PURPOSE:Exposure to low concentrations of toluene diisocyanate (TDI) leads to immune-mediated chemical-induced asthma. The role of the adaptive immune system has already been thoroughly investigated; nevertheless, the involvement of innate immune cells in the pathophysiology of chemical-induced asthma is still unresolved. The aim of the study is to investigate the role of innate lymphoid cells (ILCs) and dendritic cells (DCs) in a mouse model for chemical-induced asthma.METHODS:On days 1 and 8, BALB/c mice were dermally treated (20 μL/ear) with 0.5% TDI or the vehicle acetone olive oil (AOO; 2:3). On days 15, 17, 19, 22 and 24, the mice received an oropharyngeal challenge with 0.01% TDI or AOO (1:4). One day after the last challenge, airway hyperreactivity (AHR) to methacholine was assessed, followed by an evaluation of pulmonary inflammation and immune-related parameters, including the cytokine pattern in bronchoalveolar lavage fluid, lymphocyte subpopulations of the lymph nodes and their ex vivo cytokine production profile, blood immunoglobulins and DC and ILC subpopulations in the lungs.RESULTS:Both DC and ILC2 were recruited to the lungs after multiple airway exposures to TDI, regardless of the prior dermal sensitization. However, prior dermal sensitization with TDI alone results in AHR and predominant eosinophilic airway inflammation, accompanied by a typical type 2 helper T (Th2) cytokine profile.CONCLUSIONS:TDI-induced asthma is mediated by a predominant type 2 immune response, with the involvement of adaptive Th2 cells. However, from our study we suggest that the innate ILC2 cells are important additional players in the development of TDI-induced asthma.

Allergic asthma is a highly prevalent inflammatory disease of the lower airways, clinically characterized by airway hyperreactivity and deterioration of airway function. Immunomodulatory probiotic bacteria are increasingly being explored to prevent asthma development, alone or in combination with other treatments. In this study, wild-type and recombinant probiotic Lactobacillus rhamnosus GR-1 were tested as preventive treatment of experimental allergic asthma in mice. Recombinant L. rhamnosus GR-1 was designed to produce the major birch pollen allergen Bet v 1, to promote allergen-specific immunomodulation. Administration of wild-type and recombinant L. rhamnosus GR-1 prevented the development of airway hyperreactivity. Recombinant L. rhamnosus GR-1 also prevented elevation of airway total cell counts, lymphocyte counts and lung IL-1β levels, while wild-type L. rhamnosus GR-1 inhibited airway eosinophilia. Of note, a shift in gut microbiome composition was observed after asthma development, which correlated with the severity of airway inflammation and airway hyperreactivity. In the groups that received L. rhamnosus GR-1, this asthma-associated shift in gut microbiome composition was not observed, indicating microbiome-modulating effects of this probiotic. These data demonstrate that L. rhamnosus GR-1 can prevent airway function deterioration in allergic asthma. Bet v 1 expression by L. rhamnosus GR-1 further contributed to lower airway inflammation, although not solely through the expected reduction in T helper 2-associated responses, suggesting involvement of additional mechanisms. The beneficial effects of L. rhamnosus GR-1 correlate with increased gut microbiome resilience, which in turn is linked to protection of airway function, and thus further adds support to the existence of a gut-lung axis.

Background: Exposure to diisocyanates is an important cause of occupational asthma (OA) in the industrialized world. Since OA occurs after long-term exposure to diisocyanates, we developed a chronic mouse model of chemical-induced asthma where toluene diisocyanate (TDI) was administered at two different exposure sites. Objectives: Evaluating the effect of long-term respiratory isocyanate exposure - with or without prior dermal exposure- on sensitization, inflammatory responses and airway hyperreactivity (AHR). Methods: On days 1 and 8, BALB/c mice were dermally treated (20 mu 1/ear) with 0.5% 2,4-toluene diisocyanate TDI or the vehicle acetone olive oil (AOO) (3:2). Starting from day 15, mice received intranasal instillations with 0.1% TDI of vehicle five times in a week, for five successive weeks. One day after the last instillation airway hyperreactivity (AHR) to methacholine was assessed, followed by an evaluation of pulmonary inflammation and structural lung changes. Immune-related parameters were assessed in the lungs (BAL and tissue), blood, cervical-and auricular lymph nodes. Results: Mice repeatedly intranasally exposed to TDI showed systemic sensitization and a mixed Th1/Th2 type immune response, without the presence of AHR. However, when mice are first dermally sensitized with TDI, followed by repeated intranasal TDI challenges, this results in a pronounced Th2 response and AHR. Conclusion: Dermal exposure to TDI determines airway hyperreactivity after repeated airway exposure to TDI.

BACKGROUND:Pulmonary function measurements are important when studying respiratory disease models. Both resistance and compliance have been used to assess lung function in mice. Yet, it is not always clear how these parameters relate to forced expiration (FE)-related parameters, most commonly used in humans. We aimed to characterize FE measurements in four well-established mouse models of lung diseases.METHOD:Detailed respiratory mechanics and FE measurements were assessed concurrently in Balb/c mice, using the forced oscillation and negative pressure-driven forced expiration techniques, respectively. Measurements were performed at baseline and following increasing methacholine challenges in control Balb/c mice as well as in four disease models: bleomycin-induced fibrosis, elastase-induced emphysema, LPS-induced acute lung injury and house dust mite-induced asthma.RESULTS:Respiratory mechanics parameters (airway resistance, tissue damping and tissue elastance) confirmed disease-specific phenotypes either at baseline or following methacholine challenge. Similarly, lung function defects could be detected in each disease model by at least one FE-related parameter (FEV0.1, FEF0.1, FVC, FEV0.1/FVC ratio and PEF) at baseline or during the methacholine provocation assay.CONCLUSIONS:FE-derived outcomes in four mouse disease models behaved similarly to changes found in human spirometry. Routine combined lung function assessments could increase the translational utility of mouse models.

Background While the importance of the Th2 cytokine IL-13 as a central mediator of airway hyperreactivity (AHR) has been described in allergic protein-induced asthma, this has never been investigated in chemical-induced asthma. Objective We examined the importance of IL-13 in a mouse model of chemical-induced AHR, using toluene-2,4-diisocyanate (TDI). Methods In a first set-up, wild type (WT) and IL-13 knockout (KO) C57Bl/6 mice were dermally treated on days 1 and 8 with 1% TDI or vehicle (acetone/olive oil) on both ears. On day 15, mice received an intranasal instillation with 0.1% TDI or vehicle. In a second set-up, WT mice sensitized with 1% TDI or vehicle, received i.v. either anti-IL-13 or control antibody prior to the intranasal challenge. Results TDI-sensitized and TDI-challenged WT mice showed AHR to methacholine, in contrast to TDI-sensitized and TDI-challenged IL-13 KO mice, which also showed lower levels of total serum IgE. TDI-sensitized and TDI-challenged IL-13 KO mice had lower numbers of T-cells in the auricular lymph nodes. TDI-treated WT mice, receiving anti-IL-13, showed no AHR, in contrast to those receiving control antibody, despite increased levels of IgE. Anti-IL-13 treatment in TDI-treated WT mice resulted in lower levels of serum IL-13, but did not induce changes in T- and B-cell numbers, and in the cytokine production profile. Conclusion and clinical relevance We conclude that IL-13 plays a critical role in the effector phase of chemical-induced, immune-mediated AHR. This implicates that anti-IL-13 treatment could have a beneficial effect in patients with this asthma phenotype.

Both 2,4-toluene diisocyanate (TDI) and 4,4-methylene diphenyl diisocyanate (MDI) can cause occupational asthma. In this study, we optimized our mouse model of chemical-induced asthma in the C57Bl/6 mice strain using the model agent TDI. Furthermore, we validated MDI in this mouse model and investigated whether cross-reactivity between TDI and MDI is present. On days 1 and 8, C57Bl/6 mice were dermally treated (20 µl/ear) with 3 % MDI, 2 % TDI or the vehicle acetone olive oil (AOO) (3:2). On day 15, they received a single oropharyngeal challenge with 0.04 % MDI, 0.01 % TDI or the vehicle AOO (4:1). One day later, airway hyperreactivity (AHR) and pulmonary inflammation in the bronchoalveolar lavage (BAL) were assessed. Furthermore, total serum IgE levels, lymphocyte subpopulations in auricular lymph nodes and cytokine levels in supernatants of lymphocytes were measured. Both dermal sensitization with TDI or MDI resulted in increased total serum IgE levels along with T and B cell proliferation in the auricular lymph nodes. The auricular lymphocytes showed an increased release of both Th2 and Th1 cytokines. Mice sensitized and challenged with either TDI or MDI showed AHR, along with a predominant neutrophil lung inflammation. Mice sensitized with MDI and challenged with TDI or the other way around showed no AHR, nor BAL inflammation. Both TDI and MDI are able to induce an asthma-like response in this mouse model. However, cross-reactivity between both diisocyanates remained absent.

Asthma may be induced by chemical sensitisers, via mechanisms that are still poorly understood. This type of asthma is characterised by airway hyperreactivity (AHR) and little airway inflammation. Since potent chemical sensitisers, such as toluene-2,4-diisocyanate (TDI), are also sensory irritants, it is suggested that chemical-induced asthma relies on neuro-immune mechanisms.We investigated the involvement of transient receptor potential channels (TRP) A1 and V1, major chemosensors in the airways, and mast cells, known for their ability to communicate with sensory nerves, in chemical-induced AHR.In vitro intracellular calcium imaging and patch-clamp recordings in TRPA1- and TRPV1-expressing Chinese hamster ovarian cells showed that TDI activates murine TRPA1, but not TRPV1. Using an in vivo model, in which an airway challenge with TDI induces AHR in TDI-sensitised C57Bl/6 mice, we demonstrated that AHR does not develop, despite successful sensitisation, in Trpa1 and Trpv1 knockout mice, and wild-type mice pretreated with a TRPA1 blocker or a substance P receptor antagonist. TDI-induced AHR was also abolished in mast cell deficient Kit(Wsh) (/Wsh) mice, and in wild-type mice pretreated with the mast cell stabiliser ketotifen, without changes in immunological parameters.These data demonstrate that TRPA1, TRPV1 and mast cells play an indispensable role in the development of TDI-elicited AHR.

To evaluate pulmonary function analysis in murine respiratory disease models mostly, airway resistance (Rn) and compliance are used. Here, we aimed to validate FEV and correlate it to changes in Rn and compliance in different mouse models of lung disease and . Using the flexiVent (Scireq, EMKA Technologies), we performed a forced oscillation perturbation to determine airway resistance (Rn), tissue elastance (E) and tissue damping (resistance, G), followed by a negative pressure forced expiration (NPFE), resulting in: FEV0.1, FEF0.1, FVC, PEF and FEV0.1/FVC to determine baseline indicators of disease. Next, airway hyperreactivity was assessed using methacholine (0 to 20 mg/ml), and both Rn and FEV0.1 were measured. The measurements were performed in three asthma models (house dust mite, chemical-induced and ovalbumin), an elastase emphysema model, a bleomycin fibrosis model, an LPS acute lung injury model and compared to healthy control mice. In the lung fibrosis model, mice showed significantly decreased FEV0.1, FEF0.1 and FVC, along with increased H and G. In the emphysema model, mice showed significantly increased FEV0.1 and FVC, along with decreased H and G. The asthma models, showed no change at baseline Rn, but we found a significant decrease in FEV0.1. During the airway hyperreactivity provocation, FEV0.1 significantly decreased, while Rn significantly increased, as expected. FEV0.1 measurements in mice show similarly results as described in human lung function assessment, both as descriptor of disease, as during airway hyperreactivity assessment. Especially for pre-clinical testing in mice, FEV0.1 is a promising alternative for classical airway resistance (Rn) measurements.

Methylisothiazolinone (MI), a widely used chemical preservative in industrial and household products, and cosmetics, has been associated with allergic contact dermatitis. However, the asthmogenic capacity of MI is currently unknown. In this study, we investigated the capacity of MI to elicit asthma-like responses in a validated mouse model. On days 1 and 8, mice (C57Bl/6 and BALB/c) were dermally treated with MI or vehicle on each ear. On day 15, mice received a single intranasal challenge with MI or vehicle. Immediately after the challenge, the early ventilatory response was measured using a double chamber plethysmograph. One day later, airway hyperreactivity, pulmonary inflammation and immune-related parameters were assessed. Dermal treatment with MI in both C57Bl/6 and BALB/c mice induced increased T- and B-cell proliferation in the auricular lymph nodes, along with IFN-γ production and limited increases in total serum IgE, confirming dermal sensitization. An airway challenge with MI led to an early ventilatory response (decreased breathing frequency), indicative for acute sensory irritation. However, 24h later no allergic respiratory response (no airway hyperreactivity (AHR) nor pulmonary inflammation) was found in either mouse strains. Our study indicates that MI can be classified as a strong dermal sensitizer and irritant, but not an asthmogen after initial dermal sensitization, followed by an airway challenge.

A key feature of occupational asthma (OA), the most common work-related lung disease in industrialized countries, is airway hyperresponsiveness (AHR). The importance of the Th2 cytokine IL-13 as a central mediator of AHR has already been described in atopic asthma. Yet, this has never been investigated in OA. Here, we examined the importance of IL-13 in a mouse model of chemical-induced AHR, using toluene-2,4-diisocyanate (TDI) as a known cause of OA. On days 1 and 8, wild type (WT) and IL-13 knockout (KO) C57Bl/6 mice were dermally sensitized with 1% TDI or vehicle (acetone/olive oil) on both ears. On day 15, mice received an intranasal challenge with 0.1% TDI or vehicle. The respiratory frequency was assessed 5 min before (baseline) and 1h after the challenge. Airway reactivity to methacholine, lung inflammation, total serum IgE, lymphocyte subpopulations in the draining auricular lymph nodes and ex vivo cytokine release by stimulated lymphocytes were assessed 24h after the challenge. In both WT and IL-13 KO mice a TDI-challenge evoked an immediate approximate 50% decrease in respiratory frequency, indicative for sensory irritation. Twenty-four hours later, TDI-treated IL-13 KO mice showed a significant lower AHR compared to WT mice, without lung inflammation. TDI-treated IL-13 KO mice showed significantly lower levels of total serum IgE, compared to TDI-treated WT mice. In the auricular lymph nodes of TDI-treated WT and IL-13 KO mice, we found increased T- and B-cell proliferation, compared to controls. Release of IL-4, IL-10 and IFN-γ was significantly lower in TDI-treated IL-13 KO mice, compared to TDI-treated WT mice. These results indicate the importance of IL-13 in immune-mediated chemical-induced AHR.

Chemosensory Transient Receptor Potential (TRP) channels on airway sensory nerves are potential targets for the treatment of chemical-induced respiratory pathologies. Therefore, we examined the role of TRPA1 and TRPV1 in a mouse model of allergic chemical-induced airway hyperresponsiveness (AHR). On days 1 and 8, wild type (WT) C57Bl/6 mice were dermally treated with 1% toluene-2,4-diisocyanate (TDI) or vehicle (acetone/olive oil). On day 15, mice received a single intranasal challenge with 0.1% TDI or vehicle. In a first set-up, these mice received an IP injection of the NK1R antagonist RP67580 , prior to the challenge. In a second set-up, the TDI challenge was replaced by a TRPA1 or TRPV1 agonist challenge. We performed in vitro intracellular calcium imaging experiments using Chinese Hamster Ovarian (CHO) cells, selectively expressing mTRPA1 or mTRPV1. A challenge with TDI evoked a 50% decrease in respiratory frequency immediately after the intranasal challenge, indicative for sensory irritation. One day later, TDI-sensitized and challenged mice showed AHR, without signs of lung inflammation. TDI-treated mice, injected with the NK1R antagonist did not develop AHR, compared to vehicle-injected mice. Replacing the TDI challenge with a specific TRPA1 or TRPV1 agonist did also not induce AHR in TDI-treated mice. The in vitro experiment showed that 0.001% TDI induced an increased calcium influx in mTRPA1-, but not TRPV1-expressing CHO cells. These results indicate an important role for TRP channels in our mouse model. Yet, merely activating TRP channels in the challenge phase is not sufficient to induce AHR, indicating the importance of the allergen-specific challenge.

Occupational asthma is the most common work-related lung disease in industrialized countries. The mechanisms of occupational asthma caused by chemicals are still not completely understood. Therefore, we used a mouse model of chemical-induced asthma to examine the role of the neurogenic system as well as the role of IL-13 and mast cells by using different knock-out mice. On days 1 and 8, wild type C57Bl/6 mice, IL-13, TRP (Transient Receptor Potential) A1, TRPV1 and mast cell deficient mice were dermally sensitized with 1% TDI (toluene-2.4-diisocyanate) or vehicle (acetone/olive oil) on both ears. On day 15, the mice received a single intranasal challenge with 0.1% TDI or vehicle. In a second experiment TDI or vehicle sensitized wild type C57Bl/6 mice received an intraperitoneal injection of the NK1R antagonist RP67580 (1µg/µl) prior to the challenge. Airway reactivity to methacholine, lung inflammation, lymphocyte subpopulations in the draining auricular lymph nodes and total serum IgE were assessed 24h after the challenge. IL-13, TRPV1, TRPA1 and mast cell deficient mice showed a significant lower airway hyperreactivity compared to wild type mice, 24h after TDI challenge, without any sign of lung inflammation. Treatment with the NK1R antagonist also resulted in a significant decrease in airway hyperreactivity. In the auricular lymph nodes T-helper cells, T-cytotoxic cells and B-cells were significantly lower in mast cell deficient and IL-13 deficient mice, compared to wild type mice. These results indicate the importance of IL-13, TRPA1 and TRPV1 channels and mast cells in the development of immune-mediated bronchial hyperreactivity.

Occupational asthma is the most common work-related lung disease in industrialized countries. The mechanisms of occupational asthma caused by chemicals are still not completely understood. Therefore, we used a mouse model of chemical-induced asthma to examine the role of the neurogenic system as well as the role of IL-13 and mast cells by using different knock-out mice. On days 1 and 8, wild type C57Bl/6 mice, IL-13, Transient Receptor Potential (TRP)V1, TRPA1 and mast cell deficient mice were dermally sensitized with 1% toluene-2.4-diisocyanate (TDI) or vehicle (acetone/olive oil) on both ears. On day 15, the mice received a single intranasal challenge with 0.1% TDI or vehicle. In a second experiment TDI or vehicle sensitized wild type C57Bl/6 mice received an intraperitoneal injection of the NK1R antagonist RP67580 (1μg/μl) prior to the challenge. Airway reactivity to methacholine, lung inflammation, lymphocyte subpopulations in the draining auricular lymph nodes and total serum IgE were assessed 24h after the challenge. IL-13, TRPV1, TRPA1 and mast cell deficient mice showed a significant lower airway hyperreactivity compared to wild type mice, 24h after TDI challenge, without any sign of lung inflammation. Treatment with the NK1R antagonist also resulted in a significant decrease in airway hyperreactivity. In the auricular lymph nodes T-helper cells, T-cytotoxic cells and B-cells were significantly lower in mast cell deficient and IL-13 deficient mice, compared to wild type mice. These results indicate the importance of IL-13, TRPA1 and TRPV1 channels and mast cells in the development of immune-mediated bronchial hyperreactivity.

RATIONALE:Airway hyperreactivity (AHR) is a key feature of bronchial asthma, and inhalation of irritants may facilitate development of nonallergic AHR. Swimmers exposed to hypochlorite (ClO(-))-containing water show a higher risk of developing AHR. We developed a mouse model in which instillation of ClO(-) before ovalbumin (OVA) induces AHR without bronchial inflammatory cells.OBJECTIVES:To investigate the mechanisms of ClO(-)-OVA-induced nonallergic AHR.METHODS:The involvement of the transient receptor potential ankyrin (TRPA)1 channel was checked in vivo by the use of TRPA1(-/-) mice and in vitro by Ca(2+) imaging experiments. The role of substance P (SP) was investigated by pretreating animals with the receptor antagonist RP67580, by replacing ClO(-) with SP in vivo, and by immunofluorescent staining of large airways of exposed mice. The role of mast cells was evaluated by exposing mast cell-deficient Kit(Wh)/Kit(Wsh) mice to ClO(-)-OVA with or without mast cell reconstitution.MEASUREMENTS AND MAIN RESULTS:ClO(-)-OVA did not induce AHR in TRPA1(-/-) mice, and ClO(-) generates a Ca(2+) influx in TRPA1-transfected cells. Pretreatment with RP67580 reduces ClO(-)-OVA-induced AHR, although no increased SP expression was shown in the airways. SP-OVA exposure resulted in the same AHR as induced by ClO(-)-OVA. Kit(Wsh)/Kit(Wsh) mice did not develop AHR in response to ClO(-)-OVA unless they were reconstituted with bone marrow-derived mast cells.CONCLUSIONS:Induction of AHR by exposure to ClO(-)-OVA depends on a neuroimmune interaction that involves TRPA1-dependent stimulation of sensory neurons and mast cell activation.

T-lymphocytes and B-lymphocytes are key players in allergic asthma, with B-lymphocytes producing antigen-specific immunoglobulins E (IgE). We used a mouse model of chemical-induced asthma and transferred B-lymphocytes from sensitized animals into naïve wild type mice, B-lymphocyte knock-out (B-KO) mice or severe combined immunodeficiency (SCID) mice. On days 1 and 8, BALB/c mice were dermally sensitized with 0.3% toluene diisocyanate (TDI) (20µl/ear). On day 15, mice were euthanized and the auricular lymph nodes isolated. B-lymphocytes (CD19+) were separated from the whole cell suspension and 175,000 cells were injected in the tail vein of naïve wild type, B-KO or SCID mice. Three days later, the mice received a single oropharyngeal challenge with 0.01% TDI (20µl) or vehicle (acetone/olive oil (AOO)) (controls). Airway reactivity to methacholine and total and differential cell counts in the bronchoalveolar lavage (BAL) fluid were measured 24 hours after challenge. B-lymphocytes of AOO or TDI-sensitized mice were characterized for the expression of surface markers and production of cytokines. We found that transfer of B-cells obtained from mice dermally sensitized to toluene diisocyanate (TDI) into naïve wild type mice, B-KO mice or SCID mice led, within three days, to an acute asthma-like phenotype after an airway challenge with TDI. This response was specific and independent of IgE. These B-lymphocytes showed antigen presenting capacities (CD80/CD86 and CD40) and consisted of B effector (Be)2- (IL-4) and Be1-lymphocytes (IFN-γ). The transferred B-lymphocytes were visualized near large airways, 24 hours after TDI challenge. Thus, B-lymphocytes can provoke an asthmatic response without the action of T-lymphocytes and without major involvement of IgE.