Airway mucosal inflammation in occupational asthma induced by toluene diisocyanate

Comparison of high- and low-molecular-weight sensitizing agents causing occupational asthma: an evidence-based insight

INTRODUCTION

The many substances used at the workplace that can cause sensitizer-induced occupational asthma are conventionally categorized into high-molecular-weight (HMW) agents and low-molecular-weight (LMW) agents, implying implicitly that these two categories of agents are associated with distinct phenotypic profiles and pathophysiological mechanisms.

AREAS COVERED

The authors conducted an evidence-based review of available data in order to identify the similarities and differences between HMW and LMW sensitizing agents.

EXPERT OPINION

Compared with LMW agents, HMW agents are associated with a few distinct clinical features (i.e. concomitant work-related rhinitis, incidence of immediate asthmatic reactions and increase in fractional exhaled nitric oxide upon exposure) and risk factors (i.e. atopy and smoking). However, some LMW agents may exhibit 'HMW-like' phenotypic characteristics, indicating that LMW agents are a heterogeneous group of agents and that pooling them into a single group may be misleading. Regardless of the presence of detectable specific IgE antibodies, both HMW and LMW agents are associated with a mixed Th1/Th2 immune response and a predominantly eosinophilic pattern of airway inflammation. Large-scale multicenter studies are needed that use objective diagnostic criteria and assessment of airway inflammatory biomarkers to identify the pathobiological pathways involved in OA caused by the various non-protein agents.

4,4'-Methylene diphenyl diisocyanate exposure induces expression of alternatively activated macrophage-associated markers and chemokines partially through Krüppel-like factor 4 mediated signaling in macrophages

Occupational exposure to the most widely used monomeric diisocyanate (dNCO), 4,4'-methylene diphenyl diisocyanate (MDI), may lead to the development of occupational asthma (OA). Alveolar macrophages with alternatively activated (M2) phenotype have been implicated in allergic airway responses and the pathogenesis of asthma. Recent in vivo studies demonstrate that M2 macrophage-associated markers and chemokines are induced by MDI-exposure, however, the underlying molecular mechanism(s) by which this proceeds is unclear.Following MDI exposure (in vivo and in vitro) M2 macrophage-associated transcription factors (TFs), markers, and chemokines were determined by RT-qPCR, western blots, and ELISA.Expression of M2 macrophage-associated TFs and markers including Klf4/KLF4, Cd206/CD206, Tgm2/TGM2, Ccl17/CCL17, Ccl22/CCL22, and CCL24 were induced by MDI/MDI-GSH exposure in bronchoalveolar lavage cells (BALCs)/THP-1 macrophages. The expression of CD206, TGM2, CCL17, CCL22, and CCL24 are upregulated by 3.83-, 7.69-, 6.22-, 6.08-, and 1.90-fold in KLF4-overexpressed macrophages, respectively. Endogenous CD206 and TGM2 were downregulated by 1.65-5.17-fold, and 1.15-1.78-fold, whereas CCL17, CCL22, and CCL24 remain unchanged in KLF4-knockdown macrophages. Finally, MDI-glutathione (GSH) conjugate-treated macrophages show increased chemotactic ability to T-cells and eosinophils, which may be attenuated by KLF4 knockdown.Our data suggest that MDI exposure may induce M2 macrophage-associated markers partially through induction of KLF4.

Mast Cells in Upper and Lower Airway Diseases: Sentinels in the Front Line

Mast cells (MCs) are fascinating cells of the innate immune system involved not only in allergic reaction but also in tissue homeostasis, response to infection, wound healing, protection against kidney injury, the effects of pollution and, in some circumstances, cancer. Indeed, exploring their role in respiratory allergic diseases would give us, perhaps, novel therapy targets. Based on this, there is currently a great demand for therapeutic regimens to enfeeble the damaging impact of MCs in these pathological conditions. Several strategies can accomplish this at different levels in response to MC activation, including targeting individual mediators released by MCs, blockade of receptors for MC-released compounds, inhibition of MC activation, limiting mast cell growth, or inducing mast cell apoptosis. The current work focuses on and summarizes the mast cells' role in pathogenesis and as a personalized treatment target in allergic rhinitis and asthma; even these supposed treatments are still at the preclinical stage.

Occupational lung disease: A narrative review of lung conditions from the workplace

Occupational lung diseases are lung conditions caused or made worse by materials when a person is exposed to a workplace. The diagnosis of an occupational disease is important for workers' decision to continue work and for their eligibility under compensation programmes. We revisit the existing lung diseases that are closely associated with the occupation at the workplace namely occupational asthma, silicosis, black lung disease, farmers' lung disease, asbestos-linked disease, and hypersensitivity pneumonitis. Occupational lung diseases contribute toward global health and economic impacts. Prevention and control of occupational lung diseases require a collaborative effort among employers, workers, occupational physicians, pulmonary physicians, industrial hygienists, and members from other disciplines.

Associations Between Glutathione-S-Transferase Genotypes and Bronchial Hyperreactivity Patients With Di-isocyanate Induced Asthma. A Follow-Up Study

Introduction: Di-isocyanates TDI (toluene di-isocyanate), MDI (diphenylmethane di-isocyanate), and HDI (hexamethylene di-isocyanate) are the most common chemicals causing occupational asthma. Di-isocyanate inhalation has been reported to induce oxidative stress via reactive oxygen and nitrogen species leading to tissue injury. Glutathione transferases (GSTs) and N-acetyltransferases (NATs) are detoxifying enzymes whose general function is to inactivate electrophilic substances. The most important genes regulating these enzymes, i.e., GSTM1, GSTP1, GSTT1, NAT1, and NAT2 have polymorphic variants resulting in enhanced or lowered enzyme activities. Since inability to detoxify harmful oxidants can lead to inflammatory processes involving activation of bronchoconstrictive mechanisms, we studied whether the altered GST and NAT genotypes were associated with bronchial hyperreactivity (BHR) in patients with di-isocyanate exposure related occupational asthma, irrespective of cessation of di-isocyanate exposure, and adequacy of asthma treatment.

Methods: Polymerase chain reaction (PCR) based methods were used to analyze nine common polymorphisms in GSTM1, GSTM3, GSTP1, GSTT1, NAT1, and NAT2 genes in 108 patients with diagnosed occupational di-isocyanate-induced asthma. The genotype data were compared with spirometric lung function and BHR status at diagnosis and in the follow-up examination on average 11 years (range 1–22 years) after the asthma diagnosis. Serum IgE and IL13 levels were also assessed in the follow-up phase.

Results: An association between BHR and GSTP1 slow activity (Val105/Val105) genotype was demonstrated in the subjects at the follow-up phase but not at the diagnosis phase. Moreover, the patients with the GSTP1 slow activity genotype exhibited characteristics of Th-2 type immune response more often compared to those with the unaltered GSTP1 gene. Interestingly, all 10 patients with the GSTP1 slow activity genotype had both the GSTM3 slow activity genotype and the unaltered GSTT1 gene.

Discussion: The results suggest associations of the low activity variants of the GSTP1 gene with BHR. The fact that these associations came up only at the follow-up phase when the subjects were not any more exposed to di-isocyanates, and used asthma medication, suggest that medication and environmental factors influence the presentation of these associations. However, due to the exploratory character of the study and relatively small study size, the findings remain to be confirmed in future studies with larger sample sizes.

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

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.

IL-4 and IL-5 secretions predominate in the airways of wistar rats exposed to toluene diisocyanate vapor

OBJECTIVES

We established a Wistar rat model of asthma caused by toluene diisocyanate (TDI) exposure, and investigated the relationship between TDI exposure concentrations and respiratory hypersensitivity, airway inflammation, and cytokine secretions in animals, to better understand the mechanism of TDI induced occupational asthma.

METHODS

Wistar rats were exposed to two different concentrations of TDI vapor four hours a day for five consecutive days. Bronchoalveolar lavage (BAL) was performed, and differential leucocytes from the BAL fluid were analyzed. Lung histopathological examination was carried out to investigate the inflammatory status in the airways. Production of cytokines interleukin (IL)-4 and IL-5 productions in the BAL fluid in vivo was determined with enzyme-linked immunosorbent assay kits.

RESULTS

The TDI-exposed rats exhibited greater airway hypersensitivity symptoms than the control rats. The BAL differential cell count and lung histopathological examination demonstrated that inflammation reactions were present in both the central and peripheral airways, characterized with marked infiltration of eosinophils in the TDI-exposed rats. The cytokine assay showed that IL-4 and IL-5 were predominantly produced in the BAL fluid in vivo.

CONCLUSIONS

These findings imply that TDI exposure concentrations may greatly affect the occurrence and extent of inflammatory events and that Th2 type cytokines may play an important role in the immunopathogenesis of TDI-induced occupational respiratory hypersensitivity.

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.

Review of the occupational exposure to isocyanates: Mechanisms of action

Polyurethanes are useful polymers in a large variety of technical and consumer products that are generally made from diisocyanates and polyols or similar compounds. Toluene diisocyanate (TDI), 4,4'-methylenediphenyl diisocyanate (MDI) and 1,6'-hexamethylene diisocyanate (HDI) are useful for polyurethane products. Isocyanates are reactive chemicals that can be handled without problems in manufacturing or technical environments. In general, consumers may only have contact with these chemicals on rare occasions. The objective of this study was to review the mechanisms of action of inhalation of isocyanates. This paper describes, in summary, the potential occupational exposure to isocyanates, the chemistry and reactivity of isocyanates, the results from genotoxicity studies, investigative toxicity studies, metabolism and results from epidemiology studies on isocyanate-exposed workers. The overall conclusion is that because humans are not exposed to high levels of respiratory isocyanate particles, concerns over the possible development of lung tumors should not be relevant. There are many mechanisms of action induced by isocyanates, but those entities are unclear. This is because these mechanisms act simultaneously and are complex.

Pathogenesis and disease mechanisms of occupational asthma

Occupational asthma (OA) is one of the most common forms of work-related lung disease in all industrialized nations. The clinical management of patients with OA depends on an understanding of the multifactorial pathogenetic mechanisms that can contribute to this disease. This article discusses the various immunologic and nonimmunologic mechanisms and genetic susceptibility factors that drive the inflammatory processes of OA.

Environmental isocyanate-induced asthma: morphologic and pathogenetic aspects of an increasing occupational disease

Occupational diseases affect more and more people every year. According to the International Labour Organization (ILO), in 2000 an estimated amount of at least 160 million people became ill as a result of occupational-related hazards or injuries. Globally, occupational deaths, diseases and injuries account for an estimated loss of 4% of the Gross Domestic Product. Important substances that are related to occupational diseases are isocyanates and their products. These substances, which are used in a lot of different industrial processes, are not only toxic and irritant, but also allergenic. Although the exposure to higher concentrations could be monitored and restricted by technical means, very low concentrations are difficult to monitor and may, over time, lead to allergic reactions in some workers, ending in an occupational disease. In order to prevent the people from sickening, the mechanisms underlying the disease, by patho-physiological and genetical means, have to be known and understood so that high risk groups and early signs in the development of an allergic reaction could be detected before the exposure to isocyanates leads to an occupational disease. Therefore, this paper reviews the so far known facts concerning the patho-physiologic appearance and mechanisms of isocyanate-associated toxic reactions and possible genetic involvement that might trigger the allergic reactions.

Asthma phenotypes in adults and clinical implications

It is becoming increasingly recognized that asthma is a heterogeneous disease, whether based on clinical factors, including the patient's age at diagnosis, symptom spectrum and treatment response, triggering factors, or the level and type of inflammation. Attempts to analyze the importance of these characteristics to the clinical presentation of asthma have led to the appreciation of numerous separate and overlapping asthma phenotypes. However, these approaches are 'biased' and based on the clinician/scientist's own experience. Recently, unbiased approaches have also been attempted using both molecular and statistical tools. Early results from these approaches have supported and expanded on the clinician's concepts. However, until specific biologic markers are identified for any of these proposed phenotypes, the definitive nature of any phenotype will remain speculative.

Mast cells in lung inflammation

Mast cells play an important role in the lung in both health and disease. Their primary role is to initiate an appropriate program of inflammation and repair in response to tissue damage initiated by a variety of diverse stimuli. They are important for host immunity against bacterial infection and potentially in the host immune response to non small cell lung cancer. In situations of ongoing tissue damage, the sustained release of numerous pro-inflammatory mediators, proteases and cytokines, contributes to the pathophysiology of lung diseases such as asthma and interstitial lung disease. A key goal is the development of treatments which attenuate adverse mast cell function when administered chronically to humans in vivo. Such therapies may offer a novel approach to the treatment of many life-threatening diseases.

Leukocyte nicotinamide adenine dinucleotide phosphate-reduced oxidase is required for isocyanate-induced lung inflammation

BACKGROUND

Isocyanates are low-molecular-weight compounds noted for inducing occupational and environmental asthma. Isocyanate-induced lung disease, an oxidant stress-dependent pulmonary inflammation, is the leading cause of occupational asthma.

OBJECTIVES

To address the role of leukocyte-produced oxidants in airway inflammation induced by toluene diisocyanate (TDI), and to elucidate the role of leukocyte nicotinamide adenine dinucleotide phosphate-reduced (NADPH) oxidase in pathogenesis by TDI.

METHODS

Wild-type mice and NADPH oxidase-deficient mice (neutrophil cytosolic factor 1 mutant, Ncf1(-/-)) were intranasally injected, challenged with inhalatory TDI, and then investigated for lung inflammation.

RESULTS

Cell infiltration in lung tissue and leukocytes in bronchoalveolar lavage, airway reactivity to a methacholine challenge, and TDI-induced inflammatory cytokine expression and nuclear factor activation in the lung tissue were all markedly lower in Ncf1(-/-) mice. Wild-type mice treated with blocking antibodies against CD4 and IL-17 showed markedly lower TDI-induced airway hyperresponsiveness.

CONCLUSION

Leukocyte NADPH oxidase is an essential regulator in TDI-induced airway inflammation through redox modification of immune responses.

Toluene diisocyanate (TDI) induces calcium elevation and interleukine-4 (IL-4) release - early responses upon TDI stimulation

Occupational exposure to toluene diisocyanats (TDI) may cause asthma. In asthma patients, the allergic syndromes correlate cytokine production with the elevation in cytosolic calcium concentration [Ca(2+)](c) of lymphocytes in airway. We previously found TDI induces calcium signaling in neuronal cells. TDI mainly gets into human body via inhalation; therefore this study investigated the possibility of TDI inducing the changes in [Ca(2+)](c) in airway. We used human lung epithelial cell line H1355, human T-cell line Jurkat, and human neuroblastoma SH-SY5Y cells to present the kinds of cells existing in airway. The changes of [Ca(2+)](c) were measured by Fura-2 fluorescent dye. Results show that TDI induced an elevation in [Ca(2+)](c )in those cell lines and two primary isolated cells, bovine adrenal chromaffin cells and human white blood cells. Cytokine release and their gene expressions of Jurkat cells and human white blood cells were measured by ELISA and reverse transcription polymerase chain reaction. TDI acutely promoted the interleukine-4 (IL-4) release significantly in both Jurkat cells and human white blood cells. TDI-induced IL-4 release was suppressed in the presence of 1,2-bis- (O-aminophenoxy)ethane-N,N,N',N'- tetraacetic acid (BAPTA), an intracellular Ca(2+) chelator, in Jurkat cells. In the hand of gene expression, TDI induced an increase in the mRNA level of TNF-alpha and IL-4 in Jurkat cells. We conclude that the release of IL-4 were coupled with the elevation in [Ca(2+)](c) induced by TDI. Further studies are required to clarify the roles of TDI-induced IL-4 secretion in acute inflammation.

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.

Matrix metalloproteinases-7, -8, -9 and TIMP-1 in the follow-up of diisocyanate-induced asthma

BACKGROUND

Diisocyanate-induced asthma (DIA) is known to be associated with poor prognosis. We wished to clarify if matrix metalloproteinases (MMP)-7, -8 or -9 or tissue inhibitor of matrix metalloproteinases (TIMP-1) are associated with the functional or inflammatory outcome in DIA patients.

METHODS

This is a longitudinal study where 17 patients with DIA diagnosed by a specific challenge test to diisocyanates were monitored. Exposure to diisocyanates was terminated seven (mean) months before the challenge test. The studies included spirometry, histamine challenge test and bronchoscopy. MMP-7, MMP-8, TIMP-1 [Enzyme-linked immunosorbent assay (ELISA)- and immunofluorometric assay-methods], MMP-9 (ELISA and zymography), interferon-gamma, tumour necrosis factor-alpha, interleukin-6, -8, -15, -17, CXCL-5/ENA-78, monocyte chemoattractant protein-1 and macrophage inhibitory factor (MIF) (ELISA) were assayed from bronchoalveolar lavage (BAL) fluid. Inhaled steroid therapy was initiated after the examinations, which were repeated at 6 months and at 3 years during the treatment. The results were compared with those of 15 healthy controls.

RESULTS

Inhaled steroid medication increased BAL levels of MMP-9 and MMP-9/TIMP-1 and decreased MMP-7 and MMP-7/TIMP-1. The increase in MMP-9 levels was associated with a decline in the TH-2 type inflammation.

CONCLUSIONS

Our data suggest that reduced TH-2 type inflammation in DIA after inhaled steroid medication is reflected as elevated MMP-9 and MMP-9/TIMP-1 levels in BAL. MIF may be the inducer of MMP-9. This might point to some protective role for MMP-9 in DIA.

Patients with mild-to-moderate asthma may develop clinically significant chronic obstructive pulmonary disease

BACKGROUND AND OBJECTIVE

Little is known about the aetiology and clinical characteristics of COPD among people who have never smoked.

METHODS

A case-control study was conducted to describe the potential risk factors for clinically significant COPD among smokers and people who had never smoked. Medical record reviews and scoring of high-resolution computed tomography (HRCT) findings were performed in patients with clinically significant COPD (defined as having post-bronchodilator FEV(1)/FVC < 0.7 and FEV(1) < 60% of the predicted values). Pathological analyses were performed in some patients following autopsy.

RESULTS

Among the 9493 subjects screened, 424 (4.5%) were diagnosed with clinically significant COPD. Forty-nine (11.6% of clinically significant COPD) were never smokers (NSCOPD), and a comparative group of 98 smoking patients with COPD was randomly selected (SMCOPD). NSCOPD was characterized by predominantly female sex (87.8%) and a high prevalence of physician-diagnosed asthma (61.2%). Similar levels of reduction in %FEV(1) and %FEF(25-75%) were found in NSCOPD and SMCOPD, but there were higher %DL(CO) values and fewer low attenuation areas on HRCT in NSCOPD. More than half of the NSCOPD patients without a history of asthma had features of asthma. More than one-third of NSCOPD patients with an asthma history had never had a severe attack. At autopsy, both NSCOPD and SMCOPD showed wall thickening and inflammatory cell infiltration in small airways, and the number of CD4(+)-T cells was increased in NSCOPD.

CONCLUSION

In elderly Japanese, COPD among never smokers is largely attributable to asthma. Airflow limitation in NSCOPD results from small airway disease (airway predominant phenotype) rather than parenchymal destruction (emphysematous phenotype).

Soluble human leucocyte antigen-G and interleukin-10 levels in isocyanate-induced asthma

BACKGROUND

We previously reported that in moderate-to-severe asthma there is a deficit of IL-10 secretion that could prevent the production of soluble HLA-G (sHLA-G), a non-classical human leucocyte antigen class I molecule with tissue-protective properties in inflammatory responses.

OBJECTIVE

Our objective was to investigate the production of sHLA-G and the secretion of IL-10 by peripheral blood mononuclear cells (PBMCs) in asthma induced by isocyanates and to compare the results with those obtained in non-occupational allergic asthma.

METHOD

sHLA-G and IL-10 were measured by ELISA in the culture supernatants of unstimulated or lipopolysaccharide (LPS)-stimulated PBMCs obtained from 20 subjects with isocyanate asthma, 16 asymptomatic subjects exposed to isocyanates, 18 subjects with non-occupational allergic asthma, and 26 healthy control subjects.

RESULTS

Occupational exposure to isocyanates was associated with high baseline levels of secretion of IL-10 by PBMCs, whether or not the exposed subjects had asthmatic symptoms. However, spontaneous production of sHLA-G by PBMC was significantly higher in subjects with isocyanate asthma compared with asymptomatic-exposed controls. In contrast, PBMCs from subjects with non-occupational allergic asthma produced sHLA-G only after LPS stimulation.

CONCLUSIONS

sHLA-G production and IL-10 secretion are influenced by workplace exposure to isocyanates and by development of asthma. The different behaviour of both sHLA-G and IL-10 in asthma induced by isocyanates compared with non-occupational allergic asthma suggests a heterogeneous biological role for HLA-G molecules and for IL-10, a key cytokine of immune and inflammatory responses.

Histamine release and inflammatory cell infiltration in airway Mucosa in methylene diphenyl diisocyanate (MDI)-induced occupational asthma

INTRODUCTION

Although methylene diphenyl diisocyanate (MDI) is widely used in industries, there have been few studies of the pathogenic mechanisms of MDI-induced occupational asthma (MDI-OA).

METHODS

We performed immunohistochemical analyses, measured inflammatory mediators and cytokines, and quantified histamine release (HR) from peripheral basophils in MDI-OA patients. Thirteen MDI-exposed workers (five MDI-OA, two MDI-induced esoinophilic bronchitis, and six asymptomatic exposed controls, AEC) were enrolled.

RESULTS AND DISCUSSION

Immunochemical analyses indicated significantly increased anti-eosinophilic cationic protein-stained cells in MDI-OA patients as compared with controls (P < 0.05). Sputum eosinophil cationic protein levels were increased after MDI-specific inhalation challenge test in MDI-OA/EB patients (P < 0.02). Sputum eosinophil counts were highly correlated with IL-8 and MMP-9 levels (P < 0.05 and P < 0.01, respectively). Basophil HR was significantly increased in MDI-OA patients after stimulations with anti-IgG4 and MDI-human serum albumin conjugates (both P < 0.05). Eosinophil activation is a major feature of airway inflammation in MDI-OA patients. Increased HR by MDI may contribute to the pathogenic mechanisms of MDI-OA.

Inflammation and functional outcome in diisocyanate-induced asthma after cessation of exposure

BACKGROUND

The clinical outcome of diisocyanate-induced asthma has been found to be poor despite cessation of exposure. Our aim was to study the outcome of diisocyanate-induced asthma after initiation of inhaled steroid treatment at a mean period of 7 months (range 2-60 months) after cessation of exposure by following up lung function and bronchial inflammation.

METHODS

Bronchoscopy was performed on 17 patients 2 days after a positive inhalation challenge test, after which budesonide 1600 mug a day was started. Bronchoscopy, spirometry, and histamine challenge tests were repeated at 6 months and on average 3 years. The results were also compared with those obtained from 15 healthy control subjects.

RESULTS

Nonspecific bronchial hyperreactivity diminished significantly (P = 0.006); however, forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) values decreased, with a median yearly reduction of FEV1 of 79 ml. The count of mast cells in bronchial mucosa decreased (P = 0.012) and that of macrophages increased (P = 0.001). Interleukin-4 level in mucosa was during the first year significantly higher than in controls but its level decreased in the follow-up. Interleukin-6, interleukin-15, and tumour necrosis factor alpha messenger-RNA levels were significantly higher in hyperreactive patients than in nonhyperreactive patients at the end of the follow-up.

CONCLUSION

Our results indicate that inflammation may persist in diisocyanate-induced asthma despite inhaled steroid medication. However, TH2-type inflammation diminished. Persistent nonspecific bronchial hyperreactivity was associated with proinflammatory acting cytokines produced mainly by macrophages. Considering the poor prognosis of the disease the findings could be utilized to develop the follow-up and treatment of diisocyanate-induced asthma.

Structural changes and airway remodelling in occupational asthma at a mean interval of 14 years after cessation of exposure

BACKGROUND

Occupational asthma (OA) may cause alterations of airways with inflammation and remodelling after cessation of exposure. Although the long-term clinical, functional and induced sputum sequelae have been examined in workers removed from exposure, the long-term pathological outcomes are unknown.

OBJECTIVE

We aimed to investigate whether airway inflammation and remodelling were present in bronchial biopsies of subjects with prior OA but without evidence of persisting asthma at a mean interval of 14 years after cessation of exposure.

METHODS

Ten clinically and functionally asymptomatic subjects with a prior diagnosis of OA were recruited and underwent bronchoscopy, bronchoalveolar lavage and bronchial biopsy. Comparisons were made with biopsies from normal control subjects. Epithelial detachment, epithelial metaplasia, mucous gland and airway smooth muscle (ASM) areas as well as the distance between the epithelium and ASM were measured by image analysis. The amount of collagen present was assessed by van Gieson staining. The numbers of TGF-beta1- and eosinophil cationic protein (ECP)-positive cells were evaluated by specific immunostaining.

RESULTS

Statistically significant increases were found in the numbers of TGF-beta1- and ECP-positive cells and in the amount of subepithelial fibrosis present in the biopsies of subjects with prior OA compared with control biopsies. The distance between the epithelium and ASM was significantly reduced in the OA group. Increases in epithelial metaplasia, ASM mass, mucous gland numbers, collagen deposition and eosinophilia in the OA group were not statistically significant. There was no evidence of ongoing inflammation in the group with prior OA as assessed by the number of T lymphocytes present.

CONCLUSION

Some aspects of airway inflammation and remodelling persist in subjects with prior OA long after cessation of exposure even in the absence of clinical, sputum and functional abnormalities. These findings are relevant to the assessment of long-term sequelae in subjects with OA when reviewed after cessation of exposure.

Asthma: defining of the persistent adult phenotypes

The common disease asthma is probably not a single disease, but rather a complex of multiple, separate syndromes that overlap. Although clinicians have recognised these different phenotypes for many years, they have remained poorly characterised, with little known about the underlying pathobiology contributing to them. Development of targeted therapies for asthma, and phenotype-specific clinical trials have raised interest in these phenotypes. Improved understanding of these phenotypes in complex diseases such as asthma will also improve our ability to link specific genotypes to their associated disease, which should help development of biomarkers. However, there is no standardised method to define asthma phenotypes. This Review analyses some of the methods that have been used to define asthma phenotypes and proposes an integrated method of classification to improve our understanding of these phenotypes.

Stem cell factor expression, mast cells and inflammation in asthma

The Kit ligand SCF or stem cell factor (SCF) is a multipotent growth factor, acting as an important growth factor for human mast cells. SCF induces chemotaxis and survival of the mast cell, as well as proliferation and differentiation of immature mast cells from CD34(+) progenitors. Additionally, SCF enhances antigen-induced degranulation of human lung-derived mast cells, and induces a mast cell hyperplasia after subcutaneous administration. SCF expression increases in the airways of asthmatic patients, and this is reversed after treatment with glucocorticoids. A role for SCF may thus be hypothesized in diseases associated with a local increase in the number and/or activation of mast cells, as occurring in the airways in asthma. SCF will be reviewed as a potential therapeutic target in asthma, to control the regulation of mast cell number and activation. We here report the main pathways of SCF synthesis and signalling, and its potential role on airway function and asthma.

Airway remodelling in asthma: current understanding and implications for future therapies

Airway remodelling refers to the structural changes that occur in the airway wall in asthma. These include epithelial hyperplasia and metaplasia, subepithelial fibrosis, muscle cell hyperplasia and angiogenesis. These structural changes result in thickening of the airway wall, airway hyperresponsiveness (AHR), and a progressive irreversible loss of lung function. The precise sequence of events that take place during the remodelling process and the mechanisms regulating these changes remain poorly understood. It is thought that airway remodelling is initiated and promoted by repeated episodes of allergic inflammation that damage the surface epithelium of the airway. However, other mechanisms are also likely to contribute to this process. Moreover, the interrelationship between airway remodelling, inflammation and AHR has not been clearly defined. Currently, there are no effective treatments that halt or reverse the changes of airway remodelling and its effects on lung function. Glucocorticoids have been unable to eliminate the progression of remodelling changes and there is limited evidence of a beneficial effect from other available therapies. The search for novel therapies that can directly target individual components of the remodelling process should be made a priority. In this review, we describe the current understanding of the airway remodelling process and the mechanisms regulating its development. The impact of currently available asthma therapies on airway remodelling is also discussed.

Airway inflammatory and immunological events in a rat model exposed to toluene diisocyanate

To investigate the inflammatory and immunological events in the airway induced by a short period of repeated exposure to toluene diisocyanate (TDI), an animal model was established, which resembled the industrial field exposure. After whole body exposure of Wistar rats to 0.38 and 1.20 ppm TDI vapor 4h a day for five consecutive days in a glass chamber, bronchoalveolar lavage (BAL) was performed. BAL fluid cellular and cytokine contents were then determined. Histopathological examinations were also carried out on the lungs. The TDI vapor exposure resulted in airway symptoms similar to those in occupational asthma. BAL fluid cellular analysis and lung histopathological examination revealed that inflammatory response was characterized by marked eosinophil infiltration of the airways. The cytokine assay revealed significant production of IL-4 in the airways of the TDI exposed rats as compared to the control rats. These findings indicated that a short period of repeated exposure to TDI vapor may cause respiratory hypersensitivity in which airway inflammatory and immunological events represented by eosinophil infiltration and Th2 cytokines may play an important role. Also, this animal model may be suitable for exploring the mechanism underlying TDI-induced occupational asthma.

Regulation of stem cell factor expression in inflammation and asthma

Stem cell factor (SCF) is a major mast cell growth factor, which could be involved in the local increase of mast cell number in the asthmatic airways. In vivo, SCF expression increases in asthmatic patients and this is reversed after treatment with glucocorticoids. In vitro in human lung fibroblasts in culture, IL-1beta, a pro-inflammatory cytokine, confirms this increased SCF mRNA and protein expression implying the MAP kinases p38 and ERK1/2 very early post-treatment, and glucocorticoids confirm this decrease. Surprisingly, glucocorticoids potentiate the IL-1beta-enhanced SCF expression at short term treatment, implying increased SCF mRNA stability and SCF gene transcription rate. This potentiation involves p38 and ERK1/2. Transfection experiments with the SCF promoter including intron1 also confirm this increase and decrease of SCF expression by IL-1beta and glucocorticoids, and the potentiation by glucocorticoids of the IL-1beta-induced SCF expression. Deletion of the GRE or kappaB sites abolishes this potentiation, and the effect of IL-1beta or glucocorticoids alone. DNA binding of GR and NF-kappaB are also demonstrated for these effects. In conclusion, this review concerns new mechanisms of regulation of SCF expression in inflammation that could lead to potential therapeutic strategy allowing to control mast cell number in the asthmatic airways.

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.

Airway inflammation in aluminium potroom asthma

AIMS

To examine whether asthma induced by exposure to aluminium potroom emissions (potroom asthma) is associated with inflammatory changes in the airways.

METHODS

Bronchial biopsy specimens from 20 asthmatic workers (8 non-smokers and 12 smokers), 15 healthy workers (8 non-smokers and 7 smokers), and 10 non-exposed controls (all non-smokers) were analysed. Immunohistofluorescent staining was performed to identify mucosal total leucocytes (CD45+ leucocytes), neutrophils, and mast cells.

RESULTS

Median RBM thickness was significantly increased in both asthmatic workers (8.2 microm) and healthy workers (7.4 microm) compared to non-exposed controls (6.7 microm). Non-smoking asthmatic workers had significantly increased median density of lamina propria CD45+ leucocytes (1519 cells/mm2 v 660 and 887 cells/mm2) and eosinophils (27 cells/mm2 v 10 and 3 cells/mm2) and significantly increased concentrations of exhaled NO (18.1 ppb v 6.5 and 5.1 ppb) compared to non-smoking healthy workers and non-exposed controls. Leucocyte counts and exhaled NO concentrations varied with smoking habits and fewer leucocytes were observed in asthmatic smokers than in non-smokers Asthmatic smokers had significantly increased numbers of eosinophils in lamina propria compared to non-exposed controls (10 v 3 cells/mm2). Both eosinophilic and non-eosinophilic phenotypes of asthma were recognised in the potroom workers and signs of airway inflammation were also observed in healthy workers.

CONCLUSIONS

Airway inflammation is a central feature of potroom asthma and exposure to potroom emissions induces pathological alterations similar to those described in other types of asthma. Cigarette smoking seems to affect the underlying mechanisms involved in asthma, as the cellular composition of airway mucosa appears different in asthmatic smokers and non-smokers.

Airway Inflammation after Cessation of Exposure to Agents Causing Occupational Asthma

Subjects with occupational asthma (OA) generally present asthma symptoms and airway hyperresponsiveness after cessation of exposure. We hypothesized that they are also left with airway inflammation. We assessed 133 subjects with OA at a mean interval of 8.7 years (0.5-20.8 years) after cessation of exposure by questionnaire, airway caliber, and responsiveness to methacholine. Satisfactory samples of induced sputum were obtained from 98 subjects. We defined three groups of subjects: (1) cured: normalization of the concentration of methacholine provoking a 20% decrease in FEV1 (PC20), (2) improved: increase in PC20 by 3.2-fold or more but PC20 still abnormal, and (3) not improved: no significant change in PC20. In all, 9/28 subjects (32.1%) with no improvement versus 6/56 (10.7%) subjects with partial and complete improvements had sputum eosinophils equal to or greater than 2% and 11/28 (39.3%) subjects versus 11/56 (19.6%) subjects showed sputum neutrophils equal to or greater than 61%. Levels of interleukin-8 and of the neutrophil-derived myeloperoxidase were significantly more elevated in sputum of subjects with no improvement. Those in the cured or improved groups had a significantly longer time lapse since diagnosis and a higher PC20 at the time of diagnosis. We conclude that failure to improve after cessation of exposure to an agent causing OA is associated with airway inflammation at follow-up.

Toluene diisocyanate exposure induces laryngo-tracheal eosinophilia, which can be ameliorated by supplementation with antioxidant vitamins in guinea pigs

OBJECTIVE

Toluene diisocyanate (TDI)-induced asthma is a common cause of occupational lung disease. In addition, a sore throat is one of the complaints of TDI-exposed workers. The aim of the present study was to determine whether TDI exposure induces laryngeal and/or tracheal lesions in experimental animals.

MATERIAL AND METHODS

Guinea pigs underwent naris application of TDI three times, and their respiratory tracts were then examined using light and electron microscopy. Some animals simultaneously received vitamins C and E. which function as antioxidant agents.

RESULTS

When TDI-treated animals showed the clinical sign of labored breathing, many eosinophils had appeared in the lamina propria and mucosa of both the larynx and trachea, which finally infiltrated the tract lumen through the ruptured epithelium. Laryngo-tracheal inflammation was more severe than that observed in the lungs. However, supplementation with antioxidant vitamins in TDI-treated animals ameliorated the respiratory eosinophilia.

CONCLUSION

Naris application of TDI induced laryngotracheitis. which was significantly suppressed by the antioxidant vitamins, This implies a preventive effect of the vitamins on this occupational disease.

The bronchoalveolar epithelial permeability in house painters as determined by Tc-99m DTPA aerosol scintigraphy

PURPOSE

Isocyanates are highly reactive chemicals used in a number of industries including paints. Therefore, house painters are known to be at risk for occupational exposure to isocyanates. Our objectives in this study were: (1) to investigate the possible effects of isocyanate exposition on the bronchoalveolar epithelial permeability in house painters by using Tc-99m DTPA radioaerosol lung scintigraphy; (2) to assess whether or not some differences exist between asthmatic and non-asthmatic house painters, and (3) to determine the relationship between Tc-99m DTPA radioaerosol lung scintigraphy and the spirometric measurements, and the work duration of house painters.

MATERIALS AND METHODS

Ten non-smoking house painters (28.8 +/- 8.8 yrs) and ten healthy volunteers underwent Tc-99m DTPA radioaerosol lung scintigraphy. Following inhalation of radiotracer through a nebulizer for 5 minutes, dynamic scintigrams (1 frame/min, up to 10 min) were taken from both lungs. ROI's were drawn over the both lung area, and time-activity curves were obtained, from which the half-time (T1/2) of Tc-99m DTPA clearance was calculated. Spirometric lung function test was measured in all house painters.

RESULTS

Mean T1/2 values (min +/- SD) were 93.74 +/- 32.79 for house painters, and 90.96 +/- 40.02 for control subjects. There was no significant difference in T1/2 values of Tc-99m DTPA clearance between house painters and controls, and between asthmatic and non-asthmatic house painters as well. No correlation was observed between T1/2 values of Tc-99m DTPA clearance and spirometric measurements. In house painters, there was a positive correlation between T1/2 values of Tc-99m DTPA clearance and work duration (r = 0.73, p = 0.016).

CONCLUSIONS

Our findings indicate that in house painters, occupational exposure to isocyanates has no effect on bronchoalveolar epithelial permeability, and the rate of Tc-99m DTPA clearance shows no difference between asthmatic and non-asthmatic house painters. The positive correlation between the rate of Tc-99m DTPA clearance and work duration needs to be confirmed in larger cohorts.

Recent developments in diisocyanate asthma

OBJECTIVE

To summarize the latest experimental findings on diisocyanate asthma and discuss the impact of these data on our understanding of disease pathogenesis and diagnosis.

DATA SOURCES

The literature reviewed includes articles from PubMed (National Library of Medicine) published within the last 3 years (1999-2001). In addition, pertinent older references are discussed to provide a historical perspective and background.

STUDY SELECTION

The data discussed were chosen to highlight key concepts relevant to diisocyanate asthma pathogenesis and are grouped accordingly.

RESULTS

In many ways, diisocyanate-induced asthma mirrors allergic asthma caused by other stimuli; however, the immune-mediated pathways believed to be central to the disease have been difficult to define. Recent studies on the human immune response to diisocyanates provide additional evidence supportive of an immune basis for pathogenesis but also highlight well-recognized differences between diisocyanate asthma and common atopic asthma. Studies on the antigenic form of diisocyanates and their interaction with epithelial tissues provide new insights that may help explain these apparent immunologic differences. Genetic factors that influence disease have begun to be identified but remain poorly characterized. Associations of particular major histocompatibility complex class II alleles with diisocyanate asthma further fuel the hypothesis that immune-dependent mechanisms underlie pathogenesis, whereas associations of glutathione S-transferase polymorphisms (in conjunction with recent studies defining the effects of diisocyanates on thiol-redox homeostasis) may implicate additional antigen-independent mechanisms. Long-term follow-up studies of diisocyanate asthma patients have confirmed the prognostic value of early removal of symptomatic patients from exposure and highlight the need for effective diagnostic tests of sensitivity and susceptibility.

CONCLUSIONS

Diisocyanate-induced asthma appears to be a multifactorial disease involving the immune system, airway epithelium, and genetic factors. The potential long-term adverse effects of diisocyanate exposure in sensitized patients underscore the need for further studies to elucidate the pathogenesis of this disease and identify biomarkers for sensitization and susceptibility.

Glutathione S-transferase GSTP1 is a susceptibility gene for occupational asthma induced by isocyanates

BACKGROUND

Polymorphism at the pi class glutathione-S-transferase locus (GSTP1) is associated with allergen-induced asthma and related phenotypes.

OBJECTIVE

We sought to determine whether GSTP1 polymorphism influences susceptibility to asthma induced by toluene diisocyanate (TDI).

METHODS

The role of GSTP1 was assessed in 131 workers exposed to TDI, 92 with TDI-induced asthma and 39 asymptomatic subjects. The phenotype of the disease was characterized by using detailed clinical history, lung volumes, airway responsiveness to methacholine, and airway responsiveness to TDI. GST genotypes were determined by using PCR-based assays.

RESULTS

In patients exposed to TDI for 10 or more years, the frequency of the GSTP1 Val/Val genotype was lower in subjects who had asthma (odds ratio, 0.23; 95% confidence interval, 0.05-1.13; P =.074). Similarly, the frequency of this genotype was significantly lower in subjects with evidence of moderate-to-severe airway hyperresponsiveness to methacholine compared with the frequency in subjects with normal or mild hyperresponsiveness (P =.033).

CONCLUSION

These data suggest that homozygosity for the GSTP1*Val allele confers protection against TDI-induced asthma and airway hyperresponsiveness. This view is supported by the finding that the protective effect increases in proportion to the duration of exposure to TDI.

Local increase in the number of mast cells and expression of nerve growth factor in the bronchus of asthmatic patients after repeated inhalation of allergen at low-dose

BACKGROUND

Repeated inhalation of allergen at low-dose induces an increase in bronchial hyper-responsiveness, without any associated symptom. The concomitant events in the bronchus have not been described.

OBJECTIVE

We have studied the dynamic number of mast cells in the airways of patients with mild asthma before and after repeated inhalation of allergen at low-dose and the expression of nerve growth factor (NGF), which is reported to promote growth and survival of mast cells.

METHODS

Twelve patients with mild asthma to cat allergen were enrolled at random in a blind placebo-controlled study, and submitted to repeated low-dose allergen exposure (1/5 of the provocative dose). Mast cells were immunolocalized using an antibody against mast cell tryptase. NGF and its high affinity receptor, TrkA, were immunolocalized using anti-NGF and anti-TrkA antibodies, respectively. NGF mRNA was quantified by competitive polymerase chain reaction (PCR) after reverse transcription of total RNA extracted from bronchial biopsy. NGF protein levels were measured by ELISA in bronchoalveolar lavage (BAL) fluid.

RESULTS

Bronchial mast cell number was increased significantly after allergen exposure as compared with before. NGF expression in the bronchus was immunolocalized mainly to epithelial cells, but also to fibroblasts, blood vessels, and a few infiltrated cells. NGF mRNA levels in bronchial biopsies were increased significantly after allergen exposure. The high affinity receptor for NGF, TrkA, was immunolocalized to the infiltrated mast cell membrane.

CONCLUSION

Our study shows that the increase in the number of mast cells and in the expression of NGF induced by allergen exposure in the bronchus of asthmatic patients is occurring before the onset of symptoms. In addition, our finding of the presence of the TrkA receptor on the membrane of the infiltrated mast cell in situ brings evidence of the mast cell as a target cell for the growth factor activity of NGF in the airways in asthma.

Glutathione S-transferase genotypes and allergic responses to diisocyanate exposure

Diisocyanates are the most common low molecular weight chemicals to cause occupational asthma. However, only some 5-10% of exposed workers develop asthma, which suggests an underlying genetic susceptibility. Diisocyanates and their metabolites may be conjugated with glutathione by glutathione S-transferases (GSTs). We examined whether polymorphisms in the GSTM1, GSTM3, GSTP1 and GSTT1 genes modify allergic responses to diisocyanate exposure. The study population consisted of 182 diisocyanate exposed workers, 109 diagnosed with diisocyanate-induced asthma and 73 without asthma. Lack of the GSTM1 gene (null genotype) was associated with a 1.89-fold risk of diisocyanate-induced asthma [95% confidence interval (CI) 1.01-3.52]. Moreover, among the asthma patients, the GSTM1 null genotype was associated with lack of diisocyanate-specific immunoglobulin (Ig)E antibodies [odds ratio (OR) 0.18, 95% CI 0.05-0.61] and with late reaction in the specific bronchial provocation test (OR 2.82, 95% CI 1.15-6.88). Similarly, GSTM3 AA genotype was related to late reaction in the specific bronchial provocation test (OR 3.75, 95% CI 1.26-11.2). The GSTP1 Val/Val genotype, on the other hand, was related to high total IgE levels (OR 5.46, 95% CI 1.15-26.0). The most remarkable effect was seen for the combination of GSTM1 null and the GSTM3 AA genotype which was strongly associated with lack of diisocyanate-specific IgE antibodies (OR 0.09, 95% CI 0.01-0.73) and with late reaction in the bronchial provocation test (OR 11.0, 95% CI 2.19-55.3). The results suggest, for the first time, that the polymorphic GSTs, especially the mu class GSTs, play an important role in inception of ill effects related to occupational exposure to diisocyanates.

Importance of inflammatory and immune components in a mouse model of airway reactivity to toluene diisocyanate (TDI)

BACKGROUND

Nearly 9 million individuals are exposed to agents in the workplace associated with asthma, and isocyanates represent the most common cause of occupationally induced asthma.

OBJECTIVES

Nonetheless, the immunological mechanisms responsible for isocyanate-induced asthma are not clear. A murine model for toluene diisocyanate (TDI) asthma is described and employed to examine inflammatory and immune components that may be involved in the disease.

METHODS

Groups (n = 6) of C57BL/6J and athymic mice were sensitized by subcutaneous injection (20 microl on day 1, 5 microl on days 4 and 11), and 7 days later challenged by inhalation (100 p.p.b., days 20, 22 and 24) with TDI. Twenty-four hours following the last challenge the tracheae and lungs were examined for histological changes as well as for the expression of Th1, Th2 and pro-inflammatory cytokines. Mice were also examined for airway reactivity to methacholine challenge and for specific and total IgE and IgG antibodies.

RESULTS

TDI sensitization resulted in increased reactivity to methacholine challenge as well as a significant inflammatory response in the trachea and nares of wild-type mice, but not in the athymic mice nor in the lungs of the C57BL/6J mice. Airway inflammation was characterized by inflammatory cell influx, goblet cell metaplasia and epithelial damage. Histological changes in the trachea were accompanied by increased mRNA expression of interleukin (IL)-4, tumour necrosis factor alpha, lymphotoxin beta, lymphotactin and Rantes, as well as TDI-specific IgG antibodies and elevated levels of total IgE. IgE-specific antibodies were not detected with this exposure regimen but were produced when the TDI concentrations were increased.

CONCLUSIONS

These studies provide a unique murine model for occupational asthma that generates both inflammatory and immune mediators similar to those occurring in TDI-induced asthma in humans.

A guide to the diagnosis and treatment of occupational asthma

Occupational asthma is the most prevalent form of occupational lung disease in industrialized nations. As increasing numbers of new chemicals are produced and new manufacturing processes are introduced, the variety of environments in which individuals may become exposed to respiratory sensitizers and irritants makes diagnosing and treating this illness even more challenging. In addition to adverse pulmonary effects, the diagnosis of occupational asthma may bring with it negative social and financial implications that may ultimately affect the patient's quality of life. For this reason, it is important for clinicians to recognize work-related respiratory symptoms early on in their course, maintain a high clinical suspicion for an occupational cause in the diagnostic work-up of asthma, and have a high degree of certainty in the diagnosis. While a number of classification schemes have been proposed to simplify the diagnostic approach to occupational asthma, the inciting factors typically involve sensitization (often by an IgE mechanism), direct airway inflammation, various pharmacologic responses, or irritant reflex pathways. Clinicians must first document the presence of asthma, then establish a relationship between asthma and the work-place. The occupational history is the key diagnostic tool, and clinical suspicions may be evaluated further by serial peak expiratory flow measurements, nonspecific hypersensitivity challenges with histamine or methacholine, collaboration with industrial/occupational hygienists to obtain workplace exposure measurements, and specific challenge testing at tertiary referral centers providing specialized laboratories. Removal from the inciting exposure is the mainstay of therapy, and pharmacologic treatment of patients with occupational asthma is similar to the treatment of patients with other forms of asthma.