Diisocyanate antigen-stimulated monocyte chemoattractant protein-1 synthesis has greater test efficiency than specific antibodies for identification of diisocyanate asthma

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Lung Gene Expression Suggests Roles for Interferon-Stimulated Genes and Adenosine Deaminase Acting against RNA-1 in Pathologic Responses to Diisocyanate

Mechanisms underlying methylene diphenyl diisocyanate (MDI) and other low molecular weight chemical-induced asthma are unclear and appear distinct from those of high molecular weight (HMW) allergen-induced asthma. We sought to elucidate molecular pathways that differentiate asthma-like pathogenic vs nonpathogenic responses to respiratory tract MDI exposure in a murine model. Lung gene expression differences in MDI exposed immune-sensitized and nonsensitized mice vs unexposed controls were measured by microarrays, and associated molecular pathways were identified through bioinformatic analyses and further compared with published studies of a prototypic HMW asthmagen (ovalbumin). Respiratory tract MDI exposure significantly altered lung gene expression in both nonsensitized and immune-sensitized mice, vs controls. Fifty-three gene transcripts were altered in all MDI exposed lung tissue vs controls, with levels up to 10-fold higher in immune-sensitized vs nonsensitized mice. Gene transcripts selectively increased in MDI exposed immune-sensitized animals were dominated by chitinases and chemokines and showed substantial overlap with those increased in ovalbumin-induced asthma. In contrast, MDI exposure of nonsensitized mice increased type I interferon stimulated genes (ISGs) in a pattern reflecting deficiency in adenosine deaminase acting against RNA (ADAR-1), an important regulator of innate, as well as "sterile" or autoimmunity triggered by tissue damage. Thus, MDI-induced changes in lung gene expression were identified that differentiate nonpathogenic innate responses in nonsensitized hosts from pathologic adaptive responses in immune-sensitized hosts. The data suggest that MDI alters unique biological pathways involving ISGs and ADAR-1, potentially explaining its unique immunogenicity/allergenicity.

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

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

Mechanistic and Therapeutic Approaches to Occupational Exposure-Associated Allergic and Non-Allergic Asthmatic Disease

PURPOSE OF REVIEW

Occupational lung disease, including asthma, is a significant cause of disability worldwide. The dose, exposure frequency, and nature of the causal agent influence the inflammatory pathomechanisms that inform asthma disease phenotype and progression. While surveillance, systems engineering, and exposure mitigation strategies are essential preventative considerations, no targeted medical therapies are currently available to ameliorate lung injury post-exposure and prevent chronic airway disease development.

RECENT FINDINGS

This article reviews contemporary understanding of allergic and non-allergic occupational asthma mechanisms. In addition, we discuss the available therapeutic options, patient-specific susceptibility and prevention measures, and recent scientific advances in post-exposure treatment conception. The course of occupational lung disease that follows exposure is informed by individual predisposition, immunobiologic response, agent identity, overall environmental risk, and preventative workplace practices. When protective strategies fail, knowledge of underlying disease mechanisms is necessary to inform targeted therapy development to lessen occupational asthma disease severity and occurrence.

New Method to Biomonitor Workers Exposed to 1,6-Hexamethylene Diisocyanate

Isocyanates such as 1,6-hexamethylene diisocyanate (HDI), 4,4'-methylenediphenyl diisocyanate, and toluene diisocyanate are highly reactive compounds that have a variety of commercial applications, including manufacturing polyurethane foam, elastomers, paints, adhesives, coatings, insecticides, and many other products. Their primary route of occupational exposure is through inhalation. Due to their high chemical reactivity, they are toxic and have adverse effects at the cellular and subcellular levels, leading to irritative and immunological reactions associated with lung disease. High concentrations of isocyanates are strong respiratory irritants. Bronchial sensitization and asthma are among the major adverse clinical reactions associated with low-level chronic exposure to isocyanates. Albumin adducts have been linked to the mechanism of occupational asthma caused by isocyanates. Isocyanates react in vivo with albumin, which is recognized by the immune system. Albumin adducts of isocyanates trigger immune responses and are probably the antigenic basis for isocyanate asthma. Sensitization to isocyanates is the main pathway for adverse health effects. Therefore, markers for the biologically effective dose such as albumin adducts of HDI are needed. A new isocyanate adduct of HDI with lysine─N^ε-[(6-amino-hexyl-amino)carbonyl]-lysine (HDI-Lys)─was synthesized and characterized by ¹H-NMR, ¹³C-NMR, and mass spectrometry (MS). Appropriate internal standards─HDI-Lys-4,4'-5,5'-d₄ (HDI-d₄-Lys) and N^ε-[(7-amino-heptyl-amino)carbonyl]-lysine (Hep-Lys)─were synthesized to establish a LC-MS/MS method for the analysis of HDI adducts in in vitro modified albumin and in workers. The presence of HDI-Lys was found after pronase digestion of albumin and confirmed by two independent chromatographic approaches: with a C8 reversed-phase column and with a hydrophilic interaction liquid chromatography column. Quantification was performed with positive electrospray ionization (ESI)-MS. The adduct peak found in vivo was confirmed with the less sensitive negative ESI-MS. In summary, these are new compounds and methods to determine isocyanate-specific adducts with albumin in workers exposed to HDI.

Literature review and evaluation of biomarkers, matrices and analytical methods for chemicals selected in the research program Human Biomonitoring for the European Union (HBM4EU)

Humans are potentially exposed to a large amount of chemicals present in the environment and in the workplace. In the European Human Biomonitoring initiative (Human Biomonitoring for the European Union = HBM4EU), acrylamide, mycotoxins (aflatoxin B1, deoxynivalenol, fumonisin B1), diisocyanates (4,4'-methylenediphenyl diisocyanate, 2,4- and 2,6-toluene diisocyanate), and pyrethroids were included among the prioritized chemicals of concern for human health. For the present literature review, the analytical methods used in worldwide biomonitoring studies for these compounds were collected and presented in comprehensive tables, including the following parameter: determined biomarker, matrix, sample amount, work-up procedure, available laboratory quality assurance and quality assessment information, analytical techniques, and limit of detection. Based on the data presented in these tables, the most suitable methods were recommended. According to the paradigm of biomonitoring, the information about two different biomarkers of exposure was evaluated: a) internal dose = parent compounds and metabolites in urine and blood; and b) the biologically effective = dose measured as blood protein adducts. Urine was the preferred matrix used for deoxynivalenol, fumonisin B1, and pyrethroids (biomarkers of internal dose). Markers of the biological effective dose were determined as hemoglobin adducts for diisocyanates and acrylamide, and as serum-albumin-adducts of aflatoxin B1 and diisocyanates. The analyses and quantitation of the protein adducts in blood or the metabolites in urine were mostly performed with LC-MS/MS or GC-MS in the presence of isotope-labeled internal standards. This review also addresses the critical aspects of the application, use and selection of biomarkers. For future biomonitoring studies, a more comprehensive approach is discussed to broaden the selection of compounds.

Acute 4,4'-Methylene Diphenyl Diisocyanate Exposure-Mediated Downregulation of miR-206-3p and miR-381-3p Activates Inducible Nitric Oxide Synthase Transcription by Targeting Calcineurin/NFAT Signaling in Macrophages

Exposure to 4,4'-methylene diphenyl diisocyanate (MDI) in the occupational setting may lead to development of occupational asthma (OA), and the underlying molecular mechanisms of MDI-induced disease pathogenesis remain an active area of research. Using a nose-only mouse inhalation model, we find that circulating microRNA (miR)-206-3p and miR-381-3p are downregulated after MDI exposure; however, cellular miR-206-3p and miR-381-3p responses after MDI aerosol exposure and their pathophysiological roles in MDI-OA are unknown. We hypothesize that miR-206-3p and miR-381-3p-regulated mechanisms cause increased expression of the inducible nitric oxide synthase (iNOS) after MDI aerosol exposure. We examined cellular miR-206-3p and miR-381-3p, calcineurins, nuclear factors of activated T cells (NFATs), and iNOS levels from both nose-only exposed murine bronchoalveolar lavage cells (BALCs) and differentiated THP-1 macrophages treated with MDI-glutathione (GSH) conjugates. Both in vivo murine MDI aerosol exposure and in vitro MDI-GSH exposures in THP-1 macrophages result in downregulation of endogenous miR-206-3p and miR-381-3p and upregulation of PPP3CA and iNOS expression. Transfection of THP-1 macrophages with miR-inhibitor-206-3p and miR-inhibitor-381-3p resulted in the upregulation of PPP3CA and iNOS. Using RNA-induced silencing complex immunoprecipitation and translational reporter assays, we verified that PPP3CA, but not iNOS, is directly targeted by both miR-206-3p and miR-381-3p. Downregulation of miR-206-3p and miR-381-3p following by MDI exposure induces calcineurin/NFAT signaling-mediated iNOS transcription in macrophages and BALCs.

Analysis of Lung Gene Expression Reveals a Role for Cl- Channels in Diisocyanate-induced Airway Eosinophilia in a Mouse Model of Asthma Pathology

Diisocyanates are well-recognized causes of asthma. However, sensitized workers frequently lack diisocyanate-specific IgE, which complicates diagnosis and suggests the disease involves IgE-independent mechanisms. We used a mouse model of methylene diphenyl diisocyanate (MDI) asthma to identify biological pathways that may contribute to asthma pathogenesis. MDI sensitization and respiratory tract exposure were performed in Balb/c, transgenic B-cell (e.g., IgE)-deficient mice and a genetic background (C57BL/6)-matched strain. Eosinophils in airway fluid were quantitated by flow cytometry. Lung tissue gene expression was assessed using whole-genome mRNA microarrays. Informatic software was used to identify biological pathways affected by respiratory tract exposure and potential targets for disease intervention. Airway eosinophilia and changes (>1.5-fold; P value < 0.05) in expression of 192 genes occurred in all three mouse strains tested, with enrichment in chemokines and a pattern associated with alternatively activated monocytes/macrophages. CLCA1 (calcium-activated chloride channel regulator 1) was the most upregulated gene transcript (>100-fold) in all exposed mouse lungs versus controls, followed closely by SLC26A4, another transcript involved in Cl- conductance. Crofelemer, a U.S. Food and Drug Administration-approved Cl- channel inhibitor, reduced MDI exposure induction of airway eosinophilia, mucus, CLCA1, and other asthma-associated gene transcripts. Expression changes in a core set of genes occurs independent of IgE in a mouse model of chemical-induced airway eosinophilia. In addition to chemokines and alternatively activated monocytes/macrophages, the data suggest a crucial role for Cl- channels in diisocyanate asthma pathology and as a possible target for intervention.

Impact of Identification of Clinical Phenotypes in Occupational Asthma

Phenotypic differences and similarities in the spectrum of occupational asthma (OA) subtypes reflect the underlying mechanisms of the diverse forms of the disease, and these phenotypes provide information as to diagnostic steps and approaches to management. In large part, the phenotype reflects the existence of immunologic mechanisms and the presence or absence of a specific IgE-antibody response to a work sensitizer. However, further differences occur between OA from high- and low-molecular-weight sensitizers (chemical sensitizers), which potentially might be relevant for nonoccupational asthma. Chemical sensitizers cause a specific response that is more likely to be a late asthmatic response and specific IgE can be identified only in a minority. Irritant-induced asthma is most easily recognized when it occurs with 1 or more high-level respiratory irritant exposure(s) but is also possible with chronic low-level exposures as in cleaners, farmers, and woodworkers, as suggested from epidemiologic studies. OA chronic obstructive pulmonary disease overlap is more common in older patients and with OA from low-molecular-weight sensitizers. Removal from exposure to the causative agent is currently advised for those with OA from sensitization: further studies with omalizumab and other biologic agents are needed to determine whether these might allow return to the same exposure.

Performance of specific immunoglobulin E tests for diagnosing occupational asthma: a systematic review and meta-analysis

OBJECTIVES

To determine the test performance parameters for the retrievable range of high-molecular-weight (HMW) and low-molecular-weight (LMW) occupational allergens and to evaluate the impact of allergenic components and the implementation of measures for test validation.

METHODS

A protocol with predefined objectives and inclusion criteria was the basis of an electronic literature search of MEDLINE and EMBASE (time period 1967-2016). The specific inhalation challenge and serial peak flow measurements were the reference standards for the specific IgE (sIgE) test parameters. All of the review procedures were reported according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

RESULTS

Seventy-one studies were selected, and 62 entered meta-analysis. Pooled pairs analysis indicated a sensitivity of 0.74(95% CI 0.66 to 0.80) and specificity of 0.71(95% CI 0.63 to 0.77) for HMW allergens and a sensitivity of 0.28(95% CI 0.18 to 0.40) and specificity of 0.89(95% CI 0.77 to 0.95) for LMW allergens. Component-specific analysis improved the test parameters for some allergens. Test validation was handled heterogeneously among studies.

CONCLUSION

sIgE test performance is rather satisfactory for a wide range of HMW allergens with the potential for component-specific approaches, whereas sensitivity for LMW allergens is considerably lower, indicating methodological complications and/or divergent pathomechanisms. A common standard for test validation is needed.

Toluene diisocyanate exposure and autotaxin-lysophosphatidic acid signalling

Toluene diisocyanate (TDI) is a reactive chemical used in manufacturing plastics. TDI exposure adversely affects workers' health, causing occupational asthma, but individuals differ in susceptibility. We recently suggested a role for signalling mediated by the enzyme autotaxin (ATX) and its product, lysophosphatidic acid (LPA), in TDI toxicity. Here we genotyped 118 TDI-exposed workers for six single-nucleotide polymorphisms (SNPs) in genes encoding proteins implicated in ATX-LPA signalling: purinergic receptor P2X7 (P2RX7), CC motif chemokine ligand 2 (CCL2), interleukin 1β (IL1B), and caveolin 1 (CAV1). Two P2RX7 SNPs (rs208294 and rs2230911) significantly modified the associations between a biomarker of TDI exposure (urinary 2,4-toluene diamine) and plasma LPA; two IL1B SNPs (rs16944 and rs1143634) did not. CAV1 rs3807989 modified the associations, but the effect was not statistically significant (p = 0.05-0.09). In vitro, TDI-exposed bronchial epithelial cells (16HBE14o-) rapidly released ATX and IL-1β. P2X7 inhibitors attenuated both responses, but confocal microscopy showed non-overlapping localizations of ATX and IL-1β, and down-regulation of CAV1 inhibited the ATX response but not the IL-1β response. This study indicates that P2X7 is pivotal for TDI-induced ATX-LPA signalling, which was modified by genetic variation in P2RX7. Furthermore, our data suggest that the TDI-induced ATX and IL-1β responses occur independently.

Review of Diagnostic Challenges in Occupational Asthma

PURPOSE OF REVIEW

Occupational asthma (OA) is one of the most frequent occupational diseases and its diagnosis is often difficult. This review summarizes its current diagnostic challenges.

RECENT FINDINGS

OA is associated with significant health and socio-economic burden. It is underdiagnosed and physicians need to adopt a stepwise approach to confirm the diagnosis. Although early removal from exposure to the offending agent is associated with a better prognosis, physicians should try to confirm the diagnosis of work-related asthma before taking a worker off work. A proper occupational and medical history is very important but is not enough to make the diagnosis of OA. Objective evidence of work-related asthma is required and this represents a serious challenge to most physicians. Measurement of non-specific bronchial responsiveness (NSBR) and spirometry may confirm the diagnosis of asthma but do not confirm the diagnosis of OA. Serial monitoring of peak expiratory flows (PEF), NSBR, and airway inflammation at and off work may confirm the diagnosis of OA but are often difficult to perform. Confirming sensitization by skin prick tests or specific IgE may help to support the diagnosis of OA. Specific inhalation challenges (SIC) in the lab or at work are considered the reference standard but are of limited access. Medical surveillance programs along with primary prevention (reducing exposure) may help to reduce the burden of OA, but the ideal program has yet to be defined. The diagnostic workup of OA remains a challenge and needs a rigorous stepwise evaluation.

New developments in work-related asthma

INTRODUCTION

Work-related asthma includes two subtypes: occupational asthma or asthma caused by specific agents (sensitizers or irritants) in the workplace, and work-exacerbated asthma or pre-existing asthma worsened by workplace exposures. Areas covered: This review provides an update on the definitions and the clinical features of the different work-related asthma subtypes as well as new insights into their etiology and the pathophysiological mechanisms involved. The diagnosis of work-related asthma should be made on objective basis using a constellation of clinical, physiologic and allergologic tests. Specific inhalation challenge with the suspected occupational agent(s) remains as the reference standard for diagnosis. A literature search was performed using the following terms: work-related asthma, occupational asthma, work-exacerbated asthma, irritant-induced asthma and etiological agents. Expert commentary: Studies focusing on the biological effects and mechanisms of environmental exposures in the development of sensitizer-induced or irritant-induced asthma in various workplace settings are of greatest interest. An integrative approach that combines clinical parameters with component-resolved diagnosis as well as inflammatory biomarkers appears to be very promising. Occupational allergy provides a good opportunity to understand the complex relationships between exposure to allergens in the workplace, interaction with genes and the co-exposures to other factors in the working environment.

Comparison of biological effects with albumin adducts of 4,4'-methylenediphenyl diisocyanate in workers

Lung sensitization and asthma are the main health effects of 4,4'-methylenediphenyl diisocyanate (MDI). Albumin adducts (isocyanate-specific adducts) of MDI might be involved in the etiology of sensitization reactions. Albumin adducts of MDI were analyzed in sera of diisocyanate-exposed worker with and without diisocyanate occupational asthma (DA), as well as in exposed workers with and without diisocyanate-specific IgG antibodies. In DA-positive workers and IgG-positive workers, albumin adducts were significantly higher versus workers without DA and those who were specific IgG negative. The odds ratio to be DA-positive was 57 times larger for workers with adduct levels above 230 fmol/mg. The odds ratio to be IgG-positive was 10 times larger for workers with adduct levels above 113 fmol/mg. Therefore, albumin adducts appear to be a good predictor of the biological effects. The albumin-adduct levels in workers without biological effects were in the range of the adduct levels found in previous studies of healthy MDI-factory and construction site workers.

Work-Related Asthma

OBJECTIVE

Summarize developed evidence-based diagnostic and treatment guidelines for work-related asthma (WRA).

METHODS

Comprehensive literature reviews conducted with article critiquing and grading. Guidelines developed by a multidisciplinary expert panel and peer-reviewed.

RESULTS

Evidence supports spirometric testing as an essential early test. Serial peak expiratory flow rates measurement is moderately recommended for employees diagnosed with asthma to establish work-relatedness. Bronchial provocation testing is moderately recommended. IgE and skin prick testing for specific high-molecular weight (HMW) antigens are highly recommended. IgG testing for HMW antigens, IgE testing for low-molecular weight antigens, and nitric oxide testing for diagnosis are not recommended. Removal from exposure is associated with the highest probability of improvement, but may not lead to complete recovery.

CONCLUSION

Quality evidence supports these clinical practice recommendations. The guidelines may be useful to providers who diagnose and/or treat WRA.

Clinical aspects of work-related asthma: past achievements, persistent challenges, and emerging triggers

OBJECTIVE

The aim of this article was to address common clinical questions pertaining to work-related asthma (WRA).

METHODS

This review is based on a presentation on WRA at the American College of Chest Physicians Course on Clinical Aspects of Occupational and Environmental Lung Disease, held in Toronto in 2013, and supplemented by a PubMed search of publications to 2013.

RESULTS

Seven clinical questions are addressed in relation to definitions, causes, diagnosis, management and emerging triggers, and challenges of WRA.

CONCLUSIONS

Although knowledge is expanding in this area, there remain challenges and uncertainties, particularly in the prevention of WRA.

Toluene diisocyanate: Induction of the autotaxin-lysophosphatidic acid axis and its association with airways symptoms

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.

Is the analysis of histamine and/or interleukin-4 release after isocyanate challenge useful in the identification of patients with IgE-mediated isocyanate asthma?

Isocyanates are a well-known and frequent cause of occupational asthma. The implementation of specific inhalation challenges (SICs) is the gold standard in asthma diagnosis supporting occupational case history, lung function testing, specific skin prick tests and the detection of specific IgE. However, the diagnosis is not always definitive. An interesting new approach, analyses of individual genetic susceptibilities, requires discrimination between a positive SIC reaction arising from IgE-mediated immune responses and one from other pathophysiological mechanisms. Hence, additional refinement tools would be helpful in defining sub-classes of occupational asthma and diagnosis. We used total IgE levels, specific IgE and SIC results for sub-classification of 27 symptomatic isocyanate workers studied. Some mutations in glutathione S-transferases (GSTs) are suspected either to enhance or to decrease the individual risk in the development of isocyanate asthma. Our patient groups were assessed for the point mutations GSTP1*I105V and GSTP1*A114V as well as deletions (null mutations) of GSTM1 and GSTT1. There seems to be a higher risk in developing IgE-mediated reactions when GSTM1 is deleted, while GSTT1 deletions were found more frequently in the SIC positive group. Blood samples taken before SIC, 30-60 min and 24h after SIC, were analyzed for histamine and IL-4, classical markers for the IgE-mediated antigen-specific activation of basophils or mast cells. We suggest that the utility of histamine measurements might provide an additional useful marker reflecting isocyanate-induced cellular reactions (although the sampling times require optimization). The promising measurement of IL-4 is not feasible at present due to the lack of a reliable, validated assay.

Immunotoxicology and its application in risk assessment

Immunotoxicology is the study of undesired modulation of the immune system by extrinsic factors. Toxicological assessments have demonstrated that the immune system is a target following exposure to a diverse group of xenobiotics including ultraviolet radiation, chemical pollutants, therapeutics, and recreational drugs. There is a well-established cause and effect relationship between suppression of the immune response and reduced resistance to infections and certain types of neoplasia. In humans, mild-to-moderate suppression of the immune response is linked to reduced resistance to common community-acquired infections, whereas opportunistic infections, which are very rare in the general population, are common in individuals with severe suppression. Xenobiotic exposure may also result in unintended stimulation of immune function. Although a cause and effect relationship between unintended stimulation of the immune response and adverse consequences has yet to be established, evidence does suggest that hypersensitivity, autoimmunity, and pathological inflammation may be exacerbated in susceptible populations exposed to certain xenobiotics. Xenobiotics can act as allergens and elicit hypersensitivity responses, or they can modulate hypersensitivity responses to other allergens such as pollen or dust mite by acting as adjuvants, enhancing the development or expression of hypersensitivity. Allergic contact dermatitis, allergic rhinitis, and asthma are the most commonly encountered types of hypersensitivity reactions resulting from chemical exposure. The immunologic effectors and mechanisms involved in autoimmune reactions are the same as those associated with responses to foreign antigens; however, the reactions are directed against the host's own cells. Thus, chemicals that induce immune suppression, nonspecific immunostimulation, or hypersensitivity may also impact autoimmunity. Risk assessment for immunotoxicity should be performed using the same approaches and principles for other noncancer effects. However, since xenobiotics may have effects on more than one aspect of immune function, immunotoxicity data should be evaluated separately for evidence of suppression, stimulation, hypersensitivity, and autoimmunity.

Serum levels of IL-10, IL-17F and IL-33 in patients with asthma: a case-control study

OBJECTIVES

The development of inflammation in asthma involves an intricate network of cytokines that recruit and activate numerous immune cells. This study was aimed to compare serum levels of IL-10, IL-17F, and IL-33 in asthmatic patients and non-asthmatic controls and correlate cytokine levels to asthma severity and various clinical, spirometric, and laboratory variables.

METHODS

Using ELISA, serum levels of IL-10, IL-17F, and IL-33 were evaluated in 44 asthmatics (14 mild persistent, 15 moderate persistent, and 15 severe persistent) and 44 controls.

RESULTS

This is one of the first reports showing a significant difference in serum levels of asthma-associated cytokines, anti-inflammatory IL-10, and pro-inflammatory IL-17F and IL-33, in the same subset of asthmatic patients. Our results showed diminished level of IL-10 and elevated levels of IL-17F and IL-33 in asthmatics than in controls (p < 0.001). Assessment of cytokine levels between subjects of different gender, age group, and BMI showed non-significant differences. Correlation analysis of cytokine levels to clinical variables showed that IL-17F is associated negatively to FVC % predicted (forced vital capacity) and FEV1% predicted (forced expiratory volume in one second) and positively to number of allergens sensitized and FEV1 reversibility. A strong negative correlation was found between IL-10 and IL-33 levels (p = 0.001).

CONCLUSIONS

Negative correlation between IL-10 and IL-33 levels may reflect a converse relationship between anti-inflammatory and pro-inflammatory cytokines in an individually balanced pattern. The association between IL-17F level and asthmatic phenotypes such as reduced FVC and FEV1, higher degree of sensitization, and post-bronchodilator reversibility needs further assessments.

Connecting glutathione with immune responses to occupational methylene diphenyl diisocyanate exposure

Methylene diphenyl diisocyanate (MDI) is among the leading chemical causes of occupational asthma world-wide, however, the mechanisms of disease pathogenesis remain unclear. This study tests the hypothesis that glutathione (GSH) reacts with MDI to form quasi-stable conjugates, capable of mediating the formation of MDI-conjugated "self" protein antigens, which may participate in pathogenic inflammatory responses. To test this hypothesis, an occupationally relevant dose of MDI (0.1%w/v) was reacted with varying concentrations of GSH (10μM-10mM), and the reaction products were characterized with regard to mass/structure, and ability to carbamoylate human albumin, a major carrier protein for MDI in vivo. LC-MS/MS analysis of GSH-MDI reaction products identified products possessing the exact mass of previously described S-linked bis(GSH)-MDI and its partial hydrolysis product, as well as novel cyclized GSH-MDI structures. Upon co-incubation of GSH-MDI reaction products with human albumin, MDI was rapidly transferred to specific lysines of albumin, and the protein's native conformation/charge was altered, based on electrophoretic mobility. Three types of modification were observed, intra-molecular MDI cross-linking, addition of partially hydrolyzed MDI, and addition of "MDI-GSH", where MDI's 2nd NCO had reacted with GSH's "N-terminus". Importantly, human albumin carbamoylated by GSH-MDI was specifically recognized by serum IgG from MDI exposed workers, with binding dependent upon the starting GSH concentration, pH, and NaCl levels. Together, the data define a non-enzymatic, thiol-mediated transcarbamoylating mechanism by which GSH may promote immune responses to MDI exposure, and identify specific factors that might further modulate this process.

Cells and mediators in diisocyanate-induced occupational asthma

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Diagnostic approach in cases with suspected work-related asthma

Background

Work-related asthma (WRA) is a major cause of respiratory disease in modern societies. The diagnosis and consequently an opportunity for prevention are often missed in practice.

Methods

Based on recent studies and systematic reviews of the literature methods for detection of WRA and identification of specific causes of allergic WRA are discussed.

Results and Conclusions

All workers should be asked whether symptoms improve on days away from work or on holidays. Positive answers should lead to further investigation. Spirometry and non-specific bronchial responsiveness should be measured, but carefully performed and validly analysed serial peak expiratory flow or forced expiratory volume in one second (FEV₁) measurements are more specific and confirm occupational asthma in about 82% of those still exposed to the causative agent. Skin prick testing or specific immunoglobulin E assays are useful to document allergy to high molecular weight allergens. Specific inhalational challenge tests come closest to a gold standard test, but lack standardisation, availability and sensitivity. Supervised workplace challenges can be used when specific challenges are unavailable or the results non-diagnostic, but methodology lacks standardisation. Finally, if the diagnosis remains unclear a follow-up with serial measurements of FEV₁ and non-specific bronchial hyperresponsiveness should detect those likely to develop permanent impairment from their occupational exposures.

Diagnosis of occupational asthma: an update

Work-related asthma (WRA) includes patients with sensitizer- and/or irritant-induced asthma in the workplace, as well as patients with preexisting asthma that is worsened by work factors. WRA is underdiagnosed; thus, the diagnosis is critical to prevent disease progression and its potential for morbidity and mortality. The interview is the first diagnostic tool to be used by physicians, and the question, "Does asthma improve away from work?" is of the highest sensitivity. However, history can show numerous false positives, and the relationships between asthma worsening and work should be confirmed by objective methods such as peak expiratory flow (PEF) at and away from work. PEF sensitivity and specificity can be enhanced in combination with nonspecific bronchial hyperresponsiveness to histamine/methacholine (NSBP) before and after 2 weeks at work and a similar period off work. Immunologic testing, especially skin prick test (SPT) or specific IgE, is useful for high molecular weight allergens and some low molecular weight agents. Other immunologic tests, as well as induced sputum, measurement of exhaled nitric oxide, exhaled breath condensate, and specific inhalation challenge (SIC) are methods that contribute to the diagnosis and are typically performed at specialized facilities. A diagnosis of occupational asthma (OA) should no longer be based on a compatible history only but should be confirmed by means of objective testing. SIC is the diagnostic gold standard. When SIC is not available, the combination of PEF measurement, NSBP test , a specific SPT, or specific IgE may be an appropriate alternative in diagnosing OA.

Interferon-γ promoter is hypermethylated in blood DNA from workers with confirmed diisocyanate asthma

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.

Occupational asthma

Occupational asthma is the most common occupational lung disease. Work-aggravated asthma and occupational asthma are two forms of asthma causally related to the workplace, while reactive airways dysfunction syndrome is a separate entity and a subtype of occupational asthma. The diagnosis of occupational asthma is most often made on clinical grounds. The gold standard test, specific inhalation challenge, is rarely used. Low molecular weight isocyanates are the most common compounds that cause occupational asthma. Workers with occupational asthma secondary to low molecular weight agents may not have elevated specific IgE levels. The mechanisms of occupational asthma associated with these compounds are partially described. Not all patients with occupational asthma will improve after removal from the workplace.

Distinct temporal patterns of immediate asthmatic reactions due to high- and low-molecular-weight agents

BACKGROUND

Exposure to occupational agents can cause immediate asthmatic reactions.

OBJECTIVE

It can be hypothesized that the pattern of immediate reactions is different for high (HMW)- and low-molecular-weight (LMW) agents. To test this, we studied the temporal features of reactions in workers who underwent specific inhalation challenges for possible occupational asthma.

METHODS

We examined 467 immediate reactions due to HMW (n = 248, 53%) and LWW (n = 219, 47%) agents in regards to timing of the maximum reaction and recovery.

RESULTS

The median duration of exposure to elicit significant immediate reactions was comparable for HMW and LMW agents (15 min). The median maximum fall in FEV (1) occurred after 20 min for LMW by comparison with 10 min for HMW agents (P < 0.001). The median timing of recovery of FEV (1) to 10% baseline was shorter for HMW (60 min) than for LMW (90 min) agents (P < 0.01), and significantly more subjects recovered to 10% baseline (89.5%) for HMW than for LMW agents (72.6%) (P < 0.001). Confounding variables such as age, atopy, baseline airway calibre and the maximum fall in FEV (1) at the time of the immediate reaction did not alter the significant effect of the nature of the agent per se. Immediate reactions were followed by a late asthmatic reaction more often in the case of LMW (37.3%) than HMW (26.2%) agents (P < 0.05). Significant changes in non-specific bronchial responsiveness were significantly (P = 0.02) more frequent after reactions to LMW (31.9%) than to HMW (21.4%) agents. We found similar trends by comparing reactions to flour (n = 113), the principal cause of reactions to HMW agents, and diisocyanates (n = 111), the principal LMW agent.

CONCLUSIONS AND CLINICAL RELEVANCE

This study shows distinct patterns for immediate reactions due to occupational agents. These results can provide useful guidelines for performing specific inhalation challenges and improve the safety of the procedure.

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

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

Is specific IgE antibody analysis feasible for the diagnosis of methylenediphenyl diisocyanate-induced occupational asthma?

Purpose

Early recognition improves the prognosis of isocyanate asthma. A major unanswered question is whether IgE-dependent mechanisms are of diagnostic value? Our objective was to appraise serological methods using various methylenediphenyl diisocyanate (MDI)-albumin conjugates and weigh up the data versus the outcome of standardized comprehensive clinical diagnostics to evaluate the viability of immunological analysis in supportive MDI-asthma diagnosis (OA_I).

Methods

Specific IgE (sIgE) and IgG (sIgG) binding was measured with fluorescence enzyme immunoassay in 43 study subjects (using conjugates prepared in-vapor, in-solution and commercial preparations). The differential clinical diagnosis included standardized measurement of pulmonary function, non-specific bronchial hyper-responsiveness, specific MDI-prick test (MDI-SPT) and specific inhalation challenge (MDI-SIC).

Results

Detailed diagnostic scheme allows the differential OA_I and MDI-induced hypersensitivity pneumonitis (P_I). The presumed OA_I diagnoses were confirmed in 84 % (45 % cases having demonstrable sIgE antibodies) with RR 5.7, P > 0.001, when OA_I diagnosis is correlated with MDI-SIC/MDI-SPT (RR 1.28 for MDI-SIC alone); sIgG antibodies were clinically relevant for P_I and not for the OA diagnosis. MDI-specific IgE data generated with commercial ImmunoCAP preparations show high correlation with our in-vapor generated MDI conjugates.

Conclusions

Isocyanate-specific IgE antibodies are not always detectable but their presence is strongly predictive of OA_I and supportive for the diagnosis. MDI-SPT can be a valuable parameter differentiating OA_I and P_I. We have confirmed and extended published data showing that isocyanate-albumin conjugates perform better in specific antibody assays when prepared with volatile phase formulations and would like to stress additionally the necessity for further refinements and standardization in clinical diagnostics procedures.

Electronic supplementary material

The online version of this article (doi:10.1007/s00420-012-0772-6) contains supplementary material, which is available to authorized users.

The epidemiology of work-related asthma

Much has been learned from epidemiologic studies conducted in the past 4 decades that can be directly applied to the management of workers affected with occupational asthma. Studies have provided information about host factors, environmental exposure, and occupational agents posing the highest risks for development of severe irreversible airway obstruction and asthma disability. Investigators have developed methods for screening workers at risk and novel interventions that may prevent new cases among exposed worker populations. Less is known about the natural history and chronic morbidity associated with work-aggravated asthma and irritant-induced asthma syndromes; more studies are needed in at-risk worker populations.

Pathogenesis and disease mechanisms of occupational asthma

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

Clinical assessment of occupational asthma and its differential diagnosis

Occupational asthma (OA) is defined as asthma caused by sources and conditions attributable to a particular occupational environment and not to stimuli encountered outside the workplace. Two types of OA are distinguished based on their appearance after a latency period or not. The most frequent type appears after a latency period leading to sensitization; the clinical assessment of this type of OA is the topic of this review. The differential diagnosis of OA is also reviewed, including work-exacerbated asthma, eosinophilic bronchitis, hyperventilation syndrome, vocal cord dysfunction, bronchiolitis, and other causes of dyspnea or cough.

Determination of isocyanate specific albumin-adducts in workers exposed to toluene diisocyanates

Toluene diisocyanates (2,4-TDI and 2,6-TDI) are important intermediates in the chemical industry. Among the main damages after low levels of TDI exposure are lung sensitization and asthma. It is therefore necessary to have sensitive and specific methods to monitor isocyanate exposure of workers. Urinary metabolites or protein adducts have been used as biomarkers in workers exposed to TDI. However, with these methods it was not possible to determine if the biomarkers result from exposure to TDI or to the corresponding toluene diamines (TDA). This work presents a new procedure for the determination of isocyanate-specific albumin adducts. Isotope dilution mass spectrometry was used to measure the adducts in albumin present in workers exposed to TDI. 2,4-TDI and 2,6-TDI formed adducts with lysine: N(ϵ)-[({3-amino-4-methylphenyl}amino)carbonyl]-lysine, N(ϵ)-[({5-amino-2-methylphenyl}amino)carbonyl]-lysine, and N(ϵ)- [({3-amino-2-methylphenyl}amino)carbonyl]-lysine. In future studies, this new method can be applied to measure TDI-exposures in workers.

Determination of a new biomarker in subjects exposed to 4,4'-methylenediphenyl diisocyanate

4,4'-Methylenediphenyl diisocyanate (MDI) is the most important of the isocyanates used as intermediates in the chemical industry. Among the main types of damage after exposure to low levels of MDI are lung sensitization and asthma. Albumin adducts of MDI might be involved in the etiology of sensitization reactions. This work presents a liquid chromatography (LC)-mass spectrometry (MS/MS) procedure for determination of isocyanate-specific albumin adducts in humans. MDI formed adducts with lysine of albumin: MDI-Lys and AcMDI-Lys. The MDI-Lys levels, 25th, 50th, 75th, 90th percentile, were 0, 65.2, 134, 244 fmol mg(-1) and 0, 30.5, 57.4, 95.8 fmol mg(-1) in the exposed construction and factory workers, respectively. This new biomonitoring procedure will allow assessment of suspected exposure sources and may contribute to the identification of individuals who are particularly vulnerable for developing bronchial asthma and other respiratory diseases after exposure to isocyanates.

Biomarkers predicting isocyanate-induced asthma

Three diisocyanates can cause occupational asthma (OA): toluene diisocyanate (TDI), 4,4 diphenylmethane diisocyanate (MDI), and 1,6-hexamethylene diisocyanate (HDI). We analyzed potential biomarkers of isocyanate-induced OA, based on investigated immunologic, genetic, neurogenic, and protein markers, because there is no serological testing method. The prevalence of serum IgG to cytokeratin (CK)18 and CK19 in TDI-OA was significantly higher than in controls, although the prevalence of these antibodies was too low for them to be used as biomarkers. Another candidate biomarker was serum IgG to tissue transglutaminase (tTG), because the prevalence of serum specific IgG to tTG was significantly higher in patients with TDI-OA than in controls. The human leukocyte antigen (HLA) DRB1*1501-DQB1*0602-DPB1*0501 haplotype may be used as a genetic marker for TDI-OA in Koreans via enhanced specific IgE sensitization in exposed subjects. The genetic polymorphisms of catenin alpha 3, alpha-T catenin (CTNNA3) were significantly associated with TDI-OA. Additionally, examining the neurokinin 2 receptor (NK2R) 7853G>A and 11424 G>A polymorphisms, the NK2R 7853GG genotype had higher serum vascular endothelial growth factor (VEGF) levels than the GA or AA genotypes among Korean workers exposed to TDI. To identify new serologic markers using a proteomic approach, differentially expressed proteins between subjects with MDI-OA and asymptomatic exposed controls in a Korean population showed that the optimal serum cutoff levels were 69.8 ng/mL for ferritin and 2.5 µg/mL for transferrin. When these two parameters were combined, the sensitivity was 71.4% and the specificity was 85.7%. The serum cytokine matrix metalloproteinase-9 (MMP-9) level is a useful biomarker for identifying cases of TDI-OA among exposed workers. Despite these possible biomarkers, more effort should be focused on developing early diagnostic biomarkers using a comprehensive approach based on the pathogenic mechanisms of isocyanate-induced OA.

Occupational asthma: what can be done to prevent it?

Occupational asthma (OA) accounts for at least 10% of cases of adult asthma and presents as intermittent asthma occurring at the workplace and remitting on weekends and holidays, or persistent asthma, especially if the diagnosis and early intervention is delayed. OA is under-recognized, challenging and time-consuming to diagnose, difficult to confirm with currently available tests and complex in terms of legal implications of disability and impairment. Over 400 agents have been identified as causing OA with allergic triggers accounting for 80-90% of cases. Managing the worker with OA is demanding as it requires the most thorough evaluation with attention to detail to provide an accurate diagnosis and develop a thoughtful treatment recommendation. This frequently has to occur in the context of various competing entities including management, unions, insurance carriers and attorneys. The primary goal is excellent employee health through interventions that may allow the worker to continue in their occupation safely. Primary, secondary and tertiary prevention measures have been adopted for various types of OA with success. Novel approaches may become available and be beneficial to identify and treat OA early before severe, chronic, unremitting and irreversible changes occur.

Pro/Con debate: Is occupational asthma induced by isocyanates an immunoglobulin E-mediated disease?

Isocyanates, low-molecular weight chemicals essential to polyurethane production, are one of the most common causes of occupational asthma, yet the mechanisms by which exposure leads to disease remain unclear. While isocyanate asthma closely mirrors other Type I Immune Hypersensitivity (Allergic) disorders, one important characteristic of hypersensitivity ('allergen'-specific IgE) is reportedly absent in a large portion of affected individuals. This variation from common environmental asthma (which typically is induced by high-molecular weight allergens) is important for two reasons. (1) Allergen-specific IgE is an important mediator of many of the symptoms of bronchial hyper-reactivity in 'allergic asthma'. Lack of allergen-specific IgE in isocyanate hypersensitive individuals suggests differences in pathogenic mechanisms, with potentially unique targets for prevention and therapy. (2) Allergen-specific IgE forms the basis of the most commonly used diagnostic tests for hypersensitivity (skin prick and RAST). Without allergen-specific IgE, isocyanates may go unrecognized as the cause of asthma. In hypersensitive individuals, chronic exposure can lead to bronchial hyperreactivity that persists years after exposure ceases. Thus, the question of whether or not isocyanate asthma is an IgE-mediated disease, has important implications for disease screening/surveillance, diagnosis, treatment and prevention. The present Pro/Con Debate, addresses contemporary, controversial issues regarding IgE in isocyanate asthma.

Occupational asthma: risk factors, diagnosis and preventive measures

In adulthood, new or recurrent asthma is caused by work in approximately 10% of cases. The term occupational asthma is reserved for those cases arising from respiratory hypersensitivity to a specific workplace agent; in others (work-exacerbated asthma) the mechanism is of nonspecific airway irritation on a background of bronchial hyper-reactivity. Some 300 workplace agents are capable of inducing asthma de novo; fortunately, most cases are attributed to a much smaller number to which exposure occurs in a few high-risk occupations. Exposure level is the most important remediable risk factor; the factors governing individual susceptibility are poorly understood. Diagnosis is generally straightforward. Management is rarely pharmacologic and often difficult since the diagnosis incurs important employment and other social consequences.

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

BACKGROUND

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

OBJECTIVE

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

METHOD

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

RESULTS

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

CONCLUSIONS

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

Tissue transglutaminase can be involved in airway inflammation of toluene diisocyanate-induced occupational asthma

BACKGROUND

This study was conducted to evaluate whether tissue transglutaminase (tTG) may be involved in airway inflammation of toluene diisocyanate-induced occupational asthma (TDI-OA).

METHODS

We enrolled 93 patients with TDI-OA, 177 asymptomatic exposed subjects, 43 patients with allergic asthma, and 70 unexposed normal controls. The prevalence of serum immunoglobulin G (IgG) to tTG in the TDI-OA group (20.2%) was significantly higher than that in the three other groups (P < 0.001).

RESULTS

TDI-OA patients with serum IgG to tTG had significantly lower methacholine PC(20) values (P < 0.02) and significantly higher prevalence of specific immunoglobulin E to vapor type TDI-human serum albumin conjugate (P < 0.01; r(2) = 0.411, P < 0.05). TDI exposure could increase tTG activity via reactive oxygen species (ROS) production, which was found to cross-link with cytokeratin 19 on immunoblot analysis.

CONCLUSION

Therefore, TDI exposure may activate tTG via ROS-mediated mechanism in the airway epithelium leading to persistent airway inflammation in TDI-OA patients.

Sequential evaluation of serum monocyte chemotactic protein 1 among asymptomatic state and acute exacerbation and remission of asthma in children

BACKGROUND

Monocyte chemotactic protein 1 (MCP-1) plays an important role in various immune and allergic disorders since it is a potent chemo-attractant for inflammatory cells, such as eosinophils, memory T cells, and monocytes.

OBJECTIVE

To investigate serum MCP-1 during asymptomatic state and acute attacks of bronchial asthma.

METHODS

In this longitudinal cohort design study, sequential serum levels of MCP-1 were measured by a sandwich enzyme-linked immunosorbent assay (ELISA). Twenty-four asthma patients' MCP-1 levels were examined at 5 time points: during the asymptomatic phase, in an acute wheezing episode, and at 1 week, 1 month, and 2 months after acute asthma attack. Fifteen children without asthma were enrolled as control.

RESULTS

During the asymptomatic phase of asthma, serum MCP-1 levels were significantly higher than that of normal controls (329.57 +/- 99.20 pg/ml vs. 213.63 +/- 77.29 pg/ml, p = 0.001). In comparison with the asymptomatic phase, the serum MCP-1 levels during the acute asthma attack were significantly higher (682.88 +/- 88.45 pg/ml vs. 329.57 +/- 99.20 pg/ml, p < 0.001). After treatment of acute asthma exacerbation, all of the serum MCP-1 levels declined within 1 week, but were still higher than control 2 months later.

CONCLUSION

In asthma patients, the consistently elevated serum levels of MCP-1 suggest its role in the pathogenesis of bronchial asthma - not only in the chronic inflammatory processes, but also in acute asthma attack exacerbation. These findings suggest a possible role for MCP-1 in the pathogenesis of asthma and a potential role for its use in anti-asthma treatment in the future.

Occupational asthma: current concepts in pathogenesis, diagnosis, and management

Occupational asthma (OA) may account for 25% or more of de novo adult asthma. The nomenclature has now better defined categories of OA caused by sensitizing agents and irritants, the latter best typified by the reactive airways dysfunction syndrome. Selecting the most appropriate diagnostic testing and management is driven by assessing whether a sensitizer is involved, and if so, identifying whether the sensitizing agent is a high-molecular-weight agent such as a protein or a low-molecular-weight reactive chemical such as an isocyanate. Increased understanding of the pathogenesis of OA from reactive chemical sensitizers is leading to development of better diagnostic testing and also an understanding of why testing for sensitization to such agents can be problematic. Risk factors for OA including possible genetic factors are being delineated better. Recently published guidelines for the diagnosis and management of occupational asthma are summarized; these reflect an increasingly robust evidence basis for recommendations. The utility of diagnostic tests for OA is being better defined by evidence, including sputum analysis performed in relation to work exposure with suspected sensitizers. Preventive and management approaches are reviewed. Longitudinal studies of patients with OA continue to show that timely removal from exposure leads to the best prognosis.