Chemical allergens--what are the issues?

The role of plastics in allergy, immunology, and human health: What the clinician needs to know and can do about it

The effects of plastics on human health include allergy, atopy, asthma, and immune disruption, but the consequences of chemicals used in plastic materials span nearly every organ system and age group as well. Behavioral interventions to reduce plastic chemical exposures have reduced exposure in low- and high-income populations, yet health care providers know little about plastic chemical effects and seldom offer steps to patients to limit exposure. Health care facilities also use many products that increase the risk of chemical exposures, particularly for at-risk populations such as children in neonatal intensive care units. Given that disparities in plastic chemical exposure are well documented, collaborative efforts are needed between scientists and health care organizations, to develop products that improve provider knowledge about chemicals used in plastic materials and support the use of safer alternatives in medical devices and other equipment.

An Evaluation of the Occupational Health Hazards of Peptide Couplers

Peptide couplers (also known as amide bond-forming reagents or coupling reagents) are broadly used in organic chemical syntheses, especially in the pharmaceutical industry. Yet, occupational health hazards associated with this chemical class are largely unexplored, which is disconcerting given the intrinsic reactivity of these compounds. Several case studies involving occupational exposures reported adverse respiratory and dermal health effects, providing initial evidence of chemical sensitization. To address the paucity of toxicological data, a pharmaceutical cross-industry task force was formed to evaluate and assess the potential of these compounds to cause eye and dermal irritation as well as corrosivity and dermal sensitization. The goal of our work was to inform health and safety professionals as well as pharmaceutical and organic chemists of the occupational health hazards associated with this chemical class. To that end, 25 of the most commonly used peptide couplers and five hydrolysis products were selected for in vivo, in vitro, and in silico testing. Our findings confirmed that dermal sensitization is a concern for this chemical class with 21/25 peptide couplers testing positive for dermal sensitization and 15 of these being strong/extreme sensitizers. We also found that dermal corrosion and irritation (8/25) as well as eye irritation (9/25) were health hazards associated with peptide couplers and their hydrolysis products (4/5 were dermal irritants or corrosive and 4/5 were eye irritants). Resulting outcomes were synthesized to inform decision making in peptide coupler selection and enable data-driven hazard communication to workers. The latter includes harmonized hazard classifications, appropriate handling recommendations, and accurate safety data sheets, which support the industrial hygiene hierarchy of control strategies and risk assessment. Our study demonstrates the merits of an integrated, in vivo -in silico analysis, applied here to the skin sensitization endpoint using the Computer-Aided Discovery and REdesign (CADRE) and Derek Nexus programs. We show that experimental data can improve predictive models by filling existing data gaps while, concurrently, providing computational insights into key initiating events and elucidating the chemical structural features contributing to adverse health effects. This interactive, interdisciplinary approach is consistent with Green Chemistry principles that seek to improve the selection and design of less hazardous reagents in industrial processes and applications.

Identifying a reference list of respiratory sensitizers for the evaluation of novel approaches to study respiratory sensitization

The induction of immunological responses that trigger bio-physiological symptoms in the respiratory tract following repeated exposure to a substance, is known as respiratory sensitization. The inducing compound is known as a respiratory sensitizer. While respiratory sensitization by high molecular weight (HMW) materials is recognized and extensively studied, much less information is available regarding low molecular weight (LMW) materials as respiratory sensitizers. Variability of symptoms presented in humans from such exposures, limited availability of (and access to) documented reports, and the absence of standardized and validated test models, hinders the identification of true respiratory sensitizers. This review aims to sort suspected LMW respiratory sensitizers based on available compelling, reasonable, inadequate, or questionable evidence in humans from occupational exposures and use this information to compose a reference list of reported chemical respiratory sensitizers for scientific research purposes. A list of 97 reported respiratory sensitizers was generated from six sources, and 52 LMW organic chemicals were identified, reviewed, and assigned to the four evidence categories. Less than 10 chemicals were confirmed with compelling evidence for induction of respiratory sensitization in humans from occupational exposures. Here, we propose the reference list for developing novel research on respiratory sensitization.

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

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

Critical Evaluation of Low-Molecular Weight Respiratory Sensitizers and Their Protein Reactivity Potential Toward Lysine Residues

Interest in the development of methods to evaluate the respiratory sensitization potential of low-molecular weight chemicals continues, but no method has yet been generally accepted or validated. A lack of chemical reference standards, together with uncertainty regarding relevant immunological mechanisms, has hampered method development. The first key event in the development of either skin or respiratory sensitization is the formation of stable adducts of the chemical with host proteins. This event is measured in the Direct Peptide Reactivity Assay using cysteine- and lysine-containing model peptides. It is hypothesized that protein reactivity and subsequent adduct formation may represent the earliest point of divergence in the pathways leading to either skin or respiratory sensitization. Direct Peptide Reactivity Assay data for 200 chemicals were compiled and grouped into respiratory, skin and nonsensitizers. Chemicals grouping was based on extensive literature research and expert judgment. To evaluate if chemical groups represent different peptide reactivity profiles, peptide reactivity data were clustered and compared with information on protein binding mechanisms and chemical categories available via the Organization for Economic Co-operation and Development. Toolbox. Respiratory sensitizers (n = 15) showed a significant (3-fold) higher lysine reactivity than skin sensitizers (n = 129). However, this difference was driven largely by the high representation of acid anhydrides among the respiratory sensitizers that showed clear lysine selectivity. Collectively, these data suggest that preferential reactivity for either cysteine or lysine is associated primarily with chemical structure, and that lysine preference is not a unifying characteristic of chemical respiratory allergens.

ChAlPred: A web server for prediction of allergenicity of chemical compounds

BACKGROUND

Allergy is the abrupt reaction of the immune system that may occur after the exposure to allergens such as proteins, peptides, or chemicals. In the past, various methods have been generated for predicting allergenicity of proteins and peptides. In contrast, there is no method that can predict allergenic potential of chemicals. In this paper, we described a method ChAlPred developed for predicting chemical allergens as well as for designing chemical analogs with desired allergenicity.

METHOD

In this study, we have used 403 allergenic and 1074 non-allergenic chemical compounds obtained from IEDB database. The PaDEL software was used to compute the molecular descriptors of the chemical compounds to develop different prediction models. All the models were trained and tested on the 80% training data and evaluated on the 20% validation data using the 2D, 3D and FP descriptors.

RESULTS

In this study, we have developed different prediction models using several machine learning approaches. It was observed that the Random Forest based model developed using hybrid descriptors performed the best, and achieved the maximum accuracy of 83.39% and AUC of 0.93 on validation dataset. The fingerprint analysis of the dataset indicates that certain chemical fingerprints are more abundant in allergens that include PubChemFP129 and GraphFP1014. We have also predicted allergenicity potential of FDA-approved drugs using our best model and identified the drugs causing allergic symptoms (e.g., Cefuroxime, Spironolactone, Tioconazole). Our results agreed with allergenicity of these drugs reported in literature.

CONCLUSIONS

To aid the research community, we developed a smart-device compatible web server ChAlPred (https://webs.iiitd.edu.in/raghava/chalpred/) that allows to predict and design the chemicals with allergenic properties.

Behaviour of chemical respiratory allergens in novel predictive methods for skin sensitisation

Asthma resulting from sensitisation of the respiratory tract to chemicals is an important occupational health issue, presenting many toxicological challenges. Most importantly there are no recognised predictive methods for respiratory allergens. Nevertheless, it has been found that all known chemical respiratory allergens elicit positive responses in assays for skin sensitising chemicals. Thus, chemicals failing to induce a positive response in skin sensitisation assays such as the local lymph node assay (LLNA) lack not only skin sensitising activity, but also the potential to cause respiratory sensitisation. However, it is unclear whether it will be possible to regard chemicals that are negative in in vitro skin sensitisation tests also as lacking respiratory sensitising activity. To address this, the behaviour of chemical respiratory allergens in the LLNA and in recently validated non-animal tests for skin sensitisation have been examined. Most chemical respiratory allergens are positive in one or more newly validated non-animal test methods, although the situation varies between individual assays. The use of an integrated testing strategy could provide a basis for recognition of most respiratory sensitising chemicals. However, a more complete picture of the performance characteristics of such tests is required before specific recommendations can be made.

Anti-hapten antibodies in response to skin sensitization

Whereas T lymphocyte (T cell) activation is the key event in the acquisition of skin sensitization and subsequent elicitation of allergic contact dermatitis, the humoral component of immune responses to organic contact allergens has received little consideration. There is evidence that, in experimental animals, topical exposure to potent contact allergens is associated with B cell activation and proliferation, and hapten-specific antibody production. However, there is very limited evidence available for anti-hapten antibody responses being induced following topical exposure of humans to contact allergens. Nevertheless, it is important to appreciate that there are almost no negative studies in which evidence for antibody production as the result of skin sensitization has been sought and not found. That is, there is absence of evidence rather than evidence of absence. Furthermore, exposure to chemical respiratory allergens, in which the skin has been implicated as a potential route of sensitization, results in anti-hapten antibody responses. It is proposed that skin sensitization to contact allergens will normally be accompanied by antibody production. The phenomenon is worthy of investigation, as anti-hapten antibodies could potentially influence and/or regulate the induction of skin sensitization. Moreover, such antibodies may provide an informative correlate of the extent to which sensitization has been acquired.

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

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

Prick testing with chemicals in the diagnosis of occupational contact urticaria and respiratory diseases

BACKGROUND

Little is known about the use of prick tests with chemicals in diagnosing occupational diseases.

OBJECTIVE

To evaluate the use of prick tests in the diagnosis of occupational contact urticaria, asthma and rhinitis caused by chemicals (undertaken at the Finnish Institute of Occupational Health).

MATERIAL AND METHODS

We retrospectively reviewed the patient and test files for the period 1 January 1991 to 31 May 2011. Prick tests were performed with chemical solutions and human serum albumin (HSA)-chemical conjugates.

RESULTS

Positive prick test reactions to isocyanate-HSA conjugates were associated with isocyanate-specific IgE in all 20 patients, and 17 patients had a relevant occupational disease. Positive reactions to chloramine-T-HSA conjugates in 10 patients also indicated the presence of specific IgE, although occupational diseases were not always diagnosed. Eleven of 17 patients with positive reactions to persulfate solutions were diagnosed with an occupational disease. Methacrylates, colophonium-related substances, amine hardeners, ethanolamines, glutaraldehyde, glyoxal, pyrocatechol and ammonium thioglycolate did not elicit any relevant prick test reactions. No generalized reactions were detected.

CONCLUSION

Prick tests can be safely used for diagnosing contact urticaria, asthma and rhinitis caused by isocyanates, chloramine-T, persulfates, and chlorhexidine, but the results should be carefully interpreted and related to clinical symptoms and other diagnostic tests.

Development of a respiratory sensitization/elicitation protocol of toluene diisocyanate (TDI) in Brown Norway rats to derive an elicitation-based occupational exposure level

Toluene diisocyanate (TDI), a known human asthmagen, was investigated in skin-sensitized Brown Norway rats for its concentration×time (C×t)-response relationship on elicitation-based endpoints. The major goal of study was to determine the elicitation inhalation threshold dose in sensitized, re-challenged Brown Norway rats, including the associated variables affecting the dosimetry of inhaled TDI-vapor in rats and as to how these differences can be translated to humans. Attempts were made to duplicate at least some traits of human asthma by using skin-sensitized rats which were subjected to single or multiple inhalation-escalation challenge exposures. Two types of dose-escalation protocols were used to determine the elicitation-threshold C×t; one used a variable C (Cvar) and constant t (tconst), the other a constant C (Cconst) and variable t (tvar). The selection of the "minimal irritant" C was based an ancillary pre-studies. Neutrophilic granulocytes (PMNs) in bronchoalveolar lavage fluid (BAL) were considered as the endpoint of choice to integrate the allergic pulmonary inflammation. These were supplemented by physiological measurements characterizing nocturnal asthma-like responses and increased nitric oxide in exhaled breath (eNO). The Cconst×tvar regimen yielded the most conclusive dose-response relationship as long C was high enough to overcome the scrubbing capacity of the upper airways. Based on ancillary pre-studies in naïve rats, the related human-equivalent respiratory tract irritant threshold concentration was estimated to be 0.09ppm. The respective 8-h time-adjusted asthma-related human-equivalent threshold C×t-product (dose), in 'asthmatic' rats, was estimated to be 0.003ppm. Both thresholds are in agreement of the current ACGIH TLV(®) of TDI and published human evidence. In summary, the findings from this animal model suggest that TDI-induced respiratory allergy is likely to be contingent on two interlinked, sequentially occurring mechanisms: first, dermal sensitizing encounters high enough to cause systemic sensitization. Second, when followed by inhalation exposure(s) high enough to initiate and amplify an allergic airway inflammation, then a progression into asthma may occur. This bioassay requires an in-depth knowledge on respiratory tract dosimetry and irritation of the involved test substance to clearly understand the dosimetry causing C- and/or C×t-dependent respiratory tract irritation and eventually asthma.

Conceptual heuristic models of the interrelationships between obesity and the occupational environment

OBJECTIVE

Research and interventions targeting the relationship between work, its attendant occupational hazards, and obesity are evolving but merit further consideration in the public health arena. In this discussion paper, conceptual heuristic models are described examining the role of obesity as both a risk factor and health outcome in the occupational setting.

METHODS

PubMed was searched using specific criteria from 2000 and onwards for evidence to support conceptual models in which obesity serves as a risk factor for occupational disease or an outcome of occupational exposures. Nine models are presented: four where obesity is a risk factor and five where it is an adverse effect.

RESULTS

A broad range of work-related health effects are associated with obesity including musculoskeletal disorders, asthma, liver disease, and cardiovascular disease, among others. Obesity can be associated with occupational hazards such as shift work, sedentary work, job stress, and exposure to some chemicals.

CONCLUSION

Identification of combinations of risk factors pertinent to obesity in the occupational environment will provide important guidance for research and prevention.

The selective peptide reactivity of chemical respiratory allergens under competitive and non-competitive conditions

It is well established that certain chemicals cause respiratory allergy. In common with contact allergens, chemicals that induce sensitization of the respiratory tract must form stable associations with host proteins to elicit an immune response. Measurement of the reactivity of chemical allergens to single nucleophilic peptides is increasingly well-described, and standardized assays have been developed for use in hazard assessment. This study employed standard and modified peptide reactivity assays to investigate the selectivity of chemical respiratory allergens for individual amino acids under competitive and non-competitive conditions. The reactivity of 20 known chemical respiratory sensitizers (including diisocyanates, anhydrides, and reactive dyes) were evaluated for reactivity towards individual peptides containing cysteine, lysine, histidine, arginine, or tyrosine. Respiratory allergens exhibited the common ability to deplete both lysine and cysteine peptides; however, reactivity for histidine, arginine, and tyrosine varied between chemicals, indicating differences in relative binding affinity toward each nucleophile. To evaluate amino acid selectivity for cysteine and lysine under competitive conditions a modified assay was used in which reaction mixtures contained different relative concentrations of the target peptides. Under these reaction conditions, the binding preferences of reference respiratory and contact allergens (dinitrochlorobenzene, dinitrofluorobenzene) were evaluated. Discrete patterns of reactivity were observed showing various levels of competitive selectivity between the two allergen classes.

Contact dermatitis: from pathomechanisms to immunotoxicology

Contact allergens are small reactive chemicals. They cause allergic contact dermatitis (ACD) by activating the innate and adaptive immune system. Contact allergens are very peculiar because of their built-in autoadjuvanticity that allows them to trigger sterile inflammation following skin penetration. The innate inflammatory response involves the triggering of pattern recognition receptors either by direct chemical interaction with such receptors or by induction of endogenous activators. I discuss here the recent findings regarding prevalence and predisposition, the identification of innate immune and stress response mechanisms relevant for sensitization and the orchestration of the innate and adaptive immune response to contact allergens. Despite still significant gaps of knowledge, recent advances in our understanding of the immunopathogenesis of ACD can now be used for the development of causative treatment strategies and of in vitro alternatives to animal testing for the identification of contact allergens in immunotoxicology.

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 sensitization and allergotoxicology

Chemical sensitization remains an important environmental and occupational health issue. A wide range of substances have been shown to possess the ability to induce skin sensitization or respiratory sensitization. As a consequence, there is a need to have appropriate methods to identify sensitizing agents. Although a considerable investment has been made in exploring opportunities to develop methods for hazard identification and characterization, there are, as yet, no validated nonanimal methods available. A state of the art of the different in vitro approaches to identify contact and respiratory capacity of chemicals is covered in this chapter.

Allergic contact dermatitis: a commentary on the relationship between T lymphocytes and skin sensitising potency

T lymphocytes mediate skin sensitisation and allergic contact dermatitis. Not unexpectedly, therefore, there is considerable interest in the use of T lymphocyte-based assays as alternative strategies for the identification of skin sensitising chemicals. However, in addition to accurate identification of hazards the development of effective risk assessments requires that information is available about the relative skin sensitising potency of contact allergens. The purpose of this article is to consider the relationships that exist between the characteristics of T lymphocyte responses to contact allergens and the effectiveness/potency of sensitisation. We propose that there are 3 aspects of T lymphocyte responses that have the potential to impact on the potency of sensitisation. These are: (a) the magnitude of response, and in particular the vigour and duration of proliferation and the clonal expansion of allergen-reactive T lymphocytes, (b) the quality of response, including the balance achieved between effector and regulatory cells, and (c) the breadth of response and the clonal diversity of T lymphocyte responses. A case is made that there may be opportunities to exploit an understanding of T lymphocyte responses to contact allergens to develop novel paradigms for predicting skin sensitising potency and new approaches to risk assessment.

Potential of coculture in vitro models to study inflammatory and sensitizing effects of particles on the lung

Exposure to particulate matter (PM) like nanoparticles (NPs) has increased in the last century due to increased combustion processes, road traffic, etc. In addition, the progress in chemical and cosmetic industry led to many new compounds, e.g. fragrances, which humans are exposed to every day. Many chemicals are known to act as contact and some as respiratory sensitizers, causing allergic reactions. Exposure to small particles of less than 100 nm in diameter is linked with an increased risk of respiratory diseases, such as asthma or rhinitis. To date already more than 1000 customer products contain eNPs without knowing much about the health effects. In comparison to chemicals, the mechanisms by which PM and eNPs can cause sensitization are still not fully understood. Validated and regulatory accepted in vitro models to assess this hazard in its full range are still missing. While a huge number of animal studies contributed to our knowledge about sensitization processes, knowledge on involved cellular mechanisms is still limited. In this review relevant in vitro models to study and elucidate these mechanisms in more detail are presented and their potential to serve as part of a tiered testing strategy is discussed.

Occupational rhinitis: consensus on diagnosis and medicolegal implications

PURPOSE OF REVIEW

Work-related rhinitis is a common disease in many working groups, frequently associated with asthma. The purpose of this review is to summarize the specific literature published within the past 12 months, to discuss the diagnostic workup and to illustrate the medicolegal aspects pertaining to this disease.

RECENT FINDINGS

Recently, there has been a growing scientific interest in work-related rhinitis, which includes both occupational rhinitis and work-exacerbated rhinitis. The epidemiological relevance and the relationships to asthma have been evaluated. New etiologic agents and populations at risk have been identified. A new definition and classification, and a diagnostic algorithm, have been proposed.

SUMMARY

In consideration of the epidemiological relevance and of the medicolegal implications, occupational rhinitis should be considered in daily clinical practice by all physicians. In adults with late-onset rhinitis, occupational causes should be queried and patients in whom an occupational association is suspected should be referred for specific assessments.

Methyl methacrylate and respiratory sensitization: a critical review

Methyl methacrylate (MMA) is a respiratory irritant and dermal sensitizer that has been associated with occupational asthma in a small number of case reports. Those reports have raised concern that it might be a respiratory sensitizer. To better understand that possibility, we reviewed the in silico, in chemico, in vitro, and in vivo toxicology literature, and also epidemiologic and occupational medicine reports related to the respiratory effects of MMA. Numerous in silico and in chemico studies indicate that MMA is unlikely to be a respiratory sensitizer. The few in vitro studies suggest that MMA has generally weak effects. In vivo studies have documented contact skin sensitization, nonspecific cytotoxicity, and weakly positive responses on local lymph node assay; guinea pig and mouse inhalation sensitization tests have not been performed. Cohort and cross-sectional worker studies reported irritation of eyes, nose, and upper respiratory tract associated with short-term peaks exposures, but little evidence for respiratory sensitization or asthma. Nineteen case reports described asthma, laryngitis, or hypersensitivity pneumonitis in MMA-exposed workers; however, exposures were either not well described or involved mixtures containing more reactive respiratory sensitizers and irritants. The weight of evidence, both experimental and observational, argues that MMA is not a respiratory sensitizer.

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.