Identification of Chemical Respiratory Allergens: Dose-Response Relationships in the Mouse IgE Test

Assessment of personal inhalation and skin exposures to polymeric methylene diphenyl diisocyanate during polyurethane fabric coating

Methylene diphenyl diisocyanate (MDI) monomers and polymeric MDI (pMDI) are aromatic isocyanates widely used in the production of polyurethanes. These isocyanates can cause occupational asthma, hypersensitivity pneumonitis, as well as contact dermatitis. Skin exposure likely contributes toward initial sensitization but is challenging to monitor and quantitate. In this work, we characterized workers' personal inhalation and skin exposures to pMDI in a polyurethane fabric coating factory for subsequent health effect studies. Full-shift personal and area air samples were collected from eleven workers in representative job areas daily for 1-2 weeks. Skin exposure to hands was evaluated concomitantly with a newly developed reagent-impregnated cotton glove dosimeter. Samples were analyzed for pMDI by liquid chromatography-tandem mass spectrometry. In personal airborne samples, the concentration of 4,4^'-MDI isomer, expressed as total NCO, had a geometric mean (GM) and geometric standard deviation (GSD) of 5.1 and 3.3 ng NCO/m³, respectively (range: 0.5-1862 ng NCO/m³). Other MDI isomers were found at much lower concentrations. Analysis of 4,4^'-MDI in the glove dosimeters exhibited much greater exposures (GM: 10 ng/cm²) and substantial variability (GSD: 20 ng NCO/cm²; range: 0-295 ng NCO/cm²). MDI inhalation exposure was well below occupational limits for MDI for all the job areas. However, MDI skin exposure to hands was substantial. These findings demonstrated the potential for substantial isocyanate skin exposure in work settings with very low airborne levels. This exposure characterization should inform future studies that aim to assess the health effects of work exposures to MDI and the effectiveness of protective measures.

Exploring structure/property relationships to health and environmental hazards of polymeric polyisocyanate prepolymer substances-2. Dermal sensitization potential in the mouse local lymph node assay

The sensitization potencies of twenty custom-designed monomer-depleted polymeric polyisocyanate prepolymer substances and their associated toluene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI) monomer precursors were investigated by means of the mouse Local Lymph Node Assay (LLNA). These polymeric prepolymers were designed to represent the structural features and physical-chemical properties exhibited by a broad range of commercial polymeric polyisocyanate prepolymers that are produced from the reaction of aromatic and aliphatic diisocyanate monomers with aliphatic polyether and polyester polyols. The normalization of LLNA responses to the applied (15-45-135 mM) concentrations showed that the skin sensitization potency of polymeric polyisocyanate prepolymers is at least 300 times less than that of the diisocyanate monomers from which they are derived. The sensitization potency of the prepolymers was shown to be mainly governed by their hydrophobicity (as expressed by the calculated octanol-water partition coefficient, log K_ow) and surfactant properties. Neither hydrophilic (log K_ow <0) nor very hydrophobic (log K_ow >25) prepolymers stimulated lymphocyte proliferation beyond that of the dosing vehicle control. The findings of this investigation challenge the generally held assumption that all isocyanate (-N=C=O) bearing substances are potential skin (and respiratory) sensitizers. Further, these findings can guide the future development of isocyanate chemistries and associated polyurethane applications toward reduced exposure and health hazard potentials.

Investigation of hypersensitivity potential of diacetyl by determining cytokine profiles

Exposure to chemicals in workplace settings leads to significant occupational diseases related to hypersensitivity reactions. In recent years, diacetyl which is used as a food additive is thought to be as an important hazard due to its sensitization potency for worker's health. Therefore, in this study, we aimed to investigate the sensitization potency of diacetyl for the purpose of its hazard evaluation. Nonradioactive ex vivo local lymph node assay: BrdU-enzyme-linked immunosorbent assay (ELISA) method with short-term and long-term exposure protocols were conducted based on animal welfare principles. As end points, lymphocyte proliferation, cytokine releases, and total serum IgE levels were measured by ELISA method. After short-term dermal exposure to diacetyl, primary Th1 cytokine interleukin-2 (IL-2) and Th2 cytokines IL-4 and IL-13 levels were significantly increased relatively to vehicle control, whereas such significant increases were not observed in long-term exposure. According to our measurements of IgE levels after long-term dermal exposures to chemicals, diacetyl led to significant increase. In conclusion, the findings that showed significant increases in IL-13 and total serum IgE levels induced with diacetyl can be relevant to respiratory sensitizing hazard of this chemical.

Thresholds in chemical respiratory sensitisation

There is a continuing interest in determining whether it is possible to identify thresholds for chemical allergy. Here allergic sensitisation of the respiratory tract by chemicals is considered in this context. This is an important occupational health problem, being associated with rhinitis and asthma, and in addition provides toxicologists and risk assessors with a number of challenges. In common with all forms of allergic disease chemical respiratory allergy develops in two phases. In the first (induction) phase exposure to a chemical allergen (by an appropriate route of exposure) causes immunological priming and sensitisation of the respiratory tract. The second (elicitation) phase is triggered if a sensitised subject is exposed subsequently to the same chemical allergen via inhalation. A secondary immune response will be provoked in the respiratory tract resulting in inflammation and the signs and symptoms of a respiratory hypersensitivity reaction. In this article attention has focused on the identification of threshold values during the acquisition of sensitisation. Current mechanistic understanding of allergy is such that it can be assumed that the development of sensitisation (and also the elicitation of an allergic reaction) is a threshold phenomenon; there will be levels of exposure below which sensitisation will not be acquired. That is, all immune responses, including allergic sensitisation, have threshold requirement for the availability of antigen/allergen, below which a response will fail to develop. The issue addressed here is whether there are methods available or clinical/epidemiological data that permit the identification of such thresholds. This document reviews briefly relevant human studies of occupational asthma, and experimental models that have been developed (or are being developed) for the identification and characterisation of chemical respiratory allergens. The main conclusion drawn is that although there is evidence that the acquisition of sensitisation to chemical respiratory allergens is a dose-related phenomenon, and that thresholds exist, it is frequently difficult to define accurate numerical values for threshold exposure levels. Nevertheless, based on occupational exposure data it may sometimes be possible to derive levels of exposure in the workplace, which are safe. An additional observation is the lack currently of suitable experimental methods for both routine hazard characterisation and the measurement of thresholds, and that such methods are still some way off. Given the current trajectory of toxicology, and the move towards the use of non-animal in vitro and/or in silico) methods, there is a need to consider the development of alternative approaches for the identification and characterisation of respiratory sensitisation hazards, and for risk assessment.

Skin sensitization induced Langerhans' cell mobilization: variable requirements for tumour necrosis factor-α

Upon antigen/allergen recognition, epidermal Langerhans' cells (LC) are mobilized and migrate to the local lymph node where they play a major role in initiating or regulating immune responses. It had been proposed that all chemical allergens induce LC migration via common cytokine signals delivered by TNF-α and IL-1β. Here the dependence of LC migration on TNF-α following treatment of mice with various chemical allergens has been investigated. It was found that under standard conditions the allergens oxazolone, paraphenylene diamine, and trimellitic anhydride, in addition to the skin irritant sodium lauryl sulfate, were unable to trigger LC mobilization in the absence of TNF-α signalling. In contrast, two members of the dinitrohalobenezene family (2,4-dinitrochlorobenzene [DNCB] and 2,4-dinitrofluorobenzene [DNFB]) promoted LC migration independently of TNF-R2 (the sole TNF-α receptor expressed by LC) and TNF-α although the presence of IL-1β was still required. However, increasing doses of oxazolone overcame the requirement of TNF-α for LC mobilization, whereas lower doses of DNCB were still able to induce LC migration in a TNF-α-independent manner. These novel findings demonstrate unexpected heterogeneity among chemical allergens and furthermore that LC can be induced to migrate from the epidermis via different mechanisms that are either dependent or independent of TNF-α. Although the exact mechanisms with regard to the signals that activate LC have yet to be elucidated, these differences may translate into functional speciation that will likely impact on the extent and quality of allergic sensitization.

Inter-relationships between different classes of chemical allergens

Although allergic sensitization of the respiratory tract induced by chemicals is not as common as skin sensitization, it is nevertheless an important occupational health issue. Respiratory allergy to chemicals, characterized typically by rhinitis and asthma, is associated with considerable morbidity and with related socioeconomic costs. Several experimental approaches have been proposed for the prospective identification of chemical respiratory allergens, but none of these has yet been validated formally. In the absence of a widely accepted method for respiratory allergen identification, it is appropriate and relevant to explore their relationship with skin-sensitizing chemicals. A series of chemicals known to cause immune-mediated respiratory allergy in humans has been examined. The majority of the respiratory allergens tested were found to elicit positive responses in one or more standard tests used for the identification of skin-sensitizing potential (guinea pig maximization test, the Buehler test and/or the local lymph node assay). We suggest that this observation might form the basis of a potentially useful paradigm for initial characterization of the respiratory-sensitizing potential of chemicals. Specifically, chemicals that fail to elicit positive responses in accepted skin-sensitization test methods might also be regarded as lacking the inherent potential to cause allergic sensitization of the respiratory tract.

Chemical allergy: translating biology into hazard characterization

The induction by chemicals of allergic sensitization and allergic disease is an important and challenging branch of toxicology. Skin sensitization resulting in allergic contact dermatitis represents the most common manifestation of immunotoxicity in humans, and many hundreds of chemicals have been implicated as skin sensitizers. There are far fewer chemicals that have been shown to cause sensitization of the respiratory tract and asthma, but the issue is no less important because hazard identification remains a significant challenge, and occupational asthma can be fatal. In all areas of chemical allergy, there have been, and remain still, intriguing challenges where progress has required a close and productive alignment between immunology, toxicology, and clinical medicine. What the authors have sought to do here is to exemplify, within the framework of chemical allergy, how an investment in fundamental research and an improved understanding of relevant biological and biochemical mechanisms can pay important dividends in driving new innovations in hazard identification, hazard characterization, and risk assessment. Here we will consider in turn three specific areas of research in chemical allergy: (1) the role of epidermal Langerhans cells in the development of skin sensitization, (2) T lymphocytes and skin sensitization, and (3) sensitization of the respiratory tract. In each area, the aim is to identify what has been achieved and how that progress has impacted on the development of new approaches to toxicological evaluation. Success has been patchy, and there is still much to be achieved, but the journey has been fascinating and there have been some very important developments. The conclusion drawn is that continued investment in research, if coupled with an appetite for translating the fruits of that research into imaginative new tools for toxicology, should continue to better equip us for tackling the important challenges that remain to be addressed.

A QSAR investigation of dermal and respiratory chemical sensitizers based on computational chemistry properties

A wide range of physicochemical properties based on molecular topology, size and shape, and semi-empirical molecular orbital theory were calculated for a variety of dermal and respiratory sensitizers, as well as some non-active substances. Compounds were randomly selected to belong to a training set of substances (approximately 90%) for development of quantitative structure-activity relationship (QSAR) models or to a test set (approximately 10%) for testing the models. A choice was made of those descriptors which were related to sensitization using standard statistics. Pattern recognition methods were then utilized to identify the combination of properties that provided the greatest contribution to the observed biological effect. Principal components (PC) analysis was then performed on the most important properties. The models derived were then applied to a test set of known sensitizers to predict their class. For dermal and respiratory sensitizers respectively, the PC model classified five (100%) of the R-43 active and two (100%) of the R42-active test set compounds correctly. Analysis of the PC loadings showed that the most useful properties distinguishing respiratory and/or dermal sensitizers from inactive substances were the molecular orbital-based terms.

Methods for the prediction of low-molecular-weight occupational respiratory sensitizers

PURPOSE OF REVIEW

There is recognition that respiratory sensitization is an occupational hazard of high concern. Despite international regulatory requirements there is no established protocol for the efficient prospective identification of chemical respiratory sensitizers. We review the predictive behaviour of available methods and suggest a possible high-throughput protocol.

RECENT FINDINGS

Animal or in-vitro tests specific to respiratory exposure and resulting in direct asthma-related outcomes have not been developed, although the use of a local lymph node assay originally designed for skin sensitization has been advocated in a respiratory context. Various methods have been used to develop quantitative structure-activity relationship models for prediction of low-molecular-weight organic chemical respiratory sensitizers. The estimated negative predictive value for all of the published models is 1, but their differences in positive predictive value can be exploited.

SUMMARY

The most pragmatic as well as valid approach for screening large numbers of industrial chemicals for respiratory sensitization hazard is likely to consist of an algorithm starting with quantitative structure-activity relationship models. Further corroboration from animal or human data, however, may be required for chemicals with a positive result by quantitative structure-activity relationship.

Dose-Response Relationships and Threshold Levels in Skin and Respiratory Allergy

A literature study was performed to evaluate dose-response relationships and no-effect levels for sensitization and elicitation in skin- and respiratory allergy. With respect to the skin, dose-response relationships and no-effect levels were found for both intradermal and topical induction, as well as for intradermal and topical elicitation of allergenic responses in epidemiological, clinical, and animal studies. Skin damage or irritation may result in a significant reduction of the no-effect level for a specific compound. With respect to the respiratory tract, dose-response relationships and no-effect levels for induction were found in several human as well as animal studies. Although dose-response relationships for elicitation were found in some epidemiological studies, concentration-response relationships were present only in a limited number of animal studies. Reported results suggest that especially relatively high peak concentrations can induce sensitization, and that prevention of such concentrations will prevent workers from developing respiratory allergy. Moreover, induction of skin sensitization may result in subsequent heightened respiratory responsiveness following inhalation exposure. The threshold concentration for the elicitation of allergic airway reactions in sensitized subjects is generally lower than the threshold to induce sensitization. Therefore, it is important to consider the low threshold levels for elicitation for recommendation of health-based occupational exposure limits, and to avoid high peak concentrations. Notwithstanding the observation of dose-response relationships and no-effect levels, due to a number of uncertainties, no definite conclusions can be drawn about absolute threshold values for allergens with respect to sensitization of and elicitation reactions in the skin and respiratory tract. Most predictive tests are generally meant to detect the potential of a chemical to induce skin and/or respiratory allergy at relatively high doses. Consequently, these tests do not provide information of dose-response relationships at lower doses such as found in, for example, occupational situations. In addition, the observed dose-response relationships and threshold values have been obtained by a wide variety of test methods using different techniques, such as intradermal exposure versus topical or inhalation exposure at the workplace, or using different endpoints, which all appear important for the outcome of the test. Therefore, especially with regard to respiratory allergy, standardized and validated dose-response test methods are urgently required in order to be able to recommend safe exposure levels for allergens at the workplace.

Intracellular expression of cytokines and granzyme B in auricular lymph nodes draining skin exposed to irritants and sensitizers

The murine local lymph node assay (LLNA) has been extensively utilized to evaluate sensitizing chemicals. However, there have been some concerns that its use to discriminate between classes of chemicals is minimal. It is thus desirable to identify better or alternative immune endpoints with in LLNA itself. Here, we evaluated the protein and/or mRNA levels of cytokines and granzyme B (GzmB), a cytotoxic lymphocyte product, to discriminate between sensitizers and irritants and to characterize the chemical sensitizers when used as supplemental indicators in LLNA endpoints. For this, CBA/N mice were topically treated daily with a well-known chemical sensitizer such as a strong contact sensitizer 1-chloro-2,4-dinitrobenzene (DNCB), a skin contact sensitizer 2-phenyl-4-ethoxymethylene-5-oxazolone (OXA), and a skin or respiratory sensitizer toluene 2,4-diisocyanate (TDI), and the non-sensitizing irritants, croton oil (CRO) and nonanoic acid (NA), for 3 consecutive days. The protein and/or mRNA levels in auricular lymph nodes draining the ear skin were then analyzed by real-time RT-PCR and immunoassay. The sensitizers, but not the irritants, evoked pronounced interleukin (IL)-2, IL-3 and IL-4 or interferon (IFN)-gamma. Significantly, different sensitizers evoked different cytokine patterns of IL-4 and IFN-gamma, as DNCB strongly up-regulated both IFN-gamma and IL-4, OXA up-regulated IFN-gamma strongly but IL-4 weakly, and TDI up-regulated IL-4 strongly but IFN-gamma weakly. The sensitizers also strongly up-regulated GzmB mRNA, while the irritants had a much weaker effect. Thus, these cytokines and GzmB mRNA may be useful as additional endpoints for discriminating between irritants and sensitizers or contact and respiratory sensitizers in the LLNA.

Animal models to test respiratory allergy of low molecular weight chemicals: a guidance

At present, there are no widely applied or fully validated test methods to identify respiratory LMW allergens, i.e. compounds that are considered capable of inducing allergic asthma. Most tests have been investigated using strong respiratory allergens. Moreover, they are meant to detect the potential of a chemical to induce respiratory sensitisation at relatively high doses. Consequently, the sensitivity of the tests is not well-known, and they do not provide information on low doses such as generally found in occupational situations, and on threshold levels to be used in risk assessment. In addition, the various test methods use different application routes, i.e. intradermal, topical or inhalation exposure, and different parameters. Therefore standardised and validated dose-response test methods are urgently required in order to be able to identify respiratory allergens and to recommend safe exposure levels for consumers and workers. In the present paper, methods or testing strategies are described to detect respiratory sensitisation and/or allergy. Overall, assays that utilize only an induction phase may serve as indicators of respiratory sensitisation potential whereas assays that use both an induction and an elicitation or challenge phase may provide information on potency and presence of thresholds. The dermal route as sensitisation route has the advantage of the respiratory tract not being exposed to the allergen prior to challenge which facilitates the distinction between irritant and allergic effects.

Repeated inhalation challenge with diphenylmethane-4,4'-diisocyanate in brown Norway rats leads to a time-related increase of neutrophils in bronchoalveolar lavage after topical induction

Diphenylmethane-4,4'-diisocyanate (MDI) is a low-molecular-weight chemical known to cause occupational asthma. The objective of this study was to evaluate the topical and inhalation routes of sensitization on the elicitation response of MDI in the Brown Norway (BN) rat model following repeated challenge exposures. BN rats were either induced topically (150 microl MDI on the flanks, booster administration to the skin of the dorsum of both ears using 75 microl/dorsum of each ear) or by inhalation (5x3 h/d, 28.3+/-3.0 mg MDI/m3 [+/-SD]). Inhalation challenge exposures with MDI (15.7+/-1.4 mg/m3, duration 30 min) were made on d 21, 35, 50, and 64. One day after each challenge, rats were rechallenged with methacholine (MCh) aerosol. Respiratory changes were monitored during challenges. One day after the MCh challenge, selected endpoints in bronchoalveolar lavage (BAL), the weights of lungs, and auricular and lung-associated lymph nodes were determined. After the first and last challenge, lymph nodes and lungs were examined by histopathology. Repeated challenge with MDI or MCh did not elicit marked changes in respiratory patterns at any time point. Mild but consistent time-related increased BAL neutrophils and slightly increased lung and lymph-node weights occurred in topically sensitized rats as compared to the remaining groups. In topically sensitized rats, in the lung histopathology revealed activated lymphatic tissue and an increased recruitment of airway eosinophils. Immunoglobulin (Ig) E determinations (serum and BAL) did not show any differences amongst the groups. Thus, high-dose topical induction with MDI was associated with a neutrophilic and eosinophilic inflammatory response in the lung after repeated inhalation challenge with MDI, with magnitude of effect dependent on the specific methodology used.

Respiratory allergy to trimellitic anhydride in rats: concentration-response relationships during elicitation

The present study investigated whether airway responses of sensitized rats to trimellitic anhydride (TMA) were concentration dependent and whether these were related to irritation by TMA. Groups of BN and Wistar rats were sensitized by two dermal applications of TMA (50% w/v, followed by 25% w/v in vehicle). Controls received vehicle (acetone-olive oil 4:1, v/v). All animals were challenged 3 wk after the first sensitization by inhalation of one of a range of concentrations of TMA (0.2-61 mg/m3 for BN rats, 15-250 mg/m3 for Wistar rats). Breathing pattern, breathing frequency, and tidal volume were measured before, during, and after challenge to assess allergic and irritative airway responses. One day after challenge, nonspecific airway responsiveness to a range of concentrations of methacholine was measured. At necropsy on the same day, blood was withdrawn for measuring total serum immunoglobulin E (IgE) and organs were weighed. Larynx, trachea and lungs were examined histopathologically. In BN rats, TMA sensitization elevated total IgE levels; subsequent inhalation challenge with 2 mg/m3 of TMA and higher caused laryngeal inflammation with squamous epithelial metaplasia, and pulmonary hemorrhages. Concentration-related decreases in breathing frequency and alterations in breathing pattern, which differed from the irritation-induced pattern, were also observed at these levels. Inhalation challenge with TMA concentrations of 12 mg/m3 and higher increased lung weight. Increased nonspecific airway responsiveness was observed at the 2 next higher tested concentrations of 46 and 61 mg/m3. In unsensitized BN rats, only laryngeal squamous metaplasia was observed, albeit at higher challenge concentrations of TMA, and decreased breathing frequency, a typical breathing pattern characteristic of irritation. Identically sensitized Wistar rats showed airway inflammation and pulmonary hemorrhages upon challenge with TMA, but no functional changes, even at distinctly irritating concentrations of TMA up to 250 mg/m3. In conclusion, TMA challenge of sensitized BN rats caused challenge concentration-related allergic airway inflammation, asthmalike changes in breathing pattern, and increased nonspecific airway responsiveness. The lowest no-observed-effect level (NOEL) based on the most sensitive endpoint investigated was 0.2 mg/m3, a value that is well below the irritation concentration. The presence of a NOEL in the sensitized BN rat suggests that assessment of safe human exposure levels is feasible.

Approaches to induce and elicit respiratory allergy: impact of route and intensity of exposure

Although a number of test protocols have been developed to predict respiratory allergenic potential, none of these are widely applied or fully accepted. However, given the serious health problems caused by respiratory allergy and the ever-increasing stream of new chemicals into workplaces, early identification of chemical respiratory allergens is important. Inhalation exposure as well as skin application have been used in predictive tests to induce respiratory tract sensitisation. While there are good indications in laboratory animals and humans that skin exposure can act as a route for respiratory tract sensitisation and vice versa, less is known about the effect of the route on the type of allergy evoked and on dose-response relationships. Although, the responses were in general more vigorous after dermal sensitisation than after inhalation sensitisation, the nature of the immune responses seemed to be qualitatively comparable. As to the intensity of exposure, dose or concentration-response relationships have been observed both during respiratory sensitisation and challenge, suggesting that assessment of safe exposure levels is feasible. Finally, a correct distinction between respiratory allergens and non-sensitising airway irritants is needed for effective risk assessment and management.

Sensitization potential of gold sodium thiosulfate in mice and guinea pigs

Since gold sodium thiosulfate (GST) has been included in a standard patch test series for diagnosis of allergic contact dermatitis from gold, the incidence of patients showing positive reactions to gold is increasing. However, there were little reports on induction of gold sensitization in animals. In this study, we have examined the sensitization potential of GST using mice and guinea pigs. In the guinea pig maximization test, 2 or 6 out of 10 animals showed positive skin responses, mainly edema, by challenge with 2% or 5% GST in 50% ethanol solution, respectively. In the mouse ear swelling test, positive ear swelling (20% greater increase in ear thickness) after challenge with GST was shown in 2 out of 6 mice those previously treated with GST. Topical exposure of mice to GST in 70% dimethylsulfoxide solution induced small increases in the lymph node weight and the lymph node cell (LNC) number in the murine local lymph node assay (LLNA). A greater degree of LNC responses were observed in the sensitive mouse lymph node assay (SLNA) compared with the LLNA, but the stimulation index of total lymph node response by GST was not so high. From these results, GST was identified as a contact allergen, but the sensitization potential was not so strong. In the mouse IgE test, treatment of mice with GST resulted in a statistically significant increase in the serum IgE antibody concentration that associated with immediate-type hypersensitivity reaction. It may suggest that the sensitization responses from gold would appear not only at the contact site but also systematically.

Induced changes in total serum IgE concentration in the Brown Norway rat: potential for identification of chemical respiratory allergens

A variety of chemicals can cause sensitization of the respiratory tract and occupational asthma that may be associated with IgE antibody production. Topical exposure to chemical respiratory allergens such as trimellitic anhydride (TMA) has been shown previously to induce increases in the total serum concentration of IgE in BALB/c strain mice. Contact allergens such as 2,4-dinitrochlorobenzene (DNCB), which apparently lack respiratory sensitizing potential, fail to provoke similar changes. However, it became apparent with time that there was some inter-animal variation in constitutive and inducible IgE levels. We have now examined the influence of topical exposure to TMA and DNCB on serum IgE levels in the Brown Norway (BN) rat. Such animals can be bled serially and thus it is possible to perform longitudinal analyses of changes in serum IgE concentration. The kinetics of IgE responses therefore can be followed on an individual animal basis, allowing discrimination between transient and sustained increases in serum IgE concentration. Rats (n = 5) were exposed on shaved flanks to 50% TMA, to 1% DNCB (concentrations that elicit comparable immune activation with respect to draining lymph node cellularity and proliferation) or to vehicle alone. Total IgE was measured by enzyme-linked immunosorbent assay in serum samples taken prior to and 14-42 days following initial exposure. Those animals having high pre-existing IgE levels (>1.0 microg ml(-1)) were excluded from subsequent analyses. The levels of serum IgE in the majority of rats exposed to DNCB or vehicle alone remained relatively stable throughout the duration of all the experiments conducted, although some animals displayed transient increases in serum IgE. Only TMA treatment was associated with a significant and sustained increase in the level of serum IgE in the majority of experiments. The elevated concentrations of IgE induced by topical exposure to TMA are persistent, the results reported here demonstrating that induced changes in IgE are maximal or near maximal at approximately 35 days, with a significant increase in IgE demonstrable for at least 42 days following the initiation of exposure. Interestingly, although TMA and DNCB at the test concentrations used were found to be of comparable overall immunogenicity with regard to lymph node activation and the induction of lymph node cell proliferation, there were apparent differences in humoral immune responses. Thus, not only did exposure to TMA stimulate increases in total serum IgE concentration and the production of specific IgE antibody, but also a more vigorous IgG antibody response was provoked by TMA compared with DNCB. These data suggest that the measurement of induced changes in serum IgE concentration in the BN strain of rat is able to differentiate between different classes of chemical allergen. Given the inter-animal variation in IgE production, it would be prudent to incorporate a concurrent assessment of responses induced by treatment with TMA as a positive control against which to assess the activity of other test materials.

Cytokine fingerprinting and hazard assessment of chemical respiratory allergy

Allergic sensitization of the respiratory tract resulting in occupational asthma and other symptoms can be caused by a variety of chemicals and represents an important occupational health problem. Although there is a need to identify and characterize those chemicals that are able to cause respiratory allergy, there are currently no well validated or widely accepted predictive test methods. Some progress has been made with guinea pig assays, but our attention in this laboratory has focused instead on the development of novel approaches based on an understanding of the nature of immune responses induced in mice by chemical allergens. We have shown that whereas contact allergens provoke in mice selective type 1 immune responses, characterized by the secretion by draining lymph node cells (LNC) of high levels of the cytokine interferon gamma (IFN-gamma), chemical respiratory allergens stimulate instead preferential type 2 responses associated with comparatively high levels of interleukins 4 and 10 (IL-4 and IL-10). The divergent immune responses provoked by different classes of chemical allergens, and the phenotypes of selective cytokine secretion that characterize such responses, form the basis of a novel method-cytokine fingerprinting--that permits chemicals that have the potential to cause respiratory allergy to be identified and distinguished from those that are associated primarily with contact sensitization. In this article the immunobiological basis for cytokine fingerprinting is considered and the development, evaluation and practical application of the assay are reviewed.

Pre-clinical methods for detecting the hypersensitivity potential of pharmaceuticals: regulatory considerations

Immune-based systemic hypersensitivities account for a significant number of adverse drug reactions. There appear to be no adequate nonclinical models to predict systemic hypersensitivity to small molecular weight drugs. Although there are very good methods for detecting drugs that can induce contact sensitization, these have not been successfully adapted for prediction of systemic hypersensitivity. Several factors have made the development of adequate models difficult. The term systemic hypersensitivity encompases many discrete immunopathologies. Each type of immunopathology presumably is the result of a specific cluster of immunologic and biochemical phenomena. Certainly other factors, such as genetic predisposition, metabolic idiosyncrasies, and concomitant diseases, further complicate the problem. Therefore, it may be difficult to find common mechanisms upon which to construct adequate models to predict specific types of systemic hypersensitivity reactions. There is some reason to hope, however, that adequate methods could be developed for at least identifying drugs that have the potential to produce signs indicative of a general hazard for immune-based reactions.

Effect of dietary vitamin E supplementation on murine nasal allergy

BACKGROUND

Although many studies have reported the effects of dietary vitamin E on the immune response, none so far has assessed its role in nasal allergy.

METHODS

Female BALB/c mice were randomized into two groups and fed a 20% casein diet (control group, 50 mg vitamin E/kg diet) or this diet supplemented with 535 mg vitamin E/kg diet (vitamin E group, 585 mg vitamin E/kg diet) for 4 weeks. During the fifth week, the mice in each group were divided into two subgroups to form a total of four treatment groups: group A (control), group B [control + toluene diisocyanate (TDI) sensitization], group C (vitamin E supplementation), and group D (vitamin E supplementation + TDI sensitization). Groups B and D were treated with two courses of intranasal application of 5% TDI in ethyl acetate, whereas groups A and C were treated with ethyl acetate alone. A week after second sensitization all groups were provoked by applying 2.5% of TDI in the vehicle and nasal allergic responses were observed for 10 minutes. Splenic lymphoproliferation, splenic cell cytokines, and the total serum IgE were measured.

RESULTS

Members of group D had lower (P < 0.01) scores of nasal response and sneezed less frequently (P < 0.01) than those of group B. Similarly, splenic lymphoproliferation and production of IL-4 and IL-5 as well as the total serum IgE levels were lower (P < 0.01) in group D than in group B.

CONCLUSIONS

The results indicate that higher doses of vitamin E supplementation may suppress nasal allergic responses.

Selective induction of type 2 cytokines following topical exposure of mice to platinum salts

Repeated topical exposure of BALB/c strain mice to organic chemical respiratory allergens, such as trimellitic anhydride (TMA), or contact allergens such as 2,4-dinitrochlorobenzene (DNCB), provokes characteristic cytokine secretion profiles consistent with the divergent activation of discrete T cell subpopulations. Under such conditions, lymph node cells (LNC) isolated from animals exposed to TMA elaborated comparatively large amounts of the type 2 cytokines interleukin 10 (IL-10) and mitogen-inducible interleukin 4 (IL-4), but only low levels of the type 1 product interferon gamma (IFN-gamma). In contrast, DNCB-activated LNC displayed the converse (type 1) cytokine secretion profile. We have now examined cytokine production induced by topical application to mice of respiratory sensitizing platinum salts; ammonium tetrachloroplatinite II, ammonium hexachloroplatinate IV and cis-dichlorodiammine platinum II. Metal salts were dissolved in dimethyl sulfoxide (DMSO). Cytokine secretion profiles were compared with those elicited following concurrent exposure to TMA or DNCB or to the vehicle acetone:olive oil (AOO) alone. All three platinum salts and TMA stimulated vigorous IL-4 and IL-10 production compared with DNCB-activated LNC; vehicle-stimulated LNC failed to elaborate detectable levels of either cytokine. However, DNCB and the DMSO vehicle provoked substantial IFN-gamma expression, whereas exposure to AOO vehicle resulted in a considerably weaker IFN-gamma response. Levels of this cytokine induced by treatment with respiratory allergens were, in the majority of cases, substantially lower than those observed with the relevant vehicle. Indeed, an inverse dose-response relationship for IFN-gamma expression was exhibited by all three platinum salts, suggestive of the elaboration by platinum salt activated LNC of an inhibitory factor or factors for IFN-gamma. These data suggest that it may be possible to identify those metal salts with respiratory sensitizing potential as a function of induced type 2 cytokine secretion patterns.

TDI inhalation in guinea-pigs involves migration of dendritic cells

Toluene diisocyanate (TDI) can cause occupational asthma, but the mechanism underlying sensitization to this chemical compound remains controversial. The present study aims to investigate whether tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) liberated in the lungs after TDI inhalation can contribute to the migration of dendritic cells from respiratory airways towards lung associated lymph nodes for presentation of TDI hapten. Exposure was studied in two modes: (1) acute exposure (experiment no. 1, 2 and 3) where animals were exposed to 2.962, 1.060, and 1.076 ppm TDI for 1, 4, and two periods of 4 h, respectively; (2) subacute exposure (experiment no. 4, 5 and 6) where animals were exposed to 0.066, 0.110, and 0.999 ppm TDI for 48 h for the two lower doses and 5 days for the highest dose. Depending on the modes of exposure, two to four post exposure times were selected. After acute exposure to 2.962 ppm TDI for 1 h, the increase in TNF-alpha and IL-6 levels in bronchoalveolar lavage (BAL) fluid was observed immediately at the end of inhalation exposure, whereas the maximum number of dendritic cells and total cells occurred at post exposure times of 48 h and 5 days, respectively. In two other acute exposures, the peak increases in TNF-alpha, IL-6 and total cell numbers were observed at 48 h post exposure time, whereas the peak increase in dendritic cells occurred at 24 h. After subacute exposure to 48 h TDI, where TDI concentrations were relatively low (0.006 or 0.110 ppm), a parallel increase in TNF-alpha and IL-6 levels, dendritic and total cell numbers were observed at 0 h post exposure time. This phenomenon was also apparent at 24 h post exposure time when the animals had been exposed to 1.999 ppm TDI for 5 days. From these results, we can conclude that dendritic cells could play a key role as antigen presenting cells in the development of TDI-induced respiratory sensitization, and that their migration toward lung-associated lymph nodes is probably conditioned by cytokine release in their micro-environment. Future work must delineate whether TNF-alpha and IL-6 are solely responsible for the migration of dendritic cells after TDI inhalation, for example by using antibodies to neutralize these cytokines.

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.

Experimental assessment of the sensitizing properties of formaldehyde

Formaldehyde causes upper respiratory tract irritation and has been reported in some investigations to be a cause of occupational allergic asthma. The data are equivocal, however, and it has proved difficult to confirm that exposure to formaldehyde induces respiratory sensitization or provokes the production of specific immunoglobulin E (IgE) antibody. In this study the sensitizing properties of formaldehyde were examined experimentally. This chemical elicited strong positive responses in three independent methods for the prospective identification of contact sensitizing chemicals-the guinea pig maximization test, the occluded patch test of Buehler and the murine local lymph node assay. In contrast, in a novel predictive test method for assessment of respiratory sensitization potential-the mouse IgE test-formaldehyde at the same test concentrations was negative. Furthermore, formaldehyde induced in mice a pattern of cytokine secretion by draining lymph node cells inconsistent with the stimulation of IgE antibody responses or respiratory sensitization. These data indicate that, although formaldehyde is a potent contact allergen, it lacks a significant potential to cause sensitization of the respiratory tract.