Persistent immune tolerance to nickel and chromium by oral administration prior to cutaneous sensitization

Nickel Allergy: Epidemiology, Pathomechanism, Clinical Patterns, Treatment and Prevention Programs

Nickel is the most common cause of contact allergy in the general population and the most frequently detected allergen in patients patch tested for suspected allergic contact dermatitis (ACD). ACD from nickel is a typical type IV hypersensitivity. Nickel allergy is mostly caused by nonoccupational exposure, such as jewelry and clothing decorations, metal tools, medical devices (mainly orthopedic and orthodontic implants, cardiovascular prosthesis), eyeglasses, utensils, keys, pigment for paint, cosmetics, and food (mainly legumes, chocolate, salmon, peanuts). Occupational exposure can involve several workers (mechanics, metalworkers, platers, hairdressers, jewelers, workers in the constructions and electronic industries), classically involving hands and forearms. The classic clinical pattern of ACD caused by nickel is characterized by eczematous dermatitis involving the sites of direct contact with the metal. Non-eczematous-patterns are reported, including lichenoid dermatitis, granuloma annulare, vitiligo-like lesions, dyshidrosiform dermatitis, and vasculitis. In the case of systemic exposure to nickel, sensitized patients could develop systemic contact dermatitis. Patch testing represents the gold standard for the diagnosis of ACD from nickel. Treatment includes avoidance of contact with products containing nickel and the patient's education about the possible use of alternative products. A recent EU nickel directive, regulating the content and release of nickel from products, has caused a decrease of nickel contact allergy in some European countries. Nickel allergy is a relevant issue of public health with significant personal, social, and economic impact. This review summarizes epidemiology, pathomechanism, clinical patterns, treatment, and prevention programs.

Allergic contact dermatitis pattern in Kuwait: nickel leads the pack. In-depth analysis of nickel allergy based on the results from a large prospective patch test series report

INTRODUCTION

Contact dermatitis is a relatively common dermatosis reported among several population groups from all around the globe. However, the data from Kuwait is unavailable. Patch tests are essential for the diagnosis of contact sensitization.

AIM

To determine a relative frequency and pattern of sensitizers to different allergens in patients of suspected contact dermatitis in Kuwait and, also to study the role of the commonest sensitizer in detail.

MATERIAL AND METHODS

Patch tests were performed in 2461 consecutive patients with a clinical diagnosis of contact dermatitis seen at our hospital between September 1, 2014 and August 31, 2015. Out of the total of 1381 (56.1%) patients with positive patch test results to at least one allergen, 546 (22.2%) patients with a single positive reaction to nickel only (single largest sensitizer) were selected as the study population for further detailed analysis.

RESULTS

At least one positive patch test reaction was found in 1381 (56.12%) patients. Nickel was found to be the most common sensitizer seen in 546 (40%) patients. The mean age was 37.3 ±13.8 years and the mean duration of disease was 27.3 ±13.8 months. Most (387/546) patients sensitized were females. The forearms/hands and wrists were the most prevalent sites (52.56% of the participants). In 58.91% of women, dermatitis was more often confined to other sites, mostly ears and the neck due to earrings and necklaces. Just more than half of the number (51.09%) of nickel allergic patients were found in the age group of 15-25 years. Hairdressers/beauticians were the most affected group followed by house workers (housewives, cleaners, housekeepers).

CONCLUSIONS

Nickel is the single most common sensitizer found in our patients, and female sex, young age, occupation with long hours of contact to nickel are high risk factors. We recommend that a directive, which limits the release of nickel from products with extended skin contact, be approved in Kuwait.

Immunotherapy of allergic contact dermatitis

The term 'immunotherapy' refers to treating diseases by inducing, enhancing or suppressing immune responses. As allergy is an excessive, detrimental immune reaction to otherwise harmless environmental substances, immunotherapy of allergic disease is aimed at the induction of tolerance toward sensitizing antigens. This article focuses on the historical developments, present state and future outlook for immunotherapy with haptens as a therapeutic modality for allergic contact dermatitis. Inspired by the effectiveness of immunotherapy in respiratory allergies, attempts were undertaken at curing allergic contact dermatitis by means of controlled administration of the sensitizing haptens. Animal and human experiments confirmed that tolerance to haptens can be induced most effectively when the induction of tolerance precedes attempted sensitization. In real life, however, therapy is sought by people who are already sensitized and an effective reversal of hypersensitivity seems more difficult to achieve. Decades of research on Rhus hypersensitivity led to a conclusion that immunotherapy can suppress Rhus dermatitis, however, only to a limited degree, for a short period of time, and at a high risk of side effects, which makes this method therapeutically unprofitable. Methodological problems with most available studies of immunotherapy of contact allergy to nickel make any definite conclusions impossible at this stage.

Does hapten exposure predispose to atopic disease? The hapten-atopy hypothesis

Contact allergy data indicates that atopics have heightened oral tolerance to haptens (chemical allergens). We speculate here, that artificially increased oral exposure to chemicals compete with dietary proteins for the development of oral tolerance, predisposing to the acquisition of food protein allergy and representing one driver for the increasing prevalence of protein allergy and/or atopy. Hapten exposure via other surfaces such as the skin and airways might also be important in promoting atopic disease. Consistent with this hypothesis it is notable that over 40 years, with the huge increase in atopic disease, there has also been an increase in dietary hapten exposure through processed food, formula milk and oral antibiotic and drug use.

Reduced frequency of atopic dermatitis in quinoline-allergic patients: the 'hapten-atopy hypothesis'

BACKGROUND

While allergy to food proteins is almost exclusively found in association with atopy, it has been our experience that contact allergy to some contact allergens/haptens with both cutaneous and gastrointestinal exposures is reduced in atopic dermatitis (AD) patients as a group.

OBJECTIVE

To assess the contact allergy rates of two classes of antimicrobial haptens, one with both cutaneous and gastrointestinal exposures (quinolines) and one with only significant cutaneous exposure (aminoglycosides), with respect to the presence or absence of AD.

METHODS

Contact allergy rates to neomycin (aminoglycoside) and quinoline mix/clioquinol in patients attending the St John's Institute of Dermatology for diagnostic patch testing were retrospectively analysed; current AD and history of AD were noted.

RESULTS

In comparison to neomycin-allergic subjects, there was a highly significant negative association between quinoline contact allergy and current presence of AD (P = 0.0028); negative association between quinoline contact allergy and a history of AD did not reach significance (P = 0.07).

CONCLUSIONS

In comparison to an antimicrobial with no significant gastrointestinal exposure (neomycin), contact allergy to quinolines is negatively associated with the presence of AD. This is in contrast to food protein allergy, which is strongly associated with atopy. Possible explanations could include (i) confounding factors or (ii) AD patients are efficient at orally tolerizing haptens and inefficient at orally tolerizing proteins, secondary to their atopic status or (iii) oral tolerance of haptens antagonizes tolerance of food proteins and also leads to an immunological shift towards atopy (hapten-atopy hypothesis).

Oral tolerance to contact allergens: a common occurrence? A review

Experimental and clinical oral tolerance to contact allergens has been reported sporadically, most notably in respect of nickel, and is generally assumed to be an uncommon phenomenon. There has recently been increased understanding of the immunological mechanisms inducing and maintaining oral tolerance. There are several contact allergens, including fragrance, antioxidant, and preservative chemicals, to which subjects are exposed through both cutaneous and oral routes. We examine the possibility that oral tolerance to contact allergens may be more common than previously thought. Animal models of oral tolerance to contact allergens indicate that cutaneous exposure to small, subsensitizing doses of contact allergens might negate any subsequent attempts to induce tolerance by oral administration. Extrapolating these observations to common human practises raises the possibility that application of contact allergens (fragrances, preservatives and antioxidants) in consumer products used by children could prevent or inhibit the later acquisition of specific tolerance resulting from 'natural' dietary exposure after weaning. Existing data on formaldehyde may conflict with this theory, though this could be explained by allergen specificity. We propose that further work in this area is needed.

Intrinsic characteristics of contact and respiratory allergens influence production of polarizing cytokines by dendritic cells

Type 1 and type 2 cytokines are primary mediators in contact allergy and aeroallergen-mediated disorders, respectively. For both types of disease, dendritic cells (DCs) are pivotal in initiating immune hyperresponsiveness. We studied whether contact and respiratory allergens possess intrinsic capacities to polarize DC towards DC1 and DC2 functions, independent of environmental factors. Human monocyte-derived DCs were exposed to the positive controls [type 1: lipopolysaccharide (LPS) + interferon-gamma; type 2: LPS + prostaglandin E(2)], contact allergens [2,4-dinitrochlorobenzene (DNCB), oxazolone (OXA), and nickel sulfate (NiSO(4))], and respiratory allergens [trimellitic anhydride (TMA) and the protein allergen derived from Dermatophagoides pteronyssinus (Der p1)]. The polarizing potentials of the allergens on DCs were determined by the secretion of type 1 [tumour necrosis factor-alpha (TNF-alpha), CXCL10, and interleukin (IL)-12p70] and type 2 (IL-10) cytokines. The contact allergens, DNCB and OXA, induced strict type 1 DC polarization, whereas the respiratory allergens, TMA and Der p1, showed strict type 2 DC polarization. The contact allergen, NiSO(4), induced both DC1 (TNF-alpha and CXCL10 production) and DC2 (decreased IL-12p70/IL-10 ratio) features. These results support the view that allergens have an intrinsic capacity to skew immune responses at the DC level, irrespective of local factors such as those determined by cutaneous or mucosal epithelial microenvironments.

Dendritic cells at the oral mucosal interface

The mucosal lining of the respiratory and digestive systems contains the largest and most complex immune system in the body, but surprisingly little is known of the immune system that serves the oral mucosa. This review focuses on dendritic cells, particularly powerful arbiters of immunity, in response to antigens of microbial or tumor origin, but also of tolerance to self-antigens and commensal microbes. Although first discovered in 1868, the epidermal dendritic Langerhans cells remained enigmatic for over a century, until they were identified as the most peripheral outpost of the immune system. Investigators' ability to isolate, enrich, and culture dendritic cells has led to an explosion in the field. Presented herein is a review of dendritic cell history, ontogeny, function, and phenotype, and the role of different dendritic cell subsets in the oral mucosa and its diseases. Particular emphasis is placed on the mechanisms of recognition and capture of microbes by dendritic cells. Also emphasized is how dendritic cells may regulate immunity/tolerance in response to oral microbes.

Dermal nickel exposure associated with coin handling and in various occupational settings: assessment using a newly developed finger immersion method

BACKGROUND

The role of nickel in causing hand dermatitis in some occupations has been difficult to assess due to problems with reliable measurement of the exposure to nickel in the workplace and lack of a definitive threshold for nickel allergic contact dermatitis. It is not uncommon to find nickel allergy on patch testing but it is difficult to determine whether this is of relevance to occupational nickel exposure or simply a reflection of past exposure to nickel-plated jewellery or other nonoccupational nickel exposure.

OBJECTIVES

To devise a simple and reproducible method to quantify the amount of nickel on the skin and to apply the technique to measure dermal nickel exposure in various occupational settings.

METHODS

A rapid and simple sampling procedure was developed for determination of nickel on the skin of workers potentially exposed to nickel by exposing individuals to nickel-releasing coins and measuring exposure by immersing the exposed thumbs and index fingers directly into graduated sample tubes containing ultrapure water and aqueous nickel extracts. The solutions were analysed by inductively coupled plasma-optical emission spectrometry after stabilization with nitric acid. The method shows advantages over alternatives such as wipe testing and tape stripping in terms of extraction efficiency, speed and ease of operation in the field. A pilot survey of dermal nickel exposure for workers in several occupational settings was conducted.

RESULTS

The study suggested that a 'normal' level of nickel on the skin is <10 ng cm(-2). Coin handling induced an appreciable increase in the amount of nickel on the skin within 2 min. Experiments indicated a linear relationship between coin handling (exposure time) and measured dermal nickel levels following standardized coin handling. A pilot survey, conducted among cashiers, shop assistants, bar staff, hairdressers and workers in the nickel industry revealed dermal nickel concentrations ranging from <0.9 to 7160 ng cm(-2). The levels of nickel on the skin of cashiers, shop assistants, bar staff and hairdressers were below the threshold level for water-soluble ionic nickel for occluded exposure at which 10% of nickel-allergic subjects react (0.01% or 100 parts per million, equivalent to 530 ng cm(-2)) and the five-times higher threshold for unoccluded exposure (500 parts per million). The levels in some nickel platers and nickel refinery workers approached or exceeded these levels. However, few cases of nickel dermatitis are observed in plating and refinery facilities, perhaps due to immune tolerance, self-selection or, for refinery workers, exposure to water-insoluble rather than water-soluble nickel compounds. The elicitation threshold for water-soluble nickel compounds cannot be compared directly with dermal exposure to water-insoluble nickel compounds as the latter release a significantly lesser amount of nickel ions.

CONCLUSIONS

We describe a reproducible, simple and rapid procedure for the assessment of nickel levels in occupationally exposed individuals.

Oral tolerance

Multiple mechanisms of tolerance are induced by oral antigen. Low doses favor active suppression, whereas higher doses favor clonal anergy/deletion. Oral antigen induces T-helper 2 [interleukin (IL)-4/IL-10] and Th3 [transforming growth factor (TGF)-beta] T cells plus CD4+CD25+ regulatory cells and latency-associated peptide+ T cells. Induction of oral tolerance is enhanced by IL-4, IL-10, anti-IL-12, TGF-beta, cholera toxin B subunit, Flt-3 ligand, and anti-CD40 ligand. Oral (and nasal) antigen administration suppresses animal models of autoimmune diseases including experimental autoimmune encephalitis, uveitis, thyroiditis, myasthenia, arthritis, and diabetes in the non-obese diabetic (NOD) mouse, plus non-autoimmune diseases such as asthma, atherosclerosis, graft rejection, allergy, colitis, stroke, and models of Alzheimer's disease. Oral tolerance has been tested in human autoimmune diseases including multiple sclerosis (MS), arthritis, uveitis, and diabetes and in allergy, contact sensitivity to dinitrochlorobenzene (DNCB), and nickel allergy. Although positive results have been observed in phase II trials, no effect was observed in phase III trials of CII in rheumatoid arthritis or oral myelin and glatiramer acetate (GA) in MS. Large placebo effects were observed, and new trials of oral GA are underway. Oral insulin has recently been shown to delay onset of diabetes in at-risk populations, and confirmatory trials of oral insulin are being planned. Mucosal tolerance is an attractive approach for treatment of autoimmune and inflammatory diseases because of lack of toxicity, ease of administration over time, and antigen-specific mechanisms of action. The successful application of oral tolerance for the treatment of human diseases will depend on dose, developing immune markers to assess immunologic effects, route (nasal versus oral), formulation, mucosal adjuvants, combination therapy, and early therapy.

[Tolerance induction towards nickel. From animal model to humans]

Nickel is the most common contact allergen in humans. Until recently, many questions concerning tolerance mechanisms to nickel were unresolved. Besides human ex vivo, intervention and observation studies, the establishment of a reproducible mouse model has contributed to the analysis of these mechanisms. A more detailed understanding of the pathogenesis of nickel allergy and tolerance towards nickel by investigations in an animal model and in human studies is a prerequisite for developing specific prevention and therapy of nickel allergy. With this article, we provide a review of the investigations concerning nickel allergy and give perspectives towards oral tolerance induction to nickel in the animal model and in humans.

Decrease in nickel sensitization in a Danish schoolgirl population with ears pierced after implementation of a nickel-exposure regulation

BACKGROUND

To reduce the skin nickel exposure of the population, the Danish Ministry of Environment issued a regulation that was implemented in 1992, and the European Union countries have recently adopted an expanded regulation.

OBJECTIVES

The aim of our combined patch testing and questionnaire investigation of girls in public schools and high schools/production schools was to evaluate whether the regulation has had an impact on the prevalence of nickel sensitization.

METHODS

To find a group of girls with ears pierced mainly after implementation of the nickel-exposure regulation in Denmark, girls were recruited from the fifth and sixth grade in 12 public schools (the public school group). After the public school level almost all girls from a public school population continue their education in high schools or other schools such as production schools or technical schools. Therefore, to find girls demographically similar to the public school girls but older, and with ears pierced before implementation of the regulation, girls from seven high schools and two production schools were recruited (the high school group). Four hundred and twenty-seven girls in the public school group (mean age 12.4 years, range 10-14) and 534 in the high school group (mean age 18.8 years, range 17-22) participated. All participants filled out a questionnaire concerning ear piercing, use of oral braces and former patch testing for nickel sensitivity. Three hundred and five girls (71.4%) in the public school group and 275 (51.5%) in the high school group were patch tested or had been tested previously and the results of these tests were included in the study. The relation between the frequency of nickel sensitization and the various factors that might influence the prevalence of nickel sensitization was evaluated by multivariate logistic regression analysis. The investigation was conducted from March 1999 to March 2000.

RESULTS

The study showed that both increasing age and having ears pierced before 1992 enhanced the prevalence of nickel sensitization. We found that 17.1% of the girls in the high school group demonstrated a positive patch test reaction to nickel. In contrast, the prevalence of nickel sensitization in the public school group was only 3.9%. Comparing girls with and without pierced ears, the prevalence of nickel sensitization was significantly higher in girls with ears pierced before, but not after, 1992 (odds ratio 3.34 and 1.20, respectively). Only in the high school group was there a tendency that wearing oral braces before ear piercing had a protective effect on nickel sensitization, but this did not reach statistical significance.

CONCLUSIONS

As we found an effect of ear piercing before but not after 1992, this study strongly suggests that implementation of the nickel-exposure regulation in 1992 in Denmark has had the intended effect of protecting the female population from becoming allergic to nickel.

Tolerance to nickel: oral nickel administration induces a high frequency of anergic T cells with persistent suppressor activity

We adapted our mouse model of allergic contact hypersensitivity to nickel for the study of tolerance. Sensitization in this model is achieved by the administration of nickel ions with H(2)O(2); nickel ions alone are unable to prime naive T cells, but can restimulate primed ones. A 4-wk course of oral or i.p. administration of 10 mM NiCl(2) to naive mice induced tolerance, preventing the induction of hypersensitivity for at least 20 wk; long term desensitization of nickel-sensitized mice, however, required continuous NiCl(2) administration. When splenic T cells of orally tolerized donors, even after a treatment-free interval of 20 wk, were transferred to naive recipients, as with lymph node cells (LNC), they specifically prevented sensitization of the recipients. The LNC of such donors were anergic, because upon in vivo sensitization with NiCl(2) in H(2)O(2) and in vitro restimulation with NiCl(2), they failed to show the enhanced proliferation and IL-2 production as seen with LNC of mice not tolerized before sensitization. As few as 10(2) bulk T cells, consisting of both CD4(+) and CD8(+) cells, were able to specifically transfer tolerance to nickel. A hypothesis is provided to account for this extraordinarily high frequency of nickel-reactive, suppressive T cells; it takes into account that nickel ions fail to act as classical haptens, but form versatile, unstable metal-protein and metal-peptide complexes. Furthermore, a powerful amplification mechanism, such as infectious tolerance, must operate which allows but a few donor T cells to tolerize the recipient.

Induction of tolerance and cross-tolerance to methacrylate contact sensitizers

Induction of immunological tolerance to contact allergens might prevent undesired sensitization, in particular to occupational sensitizers, e.g., methacrylates (MA). Here, using a guinea pig model, we studied to which extent tolerance to one methacrylate might result in cross-tolerance to other congeners. Strong tolerance to the monomethacrylates hydroxy-ethyl MA (HEMA) and methyl MA, but not to the dimethacrylate ethylene-glycol MA (EGDMA) could be induced. The induced tolerance was stable, could not be broken by repeated sensitization attempts, and was mediated by specific suppressor cells, as demonstrated in T cell transfer experiments. In HEMA-tolerized animals, strong cross-tolerance to methacrylate congeners, including EGDMA, itself being nontolerogenic and showing the lowest cross-reactivity to HEMA, was found. Thus, oral application of contact allergens, to which skin contact cannot be avoided, e.g., in occupational settings, can induce broad cross-tolerance to related substances and might offer a promising preventive approach.

Bone healing and mineralization, implant corrosion, and trace metals after nickel-titanium shape memory metal intramedullary fixation

Its shape memory effect, superelasticity, and good wear and damping properties make the NiTi shape memory alloy a material with fascinating potential for orthopedic surgery. It provides a possibility for making self-locking, self-expanding, and self-compressing implants. Problems, however, may arise because of its high nickel content. The purpose of this work was to determine the corrosion of NiTi in vivo and to evaluate the possible deleterious effects of NiTi on osteotomy healing, bone mineralization, and the remodeling response. Femoral osteotomies of 40 rats were fixed with either NiTi or stainless steel (StSt) intramedullary nails. The rats were killed at 2, 4, 8, 12, 26, and 60 weeks. Bone healing was examined with radiographs, peripheral quantitative computed tomography, (pQCT) and histologically. The corrosion of the retrieved implants was analyzed by electron microscopy (FESEM). Trace metals from several organs were determined by graphite furnace atomic absorption spectrometry (GF-AAS) or by inductively coupled plasma-atomic emission spectrometry (ICP-AES). There were more healed bone unions in the NiTi than in the StSt group at early (4 and 8 weeks) time points. Callus size was equal between the groups. The total and cortical bone mineral densities did not differ between the NiTi and StSt groups. Mineral density in both groups was lower in the osteotomy area than in the other areas along the nail. Density in the nail area was lower than in the proximal part of the operated femur or the contralateral femur. Bone contact to NiTi was close. A peri-implant lamellar bone sheet formed in the metaphyseal area after 8 weeks, indicating good tissue tolerance. The FESEM assessment showed surface corrosion changes to be more evident in the StSt implants. There were no statistically significant differences in nickel concentration between the NiTi and StSt groups in any of the organs. NiTi appears to be an appropriate material for further intramedullary use because it has good biocompatibility in bone tissue.

Comparison of personal history with patch test results in metal allergy

In order to compare the validity of patient personal history of contact sensitivity to metal alloys with patch test results, 160 patients with hand eczema were patch tested with a standard series according to the ICDRG after a special questionnaire. In 65%, history and patch test results were identical. Seventy-eight (48.8%) patients thought they would be allergic to metal ions, whereas the patch test revealed a positive result in only 21.3% cases. Positive history but negative test was more frequent in women; in the male group, negative history and positive patch test was the most common finding. Although 82 patients had a negative history, the patch test was positive for contact sensitivity to metal allergens in 12 of them. Both false positive patch tests and false negative histories are possible. Since many factors influence a positive patch test, not only the patient's history but also a synopsis of the anamnesis and patch testing will help to achieve the correct diagnosis of metal contact hypersensitivity.

Biocompatibility of nickel-titanium shape memory metal and its corrosion behavior in human cell cultures

Nickel-titanium alloy (Nitinol) is a metallic biomaterial that has a unique thermal shape memory, superelasticity, and high damping properties. Nitinol is potentially very useful in orthopedic surgery, for example. At present, there are not enough confirmative biocompatibility data available on Nitinol. The aim of our study was to clarify the primary cytotoxicity and corrosion rate of Nitinol in human cell cultures. Comparisons were made with stainless steel (Stst), titanium (Ti), composite material (C), and control cultures with no test discs. Human osteoblasts (OB) and fibroblasts (FB) were incubated for 10 days with test discs of equal size, 6 x 7 mm. The cultures were photographed and the cells counted. Samples from culture media were collected on days 2, 4, 6, and 8, and the analysis of metals in the media was done using flameless atomic absorption spectrophotometry. The proliferation of FB was 108% (Nitinol), 134% (Ti) (p < 0.02), 107% (Stst), and 48% (C)(p < 0.0001) compared to the control cultures. The proliferation of OB was 101% (Nitinol), 100% (Ti), 105% (Stst), and 54% (C) (p < 0.025) compared to the controls. Initially, Nitinol released more nickel (129-87 micrograms/L) into the cell culture media than Stst (7 micrograms/L), but after 2 days the concentrations were about equal (23-5 micrograms/L versus 11-1 micrograms/L). The titanium concentrations from both Nitinol and Ti samples were all < 20 micrograms/L. We conclude that Nitinol has good in vitro biocompatibility with human osteoblasts and fibroblasts. Despite the higher initial nickel dissolution, Nitinol induced no toxic effects, decrease in cell proliferation, or inhibition on the growth of cells in contact with the metal surface.

Assessment of the sensitization potential of five metal salts in the murine local lymph node assay

The murine local lymph node assay (LLNA) has been proposed as a predictive test for the identification of sensitizing agents. We used this test to compare the sensitization potential of NiSO4, K2Cr2O7, CoCl2, Na2PtCl6 and BeSO4, salts of metals which have all been associated with allergic contact dermatitis and either bronchial asthma orinterstitial lung disease, by either humoral or cell-mediated allergic mechanisms. BALB/c mice (n = 3 per concentration studied, three concentrations studied per metal) received three daily applications of the metal salt (in DMSO) on the dorsum of both ears. On the fourth day the draining auricular lymph nodes were removed and the incorporation of [3H]-thymidine in the lymphocytes in culture was compared to that of concurrent vehicle-treated control mice, thus enabling to derive a stimulation index (SI), indicative of immunological sensitization potential. Each experiment was performed three times. Oxazolone and toluene diisocyanate, chosen as positive controls, yielded strongly positive SI values (> 20 and > 30 respectively). Na2PtCl6 (SI 2.6 +/- 1.0 at 2.5%), CoCl2 (SI 2.8 +/- 0.5 at 5%) and possibly also K2Cr2O7 (SI 2.1 +/- 1.2 at 0.5%) were positive in the LLNA, whereas NiSO4 (SI 0.9 +/- 0.2 at 5%) and BeSO4 (SI 1.3 +/- 0.6 at 4%) were negative. Although our results are still limited by the fact that only one mice strain was tested, they indicate that there is no strict relationship between the sensitization potential of metal salts, as evaluated in the murine LLNA, and their potential to cause either respiratory or dermal allergic disease. Consequently, caution should be exercised before proposing the murine LLNA as a valid test to predict the sensitization potential of low molecular weight chemicals.

Lack of oral tolerance but oral priming for contact sensitivity to dinitrofluorobenzene in major histocompatibility complex class II-deficient mice and in CD4+ T cell-depleted mice

Oral tolerance is defined by immune unresponsiveness after oral administration of soluble antigens and by antigen-specific inhibition of peripheral immune responses induced by prior antigen feeding. The aim of this study was to investigate the implication of the major histocompatibility complex (MHC) class II presentation pathway to CD4+ T cells in oral tolerance of contact sensitivity (CS) to the hapten dinitrofluorobenzene (DNFB). We used MHC class II knockout (AB0/0) and invariant chain knockout (Ii0/0) mice, which have, respectively, a total or partial defect in class II-restricted activation of CD4+ T cells, as well as normal C57BL/6 mice depleted of CD4+ T cells by injection of a specific antibody. Intragastric administration of DNFB prior to skin sensitization induced specific inhibition of contact sensitivity to DNFB in A beta +/0 and Ii+/0 heterozygotes comparable to that observed in C57BL/6 mice. In contrast, no oral tolerance was observed in either MHC class II-deficient A beta 0/0 and Ii0/0 homozygote mutants or in syngeneic anti-CD4-depleted C57Bl/6 mice. Moreover, a single oral administration of DNFB, without skin sensitization, could prime A beta 0/0, Ii0/0 as well as anti-CD4-depleted C57BL/6 mice for DNFB-specific CS. These findings demonstrate that the class II/CD4 pathway is involved in oral tolerance manifested both as the inhibition of CS by hapten feeding prior to skin sensitization, and as immune unresponsiveness of normal mice to oral administration of hapten. Furthermore, our data provide evidence that a single oral feeding with DNFB is able to prime mice for hapten-specific CS, provided that the class II/ CD4 pathway is bypassed.

Oral tolerance is determined at the level of draining lymph nodes

In the skin and in the epithelium of the oral mucosa a comparable network of Langerhans cells can be found. Antigen application on either epithelium leads to rapid emigration of Langerhans cells to the draining lymph nodes. Application on the oral mucosa leads to tolerance induction while application on the skin results in sensitization of the animal. Here we show that there are no differences in the antigen presentation capacity of oral mucosa- and skin-derived dendritic cells. However, measurement of IFN-gamma and IL-5 production, as representatives of Th1 and Th2 cytokines respectively, in total lymph node suspensions after sensitization via the skin or oral mucosa demonstrated a skewing of the response towards Th2 after antigen application on the oral mucosa. Together with our previous studies, in which it was shown that oral tolerance induction is not inherent to oral mucosa-derived dendritic cells, we postulate that oral tolerance is determined at the level of draining lymph nodes influenced by local cytokine profiles.

Oral tolerance to haptens: intestinal epithelial cells from 2,4-dinitrochlorobenzene-fed mice inhibit hapten-specific T cell activation in vitro

The mechanisms underlying the induction of immunological tolerance after feeding soluble exogenous antigens, including proteins and haptens, are still unclear. Using a model of oral tolerance to the contact-sensitizing hapten 2,4-dinitrochlorobenzene (DNCB), we have compared the ability-of intestinal epithelial cells and of Peyer's patch APC to present DNCB in vitro or ex vivo after oral feeding, to specific peripheral lymph node T cells from DNCB-sensitized mice. In contrast to Peyer's patch APC, which induce efficient hapten-specific T cell activation upon exposure to the hapten either in vitro or in vivo, mature MHC class-II-positive intestinal epithelial cells were unable to induce T cell activation in either case. Interestingly, enterocytes from DNCB-fed mice exerted a dramatic inhibitory effect on the proliferative response of hapten-primed T cells in response to dinitrobenzene sulfonate presented by syngeneic spleen cells. This inhibitory effect, which was also observed with supernatant of intestinal epithelial cells from DNCB-fed mice, could be reversed by neutralizing anti-transforming growth factor (TGF)-beta antibodies. In addition, pre-incubation of hapten-sensitized T cells with enterocytes from DNCB-fed mice induced T cell anergy, which could be reversed by exogenous interleukin-2 or interleukin-4. These data demonstrate that intestinal epithelial cells activated in vivo by oral administration of DNCB are able to block proliferation of activated T cells through secretion of immunosuppressive cytokines such as TGF-beta. It is proposed that intestinal epithelial cells may play a significant role in oral tolerance by limiting T cell-mediated hypersensitivity responses.

Allergenicity and tolerogenicity of amlexanox in the guinea pig

Amlexanox (AMLX), an anti-allergic agent, is available in Japan as Elics opthalmic solution, Solfa nasal douche and Solfa tablets. Cases of allergic contact dermatitis induced by Elics ophthalmic solution, which contains 0.25% AMLX, were reported within a year of its introduction. We therefore examined the contact sensitizing potency of AMLX. Guinea pigs sensitized to 0.25% AMLX exhibited a strong positive patch test reaction. Further, AMLX-sensitized animals developed rashes following oral and systemic challenge with AMLX. This animal model reflected the clinical experience of systemic contact dermatitis due to AMLX. The non-responsiveness induced by oral administration of AMLX to AMLX-induced animals was transient, and clinical prophylaxis by desensitization with oral AMLX may only increase the risk of systemic contact dermatitis. On the other hand, there have been few reports of drug eruption from oral Solfa tablets in spite of their wide use. Therefore, we also examined the induction of tolerance by oral administration of AMLX. Oral administration of AMLX before sensitization resulted in complete non-responsiveness. It seems likely that a substantial reduction in the risk of AMLX sensitization by Elics may be achieved by prior oral administration of Solfa tablets containing AMLX.

Non-sensitizing epicutaneous skin tests prevent subsequent induction of immune tolerance

Oral administration of nickel or chromium to naive guinea pigs results in immune unresponsiveness to subsequent induction of allergic contact hypersensitivity. Such "oral tolerance" depends on the oral dose, is antigen specific, T-suppressor-cell mediated, and very persistent. In contrast, oral antigen administration to sensitized animals results at best in transient desensitization. Here we report that even non-sensitizing epicutaneous skin contacts prevented the subsequent induction of oral tolerance. These data support the view that primed T cells are less sensitive to suppressor T-cell function than naive T cells.

Immunoregulation of T cell-mediated skin hypersensitivity

The recent extensive research on the different functions of T cells differing in cytokine production profiles has opened promising venues for further research on mechanisms and therapeutic options. Clearly, the routing hypothesis as described above still leaves many questions unanswered, such as the question why some chemicals may elicit strong Th2 responses and IgE antibody production even when applied to the skin, without apparent reduction of delayed allergic reactivity (Dearman et al., 1991). The preliminary understanding of regulatory mechanisms in allergic contact dermatitis has not yet led to further therapeutic progress. So far, no methods of permanent desensitization have been devised. Nevertheless, major cell types and mediators involved in allergic contact dermatitis have been identified. How T cells specifically recognize distinct allergens, and how these and other inflammatory cells interact to generate inflammation has begun to be understood. Moreover, the recently defined cellular interaction molecules and mediators provide promising targets for anti-inflammatory drugs. Obviously, drugs found to be effective in preventing severe T cell-mediated conditions, e.g. rejection of a vital organ graft, should be very safe before their use in allergic contact dermatitis would seem appropriate. To date, prudence favours any measure to prevent allergic contact dermatitis, be it through legal actions to outlaw the use of certain materials, or through avoiding personal contacts with these materials. In the meantime, for difficult-to-avoid allergens, further studies on the potential value of tolerogenic treatments should be intensified.

Nickel sulfate-specific suppressor T cells induced by nickel sulfate in drinking water

Suppressor T cell function was studied in nickel sulfate (NiSO4) delayed type hypersensitivity (DTH). NiSO4 in drinking water administered orally to normal mice for 10 weeks elicited no significant footpad swelling. However, after drinking water for 7 weeks, suppression of footpad swelling response was not detected. Suppression of footpad swelling response was mediated by CD4-8+ T cells. However, these suppressor T cells did not overcome CD4+8- helper T cells by co-transfer to recipient mice. Unresponsiveness to NiSO4 by oral administration of antigen was due to suppressor T cells.

Oral induction of tolerance to nickel sensitization in mice

Antigen contact via the alimentary tract prior to sensitization may result in systemic immunologic unresponsiveness ("oral tolerance"). The induction of oral tolerance seems an attractive strategy to combat undesired immune responses, such as allograft rejection and autoimmune and allergic diseases. We describe clear and reproducible sensitization to nickel in mice reared under nickel-free conditions. Hypersensitivity was induced by injecting nickel sulfate intradermally into the flank skin and elicited by injecting the metal salt into the pinnae of the ears. The effectiveness of orally induced hyporesponsiveness could be inferred from a low degree of hypersensitivity obtained with mice raised and maintained in cages with nickel-releasing covers and water nipples. This mouse model for the assay of nickel hypersensitivity was used for oral tolerance studies by administrating non-toxic doses of nickel sulfate in drinking water or intragastrically prior to sensitization. In these animals, the development of delayed-type hypersensitivity was suppressed in a dose-dependent way, and the hyporesponsiveness could be transferred by CD8+ cells. The antigen specificity of this oral tolerance could be demonstrated by the concomitant use of sensitization and challenge procedures for nickel and chromium. The hypersensitivity assay described provides a versatile, highly reproducible experimental model to study immunoregulation of oral tolerance to clinically relevant metal allergens.