Dendritic Epidermal T Cells Research Articles

Skin-Resident γδ T Cells Mediate Potent and Selective Antitumor Cytotoxicity through Directed Chemotactic Migration and Mobilization of Cytotoxic Granules

Dendritic epidermal T cells (DETCs) are a unique subset of γδ T cells that reside predominantly in mouse epidermis, yet their antitumor functions remain enigmatic. Here we report that DETCs mediate potent and exquisitely selective cytotoxicity against diverse tumor types while sparing healthy cells. In vitro, DETCs induced apoptosis in melanoma, hepatoma, colon carcinoma and lymphoma lines in a dose- and time-dependent manner that required direct cell-cell contact. In vivo, adoptive DETC transfer significantly suppressed melanoma growth and metastasis while prolonging survival. Mechanistically, DETCs upregulated perforin/granzyme B expression upon tumor recognition, and inhibition of this pathway ablated cytotoxicity. DETCs selectively homed to and formed intimate contacts with tumor cells in vivo through directed chemotaxis and aggregation. Tumor engagement triggered pro-inflammatory DETC activation while dampening immunosuppressive factors in the microenvironment. Notably, mTOR signaling coupled tumor recognition to DETC trafficking, cytotoxicity and inflammatory programs, as rapamycin treatment impaired effector functions and therapeutic efficacy. Collectively, these findings establish DETCs as multidimensional antitumor effectors and provide insights for harnessing their unique biology for cancer immunotherapy.

Tick extracellular vesicles undermine epidermal wound healing during hematophagy.

Wound healing has been extensively studied through the lens of inflammatory disorders and cancer, but limited attention has been given to hematophagy and arthropod-borne diseases. Hematophagous ectoparasites, including ticks, subvert the wound healing response to maintain prolonged attachment and facilitate blood-feeding. Here, we unveil a strategy by which extracellular vesicles (EVs) ensure blood-feeding and arthropod survival in three medically relevant tick species. We demonstrate through single cell RNA sequencing and murine genetics that wildtype animals infested with EV-deficient Ixodes scapularis display a unique population of keratinocytes with an overrepresentation of pathways connected to wound healing. Tick feeding affected keratinocyte proliferation in a density-dependent manner, which relied on EVs and dendritic epidermal T cells (DETCs). This occurrence was linked to phosphoinositide 3-kinase activity, keratinocyte growth factor (KGF) and transforming growth factor β (TGF-β) levels. Collectively, we uncovered a strategy employed by a blood-feeding arthropod that impairs the integrity of the epithelial barrier, contributing to ectoparasite fitness.

Diminished γδ T Cells during Murine Allergic Skin Inflammation Is Mediated by IL-4 Signaling in Keratinocytes.

Atopic dermatitis results in diminished barrier function and altered production of antimicrobial peptides. Dendritic epidermal T cells (DETCs) play an important role in the wound repair and inflammation process. Our previous work identified an IL-4-dependent loss of DETCs in Stat6VT mice and in the MC903-induced skin inflammation mouse model. However, the mechanisms through which IL-4 mediates the loss of DETCs are unclear. In this study, we show that IL-4Rα germline knockout mice (Il4ra-/-) have increased DETCs, faster wound healing, and increased epidermal differentiation complex gene and fibronectin expression. The absence of IL-4Rα minimized the MC903-induced loss of DETCs, and reciprocal bone marrow chimera experiments in Il4ra-/- and wild-type mice demonstrated structural nonhematopoietic IL-4-responsive cell-mediated DETC homeostasis. Skin keratinocyte-derived IL-15 decreased dramatically in the MC903 model, while injection of IL-15 rescued DETC loss by promoting DETC proliferation and limiting apoptosis. Conditional deletion of IL-4Rα from keratinocytes using Il4rafl/fl K14-Cre mice showed an increase of DETCs, increased IL-15 production, and diminished skin inflammation following wounding. These results suggest that IL-4-dependent effects on DETCs in allergic skin inflammation are mediated by the IL-4Rα receptor of keratinocytes.

Dendritic epidermal T cell hydrogel induces the polarization of M2 macrophages to promote the healing of deep tissue pressure injury

Dendritic epidermal T cells (DETCs) have been shown to promote wound healing. However, the mechanisms involved need to be better understood. In the present study, we investigated the role and mechanism of DETCs in deep tissue pressure injury (DTPI). We established the DTPI model using C57BL/6 mice. Then, DTPI was evaluated and analyzed by histological staining, immunohistochemistry, real-time PCR, Western blotting, and flow cytometry in different treatment groups (DETCs, DETCs/gel, Matrigel, Saline, and Normal group). The results showed that insulin-like growth factor 1 and vascular endothelial growth factor-A expression increased after local DETCs and DETCs/gel implantation in DTPI on days 3 and 7. M1 (inducible nitric oxide synthas-marked) macrophages were predominant at 3 days after DTPI. At 7 days, M1 macrophages were decreased, and M2 (CD206-marked) macrophages were increased in the DETCs and DETCs/gel groups. In vitro, in the co-culture of DETCs and RAW264.7, CD206 expression was significantly increased in M2 macrophages. In addition, Interleukin-17A initially inhibited wound healing 1 day after injury. However, it promoted wound healing at 7, 14, and 21 days after treatment with DETCs and DETCs/gel, respectively. In conclusion, our data suggest that exogenous DETCs improve DTPI wound healing by regulating M1 to M2 macrophage polarization.

TCR signaling and cellular metabolism regulate the capacity of murine epidermal γδ T cells to rapidly produce IL-13 but not IFN-γ.

Resident epidermal T cells of murine skin, called dendritic epidermal T cells (DETCs), express an invariant γδ TCR that recognizes an unidentified self-ligand expressed on epidermal keratinocytes. Although their fetal thymic precursors are preprogrammed to produce IFN-γ, DETCs in the adult epidermis rapidly produce IL-13 but not IFN-γ early after activation. Here, we show that preprogrammed IFN-γ-producing DETC precursors differentiate into rapid IL-13 producers in the perinatal epidermis. The addition of various inhibitors of signaling pathways downstream of TCR to the in vitro differentiation model of neonatal DETCs revealed that TCR signaling through the p38 MAPK pathway is essential for the functional differentiation of neonatal DETCs. Constitutive TCR signaling at steady state was also shown to be needed for the maintenance of the rapid IL-13-producing capacity of adult DETCs because in vivo treatment with the p38 MAPK inhibitor decreased adult DETCs with the rapid IL-13-producing capacity. Adult DETCs under steady-state conditions had lower glycolytic capacity than proliferating neonatal DETCs. TCR stimulation of adult DETCs induced high glycolytic capacity and IFN-γ production during the late phase of activation. Inhibition of glycolysis decreased IFN-γ but not IL-13 production by adult DETCs during the late phase of activation. These results demonstrate that TCR signaling promotes the differentiation of IL-13-producing DETCs in the perinatal epidermis and is needed for maintaining the rapid IL-13-producing capacity of adult DETCs. The low glycolytic capacity of adult DETCs at steady state also regulates the rapid IL-13 response and delayed IFN-γ production after activation.

Widespread and dynamic expression of granzyme C by skin-resident antiviral T cells.

After recognition of cognate antigen (Ag), effector CD8+ T cells secrete serine proteases called granzymes in conjunction with perforin, allowing granzymes to enter and kill target cells. While the roles for some granzymes during antiviral immune responses are well characterized, the function of others, such as granzyme C and its human ortholog granzyme H, is still unclear. Granzyme C is constitutively expressed by mature, cytolytic innate lymphoid 1 cells (ILC1s). Whether other antiviral effector cells also produce granzyme C and whether it is continually expressed or responsive to the environment is unknown. To explore this, we analyzed granzyme C expression in different murine skin-resident antiviral lymphocytes. At steady-state, dendritic epidermal T cells (DETCs) expressed granzyme C while dermal γδ T cells did not. CD8+ tissue-resident memory T cells (TRM) generated in response to cutaneous viral infection with the poxvirus vaccinia virus (VACV) also expressed granzyme C. Both DETCs and virus-specific CD8+ TRM upregulated granzyme C upon local VACV infection. Continual Ag exposure was not required for maintained TRM expression of granzyme C, although re-encounter with cognate Ag boosted expression. Additionally, IL-15 treatment increased granzyme C expression in both DETCs and TRM. Together, our data demonstrate that granzyme C is widely expressed by antiviral T cells in the skin and that expression is responsive to both environmental stimuli and TCR engagement. These data suggest that granzyme C may have functions other than killing in tissue-resident lymphocytes.

Ets1 and IL17RA cooperate to regulate autoimmune responses and skin immunity to Staphylococcus aureus.

Ets1 is a lymphoid-enriched transcription factor that regulates B- and Tcell functions in development and disease. Mice that lack Ets1 (Ets1 KO) develop spontaneous autoimmune disease with high levels of autoantibodies. Naïve CD4 + T cells isolated from Ets1 KO mice differentiate more readily to Th17 cells that secrete IL-17, a cytokine implicated in autoimmune disease pathogenesis. To determine if increased IL-17 production contributes to the development of autoimmunity in Ets1 KO mice, we crossed Ets1 KO mice to mice lacking the IL-17 receptor A subunit (IL17RA KO) to generate double knockout (DKO) mice. In this study, the status of the immune system of DKO and control mice was assessed utilizing ELISA, ELISpot, immunofluorescent microscopy, and flow cytometric analysis of the spleen, lymph node, skin. The transcriptome of ventral neck skin was analyzed through RNA sequencing. S. aureus clearance kinetics in in exogenously infected mice was conducted using bioluminescent S. aureus and tracked using an IVIS imaging experimental scheme. We found that the absence of IL17RA signaling did not prevent or ameliorate the autoimmune phenotype of Ets1 KO mice but rather that DKO animals exhibited worse symptoms with striking increases in activated B cells and secreted autoantibodies. This was correlated with a prominent increase in the numbers of T follicular helper (Tfh) cells. In addition to the autoimmune phenotype, DKO mice also showed signs of immunodeficiency and developed spontaneous skin lesions colonized by Staphylococcus xylosus. When DKO mice were experimentally infected with Staphylococcus aureus, they were unable to clear the bacteria, suggesting a general immunodeficiency to staphylococcal species. γδ T cells are important for the control of skin staphylococcal infections. We found that mice lacking Ets1 have a complete deficiency of the γδ T-cell subset dendritic epidermal T cells (DETCs), which are involved in skin woundhealing responses, but normal numbers of other skin γδ T cells. To determine if loss of DETC combined with impaired IL-17 signaling might promote susceptibility to staph infection, we depleted DETC from IL17RA KO mice and found that the combined loss of DETC and impaired IL-17 signaling leads to an impaired clearance of the infection. Our studies suggest that loss of IL-17 signaling can result in enhanced autoimmunity in Ets1 deficient autoimmune-prone mice. In addition, defects in wound healing, such as that caused by loss of DETC, can cooperate with impaired IL-17 responses to lead to increased susceptibility to skin staph infections.

Skin Whole-Mount Immunofluorescent Staining Protocol, 3D Visualization, and Spatial Image Analysis.

The use of polychromatic immunofluorescent staining on whole-mount skin enables cell type characterization and aids in the delineation of the physiological and immunological strategies used by the skin to combat pathogens. Using whole-mount skin for polychromatic immunofluorescent staining removes the need for histological sectioning and enables the visualization of anatomical structures and immune cell types in three dimensions. Here we present a detailed protocol for immunostaining with fluorescence-conjugated primary antibodies in whole-mount skin to reveal structural landmarks and specific immune cell types using confocal laser scanning microscopy (CLSM) (Basic Protocol 1). The optimized staining panel reveals structural features such as blood vessels (CD31 antibody) and the lymphatic network (LYVE-1 antibody), in combination with MHCII antibodies for antigen-presenting cells (APCs), CD64 for macrophages and monocytes, CD103 for dendritic epidermal T cells (DETC), and CD326 for Langerhans cells (LC). Basic Protocol 2 describes image visualization pipelines using open-source software (ImageJ/FIJI), enabling four visualization options (z-projections, orthogonal views, 3D visualization, and animation). Basic Protocol 3 describes a quantitative analysis pipeline using CellProfiler to characterize the spatial relationship between cell types using mathematical indices such as Spatial Distribution Index (SDI), Neighborhood Frequency (NF), and Normalized Median Evenness (NME). These protocols will enable researchers to stain, record, analyze, and interpret data from whole-mount skin using commercially available reagents in a CLSM-equipped laboratory and freely available analysis software. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Immunofluorescent staining and imaging for whole-mount mouse skin Basic Protocol 2: File rendering and visualization using FIJI Basic Protocol 3: Spatial image analysis using CellProfiler.

Dendritic epidermal T cells (DETC) are not required for control of skin Staph infections

Abstract Staphylococcal bacteria are a common cause of skin infections in mice and humans. γδ T cells and the cytokine IL-17 are important in controlling these infections. To test roles for IL-17 in autoimmune Ets1 knockout (KO) mice, we generated double knockout (DKO) mice lacking both Ets1 and IL-17RA. We found that DKO mice develop worse autoimmune disease than Ets1 KO mice and are also susceptible to spontaneous Staphylococcus xylosus skin infections. While IL-17RA KO mice also develop skin lesions, these lesions are found at a higher rate and increased severity in DKO mice. Furthermore, exogenous infection of DKO skin with bioluminescent Staphylococcus aureus results in a failure to clear the bacteria, while IL-17RA KO mice are able to clear. Given that γδ T cells are important in controlling Staph skin infections, we examined these populations and found that both Ets1 KO and DKO mice lack the dendritic epidermal T cells (DETC), while other γδ T cell subsets are present. Further analysis showed that DETC progenitors are present in the fetal thymus of Ets1 KO mice, but DETC are missing from the skin of P5 and adult mice lacking Ets1. We hypothesized that loss of DETC (due to absence of Ets1) might cooperate with loss of IL-17 signaling (due to loss of IL-17RA) to create susceptibility to skin infections. To determine if DETC have a specific contribution to the skin immune response to Staphylococcal bacteria, we depleted DETC from wild-type mice using antibody against TCR Vγ5 followed by S. aureus infection. We found that DETC are not required to clear skin Staph infections, since depleted mice cleared with the same kinetics as non-depleted mice. Studies are in progress to further examine the roles of other γδ T cell populations in clearance of skin Staph infections. Supported by grant from NIH (R01 AI122720)

NKG2D Ligand Expression Induced by Oxidative Stress Mitigates Cutaneous Ischemia-Reperfusion Injury.

Pressure ulcers represent a crucial clinical problem, especially in hospitalized patients. Ischemia-reperfusion (I-R) is an important cause of these lesions. Natural killer (NK), invariant NK T (iNKT), and dendritic epidermal T-cells, which express the natural killer group 2, member D (NKG2D) receptor, have been reported to have physiological roles in skin tissue repair and wound healing. However, a role for NKG2D-NKG2D ligand interactions in I-R-induced skin injury has not been determined. Using a murine pressure ulcer model, we demonstrated that I-R-induced ulcers in NKG2D-deficient mice were larger than those in wild-type or T-cell receptor δ knockout mice. Histopathological evaluation revealed that accumulation of macrophages and neutrophils at the peripheral deep dermis and subcutaneous tissue of the ulcers was enhanced in NKG2D-deficient mice. Rae-1 mRNA, which encodes an NKG2D ligand, was induced, and RAE-1 protein was detected immunohistochemically in fibroblasts and inflammatory cells in the dermis after reperfusion. RAE-1 expression was also increased in primary mouse fibroblasts treated with sodium arsenite. These results suggested that NKG2D ligand expression was induced by oxidative stress after I-R injury and support a putative role for this ligand in wound repair. Furthermore, the influx of NKG2D-positive cells at I-R sites may mitigate pressure ulcers via NKG2D-NKG2D ligand interactions.

Ets1 regulates production of dendritic epidermal T cells (DETC) and cooperates with IL17Ra signaling to regulate immune responses to Staphylococcal skin infection

Abstract Ets1 is a lineage-specific transcription factor regulating lymphocyte differentiation. Mice that lack Ets1 (Ets1 KO) develop autoimmune disease with enhanced B and T cell activation, including increased production of IL-17. To determine if IL-17 contributes to autoimmunity, we crossed Ets1 KO mice to mice lacking the IL17 receptor A subunit (IL17RA KO) to generate double knock out (DKO) mice. We found that loss of IL17RA did not prevent or ameliorate autoimmunity, but that DKO animals exhibited worse symptoms. DKO mice also showed susceptibility to skin infections with Staphylococcal bacteria. To define the molecular mechanisms that might underlie this phenotype, we assessed gene expression in skin of DKO mice and control mice, which showed reduced expression of Skint genes. Skint proteins are involved in γδ T cell development and skin wound healing responses. We examined the presence of subsets of γδ T cells in the skin including dendritic epidermal T cells (DETC), whose role in murine wound healing responses is well described, and dermal γδ T cells that are important for anti-Staphylococcal immunity. Loss of Ets1 leads to a complete absence of DETC in the skin of mice. On the other hand, dermal γδ T cells are present in all genotypes. While DETC are absent from the skin of both Ets1 KO mice and DKO mice, only DKO mice show enhanced susceptibility to skin Staphylococcal infections, indicating that Ets1 and IL17RA regulate additional aspects of skin immunity. We propose that impaired responses to skin Staph infections in DKO mice are driven both by impaired IL17RA signaling and impaired wound healing. We further propose that the chronic bacterial infection in the skin results in enhanced immune activation and enhanced autoimmunity in DKO mice. Funded by NIH R01 AI122720 and the Lupus Research Alliance.

Skin γδ T Cells and Their Function in Wound Healing.

For the skin immune system, γδ T cells are important components, which help in defensing against damage and infection of skin. Compared to the conventional αβ T cells, γδ T cells have their own differentiation, development and activation characteristics. In adult mice, dendritic epidermal T cells (DETCs), Vγ4 and Vγ6 γδ T cells are the main subsets of skin, the coordination and interaction among them play a crucial role in wound repair. To get a clear overview of γδ T cells, this review synopsizes their derivation, development, colonization and activation, and focuses their function in acute and chronic wound healing, as well as the underlining mechanism. The aim of this paper is to provide cues for the study of human epidermal γδ T cells and the potential treatment for skin rehabilitation.

γδ T Cell‒Mediated Wound Healing Is Diminished by Allergic Skin Inflammation

Atopic dermatitis results in profound changes in the function of the skin that include diminished barrier function and altered production of antimicrobial peptides. Our previous work in a model of allergic skin inflammation identified a defect in the wound healing process that was dependent on IL-4. In this report, we show that allergic skin inflammation results in a dramatic decrease in the presence of the Vγ3+ dendritic epidermal T-cell (DETC) population of γδ T cells in the skin. In mice that express an active signal transducer and activator of transcription 6 in T cells, DETCs are lost early in life. The loss of DETCs is entirely dependent on IL-4 and is recovered with a genetic deficiency of IL-4. Moreover, injection of IL-4 into wild-type mice results in acute loss of the DETC population. A similar loss of DETCs was observed in mice treated topically with MC903. Wounding of skin from Stat6VT-transgenic or MC903-treated mice resulted in decreased production of DETC-dependent cytokines in the skin, coincident with diminished wound closure. Importantly, intradermal injection of the DETC-produced cytokine fibroblast GF 7 rescued the rate of wound closure in mice with allergic skin inflammation. Together, these results suggest that the atopic environment diminishes prohealing T-cell populations in the skin, resulting in attenuated wound healing responses.

Dendritic epidermal T cells secreting exosomes promote the proliferation of epidermal stem cells to enhance wound re-epithelialization

BackgroundEfficient re-epithelialization is important for successful skin wound healing. The proportion of epidermal stem cells (EpSCs) and dendritic epidermal T cells (DETCs) determines the extent of wound re-epithelialization, especially in large areas of skin tissue loss. However, it remains unknown whether and how DETCs regulate the status of EpSCs to impact wound re-epithelialization.MethodsTo investigate how DETCs regulate EpSCs in skin re-epithelialization, we utilized normal or full-thickness skin deficient wide type (WT) mice and Tcrσ knockout (Tcrσ−/−) mice with DETCs or DETCs-derived exosomes (Exos) treatment. Flow cytometry analysis (FCAS), BrdU labelled experiments, immunofluorescence and immunohistochemical assays were performed to detect the proportion of EpSCs in the epidermis. Wound closure rate and re-epithelialization were assayed by a macroscopical view and hematoxylin–eosin (H&E) staining. EpSCs in vitro were co-cultured with DETCs in a transwell-dependent or -independent manner, or supplement with GW4869 or Exos (5 µg/mL, 15 µg/mL and 45 µg/mL), and the proliferation of EpSCs was detected by means of FCAS and CFSE.ResultsOur data showed that the proportion of CD49fbriCD71dim cells, K15+ cells and BrdU+ cells in the normal epidermis of Tcrδ−/− mice had no significant difference compared to WT mice. For wounded Tcrδ−/− mice, DETCs treatment increase the proportion of CD49fbriCD71dim cells, K15+ cells and BrdU+ cells in the epidermis around the wound in comparison to PBS treatment. DETCs significantly increased the number of CD49fbriCD7dim cells and K15+ cells through transwell-dependent or -independent manners relative to control group. Furthermore, Exos stimuli remarkedly promote the proliferation of EpSCs compared to control group, while the increasement was suppressed when DETCs were interfered with GW4869. Gross observation and H&E staining showed that Exos significantly accelerated wound closure and increased re-epithelialization length in Tcrδ−/− mice when compared to control mice. Additionally, we found in vivo that Exos observably facilitated the proliferation of CD49fbriCD7dim cells and K15+ cells.ConclusionsWe revealed that DETCs enhanced the proliferation of EpSCs in the epidermis around the wounds to accelerate re-epithelialization in which Exos played important roles in the remote regulation of EpSCs proliferation. Together, these findings suggest a mechanistic link among DETC-derived exosomes, the proliferation of EpSCs, and wound re-epithelialization in the skin.

Vγ5Vδ1 TCR signaling is required to different extents for embryonic versus postnatal development of DETCs.

γδ T cells expressing Vγ5Vδ1 TCR originally develop in the embryonic thymus and migrate to the epidermis, forming dendritic epidermal T cells (DETCs) throughout life. It is thought that a TCR signal is essential for their development; e.g., lack of TCR signal-transducer ZAP70 significantly decreases DETC numbers. On the other hand, lack of ZAP70 does not affect Vγ5Vδ1+ T cells in the embryonic thymus; thus, the involvement of TCR signaling remains elusive. Here, we used SKG mice with attenuated TCR signaling rather than gene-knockout mice. In SKG mice, Vγ5+ T cells showed a marked decrease [10% of wild-type (WT)] in adult epidermis; however, there was just a moderate decrease (50% of WT) in the embryonic thymus. In early postnatal epidermis in SKG mice, substantial numbers of Vγ5+ T cells were observed (50% of WT). Their activation markers including CD122, a component of the IL-15 receptor indispensable for DETC proliferation, were comparable to those of WT. However, the Vγ5+ T cells in SKG mice did not proliferate and form DETCs thereafter. Furthermore, in SKG/+ mice, the number of thymic Vγ5Vδ1+ T cells increased, compared to SKG mice; however, the number of DETCs remained significantly lower than in WT, similar to SKG mice. Our results suggest that signaling via Vγ5Vδ1 TCR is indispensable for DETC development, with distinct contributions to embryonic development and postnatal proliferation.

γδ T cell costimulatory ligands in antitumor immunity.

Antitumor immunity relies on the ability of T cells to recognize and kill tumor targets. γδ T cells are a specialized subset of T cells that predominantly localizes to non-lymphoid tissue such as the skin, gut, and lung where they are actively involved in tumor immunosurveillance. γδ T cells respond to self-stress ligands that are increased on many tumor cells, and these interactions provide costimulatory signals that promote their activation and cytotoxicity. This review will cover costimulatory molecules that are known to be critical for the function of γδ T cells with a specific focus on mouse dendritic epidermal T cells (DETC). DETC are a prototypic tissue-resident γδ T cell population with known roles in antitumor immunity and are therefore useful for identifying mechanisms that may control activation of other γδ T cell subsets within non-lymphoid tissues. This review concludes with a brief discussion on how γδ T cell costimulatory molecules can be targeted for improved cancer immunotherapy.

MiRNA-17-92 cluster is required for the embryonic development of Langerhans cells and dendritic epidermal T cells

Abstract Mouse epidermis contains two major immune cells, antigen presenting Langerhans cells (LCs) and dendritic epidermal T cells (DETCs), which regulate skin immunity and involve in disease pathogenesis. Recent lineage-tracing studies have uncovered that mouse DETCs and LCs are derived from embryonic yolk-sac-derived hematopoietic precursors and self-maintain after birth. However, detailed regulating mechanisms related to their ontogeny and homeostasis remain unclear. MicroRNAs (miRNAs) are important post transcriptional regulators of protein-coding genes. Using a CSF1R-cre-mediated Dicer deletion mouse model, we found the critical involvement of miRNAs in the ontogeny of both LCs and DETCs. To further investigate the role of individual miRNAs in the ontogeny of LCs and DETCs, we evaluated the expression of miRNAs in the precursors of LCs and DETCs at different embryonic developmental stages and identified that miR17-92 cluster was highly expressed and dynamically regulated. We next generated a Csf1rCre-mediated miR17-92 deletion mouse model (miR17-92 KO) and found that conditionally deletion of miR17-92 led to significantly reduced number and interrupted phenotypes of epidermis LC and DETC precursors at E18.5 and P0 of miR17-92 KO embryos. Defective LC precursors were also identified at E14.5 and E16.5 embryonic skin, while diminished number and blocked maturation of Vg3+ DETC precursors were identified in the thymus of the same embryonic stages in miR17-92 KO mice. Overall, our results indicate that miR17-92 serves as a key epigenetic regulator in the ontogeny of LCs and DETCs. Detailed molecular mechanisms underlining the miR17-92 mediated LC and DETC developmental regulation are currently under investigation.

Skin-resident immune cells actively coordinate their distribution with epidermal cells during homeostasis.

Organs consist of multiple cell types that ensure proper architecture and function. How different cell types coexist and interact to maintain their homeostasis in vivo remains elusive. The skin epidermis comprises mostly epithelial cells, but also harbours Langerhans cells (LCs) and dendritic epidermal T cells (DETCs). Whether and how distributions of LCs and DETCs are regulated during homeostasis is unclear. Here, by tracking individual cells in the skin of live adult mice over time, we show that LCs and DETCs actively maintain a non-random spatial distribution despite continuous turnover of neighbouring basal epithelial cells. Moreover, the density of epithelial cells regulates the composition of LCs and DETCs in the epidermis. Finally, LCs require the GTPase Rac1 to maintain their positional stability, density and tiling pattern reminiscent of neuronal self-avoidance. We propose that these cellular mechanisms provide the epidermis with an optimal response to environmental insults.

Tracking skin and immune cell interactions.

The distribution of skin immune cells, namely Langerhans cells (LCs) and dendritic epidermal T cells (DETCs), is well-documented, but the mechanisms underlying their pattern maintenance remained obscure. A study now finds that LCs maintain their distribution patterns depending upon Rac1 and that the density of LCs and DETCs is regulated by the density of epithelial cells.

Loss of IL17 signaling in lupus-prone Ets1 knockout mice leads to worsened autoimmunity combined with increased susceptibility to Staphylococcal skin infections

Abstract Ets1 is a lineage-specific transcription factor that regulates B and T cell functions in development and disease. Mice that lack Ets1 (Ets1 KO) develop autoimmune disease with high levels of autoantibodies. Naïve CD4+ T cells isolated from Ets1 KO mice differentiate more readily to IL17 producing Th17 cells. To determine if IL17 production contributes to the observed autoimmunity in Ets1 KO mice, we crossed Ets1 KO mice to mice lacking the IL17 receptor A subunit (IL17RA KO) to generate double knock out (DKO) mice. We found that the absence of IL17RA signaling did not ameliorate the autoimmune phenotype of Ets1 KO mice. Instead, DKO animals exhibited worse symptoms with increases in activated B cells, autoantibody titers, T helper 2, and T follicular helper cells. DKO mice showed aspects of immunodeficiency, developing spontaneous skin lesions colonized by Staphylococcus xylosus. When DKO mice were infected with Staphylococcus aureus they were unable to clear the bacteria, indicating a general immunodeficiency to Staph bacteria. Gene expression analysis revealed diminished expression of the Skint gene family in DKO skin. Skint genes play important roles in the maintenance of TCRγδ+ dendritic epidermal T cells (DETC) and in skin wound healing. DKO mice had reduced numbers of DETC in the skin, which may lead to increased susceptibility to Staph infections. We propose that Staph skin infections in DKO mice leads to enhanced immune activation and enhanced autoimmunity. Our studies suggest that therapies targeting IL17RA signaling in autoimmune diseases may result in increased autoimmunity or to increased susceptibility to skin Staph infections.