antigen-presenting cells (APCs). We conclude that human epidermal LCs obtained by the CD1c cell-sorting protocol are optimal candidates with which to elucidate the properties and capabilities of immature cells and to develop immunotherapeutic vaccines.

Analysis of interleukin-1alpha (IL-1alpha) and interleukin-8 (IL-8) expression and release in in vitro reconstructed human epidermis for the prediction of in vivo skin irritation and/or sensitization

In the present study, reconstructed human epidermis (RHE) was used as an in vitro model to discriminate 1-chloro-2,4-dinitrobenzene (DNCB), nickel sulfate (NiSO(4)), oxazolone (OXA), 2,4-dinitrofluorobenzene (DNFB) and 2,4,6-trinitrobenzenesulfonic acid (TNBS) as skin sensitizers from benzalkonium chloride (BC), benzoic acid (BA) and sodium lauryl sulfate (SLS) as skin irritants. Our criteria were (a) the differential IL-1alpha and IL-8 synthesis and release (b) cytotoxicity assessment by MTT assay. When the RHE are topically treated with the sensitizers, very low levels of extra- and intracellular IL-1alpha are observed although they induce significant cytotoxicity. In contrast, they exhibit a sharp maximum of IL-8 release. In the presence of the tested irritants, we observe the inverse cytokine release profile, although they induce dose-dependent cytotoxicity profiles similar to those observed with the sensitizers. Finally, IL-1alpha mRNA upregulation is observed after topical application of both sensitizers and irritants, but only the latter significantly increase extracellular IL-1alpha. In conclusion, our results suggest that the associated determination of IL-8, with IL-1alpha, and MTT conversion are at least necessary to discriminate and classify, in a single assay, irritant and sensitizing agents and represent a potential in vitro alternative to two classical in vivo assays.

Beyond neurons: evidence that immune and glial cells contribute to pathological pain states

Chronic pain can occur after peripheral nerve injury, infection, or inflammation. Under such neuropathic pain conditions, sensory processing in the affected body region becomes grossly abnormal. Despite decades of research, currently available drugs largely fail to control such pain. This review explores the possibility that the reason for this failure lies in the fact that such drugs were designed to target neurons rather than immune or glial cells. It describes how immune cells are a natural and inextricable part of skin, peripheral nerves, dorsal root ganglia, and spinal cord. It then examines how immune and glial activation may participate in the etiology and symptomatology of diverse pathological pain states in both humans and laboratory animals. Of the variety of substances released by activated immune and glial cells, proinflammatory cytokines (tumor necrosis factor, interleukin-1, interleukin-6) appear to be of special importance in the creation of peripheral nerve and neuronal hyperexcitability. Although this review focuses on immune modulation of pain, the implications are pervasive. Indeed, all nerves and neurons regardless of modality or function are likely affected by immune and glial activation in the ways described for pain.

Dendritic cells phagocytose and are activated by Treponema pallidum

Cell-mediated immune processes play a prominent role in the clinical manifestations of syphilis, a sexually transmitted disease of humans caused by spirochetal bacterium Treponema pallidum. The immune cell type that initiates the early immune response to T. pallidum thus far has not been identified. However, dendritic cells (DCs) are the first immune-competent cells to encounter antigens within skin or mucous membranes, the principal sites of early syphilitic infection. In the present study, immature DC line XS52, derived from murine skin, was utilized to examine T. pallidum-DC interactions and subsequent DC activation (maturation). Electron microscopy revealed that T. pallidum was engulfed by DCs via both coiling and conventional phagocytosis and was delivered to membrane-bound vacuoles. The XS52 DC line expressed surface CD14 and mRNA for Toll-like receptors 2 and 4, molecules comprising important signaling components for immune cell activation by bacterial modulins. Both T. pallidum and a synthetic lipopeptide (corresponding to the 47-kDa major membrane lipoprotein) activated the XS52 DC line, as indicated by the secretion of interleukin-12 (IL-12), IL-1beta, tumor necrosis factor alpha, and IL-6 and elevated surface expression of CD54. The combined data support the contention that DCs stimulated by T. pallidum and/or its proinflammatory membrane lipoproteins are involved in driving the cellular immune processes that typify syphilis.

Dendritic cells, implications on function from studies of the afferent lymph veiled cell

Studies of afferent lymph veiled cells (ALVC) show that the full biological function of dendritic cells in peripheral tissue is not explained by a simple model in which immature dendritic cells at the body surface take up antigen, migrate via the afferent lymph ducts, mature and then effectively present antigens to T-cells in the draining lymph node. Furthermore, it is evident from various investigations that the dendritic cells in afferent lymph draining from the body surfaces are not a homogeneous population of cells. They comprise a mixture of cell phenotypes defined by staining with monoclonal antibodies, and the different sub-populations have distinct biological functions and roles in vivo. The molecular basis for differences between the function of afferent lymph dendritic cell subsets is only now being explored and defined but some progress has been made in understanding the role of co-stimulatory molecules. It should be possible to exploit knowledge of the functions of these cells and aid future vaccination strategies in domesticated animals thereby improving animal health and reducing economic loss, and, as a consequence, improving human health. By deliberately targeting functionally distinct subsets of either precursor or mature dendritic cells in vivo, it should become feasible to achieve an appropriately biased immune response.

Investigation of induced changes in interleukin 1beta mRNA expression by cultured human dendritic cells as an in vitro approach to skin sensitization testing

It has been reported previously that in vitro treatment of human blood derived dendritic cells (DC) with contact allergens provokes the elevated expression of mRNA for interleukin (IL) 1beta, under conditions where similar treatment of cells with the non-sensitizing skin irritant sodium lauryl sulfate (SLS) did not alter IL-1beta mRNA levels (Reutter et al., 1997). The purpose of the present investigation was to evaluate further this phenomenon and to explore the potential utility of this approach for the purpose of skin sensitization testing. Human peripheral blood progenitor cells prepared from healthy adult volunteers were cultured in the presence of IL-4 and granulocyte/macrophage colony stimulating factor. After 5 days of culture, the majority of cells had a Langerhans cell-like phenotype, with characteristic dendritic morphology and cell surface expression of CD83, major histocompatibility complex class II and CD1a determinants. These blood-derived DC were cultured in the presence of the contact allergen 2,4-dinitrofluorobenzene (DNFB), SLS or vehicle alone and mRNA expression for IL-1beta, IL-6 and IL-18 was analysed by semiquantitative reverse transcriptase polymerase chain reaction. Constitutive expression of all three cytokines was observed for DC isolated from all donors examined. Exposure to DNFB resulted in upregulation of IL-1beta mRNA (two- to threefold) in cells derived from three out of eight donors whereas IL-6 and IL-18 were largely unaffected by allergen exposure. In contrast, SLS treatment did not induce IL-1beta mRNA expression in any of the donors investigated. Analysis of cytokine mRNA expression using the protocol described by Reutter et al. (1997), did not increase the sensitivity of measurement of induced cytokine expression. Although selected upregulation of IL-1beta by blood derived DC has been confirmed, a wider range of contact allergens and irritants need to be assessed before this approach could be considered for hazard identification.

Cytokines and chemokines in the initiation and regulation of epidermal Langerhans cell mobilization

Langerhans cells (LC) are members of the wider family of dendritic cells. LC reside in the epidermis where they serve as sentinels of the immune system, their responsibilities being to sample the external environment for changes and challenges and to deliver information (antigen) to responsive T lymphocytes within skin draining lymph nodes. The ability of LC to migrate from the epidermis to regional lymph nodes is therefore of pivotal importance to the induction of cutaneous immune responses. The journey that LC have to make from the skin has a number of requirements. Initially it is necessary that LC disassociate themselves from surrounding keratinocytes and are liberated from other influences that encourage their retention in the epidermis. Subsequently, migrating LC must successfully traverse the basement membrane of the dermal-epidermal junction and make their way, via afferent lymphatics, to draining lymph nodes. Effective entry into lymph nodes is necessary, as is correct positioning of cells within the paracortex. There is increasing evidence that both cytokines and chemokines, and their interaction with appropriate receptors expressed by LC, orchestrate the mobilization and movement of these cells. We here consider the parts played by these molecules, and how collectively they induce and direct LC migration.

Local lymph node assay: use in hazard and risk assessment

The murine local lymph node assay (LLNA) was developed as an alternative method for the identification of chemicals that have the ability to cause skin sensitization and allergic contact dermatitis. The assay now has been evaluated extensively in the context of both national and international inter-laboratory collaborative trials and has been the subject of detailed comparisons with guinea pig test methods and human skin sensitization data. On the basis of these evaluations the LLNA has been endorsed recently by the US Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) as a stand-alone method for skin sensitization testing. The assay offers a number of important benefits compared with conventional guinea pig test methods, among these being provision of an objective and quantitative endpoint. Moreover, the LLNA provides advantages in the context of animal welfare; compared with guinea pig tests, fewer animals are required and these animals are subject to less trauma. It is important now that the validation status of the LLNA is recognized and the method applied widely so that these advantages may be realized. Hazard identification represents only the first step in the risk assessment process. A full toxicological evaluation of skin sensitization activity requires an understanding of relative potency. Guinea pig methods do not lend themselves readily to assessment of potency, and interest recently has focused on the utility of the LLNA for this purpose. Contained within this review article are brief descriptions of the history of the LLNA and the immunobiological basis for the method, together with detailed accounts of the conduct and interpretation of the assay. Procedural modifications to, and alternative endpoints for, the LLNA are considered also. Finally, the current regulatory status of the LLNA is summarized and the application of the method for the purposes of defining relative potency and developing risk assessments is reviewed.

Multiple sclerosis is associated with high levels of circulating dendritic cells secreting pro-inflammatory cytokines

Recent evidence emphasises a pivotal role for dendritic cells (DC) in the control of immunity by priming and tolerising T cells. DC capture and process antigens, express co-stimulatory molecules, migrate to lymphoid organs and secrete cytokines to initiate immune responses. In multiple sclerosis (MS), autoreactive T cells are proposed to play a pathogenic role by secreting pro-inflammatory cytokines, but studies on DC are lacking. To evaluate the involvement of DC in patients with MS, a modified procedure was used to prepare DC from blood of patients with MS and healthy subjects. DC were found to be potent stimulators of T cells in allogeneic and, to a lesser extent, in autologous mixed leukocyte reaction (MLR). Enzyme-linked immunospot (ELISPOT) assays were adopted to determine levels of IFN-gamma, TNF-alpha, IL-6 and IL-10 secreting DC vs. mononuclear cells (MNC). Proportionally more DC than MNC secreted IFN-gamma and IL-10 in both MS and healthy subjects. Patients with MS had higher levels of IFN-gamma, TNF-alpha and IL-6 secreting DC than healthy subjects. The differences for IFN-gamma and TNF-alpha secreting cells were confined to the subgroup of untreated MS patients and not observed in the subgroup examined during ongoing treatment with IFN-beta. Circulating DC secreting pro-inflammatory cytokines may represent another focus for the study of both immuno-pathogenesis and therapeutic interventions in MS.

Defective immune response and severe skin damage following UVB irradiation in interleukin-6-deficient mice

Interleukin-6 (IL-6), a multifunctional cytokine, is induced in the acute-phase reaction following ultraviolet (UV) irradiation of humans and mice. Using IL-6-deficient (IL-6-/-) mice, we investigated the role of IL-6 in immunosuppression and inflammatory responses caused by UVB (280-320 nm) radiation. The IL-6-/- mice had a defective contact hypersensitivity (CHS) in response to the sensitizers 2,4-dinitrofluorobenzene and oxazolone. The injection of recombinant IL-6 (rIL-6) into these mice resulted in a marked recovery of the CHS. Serum IL-6 was significantly elevated by UV irradiation of wild-type B6 J/129Sv (IL-6+/+) mice but was not detectable in IL-6-/- mice. Interestingly, there was no induction of serum interleukin-10 (IL-10) by UV irradiation of IL-6-/- mice, whereas UV exposure caused a significant increase in serum IL-10 levels in IL-6+/+ mice. Injection of rIL-6 into IL-6-/- mice increased IL-10 to levels similar to those of IL-6+/+ mice. Being different from IL-6+/+ mice, no epidermal proliferation was found at 48 hr in the IL-6-/- mice, but delayed cell proliferation was observed at 72 hr after UV exposure. Immunohistochemical analysis demonstrated that the epidermis was capable of synthesizing IL-6 at 72 hr after UV irradiation of IL-6+/+ mice. In addition, the IL-6-positive cells appeared to be Langerhans' cells, which were detected with dendritic cell-reactive S-100 antibody. The present study strongly suggests that IL-6 may play a crucial role in the alteration of cutaneous immune responses following UV exposure, and provides evidence that IL-6 is a potent inducer of IL-10. Furthermore, IL-6 production induced by UV radiation appears to be an important early signal for repair of UV-caused skin damage.

Interactions of noradrenalin and tumour necrosis factor alpha, interleukin 4 and interleukin 6 in the control of lipolysis from adipocytes around lymph nodes

The contributions of inflammatory and immunosuppressive cytokines and noradrenalin to the control of lipolysis in adipocytes surrounding and remote from lymph nodes were investigated in healthy adult guinea-pigs. A few hours after excision from fasting animals, spontaneous lipolysis in adipocytes from around the popliteal and mesenteric lymph nodes and omental "milky spots" was significantly lower than in those from elsewhere in the same depots, and much lower than in perirenal, epididymal or parametrial adipocytes. The perinodal adipocytes were consistently more sensitive to noradrenalin at 10(-8), 10(-7)and 10(-5) M, and their maximum rate of lipolysis was higher. They also responded more strongly to pre-incubation for 24 h with tumour necrosis factor alpha interleukin 6 and interleukin 4 than those elsewhere in the same depots. Tumour necrosis factor alpha and interleukin 6 applied alone stimulated lipolysis, but combined with interleukin 4, they suppressed glycerol release, especially in perinodal adipocytes, thereby creating large within-depot differences. These cytokines had minimal effects on lipolysis in perirenal or gonadal adipocytes. The authors conclude that adipocytes surrounding lymph nodes contribute little to whole-body energy supply during fasting, but are more sensitive than all others to cytokines and to noradrenalin, having higher maximum but lower minimum rates of lipolysis. These properties equip perinodal adipocytes for local interactions with lymphoid tissue.

Langerhans cells and chemical allergy

Epidermal Langerhans cells (LCs) play a pivotal role in the induction of cutaneous immune responses, including those provoked by chemical allergens. The delivery by LCs of allergen to draining lymph nodes requires cell migration from the skin, a process that is dependent upon the availability of epidermal cytokines -particularly TNF-alpha and IL-1beta. Here we consider the ways in which these cytokines interact with LCs to both induce and regulate their mobilization in response to skin sensitization. In addition, the effects of these cytokines on both the selectivity of LC migration from the skin and protection of LCs from cell death are considered. Finally, the possible counter-regulatory activity of other cutaneous cytokines and the influence of LCs on the development of selective T lymphocyte responses are explored.

Interleukin 6 influences germinal center development and antibody production via a contribution of C3 complement component

Mice rendered deficient for interleukin (IL) 6 by gene targeting were evaluated for their response to T cell-dependent antigens. Antigen-specific immunoglobulin (Ig)M levels were unaffected whereas all IgG isotypes showed varying degrees of alteration. Germinal center reactions occurred but remained physically smaller in comparison to those in the wild-type mice. This concurred with the observations that molecules involved in initial signaling events leading to germinal center formation were not altered (e.g., B7.2, CD40 and tumor necrosis factor R1). T cell priming was not impaired nor was a gross imbalance of T helper cell (Th) 1 versus Th2 cytokines observed. However, B7.1 molecules, absent from wild-type counterparts, were detected on germinal center B cells isolated from the deficient mice suggesting a modification of costimulatory signaling. A second alteration involved impaired de novo synthesis of C3 both in serum and germinal center cells from IL-6-deficient mice. Indeed, C3 provided an essential stimulatory signal for wild-type germinal center cells as both monoclonal antibodies that interrupted C3-CD21 interactions and sheep anti-mouse C3 antibodies caused a significant decrease in antigen-specific antibody production. In addition, germinal center cells isolated from C3-deficient mice produced a similar defect in isotype production. Low density cells with dendritic morphology were the local source of IL-6 and not the germinal center lymphocytes. Adding IL-6 in vitro to IL-6-deficient germinal center cells stimulated cell cycle progression and increased levels of antibody production. These findings reveal that the germinal center produces and uses molecules of the innate immune system, evolutionarily pirating them in order to optimally generate high affinity antibody responses.

Spontaneous cytokine gene expression in normal guinea pig blood and tissues

The authors report, for the first time, the cloning, characterization and sequencing of guinea pig cDNAs for interleukin (IL)-2, IL-10, IL-12p40, and transforming growth factor beta (TGF-beta). Partial cDNAs for two additional cytokines, IL-1alpha and TNF-alpha, whose sequences are present in the GenEMBL database, were also cloned. The IL-10 clone is a full-length cDNA, while the remaining clones are partial cDNAs. The guinea pig cDNA sequences have high identity with their mouse and human counterparts. Northern blot analysis revealed that the guinea pig transcripts range in size from 1.0 kb to 2.2 kb. The constitutive expression of cytokines in two strains of guinea pig (C4D, Albany) that differ in susceptibility to infection with Treponema pallidum was examined. Since susceptibility to T. pallidum is also age dependent, both neonates and adults were examined. Spontaneous cytokine expression was examined in peripheral blood, skin, spleen, lymph node, brain, and peritoneal cells. In skin, lymph node, and peripheral blood, very low levels of IL-1alpha, IL-12p40, tumour necrosis factor alpha (TNF-alpha), and TGF-beta and moderate levels of IL-2 and IL-10 were observed. Cytokine gene expression was not observed in spleen and brain. Peritoneal cells expressed only TGF-beta. Age- and strain-associated differences were not observed, except for IL-12p40, which was elevated in guinea pigs resistant to T. pallidum infection (C4D neonates, Albany adults).

Interleukin-6, hepatocyte growth factor, and their receptors in biliary epithelial cells during a type I ductular reaction in mice: interactions between the periductal inflammatory and stromal cells and the biliary epithelium

The interleukin-6 (IL-6)/gp-80 and hepatocyte growth factor (HGF)/met ligand/receptor systems have been shown to stimulate biliary epithelial cell (BEC) DNA synthesis in vitro. The mRNA and protein production of these two in vitro mitogens were mapped in vivo during the first week after bile duct ligation (BDL) when peak BEC DNA synthesis is seen. Changes around the biliary tree were compared with those seen in the peripheral liver using a combination of Northern blotting and a unique biliary tree isolation technique, in which the bile ducts and the surrounding portal stroma and inflammatory cells are separated from the hepatocytes by perfusion digestion. Further localization was performed with in situ hybridization and immunohistochemistry. In the normal liver, there is low-level expression of HGF mRNA by periportal stellate cells, and HGF protein localizes to these cells and to neutrophils; extracellular HGF protein is present in the bile. There is no detectable IL-6 mRNA by Northern analysis or IL-6 protein expression in the normal liver, but both met and IL-6 receptor (IL-6R) mRNA are detectable; met mRNA is expressed strongly in the biliary tree, and met protein is expressed weakly on hepatocytes and strongly on BEC. IL-6R mRNA is weakly expressed in the biliary tree, and IL-6R protein is detectable on hepatocytes, with a periportal-to-perivenular gradient, but not on BEC. During the first 3 days after BDL, HGF mRNA expression is increased in both the biliary tree and in the peripheral liver, and production is localized to stellate cells, periductal neutrophils, and stromal cells, which typically accompany the proliferating ductules. IL-6 mRNA and protein were detected only near the biliary tree after BDL, and not in the peripheral liver, and the production was localized to periductal hematolymphoid cells, which had the morphological appearance of macrophages and/or dendritic cells. There is also a distinct up-regulation of met and gp-80 mRNA and protein in the biliary tree, which is stronger than that seen in the peripheral liver. Met protein expression is increased, and IL-6R(gp-80) protein is induced on the proliferating BEC, consistent with the participation of both the HGF/met and IL-6/gp-80 systems in the early phases of type I ductular reactions. These observations show that periductal hematolymphoid and stromal cells are the source of BEC growth factors, and receptors for these factors are up-regulated on BEC during active ductular proliferation. Complex interactions between the inflammatory, stromal, and BEC results in a dysmorphogenic repair response that eventually leads to cirrhosis.

Adhesive and/or Signaling Functions of CD44 Isoforms in Human Dendritic Cells

The regulation and function of the CD44 family of surface glycoproteins were investigated in human monocyte-derived dendritic cells (DCs). Variant CD44 isoform transcripts encoding exons v3, v6, and v9 are differently regulated during the differentiation of monocytes into DCs. TNF-α treatment, which induces the maturation of DCs, up-regulates the expression of all v3-, v6-, and v9-containing isoforms examined. CD44 molecules are involved in the adhesion of DCs to immobilized hyaluronate (HA), and v3- and v6-containing variants participate in this function, whereas anti-CD44v9 mAbs were unable to inhibit DC adhesion to HA. The consequences of ligand binding to CD44 were examined by culturing DCs on dishes coated with HA or various anti-CD44 mAbs. HA, the anti-pan CD44 mAb J173, and mAbs directed against v6- and v9-containing (but not v3-containing) isoforms provoked DC aggregation, phenotypic and functional maturation, and the secretion of IL-8, TNF-α, IL-1β, and granulocyte-macrophage CSF. In addition, IL-6, IL-10, and IL-12 were released by DCs stimulated with either J173 or HA, although these cytokines were not detected or were found only at low levels in the culture supernatants of DCs treated with anti-CD44v6 or anti-CD44v9 mAbs. Our study points to distinct capacities of the v3-, v6-, and v9-containing isoforms expressed by human DCs to mediate cell adhesion to HA and/or a signal inducing DC maturation and the secretion of cytokines.

Regulation of T helper cell differentiation in vivo by soluble and membrane proteins provided by antigen-presenting cells

The aim of this study was to test whether the nature of the antigen-presenting cell (APC) can influence the Th1/Th2 balance in vivo. Our data show that dendritic cells (DC), pulsed extracorporeally with antigen, induced the development of cells secreting IL-2, IFN-gamma and IL-4 upon antigen rechallenge in vitro. Priming with peritoneal macrophages sensitized cells that produced IL-4 but not IFN-gamma. To identify the factors involved in T helper development, mice were primed with APC with or without treatment with neutralizing antibodies to costimulatory molecules or cytokines. Our results indicate that priming with DC or macrophages is strictly dependent on the CD28-CTLA4/B7 interaction. Of note, CD86 provides the initial signal to induce naive T cells to become IL-4 producers, whereas CD80 is a more neutral differentiation signal. IL-12, released by the DC, appears as a potent and obligatory inducer of differentiation for IFN-gamma-producing cells. IL-6, although produced by both APC populations, is necessary to direct activation of the Th2-type response by macrophages but not by DC.

Haemophilus ducreyi infection causes basal keratinocyte cytotoxicity and elicits a unique cytokine induction pattern in an In vitro human skin model

Haemophilus ducreyi is the etiologic agent of the sexually transmitted genital ulcer disease chancroid. Predominantly a cutaneous pathogen, H. ducreyi is present in chancroid ulcers that are characterized by extensive neutrophil accumulation in intraepidermal lesions accompanied by a mononuclear infiltrate in the dermis. We used an in vitro human skin model composed of foreskin fibroblasts and keratinocytes to examine host skin cell interactions with H. ducreyi 35000. Bacteria replicated and persisted in artificial skin for at least 14 days. We observed H. ducreyi inside suprabasal keratinocytes using transmission electron microscopy. Although no bacteria were seen in the basal keratinocyte region, these cells were disrupted in infected cocultures. H. ducreyi infection stimulated increased secretion of interleukin-6 (IL-6) and IL-8 by skin cells. Conversely, tumor necrosis factor alpha and IL-1alpha levels were not elevated. IL-8 produced in response to H. ducreyi infection may be involved in recruiting polymorphonuclear leukocytes and other inflammatory cells, thereby contributing to the tissue necrosis and ulcer formation characteristic of chancroid.

TNF-alpha, RANTES, and MCP-1 are major chemoattractants of murine Langerhans cells to the regional lymph nodes

We have previously reported that lymph node cells generated chemotactic factors for Langerhans cells (LCs) in the induction phase of contact dermatitis. In order to clarify the chemotactic factors involved in migration to the regional lymph nodes, we investigated the migratory activity of murine LCs toward several cytokines and chemokines in vitro. One-day cultured LC-enriched epidermal cells were added to the upper compartment of a modified Boyden chamber and cytokines were added to the lower compartment. We counted dendritic cells migrated to the lower chamber as LCs under phase contrast microscopy. About 99% of migrated dendritic cells were positively reacted with anti-Ia(d) and NLDC145 antibodies and considered to be LCs. We could detect LC migration more accurately by this direct examination than by counting the migrated cells in the filter membrane of a Boyden chamber. In our system, migration of murine epidermal LCs was stimulated by TNF-alpha, RANTES and MCP-1, but not by GM-CSF, IL-1beta, IL-4, and IL-6. TNF-alpha induced LC migration at concentrations from 4 x 10(3) U/ml to 5 x 10(4) U/ml. RANTES at concentrations from 10 to 100 ng/ml and MCP-1 at a concentration of 100 ng/ml induced LC migration in a dose-dependent manner. These data confirmed that TNF-alpha, RANTES, and MCP-1 induced LC migration from epidermis during contact sensitization.