Biological effects of inhaled crude oil. VI. Immunotoxicity.

Crude oil is an unrefined petroleum product that is a mixture of hydrocarbons and other organic material. Studies on the individual components of crude oil and crude oil exposure itself suggest it has immunomodulatory potential. As investigations of the immunotoxicity of crude oil focus mainly on ingestion and dermal exposure, the effects of whole-body inhalation of 300 ppm crude oil vapor [COV; acute inhalation exposure: (6 h × 1 d); or a 28 d sub-chronic exposure (6 h/d × 4 d/wk. × 4 wks)] was investigated 1, 28, and 90 d post-exposure in Sprague-Dawley rats. Acute exposure increased bronchoalveolar lavage (BAL) fluid cellularity, CD4+ and CD8+ cells, and absolute and percent CDllb+ cells only at 1 d post-exposure; additionally, NK cell activity was suppressed. Sub-chronic exposure resulted in a decreased frequency of CD4+ T-cells at 1 d post-exposure and an increased number and frequency of B-cells at 28 d post-exposure in the lung-associated lymph nodes. A significant increase in the number and frequency of B-cells was observed in the spleen at 1 d post-exposure; however, NK cell activity was suppressed at this time point. No effect on cellularity was identified in the BALF. No change in the IgM response to sheep red blood cells was observed. The findings indicate that crude oil inhalation exposure resulted in alterations in cellularity of phenotypic subsets that may impair immune function in rats.

The Respiratory Environment Diverts the Development of Antiviral Memory CD8 T Cells.

Our understanding of memory CD8+ T cells has been largely derived from acute, systemic infection models. However, memory CD8+ T cells generated from mucosal infection exhibit unique properties and, following respiratory infection, are not maintained in the lung long term. To better understand how infection route modifies memory differentiation, we compared murine CD8+ T cell responses to a vesicular stomatitis virus (VSV) challenge generated intranasally (i.n.) or i.v. The i.n. infection resulted in greater peak expansion of VSV-specific CD8+ T cells. However, this numerical advantage was rapidly lost during the contraction phase of the immune response, resulting in memory CD8+ T cell numerical deficiencies when compared with i.v. infection. Interestingly, the antiviral CD8+ T cells generated in response to i.n. VSV exhibited a biased and sustained proportion of early effector cells (CD127loKLRG1lo) akin to the developmental program favored after i.n. influenza infection, suggesting that respiratory infection broadly favors an incomplete memory differentiation program. Correspondingly, i.n. VSV infection resulted in lower CD122 expression and eomesodermin levels by VSV-specific CD8+ T cells, further indicative of an inferior transition to bona fide memory. These results may be due to distinct (CD103+CD11b+) dendritic cell subsets in the i.n. versus i.v. T cell priming environments, which express molecules that regulate T cell signaling and the balance between tolerance and immunity. Therefore, we propose that distinct immunization routes modulate both the quality and quantity of antiviral effector and memory CD8+ T cells in response to an identical pathogen and should be considered in CD8+ T cell-based vaccine design.

Surface area- and mass-based comparison of fine and ultrafine nickel oxide lung toxicity and augmentation of allergic response in an ovalbumin asthma model.

Background: The correlation of physico-chemical properties with mechanisms of toxicity has been proposed as an approach to predict the toxic potential of the vast number of emerging nanomaterials. Although relationships have been established between properties and the acute pulmonary inflammation induced by nanomaterials, properties' effects on other responses, such as exacerbation of respiratory allergy, have been less frequently explored.Methods: In this study, the role of nickel oxide (NiO) physico-chemical properties in the modulation of ovalbumin (OVA) allergy was examined in a murine model. Results: 181 nm fine (NiO-F) and 42 nm ultrafine (NiO-UF) particles were characterized and incorporated into a time course study where measured markers of pulmonary injury and inflammation were associated with NiO particle surface area. In the OVA model, exposure to NiO, irrespective of any metric was associated with elevated circulating total IgE levels. Serum and lung cytokine levels were similar with respect to NiO surface area. The lower surface area was associated with an enhanced Th2 profile, whereas the higher surface area was associated with a Th1-dominant profile. Surface area-normalized groups also exhibited similar alterations in OVA-specific IgE levels and lung neutrophil number. However, lung eosinophil number and allergen challenge-induced alterations in lung function related more to particle size, wherein NiO-F was associated with an increased enhanced pause response and NiO-UF was associated with increased lung eosinophil burden.Conclusions: Collectively, these findings suggest that although NiO surface area correlates best with acute pulmonary injury and inflammation following respiratory exposure, other physico-chemical properties may contribute to the modulation of immune responses in the lung.

A direct and nonredundant role for thymic stromal lymphopoietin on antiviral CD8 T cell responses in the respiratory mucosa.

Mucosally produced thymic stromal lymphopoietin (TSLP) regulates Th2 responses by signaling to dendritic cells and CD4 T cells. Activated CD8 T cells express the TSLP receptor (TSLPR), yet a direct role for TSLP in CD8 T cell immunity in the mucosa has not been described. Because TSLP shares signaling components with IL-7, a cytokine important for the development and survival of memory CD8 T cells in systemic infection models, we hypothesized that TSLP spatially and nonredundantly supports the development of these cells in the respiratory tract. In this study, we demonstrate that influenza infection induces the early expression of TSLP by lung epithelial cells with multiple consequences. The global loss of TSLP responsiveness in TSLPR(-/-) mice enhanced morbidity and delayed viral clearance. Using a competitive adoptive transfer system, we demonstrate that selective loss of TSLPR signaling on antiviral CD8 T cells decreases their accumulation specifically in the respiratory tract as early as day 8 after infection, primarily due to a proliferation deficiency. Importantly, the subsequent persistence of memory cells derived from this pool was also qualitatively and quantitatively affected. In this regard, the local support of antiviral CD8 T cells by TSLP is well suited to the mucosa, where responses must be tempered to prevent excessive inflammation. Taken together, these data suggest that TSLP uniquely participates in local immunity in the respiratory tract and modulation of TSLP levels may promote long-term CD8 T cell immunity in the mucosa when other prosurvival signals are limiting.

Systemic and immunotoxicity induced by topical application of perfluorohexane sulfonic acid (PFHxS) in a murine model.

Per- and polyfluoroalkyl substances (PFAS) are a large group of stable synthetic surfactants that are incorporated into numerous products for their water and oil resistance and have been associated with adverse health effects. The present study evaluated the systemic and immunotoxicity of sub-chronic 28- or 10-day dermal exposure of PFHxS (0.625-5% or 15.63-125 mg/kg/dose) in a murine model. Elevated levels of PFHxS were detected in the serum and urine, suggesting that absorption is occurring through the dermal route. Liver weight (% body) significantly increased and spleen weight (% body) significantly decreased with PFHxS exposure, which was supported by histopathological changes. Additionally, PFHxS significantly reduced the humoral immune response and altered immune subsets in the spleen, suggesting immunosuppression. Gene expression changes were observed in the liver, skin, and spleen with genes involved in fatty acid metabolism, necrosis, and inflammation. Immune-cell phenotyping identified significant decreases in B-cells, NK cells, and CD11b+ monocyte/macrophages in the spleen along with increases in CD4+ and CD8+ T-cells, NK cells, and neutrophils in the skin. These findings support dermal PFHxS-induced liver damage and immune suppression. Overall, data support PFHxS absorption through the skin and demonstrate immunotoxicity via this exposure route, suggesting the need for further examination.

Systemic and immunotoxicity induced by topical application of perfluoroheptane sulfonic acid (PFHpS) or perfluorooctane sulfonic acid (PFOS) in a murine model.

Per- and polyfluoroalkyl substances (PFAS) are a large group of synthetic surfactants of over 12,000 compounds that are incorporated into numerous products for their chemical and physical properties. Studies have associated PFAS with adverse health effects. Although there is a high potential for dermal exposure, these studies are lacking. The present study evaluated the systemic and immunotoxicity of subchronic 28- or 10-days of dermal exposure, respectively, to PFHpS (0.3125-2.5% or 7.82-62.5 mg/kg/dose) or PFOS (0.5% or 12.5 mg/kg/dose) in a murine model. Elevated levels of PFHpS were detected in the serum and urine, suggesting that absorption is occurring through the dermal route. PFHpS induced significantly increased relative liver weight, significantly decreased relative spleen and thymus weight, altered serum chemistries, and altered histopathology. Additionally, PFHpS significantly reduced the humoral immune response and altered immune subsets in the spleen, suggesting immunosuppression. Gene expression changes were observed in the liver, skin, and spleen of genes involved in fatty acid metabolism, necrosis, and inflammation. Immune-cell phenotyping identified significant decreases in B-cells and CD11b+ monocyte and/or macrophages in the spleen along with decreases in eosinophils and dendritic cells in the skin. These findings support PFHpS absorption through the skin leading to liver damage and immune suppression.

Effects of inhaled tier-2 diesel engine exhaust on immunotoxicity in a rat model: A hazard identification study. Part II. Immunotoxicology.

Diesel exhaust (DE) is an air pollutant containing gaseous compounds and particulate matter. Diesel engines are common on gas extraction and oil sites, leading to complex DE exposure to a broad range of compounds through occupational settings. The US EPA concluded that short-term exposure to DE leads to allergic inflammatory disorders of the airways. To further evaluate the immunotoxicity of DE, the effects of whole-body inhalation of 0.2 and 1 mg/m3 DE (total carbon; 6 h/d for 4 days) were investigated 1-, 7-, and 27-days post exposure in Sprague-Dawley rats using an occupationally relevant exposure system. DE exposure of 1 mg/m3 increased total cellularity, number of CD4+ and CD8+ T-cells, and B-cells at 1 d post-exposure in the lung lymph nodes. At 7 d post-exposure to 1 mg/m3, cellularity and the number of CD4+ and CD8+ T-cells decreased in the LLNs. In the bronchoalveolar lavage, B-cell number and frequency increased at 1 d post-exposure, Natural Killer cell number and frequency decreased at 7 d post-exposure, and at 27 d post-exposure CD8+ T-cell and CD11b+ cell number and frequency decreased with 0.2 mg/m3 exposure. In the spleen, 0.2 mg/m3 increased CD4+ T-cell frequency at 1 and 7 d post-exposure and at 27 d post-exposure increased CD4+ and CD8+ T-cell number and CD8+ T-cell frequency. B-cells were the only immune cell subset altered in the three tissues (spleen, LLNs, and BALF), suggesting the induction of the adaptive immune response. The increase in lymphocytes in several different organ types also suggests an induction of a systemic inflammatory response occurring following DE exposure. These results show that DE exposure induced modifications of cellularity of phenotypic subsets that may impair immune function and contribute to airway inflammation induced by DE exposure in rats.

Systemic toxicity induced by topical application of perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHxA), and perfluoropentanoic acid (PFPeA) in a murine model.

Per- and polyfluoroalkyl substances (PFAS) are a class of synthetic structurally diverse chemicals incorporated into industrial and consumer products. PFHpA, PFHxA, and PFPeA are carboxylic PFAS (C7, C6, C5, respectively) labeled as a safer alternative to legacy carboxylic PFAS due to their shorter half-life in animals. Although there is a high potential for dermal exposure, these studies are lacking. The present study conducted analyses of serum chemistries, immune phenotyping, gene expression, and histology to evaluate the systemic toxicity of a sub-chronic 28-day dermal exposure of alternative PFAS (1.25-5% or 31.25-125 mg/kg/dose) in a murine model. Liver weight (% body) significantly increased with PFHpA, PFHxA, and PFPeA exposure and histopathological changes were observed in both the liver and skin. Gene expression changes were observed with PPAR isoforms in the liver and skin along with changes in genes involved in steatosis, fatty acid metabolism, necrosis, and inflammation. These findings, along with significant detection levels in serum and urine, support PFAS-induced liver damage and PPARα, δ, and γ involvement in alternative PFAS systemic toxicity and immunological disruption. This demonstrates that these compounds can be absorbed through the skin and brings into question whether these PFAS are a suitable alternative to legacy PFAS.

Exposure to the anti-microbial chemical triclosan disrupts keratinocyte function and skin integrity in a model of reconstructed human epidermis.

Triclosan is an anti-microbial chemical incorporated into products that are applied to the skin of healthcare workers. Exposure to triclosan has previously been shown to be associated with allergic disease in humans and impact the immune responses in animal models. Additionally, studies have shown that exposure to triclosan dermally activates the NLRP3 inflammasome and disrupts the skin barrier integrity in mice. The skin is the largest organ of the body and plays an important role as a physical barrier and regulator of the immune system. Alterations in the barrier and immune regulatory functions of the skin have been demonstrated to increase the risk of sensitization and development of allergic disease. In this study, the impact of triclosan exposure on the skin barrier and keratinocyte function was investigated using a model of reconstructed human epidermis. The apical surface of reconstructed human epidermis was exposed to triclosan (0.05-0.2%) once for 6, 24, or 48 h or daily for 5 consecutive days. Exposure to triclosan increased epidermal permeability and altered the expression of genes involved in formation of the skin barrier. Additionally, exposure to triclosan altered the expression patterns of several cytokines and growth factors. Together, these results suggest that exposure to triclosan impacts skin barrier integrity and function of human keratinocytes and suggests that these alterations may impact immune regulation.

Exposure to the immunomodulatory chemical triclosan differentially impacts immune cell populations in the skin of haired (BALB/c) and hairless (SKH1) mice.

Workers across every occupational sector have the potential to be exposed to a wide variety of chemicals, and the skin is a primary route of exposure. Furthermore, exposure to certain chemicals has been linked to inflammatory and allergic diseases. Thus, understanding the immune responses to chemical exposures on the skin and the potential for inflammation and sensitization is needed to improve worker safety and health. Responses in the skin microenvironment impact the potential for sensitization; these responses may include proinflammatory cytokines, inflammasome activation, barrier integrity, skin microbiota, and the presence of immune cells. Selection of specific mouse strains to evaluate skin effects, such as haired (BALB/c) or hairless (SKH1) mice, varies dependent on experimental design and needs of a study. However, dermal chemical exposure may impact reactions in the skin differently depending on the strain of mouse. Additionally, there is a need for established methods to evaluate immune responses in the skin. In this study, exposure to the immunomodulatory chemical triclosan was evaluated in two mouse models using immunophenotyping by flow cytometry and gene expression analysis. BALB/c mice exposed to triclosan (2%) had a higher number and frequency of neutrophils and lower number and frequency of dendritic cells in the skin compared to controls. Although these changes were not observed in SKH1 mice, SKH1 mice exposed to triclosan had a higher number and frequency of type 2 innate lymphoid cells in the skin. Taken together, these results demonstrate that exposure to an immunomodulatory chemical, triclosan, differentially impacts immune cell populations in the skin of haired and hairless mice. Additionally, the flow cytometry panel reported in this manuscript, in combination with gene expression analysis, may be useful in future studies to better evaluate the effect of chemical exposures on the skin immune response. These findings may be important to consider during strain selection, experimental design, and result interpretation of chemical exposures on the skin.

Systemic toxicity induced by topical application of heptafluorobutyric acid (PFBA) in a murine model.

Heptafluorobutyric acid (PFBA) is a synthetic chemical belonging to the per- and polyfluoroalkyl substances (PFAS) group that includes over 5000 chemicals incorporated into numerous products. PFBA is a short-chain PFAS (C4) labeled as a safer alternative to legacy PFAS which have been linked to numerous health effects. Despite the high potential for dermal exposure, occupationally and environmentally, dermal exposure studies are lacking. Using a murine model, this study analyzed serum chemistries, histology, immune phenotyping, and gene expression to evaluate the systemic toxicity of sub-chronic dermal PFBA 15-day (15% v/v or 375 mg/kg/dose) or 28-day (3.75-7.5% v/v or 93.8-187.5 mg/kg/dose) exposures. PFBA exposure produced significant increases in liver and kidney weights and altered serum chemistries (all exposure levels). Immune-cell phenotyping identified significant increases in draining lymph node B-cells (15%) and CD11b + cells (3.75-15%) and skin T-cells (3.75-15%) and neutrophils (7.5-15%). Histopathological and gene expression changes were observed in both the liver and skin after dermal PFBA exposure. The findings indicate PFBA induces liver toxicity and alterations of PPAR target genes, suggesting a role of a PPAR pathway. These results demonstrate that sustained dermal exposure to PFBA induces systemic effects and raise concerns of short-chain PFAS being promoted as safer alternatives.

Dermal Exposure to the Immunomodulatory Antimicrobial Chemical Triclosan Alters the Skin Barrier Integrity and Microbiome in Mice.

Triclosan is an antimicrobial chemical used in healthcare settings that can be absorbed through the skin. Exposure to triclosan has been positively associated with food and aeroallergy and asthma exacerbation in humans and, although not directly sensitizing, has been demonstrated to augment the allergic response in a mouse model of asthma. The skin barrier and microbiome are thought to play important roles in regulating inflammation and allergy and disruptions may contribute to development of allergic disease. To investigate potential connections of the skin barrier and microbiome with immune responses to triclosan, SKH1 mice were exposed dermally to triclosan (0.5-2%) or vehicle for up to 7 consecutive days. Exposure to 2% triclosan for 5-7 days on the skin was shown to increase transepidermal water loss levels. Seven days of dermal exposure to triclosan decreased filaggrin 2 and keratin 10 expression, but increased filaggrin and keratin 14 protein along with the danger signal S100a8 and interleukin-4. Dermal exposure to triclosan for 7 days also altered the alpha and beta diversity of the skin and gut microbiome. Specifically, dermal triclosan exposure increased the relative abundance of the Firmicutes family, Lachnospiraceae on the skin but decreased the abundance of Firmicutes family, Ruminococcaceae in the gut. Collectively, these results demonstrate that repeated dermal exposure to the antimicrobial chemical triclosan alters the skin barrier integrity and microbiome in mice, suggesting that these changes may contribute to the increase in allergic immune responses following dermal exposure to triclosan.

Prior Exposure to Ortho-Phthalaldehyde Augments IgE-Mediated Immune Responses to Didecyldimethylammonium Chloride: Potential for 2 Commonly Used Antimicrobials to Synergistically Enhance Allergic Disease.

Health-care workers have an increased incidence of allergic disease compared with the general public and are exposed to a variety of high-level disinfectants. Although exposure to these agents has been associated with allergic disease, findings between epidemiology and animal studies often conflict respecting immunological mechanisms. Therefore, we hypothesized that previous exposure to a representative IgE-mediated sensitizer (ortho-phthalaldehyde [OPA]) alters immune responses to a representative T-cell-mediated sensitizer (didecyldimethlyammonium chloride [DDAC]). Here, BALB/c mice were topically exposed to OPA (0.5%) for 3 days, rested, then topically exposed to DDAC (0.0625%, 0.125%, and 0.25%) for 14 days. Coexposure resulted in phenotypic changes in draining lymph node (dLN) cells, including a decreased frequency of CD8+ T cells and increased frequency and number of B cells compared with DDAC-only treated mice. The coexposed mice also had enhanced Th2 responses, including significant alterations in: dLN Il4 (increased), B-cell activation (increased), CD8+ T-cell activation (decreased), and local and systemic IgE production (increased). These changes were not observed if mice were exposed to DDAC prior to OPA. Exposure to OPA alone shows Th2 skewing, indicated by increased activation of skin type 2 innate lymphoid cells, increased frequency and activation of draining lymph node B cells, and increased levels of type 2 cytokines. These findings suggest that the OPA-induced immune environment may alter the response to DDAC, resulting in increased IgE-mediated immune responses. This data may partially explain the discordance between epidemiological and laboratory studies regarding disinfectants and provide insight into the potential immunological implications of mixed chemical exposures.

Potential classification of chemical immunologic response based on gene expression profiles.

Occupational immune diseases are a serious public health burden and are often a result of exposure to low molecular weight (LMW) chemicals. The complete immunological mechanisms driving these responses are not fully understood which has made the classification of chemical allergens difficult. Antimicrobials are a large group of immunologically-diverse LMW agents. In these studies, mice were dermally exposed to representative antimicrobial chemicals (sensitizers: didecyldimethylammonium chloride (DDAC), ortho-phthalaldehyde (OPA), irritants: benzal-konium chloride (BAC), and adjuvant: triclosan (TCS)) and the mRNA expression of cytokines and cellular mediators was evaluated using real-time qPCR in various tissues over a 7-days period. All antimicrobials caused increases in the mRNA expression of the danger signals Tslp (skin), and S100a8 (skin, blood, lung). Expression of the TH2 cytokine Il4 peaked at different timepoints for the chemicals based on exposure duration. Unique expression profiles were identified for OPA (Il10 in lymph node, Il4 and Il13 in lung) and TCS (Tlr4 in skin). Additionally, all chemicals except OPA induced decreased expression of the cellular adhesion molecule Ecad. Overall, the results from these studies suggest that unique gene expression profiles are implicated following dermal exposure to various antimicrobial agents, warranting the need for additional studies. In order to advance the development of preventative and therapeutic strategies to combat immunological disease, underlying mechanisms of antimicrobial-induced immunomodulation must be fully understood. This understanding will aid in the development of more effective methods to screen for chemical toxicity, and may potentially lead to more effective treatment strategies for those suffering from immune diseases.

Immunotoxicity and allergenic potential induced by topical application of perfluorooctanoic acid (PFOA) in a murine model.

Perfluorooctanoic acid (PFOA) is a per- and polyfluoroalkyl substance (PFAS) once used as a surfactant in the polymerization of chemicals. Because of its ubiquitous nature and long half-life, PFOA is commonly detected in the environment, wildlife, and humans. While skin exposure to PFOA is of concern, studies evaluating the immunotoxicity of dermal exposure are lacking. These studies evaluated the immunotoxicity of PFOA (0.5-2% w/v, or 12.5-50 mg/kg/dose) following dermal exposure using a murine model. PFOA (0.5-2%) was not identified to be an irritant or sensitizer using the local lymph node assay. The IgM antibody response to sheep red blood cell. was significantly reduced in the spleen following 4-days of dermal exposure (2%). PFOA exposure produced a significant decrease in thymus (1 and 2%) and spleen (0.5-2%) weight along with an increase in liver weight (0.5-2%). Immune cell phenotyping identified a reduction in the frequency (1 and 2%) and number (0.5-2%) of splenic B-cells. To further define the mechanism of immunotoxicity, gene expression was also evaluated in the skin. The findings support a potential involvement of the nuclear receptor PPARα. These results demonstrate that dermal exposure to PFOA is immunotoxic and raise concern about potential adverse effects from dermal exposure.

Topical Application of the Antimicrobial Agent Triclosan Induces NLRP3 Inflammasome Activation and Mitochondrial Dysfunction.

5-Chloro-2-(2,4-dichlorophenoxy)phenol (triclosan) is an antimicrobial chemical widely used in consumer household and clinical healthcare products. Human and animal studies have associated triclosan exposure with allergic disease. Mechanistic studies have identified triclosan as a mitochondrial uncoupler; recent studies suggest that mitochondria play an important role in immune cell function and are involved in activation of the NLRP3 inflammasome. In this study, early immunological effects were evaluated via NLRP3 activation following dermal triclosan application in a BALB/c murine model. These investigations revealed rapid caspase-1 activation and mature IL-1ß secretion in the skin and draining lymph nodes (dLNs) after 1.5% and 3% triclosan exposure. Correspondingly, pro-Il-1b and S100a8 gene expression increased along with extracellular ATP in the skin. Peak gene expression of chemokines associated with caspase-1 activation occurred after 2 days of exposure in both skin tissue and dLNs. Phenotypic analysis showed an increase in neutrophils and macrophages in the dLN and myeloid and inflammatory monocytes in the skin tissue. Triclosan also caused mitochondrial dysfunction shown through effects on mitochondrial reactive oxygen species, mass, mitochondrial membrane potential, and mitochondrial morphology. These results indicate that following triclosan exposure, activation of the NLRP3 inflammasome occurs in both the skin tissue and dLNs, providing a possible mechanism for triclosan's effects on allergic disease and further support a connection between mitochondrial involvements in immunological responses.

Topical exposure to triclosan inhibits Th1 immune responses and reduces T cells responding to influenza infection in mice.

Healthcare workers concurrently may be at a higher risk of developing respiratory infections and allergic disease, such as asthma, than the general public. Increased incidence of allergic diseases is thought to be caused, in part, due to occupational exposure to chemicals that induce or augment Th2 immune responses. However, whether exposure to these chemical antimicrobials can influence immune responses to respiratory pathogens is unknown. Here, we use a BALB/c murine model to test if the Th2-promoting antimicrobial chemical triclosan influences immune responses to influenza A virus. Mice were dermally exposed to 2% triclosan for 7 days prior to infection with a sub-lethal dose of mouse adapted PR8 A(H1N1) virus (50 pfu); triclosan exposure continued until 10 days post infection (dpi). Infected mice exposed to triclosan did not show an increase in morbidity or mortality, and viral titers were unchanged. Assessment of T cell responses at 10 dpi showed a decrease in the number of total and activated (CD44hi) CD4+ and CD8+ T cells at the site of infection (BAL and lung) in triclosan exposed mice compared to controls. Influenza-specific CD4+ and CD8+ T cells were assessed using MHCI and MHCII tetramers, with reduced populations, although not reaching statistical significance at these sites following triclosan exposure. Reductions in the Th1 transcription factor T-bet were seen in both activated and tetramer+ CD4+ and CD8+ T cells in the lungs of triclosan exposed infected mice, indicating reduced Th1 polarization and providing a potential mechanism for numerical reduction in T cells. Overall, these results indicate that the immune environment induced by triclosan exposure has the potential to influence the developing immune response to a respiratory viral infection and may have implications for healthcare workers who may be at an increased risk for developing infectious diseases.

Novel cutaneous mediators of chemical allergy.

Chemical allergy can manifest into allergic contact dermatitis and asthma and the importance of skin sensitization in both of these diseases is increasingly being recognized. Given the unique characteristics of chemical allergy, coupled with the distinct immunological microenvironment of the skin research is still unraveling the mechanisms through which sensitization and elicitation occur. This review first describes the features of chemical sensitization and the known steps that must occur to develop a chemical allergy. Next, the unique immunological properties of the skin - which may influence chemical sensitization - are highlighted. Additionally, mediators involved with the development of allergy are reviewed, starting with early ones - including the properties of haptens, skin integrity, the microbiome, the inflammasome, and toll-like receptors (TLR). Novel cellular mediators of chemical sensitization are highlighted, including innate lymphoid cells, mast cells, T-helper (TH) cell subsets, and skin intrinsic populations including γδ T-cells and resident memory T-cells. Finally, this review discusses two epigenetic mechanisms that can influence chemical sensitization, microRNAs and DNA methylation. Overall, this review highlights recent research investigating novel mediators of chemical allergy that are present in the skin. It also emphasizes the need to further explore these mediators to gain a better understanding of what makes a chemical an allergen, and how best to prevent the development of chemical-induced allergic diseases.

Contribution of antimicrobials to the development of allergic disease.

Antimicrobials represent a broad class of chemicals with the intended purpose of eliminating or controlling the growth of harmful microorganisms. Exposure can occur occupationally or through the use or consumption of consumer products. The use of antimicrobial agents has been associated with an increased incidence of allergic diseases, including asthma, atopic dermatitis, and less commonly, anaphylaxis. Very diverse immunological mechanisms and mediators have been identified in the sensitization response to antimicrobial chemicals and the importance of the local microenviroment in the response is increasingly being recognized. A complete understanding of the mechanisms of allergic diseases resulting from antimicrobial exposure will help to ensure safe environments and exposure limits.

Topical Application of the Quaternary Ammonium Compound Didecyldimethylammonium Chloride Activates Type 2 Innate Lymphoid Cells and Initiates a Mixed-Type Allergic Response.

Didecyldimethylammonium chloride (DDAC) is an antimicrobial dialkyl-quaternary ammonium compound used in industrial and commercial products. Clinical data suggest that DDAC exposure elicits multiple types of hypersensitivity reactions; here, we confirm this observation in a BALB/c murine model. To examine the immunological mechanism behind this mixed-type response and the potential involvement of type 2 innate lymphoid cells (ILC2s), we assessed early immune responses in the skin following topical DDAC exposure (0.125% and 0.5%). DDAC exposure resulted in a rapid and dramatic increase in the Th2-skewing and ILC2-activating cytokine thymic stromal lymphopoietin. Correspondingly, dermal ILC2s were activated 24 h after DDAC exposure, resulting in increased expression of CD25, ICOS and KLRG1, and decreased CD127 throughout 7 days of exposure. Following ILC2 activation, the Th2 cytokine IL-4 was elevated compared with control mice in total ear protein lysate (0.5% DDAC). Rag2-/- mice were used to determine a functional role for ILC2s in DDAC-induced sensitization. ILC2s from Rag2-/- mice were similarly activated by DDAC and, importantly, produced significant levels of IL-4 and IL-5 in the skin (0.5% DDAC). These data indicate that ILC2s contribute to early Th2 immune responses following DDAC exposure. ILC2s have been previously implicated in allergic responses, but to our knowledge have not been thoroughly investigated in chemical sensitization. These results indicate that following DDAC exposure, skin ILC2s become activated and produce Th2 cytokines, providing a possible mechanism for the development of the mixed-type allergic responses commonly observed with chemical sensitizers.