Crucial role for human Toll-like receptor 4 in the development of contact allergy to nickel

The varieties of immunological experience: of pathogens, stress, and dendritic cells

In the 40 years since their discovery, dendritic cells (DCs) have been recognized as central players in immune regulation. DCs sense microbial stimuli through pathogen-recognition receptors (PRRs) and decode, integrate, and present information derived from such stimuli to T cells, thus stimulating immune responses. DCs can also regulate the quality of immune responses. Several functionally specialized subsets of DCs exist, but DCs also display functional plasticity in response to diverse stimuli. In addition to sensing pathogens via PRRs, emerging evidence suggests that DCs can also sense stress signals, such as amino acid starvation, through ancient stress and nutrient sensing pathways, to stimulate adaptive immunity. Here, I discuss these exciting advances in the context of a historic perspective on the discovery of DCs and their role in immune regulation. I conclude with a discussion of emerging areas in DC biology in the systems immunology era and suggest that the impact of DCs on immunity can be usefully contextualized in a hierarchy-of-organization model in which DCs, their receptors and signaling networks, cell-cell interactions, tissue microenvironment, and the host macroenvironment represent different levels of the hierarchy. Immunity or tolerance can then be represented as a complex function of each of these hierarchies.

Eosinophil-dependent skin innervation and itching following contact toxicant exposure in mice

BACKGROUND

Contact toxicant reactions are accompanied by localized skin inflammation and concomitant increases in site-specific itch responses. The role(s) of eosinophils in these reactions is poorly understood. However, previous studies have suggested that localized eosinophil-nerve interactions at sites of inflammation significantly alter tissue innervation.

OBJECTIVE

To define a potential mechanistic link between eosinophils and neurosensory responses in the skin leading to itching.

METHODS

BALB/cJ mice were exposed to different contact toxicants, identifying trimellitic anhydride (TMA) for further study on the basis of inducing a robust eosinophilia accompanied by degranulation. Subsequent studies using TMA were performed with wild type versus eosinophil-deficient PHIL mice, assessing edematous responses and remodeling events such as sensory nerve innervation of the skin and induced pathophysiological responses (ie, itching).

RESULTS

Exposure to TMA, but not dinitrofluorobenzene, resulted in a robust eosinophil skin infiltrate accompanied by significant levels of degranulation. Follow-up studies using TMA with wild type versus eosinophil-deficient PHIL mice showed that the induced edematous responses and histopathology were, in part, causatively linked with the presence of eosinophils. Significantly, these data also demonstrated that eosinophil-mediated events correlated with a significant increase in substance P content of the cutaneous nerves and an accompanying increase in itching, both of which were abolished in the absence of eosinophils.

CONCLUSIONS

Eosinophil-mediated events following TMA contact toxicant reactions increase skin sensory nerve substance P and, in turn, increase itching responses. Thus, eosinophil-nerve interactions provide a potential mechanistic link between eosinophil-mediated events and neurosensory responses following exposure to some contact toxicants.

Neutrophils are required for both the sensitization and elicitation phase of contact hypersensitivity

Weber et al. report that neutrophils are required for both the sensitization and elicitation phase of contact hypersensitivity. Their results identify a novel role for neutrophils in shaping the adaptive immune response.

Allergic contact dermatitis and its animal model, contact hypersensitivity (CHS), are T cell–mediated inflammatory skin diseases induced by contact allergens. Though numerous cellular and molecular players are known, the mechanism of chemical-induced sensitization remains poorly understood. Here, we identify neutrophils as crucial players in the sensitization phase of CHS. Genetic deficiency of neutrophils caused by myeloid-specific deletion of Mcl-1 or antibody-mediated depletion of neutrophils before sensitization abrogated the CHS response. Neutrophil deficiency reduced contact allergen-induced cytokine production, gelatinase release, and reactive oxygen species production in naive mice. Mast cell deficiency inhibited neutrophil accumulation at the site of sensitization. In turn, neutrophils were required for contact allergen-induced release of further neutrophil-attracting chemokines, migration of DCs to the draining lymph nodes, and priming of allergen-specific T cells. Lymph node cells from mice sensitized in the absence of neutrophils failed to transfer sensitization to naive recipients. Furthermore, no CHS response could be induced when neutrophils were depleted before elicitation or when normally sensitized lymph node cells were transferred to neutrophil-deficient recipients, indicating an additional role for neutrophils in the elicitation phase. Collectively, our data identify neutrophils to be critically involved in both the sensitization and elicitation phase of CHS.

Interferon induction by RNA viruses and antagonism by viral pathogens

Interferons are a group of small proteins that play key roles in host antiviral innate immunity. Their induction mainly relies on host pattern recognition receptors (PRR). Host PRR for RNA viruses include Toll-like receptors (TLR) and retinoic acid-inducible gene I (RIG-I) like receptors (RLR). Activation of both TLR and RLR pathways can eventually lead to the secretion of type I IFNs, which can modulate both innate and adaptive immune responses against viral pathogens. Because of the important roles of interferons, viruses have evolved multiple strategies to evade host TLR and RLR mediated signaling. This review focuses on the mechanisms of interferon induction and antagonism of the antiviral strategy by RNA viruses.

p38 Mitogen-Activated Protein Kinase in beryllium-induced dendritic cell activation

Dendritic cells (DC) play a role in the regulation of immune responses to haptens, which in turn impact DC maturation. Whether beryllium (Be) is able to induce DC maturation and if this occurs via the MAPK pathway is not known. Primary monocyte-derived DCs (moDCs) models were generated from Be non-exposed healthy volunteers as a non-sensitized cell model, while PBMCs from BeS (Be sensitized) and CBD (chronic beryllium disease) were used as disease models. The response of these cells to Be was evaluated. The expression of CD40 was increased significantly (p<0.05) on HLA-DP Glu69+ moDCs after 100 μM BeSO₄-stimulation. BeSO₄ induced p38MAPK phosphorylation, while IκB-α was degraded in Be-stimulated moDCs. The p38 MAPK inhibitor SB203580 blocked Be-induced NF-κB activation in moDCs, suggesting that p38MAPK and NF-κB are dependently activated by BeSO₄. Furthermore, in BeS and CBD subjects, SB203580 downregulated Be-stimulated proliferation in a dose-dependent manner, and decreased Be-stimulated TNF-α and IFNγ cytokine production. Taken together, this study suggests that Be-induces non-sensitized Glu69+ DCs maturation, and that p38MAPK signaling is important in the Be-stimulated DCs activation as well as subsequent T cell proliferation and cytokine production in BeS and CBD. In total, the MAPK pathway may serve as a potential therapeutic target for human granulomatous lung diseases.

Immunology and skin in health and disease

The skin is a complex organ that, in addition to providing a strong barrier against external insults, serves as an arena for a wide variety of inflammatory processes, including immunity against infections, tumor immunity, autoimmunity, and allergy. A variety of cells collaborate to mount functional immune responses, which are initiated by resident populations and evolve through the recruitment of additional cell populations to the skin. Inflammatory responses are quite diverse, resulting in a wide range of signs and symptoms that depend on the initiating signals, characteristics of the infiltrating cell populations, and cytokines that are produced (cytokines are secreted protein that allows for cell-cell communication; usually refers to communication between immune-immune cells or stromal-immune cells). In this work, we will review the skin architecture and resident and recruited cell populations and discuss how these populations contribute to inflammation using human diseases and treatments when possible to illustrate their importance within a clinical context.

Interaction of Materials and Biology in Total Joint Replacement - Successes, Challenges and Future Directions

Total joint replacement (TJR) has revolutionized the treatment of end-stage arthritic disorders. This success is due, in large part, to a clear understanding of the important interaction between the artificial implant and the biology of the host. All surgical procedures in which implants are placed in the body evoke an initial inflammatory reaction, which generally subsides over several weeks. Thereafter, a series of homeostatic events occur leading to progressive integration of the implant within bone and the surrounding musculoskeletal tissues. The eventual outcome of the operation is dependent on the characteristics of the implant, the precision of the surgical technique and operative environment, and the biological milieu of the host. If these factors and events are not optimal, adverse events can occur such as the development of chronic inflammation, progressive bone loss due to increased production of degradation products from the implant (periprosthetic osteolysis), implant loosening or infection. These complications can lead to chronic pain and poor function of the joint reconstruction, and may necessitate revision surgery or removal of the prosthesis entirely. Recent advances in engineering, materials science, and the immunological aspects associated with orthopaedic implants have fostered intense research with the hope that joint replacements will last a lifetime, and facilitate pain-free, normal function.

Signaling pathways activated by a protease allergen in basophils

Allergic diseases represent a significant burden in industrialized countries, but why and how the immune system responds to allergens remain largely unknown. Because many clinically significant allergens have proteolytic activity, and many helminths express proteases that are necessary for their life cycles, host mechanisms likely have evolved to detect the proteolytic activity of helminth proteases, which may be incidentally activated by protease allergens. A cysteine protease, papain, is a prototypic protease allergen that can directly activate basophils and mast cells, leading to the production of cytokines, including IL-4, characteristic of the type 2 immune response. The mechanism of papain's immunogenic activity remains unknown. Here we have characterized the cellular response activated by papain in basophils. We find that papain-induced IL-4 production requires calcium flux and activation of PI3K and nuclear factor of activated T cells. Interestingly, papain-induced IL-4 production was dependent on the immunoreceptor tyrosine-based activation motif (ITAM) adaptor protein Fc receptor γ-chain, even though the canonical ITAM signaling was not activated by papain. Collectively, these data characterize the downstream signaling pathway activated by a protease allergen in basophils.

Nickel induces interleukin-1β secretion via the NLRP3-ASC-caspase-1 pathway

Exposure to nickel (Ni(2+)) can trigger allergic reactions in susceptible individuals, which is widely accepted as the major cause of allergic contact hypersensitivity (CHS) worldwide. Although Ni(2+)-induced proinflammatory responses clearly play a pivotal role in CHS, the underlying molecular mechanism has not been fully defined. Here we report that Ni(2+) activates the NLRP3-ASC-caspase-1 immune signaling pathway in antigen-presenting cells, leading to the proteolytic processing and secretion of a proinflammatory cytokine, interleukin-1β (IL-1β). The activation of this signaling axis is independent of phagolysosome-cathepsin B pathway. Instead, Ni(2+) induces mitochondrial reactive oxygen species accumulation and cation fluxes, both of which are required for activating the NLRP3-ASC-caspase-1 pathway. Together, these results identified a novel innate immune signaling pathway (NLRP3-ASC-caspase-1-IL-1β) activated by Ni(2+) and provided a mechanistic basis for optimizing the therapeutic intervention against Ni(2+)-induced allergy in patients.

The biochemical effects of extracellular Zn(2+) and other metal ions are severely affected by their speciation in cell culture media

Investigations of physiological and toxicological effects of metal ions are frequently based on in vitro cell culture systems, in which cells are incubated with these ions in specialized culture media, instead of their physiological environment. This allows for targeted examination on the cellular or even molecular level. However, it disregards one important aspect, the different metal ion speciation under these conditions. This study explores the role of culture conditions in investigations with zinc ions (Zn(2+)). Their concentration is buffered by several orders of magnitude by fetal calf serum. Due to the complexity of serum and its many zinc-binding components, zinc speciation in culture media cannot be completely predicted. Still, the primary effect is due to the main Zn(2+)-binding protein albumin. Buffering reduces the free Zn(2+) concentration, thereby diminishing its biological effects, such as cytotoxicity and the impact on protein phosphorylation. This is not limited to Zn(2+), but is also observed with Ag(+), Cu(2+), Pb(2+), Cd(2+), Hg(2+), and Ni(2+). Usually, the serum content of culture media, and thereby their metal buffering capacity, is only a fraction of that in the physiological cellular environment. This leads to systematic over-estimation of the effects of extracellular metal ions when standard cell culture conditions are used as model systems for assessing potential in vivo effects.

The immunobiology of cobalt: demonstration of a potential aetiology for inflammatory pseudotumours after metal-on-metal replacement of the hip

Abnormal wear of cobalt-containing metal-on-metal joints is associated with inflammatory pseudotumours. Cobalt ions activate human toll-like receptor 4 (TLR4), which normally responds to bacterial lipopolysaccharide (LPS) in sepsis. Activation of TLR4 by LPS increases the expression of chemokines IL-8 and CXCL10, which recruit leukocytes and activated T-cells, respectively. This study was designed to determine whether cobalt induces a similar inflammatory response to LPS by promoting the expression of IL-8 and CXCL10. A human monocytic cell line, derived from acute monocytic leukaemia, was treated with cobalt ions and expression of IL-8 and CXCL10 measured at mRNA and protein levels. Cobalt-treated macrophages showed a 60-fold increase in IL-8 mRNA, and an eightfold increase in production of the mature chemokine (both p < 0.001); expression of the CXCL10 gene and protein was also significantly increased by cobalt (both p < 0.001). Experiments were also performed in the presence of CLI-095, a TLR4-specific antagonist which abrogated the cobalt-mediated increase in IL-8 and CXCL10 expression. These findings suggest that cobalt ions induce inflammation similar to that observed during sepsis by the simultaneous activation of two TLR4-mediated signalling pathways. These pathways result in increased production of IL-8 and CXCL10, and may be implicated in pseudotumour formation following metal-on-metal replacement.

Possible implications of Ni(II) on oral IL-1β-induced inflammatory processes

OBJECTIVES

Nickel (Ni) is one of the main metal elements in orthodontic and prosthetic devices. Different effects of Ni are described ranging from an induction of local inflammation to allergy and cancerous/mutagenic properties. Inflammatory reactions are frequently observed in the oral cavity, but the interrelationship of Ni with those events is still unknown. Therefore, we focused on the impact of Ni on inflammation in vitro.

METHODS

In accordance to previous immersion tests of our lab, human gingival fibroblasts (HGFs) (n=6) were exposed to a pro-inflammatory environment using interleukin-1 beta (IL-1β) and additionally stimulated with different Ni(II) concentrations (400 and 4000ng/ml). At varying time points the expression of pro- and anti-inflammatory as well as matrix degeneration proteins, i.e. MMPs, were analyzed. Furthermore, proliferation assays, wound healing tests and the detection of NF-κB activation were conducted. Unstimulated HGFs served as control.

RESULTS

Our experiments showed that low clinical average Ni(II) levels did not alter pro-inflammatory cytokines significantly compared to control (p>0.05). Instead, a 10-fold higher dose up-regulated these mediators significantly in a time-dependent manner (p<0.01). This was even more pronounced combining both Ni(II) concentrations with an inflammatory condition (p<0.001), MMP expressions were in line with our findings (p<0.001). The mRNA data were supported by proliferation and wound closure assays (p<0.001). However, the combination of both stimuli induced contradictory results. Analyzing NF-κB activation revealed that our results may be in part attributed to NF-κB.

SIGNIFICANCE

Our in vitro study implicated that Ni(II) has various modifying effects on IL-1β-induced inflammatory processes depending on the concentration.

Human annexins A1, A2, and A8 as potential molecular targets for Ni(II) ions

Nickel is harmful for humans, but molecular mechanisms of its toxicity are far from being fully elucidated. One of such mechanisms may be associated with the Ni(II)-dependent peptide bond hydrolysis, which occurs before Ser/Thr in Ser/Thr-Xaa-His sequences. Human annexins A1, A2, and A8, proteins modulating the immune system, contain several such sequences. To test if these proteins are potential molecular targets for nickel toxicity we characterized the binding of Ni(II) ions and hydrolysis of peptides Ac-KALTGHLEE-am (A1-1), Ac-TKYSKHDMN-am (A1-2), and Ac-GVGTRHKAL-am (A1-3), from annexin A1, Ac-KMSTVHEIL-am (A2-1) and Ac-SALSGHLET-am (A2-2), from annexin A2, and Ac-VKSSSHFNP-am (A8-1), from annexin A8, using UV-vis and circular dichroism (CD) spectroscopies, potentiometry, isothermal titration calorimetry, high-performance liquid chromatography (HPLC), and electrospray ionization mass spectrometry (ESI-MS). We found that at physiological conditions (pH 7.4 and 37 °C) peptides A1-2, A1-3, A8-1, and to some extent A2-2 bind Ni(II) ions sufficiently strongly in 4N complexes and are hydrolyzed at sufficiently high rates to justify the notion that these annexins can undergo nickel hydrolysis in vivo. These results are discussed in the context of specific biochemical interactions of respective proteins. Our results also expand the knowledge about Ni(II) binding to histidine peptides by determination of thermodynamic parameters of this process and spectroscopic characterization of 3N complexes. Altogether, our results indicate that human annexins A1, A2, and A8 are potential molecular targets for nickel toxicity and help design appropriate cellular studies.

Chronic allergic contact dermatitis promotes skin cancer

Allergic contact dermatitis (ACD) is well recognized as an adverse event associated with implantable medical devices that contain allergenic materials like nickel; however, other cutaneous consequences of chronic exposure to allergens in implanted devices are not well understood. Here, we present a clinical case of Marjolin's ulcer, an invasive squamous cell carcinoma (SCC) that developed in response to chronic ACD caused by an orthopedic implant. We used a standard murine model of contact hypersensitivity to determine whether chronic ACD promotes skin carcinogenesis. Chronic application of 1-fluoro-2,4-dinitrobenzene (DNFB) to carcinogen-treated skin led to the development of papillomas and aggressive SCC. DNFB-driven chronic ACD was marked by type 2 inflammation, which mediated skin carcinogenesis, as mice unable to mount an inflammatory response were less likely to develop skin tumors. Importantly, we found similar tumor-promoting inflammation surrounding the SCC in our patient. Our findings demonstrate that chronic ACD caused by constant exposure to an allergen can promote tumorigenesis at skin sites with preexisting cancer-initiated cells. Moreover, our results suggest that patients with implantable devices placed in close proximity to the skin should be monitored for ACD and highlight the importance of patch testing prior to the placement of such devices.

Molecular and cellular regulation of toll-like receptor-4 activity induced by lipopolysaccharide ligands

As well as being the primary signaling receptor for bacterial endotoxin or lipopolysaccharide Toll-like receptor-4 function is modulated by numerous factors not only in the context of microbial pathogenesis but also autoimmune and allergic diseases. TLR4 is subject to multiple levels of endogenous control and regulation from biosynthesis and trafficking to signal transduction and degradation. On the other hand regulation of TLR4 activity breaks down during Gram −ve sepsis leading to systemic damage, multi organ failure, and death. In this article, we review how TLR4 traffics from the early secretory pathway, the cis/trans Golgi to the cell surface and endolysosomal compartments. We will present evidence about how these processes influence signaling and can potentially lead to increased sensitivity to ligand-dependent activation as well as ligand-independent constitutive activation that may contribute to pathogenesis in sepsis. We will also discuss how sustained signaling may be coupled to endocytosis and consider the potential molecular mechanisms of immuno-modulators that modify TLR4 signaling function including the cat allergen FelD1 and endogenous protein ligands such as the extracellular matrix protein tenascin C and calprotectin (MRP8/14).

Resin monomers act as adjuvants in Ni-induced allergic dermatitis in vivo

Resin monomers (RMs) are inflammatory agents and are thought to cause allergic contact dermatitis (ACD). However, mouse models are lacking, possibly because of the weak antigenicities of RMs. We previously reported that inflammatory substances can promote the allergic dermatitis (AD) induced by intradermally injected nickel (Ni-AD) in mice. Here, we examined the effects of RMs on Ni-AD. To sensitize mice to Ni, a mixture containing non-toxic concentrations of NiCl2 and an RM [either methyl methacrylate (MMA) or 2-hydroxyethyl methacrylate (HEMA)] was injected intraperitoneally or into ear-pinnae intradermally. Ten days later, a mixture containing various concentrations of NiCl2 and/or an RM was intradermally injected into ear-pinnae, and ear-swelling was measured. In adoptive transfer experiments, spleen cells from sensitized mice were transferred intravenously into non-sensitized recipients, and 24 h later NiCl2 was challenged to ear-pinnae. Whether injected intraperitoneally or intradermally, RM plus NiCl2 mixtures were effective in sensitizing mice to Ni. AD-inducing Ni concentrations were greatly reduced in the presence of MMA or HEMA (at the sensitization step from 10 mM to 5 or 50 µM, respectively, and at the elicitation step from 10 µM to 10 or 100 nM, respectively). These effects of RMs were weaker in IL-1-knockout mice and in macrophage-depleted mice. Cell-transfer experiments in IL-1-knockout mice indicated that both the sensitization and elicitation steps depended on IL-1. Challenge with an RM alone did not induce allergic ear-swelling in mice given the same RM + NiCl2 10 days before the challenge. These results suggest that RMs act as adjuvants, not as antigens, to promote Ni-AD by reducing the AD-inducing concentration of Ni, and that IL-1 and macrophages are critically important for the adjuvant effects. We speculate that what were previously thought of as "RM-ACD" might include ACD caused by antigens other than RMs that have undergone promotion by the adjuvant effects of RMs.

Toll-like receptor 3 increases allergic and irritant contact dermatitis

There is increasing recognition of the role of Toll-like receptor 3 (TLR3) in noninfectious inflammatory diseases, but the function of TLR3 in inflammatory skin diseases is unclear. We investigated the functions of TLR3 in allergic and irritant contact dermatitis (ICD). The contact hypersensitivity (CHS) response was lower in Toll-like receptor 3 knockout (Tlr3 KO) mice, and was greater in TLR3 transgenic (Tg) mice than in wild-type (WT) mice after challenge with 2,4,6-trinitro-1-chlorobenzene. Adoptive transfer of immunized lymph node cells from Tlr3 KO mice induced CHS in WT recipients. In contrast, adoptive transfer of those from WT mice did not fully induce CHS in Tlr3 KO recipients. The ICD reaction following croton oil application was lower in Tlr3 KO mice, and was greater in TLR3 Tg mice than in WT mice. Maturation, migration, and antigen presentation of dendritic cells and proliferation of lymphocytes between WT mice and Tlr3 KO mice were comparable. These results show that TLR3 enhances antigen-independent skin inflammation in the elicitation phase of allergic contact dermatitis and in ICD.

Systemic drugs inducing non-immediate cutaneous adverse reactions and contact sensitizers evoke similar responses in THP-1 cells

Contact sensitizers induce phenotypic and functional changes in dendritic cells (DC) that enhance their antigen-presenting capacity and, ultimately, modulate the T cell response. To evaluate if there is a similar effect of drugs causing T-cell-mediated cutaneous adverse drug reactions (CADR), we studied the in vitro effect of drugs on THP-1 cells, a cell line widely used to evaluate the early molecular and cellular events triggered by contact sensitizers. The effect of allopurinol, oxypurinol, ampicillin, amoxicillin, carbamazepine and sodium valproate, at EC30 concentrations, was evaluated on p38 MAPK activation, by Western Blot, and on the expression of genes coding for DC maturation markers, pro-inflammatory cytokine/chemokines and hemeoxygenase 1 (HMOX1), by real-time RT-PCR. Results were compared with lipopolysaccharide (LPS), a DC maturation stimulus, and the strong contact sensitizer, 1-fluoro-2,4-dinitrobenzene (DNFB). All drugs studied significantly upregulated HMOX1 gene transcription and all, except the anticonvulsants, also upregulated IL8. Allopurinol and oxypurinol showed the most intense effect, in a magnitude similar to DNFB and superior to betalactams. Transcription of CD40, IL12B and CXCL10 genes by drugs was more irregular. Moreover, like DNFB, all drugs activated p38 MAPK, although significantly only for oxypurinol. Like contact sensitizers, drugs that cause non-immediate CADR activate THP-1 cells in vitro, using different signalling pathways and affecting gene transcription with an intensity that may reflect the frequency and severity of the CADR they cause. Direct activation of antigen-presenting DC by systemic drugs may be an important early step in the pathophysiology of non-immediate CADR.

Cobalt and Nickel

Cobalt and nickel play key roles in biological systems as cofactors in a small number of important enzymes. The majority of these are found in microbes. Evidence for direct roles for Ni(II) and Co(II) enzymes in higher organisms is limited, with the exception of the well-known requirement for the cobalt-containing vitamin B12 cofactor and the Ni-dependent urease in plants. Nonetheless, nickel in particular plays a key role in human health because of its essential role in microbes that inhabit various growth niches within the body. These roles can be beneficial, as can be seen with the anaerobic production and consumption of H2 in the digestive tract by bacteria and archaea that results in increased yields of short-chain fatty acids. In other cases, nickel has an established role in the establishment of pathogenic infection (Helicobacter pylori urease and colonization of the stomach). The synthesis of Co- and Ni-containing enzymes requires metal import from the extracellular milieu followed by the targeting of these metals to the appropriate protein and enzymes involved in metallocluster or cofactor biosynthesis. These metals are toxic in excess so their levels must be regulated carefully. This complex pathway of metalloenzyme synthesis and intracellular homeostasis requires proteins that can specifically recognize these metals in a hierarchical manner. This chapter focuses on quantitative and structural details of the cobalt and nickel binding sites in transport, trafficking and regulatory proteins involved in cobalt and nickel metabolism in microbes.

Allergic contact dermatitis in psoriasis patients: typical, delayed, and non-interacting

Psoriasis is characterized by an apoptosis-resistant and metabolic active epidermis, while a hallmark for allergic contact dermatitis (ACD) is T cell-induced keratinocyte apoptosis. Here, we induced ACD reactions in psoriasis patients sensitized to nickel (n = 14) to investigate underlying mechanisms of psoriasis and ACD simultaneously. All patients developed a clinically and histologically typical dermatitis upon nickel challenge even in close proximity to pre-existing psoriasis plaques. However, the ACD reaction was delayed as compared to non-psoriatic patients, with a maximum intensity after 7 days. Whole genome expression analysis revealed alterations in numerous pathways related to metabolism and proliferation in non-involved skin of psoriasis patients as compared to non-psoriatic individuals, indicating that even in clinically non-involved skin of psoriasis patients molecular events opposing contact dermatitis may occur. Immunohistochemical comparison of ACD reactions as well as in vitro secretion analysis of lesional T cells showed a higher Th17 and neutrophilic migration as well as epidermal proliferation in psoriasis, while ACD reactions were dominated by cytotoxic CD8+ T cells and a Th2 signature. Based on these findings, we hypothesized an ACD reaction directly on top of a pre-existing psoriasis plaque might influence the clinical course of psoriasis. We observed a strong clinical inflammation with a mixed psoriasis and eczema phenotype in histology. Surprisingly, the initial psoriasis plaque was unaltered after self-limitation of the ACD reaction. We conclude that sensitized psoriasis patients develop a typical, but delayed ACD reaction which might be relevant for patch test evaluation in clinical practice. Psoriasis and ACD are driven by distinct and independent immune mechanisms.

A critical appraisal of the process of regulatory implementation of novel in vivo and in vitro methods for chemical hazard and risk assessment

Regulatory toxicology urgently needs applicable alternative test systems that reduce animal use, testing time, and cost. European regulation on cosmetic ingredients has already banned animal experimentation for hazard identification, and public awareness drives toward additional restrictions in other regulatory frameworks as well. In addition, scientific progress stimulates a more mechanistic approach of hazard identification. Nevertheless, the implementation of alternative methods is lagging far behind their development. In search for general bottlenecks for the implementation of alternative methods, this manuscript reviews the state of the art as to the development and implementation of 10 diverse test systems in various areas of toxicological hazard assessment. They vary widely in complexity and regulatory acceptance status. The assays are reviewed as to parameters assessed, biological system involved, standardization, interpretation of results, extrapolation to human hazard, position in testing strategies, and current regulatory acceptance status. Given the diversity of alternative methods in many aspects, no common bottlenecks could be identified that hamper implementation of individual alternative assays in general. However, specific issues for the regulatory acceptance and application were identified for each assay. Acceptance of one-in-one replacement of complex in vivo tests by relatively simple in vitro assays is not feasible. Rather, innovative approaches using test batteries are required together with metabolic information and in vitro to in vivo dose extrapolation to convincingly provide the same level of information of current in vivo tests. A mechanistically based alternative approach using the Adverse Outcome Pathway concept could stimulate further (regulatory) acceptance of non-animal tests.

Beneficial autoimmunity at body surfaces - immune surveillance and rapid type 2 immunity regulate tissue homeostasis and cancer

Epithelial cells (ECs) line body surface tissues and provide a physicochemical barrier to the external environment. Frequent microbial and non-microbial challenges such as those imposed by mechanical disruption, injury or exposure to noxious environmental substances including chemicals, carcinogens, ultraviolet-irradiation, or toxins cause activation of ECs with release of cytokines and chemokines as well as alterations in the expression of cell-surface ligands. Such display of epithelial stress is rapidly sensed by tissue-resident immunocytes, which can directly interact with self-moieties on ECs and initiate both local and systemic immune responses. ECs are thus key drivers of immune surveillance at body surface tissues. However, ECs have a propensity to drive type 2 immunity (rather than type 1) upon non-invasive challenge or stress – a type of immunity whose regulation and function still remain enigmatic. Here, we review the induction and possible role of type 2 immunity in epithelial tissues and propose that rapid immune surveillance and type 2 immunity are key regulators of tissue homeostasis and carcinogenesis.

The balance between pro- and anti-inflammatory cytokines is crucial in human allergic contact dermatitis pathogenesis: the role of IL-1 family members

The interleukin (IL)-1 family includes 11 members that are important in inflammatory processes. It includes various agonists and two antagonists, IL-1Ra and IL-36Ra. Our aim was to investigate whether the IL-1 family is involved in allergic contact dermatitis (ACD). The expression of IL-1 family members was evaluated by PCR and immunohistochemistry in the positive patch test reaction site (involved skin) and in the uninvolved skin of ACD patients. We also examined these cytokines in an ex vivo model of ACD. The antagonistic activity of IL-36Ra was evaluated by injecting recombinant IL-36Ra in uninvolved skin biopsies of ACD patients. IL-1Ra and IL-36Ra expression was quantified in mononuclear cells of nickel-sensitized patients challenged in vitro with nickel. IL-33 involvement in ACD was investigated by intra-dermal injection of anti-IL-33 in the uninvolved skin of patients ex vivo. Results showed that IL-1β, IL-1Ra, IL-36α, IL-36β, IL-36γ and IL-33 expression, but not IL-36Ra expression, was enhanced in ACD-involved skin. Immunohistochemical analysis and ex vivo skin cultures confirmed these results. Injection of anti-IL-33 in ACD-uninvolved skin inhibited IL-8 expression, whereas IL-36Ra inhibited IL-36α, IL-36β, IL-36γ and IL-8 expression. Nickel induced IL-1Ra expression in lymphocytes of nickel-sensitized patients. Hence, various IL-1 agonists and antagonists may be involved in ACD pathogenesis.

Peripheral blood lymphocyte typing as a useful tool to objectify the oral mucosa patch test in the diagnosis of allergic contact mucositis to nickel

Nickel (Ni) exposure through the intestinal mucosa may cause a hypersensitivity reaction recently defined as allergic contact mucositis (ACM). This condition is identifiable by the oral mucosa patch test (omPT), a qualitative and subjective examination that requires clinical expertise. Our aim was to evaluate if a peripheral blood lymphocyte typing performed before and after the omPT for Ni may be able to objectify this examination for diagnostic purposes. Thirty patients with symptoms referable to the ingestion of Ni-rich foods were subjected to omPT for Ni. Before and after the omPT, each patient underwent blood sampling for the typing of total lymphocytes and their subsets (T, T helper or Th, T cytotoxic or Tc, B, natural killer or NK). Statistical analysis was performed by Student t test and receiver operating characteristic (ROC) curve analysis. According to the omPT outcomes, 18 patients were defined as Ni-sensitive and the remaining 12 as controls. In Ni-sensitive patients, the number of total, T, Th, Tc, and B lymphocytes/μL whole blood increased after the omPT (p<0.0001 for the first three, p=0.0004 and p=0.0001 for the last two lymphocyte types). No omPT-dependent lymphocyte increase was observed in controls. The post/pre omPT cell ratio, especially if calculated for Th lymphocytes, appears to be an effective index for diagnostic purposes (sensitivity=100%, specificity=83.3%, Youden index=0.833, area under curve (AUC)=0.926, p<0.0001). In conclusion, the peripheral blood lymphocyte typing with calculation of post/pre omPT cell ratio has the potential to support the omPT in diagnosing ACM, with the advantage of providing quantitative and objective data.

Downregulation of TLR4 and 7 mRNA expression levels in broiler's spleen caused by diets supplemented with nickel chloride

Toll-like receptors (TLRs) are important immune receptors in discriminating self from nonself and in initiating the innate and adaptive immune response. TLR4 and TLR7 have been proven to be highly expressed in chicken's spleen. Thus, this study was to evaluate the TLR4 and TLR7 messenger RNA (mRNA) expression levels in the spleen of broilers fed diets supplemented with nickel chloride (NiCl2) using the methods of quantitative real-time PCR (qRT-PCR). Two hundred forty-one-day-old avian broilers were equally divided into 4 groups and fed on a corn-soybean basal diet as control diet or the same basal diet supplemented with 300, 600, and 900 mg/kg of NiCl2 for 42 days. Results showed that TLR4 and TLR7 mRNA expression levels in the spleen were lower (P < 0.05 or P < 0.01) in the 300, 600, and 900 mg/kg groups than those in the control group. It was concluded that dietary NiCl2 in excess of 300 mg/kg could lower TLR4 and TLR7 mRNA expression levels in the spleen of broilers, implying that NiCl2 could impair the innate and adaptive immunity in spleen by injuring immunocytes and/or decreasing the content of cytokines through TLRs.

Heme on innate immunity and inflammation

Heme is an essential molecule expressed ubiquitously all through our tissues. Heme plays major functions in cellular physiology and metabolism as the prosthetic group of diverse proteins. Once released from cells and from hemeproteins free heme causes oxidative damage and inflammation, thus acting as a prototypic damage-associated molecular pattern. In this context, free heme is a critical component of the pathological process of sterile and infectious hemolytic conditions including malaria, hemolytic anemias, ischemia-reperfusion, and hemorrhage. The plasma scavenger proteins hemopexin and albumin reduce heme toxicity and are responsible for transporting free heme to intracellular compartments where it is catabolized by heme-oxygenase enzymes. Upon hemolysis or severe cellular damage the serum capacity to scavenge heme may saturate and increase free heme to sufficient amounts to cause tissue damage in various organs. The mechanism by which heme causes reactive oxygen generation, activation of cells of the innate immune system and cell death are not fully understood. Although heme can directly promote lipid peroxidation by its iron atom, heme can also induce reactive oxygen species generation and production of inflammatory mediators through the activation of selective signaling pathways. Heme activates innate immune cells such as macrophages and neutrophils through activation of innate immune receptors. The importance of these events has been demonstrated in infectious and non-infectious diseases models. In this review, we will discuss the mechanisms behind heme-induced cytotoxicity and inflammation and the consequences of these events on different tissues and diseases.

The molecular mechanism for effects of TiN coating on NiTi alloy on endothelial cell function

The aim of this study is to systematically investigate the molecular mechanism of different effects of nickel titanium (NiTi) alloy surface and titanium nitride (TiN) coating on endothelial cell function. Release of nickel (Ni) ion from bare and TiN-coated NiTi alloys and proliferation of endothelial cells on the two materials were evaluated, and then influence of the two materials on cellular protein expression profiles was investigated by proteomic technology. Subsequently, proteomic data were analyzed with bioinformatics analyses and further validated using a series of biological experiments. Results showed that although the two materials did not affect cell proliferation, the Ni ions released from bare NiTi alloy generated inhibition on pathways associated with actin cytoskeleton, focal adhesion, energy metabolism, inflammation, and amino acid metabolism. In comparison, TiN coating not only effectively prevented release of Ni ions from NiTi alloy, but also promoted actin cytoskeleton and focal adhesion formation, increased energy metabolism, enhanced regulation of inflammation, and promoted amino acid metabolism. Furthermore, the two processes, "the initial mediation of adsorbed serum protein layer to endothelial cell adhesion and growth on the two materials" from our previous study, and "the following action of the two materials on cellular protein expression profile", were linked up and comprehensively analyzed. It was found that in stage of cell adhesion (within 4 h), release of Ni ions from bare NiTi alloy was very low, and the activation of adsorbed proteins to cell adhesion and growth related biological pathways (such as regulation of actin cytoskeleton, and focal adhesion pathways) was almost as same as TiN-coated NiTi alloy. This indicated that the released Ni ions did not affect the mediation of adsorbed proteins to endothelial cell adhesion. However, in stage of cell growth and proliferation, the release of Ni ions from bare NiTi alloy increased with time and reached a higher level, which inhibited endothelial cell function at molecular level, whereas TiN coating improved endothelial cell function.

Selective antibody intervention of Toll-like receptor 4 activation through Fc γ receptor tethering

Inflammation is mediated mainly by leukocytes that express both Toll-like receptor 4 (TLR4) and Fc γ receptors (FcγR). Dysregulated activation of leukocytes via exogenous and endogenous ligands of TLR4 results in a large number of inflammatory disorders that underlie a variety of human diseases. Thus, differentially blocking inflammatory cells while sparing structural cells, which are FcγR-negative, represents an elegant strategy when targeting the underlying causes of human diseases. Here, we report a novel tethering mechanism of the Fv and Fc portions of anti-TLR4 blocking antibodies that achieves increased potency on inflammatory cells. In the presence of ligand (e.g. lipopolysaccharide (LPS)), TLR4 traffics into glycolipoprotein microdomains, forming concentrated protein platforms that include FcγRs. This clustering produces a microenvironment allowing anti-TLR4 antibodies to co-engage TLR4 and FcγRs, increasing their avidity and thus substantially increasing their inhibitory potency. Tethering of antibodies to both TLR4 and FcγRs proves valuable in ameliorating inflammation in vivo. This novel mechanism of action therefore has the potential to enable selective intervention of relevant cell types in TLR4-driven diseases.

A critical role for thymic stromal lymphopoietin in nickel-induced allergy in mice

Ni is the most frequent cause of contact allergy induced by metals. However, the underlying mechanism of this induction is unknown. Our previous research demonstrates that activation of dendritic cells (DCs) through p38MAPK/MKK6 is required for Ni-induced allergy in mice. In the current study, we investigated the cellular and molecular mechanisms underlying Ni-induced allergy using a mouse model that involves injecting Ni into the ear, with or without Freund's incomplete or complete adjuvants. Nickel had greater potential to cause allergic reactions compared with palladium and gold. Among the proteins expressed at higher levels in mice with Ni-induced allergy, we focused on thymic stromal lymphopoietin (TSLP), which is produced in abundance by keratinocytes. We detected increased expression of the TSLP receptor (TSLPR) in DCs from cervical lymph nodes of mice with Ni-induced allergy, suggesting that DCs in ear tissues were activated through TSLPR signaling induced by keratinocyte-derived TSLP. Furthermore, delayed-type hypersensitivity reactions in mice with Ni-induced allergy were decreased significantly by injection of a Tslp-short interfering RNA along with atelocollagen in the ear skin. These results suggest that Ni allergy may be triggered by a TSLP/TSLPR-mediated interaction between epithelial and immune cells.

Immunological characterization of the allergic contact mucositis related to the ingestion of nickel-rich foods

BACKGROUND

The ingestion of nickel (Ni)-rich foods may result in allergic contact mucositis (ACM), a not yet well defined condition identifiable by oral mucosa patch test (omPT). Our aim was to characterize immunologically the ACM taking advantage from the allergen exposure that occurs during the omPT for Ni.

METHODS

Thirty-seven symptomatic patients underwent to omPT for Ni. Before and after omPT, serum and urine Ni concentrations were determined by mass spectrometry, the white blood cells were counted by hemochromocytometric assay, the peripheral lymphocyte typing was carried out by flow cytometry, total IgE and cytokine serum concentrations were measured by immunoenzymatic assays. The local lymphocyte typing was performed by immunohistochemistry only after omPT.

RESULTS

According to the omPT outcomes, 25 patients were defined as Ni-sensitive and the remaining 12 as controls. After omPT, serum and urine Ni concentrations increased significantly in all patients, while a significant increment of circulating lymphocytes and neutrophils was highlighted, respectively, in Ni-sensitive and control patients. Consistently, the Th and Tc circulating lymphocytes, as well as the Th/Tc ratio increased significantly in Ni-sensitive patients after omPT. No noteworthy increment in serum concentrations of total IgE and selected cytokines was observed in any patient after omPT. The presence of CD3+, CD4+, and CD8+ cells was highlighted on the oral mucosa biopsy samples taken from Ni-sensitive patients after omPT.

CONCLUSIONS

In patients with ACM, a local adaptive response with increased lymphocyte trafficking appears to be the most likely mechanism of reaction to Ni administered with the omPT.

TLR4-dependant immune response, but not hepatitis B virus reactivation, is important in radiation-induced liver disease of liver cancer radiotherapy

Toll-like receptor 4 (TLR4) is an important trigger of the immune response against hepatitis B virus (HBV) infection and liver injuries. The roles of HBV reactivation versus TLR4-dependant immune response may be critical factors in preventing radiation-induced liver diseases (RILDs) after liver cancer radiotherapy. This study consists of three phases. In the primary phase, livers of mutant TLR4 (TLR4(-)) mice were irradiated with 30 Gy in either the absence or presence of HBV infection. The latter was done by introduction of plasmid pAAV/HBV 1.2. In the advanced phase, RILDs were compared in normal TLR4 (TLR4(+)) versus TLR4(-) mice. In the validation phase, 28 liver cancer patients who had undergone radiotherapy before hepatectomy were enrolled. Liver biopsies near tumors, irradiated with 35-48 Gy, were used to construct tissue microarrays. HBV reactivation, TLR4 expression, and severity of RILDs were studied in both mouse and human. More HBV reactivation, without significant RILD, was observed in irradiated versus unirradiated TLR4(-) mice. RILD scores of TLR4(+) mice were higher than TLR4(-) mice. In humans, serious RILDs tended to develop in patients with high TLR4 expression, but not in patients with low TLR4 or high HBV surface antigen expression. High TLR4 expression was seen in only 2 of 12 HBV-reactive patients, but in HBV-nonreactive patients, it was seen in 6 of 9 (P < 0.03). In summary, RILDs correlated with high TLR4 expression, but not with HBV reactivation, which is inhibited in liver with high TLR4 expression after liver cancer radiotherapy.

Potential association between TLR4 and chitinase 3-like 1 (CHI3L1/YKL-40) signaling on colonic epithelial cells in inflammatory bowel disease and colitis-associated cancer

Inflammatory bowel disease (IBD) is a group of inflammatory disorders in the small and large intestines. Several studies have proved that persistent and disregulated host/microbial interactions are required for the development of IBD. It is well known that chronic IBD is strongly associated with an increased risk of developing colorectal cancer by 0.5-1% annually, 8-10 years after the initial diagnosis. To detect the tiny dysplasia or early stage of cancer in chronic IBD patients, a tremendous amount of effort is currently directed for improving colonoscopic technology and noninvasive serological marker development. However, there is only a limited amount of data available to understand the exact mechanism of how long term chronic colitis is connected to the development of colorectal tumors. Recently, our group has identified significantly increased expression of chitinase 3-like 1 (CHI3L1) molecule in non-dysplastic mucosa from patients with IBD and remote dysplasia/cancer, compared to patients with IBD without dysplasia or healthy controls. CHI3L1 seems to contribute to the proliferation, migration, and neoplastic progression of colonic epithelial cells (CECs) under inflammatory conditions. Furthermore, the TLR4-mediated intracellular signaling cascade is likely to interact with CHI3L1 signaling in CECs. In this review article, we have concisely summarized the cellular and molecular mechanisms underlining the development of IBD and colitis-associated cancer, with particular focus on the TLR4- and CHI3L1-signaling pathways in CECs.