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Do Low Molecular Weight Agents Cause More Severe Asthma than High Molecular Weight Agents?

  • Olga Meca,

    Affiliation Servicio de Neumología, Hospital General Universitario Morales Messeguer, Murcia, Spain

  • María-Jesús Cruz ,

    mj.cruz@vhir.org

    Affiliations Servicio de Neumología, Hospital Universitario Vall d’Hebron, Barcelona, Catalonia, Spain, Centro de Investigación en Red de Enfermedades Respiratorias (CIBERES), Instituto de Salud Carlos III (ISCIII), Barcelona, Spain

  • Mónica Sánchez-Ortiz,

    Affiliations Servicio de Neumología, Hospital Universitario Vall d’Hebron, Barcelona, Catalonia, Spain, Centro de Investigación en Red de Enfermedades Respiratorias (CIBERES), Instituto de Salud Carlos III (ISCIII), Barcelona, Spain

  • Francisco-Javier González-Barcala,

    Affiliation Respiratory Department, Clinic University Hospital, Santiago de Compostela, Spain

  • Iñigo Ojanguren,

    Affiliations Servicio de Neumología, Hospital Universitario Vall d’Hebron, Barcelona, Catalonia, Spain, Centro de Investigación en Red de Enfermedades Respiratorias (CIBERES), Instituto de Salud Carlos III (ISCIII), Barcelona, Spain

  • Xavier Munoz

    Affiliations Servicio de Neumología, Hospital Universitario Vall d’Hebron, Barcelona, Catalonia, Spain, Centro de Investigación en Red de Enfermedades Respiratorias (CIBERES), Instituto de Salud Carlos III (ISCIII), Barcelona, Spain, Department of Cell Biology, Physiology and Immunology, Universitat Autònoma de Barcelona, Catalonia, Spain

Do Low Molecular Weight Agents Cause More Severe Asthma than High Molecular Weight Agents?

  • Olga Meca, 
  • María-Jesús Cruz, 
  • Mónica Sánchez-Ortiz, 
  • Francisco-Javier González-Barcala, 
  • Iñigo Ojanguren, 
  • Xavier Munoz
PLOS
x

Abstract

Introduction

The aim of this study was to analyse whether patients with occupational asthma (OA) caused by low molecular weight (LMW) agents differed from patients with OA caused by high molecular weight (HMW) with regard to risk factors, asthma presentation and severity, and response to various diagnostic tests.

Methods

Seventy-eight patients with OA diagnosed by positive specific inhalation challenge (SIC) were included. Anthropometric characteristics, atopic status, occupation, latency periods, asthma severity according to the Global Initiative for Asthma (GINA) control classification, lung function tests and SIC results were analysed.

Results

OA was induced by an HMW agent in 23 patients (29%) and by an LMW agent in 55 (71%). A logistic regression analysis confirmed that patients with OA caused by LMW agents had a significantly higher risk of severity according to the GINA classification after adjusting for potential confounders (OR = 3.579, 95% CI 1.136–11.280; p = 0.029). During the SIC, most patients with OA caused by HMW agents presented an early reaction (82%), while in patients with OA caused by LMW agents the response was mainly late (73%) (p = 0.0001). Similarly, patients with OA caused by LMW agents experienced a greater degree of bronchial hyperresponsiveness, measured as the difference in the methacholine dose-response ratio (DRR) before and after SIC (1.77, range 0–16), compared with patients with OA caused by HMW agents (0.87, range 0–72), (p = 0.024).

Conclusions

OA caused by LMW agents may be more severe than that caused by HMW agents. The severity of the condition may be determined by the different mechanisms of action of these agents.

Introduction

The term”work-related asthma” encompasses both occupational asthma (OA) and work-exacerbated asthma (WEA) [1]. OA is characterized by variable airflow limitation and/or hyperresponsiveness and/or inflammation due to causes and conditions attributable to a particular occupational environment and not to stimuli encountered outside the workplace [2], while WEA is defined as the aggravation of pre-existing or coincident (adult new-onset) asthma due to workplace environmental exposure [3]. OA is subdivided into immunological or non-immunological forms, with the reactive airway dysfunction syndrome (RADS) being the most characteristic example of the latter presentation [4]. A recent evidence-based review of the literature identified 372 causative agents of immunological asthma and 184 different causes of irritant or non-immunological OA [5].

Immunological OA, caused by workplace sensitizers, is characterized by the appearance of work-related asthma symptoms after a latency period. The causative agent may be either a high or a low molecular weight agent (HMW and LMW, respectively). HMW agents are protein-derived antigens and are generally considered to cause sensitization through an IgE-mediated mechanism and so allergy skin-prick test and measurements of allergen-specific antibodies can aid diagnosis [6]. Although specific IgE antibodies have also been detected in OA induced by some LMW agents [7], and several studies have suggested that immunologic mechanisms are involved in LMW-related OA [89], the exact mechanisms have not yet been fully characterized. In fact, the few studies carried out to date have demonstrated variable patterns of response to HMW and LMW agents; in the main, HMW agents seem to induce early or dual asthmatic reactions, while LMW agents produce delayed reactions [1011].

It is not known whether differences in the pathogenesis of immunological OA also lead to differences in clinical presentation. Early studies in the 1990s suggested that the natural history of the onset of OA varies according to the sensitizing agent, and that factors such as age, gender, atopy, rhinitis, and smoking habit might influence the development of the condition [10]. However, recent studies suggest that the intensity of exposure may affect the risk of development of symptoms and sensitization more than host markers or the type of agent [12]. Whether or not the severity of asthma is related to the type of causal agent is also unclear.

The objective of this study was to analyse the differences in relation to possible risk factors, asthma presentation and severity, and response to various diagnostic tests in patients with OA caused by either HMW or LMW agents.

Patients and Methods

Type of study

Retrospective study using data from medical charts, conducted at an OA referral centre. The local Ethics Committee approved the study (Hospital Valld’Hebron Ethics Committee approval PR(AG)26/2006). All subjects were contacted specifically to be included in this study and they signed informed consent documents for participation.

Subjects

All subjects (n = 78) with final diagnosis of OA after a positive specific inhalation challenge (SIC) between January 2008 and December 2013 were included. Medical charts of all subjects were reviewed by the authors. Demographic data such as sex, age, smoking habit, atopy, dermatitis, rhinitis, conjunctivitis, type of employment, agents, exposures, time between start of exposure and start of symptoms, time between start of symptoms and diagnosis, time subjects were away from work until diagnosis, treatment, and severity of asthma according to the Global Initiative for Asthma (GINA) control classification [13] at diagnosis were recorded. Asthma severity was defined in accordance with GINA classification, on the basis of the intensity of treatment required to achieve good control of the condition. Asthma which was well controlled with low intensity treatment such as low-dose inhaled corticosteroids (IC), leukotriene modifiers or chromones was defined as mild. Asthma requiring high intensity treatment to maintain good control, or in which good control was not achieved despite high intensity treatment, was defined as severe. Blood analysis results, including eosinophil count and total IgE, spirometry, methacholine and SIC were assessed.

Atopy and smoking status

Patients were considered atopic if they had at least one positive prick test to any common environmental allergen. Non-smokers were patients who had never smoked and ex-smokers were those who had not smoked for at least six months. The number of pack-years was calculated.

Spirometry and methacholine challenge

Spirometry was performed with a Datospir 200 (Sibel, Barcelona) instrument, following the European Respiratory Society (ERS) and American Thoracic Society (ATS) guidelines [14]. The reference values used were those proposed for the Mediterranean population [15]. Bronchial challenge with methacholine was performed in accordance with Spanish guidelines [16]. Briefly, a Mefar MB3 (Mefar, Ele H2O, Medicalli, Brescia, Italy) dosimeter was used, and increasing concentrations of methacholine (from 0.03 mg/ml to 16 mg/ml) were inhaled at three-minute intervals until FEV1 had fallen by 20% compared with its baseline value or until the subject had inhaled the maximum concentration of methacholine. The provocative concentration of methacholine causing a 20% drop in FEV1 was designated as PC20 and expressed in mg/ml. The methacholine challenge was considered negative if the PC20 was higher than 16 mg/ml. In all patients, the methacholine dose-response ratio (DRR) was calculated as the percentage fall in FEV1 at the last concentration, divided by the total concentration administered.

Specific Inhalation challenge

SIC was carried out according to the guidelines proposed by our group [17]. Briefly, subjects were examined on five consecutive days. Inhaled corticosteroids were withheld 48 hours before SIC. On the first day (control day), full medical and occupational histories were collected, and skin-prick tests with a battery of common allergens, radiography study, pulmonary function testing and methacholine challenge were performed. On day 2, a first placebo inhalation challenge was performed. On days 3 and 4, subjects underwent SIC with the suspected workplace agent. On day 5, pulmonary function test and methacholine challenge were repeated. Changes in lung function were monitored in each patient by measuring FEV1 every 10 minutes during the first hour after exposure and then every hour until 15 hours after inhalation. Response was considered positive when FEV1 fell more than 20% compared with the baseline value in the absence of any change to placebo. Asthma response was defined as early when the fall in FEV1 occurred within 1 h of the last inhalation of the sensitizing agent, and as late when the fall in FEV1 was observed between 2–8 h following the challenge. Finally, a combination of an early and late response was defined as a “dual asthma response”.

Statistical analysis

The characteristics of the subjects are expressed as the median and range unless otherwise stated. A one-sample Kolmogorov-Smirnov test, calculated to assess normality, showed non-normal distribution of the parameters studied. Between-group differences were analysed by the Mann-Whitney test and within-group differences by the Wilcoxon signed rank test. Differences were considered significant at a p value of ≤0.05. Multivariate logistic regression was used to analyse the independent association between asthma severity and the type of agent involved. All variables that were related to the quantities of interest and/or factors previously reported in the literature were considered as potential confounders. Results were reported using odds ratios (OR) and 95% confidence intervals (CI). SPSS release 17.0 for Windows (SPSS; Chicago, IL) and GraphPad InStat4 (GraphPad Software Inc; San Diego, CA) were used for the statistical analyses.

Results

Of the 78 patients with final diagnosis of OA, 23 responded to HMW agents and 55 to LMW agents. The various sensitizing agents responsible for OA are shown in Table 1. In the group sensitized to HMW agents, flour was the more prevalent (48% of cases). For LMW agents, isocyanates and persulphates were the most prevalent (36% and 24% of cases respectively). Subjects’ demographic data are summarized in Table 2. Although the percentage of patients with atopy was similar in the two groups, patients with OA caused by HMW more frequently presented rhinitis and conjunctivitis than patients with OA caused by LMW.

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Table 1. Sensitizing agents responsible for OA in the study population.

https://doi.org/10.1371/journal.pone.0156141.t001

Table 3 presents data on the occupational exposure of patients, severity of asthma and the treatment they were receiving at the time of diagnosis. Patients with OA caused by LMW agents seemed to have more severe asthma than those with OA caused by HMW agents and a greater use of long-acting beta-antagonists (LABA), probably related to the greater severity. No differences were seen between the groups in other variables. A logistic regression analysis confirms that patients with OA caused by LMW agents had a significantly higher risk of asthma severity according to the GINA classification after adjusting for potential confounders (OR = 7.16, 95% CI: 1.13–15,20; p = 0.036) (Table 4).

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Table 3. Data on occupational exposure, asthma severity and treatment received by patients at the time of diagnosis.

https://doi.org/10.1371/journal.pone.0156141.t003

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Table 4. Logistic regression analysis with patients exposed to HMW agents as independent variable comparing patients with intermittent or mild asthma and those with moderate or severe asthma.

https://doi.org/10.1371/journal.pone.0156141.t004

Finally, Table 5 shows the results in the SIC, suggesting that HMW agents typically induced an early reaction, whereas LMW typically induced a delayed reaction (p = 0.0001). In patients with OA caused by HMW agents SIC was positive with a shorter exposure time (p = 0.025) and these patients required more rescue medication during the SIC (p = 0.003) than those with OA caused by LMW agents. However, patients with OA caused by LMW agents presented a greater degree of bronchial hyperresponsiveness after the SIC, measured as the difference in the values of methacholine DRR (p = 0.024). No differences were found in the fall in FEV1, regardless of the type of response (early, late or dual) or type of agent. Considering the population as a whole, patients requiring treatment with IC alone had a greater decrease in FEV1 after SIC than those taking IC + LABA; median (range): 27.5 (16. 61) and 21 (15–48), respectively, p = 0.005. These differences are not observed when the population is divided into LMW and HMW groups.

Discussion

To our knowledge, this is the first study to show that OA produced by LMW agents may be more severe than that produced by HMW agents. In fact, few studies have assessed the severity of OA at the time of diagnosis, even though it is acknowledged that OA in general may be a particularly severe form of the disease, for three main reasons: 1) the asthma persists in all patients with OA who remain in contact with the causal agent and worsens in 50% in spite of treatment; likewise, it may persist in 50% of patients even though they avoid exposure, and may worsen in 10–40% [1821]; 2) there have been reports of patients who died after developing acute asthma after occupational exposure to agents to which they were sensitized [2223]; and 3) patients with OA and WEA consume ten times more medical resources than patients with non-work-related asthma [24]. Other reasons that may explain why OA may be more severe than non-OA are the difficulty of diagnosis, the difficulty of management, generally higher levels of exposure (peaks) in the workplace than in other environments, co-exposures to irritants, and so on.

Interestingly, in the Epidemiological Study on the Genetics and Environment of Asthma (EGEA study) of patients with severe asthma, Le Moual et al [25] found that up to 30% may be exposed to OA-causing agents and that the condition may be more severe in those who are exposed simultaneously to both HMW and LMW agents. The recent observation that persistent occupational exposure to asthmagens (either HMW or LMW) is associated with uncontrolled adult-onset asthma [26] or more severe forms of the disease [25, 27] supports this hypothesis. Furthermore, a longer latency between onset of symptoms and diagnosis of OA carries a worse prognosis for persistence and severity of asthma, whether or not exposure to the causative agent is avoided [2829]. However, in our study it does not seem that either the total exposure time, or the latency between onset of symptoms and diagnosis were associated with the greater severity recorded in LMW-related asthma. In fact, in agreement with Dufour et al [11], we did not find any differences in the latency period before the onset of symptoms or in the duration of exposure between HMW and LMW agents. In this regard, several authors have pointed out that the length of time necessary for sensitization may depend, among other factors such as genetics or the concentration of inhaled agents [30], upon the nature of each agent rather than on the molecular weight of the agent alone. In this sense, in contrast to the results found in our study, Descatha et al [31], comparing the characteristics of patients with OA to HMW and LMW agents, found that the severity of the disease at the time of diagnosis does not appear to be influenced by the molecular weight of the causal agent.

In the present study, we did not find any association that might explain why OA is more severe when caused by LMW agents. A plausible hypothesis is that agents with different mechanisms of action may trigger different responses in terms of both inflammation and bronchial hyperresponsiveness, thus altering the degree of severity. In line with other authors [1011, 17] we found that in the context of the challenge test, HMW agents tend to present an early airway response, while in the case of LMW the response is usually late, although early reactions can occur with LMW agents and late reactions with HMW agents. It is generally accepted that HMW agents cause asthma through an IgE-mediated mechanism, that is, via a Th2 response, and generate a clearly eosinophilic airway inflammation; they are also associated with a higher proportion of patients with rhinitis and conjunctivitis [6], as we observed in the present study. In this regard, Malo et al [32] found that the prevalence of symptoms did not differ for HMW and LMW agents, although rhinitis was more intense for HMW than for LMW. Likewise, it is recognized that eosinophilic asthma generally responds well to treatment with IC [13].

The situation is the reverse in the case of patients with OA caused by LMW agents. In fact, the pathogenesis of OA caused by LMW agents remains largely unclear. The data available suggest that the T-cell subsets and cytokine profiles involved in LMW-induced OA may differ from those operating in atopic asthma. Although some of them induce IgE-mediated responses [6], most induce asthma through a non-IgE related mechanism [33] in which non adaptative immune responses might play a role [34]. The possible role of non-immunological mechanisms such as epithelial injury, remodeling of the airway wall, oxidative stress or neurogenic inflammation are under debate [35]. This means that although the inflammation is eosinophilic in some patients, in many others it is neutrophilic or mixed, and in these cases the response to IC treatment is lower [35], these patients may require more treatment and their condition may therefore be classified as more severe [13].

Finally, another interesting result of this study is the observation that individuals with OA caused by LMW agents present greater bronchial hyperresponsiveness 24 hours after the SIC. In this sense, Vandenplas et al [36] demonstrated that SIC to LMW agents is the principal risk factor for the occurrence of asthmatic reactions requiring administration of short-acting beta agonists with or without oral or intravenous corticosteroids. We cannot rule out the possibility that different intrinsic mechanisms may be at work in thepathogenesis of OA caused by HMW or LMW agents. The IgE-mediated response characteristic of HMW agents causes a histamine release which in turn leads to a fall in FEV1 and also, since it is an isolated exposure, a return to baseline levels within a short period of time, which may mean that the degree of bronchial hyperresponsiveness remains unchanged. In OA caused by LMW agents, on the other hand, in addition to possible inflammatory mechanisms, the bronchial hyperresponsiveness may depend on a neuroimmune interaction involving both mast cell activation and the transient receptor potential ankyrin (TRPA)1-dependent stimulation of sensory neurons [37].

Without doubt, the main limitation of this study is its retrospective nature. We do not have objective measures of the degree of asthma control in our patients and so we cannot be sure that the classification of asthma severity at the time of diagnosis was correct. However, the data (including the treatment required by patients) were recorded at the time the SIC was conducted. It is essential that asthma is controlled before performing SIC, because otherwise the results may be misinterpreted and false positives may be obtained [17]. Prior to the SIC, asthma control is usually established by checking that there are no clinical changes or changes in pulmonary function after administration of a placebo [38]. None of our patients presented any such alterations and all underwent the SIC, so it can probably be assumed that their disease was controlled and that the severity was correctly classified. Another limitation is the small number of participants. We can not rule out the possibility that other variables might have reached statistically significant values with a larger number of observations. Finally, some authors have suggested that the outcome of OA varies according to geographical location [29]. This study was conducted in a European country, in which IC are widely used in the treatment of asthma–a practice which may alter the natural history of the disease [39].

In conclusion, this study demonstrates that OA caused by LMW agents may be more severe than that caused by HMW agents. However, the characteristics of the study do not allow us to draw any conclusions about the prognosis of the disease, especially since no differences were found in the baseline lung function, emergency visits or hospitalizations between patients with OA exposed to HMW or LMW agents.The confirmation that most LMW agents induce a delayed response and HMW agents an early response in the SIC, and the differences in the degree of bronchial hyperresponsiveness after the challenge, suggest that the two types of agent have different mechanisms of action. Equally, the absence of any variables associated with the increased severity caused by LMW agents in the present study suggests that these different mechanisms of action are also responsible for the severity of OA. Future studies with larger study populations are necessary to confirm these findings.

Acknowledgments

MJC is a researcher supported by the Miguel Servet programme from Instituto de Salud Carlos III (CP12/03101). The funders had no role in the study design, the data collection or analysis, the decision to publish, or the preparation of the manuscript.

Author Contributions

Conceived and designed the experiments: XM FJGB MJC. Performed the experiments: XM OM IO MSO. Analyzed the data: XM OM IO MSO. Contributed reagents/materials/analysis tools: XM OM IO MJC. Wrote the paper: OM MJC MSO FJGB IO XM. Drafting the manuscript for important intellectual content: OM MJC MSO FJGB IO XM.

References

  1. 1. Baur X, Sigsgaard T, Aasen TB, Burge PS, Heederik D, Henneberger P, et al on behalf of the ERS task Force on the Management of Work-Related-Asthma. Guidelines for the management of work-related asthma. Eur Respir J 2012;39:529–45. pmid:22379148
  2. 2. Bernstein IL, Bernstein DI, Chan-Yeung M, Malo JL. Definitions and classification of asthma in the workplace. In: Malo JL, Chan-Yeung M and Bernstein DI, editors. Asthma in the workplace.Fourth Edition. Boca Raton; CRC Press; 2013, pp 1–5.
  3. 3. Tarlo SM, Balmes J, Balkisson R, Beach J, Beckett W, Bernstein D, et al. ACCP consensus statement; diagnosis and management of work-related asthma. Chest 2008;134:1S–41S. pmid:18779187
  4. 4. Brooks SM, Weiss MA, Bernstein IL. Reactive airways dysfunction syndrome (RADS).Persistent asthma syndrome after high level irritant exposures. Chest 1985;88:376–84. pmid:4028848
  5. 5. Baur X. A compendium of causative agents of occupational asthma.J Occup Med Toxicol 2013;8:15. pmid:23706060
  6. 6. Maestrelli P, Boschetto P, Fabbri LM,Mapp CE. Mechanisms of occupational asthma. J Allergy Clin Immunol 2009;123:531–42. pmid:19281901
  7. 7. Mapp CE, Boschetto P, Maestrelli P, Fabbri LM. Occupational asthma. Am J Respir Crit Care Med 2005;172:280–305. pmid:15860754
  8. 8. Jones MG, Nielsen J, Wekch J, Harris J, Welinder H, Bensryd I, et al. Association of HLA-DQ5 and HLA-DR1 with sensitization to organic aid anhydrides. Clin Exp Allergy 2004;34;812–16. pmid:15144476
  9. 9. Bernstein DI, Kashon M, Lummus ZL, Johnson VJ, Fluharty K, Gautrin D, et al. CTNNA3 (α-catenin) gene variants are associated with diisocyanate asthma, a replication study in a Caucasian worker population. Toxicol Sci 2013;131:242–6. pmid:22977168
  10. 10. Malo JL, Ghezzo H, D'Aquino C, L'Archeveque J, Cartier A, Chan-Yeung M. Natural hystory of occupational asthma: relevance of type of agent and other factors in the rate of development of symptoms in affected subjects. J Allergy Clin Immunol 1992;90:937–944. pmid:1460199
  11. 11. Dufour MH, Lemiére C, Prince P, Boulet LP. Comparative airway response to high-versus low-molecular weight agents in occupational asthma. Eur Respir J 2009;33:734–739. pmid:19129274
  12. 12. Vandenplas O. Occupational asthma: etiologies and risk factors. Allergy Asthma immunol Res 2011;3:157–167. pmid:21738881
  13. 13. Global Initiative for Asthma (GINA). Global strategy for asthma management and prevention 2010, Available from http://www.ginasthma.com.
  14. 14. Miller MR, Hankinson J, Brusasco V, Burgos F, Casaburi R, Coates A, et al; ATS/ERS Task Force. Standardisation of spirometry. Eur Respir J 2005; 26(2):319–38. pmid:16055882
  15. 15. Roca J, Sanchis J, Agusti-Vidal A, Segarra F, Navajas D, Rodriguez-Roisin R, et al. Spirometric references values from a Mediterranean population. Bull Eur Physiopathol Respir 1986;22:217–2. pmid:3730638
  16. 16. Perpiñá-Tordera M, García Río F, Álvarez Gutierrez FJ, Cisneros Serrano C, CompteTorrero L, Entrenas Costa LM, et al; Spanish Society of Pulmonology and Thoracic Surgery (SEPAR). Guidelines for the study of nonspecific bronchial hyperresponsiveness in asthma.Spanish Society of Pulmonology and Thoracic Surgery (SEPAR). Arch Bronconeumol. 2013;49(10):432–46. pmid:23896599
  17. 17. Cruz MJ, Muñoz X. The current diagnostic role of the specific occupational laboratory challenge test. Curr Opin Allergy Immunol 2012;12:119–25.
  18. 18. Cote J, Kennedy S, Chan-Yeung M. Outcome of patients with cedar asthma with continuous exposure. Am Rev Respir Dis 1990;141:373–6. pmid:1689129
  19. 19. Paggiaro PL, Loi AM, Rossi O, Ferrante B, Pardi F, Roselli MG, et al. Follow-up study of patients with respiratory disease due to toluene diisocyanate (TDI). Clin Allergy 1984;14:463–9. pmid:6091946
  20. 20. Chan-Yeung M. Immunologic and nonimmunologic mechanisms in asthma due to western red cedar (Thujaplicata). J Allergy Clin Immunol 1982;70:32–7. pmid:6177724
  21. 21. Malo JL, Ghezzo H, L'Archevêque J, Lagier F, Perrin B, Cartier A. Is the clinical history a satisfactory means of diagnosing occupational asthma?. Am Rev Respir Dis 1991;143:528–32. pmid:2001062
  22. 22. Ortega HG, Kreiss K, Schill DP, Weissman DN. Fatal asthma from powdering shark cartilage and review of fatal occupational asthma literature. Am J Ind Med 2002;42:50–4. pmid:12111690
  23. 23. Chester DA, Hanna EA, Pickelman BG, Rosenman KD. Asthma death after spraying polyurethane truck bedliner. Am J Ind Med 2005;48:78–84. pmid:15940723
  24. 24. Lemière C, Boulet LP, Chaboillez S, Forget A, Chiry S, Villeneuve H, et al. Work-exacerbated asthma and occupational asthma: do they really differ?. J Allergy Clin Immunol. 2013;131:704–10. pmid:23058644
  25. 25. Le Moual N, Siroux V, Pin I, Kauffmann F, Kennedy SM; Epidemiological Study on the Genetics and Environment of Asthma. Asthma severity and exposure to occupational asthmogens. Am J Respir Crit Care Med 2005;172:440–5. pmid:15961697
  26. 26. Le Moual N, Carsin AE, Siroux V, Radon K, Norback D, Torén K, et al. Occupational exposures and uncontrolled adult-onset asthma in the European Community Respiratory Health Survey II. Eur Respir J 2014;43:374–86. pmid:23949964
  27. 27. Malo JL. Asthma may be more severe if it is work-related. Am J Respir Crit Care Med 2005;172:406–7. pmid:16081550
  28. 28. Vandenplas O, Dressel H, Wilken D, Jamart J, Heederik D, Maestrelli P, et al. Management of occupational asthma: cessation or reduction of exposure? A systematic review of available evidence. Eur Respir J 2011;38:804–11. pmid:21436354
  29. 29. Rachiotis G, Savani R, Brant A, MacNeill SJ, Newman Taylor A, Cullinan P. The outcome of occupational asthma after cessation of exposure: a systematic review. Thorax 2007;62:147–52. pmid:17040933
  30. 30. Vandenplas O, Malo JL. Inhalation challenges with agents causing occupational asthma. Eur Respir J 1997;10:2612–29. pmid:9426105
  31. 31. Descatha A, Leproust H, Choudat D, Garnier R, Pairon JC, Ameille J. Factors associated with severity of occupational asthma with a latency period at diagnosis. Allergy 2007;62(7):795–801. pmid:17573728
  32. 32. Malo JL, Lemière C, Desjardins A, Cartier A. Prevalence and intensity of rhinoconjunctivitis in subjects with occupational asthma. Eur Respir J 1997;10(7):1513–5. pmid:9230239
  33. 33. Hur GY, Kim SH, Park SM, Ye YM, Kim CW, Jang AS, et al. Tissue transglutaminenase can be involved in airway inflammation of toluene diisocyanate-induced occupational asthma. J Clin Immunol 2009; 29:786–94 pmid:19562471
  34. 34. Wisnewski AV, Liu Q, Liu J, Redlich CA. Human innate immune responses to hexamethylenediisocyanate (HDI) and HDI-albumin conjugates. Clin Exp Allergy 2008;38:957–67. pmid:18498542
  35. 35. Maestrelli P, Yucesoy B, Park HS, Wisnewski AV. Mechanisms, genetics and pathophysiology. In: Malo JL, Chan-Yeung M and Bernstein DI, editors. Asthma in the workplace. Fourth Edition. Boca Raton; CRC Press; 2013, pp 40–56.
  36. 36. Vandenplas O, D’Alpaos V, Evrard G, Jamart J. Incidence of severe asthmatic reactions after challenge exposure to occupational agents. Chest 2013; 143: 1261–8. pmid:23117442
  37. 37. Hox V, Vanoirbeek JA, Alpizar YA, Voedisch S, Callebaut I, Bobic S, et al. Crucial role of transient receptor potential ankyrin 1 and mast cells in induction of nonallergic airway hyperreactivity in mice. Am J Respir Crit Care Med 2013;187(5):486–93. pmid:23262517
  38. 38. Vandenplas O, Suojalehto H, Aasen TB, Baur X, Burge PS, de Blay F, et al; ERS Task Force on Specific Inhalation Challenges with Occupational Agents. Specific inhalation challenge in the diagnosis of occupational asthma: consensus statement. Eur Respir J 2014;43:1573–87 pmid:24603815
  39. 39. Girard F, Chaboillez S, Cartier A, Côte J, Hargreave FE, Labrecque M, et al. An effective strategy for diagnosing occupational asthma: use of induced sputum. Am J Respir Crit Care Med 2004;170:845–50. pmid:15271693