Activation Of Langerhans Cells Research Articles

Integrin α5 regulates motility of human monocyte-derived Langerhans cells during immune response.

Langerhans cells (LCs) are mainly present in the epidermis and mucosa, and have important roles during skin infection. Migration of LCs to lymph nodes is essential for antigen presentation. However, due to the difficulties in isolating and culturing human LCs, it is not fully understood how LCs move and interact with the extracellular matrix (ECM) through their adhesion molecules such as integrin, during the immune responses. In this study, we aimed to investigate LC motility, cell shape and the role of integrin under inflammatory conditions using monocyte-derived Langerhans cells (moLCs) as a model. As a result, lipopolysaccharide (LPS) stimulation increased adhesion on fibronectin coated substrate and integrin α5 expression in moLCs. Time-lapse imaging of moLCs revealed that stimulation with LPS elongated cell shape, whilst decreasing their motility. Additionally, this decrease in motility was not observed when pre-treated with a neutralising antibody targeting integrin α5. Together, our data suggested that activation of LCs decreases their motility by promoting integrin α5 expression to enhance their affinity to the fibronectin, which may contribute to their migration during inflammation.

Disrupted Neural Regeneration in Dry Eye Secondary to Ankylosing Spondylitis-With a Theoretical Link between Piezo2 Channelopathy and Gateway Reflex, WDR Neurons, and Flare-Ups.

This study aimed at analyzing the corneal neural regeneration in ankylosing spondylitis patients using in vivo corneal confocal microscopy in correlation with Langerhans cell density, morphology, and dry eye parameters. Approximately 24 ankylosing spondylitis subjects and 35 age- and gender-matched control subjects were enrolled. Data analysis showed that all corneal nerve-fiber descriptives were lower in the ankylosing spondylitis group, implicating disrupted neural regeneration. Peripheral Langerhans cell density showed a negative correlation with nerve fiber descriptions. A negative correlation between tear film break-up time and corneal nerve fiber total branch density was detected. The potential role of somatosensory terminal Piezo2 channelopathy in the pathogenesis of dry eye disease and ankylosing spondylitis is highlighted in our study, exposing the neuroimmunological link between these diseases. We hypothesized earlier that spinal neuroimmune-induced sensitization due to this somatosensory terminal primary damage could lead to Langerhans cell activation in the cornea, in association with downregulated Piezo1 channels on these cells. This activation could lead to a Th17/Treg imbalance in dry eye secondary to ankylosing spondylitis. Hence, the corneal Piezo2 channelopathy-induced impaired Piezo2-Piezo1 crosstalk could explain the disrupted neural regeneration. Moreover, the translation of our findings highlights the link between Piezo2 channelopathy-induced gateway to pathophysiology and the gateway reflex, not to mention the potential role of spinal wide dynamic range neurons in the evolution of neuropathic pain and the flare-ups in ankylosing spondylitis and dry eye disease.

OS03-07: Photobiomodulation Controls Keratinocytes Inflammatory Response through Nrf2 and Reduces Langerhans Cells Activation

OS03-07: Photobiomodulation Controls Keratinocytes Inflammatory Response through Nrf2 and Reduces Langerhans Cells Activation

Evidence of Disruption in Neural Regeneration in Dry Eye Secondary to Rheumatoid Arthritis.

The purpose of our study was to analyze abnormal neural regeneration activity in the cornea through means of confocal microscopy in rheumatoid arthritis patients with concomitant dry eye disease. We examined 40 rheumatoid arthritis patients with variable severity and 44 volunteer age- and gender-matched healthy control subjects. We found that all examined parameters were significantly lower (p < 0.05) in rheumatoid arthritis patients as opposed to the control samples: namely, the number of fibers, the total length of the nerves, the number of branch points on the main fibers and the total nerve-fiber area. We examined further variables, such as age, sex and the duration of rheumatoid arthritis. Interestingly, we could not find a correlation between the above variables and abnormal neural structural changes in the cornea. We interpreted these findings via implementing our hypotheses. Correspondingly, one neuroimmunological link between dry eye and rheumatoid arthritis could be through the chronic Piezo2 channelopathy-induced K2P-TASK1 signaling axis. This could accelerate neuroimmune-induced sensitization on the spinal level in this autoimmune disease, with Langerhans-cell activation in the cornea and theorized downregulated Piezo1 channels in these cells. Even more importantly, suggested principal primary-damage-associated corneal keratocyte activation could be accompanied by upregulation of Piezo1. Both activation processes on the periphery would skew the plasticity of the Th17/Treg ratio, resulting in Th17/Treg imbalance in dry eye, secondary to rheumatoid arthritis. Hence, chronic somatosensory-terminal Piezo2 channelopathy-induced impaired Piezo2-Piezo1 crosstalk could result in a mixed picture of disrupted functional regeneration but upregulated morphological regeneration activity of these somatosensory axons in the cornea, providing the demonstrated abnormal neural corneal morphology.

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.

The immunological effects of intradermal particle-based vaccine delivery using a novel microinjection needle studied in a human skin explant model.

For intradermal (ID) immunisation, novel needle-based delivery systems have been proposed as a better alternative to the Mantoux method. However, the penetration depth of needles in the human skin and its effect on immune cells residing in the different layers of the skin has not been analyzed. A novel and user-friendly silicon microinjection needle (Bella-muTM) has been developed, which allows for a perpendicular injection due to its short needle length (1.4-1.8mm) and ultrashort bevel. We aimed to characterize the performance of this microinjection needle in the context of the delivery of a particle-based outer membrane vesicle (OMV) vaccine using an ex vivo human skin explant model. We compared the needles of 1.4 and 1.8mm with the conventional Mantoux method to investigate the depth of vaccine injection and the capacity of the skin antigen-presenting cell (APC) to phagocytose the OMVs. The 1.4mm needle deposited the antigen closer to the epidermis than the 1.8mm needle or the Mantoux method. Consequently, activation of epidermal Langerhans cells was significantly higher as determined by dendrite shortening. We found that five different subsets of dermal APCs are able to phagocytose the OMV vaccine, irrespective of the device or injection method. ID delivery using the 1.4mm needle of a OMV-based vaccine allowed epidermal and dermal APC targeting, with superior activation of Langerhans cells. This study indicates that the use of a microinjection needle improves the delivery of vaccines in the human skin.

Immune activation of vaginal human Langerhans cells increases susceptibility to HIV-1 infection

Vaginal inflammation increases the risk for sexual HIV-1 transmission but underlying mechanisms remain unclear. In this study we assessed the impact of immune activation on HIV-1 susceptibility of primary human vaginal Langerhans cells (LCs). Vaginal LCs isolated from human vaginal tissue expressed a broad range of TLRs and became activated after exposure to both viral and bacterial TLR ligands. HIV-1 replication was restricted in immature vaginal LCs as only low levels of infection could be detected. Notably, activation of immature vaginal LCs by bacterial TLR ligands increased HIV-1 infection, whereas viral TLR ligands were unable to induce HIV-1 replication in vaginal LCs. Furthermore, mature vaginal LCs transmitted HIV-1 to CD4 T cells. This study emphasizes the role for vaginal LCs in protection against mucosal HIV-1 infection, which is abrogated upon activation. Moreover, our data suggest that bacterial STIs can increase the risk of HIV-1 acquisition in women.

Effect of ultrasound treatment of the skin on activation of Langerhans cells and antibody production in rodents.

In this study, we investigated whether stimulating the skin with ultrasound (US) could activate Langerhans cells (LCs) - antigen-presenting cells in the epidermis and stimulate antibody production following the subcutaneous and intradermal injection of ovalbumin (OVA) in hairless rats and BALB/c mice. Three different US frequencies (20 kHz, 1, and 3 MHz) were used and the expression of langerin was monitored as a marker for the activation of LCs in the epidermal sheet. In hairless rats, the langerin signal peaked at 12 h post-US treatment and returned to control levels at 24 h. Its expression increased with increasing irradiation time, up to 20 min, and 20 kHz US induced the highest langerin expression among the three frequencies tested. These results were reproduced in BALB/c mice. When the skin was pretreated with 20 kHz US at 0.41 W/cm2 for 10 min, the production of OVA-specific immunoglobulin G1 in mice increased by 2.8- and 3.4-fold 28 days after subcutaneous or intradermal OVA injections, respectively. These findings indicate that stimulating the skin with US can trigger skin immune responses, leading to effective antigen-specific antibody production. US-assisted transdermal vaccine delivery delivers antigens to the skin and evokes an immune response, providing an effective noninvasive immunization strategy.

MTORC1 signaling in antigen-presenting cells of the skin restrains CD8+ Tcell priming.

How mechanistic target of rapamycin complex 1 (mTORC1), a key regulator of cellular metabolism, affects dendritic cell (DC) metabolism and Tcell-priming capacity has primarily been investigated invitro, but how mTORC1 regulates this invivo remains poorly defined. Here, using mice deficient for mTORC1 component raptor in DCs, we find that loss of mTORC1 negatively affects glycolytic and fatty acid metabolism and maturation of conventional DCs, particularly cDC1s. Nonetheless, antigen-specific CD8+ Tcell responses to infection are not compromised and are even enhanced following skin immunization. This is associated with increased activation of Langerhans cells and a subpopulation of EpCAM-expressing cDC1s, of which the latter show an increased physical interaction with CD8+ Tcells in situ. Together, this work reveals that mTORC1 limits CD8+ Tcell priming invivo by differentially orchestrating the metabolism and immunogenicity of distinct antigen-presenting cell subsets, which may have implications for clinical use of mTOR inhibitors.

A clinical review: Covid-19 and dermatology

On March 11, 2020, the World Health Organization (WHO) declared Corona Virus Disease-2019(COVID-19) as a pandemic disease caused by SARS-CoV-2. During the COVID-19 pandemic, the importance of dermatology practice in patient management has emerged. Skin involvement was rarely documented in the first reported case series. The reason for this has been shown to be that a complete dermatological examination can not be performed in cases. Over time, significantly higher rates of skin findings have been reported.The mechanism of skin lesions associated with COVID-19 is not yet clear. The most common view is that lymphocytic vasculitis caused by vascularly located viral particles and langerhans cell activation is caused by an immune response to infection leading to vasodilation and spongiosis.Keratinocytes are thought to be secondary targets.It has been emphasized that skin findings are encountered at rates varying between 2-20% in COVID-19 patients. Casas et al. performed the first prospective study to classify the skin manifestations of COVID-19 into five major groups, including pseudo-chilblains (19%), other vesicular eruptions (9%), maculopapuler eruption (47%), livedo or necrosis (6%) and urticarial lesions (19%).

BMPR1a Is Required for the Optimal TGFβ1-Dependent CD207+ Langerhans Cell Differentiation and Limits Skin Inflammation through CD11c+ Cells

The cytokine TGFβ1 induces epidermal Langerhans cell (LC) differentiation from human precursors, an effect mediated through BMPR1a/ALK3 signaling, as revealed from ectopic expression and receptor inhibition studies. Whether TGFβ1‒BMPR1a signaling is required for LC differentiation invivo remained incompletely understood. We found that TGFβ1-deficient mice show defective perinatal expansion and differentiation of LCs. LCs can be identified within the normal healthy human epidermis by anti-BMPR1a immunohistology staining. Deletion of BMPR1a in all (vav+) hematopoietic cells revealed that BMPR1a is required for the efficient TGFβ1-dependent generation of CD207+ LC-like cells from CD11c+ intermediates invitro. Similarly, BMPR1a was required for the optimal induction of CD207 by preformed major histocompatibility complex II‒positive epidermal resident LC precursors in the steady state. BMPR1a expression is strongly upregulated in epidermal cells in psoriatic lesions, and BMPR1aΔCD11c mice showed a defect in the resolution phase of allergic and psoriatic skin inflammation. Moreover, whereas LCs from these mice expressed CD207, BMPR1a counteracted LC activation and migration from skin explant cultures. Therefore, TGFβ1‒BMPR1a signaling seems to be required for the efficient induction of CD207 during LC differentiation in the steady state, and bone marrow‒derived lesional CD11c+ cells may limit established skin inflammation through enhanced BMPR1a signaling.

A Multi-Organ-on-Chip Approach to Investigate How Oral Exposure to Metals Can Cause Systemic Toxicity Leading to Langerhans Cell Activation in Skin.

Investigating systemic toxicity in vitro is still a huge challenge. Here, a multi-organ-on-chip approach is presented as a typical case of topical exposure of oral mucosa to metals, which are known to activate the immune system and in turn may result in skin inflammation. Reconstructed human gingiva (RHG) and reconstructed human skin containing MUTZ-3–derived Langerhans cells (MUTZ-LC) in the epidermis (RHS-LC) were incorporated into a HUMIMIC Chip3plus, connected by dynamic flow and cultured for a total period of 72 h. Three independent experiments were performed each with an intra-experiment replicate in order to assess the donor and technical variations. After an initial culture period of 24 h to achieve stable dynamic culture conditions, nickel sulfate was applied topically to RHG for 24 h, and LC activation (maturation and migration) was determined in RHS-LC after an additional 24 h incubation time. A stable dynamic culture of RHG and RHS-LC was achieved as indicated by the assessment of glucose uptake, lactate production, and lactate dehydrogenase release into the microfluidics compartment. Nickel exposure resulted in no major histological changes within RHG or RHS-LC, or cytokine release into the microfluidics compartment, but did result in an increased activation of LC as observed by the increased mRNA levels of CD1a, CD207, HLA-DR, and CD86 in the dermal compartment (hydrogel of RHS-LC (PCR)). This is the first study to describe systemic toxicity and immune cell activation in a multi-organ setting and can provide a framework for studying other organoids in the future.

Early antitumor activity of oral Langerhans cells is compromised by a carcinogen

Early diagnosis of oral squamous cell carcinoma (OSCC) remains an unmet clinical need. Therefore, elucidating the initial events of OSCC preceding tumor development could benefit OSCC prognosis. Here, we define the Langerhans cells (LCs) of the tongue and demonstrate that LCs protect the epithelium from carcinogen-induced OSCC by rapidly priming αβT cells capable of eliminating γH2AX+ epithelial cells, whereas γδT and natural killer cells are dispensable. The carcinogen, however, dysregulates the epithelial resident mononuclear phagocytes, reducing LC frequencies, while dendritic cells (DCs), macrophages, and plasmacytoid DCs (pDCs) populate the epithelium. Single-cell RNA-sequencing analysis indicates that these newly differentiated cells display an immunosuppressive phenotype accompanied by an expansion of T regulatory (Treg) cells. Accumulation of the Treg cells was regulated, in part, by pDCs and precedes the formation of visible tumors. This suggests LCs play an early protective role during OSCC, yet the capacity of the carcinogen to dysregulate the differentiation of mononuclear phagocytes facilitates oral carcinogenesis.

Analysis of immune response induction mechanisms implicating the dose-sparing effect of transcutaneous immunization using a self-dissolving microneedle patch

Transcutaneous immunization (TCI) is an effective vaccination method that is easier and less painful than the conventional injectable vaccination method. We previously developed self-dissolving microneedle patches (sdMN) and demonstrated that this TCI method has a high vaccination efficacy in mice and humans. To elucidate the mechanism of immune response induction, which is the basis for the efficacy and safety of TCI with sdMN, we examined the local reaction of the skin where sdMN was applied and the kinetics and differentiation status of immune cells in the draining lymph nodes (DLNs). We found that gene expression of the proinflammatory cytokine Il1b and the downstream transcription factor Irf7 was markedly upregulated in skin tissues after sdMN application. Moreover, activation of Langerhans cells and CD207− dermal dendritic cells, which are subsets of antigen-presenting cells (APCs) in the skin, and their migration to the DLNs were promoted. Furthermore, the activated APC subsets promoted CD4+ T cell and B cell differentiation and the formation of germinal centers, which are the sites of high-affinity antibody production. These phenomena associated with sdMN application may contribute to the efficient production of antigen-specific antibodies after TCI using sdMN. These findings provide essential information regarding immune response induction mechanisms for the development and improvement of TCI preparations.

Dynamic Immune/Inflammation Precision Medicine: The Good and the Bad Inflammation in Infection and Cancer

Normal or “good” inflammation process starts from a local cellular response against injury or any infectious agent, with the activation of neutrophils, macrophages, Langerhans cells, dendritic cells, and innate immune cells. Cytokines and chemokines are produced to amplify the local inflammatory process followed by the migration of immune cells to the regional lymph nodes where adaptive immune response is initiated. Systemic inflammation enhances the biological response to mobilize additional cells from central and peripheral immune/hematopoietic system. Local mechanisms to limit inflammation are initiated and lead to healing. During the normal inflammatory process, there is a balance between the production of inflammatory chemokines/cytokines such as Tumor Necrosis Factor (TNF)-α, interleukin (IL)-6 and IL-1 and the production of compounds that limit inflammation and have an immune suppressive effect, such as IL-10 and Transforming Factor (TGF) β. IL-6 and IL-6/soluble IL-6 Receptor (R) complex stimulate liver cells to produce inflammatory proteins, which represents the systemic inflammation response. The magnitude and the duration of the systemic inflammatory response are linked to the cause, under genetic and epigenetic control. Significant inflammation as seen in septic shock, in severe forms of infections or in certain active cancers, represents the “bad inflammation”, correlated with a poor prognosis. In addition, the persistence of a chronic smoldering inflammation may lead to pathological situations which are observed in the majority of inflammatory, degenerative, dysmetabolic, or dysimmune diseases and cancer. Chronic smoldering inflammation is a cross between different pathological situations possibly linked. In addition, within the tumor microenvironment, inflammatory process results from different cellular mechanisms modulated by metabolic and vascular changes. On the contrary, a limited and balanced inflammation initiates the normal immune response, including the adaptive response which amplifies any immunotherapy, including vaccines. Immune checkpoint inhibitors and chimeric antigen receptor (CAR) T-cells are associated with cytokine release syndrome, a clinical risk leading to the use of anti-cytokine drugs. Nowadays, it is time to monitor the dynamic inflammatory process for a better immune precision medicine in both infections and cancer.

Impact of Glycan Linkage to Staphylococcus aureus Wall Teichoic Acid on Langerin Recognition and Langerhans Cell Activation.

Staphylococcus aureus is the leading cause of skin and soft tissue infections. It remains incompletely understood how skin-resident immune cells respond to invading S. aureus and contribute to an effective immune response. Langerhans cells (LCs), the only professional antigen-presenting cell type in the epidermis, sense S. aureus through their pattern-recognition receptor langerin, triggering a proinflammatory response. Langerin recognizes the β-1,4-linked N-acetylglucosamine (β1,4-GlcNAc) but not α-1,4-linked GlcNAc (α1,4-GlcNAc) modifications, which are added by dedicated glycosyltransferases TarS and TarM, respectively, on the cell wall glycopolymer wall teichoic acid (WTA). Recently, an alternative WTA glycosyltransferase, TarP, was identified, which also modifies WTA with β-GlcNAc but at the C-3 position (β1,3-GlcNAc) of the WTA ribitol phosphate (RboP) subunit. Here, we aimed to unravel the impact of β-GlcNAc linkage position for langerin binding and LC activation. Using genetically modified S. aureus strains, we observed that langerin similarly recognized bacteria that produce either TarS- or TarP-modified WTA, yet tarP-expressing S. aureus induced increased cytokine production and maturation of in vitro-generated LCs compared to tarS-expressing S. aureus. Chemically synthesized WTA molecules, representative of the different S. aureus WTA glycosylation patterns, were used to identify langerin-WTA binding requirements. We established that β-GlcNAc is sufficient to confer langerin binding, thereby presenting synthetic WTA molecules as a novel glycobiology tool for structure-binding studies and for elucidating S. aureus molecular pathogenesis. Overall, our data suggest that LCs are able to sense all β-GlcNAc-WTA producing S. aureus strains, likely performing an important role as first responders upon S. aureus skin invasion.

FOXP3, CD208, and CD206 Expression in Canine Cutaneous Histiocytoma.

Canine cutaneous histiocytoma (CCH) is a noninfectious tumor that spontaneously regresses. It is suggested that this regression is due to tumor cell maturation, which is responsible for CD8 lymphocyte activation and tumor cell destruction. Nevertheless, the possible role of the immune microenvironment in tumor regression has not been investigated to date. The aim of this study was to investigate the expression of CD208 and FoxP3 as markers of dendritic cells and regulatory T lymphocytes, respectively, and tumor cell expression of CD206 as a marker of Langerhans cell activation, and relate these parameters to the different phases of CCH and to intratumoral T cell infiltration. Formalin-fixed, paraffin-embedded samples from 31 CCH were evaluated. In each case, the mitotic count and regression phase were recorded. Within the tumor, a quantitative evaluation of immunolabeled CD208+ cells, FoxP3+ cells, and CD3+ lymphocytes was performed, as well as the CD206+ tumor cell location. Intratumoral CD208+ cells correlated with CD3+ lymphocytic infiltration. The possible role of dendritic cells in tumor regression was not confirmed since CD208 seemed to be a nonspecific marker for canine dendritic cells. FoxP3+ lymphocyte density was not correlated with any parameter. Neoplastic Langerhans cells presented progressive CD206 expression, from the bottom of the tumor to the epidermis, which correlated with the tumor regression phase and with intratumoral T lymphocyte infiltration. In conclusion, we confirmed a CD206 phenotype change in tumor cells in a spatial group-related pattern, supporting the hypothesis that tumoral Langerhans cells acquire a mature phenotype with tumor regression.

Selective AhR knockout in langerin-expressing cells abates Langerhans cells and polarizes Th2/Tr1 in epicutaneous protein sensitization.

The aryl hydrocarbon receptor (AhR) represents an environmental sensor regulating immune responses. In the skin, AhR is expressed in several cell types, including keratinocytes, epidermal Langerhans cells (LC), and dermal dendritic cells (DC). The mechanisms how AhR activates or inhibits cutaneous immune responses remain controversial, owing to differences in the cell-specific functions of AhR and the different activating ligands. Therefore, we sought to investigate the role of AhR in LC and langerin+ and negative DC in the skin. To this aim, we generated Langerin-specific and CD11c-specific knockout (-/-) mice lacking AhR, respectively, in LC and Langerin+ dermal DC and in all CD11c+ cells. These were then tested in an epicutaneous protein (ovalbumin, Ova) sensitization model. Immunofluorescence microscopy and flow cytometry revealed that Langerin-AhR-/- but not CD11c-AhR-/- mice harbored a decreased number of LC with fewer and stunted dendrites in the epidermis as well as a decreased number of LC in skin-draining lymph nodes (LN). Moreover, in the absence of AhR, we detected an enhanced T helper type-2 (Th2) [increased interleukin 5 (IL-5) and interleukin 13 (IL-13)] and T regulatory type-1 (Tr1) (IL-10) response when LN cells were challenged with Ova in vitro, though the number of regulatory T cells (Treg) in the LN remained comparable. Langerin-AhR-/- mice also exhibited increased blood levels of Ova-specific immunoglobulin E (IgE). In conclusion, deletion of AhR in langerin-expressing cells diminishes the number and activation of LC, while enhancing Th2 and Tr1 responses upon epicutaneous protein sensitization.

Syndecan 4 Upregulation on Activated Langerhans Cells Counteracts Langerin Restriction to Facilitate Hepatitis C Virus Transmission.

Sexually transmitted Hepatitis C virus (HCV) infections and high reinfections are a major concern amongst men who have sex with men (MSM) living with HIV-1 and HIV-negative MSM. Immune activation and/or HIV-1 coinfection enhance HCV susceptibility via sexual contact, suggesting that changes in immune cells or external factors are involved in increased susceptibility. Activation of anal mucosal Langerhans cells (LCs) has been implicated in increased HCV susceptibility as activated but not immature LCs efficiently retain and transmit HCV to other cells. However, the underlying molecular mechanism of transmission remains unclear. Here we identified the Heparan Sulfate Proteoglycan Syndecan 4 as the molecular switch, controlling HCV transmission by LCs. Syndecan 4 was highly upregulated upon activation of LCs and interference with Heparan Sulfate Proteoglycans or silencing of Syndecan 4 abrogated HCV transmission. These data strongly suggest that Syndecan 4 mediates HCV transmission by activated LCs. Notably, our data also identified the C-type lectin receptor langerin as a restriction factor for HCV infection and transmission. Langerin expression abrogated HCV infection in HCV permissive cells, whereas langerin expression on the Syndecan 4 expressing cell line strongly decreased HCV transmission to a target hepatoma cell line. These data suggest that the balanced interplay between langerin restriction and Syndecan 4 transmission determines HCV dissemination. Silencing of langerin enhanced HCV transmission whereas silencing Syndecan 4 on activated LCs decreased transmission. Blocking Heparan Sulfate Proteoglycans abrogated HCV transmission by LCs ex vivo identifying Heparan Sulfate Proteoglycans and Syndecan 4 as potential targets to prevent sexual transmission of HCV. Thus, our data strongly suggest that the interplay between receptors promotes or restricts transmission and further indicate that Syndecan 4 is the molecular switch controlling HCV susceptibility after sexual contact.

Migratory dendritic cells in skin-draining lymph nodes have nickel-binding capabilities

Nickel (Ni) is the most frequent metal allergen and induces Th1-dependent type-IV allergies. In local skin, epidermal Langerhans cells (LCs) and/or dermal dendritic cells (DCs) uptake antigens and migrate to draining lymph nodes (LNs). However, the subsets of antigen-presenting cells that contribute to Ni presentation have not yet been identified. In this study, we analyzed the Ni-binding capabilities of murine DCs using fluorescent metal indicator Newport Green. Elicitation of Ni allergy was assessed after intradermal (i.d.) injection of Ni-treated DCs into ear pinnae of Ni-sensitized mice. The Ni-binding capabilities of MHC class IIhi CD11cint migratory DCs were significantly stronger than those of MHC class IIint CD11chi resident DCs and CD11cint PDCA1+ MHC class IIint B220+ plasmacytoid DCs. Migratory DCs in skin-draining and mandibular LNs showed significantly stronger Ni-binding capabilities than those in mesenteric and medial iliac LNs. An i.d. injection of IL-1β induced the activation of LCs and dermal DCs with strong Ni-binding capabilities. Ni-binding LCs were detected in draining LNs after i.d. challenge with IL-1β and Ni. Moreover, an i.d. injection of Ni-treated DCs purified from skin-draining LNs elicited Ni-allergic inflammation. These results demonstrated that migratory DCs in skin-draining LNs have strong Ni-binding capabilities and elicit Ni allergy.