Cutaneous dermal Ia+ cells are capable of initiating delayed type hypersensitivity responses

Langerhans cells and more: langerin-expressing dendritic cell subsets in the skin

Langerhans cells (LCs) are antigen-presenting dendritic cells (DCs) that reside in epithelia. The best studied example is the LC of the epidermis. By electron microscopy, their identifying feature is the unique rod- or tennis racket-shaped Birbeck granule. The phenotypic hallmark is their expression of the C-type lectin receptor langerin/CD207. Langerin, however, is also expressed on a recently discovered population of DC in the dermis and other tissues of the body. These 'dermal langerin(+) dendritic cells' are unrelated to LCs. The complex field of langerin-negative dermal DCs is not dealt with here. In this article, we briefly review the history, ontogeny, and homeostasis of LCs. More emphasis is laid on the discussion of functional properties in vivo. Novel models using genetically engineered mice are contributing tremendously to our understanding of the role of LCs in eliciting adaptive immune responses against pathogens or tumors and in inducing and maintaining tolerance against self antigens and innocuous substances in vivo. Also, innate effector functions are increasingly being recognized. Current activities in this area are reviewed, and possibilities for future exploitation of LC in medicine, e.g. for the improvement of vaccines, are contemplated.

Stress-induced neurogenic inflammation in murine skin skews dendritic cells towards maturation and migration: key role of intercellular adhesion molecule-1/leukocyte function-associated antigen interactions

The skin continuously serves as a biosensor of multiple exogenous stressors and integrates the resulting responses with an individual's central and peripheral endogenous response systems to perceived stress; it also acts to protect against external challenges such as wounding and infection. We have previously shown in mice that stress induces nerve growth factor- and substance P-dependent neurogenic inflammation, which includes the prominent clustering of MHC class II(+) cells. Because the contribution of dendritic cells (DCs) in response to stress is not well understood, we examined the role of DCs in neurogenic inflammation in murine skin using a well-established murine stress model. We show that sound stress increases the number of intradermal langerin(+) and CD11c(+) DCs and induces DC maturation, as indicated by the up-regulated expression of CD11c, MHC class II, and intercellular adhesion molecule-1 (ICAM-1). Blocking of ICAM-1/leukocyte function-associated antigen-1 interactions significantly abrogated the stress-induced numeric increase, maturation, and migration of dermal DCs in vivo and also reduced stress-induced keratinocyte apoptosis and endothelial cell expression of ICAM-1. In conclusion, stress exposure causes a state of immune alertness in the skin. Such adaptation processes may ensure protection from possible infections on wounding by stressors, such as attack by predators. However, present-day stressors have changed and such adaptations appear redundant and may overrun skin homeostasis by inducing immune dermatoses.

"Dermal dendritic cells" comprise two distinct populations: CD1+ dendritic cells and CD209+ macrophages

A key cell type of the resident skin immune system is the dendritic cell (DC), which in normal skin is located in two distinct microanatomical compartments: Langerhans cells (LCs), mainly in the epidermis, and dermal DCs (DDCs), in the dermis. Here, the lineage of DDCs was investigated using monoclonal antibodies and immunohistology. We provide evidence that "DDC" comprise at least two major phenotypic populations of dendritic-appearing cells, immature DC expressing CD1, CD11c and CD208; and macrophages expressing CD209, CD206, CD163, and CD68. These data suggest that dermal dendritic-appearing macrophages comprise a novel part of the innate immune response in the resident skin immune system.

Direct microscopic quantification of dynamics of Plasmodium berghei sporozoite transmission from mosquitoes to mice

The number of malaria sporozoites delivered to a host by mosquitoes is thought to have a significant influence on the subsequent course of the infection in the mammalian host. We did studies with Anopheles stephensi mosquitoes with salivary gland infections of Plasmodium berghei sporozoites expressing a red fluorescent protein. After individual mosquitoes fed on an ear pinna or the ventral abdomen of a mouse, fluorescence microscopy was used to count numbers of sporozoites. Mosquitoes allowed to feed on the ear for periods of 3 versus 15 min deposited means of 281 versus 452 sporozoites, respectively, into the skin; this may have epidemiological implications because mosquitoes can feed for longer periods of time on sleeping hosts. Mosquitoes feeding on the ventral abdomen injected sporozoites not only into the skin but also into the underlying peritoneal musculature. Although mosquitoes injected fewer sporozoites into the abdominal tissues, more of these were reingested into the mosquito midgut, probably a consequence of easier access to blood intake from the abdominal area. The most consistent parameter of sporozoite transmission dynamics under all conditions of mosquito probing and feeding was the relatively slow release rate of sporozoites (approximately 1 to 2.5 per second) from the mosquito proboscis. The numbers of sporozoites introduced into the host by mosquitoes and the transmission efficiencies of sporozoite delivery are multifactorial phenomena that vary with length of probing time, skin site being fed upon, and numbers of sporozoites within the salivary glands.

Langerhans cells and lymph node dendritic cells express the tight junction component claudin-1

Claudin-1 is a critical structural component of tight junctions that have an important role in adhesive properties, barrier function, and paracellular transport of epithelia and other nonhematopoietic tissues. We found claudin-1 in murine CD207+ Langerhans cells (LC) residing in epidermis. Claudin-1 was not detected in other skin dendritic cells (DC). LC expressed claudin-1 in steady state and inflamed skin. Claudin-1 was demonstrated further in lymph node LC under steady state and inflammatory conditions, including after direct tracking with tetramethylrhodamine-isothiocyanate (TRITC). All subsets of skin draining lymph node DC defined by CD205, CD11b, CD11c, and CD8, including a presumably blood-borne lymph node resident CD8+CD207+ LC population, were claudin-1+. TRITC tracking demonstrated claudin-1 in CD207- skin migrant DC in the lymph node, suggesting upregulation of this molecule during migration or once arrived in the lymph node. Claudin-1 expression in CD207+ cells was confirmed at the protein and mRNA levels. Transforming growth factor-beta, a factor critical for the induction of LC in vitro and in vivo, stimulated the accumulation of claudin-1 mRNA and protein when added to bone marrow cells cultured with GM-CSF and IL-4. Claudin-1 may thus have an important function in adhesion and/or migration of LC.

Cutaneous dendritic cells

Cutaneous dendritic cells (DC) include epidermal Langerhans cells (LC), interstitial/dermal dendritic cells (DDC), as well as plasmacytoid DC (pDC) that occur under pathological conditions. These immune cells have a spectrum of different functions with implications that extend far beyond the skin. They have the potential to internalize particulate agents and macromolecules, and display migratory properties that endow them with the unique capacity to journey between skin and draining lymph nodes where they encounter antigen-specific T lymphocytes. Herein, we will review the features of human and mouse cutaneous DC, emphasizing characteristics representative of their life-cycle stages that occur within the skin.

Hair follicle regeneration using grafted rodent and human cells

Hair follicle regeneration involves epithelial-mesenchymal interactions (EMIs) of follicular epithelial and dermal papilla (DP) cells. Co-grafting of those cellular components from mice allows complete hair reconstitution. However, regeneration of human hair in a similar manner has not been reported. Here, we investigated the possibility of cell-based hair generation from human cells. We found that DP-enriched cells (DPE) are more critical than epidermal cells in murine hair reconstitution on a cell number basis, and that murine DPE are also competent for hair regeneration with rat epidermal cells. Co-grafting of human keratinocytes derived from neonatal foreskins with murine DPE produced hair follicle-like structures consisting of multiple epidermal cell layers with a well-keratinized innermost region. Those structures expressed hair follicle-specific markers including hair keratin, and markers expressed during developmental stages. However, the lack of regular hair structures indicates abnormal folliculogenesis. Similar hair follicle-like structures were also generated with cultured human keratinocytes after the first passage, or with keratinocytes derived from adult foreskins, demonstrating that epidermal cells even at a mature stage can differentiate in response to inductive signals from DP cells. This study emphasizes the importance of EMI in follicular generation and the differentiation potential of epidermal keratinocytes.

Clinical and immunohistochemical assessment of the effect of cyclosporin in keratinocytes and dermal dendrocytes in psoriasis

BACKGROUND

Cyclosporine is a potent immunosupressor, which induces cytokeratin expression pattern changes and dermal dendrocytes number increase.

OBJECTIVES

To evaluate its clinical effect in psoriasis, on keratinocytic proliferation and differentiation, and on dermal dendrocytes proliferation.

METHODS

Thirty patients with psoriasis were treated and evaluated for 8 weeks. Clinical improvement was evaluated by Psoriasis Area and Severity Index (PASI). Biopsies were performed initially and after 8 weeks. Immunohistochemistry [CK markers 10, 14, and 16, and factor XIIIa+ (FXIIIa+)] was performed.

RESULTS

Mean PASI before treatment was 26.32 and 3.71 after. Mean initial and final PASI difference was 22.61 (p < 0.001). Two patients had serum creatinine and six uric acid increase. Before and after treatment, mean numbers per field of dermal dendrocytes were 7.07 and 3.68, respectively. Mean difference was 3.39, with p < 0.001. CK10 immunohistochemical pattern demonstrated recovery of normal expression pattern in 26 patients, while CK14 pattern demonstrated improvement in 21 patients.

CONCLUSIONS

Cyclosporine was effective and safe for psoriasis in low doses, with significant decrease of PASI and dermal dendrocytes number after 8 weeks of therapy. CK10 and 14 pattern changed and, less prominently, CK16 expression. These modifications occur later than the PASI and dermal dendrocytes variation.

Migratory Langerhans cells in mouse lymph nodes in steady state and inflammation

Dendritic cells cells induce immunity or-in the steady state-maintain peripheral tolerance. Little is known in that regard about Langerhans cells. Therefore, we investigated migrating Langerhans cells in the steady-state versus inflammation. Increased numbers of Langerhans cells, as determined by immunostaining for Langerin/CD207, appeared in the lymph nodes in response to a contact allergen. Whereas a large proportion of Langerhans cells expressed CD86 in the steady state, CD40, and CD80 were found on a smaller percentage. During inflammation, more CD40(+), CD80(+), CD274/B7-H1/PD-L1(+), and CD273/B7-DC/PD-L2(+) Langerhans cells were found in the lymph nodes, and they expressed higher levels of these molecules. CD275/inducible T cell co-stimulator (ICOS) ligand was not detected. Langerhans cells in the nodes of contact allergen-treated mice produced more IL-12p40/70. This correlated with more interferon-gamma being produced by activated lymph node T cells. Epicutaneous immunization with ovalbumin under inflammatory conditions led to a more vigorous proliferation of antigen-specific CD4 T cells in vitro and in vivo as compared with immunization in the steady state. The latter modality, however did not induce strong CD4 T cell tolerance in this model. Thus, the overall phenotype of Langerhans cells is not an indicator for their immunogenic or tolerogenic potential.

Up-regulation of cell surface Toll-like receptor 4-MD2 expression on dendritic epidermal T cells after the emigration from epidermis during cutaneous inflammation

BACKGROUND

Mouse epidermis contains a population of gammadelta T cells, termed dendritic epidermal T cells (DETCs), which uniformly express the invariant Vgamma3 T cell receptor. Certain DETC lines were reported to respond to Gram-negative bacteria in the presence of immobilized anti-CD3 monoclonal antibody or to lipopolysaccharide (LPS) in the presence of B cell lines.

OBJECTIVE

To determine whether DETCs express the primary signaling receptor for LPS, Toll-like receptor (TLR) 4-MD2.

METHODS

We analyzed expression of TLR4-MD2 in three independent DETC lines as well as in freshly isolated DETCs.

RESULTS

All DETC lines expressed TLR4 and MD2 transcripts and TLR4-MD2 protein complex intracellularly, but none expressed TLR4-MD2 on the cell surface. By immunoblotting, only the immature form of TLR4 protein was detected in the DETC lines. The DETC lines did not respond to LPS even in the presence of immobilized anti-CD3 monoclonal antibody. Freshly isolated DETCs and their fetal thymic precursors also lacked cell surface expression of TLR4-MD2, but a small subpopulation of dermal Vgamma3 T cells isolated from croton oil-painted skin expressed TLR4-MD2 on the cell surface. Similarly, Vgamma3 T cells emigrated from organ-cultured epidermis expressed cell surface TLR4-MD2.

CONCLUSIONS

These results demonstrate that DETCs do not constitutively express cell surface TLR4-MD2, but TLR4-MD2 expression may be up-regulated when DETCs emigrate from epidermis during cutaneous inflammation.

Contact allergens and irritants show discrete differences in the activation of human monocyte-derived dendritic cells: consequences for in vitro detection of contact allergens

In recent years test systems have been described that may be applied routinely to discriminate between contact allergens and irritants in vitro. Using human monocyte-derived dendritic cells (MoDC), this study was designed to refine the settings of a potential routine screening protocol for contact allergens and to investigate the so far poorly defined concentration dependency of contact allergen-specific effects. MoDC were generated by 6 days of culture in the presence of IL-4 and GM-CSF and were then cultured for 24 or 48 h in medium with lipopolysaccharide (LPS), contact allergens [picrylsulphonic acid (TNBS), 1-chloro-2,4-dinitrobenzene (DNCB)] or irritants [sodium dodecyl sulphate (SDS), benzalkonium chloride (BAC)] that were free of detectable endotoxin contamination. The induction of CD86 and HLA-DR expression was quantified by flow cytometry as markers for MoDC activation. LPS activation upregulated CD86 about 20-fold and HLA-DR expression about 4-fold. Compared to LPS, contact allergens had weaker effects. TNBS and DNCB induced activation marker upregulation starting slightly below the cytotoxic concentration and increasing in a dose-dependent manner. However, at partially cytotoxic concentrations, irritants also induced CD86 and HLA-DR expression, as confirmed by flow cytometry and quantitative RT-PCR. Both SDS and BAC induced activation marker expression on surviving MoDC, when more than 50% of the MoDC population had been killed by the treatment. Consequently, routine testing of unknown substances would need to quantify activation marker expression as well as cytotoxicity in parallel. In the concentration range around the lowest cytotoxic concentration, the assay may be able to discriminate between contact allergens and irritants.

iC3b arrests monocytic cell differentiation into CD1c-expressing dendritic cell precursors: a mechanism for transiently decreased dendritic cells in vivo after human skin injury by ultraviolet B

Our previous data indicated that C3, its bioactive product iC3b, and the iC3b ligand CD11b are critical for ultraviolet-induced immunosuppression. We thus hypothesized that iC3b is an important skin-based factor regulating CD11b+ monocytic cell function in the acute post-ultraviolet period. Although monocytic cell migration peaked at 1-3 d after ultraviolet exposure of skin, dermal CD1c dendritic cells underwent a rapid and prolonged depletion that did not recover until day 7. Because ultraviolet-induced iC3b deposits are reciprocally maximal on day 3, but fade by day 7, we next hypothesized that iC3b can be responsible for the delay in differentiation into dendritic cells of monocytic cells migrating into ultraviolet-exposed skin. Analysis of dermal cells derived from keratome biopsies suggested that iC3b exposure could inhibit the development of CD1c+ dermal cells. To model newly immigrating blood monocytes entering ultraviolet-exposed, iC3b-containing dermis, purified monocytes from human blood were induced with granulocyte-macrophage colony stimulating factor to generate a population of dendritic cell precursors expressing CD1c. Incubation with iC3b markedly inhibited the appearance of CD1c+ cells (p<0.05) and induced CD1c-CD14+ cells. This inhibition was reversed by coincubation with an anti-CD11b antibody that blocks the iC3b binding site. Other functions associated with dendritic cell maturation were also inhibited by iC3b, such as interleukin-12p70 production as well as CD80 and CD40 expression. Restimulation of monocytes for DC maturation revealed that iC3b induced a temporary inhibition of DC differentiation. Thus, a human skin response in which iC3b is transiently (3-7 d) generated in dermis, such as ultraviolet, can arrest monocytic skin-infiltrating cells from undergoing dendritic cell precursor differentiation.

IL-1beta is essential for langerhans cell activation and antigen delivery to the lymph nodes during contact sensitization: evidence for a dermal source of IL-1beta

IL-1beta(-/-) mice manifest an impaired contact hypersensitivity response to the hapten trinitrochlorobenzene, with the principle defect expressed during the sensitization phase of this response. Following application of hapten to the skin, epidermal Langerhans cells of IL-1beta(-/-) mice failed to demonstrate the classical phenotype of activation. In addition, the delivery of epicutaneously applied fluorescein isothiocyanate to draining lymph nodes was decreased in IL-1beta(-/-) mice. Hapten delivery to draining lymph nodes could be restored by intradermal injection of recombinant IL-1beta. Reconstitution of lethally irradiated IL-1beta(-/-) mice by transfer of wild-type bone marrow restored hapten-stimulated IL-1beta mRNA expression, demonstrating that IL-1beta production was dependent on bone marrow-derived cells. In wild-type skin, IL-1beta expression was upregulated in a time- and dose-dependent fashion following hapten application. Interestingly, prominent IL-1beta expressing cells were found in the dermis, suggesting that dermal cells may contribute significantly to the contact hypersensitivity response.

Phenotypic and functional outcome of human monocytes or monocyte-derived dendritic cells in a dermal equivalent

The dermis harbors a true dendritic cell population that could elicit primary allogeneic T cell responses in vitro and contact hypersensitivity reactions in vivo. The origin of dermal dendritic cells remains poorly understood, however. In this study, we analyzed the fate of monocytes or monocyte-derived dendritic cells in a dermal equivalent. Freshly isolated monocytes or monocytes cultured for 6 d with either GM-CSF/IL-4 or GM-CSF/IL-4/TGF-beta 1 (TGF-DC) were seeded in a collagen solution with normal human fibroblasts. The lattices were cultured for 7--14 d in the presence, or absence, of the exogenous cytokines, before phenotypic and functional studies were performed. Supply of exogenous cytokines allows the appearance of typical CD1a(+)/CD14(-)/CD68(low) dendritic cells with significant allostimulatory property, regardless of the cell type incorporated into the lattices. In cytokine-free conditions, monocytes and GM-CSF/IL-4-derived dendritic cells give rise to a CD1a(-)/CD14(+)/CD68(high) monocyte/macrophage population with no allostimulatory property. When incorporated into the lattices in the absence of exogenous cytokines the TGF-DC express few CD68 and FXIIIa. Interestingly, these cells do not all convert into the CD14(+)/CD1a(-) population. Indeed, a small HLA-DR(+)/CD1a(+)/CD14(-) subset was consistently found, which represents about one-third of the HLA-DR(+) cells. Moreover, TGF-DC recovered from the lattices after culture without cytokines do display a significant allostimulatory function. Thus, in the absence of exogenous cytokines, only Langerhans-cell-like dendritic cells can retain the typical dendritic cell features when inserted in a dermal environment. Taken together, these results may provide evidence supporting an epidermal origin of dermal dendritic cells.

Migration of dendritic cells into lymphatics-the Langerhans cell example: routes, regulation, and relevance

Dendritic cells are leukocytes of bone marrow origin. They are central to the control of the immune response. Dendritic cells are highly specialized in processing and presenting antigens (microbes, proteins) to helper T lymphocytes. Thereby, they critically regulate further downstream processes such as the development of cytotoxic T lymphocytes, the production of antibodies by B lymphocytes, or the activation of macrophages. A new field of dendritic cell biology is the study of their potential role in inducing peripheral tolerance. The immunogenic/tolerogenic potential of dendritic cells is increasingly being utilized in immunotherapy, particularly for the elicitation of antitumor responses. One very important specialization of dendritic cells is their outstanding capacity to migrate from sites of antigen uptake to lymphoid organs. Much has been learned about this process from studying one particular type of dendritic cell, namely, the Langerhans cell of the epidermis. Therefore, the migratory properties of Langerhans cells are reviewed. Knowledge about this "prototype dendritic cell" may help researchers to understand migration of other types of dendritic cells.

Anatomical origin of dendritic cells determines their life span in peripheral lymph nodes

Dendritic cells (DCs) exhibit considerable heterogeneity in their anatomical location, surface phenotype, and functional properties. In this study, we demonstrate that peripheral lymph nodes contain at least four major, functionally separable, and independently derived, DC subsets, which can be clearly demarcated by their CD11c, CD40, and CD8 expression pattern. Surprisingly, all DCs derived directly from the bone marrow, the myeloid- and the lymphoid-related subsets, turned over fast with t(1/2) of a couple of days. In contrast, DCs exported from the skin, both dermal and epidermal, accumulated 3- to 4-fold slower, turnover that is dramatically increased by cutaneous inflammation.

Suprathreshold doses of hapten are required to induce both contact hypersensitivity and tolerance

Whereas both high (conventional) and low (optimal) doses of epicutaneously applied hapten induce contact hypersensitivity in normal mice, only conventional doses retain their capacity to induce contact hypersensitivity after acute, low dose ultraviolet B radiation in UVB-resistant mice. Recent evidence indicates that conventional doses of hapten as well as acute, low dose ultraviolet B radiation destroy virtually all epidermal Langerhans cells, which leads to the conclusions that (a) dermal antigen presenting cells have a prominent role to play in contact hypersensitivity induction, and that (b) Langerhans cell provide this function only in normal skin, and only if non-toxic amounts of hapten are present. We have now explored the ability of suprathreshold, threshold, and sub-threshold doses of hapten to induce tolerance when painted on or injected into normal skin or skin exposed to ultraviolet B radiation. Our results indicate that a single exposure of low dose, ultraviolet B radiation generated tolerance-promoting signals within the epidermis when a threshold dose of hapten was painted on the exposed site. By contrast, suprathreshold doses of hapten painted on skin after four consecutive daily doses of ultraviolet B radiation led to tolerance that arose exclusively from cells within the dermis. In absence of ultraviolet B radiation, epicutaneously applied hapten failed uniformly to induce tolerance, whether applied at suprathreshold, threshold or sub-threshold doses. We conclude that normal skin lacks cells with inherent tolerance-promoting capacity, but that cells of this type can emerge within either epidermis or dermis after exposure to acute, low dose ultraviolet B radiation.

Cytokines and chemokines in the initiation and regulation of epidermal Langerhans cell mobilization

Langerhans cells (LC) are members of the wider family of dendritic cells. LC reside in the epidermis where they serve as sentinels of the immune system, their responsibilities being to sample the external environment for changes and challenges and to deliver information (antigen) to responsive T lymphocytes within skin draining lymph nodes. The ability of LC to migrate from the epidermis to regional lymph nodes is therefore of pivotal importance to the induction of cutaneous immune responses. The journey that LC have to make from the skin has a number of requirements. Initially it is necessary that LC disassociate themselves from surrounding keratinocytes and are liberated from other influences that encourage their retention in the epidermis. Subsequently, migrating LC must successfully traverse the basement membrane of the dermal-epidermal junction and make their way, via afferent lymphatics, to draining lymph nodes. Effective entry into lymph nodes is necessary, as is correct positioning of cells within the paracortex. There is increasing evidence that both cytokines and chemokines, and their interaction with appropriate receptors expressed by LC, orchestrate the mobilization and movement of these cells. We here consider the parts played by these molecules, and how collectively they induce and direct LC migration.

Morphea limited to the superficial reticular dermis: an underrecognized histologic phenomenon

Morphea (localized scleroderma) is a disease of unknown etiology, presenting as circumscribed areas of indurated skin. Histologically, most cases of morphea feature thickened collagen bundles in the deep reticular dermis, sometimes also extending into the superficial dermis or into the subcutis. We present six cases of morphea in which typical histologic features were restricted to the superficial dermis and contrast these with 27 additional biopsies of conventional morphea seen during the same time period. Sections were stained for elastic fibers, and dermal dendritic cells were labeled with antibodies to CD34 and Factor XIIIa. All six cases showed thickened collagen bundles restricted to the superficial dermis, sparing the deep dermis and without associated evidence of lichen sclerosus et atrophicus (LSA). Dermal elastic fibers were not appreciably decreased in number. There was loss of CD34-positive dermal spindle cells in each of our six superficial examples of morphea, which was restricted to the area of altered collagen in four of the six cases. This report highlights the distinctly uncommon phenomenon of morphea presenting solely as alteration of the superficial reticular dermis, without features of LSA. The selective loss of CD34-labeled spindle cells may provide information regarding the role of these putative immune accessory cells in morphea. Recognition of this manifestation of morphea may be helpful diagnostically.

Dermal dendritic cells associated with T lymphocytes in normal human skin display an activated phenotype

The CMRF-44 and CD83 (HB15) antigens are associated with functional maturation and activation of blood dendritic cells (DC). We describe the expression of these antigens on freshly isolated epidermal Langerhans cells and dermal DC as well as the distribution of CD83+/ CMRF-44++-activated DC within sections of normal human skin. Fresh Langerhans cells were prepared by standard techniques and large numbers of enriched (25%-55%), viable dermal DC were obtained using an improved collagenase treatment protocol with density gradient enrichment. Freshly isolated Langerhans cells and dermal DC had similar costimulator and activation antigen expression, and both stimulated moderate levels of allogeneic T lymphocyte proliferation as determined in the 7 d mixed leukocyte reaction. In situ labeling of DC within skin sections revealed a population of CD83 and CMRF-44 positive dermal cells of which most (approximately 75%) were in intimate contact with CD3+ T lymphocytes, especially in the adnexal regions. In contrast, only 25%-30% of the more numerous CD1a++ dermal DC population were directly apposed to T lymphocytes. The CMRF-44++ dermal DC population stimulated an allogeneic mixed leukocyte reaction, confirming their identity as DC. These data, plus comparative data obtained for migratory dermal DC, suggest that only a small proportion of dermal DC have been triggered to a more advanced state of differentiation or activation. The striking association of the activated dermal DC population with T lymphocytes suggests that communication between these two cell types in situ may occur early in the immune response to cutaneous antigen.

Dermal dendrocytes participate in the cellular pathology of experimental acute graft-versus-host disease

In a well established murine model relevant to human disease, graft-versus-host disease results from recognition of recipient minor histocompatibility antigens by donor bone marrow-derived T lymphocytes. Previous studies suggest that factor XIIIa-positive dermal dendrocytes may be involved in the pathogenesis of disorders involving antigen presentation to T cells and dermal fibrosis. This study was undertaken to determine (i) whether normal murine skin contains factor XIIIa-positive dermal dendrocytes, and (ii) whether such cells participate in the pathophysiology of acute graft-versus-host disease. Graft-versus-host disease was produced using B10.BR CD8+ donor T cells administered to CBA recipients. Skin samples were collected weekly for a 5-week period and evaluated by immunohistochemistry and electron microscopy. Our data indicate that normal murine dermis contains factor XIIIa-positive cells localized primarily around deep dermal microvessels. Ultrastructural analyses reveal these cells to have long processes, pinocytotic vesicles, fibronexuses, and intimate associations with mast cells. During graft-versus-host disease, factor XIIIa-positive dendrocytes appeared within the superficial dermis. By ultrastructure, the dendrocytes were hypertrophic and highly branched, and demonstrated an intimate relationship with neighboring cells. In conclusion, factor XIIIa-positive dendrocytes comprise a normal component of the murine dermis and undergo alterations in experimental acute graft-versus-host disease consistent with participation in disease pathophysiology.

In human skin, UVB initiates early induction of IL-10 over IL-12 preferentially in the expanding dermal monocytic/macrophagic population

In contrast to Langerhans cells, which make interleukin (IL)-12, differentiated macrophages that infiltrate the epidermis 72 h after ultraviolet B (UV) irradiation potently produce IL-10 mRNA and secrete IL-10 protein. We asked whether differentiated UV macrophages in the epidermis acquired their activated, IL-10hi status as a result of entering the epidermis or as a result of encountering UV-induced changes in the dermal microenvironment. In this study, sequential section immunostaining directly showed dynamic and reciprocal changes of infiltrating CD11b+ macrophages and CD1a+ Langerhans cell loss in human epidermis and dermis after in vivo UV exposure in relation to the microanatomic localization of newly appearing dermal cells that stain for IL-10 mRNA by in situ hybridization. Using quantitative reverse transcriptase polymerase chain reaction on purified dermal cell subsets, the first significant rise in IL-10 mRNA occurred 6 h after UV in the dermal CD11b+ (CD1-, 3-, 24-, 56-) monocytic/macrophagic population. Significant induction of IL-10 mRNA 24 h post-UV was limited to the CD11b+ CD1- subset (p = 0.006). The fold increase of IL-10 mRNA relative to 0 h by the CD11b+ dermal monocytic/macrophagic population peaked at 24-48 h and tapered thereafter. Intense IL-10 production by macrophages in the epidermis appeared to follow dermal changes, with maximum production at 72 h, indicating migration/activation of this population from the dermis, and the remainder of dermal cells, depleted of monocyte/macrophages and Langerhans cell-like antigen-presenting cells, showed no increase in IL-10 at any time point post-UV. IL-10 protein-producing CD11b+ macrophages in the dermis were also documented by flow cytometry. IL-12 mRNA was differentially regulated from IL-10 after UV, in that IL-12 was consistently downregulated in the CD11b+ monocytic/macrophagic population (p < 0.0002). Taken together, monocytic/macrophagic cells with high IL-10 and low IL-12 expression initially appear in the dermis as early as 6 h, and then appear in the epidermis, implicating the dermis as the primary site of activation/signaling for IL-10 upregulation in cutaneous antigen-presenting cells.

Human dermal dendritic cells process and present soluble protein antigens

Recently, a novel type of dendritic antigen-presenting cell has been identified in the dermis of normal human and mouse skin. These dermal dendritic cells (DDC) occur in higher numbers than epidermal Langerhans cells, represent a distinct differentiation pathway of dendritic cells, and are as potent as Langerhans cells in the activation of superantigen specific T cells. As yet, nothing is known about their capacity to take up, process, and present soluble protein antigens. We used the model of tetanus toxoid (TT) driven T cell proliferation to address these questions. To test for active internalization of TT protein, gold labeled TT was incubated with Langerhans cells and DDC and could be traced to multivesicular endo-lysosomal compartments. DDC internalize TT through a receptor-mediated, clathrin-independent pathway, whereas Langerhans cells predominantly use macropinocytosis. To verify that DDC process TT by the exogenous pathway of antigen presentation, we pulsed DDC with TT protein or TT peptide after preincubation with chloroquine. Preincubation with chloroquine diminished the capacity of DDC to induce TT protein specific T cell proliferation (70-80%), but was not effective to suppress TT peptide induced T cell responses. DDC were as potent as Langerhans cells and 5-10 x more potent than plastic adherent monocytes in the presentation of TT to autologous resting T cells. Furthermore, as few as 50 DDC (stimulator:responder ratio of 1:1000) were able to induce a significant TT specific T cell proliferation. Because a subpopulation of DDC expresses low levels of CD1a, a phenotypic marker of Langerhans cells, sorting of CD1a positive and negative DDC was performed. On a per cell basis, CD1a positive and negative DDC were equally potent at mediating TT specific T cell proliferation. Thus, DDC are able to internalize, process, and present soluble protein antigens such as TT and may therefore play an important role in the regulation of skin immune responses.

Entry into afferent lymphatics and maturation in situ of migrating murine cutaneous dendritic cells

An important property of dendritic cells (DC), which contributes crucially to their strong immunogenic function, is their capacity to migrate from sites of antigen capture to the draining lymphoid organs. Here we studied in detail the migratory pathway and the differentiation of DC during migration in a skin organ culture model and, for comparison, in the conventional contact hypersensitivity system. We report several observations on the capacity of cutaneous DC to migrate in mouse ear skin. (i) Upon application of contact allergens in vivo the density of Langerhans cells in epidermal sheets decreased, as determined by immunostaining for major histocompatibility complex class II, ADPase, F4/80, CD11b, CD32, NLDC-145/DEC-205, and the cytoskeleton protein vimentin. Evaluation was performed by computer assisted morphometry. (ii) Chemically related nonsensitizing or tolerizing compounds left the density of Langerhans cells unchanged. (iii) Immunohistochemical double-staining of dermal sheets from skin organ cultures for major histocompatibility complex class II and CD54 excluded blood vessels as a cutaneous pathway of DC migration. (iv) Electron microscopy of organ cultures revealed dermal accumulations of DC (including Birbeck granule containing Langerhans cells) within typical lymphatic vessels. (v) Populations of migrating DC in organ cultures upregulated markers of maturity (the antigen recognized by monoclonal antibody 2A1, CD86), but retained indicators of immaturity (invariant chain, residual antigen processing function). These data provide additional evidence that during both the induction of contact hypersensitivity and in skin organ culture, Langerhans cells physically leave the epidermis. Both Langerhans cells and dermal DC enter lymphatic vessels. DC mature while they migrate through the skin.

The anagen hair cycle induces systemic immunosuppression of contact hypersensitivity in mice

Contact hypersensitivity (CHS) to picryl chloride (PCl) is depressed in C57BL/6 mice when CHS is induced via early anagen skin. We have now further dissected this phenomenon in vivo. The elicitation phase for CHS was suppressed when anagen was induced 4 days after PCl sensitization of telogen animals. Sensitization of mice via abdominal skin with all hair follicles in telogen, and back skin follicles in anagen, significantly reduced the magnitude of the ear swelling response. Consecutive applications of two sensitizing doses of hapten, first on induced anagen back skin and then on telogen abdominal skin 7 days later, failed to induce tolerance. Furthermore, spleen cell transfer of sensitized anagen mice into telogen mice did not inhibit CHS response in the recipients. The current study suggests that a temporary state of systemic hyporesponsiveness, mediated, e.g., by hair cycle-dependent production of immunosuppressive cytokines rather than hapten-specific T suppressor cell activities, plays a critical role.

Naïve, hapten-specific human T lymphocytes are primed in vitro with derivatized blood mononuclear cells

Our goal is to develop an in vitro system for priming naïve, hapten-specific human T cells similar to the effector cells that mediate contact hypersensitivity in vivo. Using strategies based on results of experiments conducted with murine cells, we stimulated peripheral blood T cells from normal human beings in vitro with peripheral blood mononuclear cells that had been pretreated with granulocyte-macrophage colony stimulating factor and then derivatized with dinitrochlorobenzene. T cells activated in this manner in vitro were compared functionally with immune T cells from individuals sensitized to dinitrochlorobenzene. We found that dinitrochlorobenzene-derivatized fresh peripheral blood mononuclear cells induced significant proliferation among immune T cells. Large amounts of interferon-gamma, but no interleukin-4, were detected in supernatant of these cultures. More interestingly, a significant number of T cells were activated when nave, hapten-specific T cells were stimulated with dinitrochlorobenzene-modified, cultured autologous peripheral blood mononuclear cells. Again, copious amounts of interferon-gamma were detected in the culture supernatants. Furthermore, this subset of T cells proliferated and secreted interferon-gamma, but not interleukin-4, when restimulated in vitro with dinitrochlorobenzene-derivatized fresh peripheral blood mononuclear cells. In these regards, in vitro activated T cells functionally resembled T cells that were harvested from the blood of individuals previously sensitized with dinitrochlorobenzene. This in vitro system for activation of naive, hapten-specific T cells offers opportunities on the one hand to study the earliest T cell and antigen-presenting cell events in the induction of human contact hypersensitivity, and on the other hand to simulate in vitro therapies with molecules designed to abort or prevent contact hypersensitivity when it causes disease.

CD101 is expressed by skin dendritic cells. Role in T-lymphocyte activation

CD101 was first described in our laboratory using two different monoclonal antibodies, BA27 and BB27, recognizing a 140-kDa disulfide-bonded homodimeric polypeptide on a small subset of circulating T lymphocytes and on most activated T cells in vitro. Further, it has been reported that most intestinal mucosal T lymphocytes expressed CD101. The gene coding for the CD101 antigen has been cloned and found to be identical to the gene coding for the recently described V7 antigen, corresponding to a type I trans-membrane protein with seven immunoglobulin-like loops in its extracellular domain. To define surface proteins that are involved in skin dendritic cell (DC) localization or function, we looked for the expression of CD1O1 on skin DC migrating from human skin explants. The majority of these DC had a phenotype of Langerhans cell (LC)-like mature DC, i.e., HLA-DR+ CD1a+ CD1c+ CD11a+ CD11c+ CD40+ CD50+ CD54+ CD58+ CD80+ CD83+ CD86+. We found that CD101 was expressed by a major subset of these HLA-DR+ CD1a+ CD1c+ LC-like skin DC. Next, we studied the effect of anti-CD101 monoclonal antibodies on primary allogeneic and on soluble antigen-specific mixed skin DC-lymphocyte reactions. We showed that two different monoclonal antibodies, BB27 and V7.1, inhibited the T-lymphocyte proliferative responses and that the inhibitory effect was overcome by high doses of exogenous IL-2. As both DC and T lymphocytes expressed CD101 molecules, we determined that the inhibitory effect was achieved both at the responder T-cell level and at the DC level. Thus, CD101 which is expressed on a subset of circulating T lymphocytes, has also been found on a subpopulation of LC-like DC. This molecule plays a major role in the activation of T cells by skin DC.

Factor XIIIa-positive dendrocytes are increased in number and size in recurrent aphthous ulcers (RAU)

The factor XIIIa-positive (FXIIIa+) cell is a potent antigen-presenting cell, which has been described as increasing in numbers in various chronic inflammatory conditions. The purpose of this study was to investigate the distribution and frequency of FXIIIa+ cells in acute recurrent aphthous ulcer (RAU) lesions compared with induced traumatic ulcer (TU) lesions and with clinically healthy oral mucosa. Samples were labeled with polyclonal rabbit anti-human FXIIIa antibodies in avidin-biotin-peroxidase complex (ABC) staining. Most of the FXIIIa-immunoreactive cells in TUs and normal mucosa were spindle-shaped, whereas a relatively large, dendritic-like cell was predominant in RAU lesions. FXIIIa+ cells were quite frequent within mononuclear cell-rich inflammatory cell infiltrates and in perivascular areas in RAU lesions. In contrast, FXIIIa+ cells were not found in mucosal epithelium or in the neutrophil-rich areas. RAU mononuclear cell-rich inflammatory cell infiltrates appeared to have greater numbers of positively stained cells than the TU-inflammatory cell infiltrates (199 +/- 67 vs 110 +/- 31 cells/mm2, P < 0.001). Overall, FXIIIa+ dendrocytes were increased in numbers, and apparently also in size, in RAU lesions (274 +/- 68/mm2) as compared to controls (177 +/- 74/mm2, P < 0.01), and to TU lesions (183 +/- 50 mm2, P < 0.01). Interestingly, relatively high numbers of FXIIIa+ dendrocytes were also found in deep connective tissue in RAU sections compared with TUs (281 +/- 80 vs 166 +/- 57, P < 0.01). The characteristic changes in the size and shape of individual FXIIIa+ cells, their typical distribution and increase in frequency in RAU lesions indicate active involvement in the local pathogenic mechanisms. Localization to perivascular areas/inflammatory cell infiltrates would be compatible with a role in antigen presentation.

MHC class I+/II- dendritic cells induce hapten-specific immune responses in vitro and in vivo

Activation requirements and biologic properties of hapten-specific, major histocompatibility complex class I-restricted CD8+ T lymphocytes are not fully understood. To address this issue, a novel CD45+/major histocompatibility complex class I+ (H-2k)/II-/CD80+ dendritic cell line, termed 80/1, which is capable of stimulating naïve, allogeneic CD8+ but not CD4+ T cells in vitro, was derivatized with trinitrobenzenesulfonic acid and co-cultured for 4 d with syngeneic, naïve CD8+ T cells. Results obtained showed that trinitrophenyl-derivatized, but not underivatized 80/1 dendritic cells, can induce vigorous proliferation ofCD8+ T cells. T-cell blasts generated in this fashion were able to lyse syngeneic, trinitrophenyl-derivatized targets but failed to lyse underivatized or trinitrophenyl-derivatized syngeneic, major histocompatibility complex class I- mutant cells or allogeneic targets. The ability of 80/1 dendritic cells to prime naïve, syngeneic T cells in vivo was tested in a contact hypersensitivity model. C3H/HeN mice were injected subcutaneously with identical numbers of (i) trinitrophenyl-derivatized 80/1 dendritic cells; (ii) trinitrophenyl-derivatized 80/1 dendritic cells fragmented by freeze-thawing cycles; (iii) trinitrophenyl-derivatized fibrosarcoma L929; and (iv) trinitrophenyl-derivatized lymphoma R1.1 cells. Whereas live trinitrophenyl-derivatized 80/1 dendritic cells were able to sensitize for contact hypersensitivity, killed hapten-derivatized 80/1 dendritic cells or control cells failed to do so. Thus, we conclude that 80/1 dendritic cells, when compared with major histocompatibility complex class I+ non-dendritic cells, can effectively prime naïve, syngeneic CD8+ T cells for hapten-specific responses, probably due to their better costimulatory and migratory properties.

Pattern of cytokine receptors expressed by human dendritic cells migrated from dermal explants

Different reasons account for the lack of information about the expression of cytokine receptors on human dendritic cells (DC): (a) DC are a trace population; (b) the proteolytic treatment used to isolate DC may alter enzyme-sensitive epitopes; and (c) low numbers of receptors per cell. In the present work the expression of cytokine receptors was analysed by flow cytometry on the population of dermal DC (DDC) that spontaneously migrate from short-term culture dermal explants. DDC obtained after dermal culture were CD1alow, CD1b+, CD1c+, human leucocyte antigen (HLA)-DR+, CD11chigh, CD11b+ and CD32+. The DC lineage was confirmed by ultrastructural analysis. DDC expressed interleukin (IL)-1R type 1 (monoclonal antibody (mAb) hIL-1R1-M1; and 6B5); IL-1R type 2 (mAb hIL-1R2-M22); IL-2R alpha chain (mAb anti-Tac; and hIL-2R-M1) and IL-2R gamma chain (mAb 3B5; and AG14C). DDC did not stain for IL-2R beta chain using four mAbs recognizing two different epitopes of IL-2R beta (mAb 2R-B; Mik-beta 1; and CF1; Mik-beta 3, respectively). DDC were also positive for the cytokine binding chains (alpha chains) of IL-3R (mAb 9F5); IL-4R (mAb hIL-4R-M57; and S456C9); and IL-7R (mAb hIL-7R-M20; and R3434). DDC showed low levels of IL-6R alpha chain (mAb B-F19; B-R6; and B-E23) and its signal transducer gp130 (mAb A2; and B1). DDC strongly expressed interferon-gamma receptor (IFN-gamma R) (mAb GIR-208) and were negative for IL-8R (mAb B-G20; and B-F25). All DDC were highly positive for granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR) alpha chain (mAb hGM-CSFR-M1; SC06; SC04, and 8G6) and to a lesser extent for the common beta chain of GM-CSFR, IL-3R and IL-5R (mAb 3D7). On the other hand, reactivity was not found for granulocyte colony-stimulating factor receptor (G-CSFR) (mAb hGCSFR-M1) nor macrophage colony-stimulating factor receptor (M-CSFR) (mAb 7-7A3-17) confirming the DC lineage of DDC. As previously reported for lymphoid DC, DDC expressed tumour necrosis factor receptort (TNFR) 75000 MW (mAb utr-1; hTNFR-M1; and MR2-1) but lacked TNFR 55000 MW (mAb htr-9; MR1-1; and MR1-2). In summary, DDC express receptors for a broad panel of cytokines, even receptors for cytokines whose effects on DC are still unknown (i.e. IL-2R alpha gamma; IL-6R alpha/gp 130; IL-7R alpha gamma).

Draining lymph node cells of contact-sensitized mice induce suppression of contact sensitivity

The application of hapten to the skin of mice can induce contact sensitivity (CS). It has also been well established that draining lymph node (DLN) cells can induce CS to the hapten used for skin painting when injected into naive mice. This is true for DLN cells recovered about 24 h after skin painting with hapten. It is unclear, however, whether DLN cells recovered shortly after hapten application have the same ability. By using an adoptive transfer assay system, we examined the ability of DLN cells recovered from mice at various times after skin painting with hapten to induce CS. DLN cells harvested 18-24 h after the application of fluorescein isothiocyanate (FITC) or 2,4-dinitrofluorobenzene (DNFB) induced strong CS when injected into naive mice. DLN cells harvested 3-6 h after the application of FITC or DNFB induced either only weak or no CS but induced suppression of the subsequent immunization to the two haptens. The suppression was hapten-specific, MHC restricted, and associated with the appearance of splenic suppressor T lymphocytes. Analyses with antibodies and ultraviolet (UV) B radiation demonstrated that suppression-inducing cells in DLNs were Ia+, Thy-1(-), and functionally UV-sensitive. These data suggest that epicutaneous sensitization with hapten first induces immunologically specific suppressor activity in the draining lymph nodes, whereas immunogenic activity becomes predominant later.

Perivascular dendritic cells of the human dental pulp

The morphological and phenotypical features of the class II molecule (HLA-DR) expressing cells in human dental pulps were compared with those of previously characterized perivascular dendritic cells in the dermis. We have further investigated how these pulpal cells are structurally related to the vascular system. Double-immunofluorescence staining revealed that a substantial portion of the pulpal HLA-DR expressing cells also expressed factor XIIIa, a marker for dendritic cells. The cells usually had a highly dendritic appearance and formed a reticular network in the pulpal connective tissue. The majority of cells also expressed macrophage-related antigens (CD14 and CD68). A small but distinct population of pulpal cells, representing approximately 13% of the class II molecule expressing cells, was devoid of a typical macrophage phenotype. This subpopulation of pulpal cells may be similar to dendritic cells present in the dermis. Confocal laser scanning microscopy showed that highly dendritic cells, found in close relation to the endothelium, had dendritic processes which were found to be in contact with the peripheral cell membrane of the endothelial cells. These cells formed a three-dimensional structure around the microvessel resembling a cellular conduit. We conclude that the human dental pulp is equipped with class II molecule-expressing perivascular dendritic cells composed of a heterogeneous cell population.

Temporal correlation between UV radiation locally-inducible tolerance and the sequential appearance of dermal, then epidermal, class II MHC+CD11b+ monocytic/macrophagic cells

We performed a time course study in order to define the in vivo relationship between the induction of active suppression of contact sensitization and the presence of various cells in ultraviolet-exposed dermis and epidermis implicated in locally inducible immune tolerance: class II major histocompatibility complex (MHC)+CD11b(lo)Gr-1- Langerhans cells (LC), class II MHC-CD45+CD3+ dendritic epidermal T cells, class II MHC+CD11b+Gr-1- monocytes or class II MHC+CD11b+Gr-1+ monocytic/macrophagic cells. Partial tolerance (50%) was first detectable 6 h after a single 72 mJ/cm2 ultraviolet B exposure and maximum tolerance at 48 h post-ultraviolet exposure. By flow cytometry, a low granularity LC subset had disappeared from the epidermis within 6 h after ultraviolet exposure, followed by a slower decrease in the high granularity Langerhans cells subset. Within the dermis at the 6-h time point, small numbers of infiltrating monocytic/macrophagic cells are already apparent. By 24 h post-ultraviolet exposure, at which time tolerance has increased to 70%, the infiltrating monocytic/macrophagic population had risen to 1.2% of the total dermal cell population and was observed for the first time in the epidermis along with other infiltrating leukocytes (i.e., polymorphonuclear leukocytes). By 48 h post-ultraviolet exposure, when a state of maximum tolerance is obtained, both constitutive epidermal and dermal antigen-presenting cell populations were at or near their nadir of depletion. The infiltrating monocyte/macrophage population, however, exhibited a dramatic increase in the epidermis at 48 and 72 h. Thus, the ability to locally induce a state of in vivo tolerance is closely associated with the expansion of class II MHC+CD11b+Gr-1+ and -monocytic/macrophagic cells in the dermis and epidermis.

Expression, but lack of calcium mobilization by high-affinity IgE Fc epsilon receptor I on human epidermal and dermal Langerhans cells

In atopic dermatitis (AD) patients, IgE molecules are demonstrated on the surface of Langerhans cells (LC). Fc epsilon RI molecules, which are present on the surface of LC in AD patients as well as normal individuals, are responsible for this binding. In this study, we have investigated phenotypic and functional characteristics of Fc epsilon RI on epidermal and dermal cell populations. Epidermal and dermal cell suspensions were prepared enzymatically with dispase followed by either trypsin or collagenase treatment, respectively. Peripheral blood basophils were negatively selected by excluding other leukocytes with surface marker staining. Consistent with previous reports, both peripheral blood basophils and epidermal LC were positively stained with anti Fc epsilon RI monoclonal antibody. In addition, an Fc epsilon RI positive population was demonstrated among dermal HLA-DR positive cells. These cells express significant amounts of HLA-DR molecules (DRHi) and co-express CD 1 a molecules, which identifies them as LC-like dendritic APC of the dermis. No other Fc epsilon RI positive population was found in the other dermal DRMid or DR- populations, except for a minor DRLo population, presumably mast cells. To analyze whether these Fc epsilon RI molecules are signal transducing for LC, intracellular calcium mobilization after crosslinking of Fc epsilon RI was measured with flow cytometry. Following crosslinking, peripheral blood basophils clearly increased intracellular calcium. On the other hand, neither normal epidermal LC nor dermal DRHiCD1a + cells changed their intracellular calcium level after Fc epsilon RI crosslinking. These data indicate that normal epidermal and dermal LC, but not basophils, are resistant to calcium flux following Fc epsilon RI engagement.

Hair cycle-dependent changes in skin immune functions: anagen-associated depression of sensitization for contact hypersensitivity in mice

To assess whether hair follicle cycling influences skin immunity, we examined the association between highly synchronized hair follicle cycling and experimental contact hypersensitivity in C57BL/6 mice. Hair cycle synchronization was performed by depilation of hair shafts on the back with telogen skin. Mice were sensitized on the lower back skin with picryl chloride between 0 and 25 d, after anagen induction by depilation, and challenged on the earlobes with picryl chloride 5 d later. The magnitude of contact hypersensitivity was significantly decreased in mice sensitized on day 1, was minimal on day 3 (early anagen), and slowly increased thereafter, reaching level comparable to day 0 on day 25 (telogen). The significantly depressed contact hypersensitivity response in anagen skin was confirmed in mice with spontaneously developed follicles. Lymph node cells taken from mice sensitized with picryl chloride on days 0, 1, and 3 after depilation were cultured in vitro in the presence of syngeneic, haptenized, Langerhans cell-enriched epidermal cells. Marked proliferative responses of lymph node cells to haptenized cells were found in mice not only of day 0, but also of days 1 and 3, suggesting that immune T cells exist even lymph node cells of the low-responsive mice. Flow cytometric analyses demonstrated that the number of intraepidermal Langerhans cells and their functions, including the expression of major histocompatibility complex class II, CD54, and CD86, and mixed epidermal cell lymphocyte reactions, were not changed in skin on days 0,1, and 3. These findings demonstrated that contact hypersensitivity is induced most effectively via skin with telogen hair follicles and that the depressed response in early anagen skin is not simply due to failure in Langerhans cell function or sensitization of T cells.

Cell-mediated immunosuppressive mechanisms induced by UV radiation

Soon after UV exposure, mast cells degranulate, possibly because of the release of the mediators and cytokines from the epidermis, and there are subsequent vascular changes and cellular infiltration. Within a few hours, the soluble mediator milieu of UV-exposed skin becomes exceedingly complex and replete with interactions. Leukocytes newly entering the skin, as well as those already in the skin, must respond to these inflammatory signals. Altered antigen presentation and immune suppression likely derive from alterations induced in the APC that comprise the post-UV leukocyte population of the skin. Many of these mechanisms may explain the effectiveness of phototherapy in atopic dermatitis and psoriasis.

Cell infiltrate in progressive pigmented purpura (Schamberg's disease): immunophenotype, adhesion receptors, and intercellular relationships

BACKGROUND

Progressive pigmented purpura (Schamberg's disease), a form of purpura pigmentosa chronica, is a lymphocytic capillaritis of unknown etiology and obscure pathogenesis. Our purpose was to assess the expression of cell membrane antigens (CD3, CD4, CD1a, CD36), of adhesion receptors (leukocyte function adhesion 1, LFA-1, endothelial leukocyte adhesion molecule 1, ELAM-1) intercellular adhesion molecule 1, ICAM-1), and the intercellular relationships in the early phase of the disease.

METHODS

Quantitative immunohistochemistry and electron-microscopy were performed on specimens of five subjects, aged 45 to 63 years. These studies were repeated in two patients after treatment with topical corticosteroid (betamethasone valerate cream 0.1%) and psoralen-ultraviolet A (PUVA).

RESULTS

The infiltrate consisted mainly of CD4+ lymphocytes and CD1a+ dendritic cells. Electron-microscopic investigation showed typical lymphocytes and two distinct types of dendritic cells. In the very early phase of the disease the adhesion receptors LFA-1 and ICAM-1 were expressed intensely by all infiltrating cells; the adhesion receptors ICAM-1 and ELAM-1 were expressed by endothelial cells. Close contact occurred between lymphocytes and dendritic cells. After PUVA (120 J per cm2) and topical steroid therapy the infiltrate disappeared completely.

CONCLUSIONS

These data suggest that a cell-mediated immune mechanism may be important in progressive pigmented purpura and that the early endothelial expression of adhesion receptors may determine the pattern of organization of the pericapillary infiltrate.

In human dermis, ultraviolet radiation induces expansion of a CD36+ CD11b+ CD1- macrophage subset by infiltration and proliferation; CD1+ Langerhans-like dendritic antigen-presenting cells are concomitantly depleted

Antigen-presenting (APC), suppressor T-cell-inducing macrophages infiltrate both human and murine epidermis after ultraviolet radiation (UVR) exposure. To determine their derivation, we prepared epidermal cell and dermal cell suspensions from human keratome biopsy specimens obtained from nonexposed skin and from UVB-irradiated sites (3 d after four times the minimal erythema dose). Simultaneous triple-marker flow cytometric analysis established the extended phenotype of macrophages infiltrating sunburned human epidermis (CD1a- CD1c- CD11b+ CD11c+ CD36+ Fc gamma RII+ DR+). This then enabled us to track dermal cells of this phenotype after UVR in relation to the heterogeneous DR+ populations in normal dermis. By both in situ immunohistology and cell suspension flow cytometry, UVR induced an expansion of bone marrow-derived DR+ cells in the perivasculature and sub-basement membrane zone of the papillary dermis. Despite an overall expansion of DR+ cells, the CD1a+ CD1c+ CD36- DR+ Langerhans-cell-like dendritic APC subset of dermal DR+ cells was depleted (p < 0.05), indicating that UVR-induced epidermal Langerhans cell loss (from 95% to 7% of DR+ epidermal cells) is not accounted for by Langerhans cell accumulation in the dermis. By contrast, UVR exposure induced a selective expansion of the dermal macrophage subset, which is phenotypically identical to the monocytic/macrophagic APCs that appear in the epidermis after UV injury (p < 0.01). Cell cycle analysis (to determine whether this expansion was accounted for entirely by infiltration) revealed no increase in the percentage of DR+ CD36+ UVR-exposed dermal cells in S/G2/M phase; however, the expanded DR+ CD36+ subset continued its already substantial level of proliferation unabated. Therefore, epidermal macrophages derive not only from transcapillary migration, but also from in situ proliferation of a dermal precursor. Taken together, these findings show that UVR creates an epidermal and dermal APC milieu which is dominated by monocytic/macrophagic cells, through depletion of cells of dentritic APC phenotype, and concomitant selective dermal expansion of a CD1a- CD1c- CD11b+ CD36+ Fc gamma RII+ DR+ (monocyte/macrophage) population.

Migratory properties and functional capacities of human skin dendritic cells

The different cell types which migrated 'spontaneously' out of human skin explants during different periods of culture were characterized. Before culture, CD1a+ dendritic cells were observed not only in the epidermis but also in the dermis, whereas CD1b+ dendritic cells were present exclusively in the dermis. The populations of migrating cells were harvested and phenotyped on 3 successive days of culture. They always contained high percentages of CD1a+ cells. The other cells that migrated were T cells and macrophages. A relatively high proportion of the CD1a+ cells that migrated during the first 24 h culture period was also CD1b+. The number of cells which were positive for both CD1a and CD1b decreased in the following 2 days of culture. However, the purified CD1a+ cell populations isolated on the 3 consecutive days did not show any difference in their capacity to stimulate allogeneic T cells. The CD1a+ cells possess potent allo-activating capacities that are independent of whether or not they are positive for CD1b+. Three days after culture about half of the CD1a+ cells were still present in the epidermis and dermis, but no CD1b+ cells could be detected in the dermis. This suggests that the CD1b+ cells represent a population of active migrating cells.

A fresh morphological and functional look at dermal dendritic cells

During the past decade, a group of cells located in the dermis and possessing a dendritic morphology have emerged from obscurity and become recognized as important members of the "dermal immune system". This group of cells is characterized by a considerable degree of immunophenotypic and functional heterogeneity. In this review, the salient features of these dermal dendritic cells are put into a dermatopathology perspective, with particular emphasis on a broad group of inflammatory and neoplastic skin diseases. There appear to be multiple subsets of dermal dendritic cells, and 17 different conditions linked to active participation of these newly recognized cells. Exactly how these different subsets of dermal dendritic cells interact amongst each other, as well as with adjacent cells such as T-lymphocytes, endothelial cells, fibroblasts, and keratinocytes in these different diseases is unclear at this time. However, isolation techniques and monoclonal antibodies capable of distinguishing these subsets, as well as functional assays, are currently available and will permit definitive conclusions to be drawn regarding their pathophysiological significance. It is highly likely that, as more data is gathered, dermal dendritic cells will be the focus of further investigative activity by dermatopathologists for the next decade, and well past the year 2000.

Both dendritic cells and memory T lymphocytes emigrate from organ cultures of human skin and form distinctive dendritic-T-cell conjugates

Prior studies of mouse skin in organ culture have shown that dendritic cells selectively emigrate from the explants over 1-3 d. This emigration may model the movements of dendritic cells that can occur in situ, as in transplantation and contact sensitivity. In this study, we cultured explants of normal human skin that had been removed with a dermatome. Dendritic cells with characteristic morphology and mixed leukocyte response-stimulatory activity emigrated. The dendritic cells had the expected phenotype, e.g., rich in major histocompatibility complex class II and accessory molecules such as B7-1, intercellular adhesion molecule-1, and leukocyte function-associated antigen-3. Small lymphocytes also were present in the emigrated populations and proved to be T cells exclusively, almost entirely of the TcR alpha beta and memory type (CD45RAweak, CD45RO LFA-3/CD58+), with a CD4:CD8 subset ratio of about 2:1. Some of the T cells were bound tightly to the dendritic cells. These conjugates did not dissociate after exposure to trypsin or to calcium- and magnesium-free medium, or during cytofluorography. This made it possible to sort distinct populations of single dendritic cells, single T cells, and conjugates of the two cell types. Conjugates would continue to form from mixtures of separated dendritic cells and T cells in culture. Therefore, cutaneous dendritic cells and memory T lymphocytes emigrate from human skin explants, and some of these cells form distinctive conjugates that we hypothesize contribute to immunologic recall reactions.

Dermal dendritic cells are important members of the skin immune system

In conclusion we have shown that motile cells with a dendritic morphology can be isolated from dermis of normal and diseased human skin. DDC bear high amounts of MHC class II molecules on their surface, and are very potent antigen presenting cells. Subpopulations of these cells acquire certain ultrastructural features of Langerhans cells in-vitro such as Birbeck granule formation and CD1a expression. These newly defined members of the dendritic cell family of APCs may be precursors of epidermal Langerhans cells and may play a role in skin immune responses. Furthermore in inflammatory dermatoses such as psoriasis, a role in the autostimulation and cytokine production of T cells could be demonstrated. Given their number, distribution, and in-vitro functional capacity, it is appropriate at this time to conclude that DDCs are indeed important members of the skin immune system.

CD36(+)-dendritic epidermal cells: a putative actor in the cutaneous immune system

In the present study we have investigated by indirect immunofluorescence staining and mixed lymphocyte reaction methods, the localization, distribution, percentage, and the immunological involvement of CD36(+)-dendritic epidermal cells (CD36(+)-DECs) in normal human skin. Human epidermal cell suspensions were obtained from skin specimen of healthy persons. First, an indirect immunofluorescent staining method was performed on frozen skin sections, freshly isolated cells, nonadherent and adherent cells and second, the allogeneic mixed epidermal cell-lymphocyte reaction (ELR) method was performed with human peripheral blood mononuclear cells and irradiated CD36(+)-DECs plus CD-1a+ (Langerhans cells) and/ConA (at 10 micrograms/mL). We found that CD36(+)-DECs were localized in the epidermis mainly in the basal layer. They were non adherent cells. The percentage of these CD36(+)-DECs was of about 2%. These CD36(+)-DECs were AE3 (which recognizes keratin normally expressed by keratinocytes) positive cells. Our immunoreactivity study using allogeneic mixed ELR, showed that CD36(+)-DECs stimulated allogeneic lymphocyte proliferation. Their stimulatory effects were important when Langerhans cells and ConA were added separately or together to the PBMCs culture. The above results suggest that CD36(+)-DECs may contribute to the immunological role of skin and could be involved in cutaneous allograft recognition and rejection.

ABBREVIATIONS

DECs: dendritic epidermal cells; ConA: concanavalin A; DPM: disintegrations per minute; ELR: epidermal cell-lymphocyte reaction; LC: Langerhans cells; PBMCs: peripheral blood mononuclear cells.

Distinction of class II MHC+ Langerhans cell-like interstitial dendritic antigen-presenting cells in murine dermis from dermal macrophages

Dermal cells are capable of initiating contact-hypersensitivity responses but the precise identification of the antigen-presenting cell within murine dermis is lacking. Class II major histocompatibility complex (MHC)+ cells with dendritic shape and lacking endothelial factor VIII but expressing the dendritic antigen-presenting cell marker NLDC-145 were observed in the perivascular and interstitial dermis of BALB/c and C3H/HeN skin. The heterogeneous class II MHC+ cells could be divided into two subsets: each was class II MHC+ CD45+ (bone marrow derived) GR-1- (non-neutrophil/macrophage) CD3- (non T), but one subset was CD11b+ (beta 2 integrin) and the other was CD11b-. Ultrastructural examination of class II MHC+ cells revealed the presence of a Langerhans cell-like/indeterminant cell subset with indented nuclei, dendritic morphology, active cytoplasm, and dense intermediate filaments. Phagolysomes and Birbeck granules were not observed in such cells, indicating these were distinct from dermal macrophages and from classical epidermal Langerhans cells, respectively. Cells with a monocyte/macrophage ultrastructural appearance were also noted, likely representing the class II MHC subset expressing CD11b and Ly6c (monocyte/endothelial antigen). Dermal cells in suspension were capable of processing and presenting large protein antigens to antigen-specific T-cell hybridomas; dermal cells also induced the syngeneic mixed lymphocyte reaction. The dermal antigen-presentation activities were totally abrogated by removal of class II MHC+ cells, but not by removal of CD11b+ cells or Ly6c+ cells, indicating that potent antigen-presenting cell activity was restricted to the class II MHC+ CD11b- Ly6c- subset (Langerhans cell-like/indeterminant cells). In conclusion, within a complex array of dermal leukocytes a murine dermal class II MHC+ cell population expressing a Langerhans cell-like/dendritic antigen-presenting cell phenotype and exhibiting potent antigen processing and presenting activity can be identified. The positioning of potent interstitial dendritic antigen-presenting cells at the interface of the vasculature with the dermal interstitium provides rapid access to an antigen-presenting cell as T cells first egress into the skin.

Isolation and characterization of migratory human skin dendritic cells

A method is described to isolate and characterize human skin dendritic cells (DC). This method is based on the migratory capacities of these cells. The cells migrated 'spontaneously' out of split-skin explants into the medium during a 24-h culture period and contained up to 75% CD1a+ cells. After removal of co-migrated T cells and macrophages, the highly enriched (> 95% CD1a+) DC showed potent allo-antigen-presenting capacities. About 25% of the CD1a+ cells were also positive for the dermal DC marker CD1b, whereas only 15-20% of the cells contained Birbeck granules, the characteristic cell organelle of the epidermal Langerhans cell. Before culture, CD1a+ DC were observed on cryostat sections not only in the epidermis but also in the dermis. After culture, the number of CD1a+ cells in both epidermis and dermis had decreased. Not all the cells had migrated during the culture period; some CD1a+ cells could still be detected in the epidermis and dermis after culture. Thus, using this method, potent allo-stimulating CD1a+ cells, migrating from both epidermis and dermis, can be obtained without the use of enzymes.

Antigen-bearing Langerhans cells in skin draining lymph nodes: phenotype and kinetics of migration

Application of the fluorescent contact sensitizer Rhodamin B on mouse epidermis was used to study the migration kinetics of Langerhans cells into the draining lymph nodes. The expression of the dendritic cell markers NLDC-145 and MIDC-8 was followed over time to determine the correlation between these markers and Langerhans cell migration. In contrast with its high expression on intraepidermal Langerhans cells, the expression of NLDC-145 on dendritic cells in the draining lymph node was low at 24 h but increased at later times; in contrast, MIDC-8 expression on dendritic cells decreased. Ten days after Rhodamin B application, antigen-bearing Langerhans cells were still present in the epidermis; application of another unrelated contact sensitizer to the epidermis at this time did not lead to migration of these residual Langerhans cells. These results indicate that not all antigen-bearing Langerhans cells migrate from the skin after application of a contact sensitizer, indicating that signals in addition to simple antigen binding are necessary for migration. During this migration from epidermis to lymph nodes Langerhans cells undergo phenotypic changes. The decreased expression of the endosomal antigens MIDC-8 and MOMA-2 correlates with differentiation from predominantly antigen-processing cells to predominantly antigen-presenting cells. The reduced expression of NLDC-145 is discussed in light of a Langerhans cell-independent pathway of antigen transportation from skin to lymph node.

Antigen-presenting capacity in normal human dermis is mainly subserved by CD1a+ cells

A proposed role for antigen-presenting dermal dendrocytes in the pathogenesis of many dermal inflammatory skin diseases remains speculative. We therefore sought to determine the phenotype and functional characteristics of antigen-presenting cells isolated from normal human dermis. Normal adult human skin was incubated overnight with dispase at 4 degrees C, the epidermis was removed, and the residual dermal preparation was then minced and digested with a mixture of hyaluronidase, collagenase, and DNAase at 37 degrees C, prior to filtration through mesh. Dermal cell suspensions thus obtained were stained using specific monoclonal antibodies, and analysed by fluorescence microscopy or flow cytometry. Mean values were as follows: CD45+ leucocytes 39%, HLA-DR+ cells 39%, Ulex europaeus agglutinin I+ endothelial cells 26%, CD1a+ cells 3.9%, CD11b+ cells 16%, CD11c+ cells 6%. Mitomycin C-treated crude dermal cell suspensions induced allostimulation of peripheral blood mononuclear cells in a 7-day culture, as assessed by 3H-TdR incorporation. Depletion of CD1a+ Langerhans-like cells from the dermal cell preparation, by 95, 74 and 90% in three separate experiments using immunomagnetic beads, reduced 3H-TdR incorporation at optimal responder-to-stimulator cell ratios by 90, 64, and 87%, respectively. Our findings suggest that, in normal human dermis, the great majority of the alloantigen-presenting capacity resides in the CD1a+ Langerhans cell-like dendritic antigen-presenting cell population, and not to any great extent in either CD1a- macrophage-like cells, or HLA-DR+ endothelial cells. The relationship of the CD1a+ dermal antigen-presenting cells to the Langerhans cell lineage remains to be determined.