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

Accurate regulatory classification of chemical respiratory allergens: The case for robust characterisation of causation

Occupational health standards, worker safety and effective regulatory classification relies upon characterisation of occupational asthma and discrimination between allergic asthma, irritant-induced asthma, and work-exacerbated asthma, and the accurate identification of chemical allergens of the respiratory tract. No in silico, in vitro or in vivo experimental method can, either alone or in combination, accurately identify chemical respiratory allergens and provide a sound basis for regulatory classification. Measurement of IgE antibody and skin prick testing can characterise allergy to proteins, but not to chemical respiratory allergens. Therefore, characterisation of causation and accurate regulatory classification of work-related asthma relies upon characterisation of clinical and workplace histories and specific inhalation challenge tests conforming to current guidelines and best practice. This manuscript reviews the important of accurate characterisation of causation in cases of work-related asthma to ensure accurate classification and robust regulation, and to promote a sound basis for clinical and experimental research. Commentaries on selected clinical case studies are provided that highlight key issues that confound attribution of causation. Specific recommendations are made regarding the design, conduct and interpretation of clinical investigations of work-related asthma that could provide a basis of more robust regulatory practice, and the more reliable identification of chemical respiratory allergens.

Nanoparticles for Topical Application in the Treatment of Skin Dysfunctions-An Overview of Dermo-Cosmetic and Dermatological Products

Nanomaterials (NM) arouse interest in various fields of science and industry due to their composition-tunable properties and the ease of modification. They appear currently as components of many consumer products such as sunscreen, dressings, sports clothes, surface-cleaning agents, computer devices, paints, as well as pharmaceutical and cosmetics formulations. The use of NPs in products for topical applications improves the permeation/penetration of the bioactive compounds into deeper layers of the skin, providing a depot effect with sustained drug release and specific cellular and subcellular targeting. Nanocarriers provide advances in dermatology and systemic treatments. Examples are a non-invasive method of vaccination, advanced diagnostic techniques, and transdermal drug delivery. The mechanism of action of NPs, efficiency of skin penetration, and potential threat to human health are still open and not fully explained. This review gives a brief outline of the latest nanotechnology achievements in products used in topical applications to prevent and treat skin diseases. We highlighted aspects such as the penetration of NPs through the skin (influence of physical-chemical properties of NPs, the experimental models for skin penetration, methods applied to improve the penetration of NPs through the skin, and methods applied to investigate the skin penetration by NPs). The review summarizes various therapies using NPs to diagnose and treat skin diseases (melanoma, acne, alopecia, vitiligo, psoriasis) and anti-aging and UV-protectant nano-cosmetics.

The use of Genomic Allergen Rapid Detection (GARD) assays to predict the respiratory and skin sensitising potential of e-liquids

Electronic cigarettes (e-cigarettes) are an increasingly popular alternative to combustible tobacco cigarettes among smokers worldwide. A growing body of research indicates that flavours play a critical role in attracting and retaining smokers into the e-cigarette category, directly contributing to declining smoking rates and tobacco harm reduction. The responsible selection and inclusion levels of flavourings in e-liquids must be guided by toxicological principles. Some flavour ingredients, whether natural extracts or synthetic, are known allergens. In this study, we used the Genomic Allergen Rapid Detection (GARD) testing strategy to predict and compare the respiratory and skin sensitising potential of three experimental and two commercial e-liquids. These novel, myeloid cell-based assays use changes in the transcriptional profiles of genomic biomarkers that are collectively relevant for respiratory and skin sensitisation. Our initial results indicate that the GARD assays were able to differentiate and broadly classify e-liquids based on their sensitisation potential, which are defined mixtures. Further studies need to be conducted to assess whether and how these assays could be used for the screening and toxicological assessment of e-liquids to support product development and commercialisation.

The utility of monitoring trimellitic anhydride (TMA)-specific IgG to predict IgE-mediated sensitization in an immunosurveillance program

BACKGROUND

Workplace exposure to trimellitic anhydride (TMA) can elicit TMA-specific IgE (sIgE), which may lead to occupational asthma (OA). An occupational immunosurveillance program (OISP) has been implemented to monitor TMA exposure and immunologic outcomes. The purpose of this study was to determine whether TMA-specific IgG (sIgG) responses can discriminate between TMA-exposed workers with and without sIgE responses.

METHODS

Serum TMA-specific antibody (IgG, IgG4, and IgE) levels were estimated longitudinally (years 2006 to 2014) in TMA-exposed workers recruited in low, medium, and high exposure areas. sIgG and sIgE titers plotted against exposure duration were compared between workers with (a) sIgG only and (b) with sIgG who developed sIgE.

RESULTS

Among 92 TMA-exposed workers continuously monitored for sIgG and sIgE, 38 developed sIgG; 11 developed a sIgE response 342.38 ± 186.03 days posthire and were removed from exposure. The average detection time of sIgG in removed workers (159 ± 92 days) was significantly shorter than for actively exposed workers with only sIgG (346 ± 187 days). Workers with earlier sIgG responses of higher titer (mean value 42.25 μg/mL) compared to delayed responders with lower sIgG titers (mean value 14.79 μg/mL) more frequently developed sIgE responses. Hierarchical clustering showed the initial magnitude and exposure time required for detectable sIgG production discriminated between workers with only sIgG from workers who subsequently produced sIgE.

CONCLUSIONS

This study demonstrates the utility of longitudinally monitoring TMA-specific antibodies in an OISP as exposed workers with early sIgG responses and of higher magnitude are more likely to develop TMA sIgE sensitization.

SerpinB2 Deficiency Results in a Stratum Corneum Defect and Increased Sensitivity to Topically Applied Inflammatory Agents

SerpinB2 (plasminogen activator inhibitor type 2) is constitutively expressed at high levels by differentiating keratinocytes in mice and humans; however, the physiological function of keratinocyte SerpinB2 remains unclear. Herein, we show that SerpinB2(-/-) mice are more susceptible to contact dermatitis after topical application of dinitrofluorobenzene, and show enhanced inflammatory lesions after topical applications of phorbol ester. Untreated SerpinB2(-/-) mice showed no overt changes in epithelial structure, and we were unable to find evidence for a role for keratinocyte SerpinB2 in regulating immunity, apoptosis, IL-1β production, proteasomal activity, or wound healing. Instead, the phenotype was associated with impaired skin barrier function and a defective stratum corneum, with SerpinB2(-/-) mice showing increased transepidermal water loss, increased overt loss of stratum corneum in inflammatory lesions, and impaired stratum corneum thickening after phorbol ester treatment. Immunoblotting suggested that SerpinB2 (cross-linked into the cornified envelope) is present in the stratum corneum and retains the ability to form covalent inhibitory complexes with urokinase. Data suggest that the function of keratinocyte SerpinB2 is protection of the stratum corneum from proteolysis via inhibition of urokinase, thereby maintaining the integrity and barrier function of the stratum corneum, particularly during times of skin inflammation. Implications for studies involving genetically modified mice treated with topical agents and human dermatological conditions, such as contact dermatitis, are discussed.

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.

Prediction of chemical respiratory sensitizers using GARD, a novel in vitro assay based on a genomic biomarker signature

Background

Repeated exposure to certain low molecular weight (LMW) chemical compounds may result in development of allergic reactions in the skin or in the respiratory tract. In most cases, a certain LMW compound selectively sensitize the skin, giving rise to allergic contact dermatitis (ACD), or the respiratory tract, giving rise to occupational asthma (OA). To limit occurrence of allergic diseases, efforts are currently being made to develop predictive assays that accurately identify chemicals capable of inducing such reactions. However, while a few promising methods for prediction of skin sensitization have been described, to date no validated method, in vitro or in vivo, exists that is able to accurately classify chemicals as respiratory sensitizers.

Results

Recently, we presented the in vitro based Genomic Allergen Rapid Detection (GARD) assay as a novel testing strategy for classification of skin sensitizing chemicals based on measurement of a genomic biomarker signature. We have expanded the applicability domain of the GARD assay to classify also respiratory sensitizers by identifying a separate biomarker signature containing 389 differentially regulated genes for respiratory sensitizers in comparison to non-respiratory sensitizers. By using an independent data set in combination with supervised machine learning, we validated the assay, showing that the identified genomic biomarker is able to accurately classify respiratory sensitizers.

Conclusions

We have identified a genomic biomarker signature for classification of respiratory sensitizers. Combining this newly identified biomarker signature with our previously identified biomarker signature for classification of skin sensitizers, we have developed a novel in vitro testing strategy with a potent ability to predict both skin and respiratory sensitization in the same sample.

Understanding engineered nanomaterial skin interactions and the modulatory effects of ultraviolet radiation skin exposure

The study of engineered nanomaterials for the development of technological applications, nanomedicine, and nano-enabled consumer products is an ever-expanding discipline as is the concern over the impact of nanotechnology on human environmental health and safety. In this review, we discuss the current state of understanding of nanomaterial skin interactions with a specific emphasis on the effects of ultraviolet radiation (UVR) skin exposure. Skin is the largest organ of the body and is typically exposed to UVR on a daily basis. This necessitates the need to understand how UVR skin exposure can influence nanomaterial skin penetration, alter nanomaterial systemic trafficking, toxicity, and skin immune function. We explore the unique dichotomy that UVR has on inducing both deleterious and therapeutic effects in skin. The subject matter covered in this review is broadly informative and will raise awareness of potential increased risks from nanomaterial skin exposure associated with specific occupational and life style choices. The UVR-induced immunosuppressive response in skin raises intriguing questions that motivate future research directions in the nanotoxicology and nanomedicine fields.

Applications of nanotechnology in dermatology

What are nanoparticles and why are they important in dermatology? These questions are addressed by highlighting recent developments in the nanotechnology field that have increased the potential for intentional and unintentional nanoparticle skin exposure. The role of environmental factors in the interaction of nanoparticles with skin and the potential mechanisms by which nanoparticles may influence skin response to environmental factors are discussed. Trends emerging from recent literature suggest that the positive benefit of engineered nanoparticles for use in cosmetics and as tools for understanding skin biology and curing skin disease outweigh potential toxicity concerns. Discoveries reported in this journal are highlighted. This review begins with a general introduction to the field of nanotechnology and nanomedicine. This is followed by a discussion of the current state of understanding of nanoparticle skin penetration and their use in three therapeutic applications. Challenges that must be overcome to derive clinical benefit from the application of nanotechnology to skin are discussed last, providing perspective on the significant opportunity that exists for future studies in investigative dermatology.

Infliximab alleviates inflammation and ex vivo airway hyperreactivity in asthmatic E3 rats

Tumor necrosis factor-α (TNF-α) has been implicated in the pathogenesis of asthma, and neutralization of TNF-α is an effective therapy for inflammatory diseases. The present study tested the idea that a TNF-α antibody, infliximab, may be useful in the management of asthma. E3 rats were immunized with ovalbumin (OVA)/alum and received infliximab intra-peritoneally. Two weeks later, OVA-PBS was instilled intranasally daily for 7 days. Bronchoalveolar lavage fluids (BALFs), serum and lung homogenates were collected for analysis of cells and inflammatory mediators. Contractile responses of lobar-bronchus segments to agonists were functionally tested. Pulmonary tissues were investigated using histological examination. The results showed that the sensitized 'model E3 rats' exhibited an increase in the total amount of inflammatory cells, primarily eosinophils, in BALF and pulmonary tissue, as well as epithelial damage. Serum levels of IgE increased and so did the levels of nitric oxide, inducible nitric oxide synthase, TNF-α and IL-4, IL-5 and IL-13 in lung homogenate and serum. Furthermore, the contractile responses in bronchi induced by endothelin-1, sarafotoxin 6c and bradykinin increased and isoprenaline-induced relaxations decreased. All these changes induced by the sensitization procedure were reduced by the infliximab treatment. The results suggest that infliximab prevents the development of local airway inflammation and antagonizes changes of the bronchial smooth muscle receptor phenotype, thereby blocking the development of airway smooth muscle hyperreactivity of asthmatic rats.

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.

The influence of dexamethasone and the role of some antioxidant vitamins in the pathogenesis of experimental bronchial asthma

BACKGROUND

Bronchial asthma is a disease characterized by paroxysmal and reversible obstruction of the airways. The imbalance between the oxidant and antioxidant system that is called oxidative stress is critical in asthma pathogenesis. It is likely, therefore, that antioxidants may be effective in the treatment of asthma. Systemic treatment with glucocorticoids has been reported to inhibit smooth muscle hypercontraction which may account partially for their beneficial effects in the treatment of asthma.

OBJECTIVE

The present study was conducted in order to study the effect of dexamethasone and some antioxidant vitamins on interleukin-4 (IL-4), immunoglobulin E (IgE) and heat shock protein 70 (Hsp70) in bronchial asthma in rats, and to recognize their possible beneficial role.

METHOD

The study was conducted on 60 adult male albino rats randomly divided into 4 groups (15 for each group): including normal control group (group A); asthma model group where rats were sensitized by ovalbumin and challenged with antigen aerosol producing bronchial asthma (group B); asthma model group treated with antioxidant vitamins (vitamin E and vitamin C) (group C); asthma model group treated with dexamethasone (group D). Blood and lung samples were collected from all groups.

RESULTS AND CONCLUSION

Our results revealed a significant decrease of serum reduced glutathione (GSH) levels among groups B, C and D as compared to group A, while there was a significant increase in group C and D as compared to group B. Antioxidant and dexamethasone treatment resulted in a significant decrease of serum IL-4, malondialdehyde (MDA), and serum IgE levels in group C and D as compared to group B. Antioxidant treatment resulted in a significant decrease of serum Hsp70 level as compared to group B, while dexamethasone treatment resulted in a significant increase of serum Hsp70 level as compared to group B. This study suggests that it is likely that a combination of antioxidant vitamins may be effective in the treatment of asthma, considering their reported effects on lowering MDA, IL-4, and IgE levels, and the similar beneficial effects of dexamethasone in addition to increasing the expression of Hsp70 in the studied model of bronchial asthma.

Mechanism of dinitrochlorobenzene-induced dermatitis in mice: role of specific antibodies in pathogenesis

BACKGROUND

Dinitrochlorobenzene-induced contact hypersensitivity is widely considered as a cell-mediated rather than antibody-mediated immune response. At present, very little is known about the role of antigen-specific antibodies and B cells in the development of dinitrochlorobenzene-induced hypersensitivity reactions, and this is the subject of the present investigation.

METHODOLOGY/PRINCIPAL FINDINGS

Data obtained from multiple lines of experiments unequivocally showed that the formation of dinitrochlorobenzene-specific Abs played an important role in the development of dinitrochlorobenzene-induced contact hypersensitivity. The appearance of dinitrochlorobenzene-induced skin dermatitis matched in timing the appearance of the circulating dinitrochlorobenzene-specific antibodies. Adoptive transfer of sera containing dinitrochlorobenzene-specific antibodies from dinitrochlorobenzene-treated mice elicited a much stronger hypersensitivity reaction than the adoptive transfer of lymphocytes from the same donors. Moreover, dinitrochlorobenzene-induced contact hypersensitivity was strongly suppressed in B cell-deficient mice with no DNCB-specific antibodies. It was also observed that treatment of animals with dinitrochlorobenzene polarized Th cells into Th2 differentiation by increasing the production of Th2 cytokines while decreasing the production of Th1 cytokines.

CONCLUSIONS/SIGNIFICANCE

In striking contrast to the long-held belief that dinitrochlorobenzene-induced contact hypersensitivity is a cell-mediated immune response, the results of our present study demonstrated that the production of dinitrochlorobenzene-specific antibodies by activated B cells played an indispensible role in the pathogenesis of dinitrochlorobenzene-induced CHS. These findings may provide new possibilities in the treatment of human contact hypersensitivity conditions.

Comparative studies of lymph node cell subpopulations and cytokine expression in murine model for testing the potentials of chemicals to induce respiratory sensitization

OBJECTIVES

To investigate immunological changes in lymph nodes based on expression of cell-specific receptors and cytokine expression profile and accompanying inflammatory reactions in lungs of mice treated with chemicals of known potentials to induce respiratory sensitization and those in which activity in this regard is unclear.

MATERIALS AND METHODS

On day 1 and 7, Balb/c mice received toluene-2,4-diisocyanate (TDI), trimellitic anhydride (TMA), 1-chloro-2,4-dinitrobenzene (DNCB), glutaraldehyde (GA), formaldehyde (FA), benzalkonium chloride (ChB) or vehicle. On day 14, they received a single intranasal instillation with the same chemical or vehicle. On day 15, auricular lymph nodes (LN) were excised and used for analyzes of T-, B-cells, expression of CD44 and for the estimation of IL-4 and IFN-gamma production after in vitro stimulation with concanavalin A (ConA) and also for IL-4 and IFN-gamma mRNA expression analyses using Real-Time PCR. Inflammatory changes in lungs were observed by estimation of TNF-alpha and MIP-2 concentrations and cell numbers and their type in BAL.

RESULTS

There were no significant changes in cell subpopulations of T helper cells in LN. The percent of B cells was significantly increased after treatment with DNCB, TDI, and GA. Increased expression of CD44 on T cells was also observed. Both IL-4 and IFN-gamma were found increased in TDI- and FA-treated mice, while only IL-4 was increased in TMA-treated mice. Real-Time PCR analyses, however, showed increased IL-4 mRNA expression for TDI- and TMA-, and IFN-gamma mRNA expression for DNCB-treated mice. We haven't observed significant changes in inflammatory reactions in the lungs of exposed animals.

CONCLUSIONS

Studying immunological changes with first determining the activation status of T cells followed by analyzes of expression of mRNA for Th1 and Th2 cytokines in murine model could be a useful method for assessment of the potentials of chemicals to induce respiratory sensitization but is not sufficient. Addition of ventilatory measurements, but not necessarily inflammatory reactions, could complete the model.

Immunoglobulin E antibodies enhance pulmonary inflammation induced by inhalation of a chemical hapten

BACKGROUND

Occupational exposure to chemicals is an important cause of asthma. Recent studies indicate that IgE antibodies enhance sensitization to chemicals in the skin.

OBJECTIVE

We investigated whether IgE might similarly promote the development of airway inflammation following inhalation of a contact sensitizer.

METHODS

A model of chemical-induced asthma is described in which introduction of the low-molecular-weight compound, trinitrobenzene sulphonic acid (TNBS), via the respiratory tract was used for both sensitization and challenge. The role of IgE antibodies in the immune response to inhaled TNBS in this model was assessed by comparing the responses of wild-type (WT) and IgE-deficient (IgE(-/-)) mice on the BALB/c background. Reconstitution of circulating IgE levels by intravenous injection of IgE antibodies into IgE(-/-) mice before sensitization was performed to confirm the role of IgE in any differences observed between the responses of WT and IgE(-/-) mice.

RESULTS

Intranasal challenge of TNBS-sensitized (but not sham-sensitized control mice) induced intense pulmonary inflammation. Macrophages, eosinophils and lymphocytes, including T, B, natural killer and natural killer T cells, were recruited to the airway and the animals displayed bronchial hyperresponsiveness (BHR) to methacholine. Serum levels of murine mast cell protease-1 (mMCP-1) were elevated suggesting mast cell activation. In contrast, the development of airway inflammation, recruitment of lymphocytes, induction of BHR and production of mMCP-1 were all significantly attenuated in IgE-deficient mice. Reconstitution of IgE(-/-) mice with IgE (of unrelated antigen specificity) before sensitization partially restored these features of asthma.

CONCLUSION

Our data indicate that IgE antibodies non-specifically enhance the development of airway inflammation induced by exposure to chemical antigens.

Chronic mouse model of TMA-induced contact hypersensitivity

Due to the steadily increasing incidence of atopic dermatitis (AD), especially in children, there is a high medical need for new therapies and improved animal models. In mice, trimellitic anhydride (TMA) is routinely used to trigger T-cell-dependent contact hypersensitivity (CHS) reactions. In this study, we compared the standard acute TMA-induced CHS in Balb/c mice with subacute and chronic models of TMA-induced ear inflammation. Compared to the acute model, the chronic CHS model more closely reflects characteristics of AD, such as typical morphological changes of the inflamed skin, strong infiltration with T cells, major histocompatibility complex II-positive cells, eosinophils, and mast cells, a T-helper cell-type (Th) 2 cytokine profile and a strong increase of serum IgE levels. Moreover, a strong lymph node involvement with T-helper cell dominance and a mixed Th1/Th2 T-cell differentiation and activation pattern was demonstrated. Importantly, as demonstrated by successful therapy with prednisolone, the chronic TMA-induced CHS model, in contrast to acute and subacute models, made prolonged therapeutic treatment of a pre-established skin inflammation possible. Altogether, we present an improved model of mouse T-cell-dependent skin inflammation for AD. We hope this model will enhance the predictive value of animal models for therapeutic treatment of atopic eczema.

The contact allergen dinitrochlorobenzene (DNCB) and respiratory allergy in the Th2-prone Brown Norway rat

All LMW respiratory allergens known to date can also induce skin allergy in test animals. The question here was if in turn skin allergens can induce allergy in the respiratory tract. Respiratory allergy was tested in Th2-prone Brown Norway (BN) rats by dermal sensitization with the contact allergen dinitrochlorobenzene (DNCB; 1%, day 0; 0.5%, day 7) and a head/nose-only inhalation challenge of 27mg/m3 of DNCB (15 min, day 21), using a protocol that successfully identified chemical respiratory allergens. Skin allergy to DNCB was examined in BN rats and Th1-prone Wistar rats in a local lymph node assay followed by a topical patch challenge of 0.1% DNCB. Sensitization of BN rats via the skin induced DNCB-specific IgG in serum, but not in all animals, and an increased number of CD4+ cells in the lung parenchyma. Subsequent inhalation challenge with DNCB did not provoke apneas or allergic inflammation (signs of respiratory allergy) in the BN rats. However, microarray analysis of mRNA isolated from the lung revealed upregulation of the genes for Ccl2 (MCP-1), Ccl4 (MIP-1beta), Ccl7 and Ccl17. Skin challenge induced considerably less skin irritation and allergic dermatitis in the BN rat than in the Wistar rat. In conclusion, the Th2-prone BN rat appeared less sensitive to DNCB than the Wistar rat; nevertheless, DNCB induced allergic inflammation in the skin of BN rats but even a relatively high challenge concentration did not induce allergy in the respiratory tract, although genes associated with allergy were upregulated in lung tissue.

Respiratory sensitization and allergy: current research approaches and needs

There are currently no accepted regulatory models for assessing the potential of a substance to cause respiratory sensitization and allergy. In contrast, a number of models exist for the assessment of contact sensitization and allergic contact dermatitis (ACD). Research indicates that respiratory sensitizers may be identified through contact sensitization assays such as the local lymph node assay, although only a small subset of the compounds that yield positive results in these assays are actually respiratory sensitizers. Due to the increasing health concerns associated with occupational asthma and the impending directives on the regulation of respiratory sensitizers and allergens, an approach which can identify these compounds and distinguish them from contact sensitizers is required. This report discusses some of the important contrasts between respiratory allergy and ACD, and highlights several prominent in vivo, in vitro and in silico approaches that are being applied or could be further developed to identify compounds capable of causing respiratory allergy. Although a number of animal models have been used for researching respiratory sensitization and allergy, protocols and endpoints for these approaches are often inconsistent, costly and difficult to reproduce, thereby limiting meaningful comparisons of data between laboratories and development of a consensus approach. A number of emerging in vitro and in silico models show promise for use in the characterization of contact sensitization potential and should be further explored for their ability to identify and differentiate contact and respiratory sensitizers. Ultimately, the development of a consistent, accurate and cost-effective model will likely incorporate a number of these approaches and will require effective communication, collaboration and consensus among all stakeholders.

Validation of a mouse model of chemical-induced asthma using trimellitic anhydride, a respiratory sensitizer, and dinitrochlorobenzene, a dermal sensitizer

BACKGROUND

Occupational asthma can be caused by chemicals. Previously, we established a murine model of immunologically mediated chemical-induced asthma using toluene diisocyanate.

OBJECTIVE

We sought to verify this model using trimellitic anhydride (TMA), a respiratory sensitizer, and 1-chloro-2,4-dinitrobenzene (DNCB), a dermal sensitizer.

METHODS

BALB/c mice received dermal applications (vehicle or chemical) on days 1 and 7. On day 10, they received an intranasal instillation (vehicle or chemical). Whole-body plethysmography (enhanced pause) was used to monitor changes in ventilatory function and methacholine reactivity. Pulmonary inflammation was assessed by using bronchoalveolar lavage (cells, TNF-alpha levels, and macrophage inflammatory protein 2 levels). Immunologic parameters included total serum IgE levels, lymphocyte distribution in auricular and cervical lymph nodes, and IL-4 and IFN-gamma levels in supernatants of lymph node cells incubated with or without concanavalin A.

RESULTS

Mice dermally treated and intranasally challenged with TMA experienced markedly increased enhanced pause immediately after intranasal challenge and increased methacholine reactivity (24 hours later). Mice similarly treated with DNCB did not show any ventilatory changes. Neutrophil influx and increased macrophage inflammatory protein 2 and TNF-alpha levels were found in bronchoalveolar lavage fluid in both TMA- and DNCB-treated mice. The proportion of CD19+ B cells was increased in auricular and cervical lymph nodes of TMA-treated mice. IL-4 and IFN-gamma levels were increased in supernatants of concanavalin A-stimulated auricular and cervical lymph node cells of TMA- or DNCB-treated mice; however, the relative proportions of IL-4 and IFN-gamma levels differed between TMA- and DNCB-treated mice. Serum total IgE levels were increased in TMA-treated mice only.

CONCLUSION

Both compounds induce a mixed T(H)1-T(H)2 response, but only TMA induced ventilatory changes.

CLINICAL IMPLICATIONS

In the workplace avoiding skin contact with chemical sensitizers might be advised to prevent chemical-induced asthma.

Methods for the identification of chemical respiratory allergens in rodents: comparisons of cytokine profiling with induced changes in serum IgE

No validated or widely recognized test methods are currently available for the prospective identification of chemicals with the potential to cause respiratory allergy. The cellular and molecular mechanisms that result in the induction of chemical sensitization of the respiratory tract are unclear, although there is evidence for the selective development of T helper 2 (Th2)-type responses and, in some cases, the production of IgE antibody. We have therefore examined the utility of cytokine profiling using BALB/c mice, together with the measurement of induced increases in the total serum concentration of IgE in the Brown Norway (BN) rat, as markers for the prospective identification of chemical respiratory allergens. Responses provoked by the reference respiratory allergen trimellitic anhydride (TMA) have been compared with those stimulated by the respiratory sensitizing diisocyanates toluene diisocyanate (TDI) and hexamethylene diisocyanate (HDI) and by the acid anhydride hexahydrophthalic anhydride (HHPA). Topical exposure of BN rats to TMA, TDI and HHPA each provoked marked immune activation (increases in lymph node cellularity and proliferation). However, only treatment with TMA stimulated vigorous increases in the total serum concentration of IgE. In contrast, exposure to HHPA, TDI or HDI failed to provoke significant changes in serum IgE concentration or induced only transient and relatively weak increases in serum IgE levels. In parallel experiments using BALB/c strain mice, however, topical application of all four chemical respiratory allergens provoked a marked Th2-type cytokine secretion profile in draining lymph node cells. These data suggest that the measurement of induced changes in serum IgE is not sufficiently sensitive for the robust identification of chemical respiratory allergens. Furthermore, irrespective of the reasons for variations in TMA-induced IgE production among BN rats, doubts remain regarding the utility of these animals for the characterization of immune responses to chemical allergens. Cytokine profiling using the BALB/c strain mouse apparently provides a more robust method for the hazard assessment of chemical respiratory allergens.

Occupational asthma: a valid model for adult asthma?

PURPOSE OF REVIEW

Developments in the understanding of causes and natural history of occupational asthma may allow improved primary, secondary and tertiary preventive strategies for occupational asthma. This may also lead to improved understanding of preventable contributing factors to the development and severity of nonoccupational asthma.

RECENT FINDINGS

Animal studies have demonstrated the opportunity to identify chemical sensitizers relevant to asthma. Studies of genetic markers in occupational asthma pose logistic difficulties, but preliminary studies suggest that glutathione S-transferase genotypes may predispose to development of occupational asthma induced by diisocyanates and these have also been implicated in nonoccupational asthma. Some occupational sensitizers/irritants are also found outside the workplace and may be relevant in nonoccupational asthma, for example cleaning agents, epoxy glues, hairdressing products. Accidental exposures to high concentrations of respiratory irritants have the potential to induce new asthma as well as aggravate underlying asthma in both occupational and nonoccupational settings.

SUMMARY

Better understanding of the pathogenesis of occupational asthma is important for affected workers, and also has potential relevance for nonoccupational asthma.