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

Chemical respiratory sensitization-Current status of mechanistic understanding, knowledge gaps and possible identification methods of sensitizers

Respiratory sensitization is a complex immunological process eventually leading to hypersensitivity following re-exposure to the chemical. A frequent consequence is occupational asthma, which may occur after long latency periods. Although chemical-induced respiratory hypersensitivity has been known for decades, there are currently no comprehensive and validated approaches available for the prospective identification of chemicals that induce respiratory sensitization, while the expectations of new approach methodologies (NAMs) are high. A great hope is that due to a better understanding of the molecular key events, new methods can be developed now. However, this is a big challenge due to the different chemical classes to which respiratory sensitizers belong, as well as because of the complexity of the response and the late manifestation of symptoms. In this review article, the current information on respiratory sensitization related processes is summarized by introducing it in the available adverse outcome pathway (AOP) concept. Potentially useful models for prediction are discussed. Knowledge gaps and gaps of regulatory concern are identified.

Reduced Isocyanate Release Using a Waterproof, Resin-Based Cast Alternative Relative to Fiberglass Casts

The effects of occupational isocyanate exposure range from asthma and contact dermatitis to neurotoxicity and cancer. Respiratory sensitization due to orthopedic cast application has been well documented. This study aims to compare the safety of standard-of-care fiberglass casts and a novel waterproof cast alternative by measuring the amount of isocyanate released during off-gassing over time. A 3D-printed arm simulator with comparable casing material amounts was placed in a sealed chamber. An isocyanate-sensing color-changing (SafeAir) tag was used to measure the levels of toxic exposure. Triplicate trials were conducted across all time periods (15 min, 1 h, and 24 h) and conditions. The bare arm simulator and freshly opened tags served as negative controls. Normalized pixel intensity indexes and isocyanate release estimates in ppb were derived from ImageJ-analyzed SafeAir tag photos. Fiberglass casts exhibited greater isocyanate release than both the waterproof alternative (p = 0.0002) and no-cast controls (p = 0.0006), particularly at 24 h. The waterproof alternative and no-cast control did not statistically differ (p = 0.1603). Therefore, the waterproof alternative released less isocyanate than the fiberglass casts. Waterproof cast alternatives may be safer than fiberglass by limiting medical professionals' exposure to toxic isocyanates and, thus, decreasing their risk of suffering occupational asthma.

β-Endorphin (an endogenous opioid) inhibits inflammation, oxidative stress and apoptosis via Nrf-2 in asthmatic murine model

Asthma, a chronic respiratory disease is characterized by airway inflammation, remodelling, airflow limitation and hyperresponsiveness. At present, it is considered as an umbrella diagnosis consisting several variable clinical presentations (phenotypes) and distinct pathophysiological mechanisms (endotypes). Recent evidence suggests that oxidative stress participates in airway inflammation and remodelling in chronic asthma. Opioids resembled by group of regulatory peptides have proven to act as an immunomodulator. β-Endorphin a natural and potent endogenous morphine produced in the anterior pituitary gland play role in pain modulation. Therapeutic strategy of many opioids including β-Endorphin as an anti‑inflammatory and antioxidative agent has not been yet explored despite its promising analgesic effects. This is the first study to reveal the role of β-Endorphin in regulating airway inflammation, cellular apoptosis, and oxidative stress via Nrf-2 in an experimental asthmatic model. Asthma was generated in balb/c mice by sensitizing with 1% Toulene Diisocyanate on day 0, 7, 14 and 21 and challenging with 2.5% Toulene Diisocyanate from day 22 to 51 (on every alternate day) through intranasal route. β-Endorphin (5 µg/kg) was administered through the nasal route 1 h prior to sensitization and challenge. The effect of β-Endorphin on pulmonary inflammation and redox status along with parameters of oxidative stress were evaluated. We found that pre-treatment of β-Endorphin significantly reduced inflammatory infiltration in lung tissue and cell counts in bronchoalveolar lavage fluid. Also, pre-treatment of β-Endorphin reduced reactive oxygen species, Myeloperoxidase, Nitric Oxide, Protein and protein carbonylation, Glutathione Reductase, Malondialdehyde, IFN-γ, and TNF-α. Reversely, β-Endorphin significantly increased Superoxide dismutase, Catalase, glutathione, Glutathione-S-Transferase, and activation of NF-E2-related factor 2 (Nrf-2) via Kelch-like ECH-associated protein 1 (Keap1), independent pathway in the lung restoring architectural alveolar and bronchial changes. The present findings reveal the therapeutic potency of β-END in regulating asthma by Keap-1 independent regulation of Nrf-2 activity. The present findings reveal the therapeutic potency of β-Endorphin in regulating asthma.

The axis of the receptor for advanced glycation endproducts in asthma and allergic airway disease

Asthma is a generalized term that describes a scope of distinct pathologic phenotypes of variable severity, which share a common complication of reversible airflow obstruction. Asthma is estimated to affect almost 400 million people worldwide, and nearly ten percent of asthmatics have what is considered "severe" disease. The majority of moderate to severe asthmatics present with a "type 2-high" (T2-hi) phenotypic signature, which pathologically is driven by the type 2 cytokines Interleukin-(IL)-4, IL-5, and IL-13. However, "type 2-low" (T2-lo) phenotypic signatures are often associated with more severe, steroid-refractory neutrophilic asthma. A wide range of clinical and experimental studies have found that the receptor for advanced glycation endproducts (RAGE) plays a significant role in the pathogenesis of asthma and allergic airway disease (AAD). Current experimental data indicates that RAGE is a critical mediator of the type 2 inflammatory reactions which drive the development of T2-hi AAD. However, clinical studies demonstrate that increased RAGE ligands and signaling strongly correlate with asthma severity, especially in severe neutrophilic asthma. This review presents an overview of the current understandings of RAGE in asthma pathogenesis, its role as a biomarker of disease, and future implications for mechanistic studies, and potential therapeutic intervention strategies.

Innate lymphoid cells in isocyanate-induced asthma: role of microRNA-155

BACKGROUND

Occupational asthma, induced by workplace exposures to low molecular weight agents such as toluene 2,4-diisocyanate (TDI), causes a significant burden to patients and society. Little is known about innate lymphoid cells (ILCs) in TDI-induced asthma. A critical regulator of ILC function is microRNA-155, a microRNA associated with asthma.

OBJECTIVE

To determine whether TDI exposure modifies the number of ILCs in the lung and whether microRNA-155 contributes to TDI-induced airway inflammation and hyperresponsiveness.

METHODS

C57BL/6 wild-type and microRNA-155 knockout mice were sensitised and challenged with TDI or vehicle. Intracellular cytokine expression in ILCs and T-cells was evaluated in bronchoalveolar lavage (BAL) fluid using flow cytometry. Peribronchial eosinophilia and goblet cells were evaluated on lung tissue, and airway hyperresponsiveness was measured using the forced oscillation technique. Putative type 2 ILCs (ILC2) were identified in bronchial biopsies of subjects with TDI-induced occupational asthma using immunohistochemistry. Human bronchial epithelial cells were exposed to TDI or vehicle.

RESULTS

TDI-exposed mice had higher numbers of airway goblet cells, BAL eosinophils, CD4⁺ T-cells and ILCs, with a predominant type 2 response, and tended to have airway hyperresponsiveness. In TDI-exposed microRNA-155 knockout mice, inflammation and airway hyperresponsiveness were attenuated. TDI exposure induced IL-33 expression in human bronchial epithelial cells and in murine lungs, which was microRNA-155 dependent in mice. GATA3⁺CD3^- cells, presumably ILC2, were present in bronchial biopsies.

CONCLUSION

TDI exposure is associated with increased numbers of ILCs. The proinflammatory microRNA-155 is crucial in a murine model of TDI asthma, suggesting its involvement in the pathogenesis of occupational asthma due to low molecular weight agents.

Physiological responses to cisplatin using a mouse hypersensitivity model

Background: The physiological mechanisms underlying the development of respiratory hypersensitivity to cisplatin (CDDP) are not well-understood. It has been suggested that these reactions are likely the result of type I hypersensitivity, but other explanations are plausible and the potential for CDDP to induce type I hypersensitivity responses has not been directly evaluated in an animal model. Objectives and Methods: To investigate CDDP hypersensitivity, mice were topically sensitized through application of CDDP before being challenged by oropharyngeal aspiration (OPA) with CDDP. Before and immediately after OPA challenge, pulmonary responses were assessed using whole body plethysmography (WBP). Results: CDDP did not induce an immediate response or alter the respiratory rate in sensitized mice. Two days later, baseline enhanced pause (Penh) values were significantly elevated (p < 0.05) in mice challenged with CDDP. When challenged with methacholine (Mch) aerosol, Penh values were significantly elevated (p < 0.05) in sensitized mice and respiratory rate was reduced (p < 0.05). Lymph node cell counts and immunoglobulin E levels also indicated successful sensitization to CDDP. Irrespective of the sensitization state of the mice, the number of neutrophils increased significantly in bronchoalveolar lavage fluid (BALF) following CDDP challenge. BALF from sensitized mice also contained 2.46 (±0.8) × 10⁴ eosinophils compared to less than 0.48 (±0.2) × 10⁴ cells in non-sensitized mice (p < 0.05). Conclusions: The results from this study indicate that dermal exposure to CDDP induces immunological changes consistent with type I hypersensitivity and that a single respiratory challenge is enough to trigger pulmonary responses in dermally sensitized mice. These data provide previously unknown insights into the mechanisms of CDDP hypersensitivity.

Inflammatory response and biomechanical properties of coaxial scaffolds for engineered skin in vitro and post-grafting

Engineered skin (ES) offers many advantages over split-thickness skin autografts for the treatment of burn wounds. However, ES, both in vitro and after grafting, is often significantly weaker, less elastic and more compliant than normal human skin. Biomechanical properties of ES can be tuned in vitro using electrospun co-axial (CoA) scaffolds. To explore the potential for coaxial scaffold-based ES use in vivo, two CoA scaffolds were fabricated with bioactive gelatin shells and biodegradable synthetic cores of polylactic acid (PLA) and polycaprolactone (PCL), and compared with gelatin monofilament scaffolds. Fibroblast and macrophage production of inflammatory cytokines interleukin 6 (IL-6) and transforming growth factor β-1 was significantly higher when cultured on PLA and PCL monofilament scaffolds compared to gelatin monofilament scaffolds. The core-shell fiber configuration significantly reduced production of pro-inflammatory cytokines to levels similar to those of gelatin monofilament scaffolds. In vitro, ES mechanical properties were significantly enhanced using CoA scaffolds; however, after grafting CoA- and gelatin-based ES to full-thickness excisional wounds on athymic mice, the in vitro mechanical advantage of CoA grafts was lost. A substantially increased inflammatory response to CoA-based ES was observed, with upregulation of IL-6 expression and a significant M2 macrophage presence. Additionally, expression of matrix metalloproteinase I was upregulated and collagen type I alpha 1 was downregulated in CoA ES two weeks after grafting. These results suggest that while coaxial scaffolds provide the ability to regulate biomechanics in vitro, further investigation of the inflammatory response to core materials is required to optimize this strategy for clinical use. STATEMENT OF SIGNIFICANCE: Engineered skin has been used to treat very large burn injuries. Despite its ability to heal these wounds, engineered skin exhibits reduced biomechanical properties making it challenging to manufacture and surgically apply. Coaxial fiber scaffolds have been utilized to tune the mechanical properties of engineered skin while maintaining optimal biological properties but it is not known how these perform on a patient especially with regards to their inflammatory response. The current study examines the biomechanical and inflammatory properties of coaxial scaffolds and uniaxial scaffolds in vitro and in vivo. The results show that the biological response to the scaffold materials is a critical determinant of tissue properties after grafting with reduced inflammation and rapid scaffold remodeling leading to stronger skin.

Lung function changes in mice sensitized to ammonium hexachloroplatinate

Occupational exposure to halogenated platinum salts can trigger the development of asthma. The risk to the general population that may result from the use of platinum in catalytic converters and its emerging use as a diesel fuel additive is unclear. To investigate pulmonary responses to platinum, we developed a mouse model of platinum hypersensitivity. Mice were sensitized through application of ammonium hexachloroplatinate (AHCP) to the shaved back on days 0, 5 and 19, and to each ear on days 10, 11 and 12. On days 24 and 29, mice were challenged by oropharyngeal aspiration with AHCP in saline. Before and immediately after challenge, pulmonary responses were assessed using whole body plethysmography (WBP). A dose-dependent increase in immediate responses was observed in AHCP-sensitized and challenged mice. On days 26 and 31, changes in ventilatory responses to methacholine (Mch) aerosol were assessed by WBP; dose-dependent increases in Mch responsiveness occurred in sensitized mice. Lymph node cell counts indicate a proliferative response in lymph nodes draining the sites of application. Bronchoalveolar lavage fluid harvested from sensitized mice contained an average of 5% eosinophils compared to less than 0.5% in non-sensitized mice (p < 0.05); significant increases in total serum immunoglobulin E were observed for all sensitized mice. Although a second airway challenge on day 29 affected some results, only one airway challenge was needed to observe changes in lung function.

Neutrophil and eosinophil granulocytes as key players in a mouse model of chemical-induced asthma

Diisocyanates are an important cause of chemical-induced occupational asthma. This type of immunologically mediated asthma is often characterized by a predominant granulocytic inflammation in the airways, rather than an infiltration by lymphocytes. We sought to determine the contribution of granulocytes in the outcome of chemical-induced asthma using general and specific leukocyte depletion strategies in an established mouse model of isocyanate asthma. On days 1 and 8, BALB/c mice received dermal applications with toluene-2,4-diisocyanate (TDI) or vehicle (acetone olive oil), followed by two ip injections of cyclophosphamide (CP, days 11 and 13), or one iv injection of antigranulocyte receptor 1 (aGR1, day 13) monoclonal antibody (mAb), or two ip injections of Ly6G-specific mAb (1A8, days 13 and 14). On day 15, the mice were challenged (oropharyngeal administration) with TDI or vehicle. The next day, we assessed methacholine airway hyperreactivity (AHR); bronchoalveolar lavage differential cell count; histopathology and total serum IgE; and auricular lymphocyte subpopulations and release of interleukin (IL)-2, IL-4, IL-10, IL-13, and gamma interferon by these lymphocytes. CP depleted all leukocyte types and completely prevented AHR and airway inflammation. aGR1 depleted granulocytes and CD8(+) lymphocytes, which resulted in a partial prevention in AHR but no decrease in airway inflammation. Depletion of Ly6G-positive granulocytes, i.e., both neutrophils and eosinophils, prevented AHR and lung epithelial damage and significantly reduced airway inflammation. Injection of aGR1 or 1A8 led to significantly changed cytokine release patterns in TDI-treated mice. Granulocytes, both neutrophils and eosinophils, are key cellular players in this model of chemical-induced asthma.

IL-33 mediates multi-walled carbon nanotube (MWCNT)-induced airway hyper-reactivity via the mobilization of innate helper cells in the lung

Allergic asthma is a chronic inflammatory disorder of the airway associated with bronchial obstruction, airway hyper-reactivity (AHR), and mucus production. The epithelium may direct and propagate asthmatic-like responses. Central to this theory is the observation that viruses, air pollution, and allergens promote epithelial damage and trigger the generation of IL-25, IL-33, and TSLP via innate pathways such as TLRs and purinergic receptors. Similarly, engineered nanomaterials promote a Th2-associated pathophysiology. In this study, we tested the hypothesis that instillation of multi-walled carbon nanotubes (MWCNT) impair pulmonary function in C57Bl/6 mice due to the development of IL-33-dependent Th2-associated inflammation. MWCNT exposure resulted in elevated levels of IL-33 in the lavage fluid (likely originating from airway epithelial cells), enhanced AHR, eosinophil recruitment, and production of Th2-associated cytokines and chemokines. Moreover, these events were dependent on IL-13 signaling and the IL-33/ST2 axis, but independent of T and B cells. Finally, MWCNT exposure resulted in the recruitment of innate lymphoid cells. Collectively, our data suggest that MWCNT induce epithelial damage that results in release of IL-33, which in turn promotes innate lymphoid cell recruitment and the development of IL-13-dependent inflammatory response.

Inhalation of ortho-phthalaldehyde vapor causes respiratory sensitization in mice

Ortho-Phthalaldehyde (OPA) has been approved for high-level sterilization of heat-sensitive medical instruments and is increasingly being used as a replacement in the healthcare industry for glutaraldehyde, a known sensitizer. Numerous case reports have been published indicating workers and patients experiencing respiratory problems, anaphylaxis, skin reactivity, and systemic antibody production. Our laboratory previously demonstrated that OPA is a dermal sensitizer in mice. The goal of the present study was to determine if OPA is a respiratory sensitizer following inhalation exposure. Mice were exposed to OPA vapor and airway and lymph nodes were examined for cytokine gene expression and alterations in lymphocyte populations. Inhalation of OPA for 3 days resulted in a concentration-dependent increase in lymphocyte proliferation, mainly B lymphocytes, in the draining lymph nodes. A secondary challenge of mice with OPA resulted in a dramatic increase in the population of B lymphocytes expressing IgE. Expression of Th2 (IL-4, IL-5, and IL-13) and anti/proinflammatory (IL-10, TNFα, and IL-1β) cytokine genes was upregulated in the lymph nodes and the nasal mucosa. Mice exposed to the higher concentrations of OPA-produced OPA-specific IgG₁ antibodies indicating systemic sensitization. These findings provide evidence that OPA has the potential to cause respiratory sensitization in mice.

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

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

Particulate matter-induced airway hyperresponsiveness is lymphocyte dependent

BACKGROUND

Exposure to airborne particulate matter (PM), a major component of air pollution, has been associated with increases in both exacerbations of and hospitalizations for asthma. We have previously shown that exposure to ambient PM collected in urban Baltimore (AUB) induces airway hyperresponsiveness (AHR), eosinophilic and neutrophilic inflammation, and the recruitment of T cells. However, the mechanism(s) by which it induces these features of asthma remains unknown.

OBJECTIVE

We investigated whether T lymphocytes play a role in AUB-induced AHR.

METHODS

We compared the effects of AUB exposure on the allergic phenotype in wild-type (WT) BALB/c mice and in mice deficient in recombinase-activating gene-1 (Rag1-/-) that lack mature lymphocytes.

RESULTS

We found that exposure of WT mice to AUB induced AHR concomitant with increases in the numbers of bronchoalveolar lavage (BAL) fluid lymphocytes, eosinophils, neutrophils, and mucus-containing cells in the lungs of WT mice. Interestingly, we show for the first time that these effects were associated with significant elevations in interleukin (IL)-17A, IL-17F, and T-helper 2 cell (TH2) (IL-13, IL-5) cytokine levels in lung cells, as well as reductions in the levels of the suppressive cytokine IL-10. Interestingly, Rag1-/- mice failed to develop AUB-induced AHR; however, AUB-induced BAL fluid cellularity, and mucus cell changes were only partially inhibited in Rag1-/- mice.

CONCLUSIONS

Taken together, our results suggest that AUB exposure increases the pathophysiological features of asthma via activation of lymphocyte-dependent pathways. These results provide a plausible biological mechanism for the strong association between PM exposure and the increased severity of asthma.

Is toluene diamine a sensitizer and is there cross-reactivity between toluene diamine and toluene diisocyanate?

Toluene diamine (TDA) is formed when toluene diisocyanate (TDI), a potent sensitizer, comes in contact with an aqueous environment. The sensitizing capacity of TDA and the cross-reactivity between TDI and TDA are unknown. TDA (5-25%) and TDI (0.3%), dissolved in acetone/olive oil (AOO) (4:1) were tested in the mouse local lymph node assay (LLNA). To determine the capacity of TDA to elicit an asthmatic response and to determine the cross-reaction with TDI, a locally developed experimental mouse model of chemical-induced asthma was used. On days 1 and 8, BALB/c mice received 20 microl of TDI (0.3%), TDA (20%), or AOO (4:1) on each ear. On day 15, they received an intranasal instillation of TDI (0.1%), TDA (0.5%) or AOO (3:2). The EC(3) of TDA in the LLNA is 19%. In the model of chemical-induced asthma, TDI induced a ventilatory response [increased Penh after challenge; increased airway hyperreactivity (AHR)], inflammatory changes (bronchoalveolar lavage neutrophils), and immunological changes (increased CD19(+) lymphocytes, IL-4 and total serum IgE), whereas TDA did not show any of these responses. Mice sensitized with TDI and challenged with TDA also did not show any airway or inflammatory response, although they had increased levels of total serum IgE. Mice sensitized with TDA and challenged with TDI did not show any response. According to the classification of sensitizers in the LLNA, TDA is a weak dermal sensitizer. In the experimental mouse model of chemical-induced asthma, TDA does not act as a respiratory sensitizer, at the concentration used. No cross-reactivity between TDI and TDA was found.

Inhalation of toluene diisocyanate vapor induces allergic rhinitis in mice

Diisocyanates are the leading cause of occupational asthma, and epidemiological evidence suggests that occupational rhinitis is a comorbid and preceding condition in patients who develop asthma. The goal of the present studies was to develop and characterize a murine model of toluene diisocyanate (TDI)-induced rhinitis. Female C57BL/6 mice were exposed to workplace-relevant concentrations of TDI vapor via inhalation for 4 h/day for 12 days with or without a 2-wk rest period and TDI challenge. Mice exposed 12 consecutive weekdays to 50 parts per billion TDI vapor showed elevated total serum IgE and increased TDI-specific IgG titers. Breathing rates were decreased corresponding with increased inspiratory time. TDI exposure elevated IL-4, IL-5, IL-13, and IFN-gamma mRNA expression in the nasal mucosa, suggesting a mixed Th1/Th2 immune response. Expressions of mRNA for proinflammatory cytokines and adhesion molecules were also up-regulated. These cytokine changes corresponded with a marked influx of inflammatory cells into the nasal mucosa, eosinophils being the predominant cell type. Removal from exposure for 2 wk resulted in reduced Ab production, cytokine mRNA expression, and cellular inflammation. Subsequent challenge with 50 parts per billion TDI vapor resulted in robust up-regulation of Ab production, cytokine gene expression, as well as eosinophilic inflammation in the nasal mucosa. There were no associated changes in the lung. The present model shows that TDI inhalation induces immune-mediated allergic rhinitis, displaying the major features observed in human disease. Future studies will use this model to define disease mechanisms and examine the temporal/dose relationship between TDI-induced rhinitis and asthma.

Th2 Cytokines in Skin Draining Lymph Nodes and Serum IgE Do Not Predict Airway Hypersensitivity to Intranasal Isocyanate Exposure in Mice

Isocyanate exposure in the workplace has been linked to asthma and allergic rhinitis. Recently, investigators have proposed that Th2 cytokine responses in lymph nodes draining the site of dermal application of chemicals including isocyanates may be used to identify sensitizers that cause asthma-like responses. The purpose of this study was to determine if the cytokine profile induced after dermal sensitization with isocyanates and serum IgE predict immediate (IHS) and methacholine-induced late (LHS) respiratory hypersensitivity responses after intranasal challenge. Dermal application of hexylmethane diisocyanate (HMDI), toluene diisocyanate (TDI), or methylene diisocyanate (MDI) significantly increased interleukin-4 (IL-4), IL-5, and IL-13 secretion in parotid lymph node cells. Isophorone diisocyanate (IPDI) increased IL-4 and IL-13, but not IL-5. Tolyl(mono)isocyanate (TMI), tetramethylene xylene diisocyanate (TMXDI), or the contact sensitizer dinitrochlorobenzene (DNCB), only induced minor increases in some of the Th2 cytokines. HMDI, TDI, MDI, and IPDI elicited greater increases in total serum IgE than DNCB, TMI, and TMXDI. All chemicals except TMXDI caused IHS after intranasal challenge of sensitized female BALB/c mice. Only HMDI-, TMI-, or TMXDI-sensitized and challenged mice had increases in LHS. All chemicals elicited epithelial cytotoxicity indicative of nasal airway irritation. The discordance between dermal cytokine profiles and respiratory responses suggests that dermal responses do not necessarily predict respiratory responses. Serum IgE also was not predictive of the respiratory responses to the isocyanates, suggesting that other unknown mechanisms may be involved.

Role of intercellular adhesion molecule-1 in a murine model of toluene diisocyanate-induced asthma

BACKGROUND

Adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) are thought to contribute to the airway inflammation and airway hyper-responsiveness (AHR) of allergic asthma. Some differences from allergic asthma have been noted, including airway neutrophilia, and the involvement of ICAM-1 in toluene diisocyanate (TDI) asthma is currently unclear.

OBJECTIVE

We utilized mice lacking ICAM-1 expression (ICAM-1(-/-)) to investigate the role of ICAM-1 in airway inflammation and AHR in TDI-induced asthma.

METHODS

Male C57BL/6J mice (ICAM-1(+/+)) and ICAM-1(-/-) mice were intranasally sensitized to TDI solution or solvent alone. Airway inflammation, AHR and cytokine secretion were assessed 24 h after challenge by TDI or solvent. The production of antigen-specific IgG and IgE by TDI sensitized and non-sensitized mice was determined.

RESULTS

TDI challenge to ICAM-1(+/+) mice induced an increase in airway inflammatory cell numbers, AHR and cytokine secretion of TNF-alpha, macrophage inflammatory protein-2 (MIP-2), IL-4, IL-5 and IFN-gamma into the bronchoalveolar lavage fluid. All these pathophysiological changes were reduced in ICAM-1(-/-) mice. Serum levels of TDI-specific IgG and IgE of ICAM-1(-/-) and ICAM-1(+/+) mice were comparable.

CONCLUSION

These results suggest that ICAM-1 plays an essential role in airway inflammation and AHR in TDI-induced asthma.

Airway inflammation and bronchial remodelling in toluene diisocyanate-exposed BALB/c mouse model

Toluene diisocyanate (TDI), a highly reactive industrial chemical, is one of the leading causes of occupation-related asthma in industrialized countries. The pathogenesis of TDI-induced asthma, however, remains not fully understood, in part due to lack of appropriate animal models. Twenty five female BALB/c mice (age: 8 weeks) were randomly divided into 5 groups: Ovabumin (OVA); OVA peptide amino acid residues No. 323-339 (Pep); TDI; alum and physiological saline. Mice were intraperitoneally injected with 25 microg OVA or pep absorbed on 300 microg alum, 300 microg alum or saline on days 0, 7 and 14. For the TDI group, mice were sensitized subcutaneously with 20 microl neat TDI on day 0; 20 microl of TDI in olive oil (1:10) on days 7 and 14; on days 21-23. Then each group was challenged intranasally with 20 microl of 1% OVA, 1% Pep, 1% TDI, 10% alum and saline respectively. On day 28, mice were killed under pentothal anesthesia. The results demonstrated that neutrophil-dominant inflammation with a few eosinophil infiltration occurred in the peri-bronchial and peri-vascular regions of the lungs. This was accompanied by hyperplasia/hypertrophy of cells lining the airways and mucus production as shown by HE staining. Positive immunohistochemical MBP staining in parenchyma was also shown. Th2 cytokine IL-4 and IgE production were significant increased 5 days after last challenge while IFN-gamma level was below the detection limit.

CONCLUSION

the clear elevation of IL-4 and IgE could allow to conclude a possible Th2-like dominated allergic response in TDI-exposed BALB/c mouse model.

Diisocyanate asthma and gene-environment interactions with IL4RA, CD-14, and IL-13 genes

BACKGROUND

Diisocyanate asthma (DA) affects 2% to 10% of exposed workers, yet the pathogenetic mechanisms underlying this disorder remain ill defined.

OBJECTIVE

To determine if specific single nucleotide polymorphisms (SNPs) of interleukin 4 receptor alpha (IL4RA), IL-13, and CD14 promoter genes are associated with DA.

METHODS

Sixty-two workers with DA confirmed by specific inhalation challenge (SIC) and 75 diisocyanate-exposed, SIC-negative workers were analyzed for SNPs associated with IL4RA, IL-13, and CD14 promoter genes.

RESULTS

No associations were found with individual SNPs and DA. When stratified according to specific diisocyanate exposure, a significant association was found between IL4RA (I50V) II and DA among individuals exposed to hexamethylene diisocyanate (HDI) (odds ratio [OR], 3.29; 95% confidence interval [CI], 1.33-8.14; P = .01) only. Similarly, the IL4RA (I50V) II and IL-13 (R110Q) RR combination was significantly associated with DA in HDI-exposed workers (OR, 4.13; 95% CI, 1.35-12.68; P = .01), as was the IL4RA (I50V) II and CD14 (C159T) CT genotype combination (OR, 5.2; 95% CI, 1.82-14.88; P = .002) and the triple genotype combination IL4RA (I50V) II, IL-13 (R110Q) RR, and CD14 (C159T) CT (OR, 6.4; 95% CI, 1.57-26.12; P = .01).

CONCLUSIONS

Gene-environmental interactions may contribute to the pathogenesis of DA, and gene-gene interactions may modulate this relationship.

Immunological determinants of ventilatory changes induced in mice by dermal sensitization and respiratory challenge with toluene diisocyanate

The objective of the study was to characterize better the immunologic mechanisms underlying a previously developed animal model of chemical-induced asthma. BALB/c and severe combined immunodeficiency disease (SCID) mice received toluene diisocyanate (TDI) or vehicle on each ear on day 1 and/or day 7. On day 10, they were intranasally challenged with TDI or vehicle. Ventilatory function was monitored by whole body plethysmography for 40 min after challenge. Reactivity to methacholine was measured 23 h later: enhanced pause and actual resistance measurements. Pulmonary inflammation was assessed 1, 6, and 24 h after challenge by bronchoalveolar lavage (BAL). Tumor necrosis factor-alpha and macrophage inflammatory protein (MIP)-2 levels were measured in BAL. Immunological parameters included total IgE, IgG1, and IgG2a in serum, lymphocyte populations in auricular and cervical lymph nodes, and IL-4 and IFN-gamma levels in supernatants of lymph node cells, cultured with or without concanavalin A. Ventilatory changes suggestive of airway obstruction and increased methacholine reactivity were observed in all TDI-sensitized and TDI intranasally instilled mice, except in SCID mice. A neutrophil influx, accompanied by an increase in MIP-2 levels, was found in BAL of all responding groups 6 and 24 h after intranasal challenge. In BALB/c mice an increased level of CD19+ B cells was found in the auricular lymph nodes. IL-4 and IFN-gamma levels were increased in supernatants of concanavalin A-stimulated auricular lymph node cells from BALB/c mice completely treated with TDI. These results indicate that our model is dependent on the presence of lymphocytes, but it is not characterized by a preferential stimulation of Th1 or Th2 lymphocytes.

Alveolar macrophages have a dual role in a rat model for trimellitic anhydride-induced occupational asthma

Occupational exposure to low molecular weight chemicals, like trimellitic anhydride (TMA), can result in occupational asthma. Alveolar macrophages (AMs) are among the first cells to encounter inhaled compounds. These cells can produce many different mediators that have a putative role in asthma. In this study, we examined the role of AMs in lung function and airway inflammation of rats exposed to TMA. Female Brown Norway rats were sensitized by dermal application of TMA or received vehicle alone on days 0 and 7. One day before challenge, rats received intratracheally either empty or clodronate-containing liposomes to deplete the lungs of AMs. On day 21, all rats were challenged by inhalation of TMA in air. Lung function parameters were measured before, during, within 1 h after, and 24 h after challenge. IgE levels and parameters of inflammation and tissue damage were assessed 24 h after challenge. Sensitization with TMA led to decreased lung function parameters during and within 1 h after challenge as compared to non-sensitized rats. AM depletion alleviated the TMA-induced drop in lung function parameters and induced a faster recovery compared to sham-depleted TMA-sensitized rats. It also decreased the levels of serum IgE 24 h after challenge, but did not affect the sensitization-dependent increase in lung lavage fluid IL-6 and tissue TNF-alpha levels. In contrast, AM depletion augmented the TMA-induced tissue damage and inflammation 24 h after challenge. AMs seem to have a dual role in this model for TMA-induced occupational asthma since they potentiate the immediate TMA-induced decrease in lung function but tended to dampen the TMA-induced inflammatory reaction 24 h later.

Delayed-type asthmatic response induced by repeated intratracheal exposure to toluene-2,4-diisocyanate in guinea pigs

BACKGROUND

A toluene-2,4-diisocyanate (TDI)-induced asthma model, in which delayed-type hypersensitivity-like asthmatic airway obstruction is elicited restrictively in the lung, has never been developed.

METHODS

Guinea pigs were percutaneously sensitized with TDI. For the challenges, once every 2 weeks for a total of 5 times, TDI mists were delivered directly to the lung through an oral cannula, with its tip being positioned in the opening of the trachea. Time-course changes in specific airway resistance (sRaw) were measured by double-flow plethysmography. Basic mechanisms underlying TDI-induced asthma were analyzed.

RESULTS

After the 2nd-5th challenges, induction of both an early increase in sRaw that peaked at 10 min and a delayed-type sRaw elevation that peaked at 22 h were observed. Interestingly, in the sensitized/challenged animals, baseline sRaw was elevated by repeated challenge as compared to that seen for non-sensitized animals. Intratracheal administration of a bronchodilator, salbutamol, strongly suppressed the early asthmatic response (EAR) but not the delayed-type asthmatic response (DAR). During DAR, both albumin leakage and fucose secretion into the bronchoalveolar lavage fluid were increased. The cysteinyl leukotriene antagonist pranlukast failed to inhibit either EAR or DAR while the corticosteroid dexamethasone significantly suppressed DAR, without significantly affecting EAR.

CONCLUSIONS

Effective delivery of TDI to the lung may induce reproducible DAR in sensitized guinea pigs with chronicity that is reflected by an increase in the sRaw baseline. DAR is not mediated by constriction of airway smooth muscles and is probably due to the concurrent presence of mucosal edema and mucus hypersecretion in the airways.

Repeated inhalation challenge with diphenylmethane-4,4'-diisocyanate in brown Norway rats leads to a time-related increase of neutrophils in bronchoalveolar lavage after topical induction

Diphenylmethane-4,4'-diisocyanate (MDI) is a low-molecular-weight chemical known to cause occupational asthma. The objective of this study was to evaluate the topical and inhalation routes of sensitization on the elicitation response of MDI in the Brown Norway (BN) rat model following repeated challenge exposures. BN rats were either induced topically (150 microl MDI on the flanks, booster administration to the skin of the dorsum of both ears using 75 microl/dorsum of each ear) or by inhalation (5x3 h/d, 28.3+/-3.0 mg MDI/m3 [+/-SD]). Inhalation challenge exposures with MDI (15.7+/-1.4 mg/m3, duration 30 min) were made on d 21, 35, 50, and 64. One day after each challenge, rats were rechallenged with methacholine (MCh) aerosol. Respiratory changes were monitored during challenges. One day after the MCh challenge, selected endpoints in bronchoalveolar lavage (BAL), the weights of lungs, and auricular and lung-associated lymph nodes were determined. After the first and last challenge, lymph nodes and lungs were examined by histopathology. Repeated challenge with MDI or MCh did not elicit marked changes in respiratory patterns at any time point. Mild but consistent time-related increased BAL neutrophils and slightly increased lung and lymph-node weights occurred in topically sensitized rats as compared to the remaining groups. In topically sensitized rats, in the lung histopathology revealed activated lymphatic tissue and an increased recruitment of airway eosinophils. Immunoglobulin (Ig) E determinations (serum and BAL) did not show any differences amongst the groups. Thus, high-dose topical induction with MDI was associated with a neutrophilic and eosinophilic inflammatory response in the lung after repeated inhalation challenge with MDI, with magnitude of effect dependent on the specific methodology used.

Altered gene expression profiles in nasal respiratory epithelium reflect stable versus acute childhood asthma

BACKGROUND

Asthma is the most common chronic disease of childhood and has a strong genetic component.

OBJECTIVE

To identify gene expression signatures that reflect asthma-related processes and to determine whether these genes were similar or distinct between stable asthma and acute exacerbations in childhood, we profiled gene expression patterns in nasal respiratory epithelial cells.

METHODS

Children who had stable asthma (asthma-S; n = 10) and children experiencing an asthma exacerbation (asthma-E; n = 10) were recruited along with nonatopic children without asthma (n = 10). RNA was prepared from nasal respiratory epithelial cells isolated from each child, initially analyzed as pooled samples from the 3 groups, and further validated by using microarrays and RT-PCR with individual patient samples.

RESULTS

Distinct gene clusters were identifiable in individual and pooled asthma-S and asthma-E samples. Asthma-E samples demonstrated the strongest and most reproducible signatures, with 314 genes of 34,886 measured as present on the chip demonstrating induction or repression of greater than 2-fold with P < .05 in each of 4 individual samples. Asthma-S-regulated genes encompassed genes that overlapped with those of asthma-E but were fewer (166) and less consistent with respect to their behavior across the asthma-E patient samples.

CONCLUSION

Exacerbated asthma status is readily distinguished based on the occurrence of strong gene expression signatures in nasal epithelial samples. Stable asthma status also exhibits differential signatures. The results suggest that there are independent gene expression signatures reflective of cells and genes poised or committed to activation by an asthma attack.

Cytokine mRNA profiles for isocyanates with known and unknown potential to induce respiratory sensitization

Isocyanates are low-molecular-weight chemicals implicated in allergic asthmatic-type reactions. Identification of chemicals likely to cause asthma is difficult due to the lack of a validated test method. One hypothesis is that differential cytokine induction (Th1 versus Th2 profiles) in the draining lymph node following dermal application can be used to identify asthmagens and distinguish them from contact allergens. In this study, we compared the cytokine mRNA profiles of six chemicals: toluene diisocyanate (TDI), diphenylmethane-4,4'-diisocyanate (MDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), isophorone diisocyanate (IPDI), p-tolyl(mono)isocyanate (TMI), and meta-tetramethylene xylene diisocyanate (TMXDI). Whereas TDI and MDI are well-known respiratory sensitizers, documentation for HMDI, IPDI, TMI, and TMXDI is limited, but suggests that HMDI and IPDI may have respiratory sensitization potential in humans and TMI and TMXDI do not. Following dermal exposure of BALB/c mice, all six isocyanates induced cytokines characteristic of a Th2 response. Although LLNAs suggested that the doses chosen for the RPA were immunologically equivalent, the isocyanates tested differentiated into two groups, high responders and low responders. However, two of the low responders (TMI and TMXDI) were further tested and induced higher levels of Th2 cytokine message than dinitrochlorobenzene (not an asthmagen). Further study of these chemicals is needed to determine whether the Th2 cytokine responses observed for these low responders is predictive of asthmagenic potential or represents an insufficient signal.

Animal models for diisocyanate asthma: answers for lingering questions

PURPOSE OF REVIEW

Diisocyanates are the leading cause of occupational asthma, the most commonly reported lung disease associated with the workplace. Clinical studies have implicated the immune system in the pathogenesis of occupational asthma, but ethical and moral issues prevent mechanistic investigations in humans. For this reason, the development and characterization of animal models are germane to further understanding of diisocyanate occupational asthma and to identify avenues for therapeutic intervention. This review will highlight important features of existing experimental animal models with emphasis on new developments.

RECENT FINDINGS

Experimental animal models of diisocyanate occupational asthma have demonstrated an immunological basis for the disease. Mice can be sensitized by dermal or respiratory exposure, suggesting that either exposure route may be important in the workplace. Recent findings show that sensitized mice develop airway hyperreactivity and inflammation, reflective of human disease. The transfer of lymphocytes or serum from sensitized mice can cause clinical disease in naive mice. Transgenic animals have identified a role for specific immunity, including the involvement of T-helper type 1/2 responses as well as CD4 and CD8 T cells in diisocyanate occupational asthma. Recent animal models have shown that sensitization can occur through subchronic inhalation of vapor-phase diisocyanate at levels as low as 20 ppb.

SUMMARY

Recent progress using animal models has been instrumental in furthering current understanding of the involvement of the immune system in disease pathogenesis. The demonstration of diisocyanate occupational asthma in a murine model after sub-chronic inhalation exposure at relevant exposure levels should provide opportunities for more accurate risk assessment data.

Methods for the identification of chemical respiratory allergens in rodents: comparisons of cytokine profiling with induced changes in serum IgE

No validated or widely recognized test methods are currently available for the prospective identification of chemicals with the potential to cause respiratory allergy. The cellular and molecular mechanisms that result in the induction of chemical sensitization of the respiratory tract are unclear, although there is evidence for the selective development of T helper 2 (Th2)-type responses and, in some cases, the production of IgE antibody. We have therefore examined the utility of cytokine profiling using BALB/c mice, together with the measurement of induced increases in the total serum concentration of IgE in the Brown Norway (BN) rat, as markers for the prospective identification of chemical respiratory allergens. Responses provoked by the reference respiratory allergen trimellitic anhydride (TMA) have been compared with those stimulated by the respiratory sensitizing diisocyanates toluene diisocyanate (TDI) and hexamethylene diisocyanate (HDI) and by the acid anhydride hexahydrophthalic anhydride (HHPA). Topical exposure of BN rats to TMA, TDI and HHPA each provoked marked immune activation (increases in lymph node cellularity and proliferation). However, only treatment with TMA stimulated vigorous increases in the total serum concentration of IgE. In contrast, exposure to HHPA, TDI or HDI failed to provoke significant changes in serum IgE concentration or induced only transient and relatively weak increases in serum IgE levels. In parallel experiments using BALB/c strain mice, however, topical application of all four chemical respiratory allergens provoked a marked Th2-type cytokine secretion profile in draining lymph node cells. These data suggest that the measurement of induced changes in serum IgE is not sufficiently sensitive for the robust identification of chemical respiratory allergens. Furthermore, irrespective of the reasons for variations in TMA-induced IgE production among BN rats, doubts remain regarding the utility of these animals for the characterization of immune responses to chemical allergens. Cytokine profiling using the BALB/c strain mouse apparently provides a more robust method for the hazard assessment of chemical respiratory allergens.

Species differences in the structure and function of the immune system

With the recent publication of regulatory guidelines from both the FDA and the CPMP addressing the investigation of immunotoxicity of new chemical entities has come the requisite increased application of immunotoxicology protocols. Importantly, the fulfillment of these protocols may require the use of different species, and while in many cases information concerning the structure and function of the immune system can be readily translated across species, there are numerous and significant species differences that need to be considered. In some cases, the generation of meaningful immunotoxicology data can be adversely affected by the choice of a species that does not adequately share the immune function of concern with man. Likewise immunotoxicology testing in one species may produce negative data in one species but positive data in another. Knowing the mechanistic basis through an understanding of species differences in the structure and function of the immune system is pivotal to success. This becomes especially true as pharmaceutical companies design and develop highly specific immunomodulatory molecules that demonstrate species-specific pharmacology. This review is an exploration of various species differences in the structure and function of the immune system and an attempt to identify those differences that may be important in the conduct of immunotoxicity tests.

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.

Recent developments in diisocyanate asthma

OBJECTIVE

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

DATA SOURCES

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

STUDY SELECTION

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

RESULTS

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

CONCLUSIONS

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

Occupational asthma: a valid model for adult asthma?

PURPOSE OF REVIEW

Developments in the understanding of causes and natural history of occupational asthma may allow improved primary, secondary and tertiary preventive strategies for occupational asthma. This may also lead to improved understanding of preventable contributing factors to the development and severity of nonoccupational asthma.

RECENT FINDINGS

Animal studies have demonstrated the opportunity to identify chemical sensitizers relevant to asthma. Studies of genetic markers in occupational asthma pose logistic difficulties, but preliminary studies suggest that glutathione S-transferase genotypes may predispose to development of occupational asthma induced by diisocyanates and these have also been implicated in nonoccupational asthma. Some occupational sensitizers/irritants are also found outside the workplace and may be relevant in nonoccupational asthma, for example cleaning agents, epoxy glues, hairdressing products. Accidental exposures to high concentrations of respiratory irritants have the potential to induce new asthma as well as aggravate underlying asthma in both occupational and nonoccupational settings.

SUMMARY

Better understanding of the pathogenesis of occupational asthma is important for affected workers, and also has potential relevance for nonoccupational asthma.

Toxicology of toluene diisocyanate

In studies on animals, toluene diisocyanate (TDI) was a contact and respiratory sensitizer, was not toxic by the oral or dermal routes, but was irritating, and toxic by inhalation. The respiratory tract was the target in acute, subchronic, and chronic exposure studies. Typically, at concentrations of above 0.1 ppm (parts per million), clinical signs of nasal irritation were evident, and histopathological investigations revealed rhinitis and epithelial hyperplasia of nasal passages. With increasing concentration, effects were more severe; affected the larynx, trachea, and lung; and, eventually, affected body weight and survival. The carcinogenicity of TDI to rats and mice was investigated. By inhalation, there was no treatment-related increase in tumor incidence in either species at the highest concentration tested (0.15 ppm). Effects of TDI were seen as rhinitis in nasal turbinates of both species, and as reduced body weight gain in mice. Through oral administration of TDI dissolved in corn oil to rats and mice (up to 120 mg/kg/day), increased incidence of a number of tumor types was seen. This route is of questionable relevance to occupational exposure. The dosing solutions were known to have degraded, and TDI would hydrolyze to diaminotoluene in the acidic stomach environment. Several in vitro tests for genotoxicity gave positive results, which can be ascribed to degradation of TDI by solvents. In properly conducted assays, in vivo TDI was negative for genotoxicity. In a two-generation reproduction study in rats, there were no effects on reproductive indices at the highest exposure concentration of 0.3 ppm TDI, which elicited toxicity in both generations. In a developmental toxicity study in rats, there was evidence of minimal fetotoxicity in the presence of maternal toxicity at 0.5 ppm, with no effects at 0.1 ppm. No treatment-related embryotoxicity or teratogenicity was observed.

Role of tumor necrosis factor in toluene diisocyanate asthma

Nearly 9 million workers are exposed to chemical agents associated with occupational asthma, with isocyanates representing the chemical class most responsible. Isocyanate-induced asthma has been difficult to diagnose and control, in part because the biologic mechanisms responsible for the disease and the determinants of exposure have not been well defined. Isocyanate-induced asthma is characterized by airway inflammation, and we hypothesized that inflammation is a prerequisite of isocyanate-induced asthma, with tumor necrosis factor (TNF)-alpha being critical to this process. To explore this hypothesis, wild-type mice, athymic mice, TNF-alpha receptor knockout (TNFR), and anti-TNF-alpha antibody-treated mice were sensitized by subcutaneous injection (20 micro l on Day 1; 5 micro l, Days 4 and 11), and challenged 7 d later by inhalation (100 ppb; Days 20, 22, and 24) with toluene diisocyanate (TDI). Airway inflammation, goblet cell metaplasia, epithelial cell damage, and nonspecific airway reactivity to methacholine challenge, measured 24 h following the last challenge, were reduced to baseline levels in TNF-alpha null mice and athymic mice. TNF-alpha deficiency also markedly abrogated TDI-induced Th2 cytokines in airway tissues, indicating a role in the development of Th2 responses. Despite abrogation of all indicators of asthma pathology, TNF-alpha neutralization had no effect on serum IgE levels or IgG-specific TDI antibodies, suggesting the lack of importance of a humoral response in the manifestation of TDI-induced asthma. Instillation studies with fluorescein-conjugated isothiocyanate and TDI suggested that TNF-alpha deficiency also resulted in a significant reduction in the migration of airway dendritic cells to the draining lymph nodes. Taken together, these results suggest that, unlike protein antigens, TNF-alpha has multiple and central roles in TDI-induced asthma, influencing both nonspecific inflammatory processes and specific immune events.

Hapten-induced hypersensitivity reactions in the airways: atopic versus non-atopic

Hypersensitivity reactions induced by low molecular weight compounds are investigated extensively in the skin. However, these reactions can also occur in the lungs of previously sensitized individuals after local airway challenge. This hapten-induced pulmonary hypersensitivity reaction resembles features observed in asthmatic patients, such as bronchial hyperreactivity, accumulation of inflammatory cells, and airway edema. We review data that hapten-induced hypersensitivity reactions in mouse airways can be models for both atopic and non-atopic asthma associated with low molecular weight compounds.

A novel mouse model of diisocyanate-induced asthma showing allergic-type inflammation in the lung after inhaled antigen challenge

BACKGROUND

Exposure to diisocyanates, a group of highly reactive, low-molecular-weight compounds, is a major cause of occupational asthma. In contrast to mouse models of atopic asthma, previous mouse models of diisocyanate-induced asthma have failed to show lung inflammation with characteristics of human disease.

OBJECTIVE

Our goal was to establish a novel mouse model of diisocyanate-induced asthma in which lung inflammation reminiscent of that seen in human asthma is generated after inhaled antigen challenge.

METHODS

BALB/c mice were epicutaneously sensitized to hexamethylene diisocyanate (HDI) and then challenged with an HDI-protein conjugate administered by means of an intranasal droplet.

RESULTS

HDI sensitization resulted in development of contact hypersensitivity and HDI-specific antibody production. Most importantly, however, vigorous inflammatory responses with characteristics of human asthma were generated in the lung after inhaled HDI challenge. Challenge of sensitized, but not unsensitized, mice resulted in airway eosinophilia, mucus hypersecretion, and production of T(H)1-type (IFN-gamma) and T(H)2-type (IL-4, IL-5, and IL-13) cytokines by lung inflammatory cells. Despite the mixed T(H)1/T(H)2 response induced by HDI sensitization, use of cytokine-deficient mice revealed that airway eosinophilia was mediated by T(H)2 cytokines and not by IFN-gamma.

CONCLUSION

We report a novel mouse model of diisocyanate-induced asthma that, in contrast to previous models, demonstrates antigen-induced lung inflammation with characteristics of human disease. This model will allow investigation of the immunopathogenesis of diisocyanate-induced asthma and should provide insight into this common form of occupational disease.