Comprehensive analysis of MHC-II expression in healthy human skin

A number of antigen-presenting cells (APCs) expressing major histocompatibility complex class II (MHC-II) have been identified in healthy human skin including the Langerhans cells of the epidermis and the three recently defined dermal APC subsets. It is well documented that in other tissues HLA-DR expression is not exclusive to APCs. Following a comprehensive analysis of the cells in human skin using flow cytometry and fluorescence immunohistochemistry, we have identified additional cell subsets that express HLA-DR. Using markers exclusive for blood and lymphatic endothelium, we demonstrated that both of these cell populations have the capacity to express HLA-DR. In addition, a small subset of dermal T lymphocytes was found to express low-level HLA-DR suggesting an activated phenotype. Dermal T lymphocytes were often in intimate contact with either CD1a(+) CD207(-) dermal APCs or CD1a(+) CD207(+) dermal Langerhans cells, possibly explaining the activated phenotype of a subset of dermal T lymphocytes.     

The subpopulation of CD4+CD25+ splenocytes that delays adoptive transfer of diabetes expresses L-selectin and high levels of CCR7

Recently, CD4(+)CD25(+) T cells have been implicated in the control of diabetes, suggesting that the inflamed islets of Langerhans in prediabetic NOD mice are under peripheral immune surveillance. Here we show that CD4(+)CD25(+) splenocytes inhibit diabetes in cotransfer with islet-infiltrating cells. Furthermore, CD62L expression is necessary for this disease-delaying effect of CD4(+)CD25(+) cells in vivo, but not for their suppressor function in vitro. We demonstrate that the CD4(+)CD25(+)CD62L(+) splenocytes express CCR7 at high levels and migrate toward secondary lymphoid tissue chemokine and ELC (macrophage-inflammatory protein-3beta), lymphoid chemokines, whereas CD4(+)CD25(+)CD62L(-) splenocytes preferentially express CCR2, CCR4, and CXCR3 and migrate toward the corresponding inflammatory chemokines. These data demonstrate that CD4(+)CD25(+)CD62L(+), but not CD4(+)CD25(+)CD62L(-), splenocytes delay diabetes transfer, and that CD4(+)CD25(+) suppressor T cells are comprised of at least two subpopulations that behave differently in cotransfer in vivo and express distinct chemokine receptor and chemotactic response profiles despite demonstrating equivalent suppressor functions in vitro.     

Differing requirements for CCR4, E-selectin, and α4β1 for the migration of memory CD4 and activated T cells to dermal inflammation

CCR4 on T cells is suggested to mediate skin homing in mice. Our objective was to determine the interaction of CCR4, E-selectin ligand (ESL), and α(4)β(1) on memory and activated T cells in recruitment to dermal inflammation. mAbs to rat CCR4 were developed. CCR4 was on 5-21% of memory CD4 cells, and 20% were also ESL(+). Anti-TCR-activated CD4 and CD8 cells were 40-55% CCR4(+), and ～75% of both CCR4(+) and CCR4(-) cells were ESL(+). CCR4(+) memory CD4 cells migrated 4- to 7-fold more to dermal inflammation induced by IFN-γ, TNF, TLR agonists, and delayed-type hypersensitivity than CCR4(-) cells. CCR4(+) activated CD4 cells migrated only 5-50% more than CCR4(-) cells to these sites. E-selectin blockade inhibited ～60% of CCR4(+) activated CD4 cell migration but was less effective on memory cells where α(4)β(1) was more important. Anti-α(4)β(1) also inhibited CCR4(-) activated CD4 cells more than CCR4(+) cells. Anti-E-selectin reduced activated CD8 more than CD4 cell migration. These findings modify our understanding of CCR4, ESL, α(4)β(1), and dermal tropism. There is no strict relationship between CCR4 and ESL for skin homing of CD4 cells, because the activation state and inflammatory stimulus are critical determinants. Dermal homing memory CD4 cells express CCR4 and depend more on α(4)β(1) than ESL. Activated CD4 cells do not require CCR4, but CCR4(+) cells are more dependent on ESL than on α(4)β(1), and CCR4(-) cells preferentially use α(4)β(1). The differentiation from activated to memory CD4 cells increases the dependence on CCR4 for skin homing and decreases the requirement for ESL.     

Selective Susceptibility of Human Skin Antigen Presenting Cells to Productive Dengue Virus Infection

Dengue is a growing global concern with 390 million people infected each year. Dengue virus (DENV) is transmitted by mosquitoes, thus host cells in the skin are the first point of contact with the virus. Human skin contains several populations of antigen-presenting cells which could drive the immune response to DENV in vivo: epidermal Langerhans cells (LCs), three populations of dermal dendritic cells (DCs), and macrophages. Using samples of normal human skin we detected productive infection of CD14⁺ and CD1c⁺ DCs, LCs and dermal macrophages, which was independent of DC-SIGN expression. LCs produced the highest viral titers and were less sensitive to IFN-β. Nanostring gene expression data showed significant up-regulation of IFN-β, STAT-1 and CCL5 upon viral exposure in susceptible DC populations. In mice infected intra-dermally with DENV we detected parallel populations of infected DCs originating from the dermis and migrating to the skin-draining lymph nodes. Therefore dermal DCs may simultaneously facilitate systemic spread of DENV and initiate the adaptive anti-viral immune response.     

Skin langerin+ dendritic cells transport intradermally injected anti-DEC-205 antibodies but are not essential for subsequent cytotoxic CD8+ T cell responses

Incorporation of Ags by dendritic cells (DCs) increases when Ags are targeted to endocytic receptors by mAbs. We have previously demonstrated in the mouse that mAbs against C-type lectins administered intradermally are taken up by epidermal Langerhans cells (LCs), dermal Langerin(neg) DCs, and dermal Langerin(+) DCs in situ. However, the relative contribution of these skin DC subsets to the induction of immune responses after Ag targeting has not been addressed in vivo. We show in this study that murine epidermal LCs and dermal DCs transport intradermally injected mAbs against the lectin receptor DEC-205/CD205 in vivo. Skin DCs targeted in situ with mAbs migrated through lymphatic vessels in steady state and inflammation. In the skin-draining lymph nodes, targeting mAbs were found in resident CD8α(+) DCs and in migrating skin DCs. More than 70% of targeted DCs expressed Langerin, including dermal Langerin(+) DCs and LCs. Numbers of targeted skin DCs in the nodes increased 2-3-fold when skin was topically inflamed by the TLR7 agonist imiquimod. Complete removal of the site where OVA-coupled anti-DEC-205 had been injected decreased endogenous cytotoxic responses against OVA peptide-loaded target cells by 40-50%. Surprisingly, selective ablation of all Langerin(+) skin DCs in Langerin-DTR knock-in mice did not affect such responses independently of the adjuvant chosen. Thus, in cutaneous immunization strategies where Ag is targeted to DCs, Langerin(+) skin DCs play a major role in transport of anti-DEC-205 mAb, although Langerin(neg) dermal DCs and CD8α(+) DCs are sufficient to subsequent CD8(+) T cell responses.     

Expression of a functional eotaxin (CC chemokine ligand 11) receptor CCR3 by human dendritic cells

Critical to the function of Ag-presenting dendritic cells (DCs) is their capacity to migrate to lymphoid organs and to sites of inflammation. A final stage of development, termed maturation, yields DCs that are strong stimulators of T cell-mediated immunity and is associated with a remodeling of the cell surface that includes a change in the levels of expression of many molecules, including chemokine receptors. We show in this study that CCR3, a chemokine receptor initially discovered on eosinophils, is also expressed by human DCs that differentiate from blood monocytes, DCs that emigrate from skin (epidermal and dermal DCs), and DCs derived from CD34+ hemopoietic precursors in bone marrow, umbilical cord blood, and cytokine-elicited peripheral blood leukapheresis. Unlike other chemokine receptors, such as CCR5 and CCR7, the expression of CCR3 is not dependent on the state of maturation. All DC subsets contain a large intracellular pool of CCR3. The surface expression of CCR3 is not modulated following uptake of particulate substances such as zymosan or latex beads. CCR3 mediates in vitro chemotactic responses to the known ligands, eotaxin and eotaxin-2, because the DC response to these chemokines is inhibited by CCR3-specific mAbs. We postulate that expression of CCR3 may underlie situations where both DCs and eosinophils accumulate in vivo, such as the lesions of patients with Langerhans cell granulomatosis.     

γδ T cell homing to skin and migration to skin-draining lymph nodes is CCR7 independent

In most species, γδ T cells preferentially reside in epithelial tissues like the skin. Lymph duct cannulation experiments in cattle revealed that bovine dermal γδ T cells are able to migrate from the skin to the draining lymph nodes via the afferent lymph. For αβ T cells, it is generally accepted that epithelial and mucosal tissue egress is regulated by expression of the CCR7 chemokine receptor. In this study, we tracked the migratory route of bovine lymph-derived γδ T cells and examined their CCR7 cell surface expression in several compartments along this route. Total lymph cells from afferent and efferent origin were labeled with PKH fluorescent dyes and injected into the bloodstream. PKH(+) cells already reappeared in the afferent lymph after 4 h. The vast majority of the PKH(+) cells retrieved from the afferent lymph were of the WC1(+) γδ T cell phenotype, proving that this PKH(+) γδ T cell subset is able to home to and subsequently exit the skin. PKH(+) γδ T cells from afferent and efferent lymph lack CCR7 surface expression and display high levels of CD62L compared with CD4 T cells, which do express CCR7. Skin homing receptors CCR4 and CCR10 in contrast were transcribed by both CD4 and γδ T cells. Our findings suggest that γδ T cell skin egress and migration into the peripheral lymphatics is CCR7-independent and possibly mediated by CD62L expression.     

Identification and characterization of pDC-like cells in normal mouse skin and melanomas treated with imiquimod

Among the different subsets of dendritic cells (DC) described in humans and mice, epidermal Langerhans cells and dermal DCs represent the only DC populations resident in normal skin. In this study we describe a population of CD4(+)CD3(-) plasmacytoid DC (pDC)-like cells that accumulate in the dermis and spleens of mice topically treated with imiquimod, a low m.w. immune response modifier with potent antiviral and antitumor activities. These CD4(+)CD3(-) cells coexpress GR-1, B220, MHC class II, and, to a lesser extent, CD11c and display the phenotypic features of pDCs described in lymphoid organs. The accumulation of pDC-like cells after imiquimod treatment was detected not only in normal skin, but also in intradermally induced melanomas. Imiquimod treatment leads either to complete regression or to a significant reduction of the tumors. The number of pDCs correlates well with the clinical response of the tumors to the drug, suggesting that the antitumor effects of imiquimod could be mediated at least in part by the recruitment of pDC-like cells to the skin. Therefore, strategies aimed at activating and directing these cells into neoplastic tissues may be a promising and novel approach for the immunotherapy of various types of cancer.     

Cutting edge: Identification of a motile IL-17-producing gammadelta T cell population in the dermis

Dendritic epidermal T cells (DETCs) are a well-studied population of γδ T cells that play important roles in wound repair. In this study, we characterize a second major population of γδ T cells in the skin that is present in the dermis. In contrast to DETCs, these Vγ5-negative cells are IL-7R(hi)CCR6(hi) retinoic acid-related orphan receptor γt(+) and are precommitted to IL-17 production. Dermal γδ T cells fail to reconstitute following irradiation and bone marrow transplantation unless the mice also receive a transfer of neonatal thymocytes. Real-time intravital imaging of CXCR6(GFP/+) mouse skin reveals dermal γδ T cells migrate at ～4 μm/min, whereas DETCs are immobile. Like their counterparts in peripheral lymph nodes, dermal γδ T cells rapidly produce IL-17 following exposure to IL-1β plus IL-23. We have characterized a major population of skin γδ T cells and propose that these cells are a key source of IL-17 in the early hours after skin infection.     

Human BDCA-1-positive blood dendritic cells differentiate into phenotypically distinct immature and mature populations in the absence of exogenous maturational stimuli: differentiation failure in HIV infection

Current immunological opinion holds that myeloid dendritic cell (mDC) precursors migrate from the blood to the tissues, where they differentiate into immature dermal- and Langerhans-type dendritic cells (DC). Tissue DC require appropriate signals from pathogens or inflammatory cytokines to mature and migrate to secondary lymphoid tissue. We show that purified blood mDC cultured in vitro with GM-CSF and IL-4, but in the absence of added exogenous maturation stimuli, rapidly differentiate into two maturational and phenotypically distinct populations. The major population resembles immature dermal DC, being positive for CD11b, CD1a, and DC-specific ICAM-3-grabbing nonintegrin. They express moderate levels of MHC class II and low levels of costimulatory molecules. The second population is CD11b(-/low) and lacks CD1a and DC-specific ICAM-3-grabbing nonintegrin but expresses high levels of MHC class II and costimulatory molecules. Expression of CCR7 on the CD11b(-/low) population and absence on the CD11b(+) cells further supports the view that these cells are mature and immature, respectively. Differentiation into mature and immature populations was not blocked by polymyxin B, an inhibitor of LPS. Neither population labeled for Langerin, E-cadherin, or CCR6 molecules expressed by Langerhans cells. Stimulation of 48-h cultured DC with LPS, CD40L, or poly(I:C) caused little increase in MHC or costimulatory molecule expression in the CD11b(-/low) DC but caused up-regulated expression in the CD11b(+) cells. In HIV-infected individuals, there was a marked decrease in the viability of cultured blood mDC, a failure to differentiate into the two populations described for normal donors, and an impaired ability to stimulate T cell proliferation.     

CCR7 ligands, SLC/6Ckine/Exodus2/TCA4 and CKbeta-11/MIP-3beta/ELC, are chemoattractants for CD56(+)CD16(-) NK cells and late stage lymphoid progenitors

Two human CC chemokines, SLC/6Ckine/Exodus2/TCA4 and CKbeta-11/MIP-3beta/ELC, are previously reported as efficacious chemoattractants for T- and B-cells and dendritic cells. SLC and CKbeta-11 share only 32% amino acid identity, but are ligands for the same chemokine receptor, CCR7. In this study, we examined chemotactic activity of SLC and CKbeta-11 for NK cells and lymphoid progenitors in bone marrow and thymus. It was found that these two CCR7 ligands are chemoattractants for neonatal cord blood and adult peripheral blood NK cells and cell lines. SLC and CKbeta-11 preferentially attract the CD56(+)CD16(-) NK cell subset over CD56(+)CD16(+) NK cells. SLC and CKbeta-11 also demonstrate selective chemotactic activity on late stage CD34(-)CD19(+)IgM- B-cell progenitors and CD4(+) and CD8(+) single-positive thymocytes, but not early stage progenitors. It was noted that SLC is an efficient desensitizer of CKbeta-11-dependent NK cell chemotaxis, while CKbeta-11 is a weak desensitizer of SLC-dependent chemotaxis. Taken together, these results suggest that SLC and CKbeta-11 have the potential to control trafficking of NK cell subsets and late stage lymphoid progenitors in bone marrow and thymus.     

In vivo differentiated cytokine-producing CD4(+) T cells express functional CCR7

Chemokines and their receptors fulfill specialized roles in inflammation and under homeostatic conditions. CCR7 and its ligands, CCL19 and CCL21, are involved in lymphocyte recirculation through secondary lymphoid organs and additionally navigate lymphocytes into distinct tissue compartments. The role of CCR7 in the migration of polarized T effector/memory cell subsets in vivo is still poorly understood. We therefore analyzed murine and human CD4(+) cytokine-producing cells developed in vivo for their chemotactic reactivity to CCR7 ligands. The responses of cells producing cytokines, such as IFN-gamma, IL-4, and IL-10, as well as of subsets defined by memory or activation markers were comparable to that of naive CD4(+) cells, with slightly lower reactivity in cells expressing IL-10 or CD69. This indicates that CCR7 ligands are able to attract naive as well as the vast majority of activated and effector/memory T cell stages. Chemotactic reactivity of these cells toward CCL21 was absent in CCR7-deficient cells, proving that effector cells do not use alternative receptors for this chemokine. Th1 cells generated from CCR7(-/-) mice failed to enter lymph nodes and Peyer's patches, but did enter a site of inflammation. These findings indicate that CD4(+) cells producing effector cytokines upon stimulation retain the capacity to recirculate through lymphoid tissues via CCR7.     

Corticosteroids prevent generation of CD34+-derived dermal dendritic cells but do not inhibit Langerhans cell development

Corticosteroids (CS) have been shown to exert strong inhibitory effects on dendritic cell (DC) differentiation and function. Those studies were mostly performed with monocyte-derived DC, which represents only one subpopulation from the wide variety of DC types. In the present study the effects of the CS dexamethasone and prednisolone were investigated on the differentiation of CD34(+) hemopoietic progenitor cells into 1) Langerhans cells (LC), which differentiate directly into CD1a(+) DC; and 2) dermal/interstitial DC, which differentiate via a CD14(+)CD1a(-) phenotype into CD14(-)CD1a(+) DC. CS present during the entire 11-day culture period, resulting in fully differentiated CD1a(+) DC, increased the percentage of langerin(+) DC within the CD1a(+) population. In line with these data, CS treatment during the first 6 days of differentiation reduced the development of CD14(+) dermal DC precursors and thereby seemed to support the generation of CD1a(+) LC precursors. Addition of CS from day 6 onward specifically blocked the development of CD1a(+) dermal DC by both inhibition of spontaneous and IL-4-induced differentiation of CD14(+) DC precursors into CD1a(+) DC as well as induction of apoptosis in CD14(+) DC precursors. Apoptosis was not found in CD14(+) macrophage precursors derived from the same CD34(+) progenitors. The development and function of LC were not affected by CS, as demonstrated by a normal T cell stimulatory capacity and IL-12 production. These data demonstrate that CS interfere with the normal development of DC from CD34(+) progenitors by specific induction of apoptosis in precursors of dermal/interstitial DC. In view of the different functional capacities of dermal/interstitial DC and Langerhans cells, this might affect the overall cellular immune response.     

Ultraviolet B radiation induces a transient appearance of IL-4+ neutrophils, which support the development of Th2 responses

UVB irradiation can cause considerable changes in the composition of cells in the skin and in cutaneous cytokine levels. We found that a single exposure of normal human skin to UVB induced an infiltration of numerous IL-4(+) cells. This recruitment was detectable in the papillary dermis already 5 h after irradiation, reaching a peak at 24 h and declining gradually thereafter. The IL-4(+) cells appeared in the epidermis at 24 h postradiation and reached a plateau at days 2 and 3. The number of IL-4(+) cells was markedly decreased in both dermis and epidermis at day 4, and at later time points, the IL-4 expression was absent. The IL-4(+) cells did not coexpress CD3 (T cells), tryptase (mast cells), CD56 (NK cells), and CD36 (macrophages). They did coexpress CD15 and CD11b, showed a clear association with elastase, and had a multilobed nucleus, indicating that UVB-induced infiltrating IL-4(+) cells are neutrophils. Blister fluid from irradiated skin, but not from control skin, contained IL-4 protein as well as increased levels of IL-6, IL-8, and TNF-alpha. In contrast to control cultures derived from nonirradiated skin, a predominant type 2 T cell response was detected in T cells present in primary dermal cell cultures derived from UVB-exposed skin. This type 2 shift was abolished when CD15(+) cells (i.e., neutrophils) were depleted from the dermal cell suspension before culturing, suggesting that neutrophils favor type 2 T cell responses in UVB-exposed skin.     

Homing and function of human skin gammadelta T cells and NK cells: relevance for tumor surveillance

Normal (noninflamed) human skin contains a network of lymphocytes, but little is known about the homing and function of these cells. The majority of alphabeta T cells in normal skin express CCR8 and produce proinflammatory cytokines. In this study we examined other subsets of cutaneous lymphocytes, focusing on those with potential function in purging healthy tissue of transformed and stressed cells. Human dermal cell suspensions contained significant populations of Vdelta1(+) gammadelta T cells and CD56(+)CD16(-) NK cells, but lacked the subsets of Vdelta2(+) gammadelta T cells and CD56(+)CD16(+) NK cells, which predominate in peripheral blood. The skin-homing receptors CCR8 and CLA were expressed by a large fraction of both cell types, whereas chemokine receptors associated with lymphocyte migration to inflamed skin were absent. Neither cell type expressed CCR7, although gammadelta T cells up-regulated this lymph node-homing receptor upon TCR triggering. Stimulation of cutaneous Vdelta1(+) gammadelta T cell lines induced secretion of large amounts of TNF-alpha, IFN-gamma, and the CCR8 ligand CCL1. In contrast to cutaneous alphabeta T cells, both cell types had the capacity to produce intracellular perforin and displayed strong cytotoxic activity against melanoma cells. We therefore propose that gammadelta T cells and NK cells are regular constituents of normal human skin with potential function in the clearance of tumor and otherwise stressed tissue cells.     

Down-regulation of Toll-like receptor expression in monocyte-derived Langerhans cell-like cells: implications of low-responsiveness to bacterial components in the epidermal Langerhans cells

In the skin, there are unique dendritic cells called Langerhans cells, however, it remains unclear why this particular type of dendritic cell resides in the epidermis. Langerhans cell-like dendritic cells (LCs) can be generated from CD14(+) monocytes in the presence of GM-CSF, IL-4, and TGF-beta1. We compared LCs with monocyte-derived dendritic cells (DCs) generated from CD14(+) monocytes in the presence of GM-CSF and IL-4 and examined the effect of exposure to two distinct bacterial stimuli via Toll-like receptors (TLRs), such as peptidoglycan (PGN) and lipopolysaccharide (LPS) on LCs and DCs. Although stimulation with both ligands induced a marked up-regulation of CD83 expression on DCs, PGN but not LPS elicited up-regulation of expression CD83 on LCs. Consistent with these results, TLR2 and TLR4 were expressed on DCs, whereas only TLR2 was weakly detected on LCs. These findings suggest the actual feature of epidermal Langerhans cells with low-responsiveness to skin commensals.     

CCR7 signaling inhibits T cell proliferation

CCR7 and its ligands, CCL19 and CCL21, are responsible for directing the migration of T cells and dendritic cells into lymph nodes, where these cells play an important role in the initiation of the immune response. Recently, we have shown that systemic application of CCL19-IgG is able to inhibit the colocalization of T cells and dendritic cells within secondary lymphoid organs, resulting in pronounced immunosuppression with reduced allograft rejection after organ transplantation. In this study, we demonstrate that the application of sustained high concentrations of either soluble or immobilized CCL19 and CCL21 elicits an inhibitory program in T cells. We show that these ligands specifically interfere with cell proliferation and IL-2 secretion of CCR7(+) cells. This could be demonstrated for human and murine T cells and was valid for both CD4(+) and CD8(+) T cells. In contrast, CCL19 had no inhibitory effect on T cells from CCR7 knockout mice, but CCR7(-/-) T cells showed a proliferative response upon TCR-stimulation similar to that of CCL19-treated wild-type cells. Furthermore, the inhibition of proliferation is associated with delayed degradation of the cyclin-dependent kinase (CDK) inhibitor p27(Kip1) and the down-regulation of CDK1. This shows that CCR7 signaling is linked to cell cycle control and that sustained engagement of CCR7, either by high concentrations of soluble ligands or by high density of immobilized ligands, is capable of inducing cell cycle arrest in TCR-stimulated cells. Thus, CCR7, a chemokine receptor that has been demonstrated to play an essential role during activation of the immune response, is also competent to directly inhibit T cell proliferation.     

Cutting edge: the orphan chemokine receptor G protein-coupled receptor-2 (GPR-2, CCR10) binds the skin-associated chemokine CCL27 (CTACK/ALP/ILC)

We recently reported the identification of a chemokine (CTACK), which has been renamed CCL27 according to a new systematic chemokine nomenclature. We report that CCL27 binds the previously orphan chemokine receptor GPR-2, as detected by calcium flux and chemotactic responses of GPR-2 transfectants. We renamed this receptor CCR10. Because of the skin-associated expression pattern of CCL27, we focused on the expression of CCL27 and CCR10 in normal skin compared with inflammatory and autoimmune skin diseases. CCL27 is constitutively produced by keratinocytes but can also be induced upon stimulation with TNF-alpha and IL-1beta. CCR10 is not expressed by keratinocytes and is instead expressed by melanocytes, dermal fibroblasts, and dermal microvascular endothelial cells. CCR10 was also detected in T cells as well as in skin-derived Langerhans cells. Taken together, these observations suggest a role for this novel ligand/receptor pair in both skin homeostasis as well as a potential role in inflammatory responses.     

CD207+ Langerhans cells constitute a minor population of skin-derived antigen-presenting cells in the draining lymph node following exposure to Schistosoma mansoni

Infectious cercariae of Schistosoma mansoni gain entry to the mammalian host through the skin where they induce a transient inflammatory influx of mononuclear cells. Some of these cells have antigen-presenting cell function (MHCII+) and have been reported to migrate to the skin-draining lymph nodes (sdLN) where they have the potential to prime CD4+ cells of the acquired immune response. Here, in mice exposed to vaccinating radiation-attenuated schistosome larvae, which induce high levels of protective immunity to challenge infection, we describe the parasite-induced migration of Langerhans cells (LCs) from the epidermal site of immunisation to the sdLN using a specific monoclonal antibody that recognises langerin (CD207). CD207+ cells with dendritic morphology were abundant in the epidermis at all times and their migration into the dermis was detected soon after vaccination. All CD207+ LCs were MHCII+ but not all MHCII+ cells in the skin were CD207+. LCs migrated from the dermis in enhanced numbers after vaccination, as detected in dermal exudate populations recovered after in vitro culture of skin biopsies. Elevated numbers of CD207+ LCs were also detected in the sdLN from 24h to 4 days after vaccination. However, compared with other dermal-derived antigen-presenting cells that were CD207-MHCII+ or CD207-CD11c+, the relative numbers of CD207+ cells in the dermal exudate population and in the sdLN were very small. Furthermore, the migration of CD207+ cells after exposure to 'protective' radiation-attenuated, compared with 'non-protective' normal cercariae, was similar in terms of numbers and kinetics. Together, these studies suggest that CD207+ LCs are only a minor component of the antigen-presenting cell population that migrates from the epidermis and they are unlikely to be important in the priming of protective CD4+ cells in the sdLN.     

α-1 antitrypsin promotes semimature, IL-10-producing and readily migrating tolerogenic dendritic cells

Tolerogenic IL-10-positive CCR7-positive dendritic cells (DC) promote T regulatory (Treg) cell differentiation upon CCR7-dependent migration to draining lymph nodes (DLN). Indeed, in human DC deficiencies, Treg levels are low. α-1 antitrypsin (AAT) has been shown to reduce inflammatory markers, promote a semimature LPS-induced DC phenotype, facilitate Treg expansion, and protect pancreatic islets from alloimmune and autoimmune responses in mice. However, the mechanism behind these activities of AAT is poorly understood. In this study, we examine interactions among DC, CD4(+) T cells, and AAT in vitro and in vivo. IL-1β/IFN-γ-mediated DC maturation and effect on Treg development were examined using OT-II cells and human AAT (0.5 mg/ml). CCL19/21-dependent migration of isolated DC and resident islet DC was assessed, and CCR7 surface levels were examined. Migration toward DLN was evaluated by FITC skin painting, transgenic GFP skin tissue grafting, and footpad DC injection. AAT-treated stimulated DC displayed reduced MHC class II, CD40, CD86, and IL-6, but produced more IL-10 and maintained inducible CCR7. Upon exposure of CD4(+) T cells to OVA-loaded AAT-treated DC, 2.7-fold more Foxp3(+) Treg cells were obtained. AAT-treated cells displayed enhanced chemokine-dependent migration and low surface CD40. Under AAT treatment (60 mg/kg), DLN contained twice more fluorescence after FITC skin painting and twice more donor DC after footpad injection, whereas migrating DC expressed less CD40, MHC class II, and CD86. Intracellular DC IL-10 was 2-fold higher in the AAT group. Taken together, these results suggest that inducible functional CCR7 is maintained during AAT-mediated anti-inflammatory conditions. Further studies are required to elucidate the mechanism behind the favorable tolerogenic activities of AAT.