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.     

CCR4 and CCR10 are expressed on epidermal keratinocytes and are involved in cutaneous immune reaction

CC chemokine ligand (CCL)17 and CCL27 produced by epidermal keratinocytes (KCs) recruit CC chemokine receptor (CCR)4 and CCR10 expressing T cells into the skin, respectively, resulting in enhanced skin inflammation. However, CCR4/CCL17 and CCR10/CCL27 interactions in epidermal KCs have not been investigated. The purpose of this study was to evaluate the role of the CCR4/CCL17 and CCR10/CCL27 loops in cutaneous immune reaction. Normal human KCs (NHKs) and HaCaT KCs expressed both CCR4 and CCR10 at mRNA and protein levels. CCR4 ligand CCL17 but not CCR10 ligand CCL27 induced production of IL-12 p40, granulocyte/monocyte colony-stimulating factor (GM-CSF) and nerve growth factor (NGF) by KCs. Both CCL17 and CCL27 induced migration of KCs in Boyden chamber assay and wound scratch assay. This study revealed that CCR4 and CCR10 are expressed on epidermal KCs and that both are functional in terms of skin cytokine production and/or migration to their ligand CCL17 and CCL27, respectively. Thus this study provided new insight into chemokine/chemokine receptors of KCs.     

Cutting Edge: Chemokine receptor CCR4 is necessary for antigen-driven cutaneous accumulation of CD4 T cells under physiological conditions

Dual expression of chemokine receptor CCR4 and E-selectin ligand is characteristic of skin-tropic CD4 T cells from blood, lymphoid organs, and the skin itself. A strong and specific correlation exists among CCR4, its ligand CCL17/TARC, and the cutaneous lymphocyte-homing process. Nevertheless, whether CCR4 function is required for skin-specific trafficking remains an open question, which we address in this study. We developed an Ag-specific, TCR-transgenic, murine CD4 T cell adoptive transfer model that induces a mixed Th1 and Th17 cutaneous response. Within the hosts, both CCR4(+/+) and CCR4(-/-) donor CD4 T cells contribute equally well to the circulating E-selectin ligand(+) pool in response to Ag. However, only CCR4(+/+) donor cells accumulate efficiently within the skin. CCR4(-/-) cells home normally to the peritoneum, showing that they do not have a general defect in lymphocyte trafficking. We conclude that under physiological conditions, CCR4 is a nonredundant, necessary component of skin-specific lymphocyte trafficking.     

Cutting edge: C-C chemokine receptor 6 is essential for arrest of a subset of memory T cells on activated dermal microvascular endothelial cells under physiologic flow conditions in vitro

Memory T cells (mTC) express multiple chemokine receptors (including CCR4 and CCR6) that may potentially be involved in their arrest on inflamed endothelia. Herein, we specifically addressed whether CCR6 is required for mTC to arrest on TNF-alpha-activated human dermal microvascular endothelial cells (HDMEC) in vitro under shear stress conditions. Recombinant liver and activation-regulated chemokine (LARC)/CCL20 (a CCR6 ligand) induced firm arrest of cutaneous lymphocyte Ag(+) mTC in a flow chamber system using purified substrates. Strikingly, desensitization of CCR6 with LARC, but not thymus and activation-regulated chemokine/CCL17 or secondary lymphoid tissue chemokine/CCL21, caused a 50-75% decrease (p < 0. 001) in arrest of mTC on HDMEC, which was indistinguishable from the reduction observed when total mTC were treated with pertussis toxin (p > 0.5). CCR6-depleted mTC also had a markedly reduced ability to arrest on HDMEC. Our results suggest that LARC production by activated endothelial cells and CCR6 expression by mTC may be critical components in the pertussis toxin-sensitive arrest of mTC on activated HDMEC.     

Up-regulation of macrophage inflammatory protein-3 alpha/CCL20 and CC chemokine receptor 6 in psoriasis

Autoimmunity plays a key role in the immunopathogenesis of psoriasis; however, little is known about the recruitment of pathogenic cells to skin lesions. We report here that the CC chemokine, macrophage inflammatory protein-3 alpha, recently renamed CCL20, and its receptor CCR6 are markedly up-regulated in psoriasis. CCL20-expressing keratinocytes colocalize with skin-infiltrating T cells in lesional psoriatic skin. PBMCs derived from psoriatic patients show significantly increased CCR6 mRNA levels. Moreover, skin-homing CLA+ memory T cells express high levels of surface CCR6. Furthermore, the expression of CCR6 mRNA is 100- to 1000-fold higher on sorted CLA+ memory T cells than other chemokine receptors, including CXCR1, CXCR2, CXCR3, CCR2, CCR3, and CCR5. In vitro, CCL20 attracted skin-homing CLA+ T cells of both normal and psoriatic donors; however, psoriatic lymphocytes responded to lower concentrations of chemokine and showed higher chemotactic responses. Using ELISA as well as real-time quantitative PCR, we show that cultured primary keratinocytes, dermal fibroblasts, and dermal microvascular endothelial and dendritic cells are major sources of CCL20, and that the expression of this chemokine can be induced by proinflammatory mediators such as TNF-alpha/IL-1 beta, CD40 ligand, IFN-gamma, or IL-17. Taken together, these findings strongly suggest that CCL20/CCR6 may play a role in the recruitment of T cells to lesional psoriatic skin.     

Expression of stromal-derived factor-1 is decreased by IL-1 and TNF and in dermal wound healing

Stromal-derived factor-1 (SDF-1) is a CXC chemokine that is believed to be constitutively expressed by stromal cells of numerous tissues. In this report, we demonstrate that dermal fibroblasts and vessels of noninflamed tissues express SDF-1. Unexpectedly, we found that expression of SDF-1 is regulated by inflammation. Expression of SDF-1 by primary cultures of human gingival fibroblasts is potently inhibited by activated macrophages via secretion of IL-1alpha and TNF-alpha. Levels of SDF-1 mRNA also decrease in acutely inflamed mouse dermal wounds. We propose that SDF-1 functions as a homeostatic regulator of tissue remodeling, whose expression stabilizes existing dermal architecture.     

CCL1-CCR8 interactions: an axis mediating the recruitment of T cells and Langerhans-type dendritic cells to sites of atopic skin inflammation

Atopic dermatitis represents a chronically relapsing skin disease with a steadily increasing prevalence of 10-20% in children. Skin-infiltrating T cells, dendritic cells (DC), and mast cells are thought to play a crucial role in its pathogenesis. We report that the expression of the CC chemokine CCL1 (I-309) is significantly and selectively up-regulated in atopic dermatitis in comparison to psoriasis, cutaneous lupus erythematosus, or normal skin. CCL1 serum levels of atopic dermatitis patients are significantly higher than levels in healthy individuals. DC, mast cells, and dermal endothelial cells are abundant sources of CCL1 during atopic skin inflammation and allergen challenge, and Staphylococcus aureus-derived products induce its production. In vitro, binding and cross-linking of IgE on mast cells resulted in a significant up-regulation of this inflammatory chemokine. Its specific receptor, CCR8, is expressed on a small subset of circulating T cells and is abundantly expressed on interstitial DC, Langerhans cells generated in vitro, and their monocytic precursors. Although DC maintain their CCR8+ status during maturation, brief activation of circulating T cells recruits CCR8 from intracytoplamic stores to the cell surface. Moreover, the inflammatory and atopy-associated chemokine CCL1 synergizes with the homeostatic chemokine CXCL12 (SDF-1alpha) resulting in the recruitment of T cell and Langerhans cell-like DC. Taken together, these findings suggest that the axis CCL1-CCR8 links adaptive and innate immune functions that play a role in the initiation and amplification of atopic skin inflammation.     

Cutting edge: differential chemokine production by myeloid and plasmacytoid dendritic cells

To examine the different roles of myeloid dendritic cells (M-DCs) and plasmacytoid dendritic cells (P-DCs) in the induction and regulation of immune response, we have studied chemokine secretion by freshly isolated DC subsets in response to bacterial, viral, and T cell-derived stimuli. M-DCs selectively produced very high levels of the homeostatic chemokines CC chemokine ligand (CCL)17 and CCL22, while P-DCs produced very little if any. In contrast, the proinflammatory chemokine CCL3 was secreted mostly by P-DCs, whereas CCL4 and CXC chemokine ligand 8 were produced by both subsets. The selective production of CCL17 and CCL22 by M-DCs but not P-DCs was confirmed in vivo by immunohistology on human reactive lymph node sections. The high production of CCR4 ligands by M-DCs suggests their capacity to selectively recruit at sites of inflammation T cells with regulatory properties or with a Th2 phenotype, whereas P-DCs, by preferentially secreting CCR1/CCR5 ligands, would mostly recruit effector T cells and, in particular, Th1-type cells.     

Differential binding of chemokines to macrophages and neutrophils in the human inflamed synovium

In chronic inflammatory foci, such as the rheumatoid joint, there is enhanced recruitment of phagocytes from the blood into the tissues. Chemokines are strongly implicated in directing the migration of these cells, although little is known regarding the chemokine receptors that could mediate their chemotaxis into the joint tissue. Therefore the objective of the study was to identify chemokine binding sites on macrophages and neutrophils within the rheumatoid synovium using radiolabeled ligand binding and in situ autoradiography. Specific binding sites for CCL3 (macrophage inflammatory protein-1alpha), CCL5 (RANTES), CCL2 (monocyte chemoattractant protein-1) and CXCL8 (IL-8) were demonstrated on CD68+ macrophages in the subintimal and intimal layers. The number and percentage of intimal cells that bound chemokines were greater in inflamed regions compared to noninflamed regions. The intensity of intimal binding varied between chemokines with the rank order, CCL3 > CCL5 > CCL2 > CXCL8. Neutrophils throughout the synovium bound CXCL8 but did not show any signal for binding CCL2, CCL3 or CCL5. Immunohistochemistry showed that both CXCR1 and CXCR2 are expressed by macrophages and neutrophils in the rheumatoid and nonrheumatoid synovia, suggesting that both of these receptors are responsible for the CXCL8 binding. The chemokine binding sites described on phagocytes may be involved in the migration of these cells into the inflamed joint.     

P-, E-, and L-selectin mediate migration of activated CD8+ T lymphocytes into inflamed skin

P- and E-selectin mediate CD4+ Th1 cell migration into the inflamed skin in a murine contact hypersensitivity model. In this model, not only CD4+ T cells but also CD8+ T cells infiltrate the inflamed skin, and the role of CD8+ type 1 cytotoxic T (Tc1) cells as effector cells has been demonstrated. Here we show that in mice deficient in both P- and E-selectin, the infiltration of CD8+ T cells in the inflamed skin is reduced, suggesting the role of these selectins in CD8+ T cell migration. We directly studied the role of selectins using in vitro-generated Tc1 cells. These cells are able to migrate into the inflamed skin of wild-type mice. This migration is partially mediated by P- and E-selectin, as shown by the reduced Tc1 cell migration into the inflamed skin of mice deficient in both P- and E-selectin or wild-type mice treated with the combination of anti-P-selectin and anti-E-selectin Abs. During P- and E-selectin-mediated migration of Tc1 cells, P-selectin glycoprotein ligand-1 appears to be the sole ligand for P-selectin and one of the ligands for E-selectin. P- and E-selectin-independent migration of Tc1 cells into the inflamed skin was predominantly mediated by L-selectin. These observations indicate that all three selectins can mediate Tc1 cell migration into the inflamed skin.     

Effects of antioxidants and nitric oxide on TNF-alpha-induced adhesion molecule expression and NF-kappaB activation in human dermal microvascular endothelial cells

Cell adhesion molecules expressed on endothelial cells in inflamed skin appear to be controlled by the actions of cytokines and reactive oxygen species. However, molecular mechanisms of the expression of adhesion molecules during skin inflammation are currently not well understood. To evaluate the role of antioxidants and nitric oxide in modulating inflammatory processes in the skin, we examined the effects of pyrrolidine dithiocarbamate (PDTC, 0.1 mM) and spermine NONOate (Sper-NO, 1 mM) on adhesion molecule expression and nuclear factor kappa B (NF-kappaB) activation induced by TNF-alpha (10 ng/ml) in cultured human dermal microvascular endothelial cells (HDMEC). Treatment of cells with TNF-alpha for 4 h significantly induced the surface expression of E-selectin and intercellular adhesion molecule-1 (ICAM-1). Treatment with TNF-alpha for 8 h significantly induced the surface expression of E-selectin, ICAM-1 and vascular cell adhesion molecule-1 (VCAM-1). The up-regulation of these adhesion molecules was suppressed significantly by pretreatment with PDTC or Sper-NO for 1 h. The mRNA expression of E-selectin, ICAM-1 and VCAM-1, and activation of NF-kappaB induced by TNF-alpha for 2 h were significantly decreased by the above two pretreatments. N-acetylcysteine (10 mM) and S-nitroso-N-acetylpenicillamine (1 mM) had no significant inhibitory effects on the cell surface and mRNA expression of these adhesion molecules stimulated by TNF-alpha. These findings indicate that both cell surface and mRNA expression of adhesion molecules in HDMEC induced by TNF-alpha are inhibited significantly by pretreatment with PDTC or Sper-NO, possibly in part through blocking the activation of NF-kappaB. These results suggest a potential therapeutic approach using antioxidant agents or nitric oxide pathway modulators in the treatment of inflammatory skin diseases.     

An Important Role of the SDF-1/CXCR4 Axis in Chronic Skin Inflammation

Inflammatory angiogenesis and vascular remodeling play key roles in the chronic inflammatory skin disease psoriasis, but little is known about the molecular mediators of vascular activation. Based on the reported elevated mRNA levels of the angiogenic chemokine stromal cell-derived factor-1 (SDF-1) and its receptor CXCR4 in psoriasis, we investigated the relevance of the SDF-1/CXCR4 axis in two experimental models of chronic psoriasis-like skin inflammation. The cutaneous expression of both SDF-1 and CXCR4 was upregulated in the inflamed skin of K14-VEGF-A transgenic mice and in imiquimod-induced skin inflammation, with expression of CXCR4 by blood vessels and macrophages. Treatment with the CXCR4 antagonist AMD3100 potently inhibited skin inflammation in both models, associated with reduced inflammatory angiogenesis and inflammatory cell accumulation, including dermal CD4⁺ cells and intraepidermal CD8⁺ T cells. Similar anti-inflammatory effects were seen after treatment with a neutralizing anti-SDF-1 antibody. In vitro, inhibition of CXCR4 blocked SDF-1-induced chemotaxis of CD11b⁺ splenocytes, in agreement with the reduced number of macrophages after in vivo CXCR4 blockade. Our results reveal an important role of the SDF-1/CXCR4 axis in skin inflammation and inflammatory angiogenesis, and they indicate that inhibition of the SDF-1/CXCR4 axis might serve as a novel therapeutic strategy for chronic inflammatory skin diseases.     

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.     

Quantitative differences in chemokine receptor engagement generate diversity in integrin-dependent lymphocyte adhesion

Chemokines control the specificity of lymphocyte homing. Numerous chemokines have been identified but the significance of redundancy in chemokine networks is unexplained. Here we investigated the biological significance of distinct chemokines binding to the same receptor. Among CCR4 ligands, skin vessels endothelial cells present C-C chemokine ligand (CCL) 17 but not CCL22 consistent with CCL17 involvement in T lymphocyte arrest on endothelial cells. However, CCL22 is much more powerful than CCL17 in the induction of rapid integrin-dependent T cell adhesion on VCAM-1 under conditions of physiological flow. The dominance of CCL22 over CCL17 extends to other CCR4-mediated phenomena such as receptor desensitization and internalization and correlates with the peculiar kinetics of CCR4 engagement by the two ligands. A similar phenomenological pattern is also shown for CXC chemokine ligand 9 and CXC chemokine ligand 11, which share binding to CXCR3. Our analysis shows how quantitative variations in chemokine receptor expression level and ligand engagement may alter the selectivity of integrin-dependent lymphocyte adhesive responses, suggesting a mechanism by which chemokine networks may either generate or break the specificity of lymphocyte subset recruitment.     

Neutrophils, monocytes, and dendritic cells express the same specialized form of PSGL-1 as do skin-homing memory T cells: cutaneous lymphocyte antigen.

Memory T cells in inflamed skin express the cutaneous lymphocyte-associated antigen (CLA), a glycosylated epitope defined by the mAb HECA-452. We previously reported that on T cells, CLA occurs almost exclusively on the protein backbone of P-selectin glycoprotein ligand-1 (PSGL-1). T cells exhibiting the CLA isoform of PSGL-1 can tether and roll on both E- and P-selectin, while T cells expressing PSGL-1 without the CLA epitope do not bind E-selectin, though they may bind P-selectin. We show here that circulating neutrophils and monocytes, and cultured blood dendritic cells, also express CLA almost entirely as an isoform of PSGL-1. These cells all tether and roll on both E- and P-selectin. A chimeric fusion protein incorporating the 19 N-terminal amino acids of mature PSGL-1 exhibited HECA-452 immunoreactivity and supported rolling of CHO cells expressing either E- or P-selectin. These findings indicate a site for the CLA modification within the distal tip of PSGL-1, previously shown to be critical for P-selectin binding and to mediate some, but not all, of the E-selectin binding of PSGL-1. We hypothesize that the types of circulating leukocytes discussed above all use CLA/PSGL-1 to tether and roll on E- and P-selectin along the vascular endothelium.     

Blood Vessels Pattern Heparan Sulfate Gradients between Their Apical and Basolateral Aspects

A hallmark of immune cell trafficking is directional guidance via gradients of soluble or surface bound chemokines. Vascular endothelial cells produce, transport and deposit either their own chemokines or chemokines produced by the underlying stroma. Endothelial heparan sulfate (HS) was suggested to be a critical scaffold for these chemokine pools, but it is unclear how steep chemokine gradients are sustained between the lumenal and ablumenal aspects of blood vessels. Addressing this question by semi-quantitative immunostaining of HS moieties around blood vessels with a pan anti-HS IgM mAb, we found a striking HS enrichment in the basal lamina of resting and inflamed post capillary skin venules, as well as in high endothelial venules (HEVs) of lymph nodes. Staining of skin vessels with a glycocalyx probe further suggested that their lumenal glycocalyx contains much lower HS density than their basolateral extracellular matrix (ECM). This polarized HS pattern was observed also in isolated resting and inflamed microvascular dermal cells. Notably, progressive skin inflammation resulted in massive ECM deposition and in further HS enrichment around skin post capillary venules and their associated pericytes. Inflammation-dependent HS enrichment was not compromised in mice deficient in the main HS degrading enzyme, heparanase. Our results suggest that the blood vasculature patterns steep gradients of HS scaffolds between their lumenal and basolateral endothelial aspects, and that inflammatory processes can further enrich the HS content nearby inflamed vessels. We propose that chemokine gradients between the lumenal and ablumenal sides of vessels could be favored by these sharp HS scaffold gradients.     

Naive T cell recruitment to nonlymphoid tissues: a role for endothelium-expressed CC chemokine ligand 21 in autoimmune disease and lymphoid neogenesis

Naive T cells are usually excluded from nonlymphoid tissues. Only when such tertiary tissues are subjected to chronic inflammation, such as in some (but not all) autoimmune diseases, are naive T cells recruited to these sites. We show that the CCR7 ligand CC chemokine ligand (CCL)21 is sufficient for attracting naive T cells into tertiary organs. We performed intravital microscopy of cremaster muscle venules in T-GFP mice, in which naive T cells express green fluorescent protein (GFP). GFP(+) cells underwent selectin-dependent rolling, but no firm adherence (sticking). Superfusion with CCL21, but not CXC chemokine ligand 12, induced integrin-dependent sticking of GFP(+) cells. Moreover, CCL21 rapidly elicited accumulation of naive T cells into sterile s.c. air pouches. Interestingly, a second CCR7 ligand, CCL19, triggered T cell sticking in cremaster muscle venules, but failed to induce extravasation in air pouches. Immunohistochemistry studies implicate ectopic expression of CCL21 as a mechanism for naive T cell traffic in human autoimmune diseases. Most blood vessels in tissue samples from patients with rheumatoid arthritis (85 +/- 10%) and ulcerative colitis (66 +/- 1%) expressed CCL21, and many perivascular CD45RA(+) naive T cells were found in these tissues, but not in psoriasis, where CCL21(+) vessels were rare (17 +/- 1%). These results identify endothelial CCL21 expression as an important determinant for naive T cell migration to tertiary tissues, and suggest the CCL21/CCR7 pathway as a therapeutic target in diseases that are associated with naive T cell recruitment.     

Differential binding of chemokines to macrophages and neutrophils in the human inflamed synovium

In chronic inflammatory foci, such as the rheumatoid joint, there is enhanced recruitment of phagocytes from the blood into the tissues. Chemokines are strongly implicated in directing the migration of these cells, although little is known regarding the chemokine receptors that could mediate their chemotaxis into the joint tissue. Therefore the objective of the study was to identify chemokine binding sites on macrophages and neutrophils within the rheumatoid synovium using radiolabeled ligand binding and in situ autoradiography. Specific binding sites for CCL3 (macrophage inflammatory protein-1α), CCL5 (RANTES), CCL2 (monocyte chemoattractant protein-1) and CXCL8 (IL-8) were demonstrated on CD68⁺ macrophages in the subintimal and intimal layers. The number and percentage of intimal cells that bound chemokines were greater in inflamed regions compared to noninflamed regions. The intensity of intimal binding varied between chemokines with the rank order, CCL3 > CCL5 > CCL2 > CXCL8. Neutrophils throughout the synovium bound CXCL8 but did not show any signal for binding CCL2, CCL3 or CCL5.     

Sostdc1 Secreted from Cutaneous Lymphatic Vessels Acts as a Paracrine Factor for Hair Follicle Growth

In our previous study, we found that lymphatic vessels stimulate hair follicle growth through paracrine effects on dermal papilla cells. However, the paracrine factors secreted from cutaneous lymphatic vessels that can activate dermal papilla cells are still unknown. In this study, we investigated whether lymphatic endothelial cells might secrete paracrine factors that activate dermal papilla cells in vitro. We found that Sostdc1 was more expressed in lymphatic endothelial cells compared with blood vascular endothelial cells. In addition, Sostdc1 expression levels were significantly increased during the anagen phase in the back skin of C57BL/6J mice, as compared to the telogen phase. We also observed that incubation of dermal papilla cells with 200 ng/mL Sostdc1 for 72 h induced the expression levels of Lef-1, a downstream target of Wnt signaling. Taken together, our results reveal that Sostdc1, a BMP antagonist, secreted from cutaneous lymphatic vessels, may act as a paracrine factor for hair follicle growth.     

CCL27-CCR10 interactions regulate T cell-mediated skin inflammation

The skin-associated chemokine CCL27 (also called CTACK, ALP and ESkine) and its receptor CCR10 (GPR-2) mediate chemotactic responses of skin-homing T cells in vitro. Here we report that most skin-infiltrating lymphocytes in patients suffering from psoriasis, atopic or allergic-contact dermatitis express CCR10. Epidermal basal keratinocytes produced CCL27 protein that bound to extracellular matrix, mediated adhesion and was displayed on the surface of dermal endothelial cells. Tumor necrosis factor-alpha and interleukin-1beta induced CCL27 production whereas the glucocorticosteroid clobetasol propionate suppressed it. Circulating skin-homing CLA+ T cells, dermal microvascular endothelial cells and fibroblasts expressed CCR10 on their cell surface. In vivo, intracutaneous CCL27 injection attracted lymphocytes and, conversely, neutralization of CCL27-CCR10 interactions impaired lymphocyte recruitment to the skin leading to the suppression of allergen-induced skin inflammation. Together, these findings indicate that CCL27-CCR10 interactions have a pivotal role in T cell-mediated skin inflammation.