Trimellitic anhydride-induced airway syndromes: clinical and immunologic studies

“In Litero” Screening: Retrospective Evaluation of Clinical Evidence to Establish a Reference List of Human Chemical Respiratory Sensitizers

Despite decades of investigation, test methods to identify respiratory sensitizers remain an unmet regulatory need. In order to support the evaluation of New Approach Methodologies in development, we sought to establish a reference set of low molecular weight respiratory sensitizers based on case reports of occupational asthma. In this context, we have developed an “in litero” approach to identify cases of low molecular weight chemical exposures leading to respiratory sensitization in clinical literature. We utilized the EPA-developed Abstract Sifter literature review tool to maximize the retrieval of publications relevant to respiratory effects in humans for each chemical in a list of chemicals suspected of inducing respiratory sensitization. The literature retrieved for each of these candidate chemicals was sifted to identify relevant case reports and studies, and then evaluated by applying defined selection criteria. Clinical diagnostic criteria were defined around exposure history, respiratory effects, and specific immune response to conclusively demonstrate occupational asthma as a result of sensitization, rather than irritation. This approach successfully identified 28 chemicals that can be considered as human respiratory sensitizers and used to evaluate the performance of NAMs as part of a weight of evidence approach to identify novel respiratory sensitizers. Further, these results have immediate implications for the development and refinement of predictive tools to distinguish between skin and respiratory sensitizers. A comparison of the protein binding mechanisms of our identified “in litero” clinical respiratory sensitizers shows that acylation is a prevalent protein binding mechanism, in contrast to Michael addition and Schiff base formation common to skin sensitizers. Overall, this approach provides an exemplary method to evaluate and apply human data as part of the weight of evidence when establishing reference chemical lists.

Identifying a reference list of respiratory sensitizers for the evaluation of novel approaches to study respiratory sensitization

The induction of immunological responses that trigger bio-physiological symptoms in the respiratory tract following repeated exposure to a substance, is known as respiratory sensitization. The inducing compound is known as a respiratory sensitizer. While respiratory sensitization by high molecular weight (HMW) materials is recognized and extensively studied, much less information is available regarding low molecular weight (LMW) materials as respiratory sensitizers. Variability of symptoms presented in humans from such exposures, limited availability of (and access to) documented reports, and the absence of standardized and validated test models, hinders the identification of true respiratory sensitizers. This review aims to sort suspected LMW respiratory sensitizers based on available compelling, reasonable, inadequate, or questionable evidence in humans from occupational exposures and use this information to compose a reference list of reported chemical respiratory sensitizers for scientific research purposes. A list of 97 reported respiratory sensitizers was generated from six sources, and 52 LMW organic chemicals were identified, reviewed, and assigned to the four evidence categories. Less than 10 chemicals were confirmed with compelling evidence for induction of respiratory sensitization in humans from occupational exposures. Here, we propose the reference list for developing novel research on respiratory sensitization.

Trimellitic anhydride facilitates transepithelial permeability disrupting tight junctions in sinonasal epithelial cells

Trimellitic anhydride (TMA) is a chemical agent classified as a low molecular weight (LMW) agent causing occupational rhinitis (OR) or asthma. Although TMA is recognized as a respiratory sensitizer, the direct and non-immunologic effects of TMA remain unclear. Air- liquid interface (ALI) cultured human nasal epithelial cells (HNECs) derived from control subjects were treated with TMA, followed by measurement of the transepithelial electrical resistance (TEER), paracellular permeability of fluorescein isothiocyanate (FITC)-dextran and immunofluorescence of tight junction proteins claudin-1 and zonula occludens-1 (ZO-1). The cytotoxicity of TMA was evaluated by lactate dehydrogenase (LDH) assay. TMA at concentrations of 2 and 4 mg/mL significantly reduced the TEER within 10 min (p = 0.0177 on 2 mg/mL; p < 0.0001 on 4 mg/mL). The paracellular permeability of FITC-dextran was significantly increased upon challenge with 4 mg/mL TMA for 3 h (p = 0.0088) and 6 h (p = 0.0004). TMA treatment induced a reduction in the fluorescence intensity of claudin-1 and ZO-1 in a dose-dependent manner. LDH assay revealed 4 mg/mL TMA induced cytotoxicity only after 6 h incubation, while 1 or 2 mg/mL TMA caused no cytotoxicity. Our results suggest that TMA has a potential to penetrate the epithelial barrier by disrupting claudin-1 and ZO-1, indicating an important role for sensitization and OR development.

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

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

Health Effects of Trimellitic Anhydride Occupational Exposure: Insights from Animal Models and Immunosurveillance Programs

Acid anhydrides are used by chemical industries as plasticizers. Trimellitic acid (TMA) is an acid anhydride widely utilized in factories to produce paints, varnishes, and plastics. In addition to causing direct irritant effects, TMA can augment antibody responses in exposed factory workers leading to occupational asthma. Therefore, industries producing TMA have implemented occupational immunosurveillance programs (OISPs) to ensure early diagnosis and medical management, involving exposure reduction/ complete removal of sensitized workers from exposure areas. Multiple animal models (mice strains, rat stains, guinea pig, swine) with different exposure patterns (dermal, nasal, vapor inhalation exposures for different time frames) have been described to elucidate the pathophysiology of TMA exposure. In TMA factories, in spite of implementing advanced environmental controls and personal protective measures to limit exposure, workers become TMA-sensitized. Animal models revealed sIgG, sIgE, sIgA, and sIgM along with pulmonary lesions, cellular infiltrates, alveolar hemorrhage, and pneumonitis associated with TMA exposure. Molecular studies showed involvement of specific functional gene clusters related to cytokine and chemokine responses, lung remodeling, and arginase function. However, thus far, there is no evidence supporting fetotoxic or carcinogenic effects of TMA. OISP data showed IgG and IgE responses in exposed factory workers. Interestingly, timelines for detectable sIgG response, in conjunction with its magnitude, have been shown to be a predictor for future sIgE response. OISPs have been very successful so far at creating a healthy and safe working environment for TMA-exposed factory workers. Graphical Abstract Trimellitic Acid (TMA), used to produce paints, varnishes and plastics, can cause irritant-mediated and immune-mediated occupational health problems. NCBI pubmed search indicated that multiple animal models (different animal types, with chronic vs. acute exposure type, using TMA dust/suspension applied via dermal or other routes) have been used by investigators to elucidate the pathobiology of TMA-exposure. Several outcomes have been measured including humoral, lung/ airway, lymph nodes and dermal/ ear thickening responses. Studies on human subjects have been conducted mostly as parts of Occupational immunosurveillance programs (OISPs) implemented to identify TMA-sensitized workers (using ImmunoCAP and Skin prick testing), monitoring them longitudinally and their medical management including exposure reduction/ complete removal of sensitized workers from exposure areas. Clinical management also includes identification of irritant-induced and/ or immune-mediated outcomes of TMA occupational exposure. Collectively, these studies have led to important insights into the pathomechanism of TMA-exposure and have been very successful at creating a safe working environment for TMA-exposed factory workers.

The utility of monitoring trimellitic anhydride (TMA)-specific IgG to predict IgE-mediated sensitization in an immunosurveillance program

BACKGROUND

Workplace exposure to trimellitic anhydride (TMA) can elicit TMA-specific IgE (sIgE), which may lead to occupational asthma (OA). An occupational immunosurveillance program (OISP) has been implemented to monitor TMA exposure and immunologic outcomes. The purpose of this study was to determine whether TMA-specific IgG (sIgG) responses can discriminate between TMA-exposed workers with and without sIgE responses.

METHODS

Serum TMA-specific antibody (IgG, IgG4, and IgE) levels were estimated longitudinally (years 2006 to 2014) in TMA-exposed workers recruited in low, medium, and high exposure areas. sIgG and sIgE titers plotted against exposure duration were compared between workers with (a) sIgG only and (b) with sIgG who developed sIgE.

RESULTS

Among 92 TMA-exposed workers continuously monitored for sIgG and sIgE, 38 developed sIgG; 11 developed a sIgE response 342.38 ± 186.03 days posthire and were removed from exposure. The average detection time of sIgG in removed workers (159 ± 92 days) was significantly shorter than for actively exposed workers with only sIgG (346 ± 187 days). Workers with earlier sIgG responses of higher titer (mean value 42.25 μg/mL) compared to delayed responders with lower sIgG titers (mean value 14.79 μg/mL) more frequently developed sIgE responses. Hierarchical clustering showed the initial magnitude and exposure time required for detectable sIgG production discriminated between workers with only sIgG from workers who subsequently produced sIgE.

CONCLUSIONS

This study demonstrates the utility of longitudinally monitoring TMA-specific antibodies in an OISP as exposed workers with early sIgG responses and of higher magnitude are more likely to develop TMA sIgE sensitization.

Trimellitic anhydride induces low-grade mast cell degranulation without specific IgE

Objectives

Low-molecular-weight (LMW) substances are known to be causative agents of occupational asthma (OA) and occupational rhinitis (OR). Although most LMW substances are irritants or allergens, some can cause immediate type immunoglobulin E (IgE)-mediated allergic reactions. Trimellitic anhydride (TMA) is one such LMW substance, which is known as an immunological sensitizer. However, the exact molecular biological details of the effects of TMA remain unclear.

Methods

We measured the β-hexosaminidase release from mast cells after directly exposing the cells to various LMW substances. The tyrosine phosphorylation of whole cellular molecules and the phosphorylation of extracellular signal-regulated kinase (ERK) were assessed by immunoblot assay.

Results

Among the LMW substances tested, only TMA induced β-hexosaminidase release. However, the mast cell degranulation induced by TMA was lower than that induced by an antigen or a calcium ionophore. Moreover, the pattern of tyrosine phosphorylation of whole cellular molecules was quite different between IgE-mediated antigen stimulation and TMA exposure. The TMA effect on mast cells was independent of not only IgE but also Ca²⁺ influx. ERK phosphorylation was not detected in mast cells exposed to TMA.

Conclusions

TMA induced mild degranulation of mast cells without IgE, even though the phosphorylation of ERK was not detected. This reaction suggests that TMA affects humans even upon first exposure. Therefore, it is imperative to avoid human exposure to high concentrations of TMA. In order to stop the development of severe asthma in individuals with OR, we need to be able to identify cases of OR caused by TMA as soon as possible.

Occupational rhinitis: an update

Occupational rhinitis is characterized by nasal congestion, rhinorrhea, nasal itching, and/or sneezing that occur secondary to exposures in the workplace. This disease can be classified into allergic or nonallergic subgroups based upon the underlying disease pathogenesis as well as the type of causative agent. While the true prevalence of occupational rhinitis is unknown, there are certain professions and occupational exposures that place workers at a higher risk for developing the disease. Additionally, occupational rhinitis can be associated with occupational asthma and upper airway symptoms may precede those of the lower respiratory tract. Taken together, occupational rhinitis is an important disease for study given its medical as well as socioeconomic implications. This review will focus on the classification of occupational rhinitis as well the prevalence, diagnosis, and treatment strategies.

Mechanisms of occupational asthma: Not all allergens are equal

Asthma is a heterogeneous lung disorder characterized by airway obstruction, inflammation and eosinophil infiltration into the lung. Both genetics and environmental factors influence the expression of asthma, and not all asthma is the result of a specific immune response to allergen. Numerous asthma phenotypes have been described, including occupational asthma, and therapeutic strategies for asthma control are similar regardless of phenotype. We hypothesized that mechanistic pathways leading to asthma symptoms in the effector phase of the disorder differ with the inciting allergen. Since route of allergen exposure can influence mechanistic pathways, mice were sensitized by identical routes with a high molecular weight occupational allergen ovalbumin and a low molecular weight occupational allergen trimellitic anhydride (TMA). Different statistical methods with varying selection criteria resulted in identification of similar candidate genes. Array data are intended to provide candidate genes for hypothesis generation and further experimentation. Continued studies focused on genes showing minimal changes in the TMA-induced model but with clear up-regulation in the ovalbumin model. Two of these genes, arginase 1 and eotaxin 1 are the focus of continuing investigations in mouse models of asthma regarding differences in mechanistic pathways depending on the allergen. Microarray data from the ovalbumin and TMA model of asthma were also compared to previous data usingAspergillus as allergen to identify putative asthma 'signature genes', i.e. genes up-regulated with all 3 allergens. Array studies provide candidate genes to identify common mechanistic pathways in the effector phase, as well as mechanistic pathways unique to individual allergens.

Immunologic effector mechanisms in animal models of occupational asthma

Occupational asthma is a form of immunotoxicity resulting from an exaggerated immune response to substances encountered in the workplace. Symptoms include reversible airway obstruction, airway hyperresponsiveness, airway remodeling, mucus production and cellular infiltration into the lung, particularly eosinophilia. The asthmatic response is divided into the induction phase, occurring after initial exposure to allergen, followed by the effector phase where a subsequent exposure to the allergen results in the respiratory symptoms. Animal models have been used to investigate the asthmatic response and this review will focus on mechanistic studies of the effector phase. Variables that may impact the effector phase include strain and species of animal, dose of allergen, route of exposure, and developmental stage of the animal. Both trimellitic anhydride (TMA) and ovalbumin are known causes of occupational asthma. Ovalbumin is also a reference protein allergen in immunology, and TMA is used as a prototype of a low molecular weight respiratory allergen. Differences in effector mechanisms for TMA and ovalbumin have been noted in different animal models. Studies in the guinea pig provide the most direct comparisons of effector mechanisms of TMA and ovalbumin, with differences in the role of the complement system and arachidonate metabolites being noted. Besides the guinea pig, the Brown Norway rat, and various mouse strains provide useful asthma models for TMA and ovalbumin. However, studies of effector mechanisms are somewhat lacking in either of these species using TMA as the allergen. Continued studies are indicated to determine if unique effector mechanisms can be identified for the many different causes of occupational asthma.

Is trimellitic anhydride skin testing a sufficient screening tool for selectively identifying TMA-exposed workers with TMA-specific serum IgE antibodies?

OBJECTIVE

Trimellitic anhydride (TMA) can elicit specific IgE-mediated immune responses leading to asthma. This single-blinded study investigated the ability of TMA skin testing to identify workers with TMA-serum specific IgE antibodies.

METHODS

Forty TMA-exposed workers who were previously screened for the presence of TMA-IgG and/or IgE serum specific antibodies were skin tested to a TMA-human serum albumin reagent by nurses blinded to their antibody responses.

RESULTS

Findings from skin-prick tests were positive in 8 of 11 workers with TMA-serum specific IgE antibodies. Intracutaneous testing, performed only on skin prick testing-negative workers, was positive in two additional workers with TMA-serum specific IgE antibodies. A significant correlation was found between serum and skin test dilutions eliciting positive responses (ρ = 0.87, P < 0.05; n = 11).

CONCLUSIONS

TMA skin testing provides an alternative and potentially more practical method for monitoring TMA-exposed workers for developing IgE sensitization.

Old and new causes of occupational asthma

International reviews suggest that the median proportion of adult cases of asthma attributable to occupational exposure is between 10% and 15%. Therefore, it is essential that clinicians have a broad knowledge of the various causes associated with occupational asthma. Occupational asthmagens are categorized as low-molecular-weight (LMW, ≤1000 kd) and high-molecular-weight (HMW, ≥1000 kd) antigens. The purpose of this article is to review the most common representative LMW and HMW causes of occupational asthma over the past 70 years, with specific emphasis on newer causes reported over the past 5 years.

Occupational rhinitis

Work-related rhinitis, which includes work-exacerbated rhinitis and occupational rhinoconjunctivitis (OR), is two to three times more common than occupational asthma. High molecular weight proteins and low molecular weight chemicals have been implicated as causes of OR. The diagnosis of work-related rhinitis is established based on occupational history and documentation of immunoglobulin E (IgE) mediated sensitization to the causative agent if possible. Management of work-related rhinitis is similar to that of other causes of rhinitis and includes elimination or reduction of exposure to causative agents combined with pharmacotherapy. If allergens are commercially available, allergen immunotherapy can be considered.

Occupational rhinitis

Work-related rhinitis, which includes work-exacerbated rhinitis and occupational rhinitis, may be two to three times more common than occupational asthma. Both high molecular weight proteins and low molecular weight chemicals have been implicated as causes of occupational rhinitis. A diagnosis is established based on occupational history and, if appropriate, documentation of IgE-mediated sensitization to the causative agent. Management of work-related rhinitis is similar to that of non-work-related rhinitis and includes elimination or reduction of exposure to offending agents combined with pharmacotherapy. If treatment allergens are commercially available, allergen immunotherapy may also be considered if appropriate.

Skin prick tests and allergy diagnosis

Skin testing remains an essential diagnostic tool in modern allergy practice. A significant variability has been reported regarding technical procedures, interpretation of results and documentation. This review has the aim of consolidating methodological recommendations through a critical analysis on past and recent data. This will allow a better understanding on skin prick test (SPT) history; technique; (contra-) indications; interpretation of results; diagnostic pitfalls; adverse reactions; and variability factors.

Diagnosis and management of work-related asthma: American College Of Chest Physicians Consensus Statement

BACKGROUND

A previous American College of Chest Physicians Consensus Statement on asthma in the workplace was published in 1995. The current Consensus Statement updates the previous one based on additional research that has been published since then, including findings relevant to preventive measures and work-exacerbated asthma (WEA).

METHODS

A panel of experts, including allergists, pulmonologists, and occupational medicine physicians, was convened to develop this Consensus Document on the diagnosis and management of work-related asthma (WRA), based in part on a systematic review, that was performed by the University of Alberta/Capital Health Evidence-Based Practice and was supplemented by additional published studies to 2007.

RESULTS

The Consensus Document defined WRA to include occupational asthma (ie, asthma induced by sensitizer or irritant work exposures) and WEA (ie, preexisting or concurrent asthma worsened by work factors). The Consensus Document focuses on the diagnosis and management of WRA (including diagnostic tests, and work and compensation issues), as well as preventive measures. WRA should be considered in all individuals with new-onset or worsening asthma, and a careful occupational history should be obtained. Diagnostic tests such as serial peak flow recordings, methacholine challenge tests, immunologic tests, and specific inhalation challenge tests (if available), can increase diagnostic certainty. Since the prognosis is better with early diagnosis and appropriate intervention, effective preventive measures for other workers with exposure should be addressed.

CONCLUSIONS

The substantial prevalence of WRA supports consideration of the diagnosis in all who present with new-onset or worsening asthma, followed by appropriate investigations and intervention including consideration of other exposed workers.

Metalworking fluid with mycobacteria and endotoxin induces hypersensitivity pneumonitis in mice

BACKGROUND

Human cases of hypersensitivity pneumonitis (HP) have been reported among machinists for over 10 yr. Although mycobacteria have been implicated as causal agents, this has not been established in experimental studies and the mechanisms remain unclear. Other constituents of in-use metalworking fluids (MWFs) may also contribute to the development of lung disease. We investigated the potential for Mycobacterium immunogenum (MI) in MWFs to induce HP.

METHODS

Mice were exposed intranasally for 3 wk to MI (isolated from MWFs), Saccharopolyspora rectivirgula (positive control), saline, endotoxin, MWFs spiked with endotoxin and/or MI, used MWFs, and particulate-fortified used MWFs. Responses were assessed 96 h after the last exposure.

RESULTS

Mice exposed to MI in MWFs developed lung pathology consistent with HP along with significantly more monocytes and neutrophils in lung lavage, increased CD4+/CD8+ T-lymphocyte ratio, and marked pulmonary lymphocytosis on histologic examination when compared with saline-treated control mice. Mice with Grade 2 or higher pathology (0-4 point scale) exhibited significantly elevated macrophage inflammatory protein-1alpha and IL-10 and a trend toward higher RANTES 96 h after the final dose. Endotoxin coexposure augmented lung pathology.

CONCLUSION

MWFs containing mycobacteria induced granulomatous lung lesions, peribronchiolar lymphocytosis, increased cell concentrations in lavage, and up-regulation of several cytokines. These findings are consistent with HP.

Arginase activity differs with allergen in the effector phase of ovalbumin- versus trimellitic anhydride-induced asthma

Both trimellitic anhydride (TMA), a small molecular weight chemical, and ovalbumin (OVA), a reference protein allergen, cause asthma with eosinophilia. To test the hypothesis that different allergens elicit symptoms of asthma via different effector pathways, gene expression was compared in lungs of Balb/c mice sensitized with either TMA or OVA, followed by intratracheal challenge with TMA conjugated to mouse serum albumin (TMA-MSA) or OVA, respectively. Sensitized animals challenged with mouse serum albumin (MSA) alone were controls. Seventy-two hours after challenge, lung eosinophil peroxidase indicated that both allergens caused the same significant change in eosinophilia. Total RNA was isolated from lung lobes of 6-8 animals in each of four treatment groups and hybridized to Affymetrix U74Av2 GeneChips. False discovery rates (q-values) were calculated from an overall F test to identify candidate genes with differences in expression for the four groups. Using a q-value cutoff of 0.1, 853 probe sets had significantly different expression across the four treatment groups. Of these 853 probe sets, 376 genes had an Experimental/Control ratio of greater than 1.2 or less than 1/1.2 for either OVA- or TMA-treated animals, and 249 of the 376 genes were uniquely up- or down-regulated for OVA or TMA (i.e., differentially expressed with the allergen). qRT-PCR analysis of selected transcripts confirmed the gene expression analysis. Increases in both arginase transcript and enzyme activity were significantly greater in OVA-induced asthma compared to TMA-induced asthma. These data suggest that pathways of arginine metabolism and the importance of nitric oxide may differ in OVA- and TMA-induced asthma.

Genistein enhancement of respiratory allergen trimellitic anhydride-induced IgE production by adult B6C3F1 mice following in utero and postnatal exposure

The objective of the present study was to determine if exposure to the phytoestrogen genistein (GEN) during immune development had any effects on the production of IgE by adult mice following dermal treatment with trimellitic anhydride (TMA), a respiratory allergen. B6C3F1 mice were exposed to GEN either by feeding at 500 ppm or by gavage (20 mg/kg) for varied periods from gestation day (GD) 14 to postnatal day (PND) 84. In utero exposure to GEN by feeding increased the production of IgE at PND 84 in male mice but not in female mice. In male mice, continuous exposure to GEN postnatally diminished the in utero exposure-induced enhancement in serum total IgE production. However, continuous exposure to GEN from GD 14 to PND 84 was required to increase serum total IgE production in female mice. In utero exposure to GEN by gavage increased the production of IgE at PND 84 in female mice but not in male mice when the mice were maintained on the NIH-07 rodent diet in which a medium level of phytoestrogens was present. The enhancement in IgE production after GEN exposure in females but not in males was associated with decreases in the percentages of CD4(+)CD25(+) T suppressor cells, and increases in the natural killer (NK) cell activity, the basal splenocyte proliferation, the expression of CD86 by B cells, and the production of IL-2 and IL-4. Overall, the results demonstrated that GEN differentially modulated the developing immune system in male and female mice, and that more IgE was produced upon exposure to TMA in the adult.

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

BACKGROUND

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

OBJECTIVE

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

RESULTS

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

CONCLUSION

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

Identifying airway sensitizers: cytokine mRNA profiles induced by various anhydrides

Exposure to low molecular weight (LMW) chemicals in the workplace has been linked to a variety of respiratory effects. Within the LMW chemicals, one of the major classes involved in these effects are the acid anhydrides. The immunological basis of respiratory hypersensitivity involves CD4+ cells. By virtue of their induction of cytokines typical of CD4+ T-helper type 2 (Th2) cells-interleukin (IL)-4, 10, and 13-respiratory sensitizers may be identified and differentiated from contact sensitizers which induce Th1 cytokines (IL-2 and IFN-gamma). Our previous work suggested that the ribonuclease protection assay (RPA) was useful in identifying the respiratory sensitizer, trimellitic anhydride (TMA), based on quantitative differences in Th2 cytokine mRNA as compared to the contact sensitizer dinitrochlorobenzene (DNCB). Therefore, the purpose of the studies described in this report was to expand the chemicals tested in the RPA. To this end, four acid anhydrides with known respiratory sensitization potential, TMA, maleic anhydride (MA), phthalic anhydride (PA) and hexahydrophthalic anhydride (HHPA), were tested. Although previously determined to induce immunologically equivalent responses in a local lymph node assay (LLNA), the initial dose chosen (2.5%) failed to induce Th2 cytokine mRNA expression. To determine if the lack of cytokine expression was related to dose, LLNAs were conducted at higher doses for each of the anhydrides. The highest doses evaluated (four- to six-fold higher than those used in the initial RPA) gave equivalent proliferative responses for the various anhydrides and were used for subsequent RPA testing. At these higher doses, significant increases in Th2 versus Th1 cytokine mRNA were observed for all anhydrides tested. These results suggest that the RPA has the potential to serve as a screen for the detection of LMW airway sensitizing chemicals. However, the basis for selecting immunologically equivalent doses may require some modification.

Occupational asthma caused by exposure to low-molecular-weight chemicals

Chemical agents cause approximately 40% of cases of occupational asthma (OA). Diagnosis of OA caused by chemicals relies on the demonstration of decrements in lung function at the workplace or during a controlled specific inhalation challenge to the suspect chemical agent. Evaluation of workers is accomplished best with a stepwise algorithmic approach and while the worker is symptomatic and still exposed at work. An early diagnosis followed by cessation of exposure can result in asthma remission and is likely to prevent progression to chronic disabling obstructive disease.

Temporal changes in cytokine gene expression profiles induced in mice by trimellitic anhydride

Prolonged (13 day) topical exposure of BALB/c strain mice to the chemical respiratory allergen trimellitic anhydride (TMA) induces a selective T helper (Th) 2 profile of cytokine secretion in cells isolated from the draining lymph node. The ability of chemical respiratory allergens to elicit preferential type 2 immune responses is a distinguishing characteristic and provides the theoretical basis for cytokine fingerprinting, a novel approach to hazard identification. This study aimed to further characterize the cytokine expression profile induced by TMA, and to investigate the kinetics of cytokine production at both the protein and mRNA level by comparison of acute (3 day) and chronic (13 day) exposure regimes. Acute exposure resulted in the expression of high levels of mRNA for both Th1- and Th2-type cytokines, including interleukins 4, 10, 15 (IL-4, IL-10, IL-15) and interferon gamma (IFN-gamma), and the inflammatory cytokine IL-6, as determined by ribonuclease protection assay (RPA). However, following chronic exposure marked down-regulation of message for IL-6 and IFN-gamma was observed along with concomitant up-regulation of IL-4 and IL-10 expression. These cytokine mRNA profiles were broadly paralleled at the protein level. There was also a marked increase with time of mRNA for the Th2 cytokine IL-9, a cytokine not associated previously with chemical allergy. These data show that as the immune response to TMA develops, the cytokine gene expression profile of allergen-activated lymph node cells evolves from a mixed Th1/Th2 phenotype to a more polarized Th2 profile.

Diisocyanate-exposed auto body shop workers: a one-year follow-up

BACKGROUND

Diisocyanates currently are the most commonly identified cause of occupational asthma in industrialized countries. Auto body shops, a common hexamethylene diisocyanate (HDI) exposure setting, are difficult to study due to their small size and episodic exposures.

OBJECTIVES

A 1-year follow-up was undertaken as an adjunct to the cross-sectional SPRAY study (Survey of Painters & Repairers of Auto bodies by Yale) to investigate the effects of HDI on auto body shop workers over time and whether or not the healthy worker effect may exist in this industry.

METHODS AND RESULTS

Forty-eight workers from seven shops were re-contacted. Thirty-four subjects who stayed at the same shop and 11 who left their original shop participated. No statistically significant changes in physiology, symptoms, and immunologic responses from baseline to follow-up were noted. However, significant differences between those who left the shops and those who stayed were noted. Those who left were younger, less experienced in the industry, and more likely to have a history of asthma (23 vs. 3%; P < 0.05), bronchial hyper-responsiveness (23 vs. 9%), HDI-specific IgG (64 vs. 29%; P < 0.05), and HDI-specific proliferation (S.I. 2.0 vs. 1.3; P < 0.05).

CONCLUSIONS

The differences in workers who stayed at their shop compared to those who left, combined with the low asthma prevalence and high job turnover rate, all suggest that a healthy worker effect may exist in the auto body industry, and may in part account for the low prevalence of asthma noted in SPRAY and other cross-sectional studies of diisocyante workers.

Melaleuca tree and respiratory disease

BACKGROUND

The role of Melaleuca quinquenervia tree as a source of allergen(s) and respiratory irritant(s) is controversial.

OBJECTIVE

Determine whether Melaleuca tree pollen or odor is medically important.

METHODS

A 2-year aeroallergen survey and skin test (ST) results of 1,017 subjects were reviewed. Sixteen subjects were selected based on positive Melaleuca pollen extract (MPE) STs. Double-blind nasal challenges with MPE were performed on six subjects. Single-blind bronchial challenges with MPE were performed on four. To evaluate the irritant effect, 11 subjects received 34 different Melaleuca odor challenges (blossoms, bark, and leaves) through a closed system for up to 30 minutes. Four inhaled an odor from cajeput oil (derived from Melaleuca leaves) for 1 hour. Spirometry was performed before and after odor challenges. Radioallergosorbent test using MPE was compared with MPE STs in 15 subjects.

RESULTS

The aeroallergens survey revealed insignificant numbers of Melaleuca pollen. Ninety-seven of 1,017 subjects were a 2+ or greater intradermal MPE ST. One of 6 double-blind nasal challenges and 1 of 4 single-blind bronchial challenges using MPE were positive in subjects with positive MPE STs. All 38 odor challenges with blossoms, bark, leaves, and cajeput oil were nonreactive. The MPE radioallergosorbent test correlated with MPE ST results.

CONCLUSIONS

The Melaleuca tree is not a significant source of aeroallergen. The Melaleuca odor is not a respiratory irritant. MPE antigen(s) has been shown to cross-react with pollen extracts from a proven aeroallergen (Bahia grass pollen) possibly explaining the few cases of positive MPE STs with positive nasal/bronchial challenges.

Trimellitic anhydride (TMA) dust induces airway obstruction and eosinophilia in non-sensitized guinea pigs

Trimellitic anhydride (TMA) causes asthma after a latency period of sensitization. In non-sensitized humans and animals, limited studies indicate that TMA exposure may also cause symptoms of asthma without a latency period. Our previous studies (J. Pharmacol. Exp. Ther. 296 (2001) 284) in a guinea pig model of TMA-induced asthma demonstrated that sensitization and the complement system were required for eosinophilia. TMA conjugated to guinea pig serum albumin (TMA-GPSA) was used to elicit the response. Since occupational exposure to TMA occurs by inhalation of dust, the present studies determined if exposure to TMA dust in a non-sensitized guinea pig elicited airway obstruction and inflammation, and whether a significantly greater response occurred after a latency period of sensitization. Guinea pigs were intradermally injected with either corn oil (non-sensitized animals) or 30% TMA (sensitized animals). Three weeks later they were challenged by intratracheal insufflation with 1 mg TMA dust or lactose dust (control) using a dry powder delivery device. Pulmonary resistance, dynamic lung compliance, mean arterial blood pressure and heart rate were monitored for 10 min. In non-sensitized guinea pigs, significant increases in pulmonary resistance and decreases in dynamic lung compliance and blood pressure occurred after TMA challenge. In sensitized animals, the same dose of TMA caused significantly greater effects compared to non-sensitized animals. In a separate experiment, cellular infiltration into the lung was determined 24 h after challenge with TMA dust or lactose dust. In both non-sensitized and sensitized animals, eosinophils in the lung tissue were increased after TMA dust challenge compared to controls. Thus, these studies suggest that the response in non-sensitized animals differs depending on whether TMA dust or TMA-GPSA is used to elicit the response. TMA dust elicits significant airway obstruction and eosinophilia in a non-sensitized animal, with even greater airway obstruction occurring in a sensitized animal.

Interleukins 5 and 13 characterize immune responses to respiratory sensitizing acid anhydrides

There is some debate regarding whether occupational asthma induced by respiratory sensitizing acid anhydrides is mediated by the induction of T helper (Th) 2-type responses and the production of IgE, with failure to detect specific IgE antibody in some symptomatic patients. In the current investigations, cytokine secretion profiles induced in draining lymph node cells (LNC) by topical application to BALB/c strain mice of trimellitic anhydride (TMA), phthalic anhydride (PA) and maleic anhydride (MA) have been examined. Responses were compared with those induced by exposure to 2,4-dinitrochlorobenzene (DNCB), a contact allergen that lacks respiratory sensitizing potential. Exposure to all three acid anhydrides stimulated vigorous expression of interleukin (IL)-5, IL-10 and IL-13 but relatively low levels of the type 1 cytokines interferon-gamma (IFN-gamma) and IL-12. In addition, TMA-activated LNC expressed high levels of mitogen-inducible IL-4 whereas MA and PA displayed a lesser potential to elaborate this cytokine. The DNCB-stimulated LNC exhibited the converse type 1 phenotype of cytokine expression. The CD4(+) Th2 cells were the primary source of type 2 cytokines. Respiratory sensitizing acid anhydrides induce a predominantly Th2 cytokine phenotype, including the expression of IL-5 and IL-13, cytokines which in the presence of only very low levels of IL-4 may provide for an IgE-independent mechanism for the development of chemical respiratory allergy. These data provide additional support for the use of cytokine secretion profiling for the prospective identification of chemical respiratory allergens.

Dose-response and time course of specific IgE and IgG after single and repeated topical skin exposure to dry trimellitic anhydride powder in a Brown Norway rat model

BACKGROUND

Trimellitic anhydride (TMA)-induced occupational asthma is thought to be associated with its ability to acylate proteins and to induce production of TMA-specific immunoglobulin (Ig)E. Though the respiratory tract is considered to be a major exposure route leading to airway sensitization, the potential role of dermal exposure producing asthmatic sensitization is not known. The present study examines the ability of dry TMA powder to sensitize Brown Norway rats when applied, topically, to the skin.

METHODS

A patch of hair was carefully clipped with scissors on the rat's back. Dry TMA powder (0.3, 1.25, 5 and 20 mg) was administered on days 0, 7, 14 and 21, and the area occluded with surgical tape overnight after each application. Residual powder recovered from the occluded skin was analyzed by proton nuclear magnetic resonance and was still predominantly TMA. Circulating anti-TMA IgE and IgG were measured by ELISA.

RESULTS

TMA elicited dose-dependent production of specific IgE and IgG. Specific antibodies were detectable 2 weeks after the first TMA exposure and peaked between 3 and 4 weeks.

CONCLUSION

The data suggest that topical skin exposure to dry TMA powder can induce allergic/immunological sensitization as demonstrated by the production of specific antibodies.

Cytokine profiling for chemical sensitizers: application of the ribonuclease protection assay and effect of dose

Exposure to chemicals in domestic and occupational settings may contribute to increases in asthma and allergy. Airway hypersensitivity (AHS) is T helper-2 (Th2) cell associated, whereas contact hypersensitivity (CHS) is T helper-1 (Th1) cell associated. The distinct cytokine profiles produced by these cells may provide a means of distinguishing respiratory sensitizers from contact sensitizers. In this study, female BALB/c mice were exposed twice on the flanks and three times on the ears using the airway sensitizer trimellitic anhydride (TMA) or the contact sensitizer dinitrochlorobenzene (DNCB). At various times following exposure, total mRNA was extracted from draining lymph node cells and cytokine mRNA profiles analyzed using a multiprobe ribonuclease protection assay (RPA). The Th2 cytokines IL4, IL10, and IL13 were significantly increased in response to TMA compared to DNCB, with optimal detection occurring 14 days following initial exposure. To determine its effect, dose was varied in flank exposures, ear exposures, or both simultaneously. When dose was varied during flank exposures only, TMA induced higher levels of Th2 cytokines than DNCB at all doses tested. DNCB did not induce Th1 cytokines at any dose tested. Variation of TMA dose during both exposures similarly induced Th2 cytokines. Dose only appeared to be a factor when TMA concentration was varied during the ear exposures alone. Thus, these studies suggest that quantitative differences in Th2 responses between TMA and DNCB may be demonstrated over a wide range of doses and these differences may be detected by RPA following dermal exposure to these sensitizers.

Trimellitic anhydride-induced cellular infiltration into Guinea pig lung varies with age but not gender

BACKGROUND

In humans the incidence of asthma changes with age and gender. Immature guinea pigs have been used to model the allergic response to the occupational allergen trimellitic anhydride (TMA) where exposure to adults is paramount. We hypothesized that the TMA-induced allergic response in immature guinea pigs was similar to mature animals, regardless of gender.

METHODS

Sexually immature and mature female and male guinea pigs were sensitized intradermally with TMA. Three weeks after sensitization they were challenged intratracheally with TMA conjugated to guinea pig serum albumin (TMA-GPSA) or GPSA as a control. Twenty-four hours later cell infiltration into the lung was determined. TMA-specific IgG(1) and IgG(2) were measured in plasma and the complement activation product C3a was measured in the bronchoalveolar lavage fluid.

RESULTS

In control animals, numbers of eosinophils and neutrophils varied with age and gender. The TMA-GPSA- induced cellular infiltration was similar in all age/gender groups. However, neutrophils in the lung tissue increased only in immature animals. IgG antibodies differed between groups but did not account for differences in cell infiltration. C3a correlated with the extent of cell infiltration in all groups except mature females.

CONCLUSIONS

TMA-induced neutrophilia differs with age. TMA-induced changes in eosinophils and macrophages did not vary with age or gender. The relationship between complement activation and inflammation in mature females differs from that in the other groups, suggesting mediators of the response may change with age and gender. Effects of age and gender need to be considered in animal models of the allergic response.

Heterogeneity of IgE epitopes of vinyl sulphone reactive dye: human serum albumin that react with IgE

BACKGROUND

Vinyl sulphone reactive dye (vRD), which consists of vinyl sulphone reactive groups and a chromogen, can elicit IgE-mediated occupational asthma (OA) by haptenation. Human serum albumin (HSA) is known as the most reliable carrier protein for the vRD, the IgE epitopes of vRD-HSA are not well characterized. In this study we evaluated the epitope of vRD-HAS-specific IgE.

METHODS

Two vRD (Remazole Black-GR and Remazole Orange-3R), Procion Red-MX-5B, which has a dichlorotriazine reactive group, and vinyl sulphone (VS), were haptenated to HSA, respectively. vRD-HSA was denatured by heat or mercaptoethanol treatment and the allergenicities of denatured and non-denatured vRD-HSA were compared by ELISA and IgE immunoblotting using the sera of six vRD-OA patients. vRD-HSA-specific, Procion Red-MX-5B (pRD)-HSA-specific and VS-HAS-specific IgE were also measured with ELISA and the cross-reactivity between them was evaluated with ELISA inhibition.

RESULTS

Denaturation of vRD-HSA by heat affected its allergenicity markedly in five of six sera of RD-OA. When vRD was conjugated to the pre-heated HSA, its allergenicity also disappeared or was markedly attenuated compared with the vRD-HSA in five of six sera. Mercaptoethanol treatment markedly affected the allergenicity of the RD-HSA in all six RD-OA sera. Immunoblotting from non-denatured PAGE showed strong IgE affinity to vRD-HSA but immunoblotting from denatured SDS PAGE did not show IgE affinity. Among six RD-OA patients, five and four patients had pRD-HSA-specific and VS-HSA-specific IgE, respectively. However, the vRD-HSA-specific IgE was neither inhibited by pRD-HSA nor VS-HSA CONCLUSION: We considered that the conformational structure of HSA would be critical for the IgE epitopes during the haptenation process and both of the chromogen and reactive groups of the vRD would contribute to the formation of IgE epitope. Our results also confirmed the heterogeneity of IgE epitopes in the RD-HSA complex.

Trimellitic anhydride-induced eosinophilia in a mouse model of occupational asthma

Trimellitic anhydride (TMA) is a low-molecular-weight chemical known to cause occupational asthma. The present study was designed to determine if TMA elicited eosinophil infiltration into lungs of sensitized mice similar to previous studies with the protein allergen ovalbumin (OA). BALB/c mice were sensitized intradermally with 0.1 ml of 3% TMA or 0.3% OA in corn oil followed by intratracheal instillation with TMA conjugated to mouse serum albumin (TMA-MSA; 30 or 400 microg) or OA (30 microg). Nonsensitized mice received corn oil vehicle intradermally and MSA (30 microg) intratracheally. The allergic response was elicited 3 weeks later by intratracheal instillation of 30 or 400 microg TMA-MSA, OA, or control MSA. Cellular infiltration into bronchoalveolar lavage fluid (BAL) was determined 72 h later. Eosinophil peroxidase (EPO) and myeloperoxidase (MPO) activity in lung homogenates was used as an estimate of numbers of eosinophils and neutrophils, respectively, in lung tissue. In TMA-sensitized mice, TMA-MSA challenge significantly increased numbers of eosinophils in BAL and EPO in lung, indicating an increase in number of eosinophils in the airway and tissue. In nonsensitized mice, TMA-MSA challenge also caused a small but significant increase in eosinophils in BAL compared to MSA control. Total IgE in both plasma and BAL was significantly higher in TMA-sensitized compared to nonsensitized mice. The eosinophil infiltration in TMA-sensitized mice was similar in magnitude to the response in OA-sensitized mice. These studies are the first to demonstrate TMA-induced eosinophilia in mouse lung and to provide a model for comparing mechanisms and mediators responsible for the substantial eosinophilia induced by TMA and OA.

Subclinical immunologic and physiologic responses in hexamethylene diisocyanate-exposed auto body shop workers

BACKGROUND

Diisocyanates are potent sensitizing agents and currently the most commonly identified cause of occupational asthma in industrialized countries. However, diisocyanate asthma is difficult to diagnose and exposure and host risk factors are unclear. Auto body shops, one of the most common hexamethylene diisocyanate (HDI) exposure settings, are particularly difficult to study due to their small size and episodic exposures. Surveillance studies of such workers are limited.

OBJECTIVES

We have initiated a cross-sectional field epidemiologic study, Survey of Painters and Repairers of Auto bodies by Yale (SPRAY), to characterize the effects of diisocyanate exposures on actively employed auto body shop workers. Methods and Results We present here questionnaire, physiologic, immunologic, and exposure data on 75 subjects enrolled in the study. No overt cases of clinically apparent diisocyanate asthma were identified based on spirometry, methacholine challenge, peak flows, and symptoms. HDI-specific lymphocyte proliferation was present in 30% of HDI-exposed workers and HDI-specific IgG in 34% of HDI-exposed workers, but they were not associated. HDI-specific IgE was detected in two workers. HDI-specific lymphocyte proliferation, increased methacholine responsiveness, and symptoms of chest tightness and shortness of breath were more common in the most heavily HDI-exposed workers, the painters. More long-term follow-up of this cohort should clarify the significance of these HDI-specific immunologic responses, physiologic changes, and symptoms.

CONCLUSIONS

These findings demonstrate the presence of HDI-specific immune responses in a large proportion of healthy HDI-exposed workers.

Assessment and treatment of laboratory animal allergy

Laboratory animal allergy (LAA) is a form of occupational sensitivity affecting up to one third or more of exposed workers. Symptoms involve the eyes, nose, skin, and lower respiratory tract. Asthma may develop in 20 to 30% of sensitized individuals. An occupational medical history is the primary tool if a diagnosis of LAA is suspected. The diagnosis is confirmed by demonstrating the presence of immunoglobulin E antibodies to laboratory animal allergens by skin testing or in vitro assays. If laboratory animal allergen-induced asthma is suspected, measurements of lung function are necessary for confirmation and assessing the degree of impairment. One approach to the problem is presented in this article. For individuals with LAA, avoidance of exposure is the primary treatment. For individuals who continue to work in the environment, pharmacological treatment of their symptoms may be necessary. Methods to prevent the development of LAA are also discussed.

Cytokine fingerprinting and hazard assessment of chemical respiratory allergy

Allergic sensitization of the respiratory tract resulting in occupational asthma and other symptoms can be caused by a variety of chemicals and represents an important occupational health problem. Although there is a need to identify and characterize those chemicals that are able to cause respiratory allergy, there are currently no well validated or widely accepted predictive test methods. Some progress has been made with guinea pig assays, but our attention in this laboratory has focused instead on the development of novel approaches based on an understanding of the nature of immune responses induced in mice by chemical allergens. We have shown that whereas contact allergens provoke in mice selective type 1 immune responses, characterized by the secretion by draining lymph node cells (LNC) of high levels of the cytokine interferon gamma (IFN-gamma), chemical respiratory allergens stimulate instead preferential type 2 responses associated with comparatively high levels of interleukins 4 and 10 (IL-4 and IL-10). The divergent immune responses provoked by different classes of chemical allergens, and the phenotypes of selective cytokine secretion that characterize such responses, form the basis of a novel method-cytokine fingerprinting--that permits chemicals that have the potential to cause respiratory allergy to be identified and distinguished from those that are associated primarily with contact sensitization. In this article the immunobiological basis for cytokine fingerprinting is considered and the development, evaluation and practical application of the assay are reviewed.

The development of an antibody to trimellitic anhydride

Acid anhydrides are a group of highly reactive chemicals used widely in the formulation of paints and plastics. Exposure to acid anhydrides causes several occupational lung diseases such as pneumonititis and asthma. Whilst anhydrides, specifically trimellitic anhydride (TMA), have been shown to bind to lung tissue in an animal model, further investigation has been hampered by the lack of a reagent which would enable the identification of primary target proteins for the binding of TMA. Our objective was to develop an antibody to TMA which would enable in vitro studies of TMA interactions with lung epithelial proteins. We developed a monoclonal antibody which binds solely to TMA. We have demonstrated that the antibody can be used to detect TMA bound to different human proteins with little non-specific binding to unconjugated proteins. We then exposed cells of the A549 lung epithelial cell line to TMA in vitro and have shown by western blotting that binding occurs in the 20-35 Kd weight range. We have developed a specific and sensitive reagent to detect TMA bound to proteins. We have used this to show that when TMA is incubated with a lung epithelial cell line, that the TMA binds to proteins with a restricted molecular weight range. These results suggest that the current paradigm for the detection of IgE to small molecular weight reactive chemicals, which presupposes that the chemical binds to serum albumin, may need further investigation.

Human leucocyte antigens (HLA) and trimellitic anhydride (TMA) immunological lung disease

Occupational immunological lung disease, due to low molecular weight, reactive chemicals such as trimellitic anhydride (TMA), is an emerging health problem. If there were a marker that was highly predictive of the ability of the immune system to recognize TMA as an allergen, better prevention strategies could be employed with at risk individuals. The purpose of this study is to evaluate whether human leucocyte antigen (HLA) class specificity is associated with the development of late respiratory systemic syndrome (LRSS) or asthma due to immunological sensitivity to trimellitic anhydride (TMA). This is a case control study of 17 individuals with LRSS, 12 with asthma and 22 TMA similarly exposed individuals who did not develop LRSS or asthma. Comparing the sensitized individuals (LRSS or asthma) with the non-sensitized individuals (controls), we found no difference in frequency of any HLA antigen. In summary, the lack of association of HLA antigens with LRSS or asthma due to TMA suggests that these will not be useful markers to identify at risk individuals.

Characterization in mice of the immunological properties of five allergenic acid anhydrides

Occupational exposure to certain acid anhydrides, including trimellitic anhydride (TMA), maleic anhydride (MA), phthalic anhydride (PA), hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA), has been associated with the development of respiratory allergy or asthma. There is considerable debate about the mechanisms through which such chemicals may cause respiratory sensitization, particularly concerning a universal requirement for specific IgE antibody. Despite the controversy regarding an obligatory role for IgE, there is a growing consensus that chemical respiratory hypersensitivity is associated with the selective development of T lymphocytes with a type 2 (Th2) phenotype. In the current investigations we have characterized in mice the nature of immune responses provoked by prolonged topical exposure to five acid anhydrides. Under application conditions where similar overall immunogenicity was achieved, we have compared cytokine responses induced by PA, MA, HHPA and MTHPA with those provoked by concurrent exposure to TMA or to the reference contact allergen 2, 4-dinitrochlorobenzene (DNCB). Lymph node cells (LNC) draining the site of topical exposure to DNCB invariably expressed high levels of the type 1 cytokines interferon-gamma (IFN-gamma) and interleukin-12 (IL-12), but only low levels of the type 2 cytokines interleukin-4 (IL-4) and interleukin-10 (IL-10). In each experiment, TMA-activated LNC displayed the converse, type 2, phenotype of cytokine production. The other acid anhydrides in each case provoked a type 2 cytokine secretion profile, with comparable IL-10 expression but somewhat less vigorous IL-4 production compared with that observed following exposure to the reference respiratory allergen TMA. In every experiment relatively low levels of IFN-gamma and IL-12 were elaborated by acid anhydride-activated LNC, with the exception of PA-stimulated LNC that displayed increased amounts of IL-12 in comparison with other acid anhydrides. Thus, prolonged topical exposure of mice to five different acid anhydrides in each case resulted in the development of a predominantly Th2-type cytokine secretion phenotype, consistent with the ability of these materials to provoke asthma and respiratory allergy through a type 2 (possibly IgE-mediated) mechanism. Taken together with the results of previous investigations with a wider range of chemical allergens, these data suggest that induced cytokine secretion patterns or 'fingerprints' allow discrimination between contact and respiratory allergens and consequently represent a suitable approach to prospective evaluation of respiratory sensitization hazard.

Important issues in occupational asthma

Although there has been a dramatic increase in awareness about the contributions of the work environment to asthma, many aspects of this illness remain to be explored in further detail. This article focuses on issues that need to be better understood. Data are reported that describe newly recognized agents in the workplace that have been shown in a sophisticated manner to induce asthma. In addition, data that further describe the mechanisms of occupational asthma and information regarding the management of occupational asthma are given. Important problems yet to be resolved include whether those who develop occupational asthma from different agents are likely to have different outcomes, whether screening is likely to have a significant effect on the outcome (and, if so, what is the best approach to screening), and identification of a clear definition of the role of immunologic-mediated parameters as they relate to the initiation of asthma attributable to low molecular weight agents and patient outcome. There is little information about "safe" levels of exposure that protect all workers. Data (such as underlying specific immunologic or genetic markers) are lacking that might aid in predicting which workers are likely to be sensitized by low molecular weight agents. This abbreviated list of unresolved issues makes the study of occupational asthma a fertile field for research.

Mechanisms of occupational asthma

BACKGROUND

The pathogenesis and the pathologic alterations of occupational asthma are similar to those of nonoccupational asthma. Occupational asthma may therefore represent a useful model of "human asthma" to investigate mechanisms and pathophysiology of asthma in general. In an occupational setting the cause and onset of asthma may be easily identified, and the natural history may be examined in follow-up studies. The mechanisms involved in occupational asthma include genetic predisposition, immunologically mediated responses, as well as nonspecific airway inflammation. In particular, high molecular weight (eg, grain dust, flour) and some low molecular weight sensitizers (eg, acid anhydrides and platinum halide salts) have been shown to induce occupational asthma through an immunoglobulin E (IgE)-dependent mechanism, while cell-dependent immunologic mechanisms are likely to be more relevant for occupational asthma induced by other low molecular weight sensitizers (eg, toluene diisocyanate and plicatic acid contained in western red cedar). The pathology of the airway mucosa of occupational asthma is remarkably similar to the pathology of nonoccupational asthma, ie, characterized by infiltration and accumulation of eosinophils, mast cells, and activated lymphocytes along with subepithelial fibrosis. In this article, the most relevant mechanisms are discussed with particular reference to the similarities and discrepancies between occupational and nonoccupational asthma.

Long term outcome of soybean epidemic asthma after an allergen reduction intervention

BACKGROUND

Asthma outbreaks due to the inhalation of soybean dust released from handling of soybean in the city harbour occurred in Barcelona, Spain from 1981 to 1987. The installation of bag filters in the responsible silo was followed by a substantial reduction of airborne soybean dust released into the atmosphere and the disappearance of asthma outbreaks. A study was undertaken to assess the relevant outcomes in asthma patients affected by soybean epidemic asthma eight years after this environmental intervention.

METHODS

A repeat case-control study was performed in 1995 on a population of subjects with epidemic and non-epidemic asthma previously assessed in 1989. The same protocol was used in both surveys to collect data from patients via a questionnaire and respiratory function, skin and laboratory tests were performed under blinded conditions with regard to epidemic and non-epidemic status. Environmental soybean allergen in pollution filters was measured by means of a RAST inhibition technique.

RESULTS

During 1995 and 1996 the 24 hour mean airborne levels of soybean allergen on a sample of 39 unloading days (range 31-269 U/m(3)) were systematically below the lowest level ever detected during an epidemic day (1500 U/m(3)). Measurable levels of serum IgE antibodies against soybean were still present in 55% of patients with epidemic asthma compared with 6.0% of those with non-epidemic asthma (p<0.05). These proportions were almost identical to those observed in 1989. The proportion of patients with soybean asthma with symptoms in 1989 who reported the absence of symptoms in 1995 was similar to the control subjects, so most of the relative risks (RRs) of improvement were near to 1. The only statistically significant differences between the two groups were a smaller proportion of patients with epidemic asthma showing improvement in terms of being woken up by attacks of coughing (RR improvement 0.47; 95% CI 0.22 to 0.99) and the need for treatment at the emergency room (RR improvement 0.63; 95% CI 0.41 to 0.96).

CONCLUSIONS

Eight years after a large reduction in the levels of airborne soybean allergen half of the former soybean epidemic asthma patients were still sensitised to soybean. These results indicate an initial improvement in soybean epidemic asthma in the two years following the intervention with no further improvement in subsequent years.

Immunoglobulin E antibody against environmental allergens in subjects with trimellitic anhydride-induced asthma

The purpose of this study was to assess the relationship between atopy and the development of occupational asthma as a consequence of exposure to trimellitic anhydride (TMA). A case-control study was performed, which comprised 16 employees identified as having TMA-induced asthma and 44 similarly exposed controls. Specific immunoglobulin E measurements in response to cat, dust mite, ryegrass, and ragweed antigens were performed. Fifty-six percent of cases and 29% of controls were found to be atopic (P = 0.098). We demonstrated that there was a trend toward employees with TMA asthma being more atopic than those without TMA asthma. Atopy as an assessment of risk for the development of TMA asthma is unlikely to be useful, although further investigation may be warranted.

Retrospective exposure assessment for a cohort study into respiratory effects of acid anhydrides

OBJECTIVES

To estimate past exposure to phthalic (PA), trimellitic (TMA) and maleic anhydride (MA) in three alkyd resin and one cushioned flooring factory to estimate exposure-response relations in a retrospective cohort study.

METHODS

Personal exposure measurements were carried out in 1992 and quantitative and qualitative information on past exposure and production processes were collected. Job titles were ranked by decreasing exposure and amalgamated into job categories and exposure groups. Multiplication factors for back calculating past exposure levels were estimated with past exposure data, or if no such data were available these factors were estimated by a panel of occupational hygienists. Exposure levels were back calculated starting with the exposure levels in 1992.

RESULTS

High exposures to PA were estimated to have occurred among workers operating the PA melting pots in factory 1 (estimated exposure in 1960-9 was 2480 micrograms.m-3). Highest concentrations of TMA were estimated to have occurred among the ink mixers in factory 2 from 1979 to 1986 (554 micrograms.m-3). Exposure in most other job titles was thought to be fairly constant over time for PA, TMA, and MA.

CONCLUSIONS

Exposure to acid anhydride at these factories has fallen during the period covered by the study. However, it is estimated that in only one job in factory 2 did past exposure to acid anhydride exceed the current occupational exposure standard. Accuracy of the estimated exposure is limited by a paucity of reliable past exposure data.

Role of the complement system in pulmonary disorders

Immune injury in the lung is classically divided into types I-IV hypersensitivity, with the complement system being involved in types II and III hypersensitivity. Anaphylaxis and asthma are generally considered prototypes of type I hypersensitivity and hypersensitivity pneumonitis as an example of type III hypersensitivity in the lung. However, in asthma, for example, increasing evidence indicates that in addition to mast cells, T lymphocytes play an important role. Therefore, considering asthma as strictly a type I mediated reaction is too simplistic. This report will review the evidence regarding the involvement of the complement system and complement activation products in anaphylaxis, asthma and immune complex disease in various experimental models of pulmonary disease. Identification of the mediators responsible for the symptoms may suggest rational targets for the continued development of effective therapy to combat immune injury in the lung.