T cell receptor (TCR) interaction with haptens: metal ions as non-classical haptens

A human 3D immune competent full-thickness skin model mimicking dermal dendritic cell activation

We have integrated dermal dendritic cell surrogates originally generated from the cell line THP-1 as central mediators of the immune reaction in a human full-thickness skin model. Accordingly, sensitizer treatment of THP-1-derived CD14-, CD11c+ immature dendritic cells (iDCs) resulted in the phosphorylation of p38 MAPK in the presence of 1-chloro-2,4-dinitrobenzene (DNCB) (2.6-fold) as well as in degradation of the inhibitor protein kappa B alpha (IκBα) upon incubation with NiSO4 (1.6-fold). Furthermore, NiSO4 led to an increase in mRNA levels of IL-6 (2.4-fold), TNF-α (2-fold) and of IL-8 (15-fold). These results were confirmed on the protein level, with even stronger effects on cytokine release in the presence of NiSO4: Cytokine secretion was significantly increased for IL-8 (147-fold), IL-6 (11.8-fold) and IL-1β (28.8-fold). Notably, DNCB treatment revealed an increase for IL-8 (28.6-fold) and IL-1β (5.6-fold). Importantly, NiSO4 treatment of isolated iDCs as well as of iDCs integrated as dermal dendritic cell surrogates into our full-thickness skin model (SM) induced the upregulation of the adhesion molecule clusters of differentiation (CD)54 (iDCs: 1.2-fold; SM: 1.3-fold) and the co-stimulatory molecule and DC maturation marker CD86 (iDCs ~1.4-fold; SM:~1.5-fold) surface marker expression. Noteworthy, the expression of CD54 and CD86 could be suppressed by dexamethasone treatment on isolated iDCs (CD54: 1.3-fold; CD86: 2.1-fold) as well as on the tissue-integrated iDCs (CD54: 1.4-fold; CD86: 1.6-fold). In conclusion, we were able to integrate THP-1-derived iDCs as functional dermal dendritic cell surrogates allowing the qualitative identification of potential sensitizers on the one hand, and drug candidates that potentially suppress sensitization on the other hand in a 3D human skin model corresponding to the 3R principles ("replace", "reduce" and "refine").

A Novel Approach to Differentiating Erosive and Reticular Lichen Planus Based on the Percentage of Dental Surfaces With Metal Restorations

Introduction Oral lichen planus (OLP) and oral lichenoid reaction (OLR) constitute clinical entities with strong but unclear etiologic relation to dental materials. The aim of this study was to evaluate a correlation between the clinical form of OLP/OLR and the number of dental metal restorations in the oral cavity thus utilizing an exposure to metal (EM) index.  Material and methods The study type is experimental, and the study design is characterized as semiquantitative research that belongs to the branch of experimental research. Twenty-nine patients were chosen based on clinical (either reticular or erosive clinical forms) and histologic findings suggestive of OLP/OLR. The files of patients were retrieved from the archives of the Department of Oral Medicine/Pathology, School of Dentistry, Aristotle University of Thessaloniki, Greece, during the period 2009-2019. The medical history of the patients did not include any disorder or medication associated with lichenoid lesions and the measurements took place concurrently with the establishment of the diagnosis, thus no treatment for the lichen planus had been administered prior to the measurements. Quantitative measurement of the percentage of dental surfaces restored through metal restorations and correlation with the clinical and histologic findings of OLP/OLR was evaluated. The EM index was evaluated on a scale of 1-3, which corresponds to the percentage of dental surfaces restored through metal restorations. The statistical analysis was performed with the Pearson chi-square test and the significance level was set at p≤0.05. Results The EM index was measured by dividing each tooth into five surfaces (occlusal, mesial, distal, buccal, lingual), subsequently multiplying the number of available teeth with the number 5 to calculate the total number of surfaces, and then counting the number of surfaces with metal restorations - both fillings and crowns (in case of metal-ceramic crowns, the respective dental surface is taken into account only in case of macroscopically exposed metal), dividing the number of surfaces with metal restorations with the total number of surfaces and multiply by 100 so that the results take the form of percentages (%) and finally classifying the percentages into three groups: 1: 0% metal restorations, 2: 1-25% metal restorations, 3: >26% metal restorations). The percentage in female patients ranged from 0% to 100%, whereas it ranged from 0% to 60% in male patients. According to the clinical form of the lichenoid lesion, the percentage ranged from 0% to 60% in reticular lichen planus cases and from 0% to 100% in erosive lichen planus cases. There was no statistical difference between lichen planus cases, in total, and in normal oral epithelium. However, the levels of EM were marginally similar between the reticular lichen planus and the erosive lichen planus (Fisher's exact test, p = 0.056). Therefore, it may be the case that the EM index is higher in erosive lichenoid lesions. Conclusion In our study, the EM index was higher in female patients and in erosive lichenoid lesions. These findings should be tested and supported by larger samples of patients since the aforementioned Fisher's Exact Test, p = 0.056 could fall below the threshold of 0.05 if more patients were included. This is the first attempt to establish a novel approach to differentiating erosive and reticular lichen planus based on the percentage of dental surfaces with metal restorations.

[Particle disease and its effects on periarticular tissue]

Particle disease is the condition caused by wear debris on surrounding tissues and influences the well-being of arthroplasty patients. This condition is multifactorial due to the type of bearing couple, head size and implant position. Subsequent periprosthetic osteolysis and soft tissue reactions, can lead to revision THA surgery. The periprosthetic synovial membrane (synovial-like interface membrane, SLIM) is used in diagnostics when the cause of implant failure is uncertain. Detailed analysis of synovial fluid and bone marrow could improve the diagnostic procedure and strengthen the cases for revision surgery and the underlying biology. A large number of research approaches on this topic have evolved and continue to be utilized in the clinic.

Unique and common TCR repertoire features of Ni2+ -, Co2+ -, and Pd2+ -specific human CD154 + CD4+ T cells

BACKGROUND

Apart from Ni²⁺ , Co²⁺ , and Pd²⁺ ions commonly trigger T cell-mediated allergic contact dermatitis. However, in vitro frequencies of metal-specific T cells and the mechanisms of antigen recognition remain unclear.

METHODS

Here, we utilized a CD154 upregulation assay to quantify Ni²⁺ -, Co²⁺ -, and Pd²⁺ -specific CD4+ T cells in peripheral blood mononuclear cells (PBMC). Involved αβ T cell receptor (TCR) repertoires were analyzed by high-throughput sequencing.

RESULTS

Peripheral blood mononuclear cells incubation with NiSO₄ , CoCl₂ , and PdCl₂ increased frequencies of CD154 + CD4+ memory T cells that peaked at ~400 μM. Activation was TCR-mediated as shown by the metal-specific restimulation of T cell clones. Most abundant were Pd²⁺ -specific T cells (mean 3.5%, n = 19), followed by Co²⁺ - and Ni²⁺ -specific cells (0.6%, n = 18 and 0.3%, n = 20) in both allergic and non-allergic individuals. A strong overrepresentation of the gene segment TRAV9-2 was unique for Ni²⁺ -specific TCR (28% of TCR) while Co²⁺ and Pd²⁺ -specific TCR favorably expressed TRAV2 (8%) and the TRBV4 gene segment family (21%), respectively. As a second, independent mechanism of metal ion recognition, all analyzed metal-specific TCR showed a common overrepresentation of a histidine in the complementarity determining region 3 (CDR3; 15% of α-chains, 34% of β-chains). The positions of the CDR3 histidine among metal-specific TCR mirrored those in random repertoires and were conserved among cross-reactive clonotypes.

CONCLUSIONS

Induced CD154 expression allows a fast and comprehensive detection of Ni²⁺ -, Co²⁺ -, and Pd²⁺ -specific CD4+ T cells. Distinct TCR repertoire features underlie the frequent activation and cross-reactivity of human metal-specific T cells.

Immunohistochemical and Histopathological Features of Persistent Gingival Enlargement in Relation to Metal Allergic Sensitisation during Orthodontic Treatment

This study aimed to analyse the immunohistochemical profile of inflammatory infiltrates in the gingival tissue of patients undergoing orthodontic treatment in relation to patients’ titanium and/or nickel allergy status. Patients with gingival enlargement received initial periodontal therapy, followed by external gingivectomy in the case of persistent gingival enlargement. The sample included 44 patients (22 had metal allergic sensitisation). Histopathological changes were assessed, and an immunohistochemical analysis was performed on formalin-fixed and paraffin-embedded gingival samples using antibodies against CD1a, CD3, CD4, CD8, CD20, CD68, and CD138. Computer-assisted image analysis was performed to evaluate the positive cell count in the gingival tissue. The gingiva of the sensitised patients was characterised by the absence of multifocal inflammatory infiltrates (p < 0.05), while pronounced exocytosis and band-like inflammatory infiltrates were more frequently observed in sensitised patients. In addition, there was an increase in Langerhans cells and T-helper lymphocytes and a decrease in naïve T-lymphocytes, cytotoxic T-lymphocytes, macrophages, and plasma cells in the sensitised subjects compared to non-sensitised. However, the differences were only statistically significant for macrophages, with a moderate effect size (82.8 vs. 133.9; p = 0.041; r = 0.308). The absence of multifocal inflammation appears to be the most characteristic histopathological feature of the gingiva of sensitised patients. Although their gingiva presented certain characteristics of late hypersensitivity immune reactions the observed changes imply dominant irritative effect e.

Quaternary ammonium compounds in hypersensitivity reactions

Quaternary ammonium compounds (QAC) are commonly used disinfectants, antiseptics, preservatives, and detergents due to their antibacterial property and represent the first used biocides before phenolic or nitrogen products. Their common structure consists of one or more quaternary ammonium bound with four lateral substituents. Their amphiphilic structure allows them to intercalate into microorganism surfaces which induces an unstable and porous membrane that explains their antimicrobial activity towards bacteria, fungi, and viruses. QAC are thus found in many areas, such as household products, medicines, hygiene products, cosmetics, agriculture, or industrial products but are also used in medical practice as disinfectants and antiseptics and in health care facilities where they are used for cleaning floors and walls. QAC exposure has already been involved in occupational asthma in healthcare workers or professional cleaners by many authors. They also have been suggested to play a role in contact dermatitis (CD) and urticaria in workers using cosmetics such as hairdressers or healthcare workers, inciting reglementary agencies to make recommendations regarding those products. However, distinguishing the irritant or sensitizing properties of chemicals is complex and as a result, the sensitizing property of QAC is still controverted. Moreover, the precise mechanisms underlying the possible sensitization effect are still under investigation, and to date, only a few studies have documented an immunological mechanism. Besides, QAC have been suggested to be responsible for neuromuscular blocking agents (NMBA) sensitization by cross-reactivity. This hypothesis is supported by a higher prevalence of quaternary ammonium (QA)-specific IgE in the professionally exposed populations, such as hairdressers, cleaners, or healthcare workers, suggesting that the sensitization happens with structurally similar compounds present in the environment. This review summarizes the newest knowledge about QAC and their role in hypersensitivities. After describing the different QAC, their structure and use, the most relevant studies about the effects of QAC on the immune system will be reviewed and discussed.

Frequencies and TCR Repertoires of Human 2,4,6-Trinitrobenzenesulfonic Acid-specific T Cells

Allergic contact dermatitis is a widespread T cell-mediated inflammatory skin disease, but in vitro monitoring of chemical-specific T cells remains challenging. We here introduce short-term CD154/CD137 upregulation to monitor human T cell responses to the experimental sensitizer 2,4,6-trinitrobenzenesulfonic acid (TNBS). Peripheral blood mononuclear cells (PBMC) from healthy donor buffy coats were TNBS-modified and incubated with unmodified PBMC. After 5 and 16 h, we detected TNBS-specific activated CD154+CD4+ and CD137+CD8+ T cells by multi-parameter flow cytometry, respectively. Activated cells were sorted for restimulation and bulk T cell receptor (TCR) high-throughput sequencing (HTS). Stimulation with TNBS-modified cells (3 mM) induced CD154 expression on 0.04% of CD4+ and CD137 expression on 0.60% of CD8+ memory T cells, respectively (means, n = 11–17 donors). CD69 co-expression argued for TCR-mediated activation, which was further supported by TNBS-specific restimulation of 10/13 CD154+CD4+ and 11/15 CD137+CD8+ T cell clones and lines. Major histocompatibility complex (MHC) blocking antibodies prevented activation, illustrating MHC restriction. The high frequencies of TNBS-specific T cells were associated with distinct common changes in the TCR β-chain repertoire. We observed an overrepresentation of tryptophan and lysine in the complementarity determining regions 3 (CDR3) (n = 3–5 donors), indicating a preferential interaction of these amino acids with the TNBS-induced epitopes. In summary, the detection of TNBS-specific T cells by CD154/CD137 upregulation is a fast, comprehensive and quantitative method. Combined with TCR HTS, the mechanisms of chemical allergen recognition that underlie unusually frequent T cell activation can be assessed. In the future, this approach may be adapted to detect T cells activated by additional chemical sensitizers.

Ni2+-Assisted Hydrolysis May Affect the Human Proteome; Filaggrin Degradation Ex Vivo as an Example of Possible Consequences

Deficiency in a principal epidermal barrier protein, filaggrin (FLG), is associated with multiple allergic manifestations, including atopic dermatitis and contact allergy to nickel. Toxicity caused by dermal and respiratory exposures of the general population to nickel-containing objects and particles is a deleterious side effect of modern technologies. Its molecular mechanism may include the peptide bond hydrolysis in X₁-S/T-c/p-H-c-X₂ motifs by released Ni²⁺ ions. The goal of the study was to analyse the distribution of such cleavable motifs in the human proteome and examine FLG vulnerability of nickel hydrolysis. We performed a general bioinformatic study followed by biochemical and biological analysis of a single case, the FLG protein. FLG model peptides, the recombinant monomer domain human keratinocytes in vitro and human epidermis ex vivo were used. We also investigated if the products of filaggrin Ni²⁺-hydrolysis affect the activation profile of Langerhans cells. We found X₁-S/T-c/p-H-c-X₂ motifs in 40% of human proteins, with the highest abundance in those involved in the epidermal barrier function, including FLG. We confirmed the hydrolytic vulnerability and pH-dependent Ni²⁺-assisted cleavage of FLG-derived peptides and FLG monomer, using in vitro cell culture and ex-vivo epidermal sheets; the hydrolysis contributed to the pronounced reduction in FLG in all of the models studied. We also postulated that Ni-hydrolysis might dysregulate important immune responses. Ni²⁺-assisted cleavage of barrier proteins, including FLG, may contribute to clinical disease associated with nickel exposure.

In Vitro Monitoring of Human T Cell Responses to Skin Sensitizing Chemicals-A Systematic Review

Background: Chemical allergies are T cell-mediated diseases that often manifest in the skin as allergic contact dermatitis (ACD). To prevent ACD on a public health scale and avoid elicitation reactions at the individual patient level, predictive and diagnostic tests, respectively, are indispensable. Currently, there is no validated in vitro T cell assay available. The main bottlenecks concern the inefficient generation of T cell epitopes and the detection of rare antigen-specific T cells. Methods: Here, we systematically review original experimental research papers describing T cell activation to chemical skin sensitizers. We focus our search on studies published in the PubMed and Scopus databases on non-metallic allergens in the last 20 years. Results: We identified 37 papers, among them 32 (86%) describing antigen-specific human T cell activation to 31 different chemical allergens. The remaining studies measured the general effects of chemical allergens on T cell function (five studies, 14%). Most antigen-specific studies used peripheral blood mononuclear cells (PBMC) as antigen-presenting cells (APC, 75%) and interrogated the blood T cell pool (91%). Depending on the individual chemical properties, T cell epitopes were generated either by direct administration into the culture medium (72%), separate modification of autologous APC (29%) or by use of hapten-modified model proteins (13%). Read-outs were mainly based on proliferation (91%), often combined with cytokine secretion (53%). The analysis of T cell clones offers additional opportunities to elucidate the mechanisms of epitope formation and cross-reactivity (13%). The best researched allergen was p-phenylenediamine (PPD, 12 studies, 38%). For this and some other allergens, stronger immune responses were observed in some allergic patients (15/31 chemicals, 48%), illustrating the in vivo relevance of the identified T cells while detection limits remain challenging in many cases. Interpretation: Our results illustrate current hardships and possible solutions to monitoring T cell responses to individual chemical skin sensitizers. The provided data can guide the further development of T cell assays to unfold their full predictive and diagnostic potential, including cross-reactivity assessments.

Immunological Mechanisms of Metal Allergies and the Nickel-Specific TCR-pMHC Interface

Besides having physiological functions and general toxic effects, many metal ions can cause allergic reactions in humans. We here review the immune events involved in the mediation of metal allergies. We focus on nickel (Ni), cobalt (Co) and palladium (Pd), because these allergens are among the most prevalent sensitizers (Ni, Co) and immediate neighbors in the periodic table of the chemical elements. Co-sensitization between Ni and the other two metals is frequent while the knowledge on a possible immunological cross-reactivity using in vivo and in vitro approaches remains limited. At the center of an allergic reaction lies the capability of a metal allergen to form T cell epitopes that are recognized by specific T cell receptors (TCR). Technological advances such as activation-induced marker assays and TCR high-throughput sequencing recently provided new insights into the interaction of Ni2+ with the αβ TCR-peptide-major histocompatibility complex (pMHC) interface. Ni2+ functionally binds to the TCR gene segment TRAV9-2 or a histidine in the complementarity determining region 3 (CDR3), the main antigen binding region. Thus, we overview known, newly identified and hypothesized mechanisms of metal-specific T cell activation and discuss current knowledge on cross-reactivity.

Drug and Chemical Allergy: A Role for a Specific Naive T-Cell Repertoire?

Allergic reactions to drugs and chemicals are mediated by an adaptive immune response involving specific T cells. During thymic selection, T cells that have not yet encountered their cognate antigen are considered naive T cells. Due to the artificial nature of drug/chemical-T-cell epitopes, it is not clear whether thymic selection of drug/chemical-specific T cells is a common phenomenon or remains limited to few donors or simply does not exist, suggesting T-cell receptor (TCR) cross-reactivity with other antigens. Selection of drug/chemical-specific T cells could be a relatively rare event accounting for the low occurrence of drug allergy. On the other hand, a large T-cell repertoire found in multiple donors would underline the potential of a drug/chemical to be recognized by many donors. Recent observations raise the hypothesis that not only the drug/chemical, but also parts of the haptenated protein or peptides may constitute the important structural determinants for antigen recognition by the TCR. These observations may also suggest that in the case of drug/chemical allergy, the T-cell repertoire results from particular properties of certain TCR to recognize hapten-modified peptides without need for previous thymic selection. The aim of this review is to address the existence and the role of a naive T-cell repertoire in drug and chemical allergy. Understanding this role has the potential to reveal efficient strategies not only for allergy diagnosis but also for prediction of the immunogenic potential of new chemicals.

Nickel Allergy of the Skin and Beyond

BACKGROUND

Hypersensitization to nickel is one of the most common contact allergies in the modern world and it is considered to be a major cause of contact dermatitis, especially for hand eczema.

OBJECTIVE

The aim of this paper is to describe many faces of the nickel allergy and to find out different diagnostic, potential strategies for treatment and prevention in hypersensitized patients. A personal clinical experience with practical clinical cases of contact dermatitis to nickel has also been presented.

METHODS

Electronic databases on this topic was carried out using PubMed-Medline.

RESULTS

The literature review identified many articles reporting for nickel contact allergy and pointing the metal as number one allergen in the frequency of positive skin patch test reactions in a large population worldwide. Herein, a summary of the current understanding and evidence on nickel allergy with practical approach and proposed recommendations to the dermatologist, general practitioner, and the allergist were prepared.

CONCLUSION

The prevalence of nickel allergy represents an important socio-economical and health issue. Metal is one of the most common sensitizing agents worldwide. The morbidity due to this metal represents the allergic contact dermatitis and it is constantly growing in many countries. There are also cases of systemic allergic contact dermatitis, where they could be easily misdiagnosed as adverse drug reactions, which lead to delay of the correct diagnosis and inappropriate treatment.

Tattoos - more than just colored skin? Searching for tattoo allergens

During tattooing, a high amount of ink is injected into the skin. Tattoo inks contain numerous substances such as the coloring pigments, impurities, solvents, emulsifiers, and preservatives. Black amorphous carbon particles (carbon black), white titanium dioxide, azo or polycyclic pigments create all varieties of color shades in the visible spectrum. Some ingredients of tattoo inks might be hazardous and allergenic chemicals of unknown potential. In Germany, about 20 % of the general population is tattooed and related adverse reactions are increasingly reported. Since tattoo needles inevitably harm the skin, microorganisms can enter the wound and may cause infections. Non-allergic inflammatory reactions (for example cutaneous granuloma and pseudolymphoma) as well as allergic reactions may emerge during or after wound healing. Especially with allergies occurring after weeks, months or years, it remains difficult to identify the specific ingredient(s) that trigger the reaction. This review summarizes possible adverse effects related to tattooing with a focus on the development of tattoo-mediated allergies. To date, relevant allergens were only identified in rare cases. Here we present established methods and discuss current experimental approaches to identify culprit allergens in tattoo inks - via testing of the patient and in vitro approaches.

Update of the risk assessment of nickel in food and drinking water

The European Commission asked EFSA to update its previous Opinion on nickel in food and drinking water, taking into account new occurrence data, the updated benchmark dose (BMD) Guidance and newly available scientific information. More than 47,000 analytical results on the occurrence of nickel were used for calculating chronic and acute dietary exposure. An increased incidence of post-implantation loss in rats was identified as the critical effect for the risk characterisation of chronic oral exposure and a BMDL 10 of 1.3 mg Ni/kg body weight (bw) per day was selected as the reference point for the establishment of a tolerable daily intake (TDI) of 13 μg/kg bw. Eczematous flare-up reactions in the skin elicited in nickel-sensitised humans, a condition known as systemic contact dermatitis, was identified as the critical effect for the risk characterisation of acute oral exposure. A BMDL could not be derived, and therefore, the lowest-observed-adverse-effect-level of 4.3 μg Ni/kg bw was selected as the reference point. The margin of exposure (MOE) approach was applied and an MOE of 30 or higher was considered as being indicative of a low health concern. The mean lower bound (LB)/upper bound (UB) chronic dietary exposure was below or at the level of the TDI. The 95th percentile LB/UB chronic dietary exposure was below the TDI in adolescents and in all adult age groups, but generally exceeded the TDI in toddlers and in other children, as well as in infants in some surveys. This may raise a health concern in these young age groups. The MOE values for the mean UB acute dietary exposure and for the 95th percentile UB raises a health concern for nickel-sensitised individuals. The MOE values for an acute scenario regarding consumption of a glass of water on an empty stomach do not raise a health concern.

TCRs with segment TRAV9-2 or a CDR3 histidine are overrepresented among nickel-specific CD4+ T cells

BACKGROUND

Nickel is the most frequent cause of T cell-mediated allergic contact dermatitis worldwide. In vitro, CD4+ T cells from all donors respond to nickel but the involved αβ T cell receptor (TCR) repertoire has not been comprehensively analyzed.

METHODS

We introduce CD154 (CD40L) upregulation as a fast, unbiased, and quantitative method to detect nickel-specific CD4+ T cells ex vivo in blood of clinically characterized allergic and non allergic donors. Naïve (CCR7+ CD45RA+) and memory (not naïve) CD154+ CD4+ T cells were analyzed by flow cytometry after 5 hours of stimulation with 200 µmol/L NiSO₄ ., TCR α- and β-chains of sorted nickel-specific and control cells were studied by high-throughput sequencing.

RESULTS

Stimulation of PBMCs with NiSO₄ induced CD154 expression on ~0.1% (mean) of naïve and memory CD4+ T cells. In allergic donors with recent positive patch test, memory frequencies further increased ~13-fold and were associated with markers of in vivo activation. CD154 expression was TCR-mediated since single clones could be specifically restimulated. Among nickel-specific CD4+ T cells of allergic and non allergic donors, TCRs expressing the α-chain segment TRAV9-2 or a histidine in their α- or β-chain complementarity determining region 3 (CDR3) were highly overrepresented.

CONCLUSIONS

Induced CD154 expression represents a reliable method to study nickel-specific CD4+ T cells. TCRs with particular features respond in all donors, while strongly increased blood frequencies indicate nickel allergy for some donors. Our approach may be extended to other contact allergens for the further development of diagnostic and predictive in vitro tests.

Pathogenic Mechanisms and Therapeutic Implication in Nickel-Induced Cell Damage

Background:

Nickel (Ni) is mostly applied in a number of industrial areas such as printing inks, welding, alloys, electronics and electrical professions. Occupational or environmental exposure to nickel may lead to cancer, allergy reaction, nephrotoxicity, hepatotoxicity, neurotoxicity, as well as cell damage, apoptosis and oxidative stress.

Methods:

In here, we focused on published studies about cell death, carcinogenicity, allergy reactions and neurotoxicity, and promising agents for the prevention and treatment of the toxicity by Ni.

Results:

Our review showed that in the last few years, more researches have focused on reactive oxygen species formation, oxidative stress, DNA damages, apoptosis, interaction with involving receptors in allergy and mitochondrial damages in neuron induced by Ni.

Conclusion:

The collected data in this paper provide useful information about the main toxicities induced by Ni, also, their fundamental mechanisms, and how to discover new ameliorative agents for prevention and treatment by reviewing agents with protective and therapeutic consequences on Ni induced toxicity.

Nuclear factor erythroid 2 - related factor 2 and its relationship with cellular response in nickel exposure: a systems biology analysis

Background

Nickel and nickel-containing compounds (NCC) are known human carcinogens. However, the precise molecular mechanisms of nickel-induced malignant transformation remain unknown. Proposed mechanisms suggest that nickel and NCC may participate in the dual activation/inactivation of enzymatic pathways involved in cell defenses against oxidative damage, where Nuclear factor-erythroid 2 related factor 2 (Nrf2) plays a central role.

Methods

For assessing the potential role of proteins involved in the Nrf2-mediated response to nickel and NCC exposure, we designed an interactome network using the STITCH search engine version 5.0 and the STRING software 10.0. The major NCC-protein interactome (NCPI) generated was analyzed using the MCODE plugin, version 1.5.1 for the detection of interaction modules or subnetworks. Main centralities of the NCPI were determined with the CentiScape 2.2 plugin of Cytoscape 3.4.0 and main biological processes associated with each cluster were assessed using the BiNGO plugin of Cytoscape 3.4.0.

Results

Water-soluble NiSO₄ and insoluble Ni₃S₂ were the most connected to proteins involved in the NCPI network. Nfr2 was detected as one of the most relevant proteins in the network, participating in several multifunctional protein complexes in clusters 1, 2, 3 and 5. Ontological analysis of cluster 3 revealed several processes related to unfolded protein response (UPR) and response to endoplasmic reticulum (ER) stress.

Conclusions

Cellular response to NCC exposure was very comparable, particularly concerning oxidative stress response, inflammation, cell cycle/proliferation, and apoptosis. In this cellular response, Nfr2 was highly centralized and participated in several multifunctional protein complexes, including several related to ER-stress. These results add evidence on the possible Ni²⁺ induced – ER stress mainly associated with insoluble NCC. In this scenario, we also show how protein degradation mediated by ubiquitination seems to play key roles in cellular responses to Ni.

Metal nanomaterials: Immune effects and implications of physicochemical properties on sensitization, elicitation, and exacerbation of allergic disease

The recent surge in incorporation of metallic and metal oxide nanomaterials into consumer products and their corresponding use in occupational settings have raised concerns over the potential for metals to induce size-specific adverse toxicological effects. Although nano-metals have been shown to induce greater lung injury and inflammation than their larger metal counterparts, their size-related effects on the immune system and allergic disease remain largely unknown. This knowledge gap is particularly concerning since metals are historically recognized as common inducers of allergic contact dermatitis, occupational asthma, and allergic adjuvancy. The investigation into the potential for adverse immune effects following exposure to metal nanomaterials is becoming an area of scientific interest since these characteristically lightweight materials are easily aerosolized and inhaled, and their small size may allow for penetration of the skin, which may promote unique size-specific immune effects with implications for allergic disease. Additionally, alterations in physicochemical properties of metals in the nano-scale greatly influence their interactions with components of biological systems, potentially leading to implications for inducing or exacerbating allergic disease. Although some research has been directed toward addressing these concerns, many aspects of metal nanomaterial-induced immune effects remain unclear. Overall, more scientific knowledge exists in regards to the potential for metal nanomaterials to exacerbate allergic disease than to their potential to induce allergic disease. Furthermore, effects of metal nanomaterial exposure on respiratory allergy have been more thoroughly-characterized than their potential influence on dermal allergy. Current knowledge regarding metal nanomaterials and their potential to induce/exacerbate dermal and respiratory allergy are summarized in this review. In addition, an examination of several remaining knowledge gaps and considerations for future studies is provided.

T-Cell Activation by Low Molecular Weight Drugs and Factors That Influence Susceptibility to Drug Hypersensitivity

Drug hypersensitivity reactions adversely affect treatment outcome, increase the length of patients' hospitalization, and limit the prescription options available to physicians. In addition, late stage drug attrition and the withdrawal of licensed drugs cost the pharmaceutical industry billions of dollars. This significantly increases the overall cost of drug development and by extension the price of licensed drugs. Drug hypersensitivity reactions are characterized by a delayed onset, and reactions tend to be more serious upon re-exposure. The role of drug-specific T-cells in the pathogenesis of drug hypersensitivity reactions and definition of the nature of the binding interaction of drugs with HLA and T-cell receptors continues to be the focus of intensive research, primarily because susceptibility is associated with expression of one or a small number of HLA alleles. This review critically examines the mechanisms of T-cell activation by drugs. Specific examples of drugs that activate T-cells via the hapten, the pharmacological interaction with immune receptors and the altered self-peptide repertoire pathways, are discussed. Furthermore, the impacts of drug metabolism, drug-protein adduct formation, and immune regulation on the development of drug antigen-responsive T-cells are highlighted. The knowledge gained from understanding the pathways of T-cell activation and susceptibility factors for drug hypersensitivity will provide the building blocks for the development of predictive in vitro assays that will prevent or help to minimize the incidence of these reactions in clinic.

Type IV Cell-Mediated Hypersensitivity Reaction Caused by Titanium Implant Following Double Calcaneal Osteotomy and First Metatarsal-Cuneiform Arthrodesis: A Case Report and Review of the Literature

Because of their inert character and desired biocompatibility, titanium implants have been universally accepted as safer alternatives to the conventional stainless steel orthopedic implants; however, recent emergence of type IV hypersensitivity reactions to titanium have included eczema, contact dermatitis, a prolonged febrile state, sterile osteonecrosis, and impaired fracture and wound healing. This report presents a patient with postoperative incision dehiscence and devascularization of surfaces in contact with titanium hardware after undergoing a double calcaneal osteotomy and a first metatarsal-cuneiform arthrodesis using titanium alloy implants. Titanium hypersensitivity was confirmed in this case through standard allergy patch testing by a board-certified immunologist. Complete healing occurred after diagnosis of the titanium allergy and hardware explant. To our knowledge, this is one of a few known allergies to titanium implants after foot and ankle surgery.

Identification and Characterization of Circulating Naïve CD4+ and CD8+ T Cells Recognizing Nickel

Allergic contact dermatitis caused by contact sensitizers is a T-cell-mediated inflammatory skin disease. The most prevalent contact allergens is nickel. Whereas, memory T cells from nickel-allergic patients are well-characterized, little is known concerning nickel-specific naïve T-cell repertoire. The purpose of this study was to identify and quantify naïve CD4+ and CD8+ T cells recognizing nickel in the general population. Using a T-cell priming in vitro assay based on autologous co-cultures between naïve T cells and dendritic cells loaded with nickel, we were able to detect a naïve CD4+ and CD8+ T-cell repertoire for nickel in 10/11 and 7/8 of the tested donors. We calculated a mean frequency of 0.49 nickel-specific naïve CD4+ T cells and 0.37 nickel-specific naïve CD8+ T cells per million of circulating naïve T cells. The activation of these specific T cells requires MHC molecules and alongside IFN-γ production, some nickel-specific T-cells were able to produce granzyme-B. Interestingly, nickel-specific naïve CD4+ and CD8+ T cells showed a low rate of cross-reactivity with cobalt, another metallic hapten, frequently mixed with nickel in many alloys. Moreover, naïve CD4+ T cells showed a polyclonal TCRβ composition and the presence of highly expanded clones with an enrichment and/or preferentially expansion of some TRBV genes that was donor and T-cell specific. Our results contribute to a better understanding of the mechanism of immunization to nickel and propose the T-cell priming assay as a useful tool to identify antigen-specific naïve T cells.

IL-27 Production and Regulation in Human Dendritic Cells Treated with the Chemical Sensitizer NiSO4

Allergic contact dermatitis (ACD) is a major cause of occupational skin disease, and nickel is among the most prevalent contact allergens. Dendritic cells (DC) play an important role in ACD and in the type of the ensuing immune response through differential phenotypes and cytokine production. The interleukin (IL)-12 cytokine family is composed of heterodimeric cytokines sharing homology at the subunit, receptors and signaling levels. We previously showed that nickel can upregulate the production of IL-12p40 and IL-23, both known to be pro-inflammatory. In this work, we aimed to extend our knowledge on nickel regulation of the IL-12 cytokine family by focusing on IL-27, a recently identified immunomodulatory cytokine from this family. We showed that nickel induced the production of IL-27 in human monocyte-derived DC (MoDC), regulating IL-22 production by human CD4+ T cells. We also showed that nickel was able to induce the expression of the two subunits of IL-27: il-27p28 and ebi3. Furthermore, we demonstrated that the production of IL-27 was dependent on the TLR4, p38 MAPK, NF-κB, and Jak-STAT signaling. However, IL-27 subunits were differentially regulated by these pathways. Indeed, both subunits were positively regulated by the TLR4 and NF-κB pathways, but only il-27p28 was also dependent on p38 MAPK and Jak-STAT pathways. Our results contribute to a better understanding of nickel-induced ACD by focusing on the IL-12 cytokine family and elucidating the mechanism of IL-27 regulation in human dendritic cells.

Evaluation of immunoresponses and cytotoxicity from skin exposure to metallic nanoparticles

Nanotechnology is an interdisciplinary science that has developed rapidly in recent years. Metallic nanoparticles (NPs) are increasingly utilized in dermatology and cosmetology, because of their unique properties. However, skin exposure to NPs raises concerns regarding their transdermal toxicity. The tight junctions of epithelial cells form the skin barrier, which protects the host against external substances. Recent studies have found that NPs can pass through the skin barrier into deeper layers, indicating that skin exposure is a means for NPs to enter the body. The distribution and interaction of NPs with skin cells may cause toxic side effects. In this review, possible penetration pathways and related toxicity mechanisms are discussed. The limitations of current experimental methods on the penetration and toxic effects of metallic NPs are also described. This review contributes to a better understanding of the risks of topically applied metallic NPs and provides a foundation for future studies.

Imaging mass spectrometry for novel insights into contact allergy - a proof-of-concept study on nickel

BACKGROUND

In spite of extensive regulation to limit exposure, nickel remains the main cause of contact allergy in the general population. More detailed knowledge on the skin uptake of haptens is required. So far, no method exists for the visualization of this clinically relevant hapten and its distribution in the skin.

OBJECTIVES

To show, in terms of a proof of concept, that imaging mass spectrometry [time of flight secondary ion mass spectrometry (ToF-SIMS)] can be applied for investigation of the penetration and distribution of nickel in human skin.

METHOD

Full-thickness human skin obtained from breast reduction surgery was exposed to nickel sulfate (5% in deionized water) for 24 h in Franz-type diffusion cells. Biopsies were obtained from nickel-treated samples and control (deionized water). The tissue was sliced, and analysed with ToF-SIMS, generating high-resolution images of ion distribution in the epidermis and upper dermis.

RESULTS

The skin layers could be discerned from the ToF-SIMS data, particularly on the basis of the collagen signal. Nickel ions were localized to the stratum corneum and upper epidermis.

CONCLUSIONS

This is the first time that ToF-SIMS has been applied to trace the distribution of a hapten in human skin. Proof of principle was shown for nickel, and the technique can, in the future, be expanded for investigation of the skin distribution of clinically relevant sensitizers in general.

Pathomechanisms of Contact Sensitization

Contact sensitization is the initial process involved in the development of an allergic reaction to xenobiotic environmental substances. Here, we briefly describe the differences between irritant and allergic contact dermatitis. Then, we highlight the essential steps involved in the development of an ACD reaction, i.e., the protein binding of haptens, genetic factors influencing the penetration of sensitizers into the skin, the different mechanisms driving the initial development of an inflammatory cytokine micromilieu enabling the full maturation of dendritic cells, the role of pre- and pro-haptens, antigen presentation and T cell activation via MHC and CD1 molecules, dendritic cell (DC) migration, and potential LC contribution as well as the different T cell subsets involved in ACD. In addition, we discuss the latest publications regarding factors that might influence the sensitizing potential such as repeated sensitizer application, penetration enhancers, humidity of the skin, microbiota, Tregs, and phthalates. Last but not least, we briefly touch upon novel targets for drug development that might serve as treatment options for ACD.

The mechanisms of nickel toxicity in aquatic environments: An adverse outcome pathway analysis

Current ecological risk assessment and water quality regulations for nickel (Ni) use mechanistically based, predictive tools such as biotic ligand models (BLMs). However, despite many detailed studies, the precise mechanism(s) of Ni toxicity to aquatic organisms remains elusive. This uncertainty in the mechanism(s) of action for Ni has led to concern over the use of tools like the BLM in some regulatory settings. To address this knowledge gap, the authors used an adverse outcome pathway (AOP) analysis, the first AOP for a metal, to identify multiple potential mechanisms of Ni toxicity and their interactions with freshwater aquatic organisms. The analysis considered potential mechanisms of action based on data from a wide range of organisms in aquatic and terrestrial environments on the premise that molecular initiating events for an essential metal would potentially be conserved across taxa. Through this analysis the authors identified 5 potential molecular initiating events by which Ni may exert toxicity on aquatic organisms: disruption of Ca²⁺ homeostasis, disruption of Mg²⁺ homeostasis, disruption of Fe^2+/3+ homeostasis, reactive oxygen species-induced oxidative damage, and an allergic-type response of respiratory epithelia. At the organ level of biological organization, these 5 potential molecular initiating events collapse into 3 potential pathways: reduced Ca²⁺ availability to support formation of exoskeleton, shell, and bone for growth; impaired respiration; and cytotoxicity and tumor formation. At the level of the whole organism, the organ-level responses contribute to potential reductions in growth and reproduction and/or alterations in energy metabolism, with several potential feedback loops between each of the pathways. Overall, the present AOP analysis provides a robust framework for future directed studies on the mechanisms of Ni toxicity and for developing AOPs for other metals. Environ Toxicol Chem 2017;36:1128-1137. © 2016 SETAC.

Immunoproteomic identification and characterization of Ni2+-regulated proteins implicates Ni2+ in the induction of monocyte cell death

Nickel allergy is the most common cause of allergic reactions worldwide, with cutaneous and systemic effects potentially affecting multiple organs. Monocytes are precursors of not only macrophages but also dendritic cells, the most potent activators of nickel hypersensitivity. Monocytes are themselves important antigen-presenting cells, capable of nickel-specific T-cell activation in vivo and in vitro, in addition to being important for immediate innate immune inflammation. To elucidate early Ni²⁺-dependent inflammatory molecular mechanisms in human monocytes, a Ni²⁺-specific proteomic approach was applied. Quantitative two-dimensional (2D) differential gel electrophoresis and Delta2D software analyses coupled with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) revealed that Ni²⁺ significantly regulated 56 protein species, of which 36 were analyzed by MALDI-MS. Bioinformatics analyses of all identified proteins resulted in Ni²⁺-associated functional annotation clusters, such as cell death, metal ion binding, and cytoskeletal remodeling. The involvement of Ni²⁺ in the induction of monocyte cell death, but not T-cell death, was observed at Ni²⁺ concentrations at or above 250 μM. Examination of caspase activity during Ni²⁺-mediated cell death revealed monocytic cell death independent of caspase-3 and -7 activity. However, confocal microscopy analysis demonstrated Ni²⁺-triggered cytoskeletal remodeling and nuclear condensation, characteristic of cellular apoptosis. Thus, Ni²⁺-specific peripheral blood mononuclear cell stimulation suggests monocytic cell death at Ni²⁺ concentrations at or above 250 μM, and monocytic effects on immune regulation at lower Ni²⁺ concentrations.

Auricular Chondritis Caused by Metal Ear Tagging in C57BL/6 Mice

Although it has been shown that auricular chondritis in rats is caused by the use of metal identification ear tags, the pathogenesis remains unclear. Based on the hypothesis that the auricular chondritis is caused by metal ions released from metal identification ear tags, we investigated the pathogenesis in male C57BL/6 mice tagged with metal identification ear tags. Twenty-six weeks after the attachment of the ear tags, visible increases in the thickness of the auricle were observed, and the concentrations of copper and iron in the tagged ears were significantly increased ( P <.05) in the tagged ears compared with the untagged ears. There was up-regulation of metallothionein (MT)-I and MT-II mRNA in the tagged ears, and this was confirmed by immunohistologic staining of the destroyed cartilage. Histopathologically, there were observed severe chondritis with extensive granulomatous inflammation, newly formed cartilage nodules, and osseous metaplasia accompanied by cellular infiltrates, such as CD4 T lymphocyte, macrophages, neutrophils, and mast cells, and expression of Th1 cytokines, such as interferon-gamma, tumor necrosis factor-alpha, and interleukin-2 in the tagged ear. Based on these results, we concluded that the release of copper and iron ions from the metal ear tags played a major role in the onset of auricular chondritis. Subsequent cellular interactions, such as CD4 T cells, macrophages, fibroblasts, and mast cells, mediated by cytokines, such as tumor necrosis factor-alpha and interferon-gamma, caused an autoimmune response that may have led to the progression of auricular chondritis as an autoimmune disease.

The antihistamine olopatadine regulates T cell activation in palladium allergy

Because of its corrosion resistance palladium (Pd) has been widely used in many consumer products ranging from fashion accessories to dental materials. Recently, however, an increase in Pd allergy cases has been reported. Metal allergy is categorized as a Type IV allergy, which is characterized as a delayed-type hypersensitivity reaction in which T cells are known to play an important role; however, the precise mechanism of their action remains unclear. Here we defined the relationship between histamine and the Pd allergic reaction specifically with respect to T cell responses. To verify the effects of histamine on T cells, we examined whether there is a change in IFN-γ production following stimulation of histamine or the antihistamine, olopatadine hydrochloride (OLP), in vitro. In addition, we assessed whether OLP administration affected the degree of footpad swelling or IFN-γ production during the Pd allergy response in mice. We found that histamine stimulation increased IFN-γ production in T cells, specifically enhancing IFN-γ production in CD8(+) T cells compared with CD4(+) T cells. Interestingly, OLP suppressed the production of IFN-γ in CD8(+) T cells, and this compound inhibited footpad swelling and IFN-γ production in mice with Pd allergy. These results suggest that histamine promotes the Type IV allergic reaction and thus, the histamine 1 receptor (H1R) might be useful therapeutic target for treatment of metal allergy.

Titanium: a review on exposure, release, penetration, allergy, epidemiology, and clinical reactivity

Exposure to titanium (Ti) from implants and from personal care products as nanoparticles (NPs) is common. This article reviews exposure sources, ion release, skin penetration, allergenic effects, and diagnostic possibilities. We conclude that human exposure to Ti mainly derives from dental and medical implants, personal care products, and foods. Despite being considered to be highly biocompatible relative to other metals, Ti is released in the presence of biological fluids and tissue, especially under certain circumstances, which seem to be more likely with regard to dental implants. Although most of the studies reviewed have important limitations, Ti seems not to penetrate a competent skin barrier, either as pure Ti, alloy, or as Ti oxide NPs. However, there are some indications of Ti penetration through the oral mucosa. We conclude that patch testing with the available Ti preparations for detection of type IV hypersensitivity is currently inadequate for Ti. Although several other methods for contact allergy detection have been suggested, including lymphocyte stimulation tests, none has yet been generally accepted, and the diagnosis of Ti allergy is therefore still based primarily on clinical evaluation. Reports on clinical allergy and adverse events have rarely been published. Whether this is because of unawareness of possible adverse reactions to this specific metal, difficulties in detection methods, or the metal actually being relatively safe to use, is still unresolved.

Mast cell histamine-mediated transient inflammation following exposure to nickel promotes nickel allergy in mice

We previously reported that allergic responses to nickel (Ni) were minimal in mice deficient in the histamine-forming enzyme histidine decarboxylase (HDC-KO), suggesting an involvement of histamine in allergic responses to Ni. However, it remains unclear how histamine is involved in the process of Ni allergy. Here, we examined the role of histamine in Ni allergy using a murine model previously established by us. Mice were sensitized to Ni by intraperitoneal injection of a NiCl2 -lipopolysaccharide (LPS) mixture. Ten days later, allergic inflammation was elicited by challenging ear-pinnas intradermally with NiCl2 . Then, ear-swelling was measured. Pyrilamine (histamine H1-receptor antagonist) or cromoglicate (mast cell stabilizer) was intravenously injected 1 h before the sensitization or the challenge. In cell-transfer experiments, spleen cells from Ni-sensitized donor mice were intravenously transferred into non-sensitized recipient mice. In both sensitized and non-sensitized mice, 1 mm or more NiCl2 (injected into ear-pinnas) induced transient non-allergic inflammation (Ni-TI) with accompanying mast cell degranulation. LPS did not affect the magnitude of this Ni-TI. Pyrilamine and cromoglicate reduced either the Ni-TI or the ensuing allergic inflammation when administered before Ni-TI (at either the sensitization or elicitation step), but not if administered when the Ni-TI had subsided. Experiments on HDC-KO and H1-receptor-KO mice, and also cell-transfer experiments using these mice, demonstrated histamine's involvement in both the sensitization and elicitation steps. These results suggest that mast cell histamine-mediated Ni-TI promotes subsequent allergic inflammatory responses to Ni, raising the possibility that control of Ni-TI by drugs may be effective at preventing or reducing Ni allergy.

Molecular Mechanisms of Nickel Allergy

Allergic contact hypersensitivity to metals is a delayed-type allergy. Although various metals are known to produce an allergic reaction, nickel is the most frequent cause of metal allergy. Researchers have attempted to elucidate the mechanisms of metal allergy using animal models and human patients. Here, the immunological and molecular mechanisms of metal allergy are described based on the findings of previous studies, including those that were recently published. In addition, the adsorption and excretion of various metals, in particular nickel, is discussed to further understand the pathogenesis of metal allergy.

The elements of life and medicines

Which elements are essential for human life? Here we make an element-by-element journey through the periodic table and attempt to assess whether elements are essential or not, and if they are, whether there is a relevant code for them in the human genome. There are many difficulties such as the human biochemistry of several so-called essential elements is not well understood, and it is not clear how we should classify elements that are involved in the destruction of invading microorganisms, or elements which are essential for microorganisms with which we live in symbiosis. In general, genes do not code for the elements themselves, but for specific chemical species, i.e. for the element, its oxidation state, type and number of coordinated ligands, and the coordination geometry. Today, the biological periodic table is in a position somewhat similar to Mendeleev's chemical periodic table of 1869: there are gaps and we need to do more research to fill them. The periodic table also offers potential for novel therapeutic and diagnostic agents, based on not only essential elements, but also non-essential elements, and on radionuclides. Although the potential for inorganic chemistry in medicine was realized more than 2000 years ago, this area of research is still in its infancy. Future advances in the design of inorganic drugs require more knowledge of their mechanism of action, including target sites and metabolism. Temporal speciation of elements in their biological environments at the atomic level is a major challenge, for which new methods are urgently needed.

Nickel ions selectively inhibit lipopolysaccharide-induced interleukin-6 production by decreasing its mRNA stability

Nickel (Ni) ions easily elute from many alloys and elicit inflammation and allergies. Previous studies have shown that infections due to the implantation of medical devices cause inflammation and enhance the elution of Ni ions (Ni²⁺). However, cross-talk between infection- and Ni²⁺-induced signaling pathways has not yet been elucidated in detail. In the present study, we investigated the effects of Ni2+ on the lipopolysaccharide (LPS)-induced production of cytokines in a LPS-induced air pouch-type inflammation model in BALB/c mice and the murine macrophage cell line RAW264. We demonstrated that Ni²⁺ inhibited the LPS-induced production of interleukin (IL)-6, but not that of tumor necrosis factor (TNF)-α both in vivo and in vitro. This inhibitory effect was also observed with cobalt ion (Co²⁺), but not with chloride ion (Cl⁻), zinc ion (Zn²⁺), or palladium ion (Pd²⁺), and was highly selective to the production of IL-6. Ni²⁺ did not inhibit the activation of ERK1/2, p38 MAPK, or JNK. Although Ni²⁺ decreased IL-6 mRNA levels, it failed to inhibit the LPS-induced activation of the IL-6 promoter. An experiment using actinomycin D, a transcription inhibitor, revealed that Ni²⁺ decreased the stability of IL-6 mRNA. Moreover, Ni²⁺ inhibited the LPS-induced expression of Arid5a, but not regnase-1. These results demonstrated that Ni²⁺ may have selectively inhibited the LPS-induced production of IL-6 by decreasing the Arid5a-dependent stabilization of IL-6 mRNA.

The effect of haptens on protein-carrier immunogenicity

The immune response against hapten is T-cell-dependent, and so requires the uptake, processing and presentation of peptides on MHC class II molecules by antigen-presenting cells to the specific T cell. Some haptens, following conjugation to the available free amines on the surface of the carrier protein, can reduce its immunogenicity. The purpose of this study was to explore the mechanism by which this occurs. Four proteins were tested as carriers and six molecules were used as haptens. The immune response to the carrier proteins was reduced > 100-fold by some of the haptens (termed carrier immunogenicity reducing haptens--CIRH), whereas other haptens did not influence the protein immunogenicity (carrier immunogenicity non-reducing haptens--nCIRH). Conjugation of the protein to a CIRH affected protein degradation by lysosomal cathepsins, leading to the generation of peptides that differ in length and sequence from those derived from the same native protein or that protein modified with nCIRH. Injection of CIRH-conjugated protein into mice induced an increase in the population of regulatory T cells. The results of this study provide a putative mechanism of action for the reduction of immune response to haptenated proteins.

The lymphocyte transformation test in allergic contact dermatitis: New opportunities

Allergic contact dermatitis (ACD) is driven by the activation and proliferation of allergen-specific memory T-lymphocytes and is currently diagnosed by patch testing with a selected panel of chemical allergens. The lymphocyte transformation test (LTT) can be used to monitor ex vivo T-lymphocyte responses to antigens, including contact allergens. The LTT is not viewed as being an alternative to patch testing, but it does seek to reflect experimentally skin sensitization to specific chemicals. The LTT is based on stimulation in vitro of antigen-driven T-lymphocyte proliferation. That is, exposure in culture of primed memory T-lymphocytes to the relevant antigen delivered in an appropriate configuration will provoke a secondary response that reflects the acquisition of skin sensitization. The technical aspects of this test and the utility of the approach for investigation of immune responses to contact allergens in humans are reviewed here, with particular emphasis on further development and refinement of the protocol. An important potential application is that it may provide a basis for characterizing those aspects of T-lymphocyte responses to contact allergens that have the greatest influence on skin sensitizing potency and this will be considered in some detail.

Setting Occupational Exposure Limits for Chemical Allergens--Understanding the Challenges

Chemical allergens represent a significant health burden in the workplace. Exposures to such chemicals can cause the onset of a diverse group of adverse health effects triggered by immune-mediated responses. Common responses associated with workplace exposures to low molecular weight (LMW) chemical allergens range from allergic contact dermatitis to life-threatening cases of asthma. Establishing occupational exposure limits (OELs) for chemical allergens presents numerous difficulties for occupational hygiene professionals. Few OELs have been developed for LMW allergens because of the unique biological mechanisms that govern the immune-mediated responses. The purpose of this article is to explore the primary challenges confronting the establishment of OELs for LMW allergens. Specific topics include: (1) understanding the biology of LMW chemical allergies as it applies to setting OELs; (2) selecting the appropriate immune-mediated response (i.e., sensitization versus elicitation); (3) characterizing the dose (concentration)-response relationship of immune-mediated responses; (4) determining the impact of temporal exposure patterns (i.e., cumulative versus acute exposures); and (5) understanding the role of individual susceptibility and exposure route. Additional information is presented on the importance of using alternative exposure recommendations and risk management practices, including medical surveillance, to aid in protecting workers from exposures to LMW allergens when OELs cannot be established.

Structural basis of chronic beryllium disease: linking allergic hypersensitivity and autoimmunity

T-cell-mediated hypersensitivity to metal cations is common in humans. How the T cell antigen receptor (TCR) recognizes these cations bound to a major histocompatibility complex (MHC) protein and self-peptide is unknown. Individuals carrying the MHCII allele, HLA-DP2, are at risk for chronic beryllium disease (CBD), a debilitating inflammatory lung condition caused by the reaction of CD4 T cells to inhaled beryllium. Here, we show that the T cell ligand is created when a Be(2+) cation becomes buried in an HLA-DP2/peptide complex, where it is coordinated by both MHC and peptide acidic amino acids. Surprisingly, the TCR does not interact with the Be(2+) itself, but rather with surface changes induced by the firmly bound Be(2+) and an accompanying Na(+) cation. Thus, CBD, by creating a new antigen by indirectly modifying the structure of preexisting self MHC-peptide complex, lies on the border between allergic hypersensitivity and autoimmunity.

Toluene diisocyanate (TDI) disposition and co-localization of immune cells in hair follicles

Diisocyanates (dNCOs) are potent chemical allergens utilized in various industries. It has been proposed that skin exposure to dNCOs produces immune sensitization leading to work-related asthma and allergic disease. We examined dNCOs sensitization by using a dermal murine model of toluene diisocyanate (TDI) exposure to characterize the disposition of TDI in the skin, identify the predominant haptenated proteins, and discern the associated antigen uptake by dendritic cells. Ears of BALB/c mice were dosed once with TDI (0.1% or 4% v/v acetone). Ears and draining lymph nodes (DLNs) were excised at selected time points between 1 h and 15 days post-exposure and were processed for histological, immunohistochemical, and proteomic analyses. Monoclonal antibodies specific for TDI-haptenated protein (TDI-hp) and antibodies to various cell markers were utilized with confocal microscopy to determine co-localization patterns. Histopathological changes were observed following exposure in ear tissue of mice dosed with 4% TDI/acetone. Immunohistochemical staining demonstrated TDI-hp localization in the stratum corneum, hair follicles, and sebaceous glands. TDI-hp were co-localized with CD11b(+) (integrin αM/Mac-1), CD207(+) (langerin), and CD103(+) (integrin αE) cells in the hair follicles and in sebaceous glands. TDI-hp were also identified in the DLN 1 h post-exposure. Cytoskeletal and cuticular keratins along with mouse serum albumin were identified as major haptenated species in the skin. The results of this study demonstrate that the stratum corneum, hair follicles, and associated sebaceous glands in mice are dendritic cell accessible reservoirs for TDI-hp and thus identify a mechanism for immune recognition following epicutaneous exposure to TDI.