Regulation of the immune response to contact sensitizers by Nrf2.

The skin is frequently exposed to chemical stress by organic chemicals or metal ions that can directly or indirectly challenge its immune components and may lead to T-cell-mediated delayed-type hypersensitivity reactions. The disruption of the skin's homeostasis by exposure to contact sensitizers (CSs) can trigger an inflammatory immune response that results in eczema and allergic contact dermatitis. The recognition of these chemicals depends on the expression of pattern recognition receptors on sentinel skin cells, mainly the innate resident immune cells orchestrating the skin's immune response and involving both oxidative and inflammatory pathways. The main driver of these both pathways is the Nrf2/Keap1 pathway, a major ubiquitous regulator of cellular oxidative and electrophilic stress, activated in various innate immune cells of the skin, including keratinocytes and epidermal Langerhans cells in the epidermis and dermal dendritic cells in the dermis. Nrf2 also shows a strong protective capacity by downregulating inflammatory pathways. In this review, the important role of Nrf2 in the regulation of the immune response to CSs will be discussed and highlighted.

Phloretin suppresses neuroinflammation by autophagy-mediated Nrf2 activation in macrophages.

BACKGROUND: Macrophages play a dual role in neuroinflammatory disorders such as multiple sclerosis (MS). They are involved in lesion onset and progression but can also promote the resolution of inflammation and repair of damaged tissue. In this study, we investigate if and how phloretin, a flavonoid abundantly present in apples and strawberries, lowers the inflammatory phenotype of macrophages and suppresses neuroinflammation. METHODS: Transcriptional changes in mouse bone marrow-derived macrophages upon phloretin exposure were assessed by bulk RNA sequencing. Underlying pathways related to inflammation, oxidative stress response and autophagy were validated by quantitative PCR, fluorescent and absorbance assays, nuclear factor erythroid 2-related factor 2 (Nrf2) knockout mice, western blot, and immunofluorescence. The experimental autoimmune encephalomyelitis (EAE) model was used to study the impact of phloretin on neuroinflammation in vivo and confirm underlying mechanisms. RESULTS: We show that phloretin reduces the inflammatory phenotype of macrophages and markedly suppresses neuroinflammation in EAE. Phloretin mediates its effect by activating the Nrf2 signaling pathway. Nrf2 activation was attributed to 5' AMP-activated protein kinase (AMPK)-dependent activation of autophagy and subsequent kelch-like ECH-associated protein 1 (Keap1) degradation. CONCLUSIONS: This study opens future perspectives for phloretin as a therapeutic strategy for neuroinflammatory disorders such as MS. TRIAL REGISTRATION: Not applicable.

Tau accumulates in Crohn's disease gut.

A sizeable body of evidence has recently emerged to suggest that gastrointestinal (GI) inflammation might be involved in the development of Parkinson's disease (PD). There is now strong epidemiological and genetical evidence linking PD to inflammatory bowel diseases and we recently demonstrated that the neuronal protein alpha-synuclein, which is critically involved in PD pathophysiology, is upregulated in inflamed segments of Crohn's colon. The microtubule associated protein tau is another neuronal protein critically involved in neurodegenerative disorders but, in contrast to alpha-synuclein, no data are available about its expression and phosphorylation patterns in inflammatory bowel diseases. Here, we examined the expression levels of tau isoforms, their phosphorylation profile and truncation in colon biopsy specimens from 16 Crohn's disease (CD) and 6 ulcerative colitis (UC) patients and compared them to samples from 16 controls. Additional experiments were performed in full thickness segments of colon of five CD and five control subjects, in primary cultures of rat enteric neurons and in nuclear factor erythroid 2-related factor (Nrf2) knockout mice. Our results show the upregulation of two main human tau isoforms in the enteric nervous system (ENS) in CD but not in UC. This upregulation was not transcriptionally regulated but instead likely resulted from a decrease in protein clearance via an Nrf2 pathway. Our findings, which provide the first detailed characterization of tau in CD, suggest that the key proteins involved in neurodegenerative disorders such as alpha-synuclein and tau, might also play a role in CD.

Cutting Edge: Nrf2 Regulates Neutrophil Recruitment and Accumulation in Skin during Contact Hypersensitivity.

Neutrophils are essential during contact hypersensitivity (CHS), a common skin allergic disease. NF-E2-related factor-2 (Nrf2) is a key regulator of redox balance and skin homeostasis playing a protective role in CHS. In this study, we investigated Nrf2 role in neutrophil recruitment during the sensitization phase of CHS. Comparing wild-type and Nrf2 knockout mice, we demonstrated that Nrf2 regulated dinitrochlorobenzene-induced xenoinflammation, notably neutrophil recruitment to sensitized skin. Nrf2 protective role was associated with high expression of antioxidant genes (ho-1, gclc, nqo1…) and decreased chemokine production (CCL2, CCL4, CCL11). Interestingly, skin sensitization induced CD36 upregulation in skin-resident macrophages. In vitro results confirmed that the transcription of cd36 gene in macrophages was dependent on Nrf2 and led to an improved capacity to phagocyte-damaged neutrophils by efferocytosis. Nrf2 emerges as a critical target in the sensitization phase of CHS regulating neutrophil recruitment and accumulation in the skin through antioxidant-dependent and -independent mechanisms.

CD36-mediated uptake of myelin debris by macrophages and microglia reduces neuroinflammation.

BACKGROUND: The presence of foamy macrophages and microglia containing intracellular myelin remnants is a pathological hallmark of neurodegenerative disorders such as multiple sclerosis (MS). Despite the importance of myelin internalization in affecting both central nervous system repair and neuroinflammation, the receptors involved in myelin clearance and their impact on the phagocyte phenotype and lesion progression remain to be clarified. METHODS: Flow cytometry, quantitative PCR, and immunohistochemistry were used to define the mRNA and protein abundance of CD36 in myelin-containing phagocytes. The impact of CD36 and nuclear factor erythroid 2-related factor 2 (NRF2) on the phagocytic and inflammatory features of macrophages and microglia was assessed using a pharmacological CD36 inhibitor (sulfo-N-succinimidyl oleate) and Nrf2-/- bone marrow-derived macrophages. Finally, the experimental autoimmune encephalomyelitis (EAE) model was used to establish the impact of CD36 inhibition on neuroinflammation and myelin phagocytosis in vivo. RESULTS: Here, we show that the fatty acid translocase CD36 is required for the uptake of myelin debris by macrophages and microglia, and that myelin internalization increased CD36 expression through NRF2. Pharmacological inhibition of CD36 promoted the inflammatory properties of myelin-containing macrophages and microglia in vitro, which was paralleled by a reduced activity of the anti-inflammatory lipid-sensing liver X receptors and peroxisome proliferator-activated receptors. By using the EAE model, we provide evidence that CD36 is essential for myelin debris clearance in vivo. Importantly, CD36 inhibition markedly increased the neuroinflammatory burden and disease severity in the EAE model. CONCLUSION: Altogether, we show for the first time that CD36 is crucial for clearing myelin debris and suppressing neuroinflammation in demyelinating disorders such as MS.

The THP-1 cell toolbox: a new concept integrating the key events of skin sensitization.

According to the current scientific consensus, one in vitro test is insufficient to cover the key events (KE) defined by the adverse outcome pathway (AOP) for skin sensitization. To address this issue we combined different end points in the same cell line to cover all KEs defined by the skin sensitization AOP. Since dendritic cells (DC) play a key role in the sensitization phase leading to the development of allergic contact dermatitis (ACD), we used THP-1 cells as a surrogate for DC. We measured ROS production and GSH depletion for KE1 (binding to proteins), Nrf2 activation pathway and gene expressions for KE2 (keratinocyte response), phenotype modifications using cell-surface markers and cytokine production for KE3 (DC activation), and T-cell proliferation for KE4 (T-cell activation). These measurements were performed using the THP-1 cell line and an original THP-1/T-cell co-culture system following exposure to a variety of chemicals, including irritant, non-sensitizers, and chemicals sensitizers (pro/prehaptens). Results showed that treatment with sensitizers such as cinnamaldehyde (100 µM) or methylisothiazolinone (150 µM) was able to trigger the three main key events (KE1, KE2, and KE3) of the sensitization phase of ACD in THP-1 cells. In addition, all sensitizers were able to induce T lymphocyte proliferation (KE4), while non-sensitizers and irritants did not. Our study shows for the first time that addressing the four main KE of skin sensitization AOP in a single cell line is an achievable task.

The nuclear factor-erythroid 2-related factor/heme oxygenase-1 axis is critical for the inflammatory features of type 2 diabetes-associated osteoarthritis.

Epidemiological findings support the hypothesis that type 2 diabetes mellitus (T2DM) is a risk factor for osteoarthritis (OA). Moreover, OA cartilage from patients with T2DM exhibits a greater response to inflammatory stress, but the molecular mechanism is unclear. To investigate whether the antioxidant defense system participates in this response, we examined here the expression of nuclear factor-erythroid 2-related factor (Nrf-2), a master antioxidant transcription factor, and of heme oxygenase-1 (HO-1), one of its main target genes, in OA cartilage from T2DM and non-T2DM patients as well as in murine chondrocytes exposed to high glucose (HG). Ex vivo experiments indicated that Nrf-2 and HO-1 expression is reduced in T2DM versus non-T2DM OA cartilage (0.57-fold Nrf-2 and 0.34-fold HO-1), and prostaglandin E2 (PGE2) release was increased in samples with low HO-1 expression. HG-exposed, IL-1ß-stimulated chondrocytes had lower Nrf-2 levels in vitro, particularly in the nuclear fraction, than chondrocytes exposed to normal glucose (NG). Accordingly, HO-1 levels were also decreased (0.49-fold) in these cells. The HO-1 inducer cobalt protoporphyrin IX more efficiently attenuated PGE2 and IL-6 release in HG+IL-1ß-treated cells than in NG+IL-1ß-treated cells. Greater reductions in HO-1 expression and increase in PGE2/IL-6 production were observed in HG+IL-1ß-stimulated chondrocytes from Nrf-2-/- mice than in chondrocytes from wild-type mice. We conclude that the Nrf-2/HO-1 axis is a critical pathway in the hyperglucidic-mediated dysregulation of chondrocytes. Impairments in this antioxidant system may explain the greater inflammatory responsiveness of OA cartilage from T2DM patients and may inform treatments of such patients.

Dendritic cells' death induced by contact sensitizers is controlled by Nrf2 and depends on glutathione levels.

Dendritic cells (DC) are known to play a major role during contact allergy induced by contact sensitizers (CS). Our previous studies showed that Nrf2 was induced in DC and controlled allergic skin inflammation in mice in response to chemicals. In this work, we raised the question of the role of Nrf2 in response to a stress provoked by chemical sensitizers in DC. We used two well-described chemical sensitizers, dinitrochlorobenzene (DNCB) and cinnamaldehyde (CinA), known to have different chemical reactivity and mechanism of action. First, we performed a RT-qPCR array showing that CinA was a higher inducer of immune and detoxification genes compared to DNCB. Interestingly, in the absence of Nrf2, gene expression was dramatically affected in response to DNCB but was slightly affected in response to CinA. These observations prompted us to study DC's cell death in response to both chemicals. DNCB and CinA increased apoptotic cells and decreased living cells in the absence of Nrf2. The characterization of DC apoptosis induced by both CS involved the mitochondrial-dependent caspase pathway and was regulated via Nrf2 in response to both chemicals. Oxidative stress induced by DNCB, and leading to cell death, was regulated by Nrf2. Unlike CinA, DNCB treatment provoked a significant reduction of intracellular GSH levels and up-regulated bcl-2 gene expression, under the control of Nrf2. This work underlies that chemical reactivity may control Nrf2-dependent gene expression leading to different cytoprotective mechanisms in DC.

Proteomics analysis of dendritic cell activation by contact allergens reveals possible biomarkers regulated by Nrf2.

Allergic contact dermatitis is a widespread disease with high clinical relevance affecting approximately 20% of the general population. Typically, contact allergens are low molecular weight electrophilic compounds which can activate the Keap1/Nrf2 pathway. We performed a proteomics study to reveal possible biomarkers for dendritic cell (DC) activation by contact allergens and to further elucidate the role of Keap1/Nrf2 signaling in this process. We used bone marrow derived dendritic cells (BMDCs) of wild-type (nrf2+/+) and Nrf2 knockout (nrf2-/-) mice and studied their response against the model contact sensitizers 2,4-dinitrochlorobenzene (DNCB), cinnamaldehyde (CA) and nickel(II) sulfate by 2-dimensional polyacrylamide gel electrophoresis (2D-PAGE) in combination with electrospray ionization tandem mass spectrometry (ESI-MS/MS). Sodium dodecyl sulfate (SDS, 100µM) served as irritant control. While treatment with nickel(II) sulfate and SDS had only little effects, CA and DNCB led to significant changes in protein expression. We found 18 and 30 protein spots up-regulated in wild-type cells treated with 50 and 100µM CA, respectively. For 5 and 10µM DNCB, 32 and 37 spots were up-regulated, respectively. Almost all of these proteins were not differentially expressed in nrf2-/- BMDCs, indicating an Nrf2-dependent regulation. Among them proteins were detected which are involved in oxidative stress and heat shock responses, as well as in signal transduction or basic cellular pathways. The applied approach allowed us to differentiate between Nrf2-dependent and Nrf2-independent cellular biomarkers differentially regulated upon allergen-induced DC activation. The data presented might contribute to the further development of suitable in vitro testing methods for chemical-mediated sensitization.

Neutrophil extracellular traps downregulate lipopolysaccharide-induced activation of monocyte-derived dendritic cells.

Polymorphonuclear neutrophils (PMN) play a central role in inflammation and participate in its control, notably by modulating dendritic cell (DC) functions via soluble mediators or cell-cell contacts. Neutrophil extracellular traps (NETs) released by PMN could play a role in this context. To evaluate NET effects on DC maturation, we developed a model based on monocyte-derived DC (moDC) and calibrated NETs isolated from fresh human PMN. We found that isolated NETs alone had no discernable effect on moDC. In contrast, they downregulated LPS-induced moDC maturation, as shown by decreased surface expression of HLA-DR, CD80, CD83, and CD86, and by downregulated cytokine production (TNF-α, IL-6, IL-12, IL-23), with no increase in the expression of tolerogenic DC genes. Moreover, the presence of NETs during moDC maturation diminished the capacity of these moDC to induce T lymphocyte proliferation in both autologous and allogeneic conditions, and modulated CD4(+) T lymphocyte polarization by promoting the production of Th2 cytokines (IL-5 and IL-13) and reducing that of Th1 and Th17 cytokines (IFN-γ and IL-17). Interestingly, the expression and activities of the lymphoid chemokine receptors CCR7 and CXCR4 on moDC were not altered when moDC matured in the presence of NETs. Together, these findings reveal a new role for NETs in adaptive immune responses, modulating some moDC functions and thereby participating in the control of inflammation.

Photobiomodulation Controls Keratinocytes Inflammatory Response through Nrf2 and Reduces Langerhans Cells Activation.

Photobiomodulation (PBM) is rapidly gaining traction as a valuable tool in dermatology for treating many inflammatory skin conditions using low levels of visible light or near-infrared radiation. However, the physiological regulatory pathways responsible for the anti-inflammatory effect of PBM have not been well defined. Since previous studies showed that nuclear factor-erythroid 2 like 2 (Nrf2) is a master regulator of the skin inflammatory response, we have addressed its role in controlling inflammation by PBM. Primary human keratinocytes (KCs) stimulated with 2,4-dinitrochlorobenzene (DNCB) to mimic pro-inflammatory stress were illuminated with two wavelengths: 660 nm or 520 nm. Both lights significantly reduced the mRNA expression of the DNCB-triggered TNF-α, IL-6, and IL-8 cytokines in KCs, while they enhanced Nrf2 pathway activation. PBM-induced Nrf2 is a key regulator of the inflammatory response in KCs since its absence abolished the regulatory effect of light on cytokines production. Further investigations of the mechanisms contributing to the immunoregulatory effect of PBM in inflamed human skin explants showed that 660 nm light prevented Langerhans cells migration into the dermis, preserving their dendricity, and decreased pro-inflammatory cytokine production compared to the DNCB-treated group. This study is the first to report that the PBM-mediated anti-inflammatory response in KCs is Nrf2-dependent and further support the role of PBM in skin immunomodulation. Therefore, PBM should be considered a promising alternative or complementary therapeutic approach for treating skin-related inflammatory diseases.

Ethylhexadecyldimethylammonium bromide, a quaternary ammonium compound, controls inflammatory response through NRF2 pathway in a human immortalized keratinocyte cell line.

Many everyday products contain quaternary ammonium compounds (QAC) and some of them are known to be skin irritants such as benzalkonium chloride. Others, such as didecyldimethylammonium chloride, have been shown to cause allergic contact dermatitis. Ethylhexadecyldimethylammonium bromide (EHD) is a QAC for which sensitization potential is not clearly known. Therefore, we have studied its mechanism in human keratinocytes (KC), the main cells of the epidermis. We used the well-described human KC cell line KERTr exposed to EHD, cinnamaldehyde (CinA), a well-known skin sensitizer, and a mixture of both. Since chemical sensitizers are known to activate the transcription factor nuclear factor (erythroid-derived 2)-like 2 (NRF2), leading to cellular detoxification and suppressed proinflammatory cytokines, protein or mRNA expression of NRF2 pathway-related enzymes and pro-inflammatory cytokines were investigated by Western blot and RT-qPCR. The activity of the NRF2 pathway on inflammation was studied by RT-qPCR in NRF2-invalidated KERTr cells. We showed that EHD cannot induce the NRF2 pathway, unlike contact sensitizers like CinA. EHD triggers an inflammatory response by inducing the mRNA expression of pro-inflammatory cytokines such as IL-1ß or IL-6. Moreover, mixing EHD and CinA inhibits the effect of CinA on NRF2 expression and mitigates the inflammatory response induced by EHD alone. EHD treatment of KERTr cells in which NRF2 has been invalidated showed an exacerbation of the inflammatory response at the transcriptional level. Hence, EHD may elicit an inflammatory response in KC via the NF-κB pathway, which could lead to irritation when applied to the skin. This inflammation is negatively controlled by the basal activity of the NRF2 pathway.

Mechanisms of IL-12 synthesis by human dendritic cells treated with the chemical sensitizer NiSO4.

Allergic contact dermatitis, caused by metallic ions, is a T cell-mediated inflammatory skin disease. IL-12 is a 70-kDa heterodimeric protein composed of IL-12p40 and IL-12p35, playing a major role in the generation of allergen-specific T cell responses. Dendritic cells (DCs) are APCs involved in the induction of primary immune responses, as they possess the ability to stimulate naive T cells. In this study, we address the question whether the sensitizer nickel sulfate (NiSO(4)) itself or in synergy with other signals can induce the secretion of IL-12p70 in human monocyte-derived DCs (Mo-DCs). We found that IL-12p40 was produced by Mo-DC in response to NiSO(4) stimulation. Addition of IFN-gamma concomitantly to NiSO(4) leads to IL-12p70 synthesis. NiSO(4) treatment leads to the activation of MAPK, NF-kappaB pathways, and IFN regulatory factor 1 (IRF-1). We investigated the role of these signaling pathways in IL-12 production using known pharmacological inhibitors of MAPK and NF-kappaB pathways and RNA interference-mediated silencing of IRF-1. Our results showed that p38 MAPK, NF-kappaB, and IRF-1 were involved in IL-12p40 production induced by NiSO(4). Moreover, IRF-1 silencing nearly totally abrogated IL-12p40 and IL-12p70 production provoked by NiSO(4) and IFN-gamma. In response to NiSO(4), we observed that STAT-1 was phosphorylated on both serine and tyrosine residues and participated to NiSO(4)-induced IRF-1 activation. N-acetylcysteine abolished STAT-1 phosphorylation, suggesting that STAT-1 activation may be dependent on NiSO(4)-induced alteration of the redox status of the cell. These results indicate that p38 MAPK, NF-kappaB, and IRF-1 are activated by NiSO(4) in Mo-DC and cooperate for IL-12 production.

Models of Dendritic Cells to Assess Skin Sensitization.

Allergic contact dermatitis (ACD) is a complex skin pathology occurring in reaction against environmental substances found in the workplace (cement, hair dyes, textile dyes), in the private environment (e.g., household products, cosmetic ingredients), or following skin exposure to drugs. Many cells are involved in the initiation of ACD during the sensitization phase. The four key events (KE) of skin sensitization AOP are covalent binding to skin proteins (KE1), keratinocyte activation (KE2), activation of DCs (KE3), and T-cell activation and proliferation (KE4), leading to the adverse outcome of ACD. Dendritic cells (DCs) are thus playing a key role in ACD pathophysiology. Indeed, in the presence of chemical sensitizers, DCs migrate from the skin to the draining lymph nodes and present peptide-chemical conjugates to T cells, leading to their activation and proliferation. In vitro methods have been actively developed to assess the activation of DCs by chemicals to establish a reliable in vitro sensitization test. Therefore, this review will detail the most used methods and protocols to develop DC models in vitro. Three different models of DCs will be addressed: 1) DCs derived from Cord Blood (CD34-DCs), 2) DCs derived from Monocytes (Mo-DCs), and 3) DCs derived from mice Bone-Marrow (BM-DCs). In addition, a model of exposition to contact sensitizers to assess KE3 of skin sensitization will be detailed for each of the models presented.

Quaternary ammonium compounds in hypersensitivity reactions.

Quaternary ammonium compounds (QAC) are commonly used disinfectants, antiseptics, preservatives, and detergents due to their antibacterial property and represent the first used biocides before phenolic or nitrogen products. Their common structure consists of one or more quaternary ammonium bound with four lateral substituents. Their amphiphilic structure allows them to intercalate into microorganism surfaces which induces an unstable and porous membrane that explains their antimicrobial activity towards bacteria, fungi, and viruses. QAC are thus found in many areas, such as household products, medicines, hygiene products, cosmetics, agriculture, or industrial products but are also used in medical practice as disinfectants and antiseptics and in health care facilities where they are used for cleaning floors and walls. QAC exposure has already been involved in occupational asthma in healthcare workers or professional cleaners by many authors. They also have been suggested to play a role in contact dermatitis (CD) and urticaria in workers using cosmetics such as hairdressers or healthcare workers, inciting reglementary agencies to make recommendations regarding those products. However, distinguishing the irritant or sensitizing properties of chemicals is complex and as a result, the sensitizing property of QAC is still controverted. Moreover, the precise mechanisms underlying the possible sensitization effect are still under investigation, and to date, only a few studies have documented an immunological mechanism. Besides, QAC have been suggested to be responsible for neuromuscular blocking agents (NMBA) sensitization by cross-reactivity. This hypothesis is supported by a higher prevalence of quaternary ammonium (QA)-specific IgE in the professionally exposed populations, such as hairdressers, cleaners, or healthcare workers, suggesting that the sensitization happens with structurally similar compounds present in the environment. This review summarizes the newest knowledge about QAC and their role in hypersensitivities. After describing the different QAC, their structure and use, the most relevant studies about the effects of QAC on the immune system will be reviewed and discussed.

The Inflammatory Response in Human Keratinocytes Exposed to Cinnamaldehyde Is Regulated by Nrf2.

Keratinocytes (KC) play a crucial role in epidermal barrier function, notably through their metabolic activity and the detection of danger signals. Chemical sensitizers are known to activate the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2), leading to cellular detoxification and suppressed proinflammatory cytokines such as IL-1ß, a key cytokine in skin allergy. We investigated the role of Nrf2 in the control of the proinflammatory response in human KC following treatment with Cinnamaldehyde (CinA), a well-known skin sensitizer. We used the well-described human KC cell line KERTr exposed to CinA. Our results showed that 250 µM of CinA did not induce any Nrf2 accumulation but increased the expression of proinflammatory cytokines. In contrast, 100 µM of CinA induced a rapid accumulation of Nrf2, inhibited IL-1ß transcription, and downregulated the zymosan-induced proinflammatory response. Moreover, Nrf2 knockdown KERTr cells (KERTr ko) showed an increase in proinflammatory cytokines. Since the inhibition of Nrf2 has been shown to alter cellular metabolism, we performed metabolomic and seahorse analyses. The results showed a decrease in mitochondrial metabolism following KERTr ko exposure to CinA 100 µM. In conclusion, the fate of Nrf2 controls proinflammatory cytokine production in KCs that could be linked to its capacity to preserve mitochondrial metabolism upon chemical sensitizer exposure.

Biodegradable nanoparticles meet the bronchial airway barrier: how surface properties affect their interaction with mucus and epithelial cells.

Despite the wide interest raised by lung administration of nanoparticles (NPs) for the treatment of various diseases, little information is available on their effect toward the airway epithelial barrier function. In this study, the potential damage of the pulmonary epithelium upon exposure to poly(lactide-co-glycolide) (PLGA) NPs has been assessed in vitro using a Calu-3-based model of the bronchial epithelial barrier. Positively and negatively charged as well as neutral PLGA NPs were obtained by coating their surface with chitosan (CS), poloxamer (PF68), or poly(vinyl alcohol) (PVA). The role of NP surface chemistry and charge on the epithelial resistance and mucus turnover, using MUC5AC as a marker, was investigated. The interaction with mucin reduced the penetration of CS- and PVA-coated NPs, while the hydrophilic PF68-coated NPs diffused across the mucus barrier leading to a higher intracellular accumulation. Only CS-coated NPs caused a transient but reversible decrease of the trans-epithelial electrical resistance (TEER). None of the NP formulations increased MUC5AC mRNA expression or the protein levels. These in vitro results highlight the safety of PLGA NPs toward the integrity and function of the bronchial airway barrier and demonstrate the crucial role of NP surface properties to achieve a controlled and sustained delivery of drugs via the pulmonary route.

Corrigendum: The Nrf2-Antioxidant Response Element Signaling Pathway Controls Fibrosis and Autoimmunity in Scleroderma.

[This corrects the article DOI: 10.3389/fimmu.2018.01896.].

Immune-competent in vitro co-culture models as an approach for skin sensitisation assessment.

There is a complex interplay between numerous cell types that act at different steps of the mechanism leading to allergic contact dermatitis. The validated in vitro methods for skin sensitisation assessment provide good statistical correspondence to local lymph node assay (LLNA) or to human data but, for the most part, poorly represent the actual in vivo situation as they generally involve single cell type culture in 2D. Significant progress has been made over the past decades to develop new technologies of data generation concurrently with novel approaches to improve the models especially by the use of co-culture. The importance of heterotypic cell-cell interactions in the in vitro assessment of skin sensitisation should not be overlooked. This review addresses the technical aspects to take into consideration when co-culturing depending on the desired objective and describes the different keratinocytes and dendritic cells co-cultures developed in 2D and 3D. To date, from a regulatory point of view, no alternative method to animal testing for skin sensitisation potential assessment using a keratinocytes and dendritic cells co-culture model is yet proposed. This review also presents several directions of further development.

Metallic haptens induce differential phenotype of human dendritic cells through activation of mitogen-activated protein kinase and NF-kappaB pathways.

Dendritic cells (DCs) play a major role in the regulation of immune responses to a variety of antigens (Ag) and haptens which participate in the process of DC maturation. Indeed, metallic haptens are able to induce DC maturation in vitro but the mechanism of this maturation is not well understood. We and others have already shown that NiSO(4) activates p38 mitogen-activated protein kinases (p38MAPK), c-jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK) and the transcription factor NF-kappaB during the early events of DCs maturation. However, the effect of other metallic haptens on DC maturation is still poorly understood. In the present study, using dendritic cells derived from CD34(+) cord blood cells, we showed that both NiSO(4) and CoCl(2) induced the expression of CD86, CD83, HLA-DR and CD40 and the production of IL-6 in human DCs while K(2)Cr(2)O(7) induced only a slight upregulation of CD86. Interestingly, only NiSO(4) was able to induce the production of IL-12p40. NiSO(4) and CoCl(2) but not K(2)Cr(2)O(7) were able to activate the MAPK pathway and the transcription factor NF-kappaB. The role of MAPKs in metals-induced DC maturation was then evaluated using well-described pharmacological inhibitors. Our results suggest that p38MAPK activation regulates the expression of CD86 and CD83 induced by NiSO(4) while it only affects the expression of CD83 induced by CoCl(2). IL-6 production induced by NiSO(4) and CoCl(2) strongly depended on all MAPKs. IL-12p40 synthesis after NiSO(4) treatment was regulated by both p38MAPK and JNK pathways whereas ERK may play an inhibitory role. Our results show that both NiSO(4) and CoCl(2) activate similar signaling pathways that are playing different roles in DC maturation depending on the hapten used.