Differential roles for CD4 and CD8 T cells after diisocyanate sensitization: genetic control of TH2-induced lung inflammation

Dermal exposure determines the outcome of repeated airway exposure in a long-term chemical-induced asthma-like mouse model

BACKGROUND

Exposure to diisocyanates is an important cause of occupational asthma (OA) in the industrialized world. Since OA occurs after long-term exposure to diisocyanates, we developed a chronic mouse model of chemical-induced asthma where toluene diisocyanate (TDI) was administered at two different exposure sites.

OBJECTIVES

Evaluating the effect of long-term respiratory isocyanate exposure - with or without prior dermal exposure- on sensitization, inflammatory responses and airway hyperreactivity (AHR).

METHODS

On days 1 and 8, BALB/c mice were dermally treated (20 μl/ear) with 0.5% 2,4-toluene diisocyanate TDI or the vehicle acetone olive oil (AOO) (3:2). Starting from day 15, mice received intranasal instillations with 0.1% TDI of vehicle five times in a week, for five successive weeks. One day after the last instillation airway hyperreactivity (AHR) to methacholine was assessed, followed by an evaluation of pulmonary inflammation and structural lung changes. Immune-related parameters were assessed in the lungs (BAL and tissue), blood, cervical- and auricular lymph nodes.

RESULTS

Mice repeatedly intranasally exposed to TDI showed systemic sensitization and a mixed Th1/Th2 type immune response, without the presence of AHR. However, when mice are first dermally sensitized with TDI, followed by repeated intranasal TDI challenges, this results in a pronounced Th2 response and AHR.

CONCLUSION

Dermal exposure to TDI determines airway hyperreactivity after repeated airway exposure to TDI.

Mass spectrometry-based analysis of murine bronchoalveolar lavage fluid following respiratory exposure to 4,4'-methylene diphenyl diisocyanate aerosol

1. Diisocyanates are highly reactive electrophiles utilized in the manufacture of a wide range of polyurethane products and have been identified as causative agents of occupational allergic respiratory disease. However, in spite of the significant occupational health burden associated with diisocyanate-induced asthma, the mechanism of disease pathogenesis remains largely unknown. 2. To better understand the fate of inhaled diisocyanates, a nose-only aerosol exposure system was constructed and utilized to expose a BALB/c mouse model to an aerosol generated from 4,4'-methylene diphenyl diisocyanate (MDI). Tissue and bronchoalveolar lavage samples were evaluated 4 and 24 h post-exposure for evidence of diisocyanate-protein haptenation, and a label-free quantitative proteomics strategy was employed to evaluate relative changes to the protein content of the cellular fraction of the lavage fluid. 3. Following MDI aerosol exposure, expression of the number of proteins with immunological or xenobiotic metabolism relevance is increased, including endoplasmin, cytochrome P450 and argininosuccinate synthase. Western blot analysis indicated MDI-conjugated protein in the lavage fluid, which was identified as serum albumin. 4. Tandem mass spectrometry analysis of MDI-albumin revealed MDI conjugation occurs at a dilysine motif at Lys525, as well as at a glutamine-lysine motif at Lys414, in good agreement with previously published in vitro data on diisocyanate-conjugated serum albumin.

IL-13 is a central mediator of chemical-induced airway hyperreactivity in mice

BACKGROUND

While the importance of the Th2 cytokine IL-13 as a central mediator of airway hyperreactivity (AHR) has been described in allergic protein-induced asthma, this has never been investigated in chemical-induced asthma.

OBJECTIVE

We examined the importance of IL-13 in a mouse model of chemical-induced AHR, using toluene-2,4-diisocyanate (TDI).

METHODS

In a first set-up, wild type (WT) and IL-13 knockout (KO) C57Bl/6 mice were dermally treated on days 1 and 8 with 1% TDI or vehicle (acetone/olive oil) on both ears. On day 15, mice received an intranasal instillation with 0.1% TDI or vehicle. In a second set-up, WT mice sensitized with 1% TDI or vehicle, received i.v. either anti-IL-13 or control antibody prior to the intranasal challenge.

RESULTS

TDI-sensitized and TDI-challenged WT mice showed AHR to methacholine, in contrast to TDI-sensitized and TDI-challenged IL-13 KO mice, which also showed lower levels of total serum IgE. TDI-sensitized and TDI-challenged IL-13 KO mice had lower numbers of T-cells in the auricular lymph nodes. TDI-treated WT mice, receiving anti-IL-13, showed no AHR, in contrast to those receiving control antibody, despite increased levels of IgE. Anti-IL-13 treatment in TDI-treated WT mice resulted in lower levels of serum IL-13, but did not induce changes in T- and B-cell numbers, and in the cytokine production profile.

CONCLUSION AND CLINICAL RELEVANCE

We conclude that IL-13 plays a critical role in the effector phase of chemical-induced, immune-mediated AHR. This implicates that anti-IL-13 treatment could have a beneficial effect in patients with this asthma phenotype.

Lessons learned from mice and man: mimicking human allergy through mouse models

The relevance of using mouse models to represent human allergic pathologies is still unclear. Recent studies suggest the limitations of using models as a standard for assessing immune response and tolerance mechanisms, as mouse models often do not sufficiently depict human atopic conditions. Allergy is a combination of aberrant responses to innocuous environmental agents and the subsequent TH2-mediated inflammatory responses. In this review, we will discuss current paradigms of allergy - specifically, TH2-mediated and IgE-associated immune responses - and current mouse models used to recreate these TH2-mediated pathologies. Our overall goal is to highlight discrepancies that exist between mice and men by examining the advantages and disadvantages of allergic mouse models with respect to the human allergic condition.

Diisocyanates, occupational asthma and IgE antibody: implications for hazard characterization

Sensitization of the respiratory tract by chemicals resulting in rhinitis and asthma is an important occupational health issue. Occupational asthma is associated with significant morbidity and can be fatal. Tests for the identification and characterization of chemicals with the potential to cause sensitization of the respiratory tract are lacking. In spite of sustained interest there are no validated or widely accepted methods available, and this presents toxicologists with a considerable challenge. One important constraint on the development of appropriate testing strategies has been uncertainty and controversy about the immunological mechanisms through which chemicals may induce sensitization of the respiratory tract. By analogy with protein respiratory allergy it is legitimate to consider that IgE antibody-dependent mechanisms may play a pivotal role. However, although many aspects of chemical respiratory allergy are consistent with reactions caused by IgE antibody, uncertainty remains because among patients with occupational asthma caused by chemical respiratory allergens there are commonly a proportion, and sometimes a significant proportion, of subjects that lack detectable IgE antibody. Here we consider the relevance of IgE antibody responses for the development of a chemical respiratory allergy to diisocyanates. A case is made that IgE antibody responses are, either directly or indirectly, closely associated with occupational asthma to the diisocyanates (and to other chemical respiratory allergens). As such the argument is advanced here that IgE antibody represents an appropriate readout for the characterization of chemical respiratory allergens, and that uncertainty about mode of action should no longer represent a hurdle in the development of suitable test methods.

B-lymphocytes as key players in chemical-induced asthma

T-lymphocytes and B-lymphocytes are key players in allergic asthma, with B-lymphocytes producing antigen-specific immunoglobulins E (IgE). We used a mouse model of chemical-induced asthma and transferred B-lymphocytes from sensitized animals into naïve wild type mice, B-lymphocyte knock-out (B-KO) mice or severe combined immunodeficiency (SCID) mice. On days 1 and 8, BALB/c mice were dermally sensitized with 0.3% toluene diisocyanate (TDI) (20µl/ear). On day 15, mice were euthanized and the auricular lymph nodes isolated. B-lymphocytes (CD19⁺) were separated from the whole cell suspension and 175,000 cells were injected in the tail vein of naïve wild type, B-KO or SCID mice. Three days later, the mice received a single oropharyngeal challenge with 0.01% TDI (20µl) or vehicle (acetone/olive oil (AOO)) (controls). Airway reactivity to methacholine and total and differential cell counts in the bronchoalveolar lavage (BAL) fluid were measured 24 hours after challenge. B-lymphocytes of AOO or TDI-sensitized mice were characterized for the expression of surface markers and production of cytokines. We found that transfer of B-cells obtained from mice dermally sensitized to toluene diisocyanate (TDI) into naïve wild type mice, B-KO mice or SCID mice led, within three days, to an acute asthma-like phenotype after an airway challenge with TDI. This response was specific and independent of IgE. These B-lymphocytes showed antigen presenting capacities (CD80/CD86 and CD40) and consisted of B effector (Be)2- (IL-4) and Be1-lymphocytes (IFN-γ). The transferred B-lymphocytes were visualized near large airways, 24 hours after TDI challenge. Thus, B-lymphocytes can provoke an asthmatic response without the action of T-lymphocytes and without major involvement of IgE.

Cells and mediators in diisocyanate-induced occupational asthma

PURPOSE OF REVIEW

Diisocyanates are the most common cause of occupational asthma in many industrialized countries, and various pathogenic mechanisms have been suggested to be involved. Occupational asthma causes airway remodeling unless diagnosed and treated within a proper time frame. However, treatment modalities are limited because of an insufficient understanding regarding underlying pathogenic mechanisms.

RECENT FINDINGS

Several immunological and nonimmunological mechanisms have been suggested, indicating that the pathogenesis of occupational asthma may be more complex than other types of asthma. Airway epithelial cells are the first to encounter diisocyanates and orchestrate various responses, such as cytokine release, oxidative stress generation, and autoantibody formation. Some evidence supports the involvement of adaptive immune responses. Additional evidence suggests that other mechanisms are involved in diisocyanate-induced occupational asthma. One such candidate mechanism is oxidative stress. Oxidative stress has been shown to trigger and aid in the development of diisocyanate-induced occupational asthma in human samples and genetic studies, and some therapeutic trials were performed based on this finding.

SUMMARY

Diisocyanate-induced occupational asthma may be caused by a complex interaction of innate and adaptive immune responses. The knowledge presented in this review may help lead to the development of new treatment modalities through an increased understanding of occupational asthma pathogenesis.

Immunotoxicity and pulmonary toxicity induced by paints in Egyptian painters

Associations between painting, sensitization, and respiratory disease have received little attention, despite the extensive use of paint and paint removal products. The objectives of this study were to investigate the possible immunotoxicity and pulmonary toxicity induced by paints in Egyptian painter workers. This study was carried out on 60 adult males. Subjects were designated as controls (n = 30 healthy persons) or paint-exposed workers (n = 30). The controls and workers were then divided into four equal groups (15 individuals/group): Group I, Control group-never smoked; Group II, Smoker controls; Groups III, paint-exposed non-smoking workers; and Group IV, paint-exposed smoker workers. A complete physical examination, chest radiograph, and pulmonary function test (PFT) were performed with each subject. Serum levels of immunoglobulin (Ig) E and interleukin (IL)-4, -6, and -10, WBC sub-set counts, total numbers of WBC, and leukocyte differentials were also assessed. The pulmonary toxicity due to the paint exposures appeared in the form of allergic manifestations in the respiratory tract, significant reductions in FVC, FEV1, FEV1/FVC ratio and PEF parameters, and a reticular pattern in both lung fields. Immunotoxicity was evidenced by increases in total leukocyte levels, total lymphocytes, CD8(+) T-lymphocytes, B (CD19(+))-lymphocytes, NK (CD3(+)CD16(+)CD56(+)) cells, and eosinophils, as well as a significant decrease in CD4+ T-lymphocyte; there were also significant elevations in serum IgE, IL-4, and IL-6, and a significant reduction in IL-10, levels in these hosts. Based on these results, we assert that repeated paint exposure is associated with pulmonary and immune system toxicities that may lead to an augmentation of allergic diseases.

Immune sensitization to methylene diphenyl diisocyanate (MDI) resulting from skin exposure: albumin as a carrier protein connecting skin exposure to subsequent respiratory responses

Background

Methylene diphenyl diisocyanate (MDI), a reactive chemical used for commercial polyurethane production, is a well-recognized cause of occupational asthma. The major focus of disease prevention efforts to date has been respiratory tract exposure; however, skin exposure may also be an important route for inducing immune sensitization, which may promote subsequent airway inflammatory responses. We developed a murine model to investigate pathogenic mechanisms by which MDI skin exposure might promote subsequent immune responses, including respiratory tract inflammation.

Methods

Mice exposed via the skin to varying doses (0.1-10% w/v) of MDI diluted in acetone/olive oil were subsequently evaluated for MDI immune sensitization. Serum levels of MDI-specific IgG and IgE were measured by enzyme-linked immunosorbant assay (ELISA), while respiratory tract inflammation, induced by intranasal delivery of MDI-mouse albumin conjugates, was evaluated based on bronchoalveolar lavage (BAL). Autologous serum IgG from "skin only" exposed mice was used to detect and guide the purification/identification of skin proteins antigenically modified by MDI exposure in vivo.

Results

Skin exposure to MDI resulted in specific antibody production and promoted subsequent respiratory tract inflammation in animals challenged intranasally with MDI-mouse albumin conjugates. The degree of (secondary) respiratory tract inflammation and eosinophilia depended upon the (primary) skin exposure dose, and was maximal in mice exposed to 1% MDI, but paradoxically limited in mice receiving 10-fold higher doses (e.g. 10% MDI). The major antigenically-modified protein at the local MDI skin exposure site was identified as albumin, and demonstrated biophysical changes consistent with MDI conjugation.

Conclusions

MDI skin exposure can induce MDI-specific immune sensitivity and promote subsequent respiratory tract inflammatory responses and thus, may play an important role in MDI asthma pathogenesis. MDI conjugation and antigenic modification of albumin at local (skin/respiratory tract) exposure sites may represent the common antigenic link connecting skin exposure to subsequent respiratory tract inflammation.

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.

Choice of mouse strain influences the outcome in a mouse model of chemical-induced asthma

Background

The development of occupational asthma is the result of interactions between environmental factors and individual susceptibility. We assessed how our model of chemical-induced asthma is influenced by using different mouse strains.

Methodology/Principal Findings

On days 1 and 8, male mice of 7 different strains (BALB/c, BP/2, A/J, C57Bl/6, DBA/2, CBA and AKR) were dermally treated with toluene-2,4-diisocyanate (TDI) (0.3%) or vehicle (acetone/olive oil, AOO, 2∶3) on each ear (20 µl). On day 15, they received an oropharyngeal instillation of TDI (0.01%) or AOO (1∶4). Airway reactivity to methacholine, total and differential cell counts in bronchoalveolar lavage (BAL) and total serum IgE and IgG_2a levels were measured. Lymphocyte subpopulations in auricular lymph nodes and in vitro release of cytokines by ConA stimulated lymphocytes were assessed. In TDI-sensitized and challenged mice, airway hyper-reactivity was only observed in BALB/c, BP/2, A/J and AKR mice; airway inflammation was most pronounced in BALB/c mice; numbers of T-helper (CD4⁺), T-activated (CD4⁺CD25⁺), T-cytotoxic (CD8⁺) and B- lymphocytes (CD19⁺) were increased in the auricular lymph nodes of BALB/c, BP/2, A/J and CBA mice; elevated concentrations of IL-4, IL-10, IL-13 and IFN-γ were detected in supernatant of lymphocytes from BALB/c, BP/2, A/J, C57Bl/6 and CBA mice cultured with concanavaline A, along with an increase in total serum IgE.

Conclusion

The used mouse strain has considerable and variable impacts on different aspects of the asthma phenotype. The human phenotypical characteristics of chemically-induced occupational asthma were best reproduced in Th2-biased mice and in particular in BALB/c mice.

Skin exposure and asthma: is there a connection?

Numerous occupational and environmental exposures that increase asthma risk have been identified. Research and prevention have focused primarily on the respiratory tract. However, recent studies suggest that the skin may also be an important route of exposure and site of sensitization that contributes to asthma development. Factors that impair skin barrier function, such as filaggrin gene mutations or skin trauma, may facilitate allergen entry and promote Th2-like sensitization and subsequent asthma. Animal studies demonstrate that skin exposure to chemical and protein allergens is highly effective at inducing sensitization, with subsequent inhalation challenge eliciting asthmatic responses. A similar role for human skin exposure to certain sensitizing agents, such as isocyanates, is likely. Skin exposure methodologies are being developed to incorporate skin exposure assessment into epidemiology studies investigating asthma risk factors.

PTEN as a unique promising therapeutic target for occupational asthma

The tumor suppressor phosphatase and tensin homologue deleted on chromosome ten (PTEN) dephophorylates phosphatidylinositol 3,4,5-triphosphate (PIP3) and is a key negative regulator of phosphoinositide kinase-3 (PI3K) signaling pathway. PTEN also suppresses cellular motility through mechanisms that may be partially independent of phosphatase activity. PTEN is one of the most commonly lost tumor suppressors in human cancers, and its down-regulation is also implicated in several other diseases including airway inflammatory diseases. There is increasing evidence regarding the protective effects of PTEN on the bronchial asthma which is induced by complex signaling networks. Very recently, as for the occupational asthma (OA) with considerable controversy for its pathobiologic mechanisms, PTEN has been considered as a key molecule which is capable of protecting toluene diisocyanate (TDI)-induced asthma, suggesting that PTEN is located at switching point of various molecular signals in OA. Knowledge of the mechanisms of PTEN regulation/function could direct to the pharmacological manipulation of PTEN. This article reviews the latest knowledge and studies on the roles and mechanisms of PTEN in OA.

Effector and regulatory mechanisms in allergic contact dermatitis

Allergic contact dermatitis (ACD), one of the commonest occupational diseases, is a T-cell-mediated skin inflammation caused by repeated skin exposure to contact allergens, i.e. nonprotein chemicals called haptens. Allergic contact dermatitis, also referred to as contact hypersensitivity, is mediated by CD8+ T cells, which are primed in lymphoid organs during the sensitization phase and are recruited in the skin upon re-exposure to the hapten. Subsets of CD4+ T cells endowed with suppressive activity are responsible for both the down-regulation of eczema in allergic patients and the prevention of priming to haptens in nonallergic individuals. Therefore, ACD should be considered as a breakdown of the skin immune tolerance to haptens. Recent advances in the pathophysiology of ACD have demonstrated the important role of skin innate immunity in the sensitization process and have revisited the dogma that Langerhans cells are mandatory for CD8+ T-cell priming. They have also introduced mast cells as a pivotal actor in the magnitude of the inflammatory reaction. Finally, the most recent studies address the nature, the mode and the site of action of the regulatory T cells that control the skin inflammation with the aim of developing new strategies of tolerance induction in allergic patients.

Lung/skin connections in occupational lung disease

PURPOSE OF REVIEW

Exposure to occupational and environmental agents can cause a spectrum of lung diseases that are predominantly immune-mediated. Research and prevention have focused primarily on the respiratory tract. Recent studies, however, suggest that the skin may also be an important route of exposure and site of sensitization. This article highlights key findings, focusing on isocyanate asthma and chronic beryllium disease.

RECENT FINDINGS

Occupational lung diseases such as isocyanate asthma and chronic beryllium disease continue to occur despite reduced airborne exposures. Although challenging to quantify, recent studies have documented isocyanate and beryllium skin exposure, even with the use of personal protective clothing. Factors that impair skin barrier function, such as trauma, may promote sensitization to such agents. Animal studies demonstrate that skin exposure to isocyanates and protein allergens is highly effective at inducing sensitization, with subsequent inhalation challenge eliciting asthmatic responses. Limited clinical studies suggest a similar role for human skin exposure to certain sensitizing agents.

SUMMARY

Recent findings support a greater focus on the role of skin exposure in the development of certain occupational and environmental lung diseases. Although further research is needed, it is prudent to reduce both skin and inhalation exposures.

A case of isocyanate-induced asthma possibly complicated by food allergy after peanut consumption: a case report

Background

Isocyanates are extensively used in the manufacture of polyurethane foams, plastics, coatings or adhesives. They are a major cause of occupational asthma in a proportion of exposed workers. Recent findings in animal models have demonstrated that isocyanate-induced asthma does not always represent an IgE-mediated sensitization, but still a mixed profile of CD4+ Th1 and TH2, as well as a CD8+ immune response. Despite immunologic similarities between this pathology and IgE-mediated food allergies, this co-morbidity is rarely reported.

Case presentation

A 50-year old man employed as vehicle body painter, for 8 years complained about breathlessness, wheezing, sneezing, nasal obstruction and excessive production of mucus during the use of DuPont Refinish Centari Tintings – an acrylic enamel tint. Symptoms occurred 15–20 minutes after workplace exposure and usually persisted until evening, or at times, up to two consecutive days. The above mentioned symptoms were associated with a decrease of lung functions parameters. The use of inhaled adrenergic bronchio-dilatators and steroids relived the symptoms.

In addition, three years ago he developed an anaphylactic reaction due to peanut consumption, experiencing urticaria, angioedema and airway obstruction. He was successfully treated in the hospital. Later, the subject exhibited labial itching, as well as orbital and perioral angioedema, 20 minutes after stationary performance of challenge test with peanuts.

Evaluating the reported data, this process might be developed rather due to induction of a TH2 profile, because in both cases have occurred IgE-mediated symptoms. A less plausible mechanism could be the presence of isocyanates in peanuts due to a probable contamination by pesticides resulting in an allergic reaction after "consumption" of di-isocyanate as long as the isocyanate contamination of peanuts has not been proven.

Conclusion

Despite the lack of relevant laboratory findings, this might be the first case of isocyanate-induced occupational asthma described in a patient who developed peanut allergy symptoms later in his life. However, in order to take further suitable precautions, further studies are necessary to elucidate the questions posed in this report.

Cell types involved in allergic asthma and their use in in vitro models to assess respiratory sensitization

This review first describes the mechanism and cell types involved in allergic asthma, which is a complex clinical disease characterized by airway obstruction, airway inflammation and airway hyperresponsiveness to a variety of stimuli. The development of allergic asthma exists of three phases, namely the induction phase, the early-phase asthmatic reaction (EAR) and the late-phase asthmatic reaction (LAR). In the induction phase, antigen-presenting cells play a major role. Most important cells in the EAR are mast cells, and during the LAR, various cell types, such as eosinophils, neutrophils, T cells, macrophages, dendritic cells (DCs), and cells that endow structure are involved. In occupational asthma, this immunological mechanism is involved in 90% of the cases. The second part of this review gives an overview of in vitro models to assess the hazardous potential of high- and low-molecular weight chemicals on the respiratory system. In order to develop a good in vitro model for respiratory allergy, the choice of appropriate cell types is important. Epithelial cells, macrophages and DCs are currently the most used models in this field of research.

Th17 and allergy

The identification of novel helper T (Th) cell subsets, i.e., IL-17-producing Th cells (Th17 cells) and regulatory T cells (Treg cells), provided new insight into our understanding of the molecular mechanisms involved in the development of infectious and autoimmune diseases as well as immune responses, and thus led to revision of the classic Th1/Th2 paradigm. Several current lines of evidence from gene-deficient mice indicate that IL-17 and Th17 cells, but not IFN-gamma and Th1 cells, are responsible for the development of autoimmune diseases such as murine arthritis and encephalomyelitis, which have classically been considered to be Th1-mediated disorders. Th17 cells may also contribute to the pathogenesis of classically recognized Th2-mediated allergic disorders. In this review, we summarize the current knowledge regarding IL-17 and Th17 cells and discuss their potential roles in the pathogenesis of allergic disorders.

Maternal allergic contact dermatitis causes increased asthma risk in offspring

Background

Offspring of asthmatic mothers have increased risk of developing asthma, based on human epidemiologic data and experimental animal models. The objective of this study was to determine whether maternal allergy at non-pulmonary sites can increase asthma risk in offspring.

Methods

BALB/c female mice received 2 topical applications of vehicle, dinitrochlorobenzene, or toluene diisocyanate before mating with untreated males. Dinitrochlorobenzene is a skin-sensitizer only and known to induce a Th1 response, while toluene diisocyanate is both a skin and respiratory sensitizer that causes a Th2 response. Both cause allergic contact dermatitis. Offspring underwent an intentionally suboptimal protocol of allergen sensitization and aerosol challenge, followed by evaluation of airway hyperresponsiveness, allergic airway inflammation, and cytokine production. Mothers were tested for allergic airway disease, evidence of dermatitis, cellularity of the draining lymph nodes, and systemic cytokine levels. The role of interleukin-4 was also explored using interleukin-4 deficient mice.

Results

Offspring of toluene diisocyanate but not dinitrochlorobenzene-treated mothers developed an asthmatic phenotype following allergen sensitization and challenge, seen as increased Penh values, airway inflammation, bronchoalveolar lavage total cell counts and eosinophilia, and Th2 cytokine imbalance in the lung. Toluene diisocyanate treated interleukin-4 deficient mothers were able to transfer asthma risk to offspring. Mothers in both experimental groups developed allergic contact dermatitis, but not allergic airway disease.

Conclusion

Maternal non-respiratory allergy (Th2-skewed dermatitis caused by toluene diisocyanate) can result in the maternal transmission of asthma risk in mice.

Diisocyanate asthma and gene-environment interactions with IL4RA, CD-14, and IL-13 genes

BACKGROUND

Diisocyanate asthma (DA) affects 2% to 10% of exposed workers, yet the pathogenetic mechanisms underlying this disorder remain ill defined.

OBJECTIVE

To determine if specific single nucleotide polymorphisms (SNPs) of interleukin 4 receptor alpha (IL4RA), IL-13, and CD14 promoter genes are associated with DA.

METHODS

Sixty-two workers with DA confirmed by specific inhalation challenge (SIC) and 75 diisocyanate-exposed, SIC-negative workers were analyzed for SNPs associated with IL4RA, IL-13, and CD14 promoter genes.

RESULTS

No associations were found with individual SNPs and DA. When stratified according to specific diisocyanate exposure, a significant association was found between IL4RA (I50V) II and DA among individuals exposed to hexamethylene diisocyanate (HDI) (odds ratio [OR], 3.29; 95% confidence interval [CI], 1.33-8.14; P = .01) only. Similarly, the IL4RA (I50V) II and IL-13 (R110Q) RR combination was significantly associated with DA in HDI-exposed workers (OR, 4.13; 95% CI, 1.35-12.68; P = .01), as was the IL4RA (I50V) II and CD14 (C159T) CT genotype combination (OR, 5.2; 95% CI, 1.82-14.88; P = .002) and the triple genotype combination IL4RA (I50V) II, IL-13 (R110Q) RR, and CD14 (C159T) CT (OR, 6.4; 95% CI, 1.57-26.12; P = .01).

CONCLUSIONS

Gene-environmental interactions may contribute to the pathogenesis of DA, and gene-gene interactions may modulate this relationship.

Promise and pitfalls in animal-based asthma research: building a better mousetrap

Asthma is one of the leading chronic diseases in the world today. An essential component of the asthma research endeavor is the animal-based experimental disease system, which provides knowledge that is not attainable through study of patients alone. Animal research is especially valuable for elucidating pathophysiology, drug testing, and as an adjunct for interpreting the results of human clinical trials. However, controversies surrounding animal systems data and at the interface between animal and human studies raise questions regarding the true utility of experimental asthma research. We consider here the considerable promise and important limitations of animal-based systems and their prospects for the future study asthma.

Prevention of IL-1 signaling attenuates airway hyperresponsiveness and inflammation in a murine model of toluene diisocyanate-induced asthma

BACKGROUND

IL-1 is a pleotropic cytokine that has been shown to play a prominent role in asthma induced by large-molecular-weight proteins. Increased IL-1 immunostaining in the submucosa of patients with toluene diisocyanate (TDI)-induced asthma has also been observed, suggesting that this cytokine might also be important in asthma associated with low-molecular-weight chemicals.

OBJECTIVE

We sought to determine the role of IL-1 signaling in airway reactivity and inflammation by using a murine model of TDI-induced asthma.

METHODS

C57BL/6 mice were exposed to TDI by means of vapor inhalation (20 ppb; 4 hours per day, 5 days per week, for 6 weeks) and then challenged 2 weeks later by inhalation with 20 ppb TDI vapor for 1 hour.

RESULTS

Sensitized-challenged mice showed increased airway hyperresponsiveness (AHR), increased levels of TDI-specific IgG1 antibodies, airway epithelial thickening, inflammation consisting of infiltrating lymphocytes and eosinophils, and increased mRNA expression of IL-4, intercellular adhesion molecule 1, and vascular cell adhesion molecule 1 in the lung. Prevention of IL-1 signaling through deletion of the IL-1 receptor type I or administration of neutralizing antibodies to both IL-1beta and IL-1alpha abrogated the development of TDI-induced asthma. A partial reduction in AHR and TDI-specific IgG1 levels was observed in mice administered anti-IL-1beta, whereas anti-IL-1alpha had no effect on either parameter. Antibodies to IL-1beta or IL-1alpha alone blocked airway inflammation and the expression of IL-4 and adhesion molecules in the lung.

CONCLUSIONS

These results suggest that IL-1 signaling is critical for AHR and airway inflammation, with IL-1beta and IL-1alpha having unique and overlapping roles in TDI-induced occupational asthma.

What makes a chemical a respiratory sensitizer?

PURPOSE OF REVIEW

In this article we consider the characteristics that are associated with chemical respiratory allergens, and that may be essential for effective sensitization of the respiratory tract.

RECENT FINDINGS

Chemical respiratory allergens share some characteristics with other chemical allergens, specifically chemical allergens that cause skin sensitization and allergic contact dermatitis. The unique and defining characteristic of chemical respiratory allergens, which in most instances distinguishes them from contact allergens, is the ability to provoke the preferential development of T helper 2-type immune responses. There are, in addition, other characteristics, such as the ability to increase matrix metalloproteinase expression or to cause perturbation of redox homeostasis, that may in some instances facilitate the induction or expression of respiratory allergy, but it is not yet clear if these attributes are common or essential properties of all chemical respiratory sensitizers.

SUMMARY

Predicting which chemical allergens may selectively induce respiratory sensitization is an important objective, but remains a significant challenge because our understanding of the relevant physicochemical characteristics and biological properties that confer on chemicals respiratory allergenic potential is incomplete.

Genetics and the occupational environment

PURPOSE OF REVIEW

This article will focus on the role of risk factors including genetic factors in the development of sensitization and occupational asthma.

RECENT FINDINGS

We will review the recent literature published on the genetics of occupational asthma, especially on genes coding for class II human leukocyte antigen and on respiratory antioxidant mechanisms. We will also discuss published work on non-occupational asthma and on allergic rhinitis because this information may contribute to a better understanding of the mechanisms involved in occupational asthma and serve to confirm data obtained on the disease. To date, although some progress has been made in the field of occupational asthma genetics, most studies were based on small sample sizes, findings were not replicated, and gene-environment interactions have not yet been established.

SUMMARY

Occupational asthma is a widespread and frequent condition and has relevant long-term adverse health and economic consequences. The search for risk factors including genetic factors in the development of the disease and an understanding of the mechanisms of interaction between genes and environment are important because the identification of individuals who are susceptible to occupational asthma together with an effective control of exposure to respiratory sensitizers in the workplace may be helpful in preventing the disease.

Allergen-induced cytokine phenotypes in mice: role of CD4 and CD8 T cell populations

BACKGROUND

CD4+ T cells expressing type 2 cytokines have been implicated in the pathogenesis of asthma to high-molecular-weight allergens. Topical exposure of BALB/c strain mice to low-molecular-weight chemical contact and respiratory allergens stimulates type 1 and type 2 cytokine secretion phenotypes, respectively.

OBJECTIVE

To examine the relative frequencies of cytokine-positive CD4+ and CD8+ T cells and their contributions to these cytokine secretion profiles. Methods Draining auricular lymph nodes were isolated 13 days after initiation of topical exposure of female BALB/c strain mice to chemical allergen, or to vehicle alone. The frequency of intracellular cytokine (IL-4 and IFN-gamma)-positive CD4+ and CD8+ lymphocytes was enumerated by flow cytometry. The relative contribution of CD4+ and CD8+ cells to cytokine secretion profiles was assessed by negative selection.

RESULTS

Exposure to allergen resulted in an increased frequency of both IFN-gamma+ CD4+ and CD8+ lymphocytes, although there were no marked differences between trimellitic anhydride (TMA)- and 2,4-dinitrochlorobenzene (DNCB)-activated lymph node cells. Treatment with TMA induced approximately five times as many IL-4+ CD4+ cells as did exposure to DNCB. This pattern of cytokine staining was also observed for a further pair of contact and respiratory allergens; respectively, formalin and fluorescein isothiocyanate.

CONCLUSION

These data demonstrate that the divergent immune responses induced in mice by different classes of chemical allergen are independent of changes in the frequency of IFN-gamma+ cells, but are associated with differential frequencies of IL-4-expressing CD4+ T cells.

Occupational asthma

Substantial epidemiologic and clinical evidence indicates that agents inhaled at work can induce asthma. In industrialized countries, occupational factors have been implicated in 9 to 15% of all cases of adult asthma. Work-related asthma includes (1) immunologic occupational asthma (OA), characterized by a latency period before the onset of symptoms; (2) nonimmunologic OA, which occurs after single or multiple exposures to high concentrations of irritant materials; (3) work-aggravated asthma, which is preexisting or concurrent asthma exacerbated by workplace exposures; and (4) variant syndromes. Assessment of the work environment has improved, making it possible to measure concentrations of several high- and low-molecular-weight agents in the workplace. The identification of host factors, polymorphisms, and candidate genes associated with OA is in progress and may improve our understanding of mechanisms involved in OA. A reliable diagnosis of OA should be confirmed by objective testing early after its onset. Removal of the worker from exposure to the causal agent and treatment with inhaled glucocorticoids lead to a better outcome. Finally, strategies for preventing OA should be implemented and their cost-effectiveness examined.

Animal models for diisocyanate asthma: answers for lingering questions

PURPOSE OF REVIEW

Diisocyanates are the leading cause of occupational asthma, the most commonly reported lung disease associated with the workplace. Clinical studies have implicated the immune system in the pathogenesis of occupational asthma, but ethical and moral issues prevent mechanistic investigations in humans. For this reason, the development and characterization of animal models are germane to further understanding of diisocyanate occupational asthma and to identify avenues for therapeutic intervention. This review will highlight important features of existing experimental animal models with emphasis on new developments.

RECENT FINDINGS

Experimental animal models of diisocyanate occupational asthma have demonstrated an immunological basis for the disease. Mice can be sensitized by dermal or respiratory exposure, suggesting that either exposure route may be important in the workplace. Recent findings show that sensitized mice develop airway hyperreactivity and inflammation, reflective of human disease. The transfer of lymphocytes or serum from sensitized mice can cause clinical disease in naive mice. Transgenic animals have identified a role for specific immunity, including the involvement of T-helper type 1/2 responses as well as CD4 and CD8 T cells in diisocyanate occupational asthma. Recent animal models have shown that sensitization can occur through subchronic inhalation of vapor-phase diisocyanate at levels as low as 20 ppb.

SUMMARY

Recent progress using animal models has been instrumental in furthering current understanding of the involvement of the immune system in disease pathogenesis. The demonstration of diisocyanate occupational asthma in a murine model after sub-chronic inhalation exposure at relevant exposure levels should provide opportunities for more accurate risk assessment data.

Advances in asthma, allergy and immunology series 2004: basic and clinical immunology

This review highlights some of the most significant advances in basic and clinical immunology that were published from August 2002 to December 2003, focusing on manuscripts that appeared in the Journal. Articles selected were those considered most relevant to Journal readers. With regard to basic immunology, this report includes articles describing FcepsilonRI expression in mucosal Langerhans cells and type II dendritic cells, mechanisms of TH1 and TH2 regulation, the role of Foxp3 in the development of CD4+CD25+ regulatory T cells, and the increasing importance of Toll receptors in immunity. Articles related to clinical immunology that were selected include the first report of lymphocyte subsets values from a large cohort of normal children; the description of new genetic defects in primary immunodeficiencies; a description of the complications of gene therapy for X-linked severe combined immunodeficiency; a report of 79 patients with hyper-IgM syndrome; a report of the mechanism of action and complications of intravenous immunoglobulin; a report of new approaches for immunotherapy; and an article on advances in HIV infection and management, including a report of defensins, small molecules with anti-HIV properties. Also summarized is an article that studied the immune system during a prolonged stay in the Antarctic, a model for human studies on the effect of environmental conditions similar to space expeditions.