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Diisocyanates are highly reactive substances and known causes of occupational asthma. Exposure occurs mainly in the occupational setting and can be assessed through biomonitoring which accounts for inhalation and dermal exposure and potential effects of protective equipment. However the interpretation of biomonitoring data can be challenging for chemicals with complex kinetic behavior and multiple exposure routes, as is the case for diisocyanates. To better understand the relation between external exposure and urinary concentrations of metabolites of diisocyanates, we developed a physiologically based kinetic (PBK) model for methylene bisphenyl isocyanate (MDI) and toluene di-isocyanate (TDI). The PBK model covers both inhalation and dermal exposure, and can be used to estimate biomarker levels after either single or chronic exposures. Key parameters such as absorption and elimination rates of diisocyanates were based on results from human controlled exposure studies. A global sensitivity analysis was performed on model predictions after assigning distributions reflecting a mixture of parameter uncertainty and population variability. Although model-based predictions of urinary concentrations of the degradation products of MDI and TDI for longer-term exposure scenarios compared relatively well to empirical results for a limited set of biomonitoring studies in the peer-reviewed literature, validation of model predictions was difficult because of the many uncertainties regarding the precise exposure scenarios that were used. Sensitivity analyses indicated that parameters with a relatively large impact on model estimates included the fraction of diisocyanates absorbed and the binding rate of diisocyanates to albumin relative to other macro molecules.We additionally investigated the effects of timing of exposure and intermittent urination, and found that both had a considerable impact on estimated urinary biomarker levels. This suggests that these factors should be taken into account when interpreting biomonitoring data and included in the standard reporting of isocyanate biomonitoring studies., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Background: Isocyanates are well-known occupational allergens, but can also be present in medical devices., Objectives: To highlight that contact sensitization to isocyanates might contribute to allergic contact dermatitis (ACD) from polyurethane (PU)-containing diabetes devices and wound dressings., Patients and Methods: Nineteen patients with suspected ACD from diabetes devices and/or wound dressings were patch tested to an isocyanate series. Four wound dressings, six diabetes devices and four monomeric isocyanate patch test preparations were analysed with gas chromatography - mass spectrometry., Results: Eight patients reacted to isocyanates and corresponding amines: 3 to isophorone diisocyanate (IPDI), 4 to 4,4'-diaminodiphenylmethane (MDA), 4 to 2,4-toluene diisocyanate (TDI) and 1 to polymeric methylene diphenyl diisocyanate (PMDI). Three of four wound dressings contained isocyanates (methylene diphenyl diisocyanate [MDI], TDI and/or IPDI), whereas five of six diabetes devices contained 4,4'-MDI, and one of them also IPDI. None of the medical devices contained 1,6-hexamethylene diisocyanate. Contrary to IPDI, and especially MDI, only the concentration of the TDI patch test preparation corresponded approximately (80%) to its label., Conclusion: Patch tests with isocyanates may be worth-while in patients with suspected ACD from PU-containing medical devices. Besides MDA, and PMDI, also TDI might potentially be a marker for MDI-sensitization., (© 2022 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

This article provides an overview of toluene diisocyanate (TDI) workplace air concentration data. Data were collected between 2005-2020 in workplaces across the United States, Canada, and the European Union by a number of different organizations, primarily using the sampling procedures published in OSHA Methods 42 and 5002. The data were then collated and organized by the International Isocyanate Institute. Air samples were collected from several market segments, with a large portion of the data (87%) from the flexible foam industry. The air samples (2534 in total) were categorized into "area" or "personal," and the personal samples were subcategorized into "task," "short term," and "long term." Most of the air sample concentrations (87%) were less than 5 ppb. However, the presence of airborne TDI greater than 5 ppb indicated the importance of respiratory protection in some situations; therefore, respirator use patterns were studied and summarized. Additionally, this article provides a summary of air sample concentrations at different flexible foam manufacturing job roles. The information on air sampling concentrations and respiratory protection during TDI applications collected in this paper could be useful for product stewardship and industrial hygiene purposes in the industries studied.

Objective: To explore the effect of transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1) on toluene diisocyanate (TDI)-induced allergic airway inflammation in mice., Methods: Thirty-two mice were randomly divided into AOO group, AOO+5Z-7-Oxozeaenol group, TDI group, and TDI+5Z-7-Oxozeaenol group. Another 32 mice were randomly divided into AOO group, TDI group, TDI +5Z-7-Oxozeaenol group, and TDI +5Z-7-Oxozeaenol + Necrostatin-1 group. TAK1 inhibitor (5Z-7-Oxozeaenol, 5 mg/kg) and/or RIPK1 inhibitor (Necrostatin-1, 5 mg/kg) were used before each challenge. Airway responsiveness, airway inflammation and airway remodeling were assessed after the treatments. We also examined the effect of TDI-human serum albumin (TDI-HSA) conjugate combined with TAK1 inhibitor on the viability of mouse mononuclear macrophages (RAW264.7) using CCK8 assay. The expressions of TAK1, mitogen-activated protein kinase (MAPK) and receptor interacting serine/threonine protease 1 (RIPK1) signal pathway in the treated cells were detected with Western blotting. The effects of RIPK1 inhibitor on the viability of RAW264.7 cells and airway inflammation of the mouse models of TDI-induced asthma were evaluated., Results: TAK1 inhibitor aggravated TDI-induced airway inflammation, airway hyper responsiveness and airway remodeling in the mouse models ( P < 0.05). Treatment with TAK1 inhibitor significantly decreased the viability of RAW264.7 cells, which was further decreased by co-treatment with TDI-HSA ( P < 0.05). TAK1 inhibitor significantly decreased the level of TAK1 phosphorylation and activation of MAPK signal pathway induced by TDI-HSA ( P < 0.05). Co-treatment with TAK1 inhibitor and TDI-HSA obviously increased the level of RIPK1 phosphorylation and caused persistent activation of caspase 8 ( P < 0.05). RIPK1 inhibitor significantly inhibited the reduction of cell viability caused by TAK1 inhibitor and TDI-HSA ( P < 0.05) and alleviated the aggravation of airway inflammation induced by TAK1 inhibitors in TDI-induced mouse models ( P < 0.05)., Conclusion: Inhibition of TAK1 aggravates TDI-induced airway inflammation and hyperresponsiveness and may increase the death of macrophages by enhancing the activity of RIPK1 and causing persistent activation of caspase 8.

Toluene diisocyanate (TDI), a major intermediate agent used in the manufacturing industry, causes respiratory symptoms when exposed to the human body. In this study, we aimed to determine the molecular mechanism of TDI toxicity. To investigate the impact of TDI exposure on global gene expression, we performed transcriptomic analysis of human bronchial epithelial cells (BEAS-2B) after TDI treatment. Differentially expressed genes (DEGs) were sorted and used for clustering and network analysis. Among DEGs, dual-specificity phosphatase 6 (DUSP6) was one of the genes significantly changed by TDI exposure. To verify the expression level of DUSP6 and its effect on lung cells, the mRNA and protein levels of DUSP6 were analyzed. Our results showed that DUSP6 was dose-dependently upregulated by TDI treatment. Thereby, the phosphorylation of ERK1/2, one of the direct inhibitory targets of DUSP6, was decreased. TDI exposure also increased the mRNA level of p53 along with its protein and activity which trans-activates DUSP6. Since TRPA1 is known as a signal integrator activated by TDI, we analyzed the relevance of TRPA1 receptor in DUSP6 regulation. Our data revealed that up-regulation of DUSP6 mediated by TDI was blocked by a specific antagonist against TRPA1. TDI exposure attenuated the apoptotic response, which suggests that it promotes the survival of cancerous cells. In conclusion, our results suggest that TDI induces DUSP6 and p53, but attenuates ERK1/2 activity through TRPA1 receptor activation, leading to cytotoxicity.

Objectives: Diisocyanates are a chemical group that are widely used at workplaces in many sectors. They are also potent skin- and respiratory sensitizers. Exposure to diisocyanates is a main cause of occupational asthma in the European Union. To reduce occupational exposure to diisocyanates and consequently the cases of diisocyanate-induced asthma, a restriction on diisocyanates was recently adopted under the REACH Regulation in the European Union., Methods: A comprehensive evaluation of the data on occupational exposure to the most important diisocyanates at workplaces was made and is reported here. The diisocyanates considered are methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI), and hexamethylene diisocyanate (HDI), accounting for more than 95% of the market volume in the EU. The exposure assessment is based on data from Chemical Safety Reports (CSRs) of REACH Registration Dossiers, workplace air monitoring data from Germany, from the UK Health and Safety Executive (HSE), and literature data relevant for the EU, and the USA., Results: Occupational exposure to diisocyanates is particularly relevant in: (i) C.A.S.E. applications (Coatings, Adhesives, Sealants, Elastomers), (ii) production of polyurethanes (PUs) (e.g. slab-stock foam), (iii) handling of partly uncured PU products (e.g. cutting, demoulding, spray application of foam), and (iv) when diisocyanates/PUs are heated (e.g. hot lamination, foundry applications/casting forms). Ranking of the reported data on inhalation to diisocyanate exposure at workplaces (maximum values) leads to following order: (i) HDI and its oligomers in coatings, (ii) MDI in spray foam applications, (iii) TDI in manufacture of foam, (iv) TDI in manufacture of PUs and PU composite materials, (v) TDI in adhesives, (vi) MDI in adhesives, (vii) MDI in manufacture of PUs and PU composite materials, (viii) TDI in coatings, (ix) MDI in manufacture of foam, and (x) HDI in adhesives., (© The Author(s) 2021. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.)

The cellular and molecular mechanisms via which MK2206, an AKT inhibitor, prevents the activation of AKT in toluene diisocyanate (TDI)‑induced asthma remain unclear. Thus, the present study aimed to evaluate the potential effects of MK2206 on airway AKT activation, inflammation and remodeling in a TDI‑induced mouse model of asthma. A total of 24 BALB/c mice were selected and randomly divided into untreated (AOO), asthma (TDI), MK2206 (TDI + MK2206), and dexamethasone (TDI + DEX) groups. Phosphorylated AKT (p‑AKT), total AKT, airway remodeling indices, α‑smooth muscle actin (α‑SMA) and collagen I levels in pulmonary tissue were measured using western blotting. Airway inflammation factors, including interleukin (IL)‑4, ‑5, ‑6, and ‑13 in bronchoalveolar lavage fluid (BALF) and IgE in serum, were determined using ELISA. Additionally, the airway hyperresponsiveness (AHR) and pulmonary pathology of all groups were evaluated. The results of the present study demonstrated that p‑AKT levels in lung protein lysate were upregulated, and neutrophil, eosinophil and lymphocyte counts were increased in the lungs obtained from the asthma group compared with the AOO group. Both MK2206 and DEX treatment in TDI‑induced mice resulted not only in the attenuation of AKT phosphorylation, but also reductions in neutrophil, eosinophil and lymphocyte counts in the lungs of mice in the asthma group. Consistently, increases in the levels of the inflammatory cytokines IL‑4, ‑5, ‑6 and ‑13 analyzed in BALF, and serum IgE in the TDI group were demonstrated to be attenuated in the TDI + MK2206 and TDI + DEX groups. Furthermore, α‑SMA and AHR were significantly attenuated in the TDI + MK2206 group compared with the TDI group. These results revealed that MK2206 not only inhibited AKT activation, but also served a role in downregulating airway inflammation and airway remodeling in chemical‑induced asthma. Therefore, the findings of the present study may provide important insight into further combination therapy.

Because of the semi-volatile nature of diisocyanates (being airborne in both physical vapor and particulate phases), their high reactivity and low occupational exposure limits, diisocyanate exposure evaluation has been challenging for industrial hygienists and laboratories. The objective of this study was to compare the toluene diisocyanate (2,4 and 2,6 isomers, TDI) concentration measured by five methods in a flexible polyurethane foam factory using different collection or derivatization approaches. The methods used were: OSHA 42 modified (filter, 1-(2-pyridyl)piperazine) (OSHA), Asset EZ4-NCO (denuder and filter, dibutylamine) (Asset), Iso-Chek (double-filter, 9-(N-methylaminomethyl) anthracene and 1,2-methoxyphenylpiperazine), DAN (filter, 1,8-diaminonaphthalene), and CIP10 (centrifugation, 1,2-methoxyphenylpiperazine). Particle real-time monitoring for concentration and size distribution was performed in parallel to improve the understanding of the potential bias between methods. The comparison study was performed over 3 days, providing 18 replicates for each of the 5 methods. Isocyanate concentrations collected for each sampling method were compared using linear mixed effect modeling. Compared to OSHA, which yielded the highest concentrations overall, the Asset and DAN methods provided the smallest biases (-29% (95% CI [-52;-6]) and -45% (95% CI [-67;-23]), respectively), while the CIP10 and Iso-Chek methods provided the largest biases (-82% (95% CI [-105;-66]) and -96% (95% CI [-118;-75]), respectively). The substantial bias of Iso-Chek and CIP10 seemed to be explained by the predominance of TDI in the form of sub-micron particles that were inadequately captured by these two methods due to their sampling principle, which are particle filtration without derivatizing agent and centrifugation respectively. Asset and DAN performance seemed to decrease as the sampling time increased. While DAN's bias could be related to a reagent deficiency on the filter, the disparities between OSHA and Asset, both considered as reference methods, highlight the fact that the mechanisms of collection, derivation and extraction do not seem to be completely controlled. Finally, an upward trend has been observed between concentrations of particles below 300 nm in size and concentration levels of TDI. It has also been observed that TDI levels increased with the TDI foam index produced at the facility.

The US Environmental protection agency (EPA) has published guidance that includes test procedures for evaluating indoor exposure to chemicals from products. One of the test procedures represents the migration test for evaluating potential dermal exposure from home furniture. Such an evaluation involves the chemical measurement of the sweat which is currently unavailable in the literature. The objective of this project was to develop and validate an analytical method for quantification of migration of 4,4'-methylenediphenyl diisocyanate (MDI), 2,6-toluene diisocyanate (2,6-TDI) and 2,4-toluene diisocyanate (2,4-TDI) from a polyurethane (PU) flexible foam to artificial sweat that meets the recommendations of the EPA test protocol. Following the EPA protocol, six synthetic sweat solutions were prepared and used in evaluation of isocyanate recovery performance. The migration tests were conducted using five foam types that were chosen and supplied by PU foam manufacturers to represent the types most commonly found in commercial products, and with formulations anticipated to have the highest potential residual TDI or MDI. Migration tests were conducted using glass fiber filters (GFF) coated with 1-(2-methoxyphenyl)piperazine (1,2-MP) and analyzed using HPLC equipped with a UV detector for quantification and a MS detector to qualify peaks. The detection limits of the method were 0.002 µg/mL for 2,6-TDI, 0.011 µg/mL for 2,4-TDI, and 0.003 µg/mL for MDI. Quantification limits were 0.006 µg/mL, 0.037 µg/mL, and 0.010 µg/mL, respectively. The recovery tests on a Teflon surface for 5 of the 6 EPA-recommended synthetic sweat solutions indicate the recovery percentage was approximately 80% for diisocyanates. Recovery for the sixth sweat solution was low, approximately 30%. TDI and MDI migration was not observed when testing was conducted on foam samples., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The authors wish to thank the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST) for providing instrument support and the International Isocyanate Institute, Inc. for their financial support. The research reported herein was performed under an agreement with the International Isocyanate Institute, Inc. Any conclusions are those of the authors and not necessarily of the Institute., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

Toluene-diisocyanate (TDI) is mainly used in the manufacturing process of polyurethane foams, and is a potent inducer of occupational asthma characterized by airway inflammation and airway hyperreactivity. Thymic stromal lymphopoietin (TSLP) plays an important role in the development of asthma, and correlating with the differentiation of Th2 and Th17 cells. However, the role of TSLP in TDI-induced asthma remains unclear. In this study, 96 TDI-exposed workers as well as a mouse model of TDI-induced asthma were investigated. The air exposure assessment result of TDI in the workplace showed that workers were exposed to inhalation of a very high concentration of TDI, approximately 8 times the recommended level, leading to a decrease in pulmonary function and an increase in inflammatory cells, as well as TSLP and IgE levels in the supernatant of sputum obtained from exposed workers. In order to further investigate the role of TSLP in the pathogenesis of TDI-induced asthma, a mouse model of TDI-induced asthma was also employed. Histopathological analysis of mouse lung and bronchus showed an obvious infiltration of inflammatory cells around the bronchus. The levels of inflammatory cells, IFN-γ, IL-4 and IL-17 in bronchoalveolar lavage fluid (BALF), the expression levels of TSLP protein and ROR-γt and IL-17 mRNA in mouse lung tissues were also significantly increased. However, after treatment with TSLP neutralizing antibody (TSLP-Ab), the degree of pulmonary and bronchial inflammation in mice was significantly alleviated, and the levels of inflammatory cells, IFN-γ, IL-4 and IL-17 in BALF, and the expression levels of ROR-γt and IL-17 mRNA in lung tissue were significantly decreased. Our data shows that TSLP plays an important role in the pathogenesis of TDI-induced asthma, and that TSLP-Ab can effectively alleviate TDI-induced airway inflammation of asthma., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Purpose: Toluene diisocyanate (TDI) is a leading cause of occupational asthma (OA). Periostin is a matricellular protein implicated in type 2 immunity-driven asthma. Its pathogenic role in TDI-OA has not been completely elucidated. The present study was performed to investigate the role of periostin in TDI-OA., Materials and Methods: Serum periostin levels were measured in subjects with TDI-OA, asymptomatic TDI-exposure controls (AECs), non-occupational asthmatics (NAs), and unexposed normal controls (NCs). To understand the mechanism by which TDI induces periostin production, primary small airway epithelial cells (SAECs) were cultured under stimulation of TDI and neutrophils from asthmatic patients., Results: Fifty-three subjects with TDI-OA, 71 AECs, 67 NAs, and 83 NCs were enrolled. Serum periostin levels were significantly higher in TDI-OA subjects than in AECs ( p =0.001), NAs ( p <0.001), and NCs ( p <0.001). In TDI-exposed subjects (TDI-OA and AEC), the PC₂₀ methacholine levels were significantly lower in subjects with a higher periostin level than in those with a lower periostin level. TDI exposure did not increase periostin production directly by SAECs; however, periostin production increased significantly after co-culture with TDI and neutrophils, which was suppressed by an antioxidant. In addition, increased release of TGF-β1 was noted from SAECs when exposed to TDI and neutrophils, which was also suppressed by an antioxidant., Conclusion: These results suggest that an increased periostin level may contribute to the progression of airway inflammation to remodeling in TDI-exposed workers. A high serum periostin level is a potential serologic marker of the phenotype of TDI-OA., Competing Interests: The authors have no financial conflicts of interest., (© Copyright: Yonsei University College of Medicine 2018.)

In 2016, the American Conference of Governmental Industrial Hygienists (ACGIH) lowered the 8-hr Threshold Limit Value - time-weighted average (TLV-TWA) for toluene diisocyanate (TDI) from 5 ppb to 1 ppb, and the 15-min short-term exposure limit (STEL) from 20 ppb to 5 ppb. We evaluated ACGIH's basis for lowering these values. It is our opinion that the ACGIH's evaluation of the evidence for occupational asthma and respiratory effects from TDI exposure does not fully integrate the results of all the available human and animal studies. We found that some studies reported occupational asthma cases at TWAs less than 5 ppb, but these cases were likely caused by peak exposures above 20 ppb. Advances in industrial hygiene have reduced peak exposures and the incidence of upset conditions, such as spills and accidents, in modern TDI facilities. Taken together, the human evidence indicates that adherence to the previous 8-hr TLV-TWA and 15-min STEL (5 ppb and 20 ppb, respectively) prevents most, if not all, cases of occupational asthma, and eliminates or reduces the risk of lung function decrements and other respiratory effects. While limited, the animal literature supports the human evidence and indicates that TDI-induced asthma is a threshold phenomenon. We conclude that ACGIH's decision to lower the TLV-TWA and STEL values for TDI is not adequately supported., (Copyright © 2018 Gradco LLC dba Gradient. Published by Elsevier Inc. All rights reserved.)

Objective: The aim of this study was to describe a study of medical monitoring methods and lessons learned in detecting health outcomes in U.S. plants producing toluene diisocyanate (TDI)., Methods: A multidisciplinary team implemented a medical and environmental monitoring program in three TDI plants., Results: Of 269 eligible workers, 197 (73%) participated and 42 (21%) met symptom and/or lung function criteria that would trigger evaluation for possible asthma over 5 years of data collection. Subsequent evaluation was delayed for most, and a web-based data collection system improved timeliness., Conclusion: Medical monitoring of TDI workers identified workers triggering further assessment per study protocol. Systems and/or personnel to ensure rapid follow-up are needed to highlight when triggering events represent potential cases of asthma needing further evaluation. Implementation of a research protocol requires resources and oversight beyond an occupational health program.

Objective: The aim of this study was to investigate lung function among toluene diisocyanate (TDI) production workers., Methods: One hundred ninety-seven U.S workers performed spirometry from 2006 through 2012. Results were compared within the study cohort and with U.S. population measures. A mixed-effects model assessed factors affecting repeated forced expiratory volume in 1 second (FEV1) measurements., Results: The cohort's mean FEV1 and forced vital capacity (FVC) percent reference values, although greater than 90%, were significantly lower and the prevalence of abnormal spirometry (predominantly restrictive pattern) was significantly higher than in the U.S., Population: Differences in lung function among workers with higher cumulative TDI exposure were in the direction of an exposure effect, but not significant., Conclusion: We found little evidence of an adverse effect of TDI exposure on longitudinal spirometry in these workers. The association between TDI exposure and the increasing prevalence of a restrictive pattern needs further exploration.

Objective: This study examines asthma risk in facilities producing toluene diisocyanate (TDI)., Methods: A total of 197 workers were monitored from 2007 to 2012. TDI air concentrations were used to estimate exposures., Results: The incidence of cases consistent with TDI-induced asthma was 0.009 per person-years (seven cases) or consistent with TDI-induced asthma or asthma indeterminate regarding work-relatedness was 0.012 (nine cases). Increased risk of cases consistent with TDI asthma was observed for cumulative (odds ratio [OR] = 2.08, 95% confidence interval [CI] 1.07 to 4.05) per logarithm parts per billion-years and peak TDI exposures (OR = 1.18, 95% CI 1.06 to 1.32) (logarithm parts per billion). There was a weak association with cumulative and peak exposures for decline of short-term forced expiratory volume in one second (FEV1). Asthma symptoms were associated with workers noticing an odor of TDI (OR 6.02; 95% CI 1.36 to 26.68)., Conclusions: There is evidence that cumulative and peak exposures are associated with TDI-induced asthma.

Toluene diisocyanate (TDI) exposure can directly activate and damage airway epithelium. Folliculin (FLCN) is a protein expressed by human airway epithelial cells (HAECs) to maintain airway epithelial integrity and survival. This study investigated the involvement of FLCN in the pathogenesis of TDI-induced occupational asthma (OA). Enzyme-linked immunosorbent assay was used to measure serum levels of FLCN in TDI-exposed subjects (93 TDI-OA patients and 119 asymptomatic exposed controls (AEC)), 200 non-occupational asthma (NOA) patients and 71 unexposed healthy normal controls (NCs). Significantly more subjects in the TDI-OA and AEC groups had high serum levels of FLCN compared to those in the NOA group (P=0.002 and P=0.001, respectively), all of which were higher than the NC group (all P<0.001). The serum level of FLCN was positively correlated with TDI exposure duration (r=0.251, P=0.027), but was negatively correlated with asthma duration of TDI-OA patients (r=-0.329, P=0.029). TDI-exposed subjects with high FLCN levels had higher serum levels of total IgE than those with lower levels. The effects of TDI exposure on FLCN production was investigated by treating HAECs (A549 cells) with TDI-human serum albumin conjugate, which showed increased expression and release of FLCN and interleukin-8 from HAECs. Co-culture with peripheral blood neutrophils also induced FLCN expression and release from HAECs. In conclusion, TDI exposure and TDI-induced neutrophil recruitment into the airways can activate and stimulate HAECs to produce FLCN, which could be involved in airway inflammation in workers exposed to TDI.

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.

Background: Aberrant activation of β-catenin signaling by both WNT-dependent and WNT-independent pathways has been demonstrated in asthmatic airways, which is thought to contribute critically in remodeling of the airways. Yet, the exact role of β-catenin in asthma is very poorly defined. As we have previously reported abnormal expression of β-catenin in a toluene diisocyanate (TDI)-induced asthma model, in this study, we evaluated the therapeutic efficacy of two small molecules XAV-939 and ICG-001 in TDI-asthmatic male BALB/c mice, which selectively block β-catenin-mediated transcription., Methods: Male BALB/c mice were sensitized and challenged with TDI to generate a chemically induced asthma model. Inhibitors of β-catenin, XAV-939, and ICG-001 were respectively given to the mice through intraperitoneally injection., Results: TDI exposure led to a significantly increased activity of β-catenin, which was then confirmed by a luciferase assay in 16HBE transfected with the TOPFlash reporter plasmid. Treatment with either XAV-939 or ICG-001 effectively inhibited activation of β-catenin and downregulated mRNA expression of β-catenin-targeted genes in TDI-asthmatic mice, paralleled by dramatically attenuated TDI-induced hyperresponsiveness and inflammation of the airway, alleviated airway goblet cell metaplasia and collagen deposition, decreased Th2 inflammation, as well as lower levels of TGFβ1, VEGF, HMGB1, and IL-1β., Conclusion: The results showed that β-catenin is a principal mediator of TDI-induced asthma, proposing β-catenin as a promising therapeutic target in asthma., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Objective: To investigate the effect of occupational toluene diisocyanate(TDI) exposure on matrix metalloproteinases-9 (MMP-9) and tissue inhibitor of metalloproteinase-1(TIMP-1), and analysis of the correlation of MMP-9,TIMP-1,MMP-9/TIMP-1 and lung function., Methods: In October 2014, based on cluster sampling, we conducted a cross-sectional study in a TDI production factory located in China's western region. 61 exposed workers were recruited from workers engaged in packing, operating and checking. Based on different levels of the external exposure, the packers were classified as high exposed group, while operators and checkers as low exposed group. 58 factory managers, matching age and agent, were selected as controls, having same work intense and not contacting the TDI or other allergens. The questionnaire surveys were used to obtain the agent, age, work age, smoking and drinking, personal and family allergic history, occupational history, and the recent health conditions. The levels of MMP-9 and TIMP-1 in serum of subjects were determind by ELISA. The time weighted average concentrations (8h-TWA) were used to describe the levels of TDI air exposure in working environment. Spearman correlation assay was used to investigate the correlation of MMP-9, TIMP-1, MMP-9/TIMP-1 and lung function, exposure time., Results: 8-hour TWA means of TDI air levels in exposed group, packers, operators and checkers were 0.39, 0.76, 0.25 mg/m(3), respectively . According to the external exposure concentration, the packers were classified as high exposed group, and the operators and checkers were classified as low exposed group. In controls, low exposed group and high exposed group, the levels of MMP-9, respectively, were (807.21±347.70),(586.91±317.50),(388.94±312.01) ng/ml (χ(2)=16.69, P<0.001), respectively, and the P50(P25-P75) of MMP-9/TIMP-1 were 4.67(2.87-6.68), 2.3(1.44-3.48), 1.11(0.59-1.48) (χ(2)=39.42, P<0.001), respectively, and the concentrations of TIMP-1, were (173.44±72.67), (236.12±51.98), (302.81±44.39) ng/ml (F=20.09, P< 0.001), respectively. The levels P50(P25-P75) of FVC, FEV1.0 and FEV1.0/FVC in exposed group were, 92.8% (86.0%-101.8%), 85.5%(76.7%-92.8%), 112.5(108.2-118.5), respectively, which were lower than that in control group (124.3%(107.9%-144.2%), 142.7%(119.1%-155.7%), 129.2(123.5-134))(Z values were 7.70, 8.97, 8.62, and all P<0.001). Spearman rank correlation analysis showed that levels of MMP-9 were positively associated with FEV1.0, and FEV1.0/FVC (r values were 0.27, 0.25, respectively, all P<0.05), and The levels of TIMP-1 were negatively associated with FVC, FEV1.0, and FEV1.0/FVC (r valuse were -0.33, -0.39, -0.39, all P<0.05).The levels of MMP-9 were negatively correlated with exposure time(r=-0.26, P=0.040). The positive correlations of MMP-9/TIMP-1 with FVC, FEV1.0, and FEV1.0/FVC were also found (r valuse were 0.34, 0.44, 0.40, all P<0.05)., Conclusion: TDI exposure could induce the downs of MMP-9 and MMP-9/TIMP-1 associated with lung functions. The MMP-9 and MMP-9/TIMP-1,in a way, could reflect the respiratory inflammatory injury caused by TDI exposure.

Objective: To investigate the effect of occupational exposure to toluene diisocyanate (TDI) on the workers' health., Methods: A total of 76 workers exposed to TDI (exposure group) and 64 management staff members (control group) were selected from a factory as the study subjects. Area sampling was performed for the place with exposure to TDI according to the method in GBZ 159-2004 Specifications of air sampling for hazardous substances monitoring in the workplace, and gas chromatography was applied to measure the concentration of TDI in workplace air. The workers' personal information was collected with questionnaire, pulmonary ventilation function was determined with a portable spirometer, hematological parameters were analyzed by automatic blood analyzer and blood chemistry analyzer, and the indicators of oxidative damage and energy metabolism were measured by the reagent kit provided by Nanjing Jiancheng Bioengineering Institute. SPSS 17 software was applied for statistical analysis., Results: The exposure group had significantly lower forced vital capacity (FVC), forced expiratory volume in 1 second(FEV1.0), and FEV1.0/FVC ratio than the control group (P <0.05). Compared with the control group, the exposure group had significantly higher red blood cell count, platelet distribution width, mean platelet volume, lymphocyte count, and neutrophil count(P<0.01), and significantly lower activities of lactate dehydrogenase(LDH), superoxide dismutase, and succinodehydrogenase (SDH)(P <0.01). In the exposure group, the length of exposure was negatively correlated with the activities of SDH and LDH in the serum (r=-0.319, P <0.05; r=-0.239, P <0.05), and the length of exposure was not found to be correlated with the activity of SOD and pulmonary function indices., Conclusion: TDI can induce inflammatory response and lung ventilation function impairment in workers exposed to TDI, as well as oxidative stress and imbalance of energy metabolism. Therefore, it can cause damage to workers' health, and protective measures should be enhanced.

Diisocyanates are industrial chemicals which have a wide range of applications in developed and developing countries. They are notorious lung toxicants and respiratory sensitizers. However, the mechanisms behind their adverse effects are not adequately characterized. Autotaxin (ATX) is an enzyme producing lysophosphatidic acid (LPA), and the ATX-LPA axis has been implicated in lung related inflammatory conditions and diseases, including allergic asthma, but not to toxicity of environmental low-molecular-weight chemicals. We investigated effects of toluene diisocyanate (TDI) on ATX induction in human lung epithelial cell models, and we correlated LPA-levels in plasma to biomarkers of TDI exposure in urine collected from workers exposed to <5ppb (parts per billion). Information on workers' symptoms was collected through interviews. One nanomolar TDI robustly induced ATX release within 10min in vitro. A P2X7- and P2X4-dependent microvesicle formation was implicated in a rapid ATX release and a subsequent protein synthesis. Co-localization between purinergic receptors and ATX was documented by immunofluorescence and confocal microscopy. The release was modulated by monocyte chemoattractant protein-1 (MCP-1) and by extracellular ATP. In workers, we found a dose-response relationship between TDI exposure biomarkers in urine and LPA levels in plasma. Among symptomatic workers reporting "sneezing", the LPA levels were higher than among non-symptomatic workers. This is the first report indicating induction of the ATX-LPA axis by an environmental low-molecular-weight chemical, and our data suggest a role for the ATX-LPA axis in TDI toxicity., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Background: Tissue transglutaminase (tTG) is a post-translational modifying enzyme located in airway epithelial cells. A potential contribution of serum specific IgG (sIgG) to tTG in airway inflammation of toluene diisocyanate (TDI)-induced occupational asthma (OA) has been suggested., Objective: To prepare a TDI-tTG conjugate and detect serum specific antibodies in sera of patients with TDI-OA to understand this mechanism., Methods: Ninety-nine patients with TDI-OA, 76 asymptomatic exposed controls, 208 patients with non-OA, and 74 unexposed controls were enrolled for this study. The TDI-tTG conjugate was prepared and confirmed by a native gel. Serum sIgG and/or sIgE antibodies to tTG, TDI-tTG, TDI conjugated to human serum albumin, cytokeratin 19, and serum cytokine levels, such as interleukin-8, transforming growth factor-β1, and tissue inhibitor of metalloproteinase-1, were measured by enzyme-linked immunosorbent assay. The level of interleukin-8 produced from airway epithelial cells (A549) treated with tTG was evaluated to investigate the inflammatory effect of tTG and TDI-tTG., Results: In the TDI-OA group, the prevalence of serum sIgG to TDI-tTG (17.2%) was higher than that of sIgG to tTG (11.1%), which were significantly higher than those of the 3 control groups (P < .05 for all groups). TDI-exposed subjects with high levels of serum sIgG to TDI-tTG had a high prevalence of sIgG to cytokeratin 19 and higher serum levels of transforming growth factor-β1 and tissue inhibitor of metalloproteinase-1. The tTG and TDI-tTG dose-dependently increased interleukin-8 production from A549 cells., Conclusion: These findings suggest that TDI exposure in the workplace binds to tTG to form a conjugate that can induce serum sIgG antibody production, airway inflammation, and airway remodeling in patients with TDI-OA., (Copyright © 2014 American College of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)

Objective: To investigate the effect of long-term exposure to toluene diisocyanate (TDI) on the lung function of TDI-exposed workers., Methods: A factory was selected for this occupational epidemiological investigation. The workers who were exposed to TDI and had complete physical examination records in recent 3 years were the exposed group (n = 45), while the company's administrative staff, logistics staff, and other non-TDI-exposed workers who had complete physical examination records in recent 3 years were the control group (n = 47). The two groups were compared in terms of lung function indices., Results: Compared with the control group, the 2009 exposure group had significantly lower forced expiratory volume in one second (FEV1.0), FEV1.0/forced vital capacity (FVC), and maximal expiratory flow at 25% of FVC (MEF25) (P < 0.05), the 2010 exposure group had significantly lower FEV1.0, FEV1.0/FVC,maximum voluntary ventilation (MVV), and maximal expiratory flow at 50% of FVC (MEF50) (P < 0.05), and the 2011 exposure group had significantly lower FEV1.0, FEV1.0/FVC, peak expiratory flow (PEF), MEF25, and MEF50 (P < 0.05)., Conclusion: Long-term exposure to TDI can lead to certain impairment of lung function in workers, which may be reflected by decreased lung function indices such as vital capacity, FVC, FEV1.0, FEV1.0/FVC, PEF, and MVV.

Flexible polyurethane foam (FPF) is produced from the reaction of toluene diisocyanate (TDI) and polyols. Limited and conflicting results exist in the literature concerning the presence of unreacted TDI remaining in FPF as determined by various solvent extraction and analysis techniques. This study reports investigations into the effect of several solvent/derivatization agent combinations on extractable TDI results and suggests a preferred method. The suggested preferred method employs a syringe-based multiple extraction of foam samples with a toluene solution of 1-(2-methoxyphenyl)-piperazine. Extracts are analyzed by liquid chromatography using an ion trap mass spectrometry detection technique. Detection limits of the method are ~10ng TDI g(-1) foam (10 ppb, w/w) for each TDI isomer (i.e. 2,4-TDI and 2,6-TDI). The method was evaluated by a three-laboratory interlaboratory comparison using two representative foam samples. The total extractable TDI results found by the three labs for the two foams were in good agreement (relative standard deviation of the mean of 30-40%). The method has utility as a basis for comparing FPFs, but the interpretation of extractable TDI results using any solvent as the true value for 'free' or 'unreacted' TDI in the foam is problematic, as demonstrated by the difference in the extracted TDI results from the different extraction systems studied. Further, a consideration of polyurethane foam chemistry raises the possibility that extractable TDI may result from decomposition of parts of the foam structure (e.g. dimers, biurets, and allophanates) by the extraction system.

Risk factors have not been identified that determine susceptibility for development of diisocyanate-induced occupational asthma (DA). We hypothesized that diisocyanate (DI) exposure could modify gene promoter regions regulating transcription of cytokine mediators and thereby influence expression of DA. A cross-sectional study was designed to investigate the promoter methylation status of candidate genes in DI-exposed workers. Subjects consisted of 131 workers in three groups: 40 cases with DA confirmed by a positive specific inhalation challenge (SIC) (DA+), 41 exposed workers with lower respiratory symptoms and negative SIC (DA-), and 50 asymptomatic exposed workers (AWs). We studied four candidate genes (GSTM1, DUSP22, IFN-γ, and IL-4) for which altered promoter methylation has been previously investigated for relationships with a variety of other environmental exposures. Methylation status was determined using methylation-specific quantitative PCR performed on genomic DNA extracted from whole blood. Results showed that relative methylation of IFN-γ promoter was significantly increased in DA+ in comparison with both comparator groups (DA- and AW), and it exhibited good sensitivity (77.5%) and specificity (80%) for identifying DA workers in a multivariate predictive model after adjusting for type of DI exposure, smoking status, methacholine PC₂₀, and gender. IL-4 promoter was slightly less methylated only in DA+ compared with AW among nonsmoking workers. Both GSTM1 and DUSP22 promoter methylations were found not associated with DA. Our finding suggests that exposure to occupational chemicals could play a heretofore undefined mechanistic role via epigenetic modification of specific genes in the promoter region.

Flexible polyurethane foam (FPF) is produced from the reaction of toluene diisocyanate (TDI) and polyols. Because of the potential for respiratory sensitization following exposure to TDI, concerns have been raised about potential consumer exposure to TDI from residual 'free TDI' in FPF products. Limited and conflicting results exist in the literature concerning the presence of unreacted TDI remaining in FPF as determined by various solvent extraction and analysis techniques. Because residual TDI results are most often intended for application in assessment of potential human exposure to TDI from FPF products, testing techniques that more accurately simulated human contact with foam were designed. To represent inhalation exposure to TDI from polyurethane foam, a test that measured the emission of TDI to air was conducted. For simulation of human dermal exposure to TDI from polyurethane foam, a migration test technique was designed. Emission of TDI to air was determined for a representative FPF using three different emission test cells. Two were commercially available cells that employ air flow over the surface of the foam [the Field and Laboratory Emission Cell (FLEC®) and the Micro-Chamber/Thermal Extraction™ cell]. The third emission test cell was of a custom design and features air flow through the foam sample rather than over the foam surface. Emitted TDI in the air of the test cells was trapped using glass fiber filters coated with 1-(2-methoxyphenyl)-piperazine (MP), a commonly used derivatizing agent for diisocyanates. The filters were subsequently desorbed and analyzed by liquid chromatography/mass spectrometry. Measurement of TDI migration from representative foam was accomplished by placing glass fiber filters coated with MP on the outer surfaces of a foam disk and then compressing the filters against the disk using a clamping apparatus for periods of 8 and 24 h. The sample filters were subsequently desorbed and analyzed in the same manner as for the emission tests. Although the foam tested had detectable levels of solvent-extractable TDI (56ng TDI g(-1) foam for the foam used in emissions tests; 240-2800ng TDI g(-1) foam for the foam used in migration tests), no TDI was detected in any of the emission or migration tests. Method detection limits (MDLs) for the emissions tests ranged from 0.03 to 0.5ng TDI g(-1) foam (0.002-0.04ng TDI cm(-2) of foam surface), whereas those for the migration tests were 0.73ng TDI g(-1) foam (0.16ng TDI cm(-2) of foam surface). Of the three emission test methods used, the FLEC® had the lowest relative MDLs (by a factor of 3-10) by virtue of its high chamber loading factor. In addition, the FLEC® cell offers well-established conformity with emission testing standard methods.

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.

Objectives: Diisocyanates (DIC) are highly reactive, low-molecular-weight chemicals which are the leading cause of occupational asthma (OA). The aim of the study was to analyze certain aspects of the pathogenesis of allergic inflammation in the airways induced by toluene diisocyanate (TDI) in an experimental model in mice., Materials and Methods: The experiment was carried out on 50 female BALB/cJ/Han/IMP mice, which were exposed by inhalation (intranasal and in the inhalation chamber) to toluene diisocyanate (2,4-TDI). After the experiment, the bronchoalveolar lavage fluid (BALF) was collected from the animals, and the composition of the induced inflammatory cells, and the concentrations of certain cytokines (IL-4, IL-5, TNF-α) were evaluated., Results: The total number of cells in BALF of the examined group of mice was significantly higher compared to the control mice. There was also a significant increase in neutrophils and eosinophils in the study group compared to the controls. The number of lymphocytes and macrophages did not differ significantly between the two groups. A statistically significant increase in the level of TNF-α was shown to occur in the group exposed to toluene diisocyanate in comparison to the control group. The concentration of IL-4 increased in the study group, compared to the control one, but the differences did not reach the level of significance, p > 0.05. Such difference was not observed for IL-5., Conclusions: We developed a murine model of TDI-induced asthma which caused the influx of inflammatory cells like eosinophils and neutrophils in the bronchoalveolar lavage fluid (BALF) in the TDI-treated mice. The increase of the concentration of some proinflammatory cytokines (TNF-α, IL-4) in BALF from the exposed mice was also observed.

Objectives: Toluene diisocyanate (TDI) is used in the manufacturing process of polyurethane (PU) foams and is a potent inducer of occupational asthma. The objective of this study was to evaluate the correlation between the exposure to total TDI (2,4- and 2,6-TDI) in air and the corresponding biomarker concentration of total TDA (2,4- and 2,6-TDA) in hydrolysed urine. The aim was also to propose an appropriate biological exposure limit for total TDA in urine., Methods: 9 workers from two production lines in a PU foam producing plant were studied. Personal exposure to TDI during four representative production shifts was monitored by an active air sampling method (filter impregnated with 1-(2-methoxyphenyl)piperazine) and quantified by high-performance liquid chromatography and diode array detection (NIOSH n° 2535, 5521). In parallel, pre-shift and post-shift urinary samples were collected from the exposed workers, and TDA concentrations were determined by gas chromatography-mass spectrometry after alkaline hydrolysis. All samples were collected on four measuring days: two Fridays (end of workweek) and two Mondays (start of workweek) separated by a weekend without exposure., Results: Strong correlations between the personal air concentrations of total TDI and the corresponding biomarker levels of total TDA in urine (r=0.816) were observed. An increase of 18.12 μg TDA/l (post-shift minus pre-shift concentration) corresponds to an exposure of 5 ppb (37 μg/m(3), the current American Conference of Governmental Industrial Hygienists threshold limit value) during the shift., Conclusions: The increase in TDA during the shift is a suitable biomarker for exposure to TDI during the same shift. Further research is needed to evaluate the use of start of week or end of week post-shift TDA in urine as biomarker since TDA was found to accumulate during the working week and thus the moment of sampling will clearly influence the result.

Occupational asthma is the principal cause of work-related respiratory disease in the industrial world. Toluene-2,4-diisocyanate (TDI) is one of the most common respiratory sensitizers leading to occupational asthma. Using a mouse model of chemical-induced asthma, we explored proteome changes in multiple compartments of mice sensitized and challenged with TDI or acetone-olive oil (AOO; vehicle). Airway reactivity to methacholine and a bronchoalveolar lavage (BAL) cell count was assessed in treated and control mice, 1 day after challenge. Subsequently, two-dimensional differential gel electrophoresis (2D-DIGE) was performed on auricular lymph nodes, BAL, and serum comparing TDI-treated and vehicle-treated control mice. The differentially expressed proteins were identified by mass spectrometry and pathway analysis was performed. TDI-treated mice exhibit increased airway reactivity (2.6-fold increase) and a neutrophilic inflammation in the BAL fluid, compared to control mice. 2D-DIGE showed 53, 210, and 40 differentially expressed proteins in the auricular lymph nodes, BAL, and serum of TDI-treated versus vehicle-treated mice, respectively. Several of the identified proteins could be linked with inflammation, neutrophil chemotaxis, and/or oxidative stress. Physiologic and immunologic readouts of the asthmatic phenotype, such as inflammation, were confirmed in three compartments by several of the differentially expressed proteins via 2D-DIGE and computerized pathway analysis.

Background: Exposure to certain substances in the workplace may lead to sensitization and increased respiratory symptoms., Objective: To evaluate the frequency of work-related specific sensitization and respiratory symptoms in carpentry apprentices with occupational exposure to wood dust and diisocyanates., Methods: Apprentices (n=101) completed an occupational and symptoms questionnaire. Spirometry and skin prick tests to aeroallergens and to a battery of 14 different woods were performed in all the participants. Blood samples were collected for total IgE measurement and detection of specific IgE to diisocyanates., Results: Half the participants (56%) had work-related respiratory symptoms: 54% due to wood dust, 15% due diisocyanates, and 9% to both. Participants with respiratory symptoms related to wood dust exposure had a significantly lower forced expiratory volume in 1 second compared with symptomatic individuals due to diisocyanates and asymptomatic individuals (P < .05). A history of rhinitis or asthma was associated with a 2.1- or 2.8-fold increase, respectively, in the likelihood of having respiratory symptoms due to wood dust exposure. Sensitization to wood was detected in 9% of participants, all of whom were atopic with a history of rhinitis and a high total IgE level (P < .05). Sensitization to diisocyanates was detected in 2% of exposed participants., Conclusions: Work-related respiratory symptoms are common in carpentry apprentices and are more frequently related to exposure to wood dust than to diisocyanates. Symptomatic participants due to wood dust exposure had a lower forced expiratory volume in 1 second. Individuals with a history of rhinitis or asthma had an increased risk of respiratory symptoms. Sensitization to wood was more common in atopic apprentices with a history of rhinitis and a high total IgE level.

Background: Toluene diisocyanate (TDI) is the most important cause of occupational asthma, but the genetic mechanism of TDI-induced asthma is still unknown., Objective: The objective of the study was to identify susceptibility alleles associated with the TDI-induced asthma phenotype., Methods: We conducted a genome-wide association study in 84 patients with TDI-induced asthma and 263 unexposed healthy normal controls using Affymetrix 500K SNPchip. We also investigated the relationships between genetic polymorphisms and transcript levels in Epstein-Barr virus-transformed lymphoblastoid cell lines from patients with TDI-induced asthma enrolled in this study., Results: Genetic polymorphisms of CTNNA3 (catenin alpha 3, alpha-T catenin) were significantly associated with the TDI-induced asthma phenotype (5.84 x 10(-6) for rs10762058, 1.41 x 10(-5) for rs7088181, 2.03 x 10(-5) for rs4378283). Carriers with the minor haplotype, HT2 [GG], of two genetic polymorphisms (rs10762058 and rs7088181) showed significantly lower PC(20) methacholine level (P=0.041) and lower mRNA expression of CTNNA3 than non-carriers (P=0.040). A genetic polymorphism in the 3' downstream region of CTNNA3 (rs1786929), as identified by DNA direct sequencing, was significantly associated with the TDI-induced asthma phenotype (P=0.015 in recessive analysis model) and the prevalence of serum-specific IgG to cytokeratin 19 (P=0.031)., Conclusion: These findings suggested that multiple genetic polymorphisms of CTNNA3 may be determinants of susceptibility to TDI-induced asthma.

Background: Volatile monoisocyanates are formed through thermal degradation when products containing polyurethane are heated. Repeated exposure to diisocyanates, such as toluene diisocyanate (TDI) are a well-known cause of occupational asthma. However, although monoisocyanates are abundant in occupational settings, there are few data concerning their ability to provoke immune reactions and asthma. We compared immune reactivity and respiratory disease following single or repeated inhalation exposures to the monoisocyanates methyl isocyanate (MIC) and isocyanic acid (ICA) with the effects of TDI., Methods: Isocyanates were administrated either as single vapor exposures or as repeated intranasal instillations in rats. Adverse health effects were monitored by analyzing airway inflammation, respiratory function and weight gain. Immune reactivity caused by repeated exposures was studied by analysis of isocyanate-specific antibodies and airway infiltration of immune competent cells., Results: Repeated exposures to TDI induced airway infiltration of neutrophils and lymphocytes, while neither MIC nor ICA provoked a detectable inflammatory response. Antibodies against isocyanate-albumin conjugates were detected in serum after both exposures to TDI and MIC, but not to ICA. TDI-exposed rats also displayed IgG antibodies against MIC-albumin conjugates. Even though MIC did not induce airway inflammation, single exposure provoked an increase in airway resistance and repeated exposures caused weight loss similar to that of TDI., Conclusions: Airway exposure to TDI produces an antibody response not only against TDI but also against MIC-protein conjugates. This indicates that immune reactivity against abundant monoisocyanates in occupational environments can occur in individuals pre-sensitized with low abundance but highly sensitizing diisocyanates., (Copyright 2009 S. Karger AG, Basel.)

Background: Although the pathogenesis of toluene diisocyanate (TDI)-induced occupational asthma (TDI-OA) is incompletely understood, several studies have suggested immunologic mechanisms, including specific IgE responses. A few studies have suggested human leukocyte antigen (HLA) associations with TDI-induced asthma in Western countries, but this is the first investigation of associations between HLA class I and II alleles and TDI-induced asthma patients in Asia, using high-resolution analysis., Methods: Patients with TDI-OA (n = 84), asymptomatic exposed controls (AECs, n = 47) and unexposed normal controls (NCs, n = 127) were enrolled. HLA class I and II genotyping was performed by the direct DNA sequencing analysis. Specific serum IgE antibodies to the vapor type TDI-albumin conjugate were measured by ELISA., Results: There was no significant association between the allele frequencies and the phenotype of TDI-OA. However, the frequency of the HLA DRB1*1501-DQB1*0602-DPB1*0501 haplotype was significantly higher in TDI-OA patients (19%) than in AEC (2.1%, p = 0.007, OR 4.429, CI 1.497-13.103) or NC (3.1%, p < 0.001, OR 7.235, CI 2.236-22.510) subjects, with statistical significance persisting after correction for multiple comparisons. DQB1*0402 was significantly associated with the presence of specific IgE to TDI-albumin conjugates in serum (p = 0.006, OR 4.552, CI 1.540-13.449). This p value remained significant after correction for multiple comparison., Conclusion: The HLA DRB1*1501-DQB1*0602-DPB1*0501 haplotype may be a genetic marker for the development of TDI-induced asthma in Koreans. Several HLA alleles that enhance specific IgE sensitization in exposed subjects are indicated., ((c) 2009 S. Karger AG, Basel.)

Background: Diisocyanates and 4,4'-diaminodiphenylmethane (MDA) are industrial sensitizers. Occupational asthma is a risk among workers exposed to diisocyanates. Exposure may also lead to contact sensitization and allergic contact dermatitis., Objective: The aim of this study was to determine the occurrence of contact sensitization to MDA and to diisocyanates among general dermatology patients., Patients and Methods: Patch testing with MDA was carried out in 1595 patients. Diphenylmethane-4,4'-diisocyanate (MDI) and toluene-2,4-diisocyanate (TDI) were tested in 1023 patients and isophorone diisocyanate (IPDI) and 1,6-hexamethylene diisocyanate (HDI) in 433 patients. The clinical data and sources of exposure are analysed., Results: MDA reactions were seen in 17 (1.1%) patients and MDI reactions in 4 patients. Six MDA-positive patients reacted to p-phenylenediamine and two to epoxy chemicals. 5/10 of the TDI reactions were seen concurrently with reactions to MDI, MDA, HDI, or to IPDI. IPDI reactions were seen in eight patients and HDI reactions in two patients. Possible sources of exposure were traced in most patients, although the association with the current dermatitis was not apparent in all cases., Conclusion: (Di)isocyanates may induce contact sensitization with or without allergic contact dermatitis.

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.

Objectives: Exposure to diisocyanates is a well known occupational hazard. The objective of this study was to determine the possibility of an association between low exposure to toluene diisocyanate (TDI) (airborne isocyanates and biomarkers of isocyanates in plasma and urine) and symptoms of the eyes and upper and lower airways., Methods: Altogether 136 workers occupationally exposed to TDI and 118 unexposed employees were studied. A physician compiled thorough medical and occupational histories and registered symptoms, total and work-related, of the eyes, nose, and lower airways. The exposure was assessed with personal air measurements and with biomarkers of exposure in plasma and urine. The average exposure in the ambient air at the workplace of the exposed participants was below 1 ppb., Results: Compared with the unexposed group, the exposed workers reported more total symptoms of the eyes and lower airways, as well as nose bleeding. A similar pattern, with even higher odds ratios, was observed for work-related symptoms. However, only eye symptoms proved to be significantly associated with the exposure, notably with all of the exposure measures. The risk was more pronounced for exposure to 2,4-TDI than for exposure to 2,6-TDI., Conclusions: Even very low exposure to TDI is related to negative health effects on exposed workers. Clear dose-response relationships were observed between three different measures of exposure and symptoms of the eyes.

Objectives: Aims of this study were to define (1) whether toluene diisocyanate (TDI) bronchial hyper-responsiveness persists in subjects with occupational asthma after long-term cessation of exposure; (2) whether evolution of specific bronchial TDI sensitization and symptoms and functional abnormalities of asthma were coincident, and (3) the determinants at the time of diagnosis of patients' outcome., Methods: Twenty-five nonatopic spray painters with occupational asthma due to TDI were re-examined 58 +/- 7 (46-73) months after removal from exposure. On both examinations, the severity of asthmatic symptoms and the need for antiasthma treatment over the past 12 months were graded and lung function tests, measurement of airway responsiveness to methacholine (PD(20)), circulating total IgE and TDI-HSA specific IgE, skin tests with common inhalant allergens and specific bronchial challenge with TDI were carried out., Results: Seven subjects were still TDI-reactors and 18 lost reactivity to it. All persistent reactors had still asthma and their symptom score, medication score, FEV(1), PD(20) and serum IgE were unchanged between assessments. In the 18 subjects no longer responsive to TDI, 8 had still features of asthma: their symptom and medication score had improved significantly, but FEV(1), PD(20) and serum IgE had not significantly changed; the other ten patients no longer reactors to TDI were also asymptomatic and their PD(20) had become normal. The duration of symptomatic exposure to TDI was the only feature at diagnosis that differentiated patients with persistent TDI airway hyper-responsiveness and asthma from those who were no longer responsive to TDI but still asthmatic and those who were no longer responsive to TDI and no longer asthmatic (4 +/- 1.6; 2.1 +/- 0.8; 0.6 +/- 0.3 years, respectively; p < 0.001)., Conclusion: our study demonstrates that airway sensitization to TDI and symptoms and functional airway abnormalities of asthma can persist for years after cessation of exposure and may have different outcome. If avoidance of the offending agent takes place within few months after the development of symptoms, remission of asthma and of TDI bronchial hyper-responsiveness can occur, whereas waiting for years makes it too late to cure asthma and, in the end, to reverse specific sensitization.

Toluene diisocyanate (TDI) is a leading cause of occupational asthma. Although considerable controversy remains regarding its pathogenesis, TDI-induced asthma is an inflammatory disease of the airways characterized by airway remodeling. Peroxisome proliferator-activated receptor gamma (PPARgamma) has been shown to play a critical role in the control of airway inflammatory responses. However, no data are available on the role of PPARgamma in TDI-induced asthma. We have used a mouse model for TDI-induced asthma to determine the effect of PPARgamma agonist, rosiglitazone, or pioglitazone, and PPARgamma on TDI-induced bronchial inflammation and airway remodeling. This study with the TDI-induced model of asthma revealed the following typical pathophysiological features: increased numbers of inflammatory cells of the airways, airway hyperresponsiveness, increased levels of Th2 cytokines (IL-4, IL-5, and IL-13), adhesion molecules (ICAM-1 and VCAM-1), chemokines (RANTES and eotaxin), TGF-beta1, and NF-kappaB in nuclear protein extracts. In addition, the mice exposed to TDI developed features of airway remodeling, including thickening of the peribronchial smooth muscle layer, subepithelial collagen deposition, and increased airway mucus production. Administration of PPARgamma agonists or adenovirus carrying PPARgamma2 cDNA reduced the pathophysiological symptoms of asthma and decreased the increased levels of Th2 cytokines, adhesion molecules, chemokines, TGF-beta1, and NF-kappaB in nuclear protein extracts after TDI inhalation. In addition, inhibition of NF-kappaB activation decreased the increased levels of Th2 cytokines, adhesion molecules, chemokines, and TGF-beta1 after TDI inhalation. These findings demonstrate a protective role of PPARgamma in the pathogenesis of the TDI-induced asthma phenotype.

Background: Adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) are thought to contribute to the airway inflammation and airway hyper-responsiveness (AHR) of allergic asthma. Some differences from allergic asthma have been noted, including airway neutrophilia, and the involvement of ICAM-1 in toluene diisocyanate (TDI) asthma is currently unclear., Objective: We utilized mice lacking ICAM-1 expression (ICAM-1(-/-)) to investigate the role of ICAM-1 in airway inflammation and AHR in TDI-induced asthma., Methods: Male C57BL/6J mice (ICAM-1(+/+)) and ICAM-1(-/-) mice were intranasally sensitized to TDI solution or solvent alone. Airway inflammation, AHR and cytokine secretion were assessed 24 h after challenge by TDI or solvent. The production of antigen-specific IgG and IgE by TDI sensitized and non-sensitized mice was determined., Results: TDI challenge to ICAM-1(+/+) mice induced an increase in airway inflammatory cell numbers, AHR and cytokine secretion of TNF-alpha, macrophage inflammatory protein-2 (MIP-2), IL-4, IL-5 and IFN-gamma into the bronchoalveolar lavage fluid. All these pathophysiological changes were reduced in ICAM-1(-/-) mice. Serum levels of TDI-specific IgG and IgE of ICAM-1(-/-) and ICAM-1(+/+) mice were comparable., Conclusion: These results suggest that ICAM-1 plays an essential role in airway inflammation and AHR in TDI-induced asthma.

Background: Inhaled isocyanate binds with cytokeratin (CK) of the epithelial cells, which could induce immune responses., Objective: To elucidate the possible existence of an isocyanate-induced, asthma-associated autoantigen from the bronchial epithelial cells, which may be associated with toluene diisocyanate (TDI)-induced asthma development., Methods: We cultured bronchial epithelial cells with incubation of TDI-human serum albumin (HSA) conjugate. Gene expression profiles of cultured epithelial cells were analyzed using a microarray technique. CK19 protein expression within the epithelial cells was confirmed by IgG immunoblot using monoclonal antibody to CK19. Serum IgG to CK19 and specific IgG and IgE antibodies to TDI-HSA conjugate were detected by enzyme-linked immunosorbent assay in 68 TDI asthma patients (group 1) and compared with 40 allergic asthma patients (group 2) and 80 unexposed healthy controls (group 3)., Results: After TDI exposure, increased expression of CK19 and CK14 genes from the culture bronchial epithelial cells was noted using microarray analysis. IgG immunoblot analysis confirmed increased expression of CK19 after the TDI exposure. The levels of serum IgG to CK19 were significantly higher in the TDI asthma group than in groups 2 and 3 (P=.008). The prevalence of IgG to CK19 was significantly higher in group 1 (38.2%) than group 2 (22.5%) or group 3 (1.3%) (P=.008). Significant associations were noted between IgG to CK19 and specific IgG to TDI-HSA conjugate and transglutaminase (P=.02) but not with specific IgE to TDI-HSA conjugate., Conclusion: We suggest that TDI exposure can augment CK19 expression from the bronchial epithelial cell, which may involve immune responses as an autoantigen to induce airway inflammation in TDI-induced asthma.

Background: Toluene diisocyanates (TDIs) are important industrial intermediates used in conjunction with polyester polyols as coreactants in the manufacture of polyurethane foam blocks, paints, etc. It is listed as a potential carcinogen by the National Toxicology Program (NTP) and International Agency for Research on Cancer (IARC) and is known to induce chromosomal aberrations., Methods: The study involved 26 people, exposed to TDI during the production of plastics. The corresponding control group was comprised of 21 people coming from the same geographic area, who were never exposed to isocyanates., Results: The concentration of TDI ranged between 0.007 mg/m3 and 0.016 mg/m3, which amounts to 0.10-0.23 MDK (extreme value of a single substance) 0.007 mg/m3. Structural chromosome aberrations (SCA) were evaluated in 200 lymphocytes of peripheral blood. The average value was 2.6. Sister chromatid exchange (SCE) was established in 50 cells, the average being 8.127. Micronucleus (MN) was established in 500 CB, with an average of 12.07. The averages of the control group were 1.89 (SCA), 5.52 (SCE), and 4.38 (MN). The difference between the groups is of statistical significance., Conclusions: The ascertained results accentuate mutagenic activity of isocyanates or their metabolic products., (Copyright 2004 Wiley-Liss, Inc.)

Background: Toluene diisocyanate (TDI)-induced asthma is a common cause of occupational asthma and it affects 5-15% of the exposed population suggesting an underlying genetic susceptibility., Methods: To investigate the role of genetic factors in the development of TDI-induced asthma, we analyzed the distribution of human leukocyte antigen (HLA) class I genes and of tumor necrosis factor (TNF)-alpha A-308G polymorphism in 142 patients with TDI-induced asthma and in 50 asymptomatic exposed subjects., Results: Neither the distribution of HLA class I antigens nor the distribution of TNF-alpha A-308G polymorphism was different between patients with TDI-induced asthma and asymptomatic exposed subjects., Conclusions: These results suggest that HLA class I antigens and TNF-alpha A-308G are not associated with susceptibility or resistance to the development of TDI-induced 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.

Eighty-seven cases of occupational asthma induced by toluene diisocyanate (TDI) were diagnosed by an inhalation challenge with TDI and methacholine. After an average follow-up interval of 11 yrs, all subjects were re-examined. Of the 87 subjects examined, 13 (15%) had remained in the same job, 44 (50.5%) had been removed from exposure for <10 yrs and 30 (34.5%) had been removed for >10 yrs. The proportion of subjects who experienced symptoms of asthma and those who were hyperresponsive to methacholine was significantly lower. Of the patients, 59% used short-acting bronchodilators, 8% long-acting bronchodilators and 18% were on regular inhaled glucocorticoids. Thus, multiple regression analysis showed a positive correlation between forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) at follow-up and FVC and FEV1 at diagnosis, and a negative correlation with smoking and with therapy with bronchodilators. Stepwise logistic regression showed that the follow-up provocative dose causing a 20% fall in the FEV1 (PD20) could be predicted from baseline PD20. These results indicate that respiratory symptoms and airway hyperresponsiveness to methacholine persist in subjects removed from exposure to TDI for >10 yrs. A more favourable prognosis was associated with a better lung function and a lower degree of airway hyperresponsiveness to methacholine at diagnosis.

Objectives: The composition of thermal degradation products from two types of polyurethane foams, one based on toluene diisocyanate (TDI) and the other on diphenylmethane diisocyanate (MDI), was analyzed and their toxic lung effects were compared., Methods: Isolated perfused lungs of guinea pig were subjected to thermal decomposition products of polyurethane foams from an aerosol generator with compartments for diluting, mixing, and sampling., Results: Thermal degradation of MDI-based polyurethane foams released MDI, phenyl isocyanate, and methyl isocyanate. The emitted particulate fraction was 75% for MDI, whereas that for TDI from TDI-based polyurethane foam was 3%. Thermal degradation products from MDI-based foam caused a pronounced dose-dependent decrease in the measured lung function parameters (conductance and compliance). In contrast, the thermal degradation products from TDI-based foam did not cause any decrease in lung function., Conclusions: Thermal degradation products generated from MDI-based polyurethane foam were more toxic to the lung than those generated from TDI-based polyurethane foam. This difference was probable due to MDI in the particle phase.

Background and Objective: Persistent asthma symptoms are associated with airway inflammation and remodeling, which may be mediated through metalloproteinase (MMP) and tissue inhibitor of metalloproteinase (TIMP). The aim of this study was to evaluate MMPs and TIMP involvement in toluene diisocyanate (TDI)-induced asthma., Materials and Method: Induced sputum was collected in eight newly diagnosed TDI-induced asthma subjects (group I) before and 7 h after the TDI and placebo challenges and in 12 subjects with TDI-induced occupational asthma diagnosed 5 years previously with persistent asthma symptoms (group II). Sera was collected in group I at diagnosis, and in group II, they were collected at the time of the study. 12 nonasthmatic healthy subjects were enrolled as controls. MMP-9, MMP-2 and TIMP-1 levels in both sputum and serum were measured by enzyme-linked immunosorbent assay (ELISA). Gelatinase activity in the sputum was confirmed by zymographic analysis., Results: The serum TIMP-1 level was significantly higher in asthma patients than in healthy controls (P = 0.01), while MMP-9 level was significantly lower in asthmatic patients (P = 0.03). There was no significant difference in MMP-2 level (P = 0.27). MMP-9 level in the sputum was significantly increased after the TDI challenges (P = 0.01). TIMP-1 level in sputum tended to increase after TDI challenges, but no statistical significance was noted (P = 0.09). MMP-9 and MMP-9/TIMP-1 levels in the sputum were significantly higher in group II than in group I (P = 0.04, P = 0.02) with no significant difference in TIMP-1 level. Minimal amount of MMP-2 was found in sputum. Zymography demonstrated that MMP-9 level increased and active form of MMP-9 was generated after the TDI bronchoprovocation test., Conclusion: TDI exposure leads to overproduction of MMP-9, which may induce airway inflammation and remodeling, and then contribute to persistent asthmatic symptoms in TDI-induced asthma.

Toluene diisocyanate (TDI) is an important industrial intermediate used in manufacturing flexible polyurethane (PUR) foams, surface coatings, cast elastomers, sealants, and adhesives. In this review long-term trends in workplace exposures to TDI are assessed in both the producing and using industries, and respiratory health effects of TDI are evaluated in relation to workplace TDI concentrations. The key respiratory health effects associated with repeated or long-term TDI exposure are bronchial asthma and an accelerated rate of decline in lung function. In the early years of the industry, annual incidence rates of occupational asthma (OA) due to TDI ranged from 1% to as high as 5 to 6%, depending on the extent of engineering and work practice controls in the various workplaces. Since the mid-1970s, annual OA incidence rates have been <1%, where 8 h TDI concentrations have been maintained below 5 ppb as determined by personal monitoring, even where short-termTDI concentrations above 20 ppb and less frequently above 40 ppb were routinely detected. In these latter settings, there is evidence that the majority of OA cases may be attributable to TDI concentrations well above 20 ppb associated with overexposure incidents. Further study is needed regarding the role of such incidents in inducing respiratory sensitization. Cross-sectional and longitudinal studies of lung function have indicated that continued exposure after development of work-related respiratory symptoms can lead to transient or accelerated fixed declines in forced expiratory volume in 1 sec (FEV1). These findings are congruent with the FEV1 declines demonstrated in general population studies of persons with persistent bronchial hyperresponsiveness or nonoccupational asthma. More recent longitudinal studies in settings with ongoing medical surveillance have provided no consistent evidence of accelerated FEV1 loss among employees exposed up to 5 ppb TDI on an 8 h time-weighted average basis.