Natural and perturbed distributions of Langerhans cells: responses to ultraviolet light, heterotopic skin grafting, and dinitrofluorobenzene sensitization

Lrig1- and Wnt-dependent niches dictate segregation of resident immune cells and melanocytes in murine tail epidermis

The barrier-forming, self-renewing mammalian epidermis comprises keratinocytes, pigment-producing melanocytes and resident immune cells as first-line host defense. In murine tail skin, interfollicular epidermis patterns into pigmented ‘scale’ and hypopigmented ‘interscale’ epidermis. Why and how mature melanocytes accumulate in scale epidermis is unresolved. Here, we delineate a cellular hierarchy among epidermal cell types that determines skin patterning. Already during postnatal development, melanocytes co-segregate with newly forming scale compartments. Intriguingly, this process coincides with partitioning of both Langerhans cells and dendritic epidermal T cells to interscale epidermis, suggesting functional segregation of pigmentation and immune surveillance. Analysis of non-pigmented mice and of mice lacking melanocytes or resident immune cells revealed that immunocyte patterning is melanocyte and melanin independent and, vice versa, immune cells do not control melanocyte localization. Instead, genetically enforced progressive scale fusion upon Lrig1 deletion showed that melanocytes and immune cells dynamically follow epithelial scale:interscale patterns. Importantly, disrupting Wnt-Lef1 function in keratinocytes caused melanocyte mislocalization to interscale epidermis, implicating canonical Wnt signaling in organizing the pigmentation pattern. Together, this work uncovers cellular and molecular principles underlying the compartmentalization of tissue functions in skin.

Summary: Pigmentation and immune surveillance functions in murine tail skin are spatially segregated by Lrig1- and Wnt-Lef1-dependent keratinocyte lineages that control the partitioning of melanocytes and tissue-resident immune cells into distinct epidermal niches.

Immunological Mechanisms in Allergic Contact Dermatitis

Purpose of the review

The understanding of the cellular and molecular pathogenesis of allergic contact dermatitis (ACD) has increased dramatically.

Recent findings

Besides CD4+ and CD8+ T cells, other cell types such as innate lymphoid cells, natural killer T cells (NKT), natural killer cells, and T regulatory cells have emerged as crucial key players. New immunological insights have unravelled that the predominant effector cell type determines the clinical pictures. Hence, a better understanding of the involvement of distinct effector cells has shed light on the diversity of ACD reactions and subsequent clinical pictures. Another new perspective has arisen in the elicitation phase. Here, Langerhans cells can play a role in the development of immune tolerance and not, as previously thought, exclusively in the allergen-driven hypersensitivity reaction. B cells also appear to play an important role in triggering ACD by secreting IgM antibodies in response to interleukin (IL)-4 produced by NKT cells, leading to complement activation and chemotaxis of immune cells.

Summary

Allergic contact dermatitis is a delayed-type hypersensitivity reaction triggered by skin contact with the chemical of interest in individuals previously sensitised to the same or a chemically related substance. The understanding of the cellular and molecular pathogenesis of allergic contact dermatitis has improved considerably. In addition to CD4+ and CD8+ T cells, other cell types such as natural killer T cells (NKT) and regulatory T cells have emerged as important participants. The binding of haptens is the first step in the development of allergic contact dermatitis. Haptens are low molecular weight (mostly <500 Dalton) chemicals that are able to penetrate the stratum corneum of the skin or can enter the body upon systemic administration. Haptens are not immunogenic per se but can be effectively recognised by the immune system after binding to a protein carrier. In the clinically inapparent sensitisation phase, Langerhans cells and dendritic cells initiate an adaptive immune response by capturing and processing antigens and presenting them to naïve T cells in the paracortical regions of the lymph nodes. In the elicitation phase, the clinical manifestations of allergic contact dermatitis are the result of a T cell-mediated inflammatory response that occurs in the skin upon re-exposure to the bite and is mediated by the activation of bite-specific T cells in the skin or other organs.

Differential Induction of IL-12 p40 and IL-10 mRNA in Human Langerhans' Cells and Keratinocytes by in Vivo Occlusion, Vehicle, and All-TRANS Retinoic Acid

Background:

Hydration and pharmacologic manipulation of the skin may have immunomodulatory effects. For instance, retinoic acid (RA) in vivo upregulates antigen-presenting cell (APC) activity of Langerhans' cells (LC).

Objective:

Our study was to determine whether RA increases LC APC activity via alteration of the potent immunoregulatory and reciprocally acting cytokines, IL-12 and IL-10.

Methods:

0.1% RA and vehicle solvent only (V) as a control were applied under occlusion on the skin of normal volunteers. Freshly selected CD1a+ LC and keratinocytes from keratome were subject to semiquantitative determination of IL-12 p40 and IL-10 mRNA levels. IL-12 p40 protein was measured by radioimmunoassay.

Results:

Occlusion alone and open vehicle alone did not induce LC immunoregulatory cytokines; LCs demonstrated significant induction of IL-12 p40 mRNA, when the vehicle was occluded for 48 hours and, to a lesser extent, IL-10 as well. IL-12 p40 mRNA could be further induced by RA-LC at the 20-hour time point; however, IL-10 mRNA was induced at the 48-hour time point. Neither occlusion nor RA significantly induced IL-12 p40 or IL-10 mRNA in CD1a keratinocytes at any time points.

Conclusion:

A tight reciprocal regulation of IL-10 and IL-12 is present in LCs and is consistent with the initial, but self-limited, inflammatory effect of occlusion and topical retinoids.

Nonredundant roles of keratinocyte-derived IL-34 and neutrophil-derived CSF1 in Langerhans cell renewal in the steady state and during inflammation

IL-34 and colony-stimulating factor 1 (CSF1) are two alternative ligands for the CSF1 receptor that play nonredundant roles in the development, survival, and function of tissue macrophages and Langerhans cells (LCs). In this study, we investigated the spatio-temporal production of IL-34 and its impact on skin LCs in the developing embryo and adult mice in the steady state and during inflammation using Il34(LacZ) reporter mice and newly generated inducible Il34-knockout mice. We found that IL-34 is produced in the developing skin epidermis of the embryo, where it promotes the final differentiation of LC precursors. In adult life, LCs required IL-34 to continually self-renew in the steady state. However, during UV-induced skin damage, LC regeneration depended on neutrophils infiltrating the skin, which produced large amounts of CSF1. We conclude that LCs require IL-34 when residing in fully differentiated and anatomically intact skin epidermis, but rely on neutrophil-derived CSF1 during inflammation. Our demonstration that neutrophils are an important source of CSF1 during skin inflammation may exemplify a mechanism through which neutrophils promote their subsequent replacement with mononuclear phagocytes.

The skin immune atlas: three-dimensional analysis of cutaneous leukocyte subsets by multiphoton microscopy

Site-specific differences in skin response to pathogens and in the course of cutaneous inflammatory diseases are well appreciated. The composition and localization of cutaneous leukocytes has been studied extensively using histology and flow cytometry. However, the precise three-dimensional (3D) distribution of distinct immune cell subsets within skin at different body sites requires visualization of intact living skin. We used intravital multiphoton microscopy in transgenic reporter mice in combination with quantitative flow cytometry to generate a 3D immune cell atlas of mouse skin. The 3D location of innate and adaptive immune cells and site-specific differences in the densities of macrophages, T cells and mast cells at four defined sites (ear, back, footpad, tail) is presented. The combinatorial approach further demonstrates an as yet unreported age-dependent expansion of dermal gamma-delta T cells. Localization of dermal immune cells relative to anatomical structures was also determined. While dendritic cells were dispersed homogeneously within the dermis, mast cells preferentially localized to the perivascular space. Finally, we show the functional relevance of site-specific mast cell disparities using the passive cutaneous anaphylaxis model. These approaches are applicable to assessing immune cell variations and potential functional consequences in the setting of infection as well as the pathogenesis of inflammatory skin conditions.

3D visualization of epidermal Langerhans cells

Langerhans cells (LCs) are intraepidermal dendritic cells that extend their dendrites between keratinocytes to form a dense network that covers the entire body. The mammalian epidermis has two diffusion barriers, the stratum corneum and tight junctions (TJs). In their resting state, LCs sit underneath these two barriers. Once activated, LCs elongate their dendrites to dock with, or penetrate through, TJs, which allows them to survey the environment between the two barriers. Here, we describe a method to visualize this dynamic interaction of TJs and LCs in 3D by using mouse ear epidermal sheets.

Visualizing dendritic cell migration within the skin

Dendritic cells (DCs) within the skin are a heterogeneous population of cells, including Langerhans cells of the epidermis and at least three subsets of dermal DCs. Collectively, these DCs play important roles in the initiation of adaptive immune responses following antigen challenge of the skin as well as being mediators of tolerance to self-antigen. A key functional aspect of cutaneous DCs is their migration both within the skin and into lymphatic vessels, resulting in their emigration to draining lymph nodes. Here, we discuss our current understanding of the requirements for successful DC migration in and from the skin, and introduce some of the microscopic techniques developed in our laboratory to facilitate a better understanding of this process. In particular, we detail our current use of multi-photon excitation (MPE) microscopy of murine skin to dissect the migratory behavior of DCs in vivo.

Expression of langerin/CD207 reveals dendritic cell heterogeneity between inbred mouse strains

Langerin/CD207 is expressed by a subset of dendritic cells (DC), the epithelial Langerhans cells. However, langerin is also detected among lymphoid tissue DC. Here, we describe striking differences in langerin-expressing cells between inbred mouse strains. While langerin+ cells are observed in comparable numbers and with comparable phenotypes in the epidermis, two distinct DC subsets bear langerin in peripheral, skin-draining lymph nodes of BALB/c mice (CD11c(high) CD8alpha(high) and CD11c(low) CD8alpha(low)), whereas only the latter subset is present in C57BL/6 mice. The CD11c(high) subset is detected in mesenteric lymph nodes and spleen of BALB/c mice, but is virtually absent from C57BL/6 mice. Similar differences are observed in other mouse strains. CD11c(low) langerin+ cells represent skin-derived Langerhans cells, as demonstrated by their high expression of DEC-205/CD205, maturation markers, and recruitment to skin-draining lymph nodes upon imiquimod-induced inflammation. It will be of interest to determine the role of lymphoid tissue-resident compared to skin-derived langerin+ DC.

Identification and expression profiling of a human C-type lectin, structurally homologous to mouse dectin-2

A number of C-type lectins on antigen-presenting cells play an important role in regulating innate immunity. Previously, we identified the mouse C-type lectins (dectin-1, and dectin-2) and human DECTIN-1. To identify human DECTIN-2, we employed degenerative polymerase chain reaction-based cDNA cloning using RNA from human Langerhans cell (LC)-like dendritic cells (DCs). This process yielded a cDNA encoding a C-type lectin with 66.5% amino acid sequence homology to mouse dectin-2, the same gene reported by Kanazawa et al. (J Invest Dermatol 2004: 122: 1522-1524) using the disparate approach of analyzing coding sequences in chromosome 12. Similar to their findings, we found gene expression in lung, spleen, and lymph node. Among resting leukocytes, it was expressed at highest levels by CD14+ monocytes, at lower levels by CD19+ B cells, and not at all by CD4+ T cells. Activation of CD19+ B cells with pokeweed mitogen down-regulated gene expression, whereas expression in CD4+ T cells was induced by Con A. Among our novel findings are an alternatively spliced transcript lacking exon 2, expression in bone marrow and tonsil, expression in CD8+ T cells that is abrogated following activation with phytohemagglutinin, restricted expression to CD1a+ LC within epidermis, and preferential expression by plasmacytoid (rather than myeloid) DC. Finally, we found that treatment with interleukin-4 (IL-4), IL-10, or UVB down regulated gene expression in CD14+ monocytes, whereas granulocyte-macrophage colony-stimulating factor, transforming growth factor-beta1, or tumor necrosis factor-alpha treatment up-regulated it. Our findings may form the basis for understanding the function of human DECTIN-2 in innate immunity.

Transcriptional regulation of dectin-2 promoter in transgenic mouse

Despite a preeminent role of epidermal Langerhans cells (LC) in inducing primary immunity, application of gene-based modification to LC function is limited by lack of well-defined transcription regulatory units that can direct LC-specific gene expression. Previously we reported that the promoter activity of a 5'-flanking region of the dectin-2 gene (Dec2FR) is highly targeted to epidermal LC of transgenic mice bearing a Dec2FR-driven Luc gene. Using the mice, in which transcription activity of Dec2FR is measured by Luc assays, presently we characterized regulation of Dec2FR activity in leukocyte subpopulations under resting and activation status. Luc activity was highly variable in LC isolated from different skin areas and detected in other DC subset (dermal DC) but the levels were much lower than in resting LC. Activation of leukocytes markedly up-regulated Luc activity in all four subpopulations (CD11c+ splenic DC, Mac-1high peritoneal macrophages, splenic B220+ B cells, and CD3+ T cells). However, these levels remained lower than those in the resting and activated LC. These findings indicate that dectin-2 promoter activity remains targeted to epidermal LC even after activation of leukocytes, suggesting a high potential of Dec2FR to engineer LC-targeted gene expression to heighten efficacy of genetic vaccination and to manipulate phenotypes of preexisting immunity (Th1 vs. Th2).

Langerhans' cells in the murine oral mucosa in the inductive phase of delayed type hypersensitivity with 1-chloro-2, 4-dinitrobenzene

We created a murine model of delayed-type hypersensitivity (DTH) to 1-chloro-2, 4-dinitrobenzene (DNCB). Using this murine model, we compared oral mucosal sensitization and skin sensitization for the difference in reaction during the elicitation phase. Evaluation of sensitizability, using the mouse ear swelling test (MEST) after oral mucosal or skin sensitization, showed that the ear swelling response peaked 24 h after challenge. The optimal induction concentration was 1.0% in both oral mucosal and skin sensitization, resulting in a positive reaction rate of 100%. However, the ear swelling response 24 h after challenge with the optimal concentration of DNCB (1.0%) was significantly lower in oral mucosal than in skin sensitization. We compared the oral mucosal and skin sensitization sites for the number of Langerhans' cells (LC) and the antigen-presenting capability in the induction phase. The numbers of F4/80+ major histocompatibility complex (MHC) class II+ LC before induction did not differ significantly between the oral mucosa and the skin. After induction, F4/80+ MHC class II+ LC increased in number, but the increase was significantly smaller in the oral mucosa than in the skin. MEST on anti-CD86 antibody-administered mice showed that ear swelling was similarly suppressed after oral mucosal or skin sensitization. In murine models of DTH after oral mucosal sensitization, the number of F4/80+CD86+ LC increased after induction, but the increase was significantly smaller than that in murine models of DTH after skin sensitization. This study showed that, in murine models of DTH, oral mucosal sensitization elicited a weaker reaction than skin sensitization. This was presumably because oral mucosal sensitization induced fewer LC, resulting in lower antigen-presenting capability.

Nitric oxide appears to be a mediator of solar-simulated ultraviolet radiation-induced immunosuppression in humans

Topical application of NG-methyl-L-arginine and 2,2'-dipyridyl were used to examine the respective roles of nitric oxide and reactive oxygen species in solar-simulated ultraviolet radiation-induced immunosuppression in humans in vivo. Immunosuppression was studied using a nickel contact hypersensitivity recall model. Ultraviolet radiation dose-responses were generated to determine the extent to which NG-methyl-L-arginine and 2,2'-dipyridyl affected the immune response. NG-methyl-L-arginine but not 2,2'-dipyridyl protected the immune system from ultraviolet radiation-induced suppression. Both NG-methyl-L-arginine and 2,2'-dipyridyl inhibited nitrite production. Nitrite is a degradation product of peroxynitrite, a cytotoxic mediator resulting from reactions between nitric oxide and reactive oxygen species. This suggests that nitric oxide, not its downstream product peroxynitrite, was likely to be responsible for solar-simulated ultraviolet radiation-induced immunosuppression. In contrast, both nitric oxide and reactive oxygen species were mediators of solar-simulated ultraviolet radiation-induced apoptosis and loss of dendritic S-100+ cells (probably Langerhans cells) from the epidermis. It is likely that different mechanisms are involved in these ultraviolet-induced endpoints and that events in addition to Langerhans cell depletion are important for local immune suppression to recall antigens in humans. Understanding the mechanisms of cutaneous ultraviolet-induced oxidative stress will assist in the future design of novel products that protect skin from photoaging and skin cancer.

Nitric oxide-mediated depletion of Langerhans cells from the epidermis may be involved in UVA radiation-induced immunosuppression

Ultraviolet A (UVA) irradiation of the dorsal skin of mice reduced the contact hypersensitivity (CHS) response and the density of epidermal Langerhans cells (LC). The roles of nitric oxide (NO) and reactive oxygen species (ROS) in these biological effects of UVA were investigated. Topical application of N(G)-monomethyl-L-arginine acetate, an inhibitor of NO production, 2,2'-dipyridyl, an iron chelater, or 4-hydroxy-tempo, a superoxide dismutase mimicking agent, inhibited UVA-induced suppression of the CHS response. N(G)-monomethyl-L-arginine acetate but not the ROS inhibitors prevented UVA from reducing LC numbers in the epidermis. This suggests that NO but not ROS produced in response to UVA mediates a depletion of LC from the epidermis, probably by signaling these cells to migrate from the skin. This could be responsible for UVA-induced immunosuppression. UVA-induced ROS can also cause immunosuppression, but by a different mechanism. Agents that inhibit or modulate NO or ROS production may be useful for preventing damage caused by the UVA component of sunlight to the skin immune system.

Tumour necrosis factor-alpha-induced migration of human Langerhans cells: the influence of ageing

BACKGROUND

Langerhans cells (LCs) play essential roles in the initiation and regulation of cutaneous immune responses mediated through their successful migration from the epidermis to draining lymph nodes while carrying antigen. Tumour necrosis factor (TNF)-alpha, a keratinocyte-derived cytokine, has recently been shown to play an important role in the mobilization of LCs from human epidermis. Although it is known that with age the immune system changes, the influence of increasing age on the function of human LCs has not been defined clearly.

OBJECTIVES

To examine the influence of age on the ability of TNF-alpha to induce LC migration.

METHODS

Ten elderly (six men, four women; mean age 76 years, range 72-79) and 10 young (six men, four women; mean age 23 years, range 18-35) volunteers received intradermal injections of 200 U of human recombinant TNF-alpha diluted in sterile saline, and control injections of sterile saline alone, at each of two paired sites identified on photoprotected buttock skin. Two hours later, paired injection sites were excised by punch biopsy. One set of paired biopsies was processed for assessment of the frequency and morphology of epidermal LCs, following preparation of epidermal sheets and immunofluorescence staining for the LC marker CD1a. The remaining paired biopsies were processed in formalin and the inflammatory response to TNF-alpha was assessed by standard histological examination.

RESULTS

Mean +/- SEM baseline values for LC frequency within epidermal sheets were significantly different between young (1156.3 +/- 38.5 cells mm(-2)) and elderly subjects (835.7 +/- 48.2 cells mm(-2); P < 0.01). Intradermal injections of 200 U of TNF-alpha caused a significant reduction in the frequency of LCs in both elderly and young subjects (P < 0.01). However, the extent of TNF-alpha-induced LC migration was substantially different between the two groups, with a mean 9% reduction in LC frequency in elderly volunteers compared with a mean 23% decrease in young subjects. Exposure to TNF-alpha was associated with a perivascular polymorphonuclear infiltrate at 2 h in all young subjects; in contrast, only 50% of the elderly individuals showed evidence of such a response.

CONCLUSIONS

There are significant differences between young and old skin with respect to both resting LC numbers and their response to TNF-alpha. These age-related changes in LC frequency and function may contribute to the altered cutaneous immune function observed in the elderly.

Functional caspase-1 is required for Langerhans cell migration and optimal contact sensitization in mice

Langerhans cell (LC) migration from epidermis to draining lymph node is a critical first step in cutaneous immune responses. Both TNF-alpha and IL-1 beta are important signals governing this process, but the potential regulatory role of IL-1 alpha processing by caspase-1 is unknown. In wild-type (WT) mice, application of the contact allergens 2,4-dinitrofluorobenzine and oxazolone lead to a marked reduction in epidermal LC numbers, but in caspase-1-deficient mice this reduction was not observed. Moreover, although intradermal injection of TNF-alpha (50 ng) induced epidermal LC migration in WT mice, this cytokine failed to induce LC migration in caspase-1-deficient mice. Intradermal IL-1 beta (50 ng) caused a similar reduction in epidermal LC numbers in both WT and caspase-1-deficient mice, indicating that, given an appropriate signal, caspase-1-deficient epidermal LC are capable of migration. Contact hypersensitivity to both 2,4-dinitrofluorobenzine and oxazolone was inhibited in caspase-1-deficient mice, indicating a functional consequence of the LC migration defect. In organ culture the caspase-1 inhibitor Ac-YVAD-cmk, but not control peptide, potently inhibited the epidermal LC migration that occurs in this system, and reduced spontaneous migration of LC was observed in skin derived from caspase-1-deficient mice. Moreover, Ac-YVAD-cmk applied to BALB/c mouse skin before application of contact sensitizers inhibited LC migration and contact hypersensitivity in vivo. Taken together, these data indicate that caspase-1 may play a central role in the regulation of LC migration and suggest that the activity of this enzyme is amenable to control by specific inhibitors both in vivo and in vitro.

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.

Studies of delayed systemic effects of ultraviolet B radiation (UVR) on the induction of contact hypersensitivity, 2. Evidence that interleukin-10 from UVR-treated epidermis is the critical mediator

Acute, low-dose ultraviolet B radiation (UVR) alters cutaneous immunity at the local site as well as systemically. Within 2-3 days of UVR exposure, recipient mice lose their capacity to develop contact hypersensitivity (CH) when hapten is painted on unexposed skin. This loss correlates temporally with a functional deficit among dendritic antigen-presenting cells within non-draining lymph nodes and spleen. In the experiments described, the delayed systemic immune deficiency following acute, low-dose UVR exposure was found to be eliminated with neutralizing anti-interleukin-10 (IL-10) antibody. Intracutaneous injection of IL-10 generated a deficiency of systemic immunity as well as a functional deficit among lymph node dendritic cells that was similar to that induced by UVR. The skin itself was found to be the source of the IL-10 responsible for these defects, and epidermis (presumably keratinocytes) rather than mast cells was found to be the source of IL-10 within UVR-exposed skin. The potential relationships are discussed between the delayed systemic immune deficit created by acute, low-dose UVR, and the systemic immune deficits caused by chronic, high-dose UVR and by a single, high-dose UVR exposure.

Tumor necrosis factor-alpha impairs contact hypersensitivity induction after ultraviolet B radiation via TNF-receptor 2 (p75)

Acute, low dose ultraviolet B radiation (UVR) impairs induction of contact hypersensitivity (CH) in genetically susceptible mice. Polymorphic alleles at the TNF-alpha locus dictate the susceptibility phenotype, and neutralizing anti-TNF-alpha antibodies restore CH induction in mice exposed to UVR. This circumstantial evidence strongly implicates TNF-alpha in the pathogenesis of failed CH induction after UVR. Using mice genetically deficient in TNF-receptor 1 (p55) or TNF-receptor 2 (p75), we now report that the capacity of TNF-alpha to impair CH induction after UVR required signaling via TNF-receptor 2, rather than TNF-receptor 1. Moreover, acting via the same receptor, TNF-alpha altered the density and morphology of class II MHC-bearing epidermal Langerhans cells. However, UVR retained its capacity to induce tolerance in both TNF-receptor 1 and TNF-receptor 2 deficient mice, indicating that TNF-alpha plays no role in the systemic immune deficit created by UVR.

Prevention of ultraviolet radiation-induced suppression of contact hypersensitivity by Aloe vera gel components

We have recently reported that Aloe vera gel contains small molecular weight immunomodulators, G1C2F1, that restore ultraviolet B (UVB)-suppressed accessory cell function of epidermal Langerhans cells (LC) in vitro. In the present study we evaluated the UVB-protective activity of G1C2F1 in vivo. Exposure of the shaved abdominal skin of mice to 2.4 KJ/m2 of UVB radiation resulted in suppression of contact sensitization through the skin to 41.1%, compared to normal unirradiated skin. Topical application of G1C2F1 immediately after irradiation reduced this suppression significantly. The percentage recovery of UVB-suppressed contact hypersensitivity (CHS) response was 52.3, 77.3, and 86.6% when the irradiated skin was treated once with 0.1, 0.5, and 2.5 mg/ml of G1C2F1-containing cream, respectively. G1C2F1 did not show nonspecific stimulatory activity on CHS response. The present study, together with the previous observation, show that Aloe vera gel contains small molecular weight immunomodulators that prevent UVB-induced immune suppression in the skin by restoration of UVB-induced damages on epidermal LC.

Reduction in number and morphologic alterations of Langerhans cells after UVB radiation in vivo are accompanied by an influx of monocytoid cells into the epidermis

Acute, low-dose ultraviolet B (UVB) radiation impairs contact hypersensitivity induction in mice by a mechanism due at least in part to Langerhans cells alterations. To better define the effects of UVB on Langerhans cells, we have compared the action of this agent on the skin of intact mice and in skin explants incubated in vitro up to 24 h. Using immunofluorescence, we detected a reduction in the length of the dendrites of Langerhans cells and a significant reduction in the number of Ia-positive Langerhans cells per unit area within 2 h of UVB; these changes reversed within 24 h in vivo, but not in vitro. By electron microscopy, the number of dendritic cells per 100 basal keratinocytes increased in vivo, but decreased in vitro by 2 h after UVB, a discordance that was significant. On the contrary, the number of dendrite profiles per dendritic cell body decreased significantly 2 h after UVB, both in vivo and in vitro. Many epidermal dendritic cells, 2 h after UVB in vivo, were deficient in cytoplasmic organelles, whereas the few cells that remained after UVB in vitro retained their Birbeck granules, and displayed many, dilated cytoplasmic vesicles. We interpret these data to mean that low doses of UVB radiation destroy the functional and morphologic integrity of epidermal Langerhans cells, and that these cells are rapidly replaced by precursor cells that mature in situ into normal-appearing Langerhans cells.

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.

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.

High and low doses of haptens dictate whether dermal or epidermal antigen-presenting cells promote contact hypersensitivity

In the induction of contact hypersensitivity (CH) to an epicutaneously applied hapten, we have previously proposed that low doses of hapten sensitize primarily through epidermal Langerhans' cells (LC), whereas high doses rely largely on dermal antigen-presenting cells (APC). To examine this issue further, we applied either high or low doses of dinitrofluorobenzene (DNFB) epicutaneously to mice. We observed reduced LC density at the site after 12 h (nadir), which returned to normal levels at 24 h only after a low dose of hapten. When a low dose of an unrelated hapten, oxazolone, was painted on skin that had been painted 12 h previously with high dose of DNFB, oxazolone-specific CH was impaired. When grafts of whole skin, dermis alone, and epidermis alone prepared from skin painted 2 h previously with low or high doses of DNFB were placed onto naive, syngeneic mice, CH was induced by whole skin after both types of doses, by epidermis only after a low dose, and by dermis only after high dose. When epidermal cell suspensions were derivatized in vitro with low or high doses of DNFB, only cells exposed to a low dose induced proliferation of hapten-specific Tcells. Thus, only a low dose of hapten reveals the APC functions of LC without the participation of dermal APC.

Failed antigen presentation after UVB radiation correlates with modifications of Langerhans cell cytoskeleton

Acute low-dose ultraviolet B radiation (UVR) impairs contact hypersensitivity (CH) induction in genetically defined strains of mice by a mechanism triggered by cis-urocanic acid (UCA) and dependent upon tumor necrosis factor-alpha (TNF-alpha). UVR, TNF-alpha, and cis-UCA cause similar morphologic changes among Langerhans cells, which spawns the speculation that UVR impairs CH induction in part by altering the Langerhans cell cytoskeleton. To examine this speculation, we studied the expression of vimentin in Langerhans cells after treatment with UVR, TNF-alpha, and cis-UCA. All treatments caused a reduction in expression of vimentin within the cytoplasm of Langerhans cells. Because partial loss of detectable vimentin may correlate with cytoskeletal disruption, we evaluated the effects of vinblastine, an agent that disrupts the cytoskeleton by disassembling microtubules, on Langerhans cell density and morphology. Epicutaneous treatment with vinblastine caused a reduction in Langerhans cell density, a loss of dendrites, and a reduction in vimentin expression. When dinitrofluorobenzene was painted on vinblastine-treated skin of BALB/c or C3H/HeN mice, only feeble CH was induced. Consequently, we propose that UVR prevents CH induction in susceptible mice by disrupting the cytoskeleton of Langerhans cells, thereby preventing them from carrying out their crucial role as antigen-presenting cells.

Induction of low zone tolerance to contact allergens in mice does not require functional Langerhans cells

Epidermal Langerhans cells are known to be the major controlling element in the development of contact hypersensitivity. Haptenic molecules permeating the skin are taken up locally by Langerhans cells and then presented to T lymphocytes in the regional lymph nodes. Despite the presence of functional Langerhans cells, however, subsensitizing doses of hapten applied epicutaneously induce tolerance. We examined epidermal Langerhans cells at the site of contact with picryl chloride or oxazolone in BALB/c and C57B1/6 mice with regard to their responding to either subsensitizing or sensitizing doses of allergen. Subsensitizing doses did not interfere with the membranous adenosine triphosphatase system on Langerhans cells, known to relate to functional readiness of the cell. Accordingly, on electron microscopy the ultrastructure of Langerhans cells was found to be like that in untreated skin. In contrast, sensitizing doses caused a significant depletion of adenosine triphosphatase-positive Langerhans cells, and electron microscopy revealed marked cellular activation of Langerhans cells, with enlarged nuclei and increased numbers of mitochondria and Birbeck granules. Furthermore, subsensitizing doses induced tolerance regardless of whether Langerhans cells were functionally intact or had their function blocked arbitrarily. Blocking was achieved either by preceding ultraviolet B irradiation at the site of application or by painting of a sensitizer before painting another sensitizer on the same site. Moreover, not even surgical removal of the site within minutes after painting could prevent the induction of tolerance. The data suggest that subsensitizing doses of contact allergens painted on normal murine skin bypass involvement of epidermal Langerhans cells.

Turnover and kinetics of epidermal Langerhans cells and their dendritic precursor cells in experimental contact dermatitis. A correlated ultrastructural-morphometric and immunohistochemical evaluation

The numerical density of epidermal Langerhans cells (LCs) in contact sensitivity and toxic contact dermatitis is still a matter of controversy, mainly due to changes in the phenotypic markers of this antigen-presenting cell during the skin reactions. Since the electron microscopic detection of Birbeck granules is the most reliable marker for the identification of normal and pathologically altered LCs, we performed an ultrastructural-morphometric time-course analysis to evaluate their epidermal turnover in the earskin of BALB/c mice after painting the ears with the hapten 2,4-dinitrofluorobenzene and the irritant croton oil. The counts revealed degeneration and depletion of epidermal LCs in both allergic and toxic dermatitis. In contrast, a slightly increased number of activated epidermal LCs was found during contact sensitization. All experimental procedures resulted in an enhanced immigration of so-called indeterminate dendritic cells which also became ultrastructurally activated and often showed Birbeck granule-like formations at their cell membrane. Immunohistochemistry with the monoclonal antibody 4F7, a new marker for dendritic precursor cells of LCs, demonstrated a significant increase in these accessory cells in the epidermis. Our results indicate that contact sensitivity and toxic skin reactions are characterized by complex but distinct changes in the turnover, kinetics and cellular properties of epidermal LCs and their dendritic precursor cells.

The role of dendritic cells in cutaneous immunity

This article reviews the role of dendritic cells in cutaneous immunity. Langerhans cells (LC) found in the epidermis are the best-characterized dendritic cell population. They have the ability to process antigen in the periphery, transport it to the draining lymph nodes (DLN) where they are able to cluster with, and activate, antigen-specific naive T cells. During migration LC undergo phenotypic and functional changes which enable them to perform this function. There are other less well-characterized dendritic cells including dendritic epidermal T cells, dermal dendrocytes and dermal "LC-like' cells. Although there is no evidence that dendritic epidermal T cells (DETC) can present antigen or migrate to lymph nodes, they do influence the intensity of cutaneous immune responses to chemical haptens. Antigen-presenting cells (APC) in the dermis may provide alternative routes of antigen presentation which could be important in the regulation of skin immune responses. Therefore, dendritic cells are vital for the induction of immune responses to antigens encountered via the skin. LC are particularly important in primary immune responses due to their ability to activate naive T cells. The faster kinetics of secondary responses, and the ability of nonprofessional APC to induce effector function in previously activated cells, suggest that antigen presentation in the DLN may be less important in responses to previously encountered antigens. In these secondary responses, dendritic and nondendritic APC in the skin may directly induce effector functions from antigen-specific recirculating cells.

Reduced antigen-presenting function of human Epstein-Barr virus (EBV)-B cells and monocytes after UVB radiation is accompanied by decreased expression of B7, intercellular adhesion molecule-1 (ICAM-1) and LFA-3

In this study, the effect of ultraviolet-B (UVB) radiation on antigen-presenting function was studied, to investigate whether antigen-presenting cells (APC) are inhibited by UVB through a common mechanism. Two types of human APC were used: EBV-B cells and monocytes, and these were irradiated in vitro with single low doses of UVB (range 0-200 J/m2). Irradiation of EBV-B cells or monocytes resulted in similar dose-dependent reduction in APC function, when determined by the allogeneic mixed leucocyte reaction (MLR) or Candida albicans- or tetanus toxoid-specific T cell response. Our study shows that the reduced APC function was not likely to be caused by alterations in antigen processing or cytokine production. However, UVB-irradiated APC displayed marked changes in adhesion molecule expression. Irradiated EBV-B cells showed reduced expression of ICAM-1 (30%), LFA-3 (25%) and B7-1 (35%), while expression of HLA-DR, CD19 and LFA-1 was not affected. UVB irradiation of monocytes did result in reduction in the expression of HLA-DR (30%), LFA-3 (40%), ICAM-1 (65%) AND B7-1 and B7-3 (90%), but had no effect on CD14, LFA-1 and ICAM-3 expression. Addition of non-irradiated cells (but not the supernatant of these cells) or CD28 antibodies partly restored T cell activation, indicating that UVB-induced reduction in APC function is at least partly mediated via impairment of co-stimulatory molecule expression.

Down-regulation of Langerhans cell protein kinase C-beta isoenzyme expression in inflammatory and hyperplastic dermatoses

The family of protein kinase C (PKC) isoenzymes plays a fundamental part in signal transduction, and thereby regulates important cellular functions, including growth, differentiation, cytokine production and adhesion molecule expression. In lesional psoriatic skin, Ca(2+)-dependent PKC activity, PKC-beta protein and epidermal Langerhans cell (LC) PKC-beta immunostaining are significantly decreased, indicating activation and subsequent down-regulation of PKC. Whether these changes occur in other inflammatory/hyperplastic dermatoses is, however, unknown. We examined PKC-alpha and PKC-beta expression in normal skin, psoriasis, cutaneous T-cell lymphoma (CTCL), lamellar ichthyosis, non-bullous ichthyosiform erythroderma, atopic dermatitis, urushiol-induced allergic contact dermatitis, and sodium lauryl sulphate (SLS)-induced irritant contact dermatitis. Cryostat sections were stained for PKC-alpha and PKC-beta, and the LC marker CD1a, using an immunoperoxidase technique and specific monoclonal antibodies. Double-labelling studies, in normal skin, revealed co-expression of PKC-beta and CD1a by epidermal LCs. Analysis of the number of PKC-beta+ and CD1a+ epidermal LCs, in diseased compared with normal skin, revealed three categories: (i) in psoriasis and CTCL, the PKC-beta+ epidermal LC number was significantly reduced, whereas the CD1a+ epidermal LC number was unchanged; (ii) in allergic and irritant contact dermatitis, both PKC-beta+ and CD1a+ epidermal LCs were significantly reduced in number; and (iii) in atopic dermatitis, the PKC-beta+ epidermal LC number was normal, and CD1a+ epidermal LCs were significantly increased in number. Moreover, the ratio of epidermal LC PKC+/CD1a+ was reduced in all the dermatoses studied, suggesting activation of PKC-beta, with subsequent down-regulation. Within the dermis, increased PKC-beta staining of infiltrating cells was observed in all the conditions studied except lamellar ichthyosis and non-bullous ichthyosiform erythroderma. These data indicate that: (i) down-regulation of LC PKC-beta occurs in a variety of inflammatory and hyperplastic skin disorders, and is not unique to psoriasis, and (ii) the pattern of epidermal LC PKC-beta and CD1a expression varies among the diseases studied. In mice, PKC activation induces LC migration. Thus, down-regulation of epidermal LC PKC-beta associated with reduced CD1a+ epidermal LCs in allergic and irritant contact dermatitis suggests that PKC-beta may transduce the signal for migration of LCs from human epidermis.

Immune surveillance and sunlight-induced skin cancer

Immune surveillance poses the existence of a recirculating pool of lymphocytes that migrate randomly through somatic tissues. Upon recognition of neoantigens on malignantly transformed cells, lymphocytes proceed to attack and destroy degenerate cells before a tumor emerges. Here, J. Wayne Streilein and colleagues review the effects of ultraviolet B irradiation on the induction of cutaneous immunity in the skin of mice and humans. Furthermore, they discuss the possibility of a genetic predisposition to skin cancer, mediated by a defect in the normal process by which contact hypersensitivity, and therefore immunogenicity, is elicited.

Mechanisms of UV-induced inflammation

The inflammation produced by exposure to ultraviolet (UV) light has been well documented clinically and histologically. However, the mechanisms by which mediators induce this clinical response remain poorly defined. It is clear that photochemistry occurring after UV absorption must be responsible for initiating these events. Some of these underlying mechanisms have been defined. After exposure to UV light, the formation of prostaglandins and the release of histamine are increased. In addition to an increase in the quantity of these mediators, an increase in sensitivity of irradiated tissue to agonist stimulation also occurs. This increased sensitivity may cause tissue to respond to agonist levels previously present. Phospholipase activity also increases, making more substrate available for prostaglandin formation. Oxygen radical-induced peroxidation of membrane lipids caused by irradiation may contribute to increased phospholipase activity. Oxygen-free radicals also participate in sunburn cell formation and in UV-induced decreases in Langerhans cell numbers. Several enzymatic and non-enzymatic mechanisms are present in skin for reducing these highly reactive oxygen species.

Dendritic cells and cutaneous immune responses to chemical allergens

This article reviews the role of epidermal Langerhans cells (LC) in the development of cutaneous immune responses to chemical allergens. Following topical exposure to sensitizing chemicals, LC, many of which bear allergen, are induced to migrate from the skin, via the afferent lymphatics, to the draining lymph nodes. The phenotypic and functional changes to which LC are subject during this process and their development into active immunostimulatory cells closely resembling lymphoid dendritic cells is discussed. The migration and maturation of LC following skin sensitization is of critical importance to the effective presentation of chemical allergens to T lymphocytes and the induction of allergic responses. Evidence is reviewed which suggests that these events are initiated and regulated by epidermal cytokines. The conclusion drawn is that an early event during the induction of skin sensitization is the production by keratinocytes of cytokines which stimulate the migration of LC from the skin and which also result in the functional maturation of LC into potent antigen-presenting cells.

Mechanisms of local, low-dose UVB-induced immunosuppression in contact hypersensitivity

Preirradiation of contact sensitizing sites to low-dose ultraviolet B (UVB) renders animals unresponsive to challenge reaction. This unresponsiveness is known as local, low-dose UVB-induced immunosuppression. Although researchers in this area have developed theories, the exact mechanisms of UVB-induced immunosuppression are still a matter of controversy. This article reviewed various scientific data on UVB-induced immunosuppression, categorizing them into individual sequential steps in the whole cascade.

Acceptance of class II major histocompatibility complex disparate skin grafts associated with suppressor cells and elevated Langerhans cell numbers

Class II major histocompatibility complex (MHC) molecules are only present on Langerhans cells (LC) in normal murine epidermis. Depletion of this antigen with the chemical carcinogen dimethylbenzanthracene (DMBA) causes I-E disparate B10.A(2R) congenic tail skin to be accepted permanently when grafted onto B10.A(4R) recipients. Adoptive transfer of spleen cells from these recipients into naive syngeneic hosts inhibited the ability of the host mice to reject untreated B10.A(2R) tail skin grafts. Hence DMBA-treated LC depleted I-E disparate skin grafts activate suppressor cells which did not inhibit BALB/c mice from rejecting a B10.A(2R) tail skin graft. In contrast, the tobacco derived carcinogen benzo(a)pyrene (BP) increased the number of epidermal LC but had no effect on either class I or class II MHC disparate skin graft survival time. This confirms that the number of class II MHC-positive LC is critical for the initiation of skin graft rejection; when the threshold level is attained graft rejection proceeds at a maximal rate that cannot be enhanced by raising the number of LC. The tolerant skin grafts had increased numbers of LC; this was not observed in syngeneic grafts and therefore may be related to the active suppression of immunity.

The immunologic properties of epidermal Langerhans cells as a part of the dendritic cell system

Dendritic cells form a system of antigen-presenting cells that is widely distributed in the body. They constitute trace populations in lymphoid and non-lymphoid tissues and in the circulation. They are characterized by their typical dendritic and "veiled" morphology, by their constitutive expression of high levels of major histocompatibility complex class II molecules on their surface, and by their outstanding capacity to initiate primary immune responses. Dendritic cells occur in two states of differentiation. In the immature state they are highly specialized for processing foreign protein antigens; in the mature state they efficiently stimulate resting antigen-specific T cells. Dendritic cells can migrate from the non-lymphoid tissues, where they reside in the immature state, via the afferent lymphatics or the blood to the T cell-dependent areas of the lymphoid organs (lymph nodes, spleen). There, they appear as mature dendritic cells. Therefore, dendritic cells are ideally suited to mediate important aspects of immunogenicity: they can acquire antigens in the tissues and process them in an immunogenic form; they can carry the immunogen to the lymphoid organs; and they can find and efficiently activate antigen-specific T cell clones and thus generate an immune response. Studies of epidermal Langerhans cells have greatly helped in establishing this concept. They can be investigated freshly isolated from the epidermis where they represent immature (tissue) dendritic cells. After 2-3 days in culture they develop into mature dendritic cells. The mechanisms of dendritic cell maturation, which can be studied best using epidermal Langerhans cells, and the specific functions of Langerhans cells in immunogenicity are discussed.

Cumulative sunlight exposure and the risk of developing skin cancer in Florida

Epidemiologic evidence suggests that the risk of developing skin cancer is higher in certain geographic regions where sunlight is excessive. Even in such high risk regions, two distinct populations of long-term residents exist: people with, and people without skin cancer. We have compared the quantitative lifetime sunlight exposure between 11 nonmelanoma skin cancer patients who have lived in South Florida for 23.7 +/- 5.1 years and 9 age-matched normal, healthy individuals who have lived in South Florida for 23.4 +/- 4.1 years. An estimation of personal cumulative sunlight exposure was determined for each subject from data collected through detailed interviews. We found that there was no detectable, significant quantitative difference in cumulative sunlight exposure during life between these two groups. Because these individuals had previously been phenotyped for the effects of ultraviolet-B (UVB) radiation on induction of contact hypersensitivity, our results suggest that UVB-susceptibility may be a better indicator of skin cancer risk than cumulative lifetime sunlight exposure. Thus, although there is little doubt that sunlight exposure is an important factor in the development of skin cancer, our results emphasize the importance of host genetic factors in the pathogenesis of this disease.

Quantitative assessment of ATPase-positive epidermal dendritic (Langerhans) cells in piglets and adult swine

To assess the distribution pattern of Langerhans cells (LC) in normal porcine skin, epidermal sheets from six anatomical sites from three age-matched groups of male and female pigs were stained for ATPase activity. This histoenzymological technique is considered specific for Langerhans cells in normal epidermis. No statistically significant differences were observed between mean Langerhans cell density per mm2 of epidermis from male and female pigs, nor between different anatomical sites in the same age group. Statistically significant differences (P less than 0.0005) were observed when comparing group A one- to two-week-old piglets (463 to 518 LC mm-2) with group B six month olds (641 to 804 LC mm-2) and group C two years and over sows (741 to 830 LC mm-2). Morphological variations in the skin of young piglets, much thinner and with rudimentary or no epidermal rete pegs, could account for this significant variation.

Quantitative evaluation of Langerhans cells in median rhomboid glossitis

Langerhans cells (LC) serve as antigen presenting cells and provide immune surveillance within epithelia. Since depression of LC number and/or function may allow tolerance to antigens, we evaluated LC in median rhomboid glossitis (MRG), a condition linked to persistent candidal infection of lingual mucosa. Material included a total of 36 cases of MRG (7 of which did not show PAS + fungi) and 6 controls. LC were identified by their expression of S-100 and HLA-DR antigens and quantified using image analysis. Equal numbers of LC were identified using S-100 + and HLA-DR + markers. The density of LC (cells/mm of basement membrane, mean +/- SD) in both PAS + MRG (2.6 +/- 1.3) and PAS-MRG (3.0 +/- 1.7) was markedly depressed compared with controls (17.2 +/- 6.4), (P less than 0.001). These findings indicate that the LC network is perturbed in MRG, and are consistent with the view that of localized defect in immune surveillance may contribute to persistent fungal infection of the oral mucosa.

Cutaneous lesions in severe combined immunodeficiency: two case reports and a review of the literature

Two patients with severe combined immunodeficiency (SCID) in whom cutaneous lesions were the first clinical feature were studied. Neither the morphology nor the histology of the lesions was uniform, although we have noted some common findings that can, in subsequent cases, lead us to suspect SCID. The immunologic defects were not uniform, representing the two poles of the spectrum of SCID. We believe that early recognition of the skin lesions is very important, since the patient's life expectancy can be increased by a bone marrow transplantation (1).

Effects on murine epidermal Langerhans cells of drugs known to cause recrudescent herpes simplex virus infection in a mouse model

A number of agents have been shown to alter the latent state of herpes simplex virus in murine sensory ganglia. However, it seems that effective triggers of recrudescent disease must act not only to reactivate latent HSV infection, but also to create a favorable environment in the skin for viral replication. The possibility that alteration of the local Langerhans cell population is one way in which effective triggers of recrudescence may act has been investigated. Of the agents tested, which affect latent HSV, only DMSO significantly altered the numbers of ATPase-bearing Langerhans cells in the epidermis, maximally reducing their density by 83% in 48 h. Xylene and retinoic acid had no discernible effect on numbers of ATPase-staining cells over the 4 d tested. However, the extent to which agents reduced ATPase-staining cell numbers did not correlate with their ability to affect the antigen-presenting capacity of the cells in HSV-specific T-cell proliferative assays in vitro. Xylene and retinoic acid markedly reduced the accessory cell function of epidermal cell suspensions, whereas DMSO had no effect.

Epidermal Langerhans cells in myelodysplastic syndromes are abnormal

The myelodysplastic syndromes (MDS) represent clonal disorders of the hematopoietic stem cell that are associated with quantitative and qualitative disturbances of the peripheral blood cells and a high risk for the transition to overt leukemia. As epidermal Langerhans cells (LC) are bone-marrow-derived cells, we were interested to see whether they are altered in patients with MDS. Epidermal sheets were prepared from biopsies taken from the thighs of nine patients with MDS and five control persons and processed for immunoperoxidase staining of CD1a antigens. The density and morphology of CD1a+ cells (i.e., LC) was evaluated by visual assessment as well as automatic image analysis. The density of LC was reduced in seven of nine patients (range, 30-75% of normal), whereas the morphology of LC appeared to be altered in all MDS patients in that the LC displayed large and bizarre cell bodies with only a few and often abnormally long dendrites. The HLA-DR expression by LC was not altered, as shown by double immunofluorescence staining of CD1a and HLA-DR antigens. Ultrastructurally, LC again appeared enlarged and often presented with bizarre nuclei, yet displayed no other abnormalities. Our findings suggest that LC are abnormal in MDS and might even indicate a more wide-spread involvement of the dendritic cell lineage in this syndrome.

Quantitative and morphometric analysis of Langerhans cells in non-exposed skin in renal transplant patients

Renal transplant recipients have a high incidence of cutaneous complications such as neoplasia and viral or fungal infections. Morphologic alterations of epidermal Langerhans cells (LC) have furthermore been described in these patients. Since these changes have been mainly found in sun-exposed skin, a direct effect of immunosuppressive therapy remains a matter of discussion. A quantitative and morphometric study of epidermal LC in non-exposed skin was performed in 28 renal transplant patients (RTP). RTP were divided in two groups according to immunosuppressive treatment: group A; azathioprine + prednisone (14 cases) and group B; cyclosporine + prednisone (14 cases). Twenty sex-age matched non-immunosuppressed patients acted as controls (group C). Epidermal sheets were obtained by incubation in EDTA and stained for ATPase activity and with the monoclonal antibody T6 (CD1) using the avidin-biotin peroxidase method. Langerhans cells were counted using a calibrated graticule (400x) and expressed as the mean number of LC/mm2. The mean area of the LC and the number of primary dendrites (pd) and secondary dendrites (sd) were determined with a morphometer adapted to an Apple II computer. The mean number of positive cells in controls was: ATPase, 677 +/- 157; T6, 695 +/- 164. Patients in group A had the maximum reduction in both ATPase and T6 LC density (ATPase, 339 +/- 142; T6, 402 +/- 194). Patients in group B had an intermediate reduction in the number of LC (ATPase, 494 +/- 121; T6, 529 +/- 112).(ABSTRACT TRUNCATED AT 250 WORDS)