Skin Exposure Contributes to Chemical-Induced Asthma: What is the Evidence? A Systematic Review of Animal Models

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.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Endotypes of occupational asthma

PURPOSE OF REVIEW

To describe recent findings in endotyping occupational asthma by addressing the role of specific biomarkers.

RECENT FINDINGS

Studies on occupational asthma endotypes have focused on immune and inflammatory patterns associated with different occupational exposures to sensitizers or irritants.Sputum neutrophilia has been found in 58.5% patients with occupational asthma caused by high molecular weight (HMW) agents, and work-related dysphonia in patients with occupational asthma was described as associated with sputum neutrophilia too. Neutrophils have been associated also with irritant-induced asthma. The measurement of specific IgE has been confirmed as a valuable diagnostic tool in occupational asthma caused by HMW agents, on the contrary, for most low-molecular-weight agents, the presence of specific IgE has been proven in a small subset of affected workers. Fractional exhaled nitric oxide has been confirmed as a marker of type 2 (T2) inflammation in occupational asthma, mostly when induced by HMW agents (e.g. flour), and it has proved to be more sensitive than spirometry in measuring the efficacy of an intervention.MicroRNA-155 has been shown to contribute to airway inflammation in occupational asthma induced by toluene diisocyanate.

SUMMARY

Occupational asthma is heterogeneous, thus monitoring multiple biomarkers is crucial to understand, which inflammatory responses are prevalent.

The IL-31/TRPV1 pathway mediates allergic asthma exacerbated by DINP dermal exposure in OVA-sensitized Balb/c mice

BACKGROUND

The potential role of dermal exposure diisononyl phthalate (DINP) as an adjuvant in allergic inflammation and asthma has been suggested. However, the current findings do not provide enough evidence to support this claim.

OBJECTIVES

The purpose of this investigation was to examine the impact and mechanisms of allergic asthma exacerbation through the dermal exposure to DINP.

METHODS

The study was undertaken using OVA-sensitized mice. Lung histopathology and airway hyperreactivity (AHR) were assessed. Expression levels of immunoglobulins (t-IgE, OVA-IgE and OVA-IgG1), cytokines (IL-31, IL-4, IL-5, IL-6, IL-13 and INF-γ), and TRPV1 were measured. To investigate the mechanism by which allergic asthma worsens due to dermal exposure to DINP, the blockade analysis using the IL-31 antagonist SB-431542 and the TRPV1 antagonist capsazepine (CZP) were performed.

RESULTS

The findings of the study revealed that the simultaneous exposure to DINP and OVA resulted in an increase in inspiratory resistance (Ri) and expiratory resistance (Re), a decrease in the minimum value of lung dynamic compliance (Cldyn), and worsened airway remodeling. Additionally, it was found that this exposure led to an increase in the levels of IL-31 and TRPV1, which are biomarkers of Th2 cytokines (IL-4, IL-5, IL-6, and IL-13), as well as immunoglobulins (Total IgE, OVA-lgE, and OVA-IgG1), while decreasing the biomarker of Th1 cytokines (IFN-γ). However, these impairments showed improvement after the administration of SB-431542 or CZP.

CONCLUSION

The findings of this research indicate that the IL-31/TRPV1 pathway plays a moderating function in OVA-induced allergic asthma worsened by dermal exposure to DINP.

Risk assessment of the asthma-induction potential of substances in spray products for car cabin detailing - based on EU's Chemical Agents Directive, using harmonised classifications and quantitative structure-activity relationship (QSAR)

Exposure to spray-formulated products for car cabin detailing is a potential risk for asthma induction. With a focus on the asthma-related endpoints sensitisation and irritation of the lungs, we performed an occupational risk assessment based on requirements in the EU Chemical Agents Directive. We identified 71 such spray products available in Denmark. We identified ingredient substances in safety data sheets and screened for harmonised classifications of respiratory sensitisation and airway irritation. For respiratory sensitisation, we also applied quantitative structure-activity relationship (QSAR). We modelled the exposure during 15 min of work inside a car cabin, and determined the risk ratio of the products by further applying occupational exposure limits - mainly derived no-effect levels (DNELs) from the European Chemicals Agency (ECHA) set on respiratory irritation. Four substances had a harmonised classification for respiratory irritation (bronopol, 2-phenoxyethanol, 2-methoxypropanol, and butan-1-ol). Seven substances were positive in the QSAR model for respiratory sensitisation (monoethanolamine, bronopol, glycerol, methyl salicylate, benzoic acid, ammonium benzoate, and sodium benzoate). Two vinyl treatment products had a risk ratio > 1 based on the level of sodium benzoate and its DNEL set on respiratory irritation. Two products had risk ratios of 0.69 and 0.73, respectively, based on 2-methyl-2 H-isothiazol-3-one and its acute DNEL set on respiratory irritation. In conclusion, 10 substances that may pose a risk for asthma induction were identified in the products. Two of the 71 products had a risk ratio > 1, meaning they may pose an asthma-induction risk in the modelled exposure scenario and using respiratory irritation DNELs from ECHA.

Diagnostics and Prevention of Occupational Allergy in Hairdressers

PURPOSE OF REVIEW

This study aims to provide an overview on current knowledge on occupational allergic diseases in hairdressers and up-to-date perspectives of prevention.

RECENT FINDINGS

Hand eczema (dermatitis) is common in hairdressers, often caused by contact allergy to one or multiple small molecules (haptens) used, e.g., for dyeing, bleaching, and waving/relaxing or by ancillary substances such as preservatives. Hairdressers, compared to other patch-tested patients, have an up to fivefold increased risk to be found sensitized, e.g., against p-phenylenediamine, ammonium persulfate, and glyceryl thioglycolate. Some of these small molecules may induce respiratory sensitization causing allergic rhinitis and/or asthma, notably persulfate salts. Occupational hazards in hairdressing are well described. This knowledge needs to be put into use for risk reduction, mainly by substitution of allergenic ingredients by less allergenic ones, education, and use of ventilation and suitable single-use gloves.

Evidential requirements for the regulatory hazard and risk assessment of respiratory sensitisers: methyl methacrylate as an example

This review addresses the need for a framework to increase the consistency, objectivity and transparency in the regulatory assessment of respiratory sensitisers and associated uncertainties. Principal issues are considered and illustrated through a case study (with methyl methacrylate). In the absence of test methods validated for regulatory use, formal documentation of the weight-of-evidence for hazard classification both at the level of integration of individual studies within lines of evidence and across a broad range of data streams was agreed to be critical for such a framework. An integrated approach is proposed to include not only occupational studies and clinical evidence for the regulatory assessment of respiratory sensitisers, but also information on structure and physical and chemical factors, predictive approaches such as structure activity analysis and in vitro and in vivo mechanistic and toxicokinetic findings. A weight-of-evidence protocol, incorporating integration of these sources of data based on predefined considerations, would contribute to transparency and consistency in the outcome of the assessment. In those cases where a decision may need to be taken on the basis of occupational findings alone, conclusions should be based on transparent weighting of relevant data on the observed prevalence of occupational asthma in various studies taking into account all relevant information including the range and nature of workplace exposures to the substance of interest, co-exposure to other chemicals and study quality.

Occupational Asthma Caused by Low-Molecular-Weight Chemicals Associated With Contact Dermatitis: A Retrospective Study

BACKGROUND

Occupational asthma (OA) may have different etiologies, but it is not clear whether the etiologic agents influence the clinical presentation, especially the co-occurrence of skin lesions.

OBJECTIVE

To determine the impact of different asthmagens on the characteristics of OA, with a focus on the occurrence of prior or concomitant skin disorders.

METHODS

In a retrospective analysis of patients who visited the Occupational and Environmental Disease Clinic of a tertiary referral hospital from 2009 to 2019, we classified patients into definite, probable, or possible OA according to prespecified diagnostic guidelines. In multivariate logistic regression with sensitivity analysis, we examined the relation of high- and low-molecular-weight (HMW and LMW) agents with the clinical presentation.

RESULTS

Of 209 cases of OA, 66 were caused by HMW agents and 143 by LMW agents. Patients with OA exposed to LMW agents had higher odds of having (had) allergic contact dermatitis (odds ratio, 5.45 [1.80-23.70]; P < .01), compared with patients exposed to HMW agents. Conversely, HMW agents were associated with higher odds of rhinitis symptoms (odds ratio of LMW/HMW, 0.33 [0.17-0.63]; P < .001) and high total IgE (odds ratio of LMW/HMW, 0.35 [0.17-0.70]; P < .01). Risk factors for having coexisting contact dermatitis included construction work, hairdressing, and exposure to metals or epoxy resins.

CONCLUSIONS

Among patients with OA, exposure to specific LMW agents was associated with a high frequency of contact dermatitis. Different types of asthmagens within HMW or LMW agents appear to determine the phenotype and comorbidity of OA.

Assessment of personal inhalation and skin exposures to polymeric methylene diphenyl diisocyanate during polyurethane fabric coating

Methylene diphenyl diisocyanate (MDI) monomers and polymeric MDI (pMDI) are aromatic isocyanates widely used in the production of polyurethanes. These isocyanates can cause occupational asthma, hypersensitivity pneumonitis, as well as contact dermatitis. Skin exposure likely contributes toward initial sensitization but is challenging to monitor and quantitate. In this work, we characterized workers' personal inhalation and skin exposures to pMDI in a polyurethane fabric coating factory for subsequent health effect studies. Full-shift personal and area air samples were collected from eleven workers in representative job areas daily for 1-2 weeks. Skin exposure to hands was evaluated concomitantly with a newly developed reagent-impregnated cotton glove dosimeter. Samples were analyzed for pMDI by liquid chromatography-tandem mass spectrometry. In personal airborne samples, the concentration of 4,4'-MDI isomer, expressed as total NCO, had a geometric mean (GM) and geometric standard deviation (GSD) of 5.1 and 3.3 ng NCO/m3, respectively (range: 0.5-1862 ng NCO/m3). Other MDI isomers were found at much lower concentrations. Analysis of 4,4'-MDI in the glove dosimeters exhibited much greater exposures (GM: 10 ng/cm2) and substantial variability (GSD: 20 ng NCO/cm2; range: 0-295 ng NCO/cm2). MDI inhalation exposure was well below occupational limits for MDI for all the job areas. However, MDI skin exposure to hands was substantial. These findings demonstrated the potential for substantial isocyanate skin exposure in work settings with very low airborne levels. This exposure characterization should inform future studies that aim to assess the health effects of work exposures to MDI and the effectiveness of protective measures.

A comprehensive summary of disease variants implicated in metal allergy

Allergic disease represents one of the most prominent global public health crises of the 21^st century. Although many different substances are known to produce hypersensitivity responses, metals constitute one of the major classes of allergens responsible for a disproportionately large segment of the total burden of disease associated with allergy. Some of the most prevalent forms of metal allergy - including allergic contact dermatitis - are well-recognized; however, to our knowledge, a comprehensive review of the many unique disease variants implicated in human cases of metal allergy is not available within the current scientific literature. Consequently, the main goal in composing this review was to (1) generate an up-to-date reference document containing this information to assist in the efforts of lab researchers, clinicians, regulatory toxicologists, industrial hygienists, and other scientists concerned with metal allergy and (2) identify knowledge gaps related to disease. Accordingly, an extensive review of the scientific literature was performed - from which, hundreds of publications describing cases of metal-specific allergic responses in human patients were identified, collected, and analyzed. The information obtained from these articles was then used to compile an exhaustive list of distinctive dermal/ocular, respiratory, gastrointestinal, and systemic hypersensitivity responses associated with metal allergy. Each of these disease variants is discussed briefly within this review, wherein specific metals implicated in each response type are identified, underlying immunological mechanisms are summarized, and major clinical presentations of each reaction are described.Abbreviations: ACD: allergic contact dermatitis, AHR: airway hyperreactivity, ASIA: autoimmune/ autoinflammatory syndrome induced by adjuvants, BAL: bronchoalveolar lavage, CBD: chronic beryllium disease, CTCL: cutaneous T-cell lymphoma, CTL: cytotoxic T-Lymphocyte, DRESS: drug reaction with eosinophilia and systemic symptoms, GERD: gastro-esophageal reflux disease, GI: gastrointestinal, GIP: giant cell interstitial pneumonia, GM-CSF: granulocyte macrophage-colony stimulating factor, HMLD: hard metal lung disease, HMW: high molecular weight, IBS: irritable bowel syndrome, Ig: immunoglobulin, IL: interleukin, LMW: low molecular weight, PAP: pulmonary alveolar proteinosis, PPE: personal protective equipment, PRR: pathogen recognition receptor, SLE: systemic lupus erythematosus, SNAS: systemic nickel allergy syndrome, Th: helper T-cell, UC: ulcerative colitis, UV: ultraviolet.

Respiratory toxicity of persulphate salts and their adverse effects on airways in hairdressers: a systematic review

Objective

To review the literature on respiratory effects of persulfate salts (PS) or hair bleaches in hairdressers and animal models exploring mechanisms behind PS-induced asthma.

Methods

A systematic review according to the PRISMA guidelines was performed. Studies published from 2000 to July 2021 that fulfilled predefined eligibility criteria were retrieved. Data were not quantitatively synthesized due to the heterogeneity of study designs, outcomes and methods.

Results

Forty-two articles were included. PS are indicated as the main cause of occupational rhinitis and asthma in hairdressers, and one of the leading causes of occupational asthma in some European countries. Bleaching products are indicated as the most important factor for development of respiratory symptoms, lung function decline, and leaving the hairdressing profession. Risk estimates from a good quality prospective study showed up to 3.9 times higher risk for wheezing and breathlessness in hairdressers aged ≥ 40 years than in matched controls, and 20 times higher risk in hairdressers to develop respiratory symptoms from exposure to bleaching powder than controls. Pathophysiological mechanisms of the respiratory response to PS are not yet fully elucidated, but may include non-specific and specific immune responses.

Conclusions

Hairdressing is associated with a wide spectrum of respiratory adverse effects, of which bleaching products were indicated as the most hazardous. Preventive measures for reducing inhalatory exposure to PS in hair salons should be re-evaluated, including adopting occupational exposure limits at EU level, and encouraging use of safer bleach formulations.

PROSPERO registration number

CRD42021238118.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00420-022-01852-w.

Enzymes and sensitization via skin exposure: A critical analysis

Some proteins, including enzymes, can induce allergic sensitization of various types, including allergic sensitization of the respiratory tract. There is now an increased understanding of the role that the skin plays in the development of IgE-mediated allergy and this prompts the question whether topical exposure to enzymes used widely in consumer cleaning products could result in allergic sensitization. Here, the evidence that proteins can interact with the skin immune system and the way they do so is reviewed, together with a consideration of the experience gained over decades of the use of enzymes in laundry and cleaning products. The conclusion drawn is that although transcutaneous sensitization to proteins can occur (typically through compromised skin) resulting in IgE antibody-mediated allergy, in practice such skin contact with enzymes used in laundry and cleaning products does not appear to pose a significant risk of allergic disease. Further, the evidence summarized in this publication support the view that proteins do not pose a risk of allergic contact dermatitis.

Occupational Exposure to Diisocyanates in the European Union

Objectives

Diisocyanates are a chemical group that are widely used at workplaces in many sectors. They are also potent skin- and respiratory sensitizers. Exposure to diisocyanates is a main cause of occupational asthma in the European Union. To reduce occupational exposure to diisocyanates and consequently the cases of diisocyanate-induced asthma, a restriction on diisocyanates was recently adopted under the REACH Regulation in the European Union.

Methods

A comprehensive evaluation of the data on occupational exposure to the most important diisocyanates at workplaces was made and is reported here. The diisocyanates considered are methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI), and hexamethylene diisocyanate (HDI), accounting for more than 95% of the market volume in the EU. The exposure assessment is based on data from Chemical Safety Reports (CSRs) of REACH Registration Dossiers, workplace air monitoring data from Germany, from the UK Health and Safety Executive (HSE), and literature data relevant for the EU, and the USA.

Results

Occupational exposure to diisocyanates is particularly relevant in: (i) C.A.S.E. applications (Coatings, Adhesives, Sealants, Elastomers), (ii) production of polyurethanes (PUs) (e.g. slab-stock foam), (iii) handling of partly uncured PU products (e.g. cutting, demoulding, spray application of foam), and (iv) when diisocyanates/PUs are heated (e.g. hot lamination, foundry applications/casting forms). Ranking of the reported data on inhalation to diisocyanate exposure at workplaces (maximum values) leads to following order: (i) HDI and its oligomers in coatings, (ii) MDI in spray foam applications, (iii) TDI in manufacture of foam, (iv) TDI in manufacture of PUs and PU composite materials, (v) TDI in adhesives, (vi) MDI in adhesives, (vii) MDI in manufacture of PUs and PU composite materials, (viii) TDI in coatings, (ix) MDI in manufacture of foam, and (x) HDI in adhesives.

Classification of chemicals as respiratory allergens based on human data: Requirements and practical considerations

Occupational asthma is an important health problem that can include exacerbation of existing asthma, or induce new asthma either through allergic sensitisation, or non-immunological mechanisms. While allergic sensitisation of the respiratory tract can be acquired to proteins, or to low molecular weight chemicals (chemical respiratory allergens) this article is on the latter exclusively. Chemical respiratory allergy resulting in occupational asthma is associated with high levels of morbidity and there is a need, therefore, that chemicals which can cause sensitisation of the respiratory tract are identified accurately. However, there are available no validated, or even widely accepted, predictive test methods (in vivo, in vitro or in silico) that have achieved regulatory acceptance for identifying respiratory sensitising hazards. For this reason there is an important reliance on human data for the identification of chemical respiratory allergens, and for distinguishing these from chemicals that cause occupational asthma through non-immunological mechanisms. In this article the reasons why it is important that care is taken in designating chemicals as respiratory allergens are reviewed. The value and limitations of human data that can aid the accurate identification of chemical respiratory allergens are explored, including exposure conditions, response characteristics in specific inhalation challenge tests, and immunological investigations.

Involvement of Innate Lymphoid Cells and Dendritic Cells in a Mouse Model of Chemical-induced Asthma

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.

The Risk of Psoriasis in Patients With Allergic Diseases: A Nationwide Population-based Cohort Study

The spectrum of allergic diseases includes atopic dermatitis (AD), allergic rhinitis (AR), and asthma. To date, the association between allergic diseases and psoriasis has not yet been completely evaluated. This study was conducted to determine the risk of psoriasis in patients with allergic diseases. A health screening database, a sub-dataset of the Korean National Health Insurance Service database, was used. All 9,718,722 subjects who underwent health examination in 2009 at age over 20 were included. Subjects with allergic diseases including AD (n = 35,685), AR (n = 1,362,713), asthma (n = 279,451) and control subjects without all three allergic diseases (n = 8,210,042), without AD (n = 9,683,037), without AR (n = 8,356,009) and without asthma group (n = 9,439,271) were analyzed. The subjects were tracked using their medical records during the 8-year period from 2010 to 2017 to identify those who developed psoriasis. Multivariate Cox regression models were used to assess the risk of psoriasis. The incidence probability of psoriasis was analyzed through the Kaplan–Meier method. The incidence of psoriasis per 1,000 person-years was 9.57, 3.78, and 4.28 in the AD, AR, and asthma groups, respectively. The AD group exhibited a significantly increased risk of developing psoriasis compared to subjects without AD (hazard ratio [HR], 3.18; 95% confidence interval [95% CI], 3.05–3.31; P < 0.001) after adjustment for confounding factors. The risk of psoriasis was significantly increased in the AR group compared to subjects without AR (HR, 1.32; 95% CI, 1.31–1.34; P < 0.001) and asthma group compared to subjects without asthma (HR, 1.30; 95% CI, 1.27–1.33; P < 0.001). Allergic diseases, particularly AD, may be a risk factor for psoriasis.

Cobalt exposure via skin alters lung immune cells and enhances pulmonary responses to cobalt in mice

Cobalt has been associated with allergic contact dermatitis and occupational asthma. However, the link between skin exposure and lung responses to cobalt is currently unknown. We investigated the effect of prior dermal sensitization to cobalt on pulmonary physiological and immunological responses after subsequent challenge with cobalt via the airways. BALB/c mice received epicutaneous applications (25 μL/ear) with 5% CoCl_2*6H₂O (Co) or the vehicle (Veh) dimethyl sulfoxide (DMSO) twice; they then received oropharyngeal challenges with 0.05% CoCl_2*6H₂O or saline five times, thereby obtaining four groups: Veh/Veh, Co/Veh, Veh/Co, and Co/Co. To detect early respiratory responses noninvasively, we performed sequential in vivo microcomputed tomography (µCT). One day after the last challenge, we assessed airway hyperreactivity (AHR) to methacholine, inflammation in bronchoalveolar lavage (BAL), innate lymphoid cells (ILCs) and dendritic cells (DCs) in the lungs, and serum IgE. Compared with the Veh/Veh group, the Co/Co group showed increased µCT-derived lung response, increased AHR to methacholine, mixed neutrophilic and eosinophilic inflammation, elevated monocyte chemoattractant protein-1 (MCP-1), and elevated keratinocyte chemoattractant (KC) in BAL. Flow cytometry in the Co/Co group demonstrated increased DC, type 1 and type 2 conventional DC (cDC1/cDC2), monocyte-derived DC, increased ILC group 2, and natural cytotoxicity receptor^-ILC group 3. The Veh/Co group showed only increased AHR to methacholine and elevated MCP-1 in BAL, whereas the Co/Veh group showed increased cDC1 and ILC2 in lung. We conclude that dermal sensitization to cobalt may increase the susceptibility of the lungs to inhaling cobalt. Mechanistically, this enhanced susceptibility involves changes in pulmonary DCs and ILCs.