Langerhans cells as stimulator cells in the murine primary epidermal cell-lymphocyte reaction: alteration by UV-B irradiation

The Origin of Skin Dendritic Cell Network and Its Role in Psoriasis

Dendritic cells (DCs) are heterogeneous groups of innate immune cells, which orchestrate immune responses by presenting antigens to cognate T cells and stimulating other types of immune cells. Although the term ‘DCs’ generally represent highly mixed subsets with functional heterogeneity, the classical definition of DCs usually denotes conventional DCs (cDCs). Skin contains a unique DC network mainly composed of embryo precursor-derived epidermal Langerhans cells (LCs) and bone marrow-derived dermal cDCs, which can be further classified into type 1 (cDC1) and type 2 (cDC2) subsets. Psoriasis is a chronic inflammatory skin disease, which is principally mediated by IL-23/IL-17 cytokine axis. In the psoriatic skins, DCs are prominent cellular sources for TNF-α and IL-23, and the use of blocking antibodies against TNF-α and IL-23 leads to a significant clinical improvement in psoriatic patients. Recent elegant human and mouse studies have shown that inflammation-induced inflammatory DCs, LCs, dermal cDC2, and monocyte-derived DCs are pivotal DC subsets in psoriatic inflammation. Thus, targeting specific pathogenic DC subsets would be a potential strategy for alleviating and preventing DC-derived IL-23-dependent psoriatic inflammation and other inflammatory dermatoses in the future.

Magnesium ions inhibit the antigen-presenting function of human epidermal Langerhans cells in vivo and in vitro. Involvement of ATPase, HLA-DR, B7 molecules, and cytokines

The combination of seawater baths and solar radiation at the Dead Sea is known as an effective treatment for patients with psoriasis and atopic dermatitis. Dead Sea water is particularly rich in magnesium ions. In this study we wished to determine the effects of magnesium ions on the capacity of human epidermal Langerhans cells to stimulate the proliferation of alloreactive T cells. Twelve subjects were exposed on four subsequent days on the volar aspects of their forearms to 5% MgCl2, 5% NaCl, ultraviolet B (1 minimal erythemal dose), MgCl2 + ultraviolet B, and NaCl + ultraviolet B. Epidermal sheets were prepared from punch biopsies and were stained for ATPase and HLA-DR. Compared with untreated skin, the number of ATPase+/HLA-DR+ Langerhans cells was significantly reduced after treatment with MgCl2 (p = 0.0063) or ultraviolet B (p = 0.0005), but not after NaCl (p = 0.7744). We next questioned whether this reduced expression of ATPase and HLA-DR on Langerhans cells bears a functional relevance. Six subjects were treated on four subsequent days with 5% MgCl2, ultraviolet B (1 minimal erythemal dose), and MgCl2 + ultraviolet B. Epidermal cell suspensions from treated and untreated skin were assessed for their antigen-presenting capacity in a mixed epidermal lymphocyte reaction with allogeneic naive resting T cells as responder cells. Treatment with MgCl2, similarly to ultraviolet B, significantly reduced the capacity of epidermal cells to activate allogeneic T cells (p = 0.0356). Magnesium ions also suppressed Langerhans cells function when added to epidermal cell suspensions in vitro. The reduced antigen-presenting capacity of Langerhans cells after treatment with MgCl2 was associated with a reduced expression by Langerhans cells of HLA-DR and costimulatory B7 molecules, and with a suppression of the constitutive tumor necrosis factor-alpha production by epidermal cells in vitro. These findings demonstrate that magnesium ions specifically inhibit the antigen-presenting capacity of Langerhans cells and may thus contribute to the efficacy of Dead Sea water in the treatment of inflammatory skin diseases.

IL-12 promotes the accessory cell function of epidermal Langerhans cells

The objective of this study was to investigate the effects of cytokines regulating cutaneous immune responses, on the accessory cell function of epidermal cells (EC). EC were treated with various cytokines, and the accessory cell function of the cytokine-pretreated EC was examined by the allogeneic mixed epidermal cell-lymphocyte reaction (MECLR). Among the cytokines examined, IFN-gamma- and IL-12-pretreated EC augmented IFN-gamma production in the MECLR, while none of the other cytokines was effective. However, the cytokine-pretreated EC did neither affect T cell proliferation nor IL-4 production in the MECLR. Next we attempted to analyze the mechanisms by which IL-12-pretreated EC increase IFN-gamma production in the MECLR. Endogenous IFN-gamma produced during the IL-12 pretreatment of EC was found to play only a minor role in modulating the function of EC. The expression of MHC class II, CD80 and CD86 on EC was not affected by IL-12. On the other hand, soluble mediators that induce IFN-gamma production during the MECLR containing IL-12-pretreated EC were identified as endogenously produced IL-12 (the major mediator) and IL-18 (the minor mediator). Furthermore, the results of depletion experiments indicate that IL-12 promotes the accessory cell function of Langerhans cells to responder T cells in inducing IFN-gamma production in the MECLR.

Ultraviolet light and interleukin-10 modulate expression of cytokines by transformed human dermal microvascular endothelial cells (HMEC-1)

Exposure of the skin to ultraviolet (UV) light causes DNA damage, inflammation, and impairment of local as well as systemic immune responses. Dermal microvascular endothelial cells are key elements for the recruitment of inflammatory cells during the pathogenesis of inflammatory skin diseases via the expression of adhesion molecules and the release of cytokines. Because UVB may directly affect the function of dermal cells it was investigated whether UVB irradiation alters the production of proinflammatory and chemotactic cytokines by endothelial cells. UVB exposure of transformed human microvascular endothelial cells (HMEC-1) resulted in a dose dependently increased mRNA expression as well as release of interleukin (IL)-1beta, IL-6, IL-8, and growth-regulated oncogene alpha (GROalpha). Maximum cytokine production was observed 16-24 h after irradiation when 7.5-12.5 mJ UVB per cm2 were used. In addition, it was examined whether IL-10, which is upregulated in keratinocytes following UVB irradiation and accounts for UV mediated immunosuppression such as inhibition of contact hypersensitivity, also affects endothelial cell cytokine production. Treatment of HMEC-1 with IL-10 significantly enhanced IL-6 and IL-8 release and further upregulated UVB-induced IL-6 and IL-8 mRNA expression. These findings demonstrate that UVB both directly and indirectly via the release of IL-10 stimulates microvascular endothelial cells to produce proinflammatory cytokines and chemokines that are required for the migration and activation of inflammatory cells in UV-mediated inflammatory skin reactions.

Despite the presence of UVB-induced DNA damage, HLA-DR+ cells from ex vivo UVB-exposed human skin are able to migrate and show no impaired allostimulatory capacity

In this study, we investigated the effect of ultraviolet B radiation on human Langerhans cell function. Normal human skin was irradiated ex vivo with single doses of ultraviolet B. For assessment of T-cell stimulatory function, cells that spontaneously migrated from epidermal sheets were used, whereas full-thickness skin biopsies were used to investigate alterations in migratory properties. The cells migrating from ultraviolet B-exposed epidermal sheets demonstrated a decrease in the percentage of HLA-DR positive Langerhans cells, as well as a reduced capacity to induce proliferation of allogeneic T cells, when compared with cells migrating from nonexposed sheets. When a correction was made for the decreased number of HLA-DR positive Langerhans cells migrating from ultraviolet B-exposed epidermis, however, it appeared that the capacity to induce T-cell proliferation was identical for Langerhans cells migrating from ultraviolet B-exposed and nonexposed epidermis. The presence of ultraviolet B-induced DNA damage could be demonstrated in the Langerhans cells from ultraviolet B-treated skin, indicating that the cells had received significant doses of ultraviolet B. As regards the effect of ultraviolet B on migratory properties of Langerhans cells, we found not only that reduced numbers of CD1a-positive Langerhans cells migrated from the ultraviolet B-exposed full-thickness skin, but also that there was a reduction in CD1a-positive Langerhans cells in the epidermis. This implies that ultraviolet B induces death of Langerhans cells as well as loss of cell surface molecules rather than altering Langerhans cells migration, whereas the Langerhans cells that were still able to migrate fully retained the capacity to activate allogeneic T cells.

Immunologic protection afforded by sunscreens in vitro

Several studies have suggested a lack of correlation between sunscreen sun protection factor and protection of the skin immune system, potentially allowing greater damage to the skin by removing the natural protective erythemal response to sun exposure. Despite this, routine testing of immune protection afforded by sunscreens is not performed by industry. Current laboratory methods for investigating the efficacy of sunscreen protection of epidermal immune function use the induction of contact hypersensitivity or epidermal cell alloantigen presentation. Animal models, cell culture systems, and in vivo human studies are commonly employed, but all these systems have significant drawbacks for use in routine testing. The purpose of this study was to develop an in vitro system for testing the immunologic protection afforded by sunscreens in human skin. Five test sunscreens plus a vehicle control were tested in a "blind" fashion for their in vitro level of immune protection. Creams were applied in a standard manner to human whole skin explants and were irradiated over a range of physiologic doses using an Oriel solar simulator. A mixed epidermal lymphocyte reaction was used to quantify epidermal alloantigen-presenting capacity, in the presence or absence of test cream, for five explants. Results consistently demonstrated that all the test sunscreens protected beyond their designated sun protection factors, whereas the vehicle conferred no protection. The explant-mixed epidermal lymphocyte reaction system gave consistent, reproducible results and may prove useful for the allocation of an immune protection factor to all sunscreens.

Langerhans cells in the development of skin cancer: a qualitative and quantitative comparison of cell markers in normal, acanthotic and neoplastic ovine skin

The distribution of Langerhans cells in normal, acanthotic and neoplastic ovine epithelium was examined using the enzyme marker Acetylcholinesterase (AchE) and monoclonal antibodies (MoAb) to CD1 (20.27) and MHC Class II (49.1 and 28.1) molecules. In normal skin, where Langerhans cells were regularly spaced within the basal layer, qualitative observations and direct pairwise testing showed that AChE was superior to the MoAb in detecting these cells. Significantly more (P < 0.01) dendritic cells were also detected with MoAb 49.1 than MoAb 20.27 or 28.1, suggesting differential expression of MHC Class II subsets and the presence of CD1- MHC Class II+ granule- dendritic cells in sheep analogous to indeterminate cells of man. In acanthotic skin, compared to normal skin, Langerhans cells were less numerous, irregular and more suprabasal in distribution and their morphology was occasionally swollen and indistinct. No difference was seen in the ability of AChE and MoAb in detecting Langerhans cells, however pairwise testing of markers did demonstrate that significantly more (P < 0.05) cells without dendritic processes were stained with MoAb 49.1 than with 20.27 or 28.1. In all squamous cell carcinomas examined dendritic cells that stained for AChE, CD1 or MHC Class II antigens were concentrated at the peripheral areas of neoplastic epithelium. Many dendritic cells were detected with MoAb to MHC Class II antigens, whereas CD1 and AChE positive dendritic cells were rare in tumor bearing tissue. The quantitative differences in the immunohistochemical staining of Langerhans cells between normal, acanthotic and neoplastic epithelium were consistent with ultrastructural studies. When compared with those of a newborn lamb, which had had very little exposure to antigens or ultraviolet radiation (UVR), the Langerhans cells of the aged sheep were deformed and contained far fewer Birbeck granules. The abnormalities were progressively more severe in acanthotic and neoplastic skin. These observed changes may have resulted from UVR induced damage and may be indicative of impaired function involved in the development of skin cancer.

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.

In vitro analysis of the phenotypical and functional properties of the 4F7+ cutaneous accessory dendritic cell

The monoclonal antibody 4F7 detects a molecule on dermal and epidermal Ia+ dendritic cells (DCs), and some of these cells are Birbeck granule-containing cells. Here we report on the phenotypical and functional characteristics of these cells which were highly enriched by 4F7-labelled immunomagnetic beads. The ultrastructural, immunocytochemical and cytochemical analyses of these preparations showed cells with the typical characteristics of DCs. The cells were found to express the DC marker NLDC145, but not 33D1. The C3bi receptor and marker F4/80 were only expressed by epidermal 4F7+ cells. The capacity of freshly isolated 4F7+ epidermal and dermal DCs to activate allogeneic T cells in a mixed leukocyte reaction was similar to the capacity of freshly isolated Langerhans cells. After culture, the epidermal cells showed a 4-5-fold increase in stimulation, whereas no difference was observed in the 4F7+ dermal DCs. We conclude that this new antibody recognizes a function-associated molecule on cutaneous DCs which are phenotypically and functionally related to Langerhans cells. The 4F7+ DCs may be precursors of epidermal Langerhans cells.

Comparative potency of different UV sources in reducing the density and antigen-presenting capacity of Langerhans cells in C3H mice

Although broadband UV-B irradiation has been shown to induce selective immunosuppression in a variety of experimental systems, the wavelength dependence of the immunomodulation and the initial events in the skin remain unclear. In the present study three UV lamps were used at suberythermal doses on C3H mice: a conventional broadband UV-B source (270-350 nm), a narrowband UV-B source (311-312 nm) and a UV-A source (320-400 nm). Their effects on the photoisomerization of the naturally occurring trans-isomer of urocanic acid (UCA) to cis-UCA, on the density of Langerhans cells and on the ability of epidermal cells to stimulate allogeneic lymphocytes in the mixed skin lymphocyte reaction (MSLR) were ascertained. Broadband UV-B irradiation was more efficient than narrowband UV-B at reducing the density and function of Langerhans cells, while UV-A irradiation was least effective. These changes were most pronounced immediately following irradiation, were dose dependent and were only detected in UV-exposed areas of skin. There was a close correlation between the UV-induced reduction in Langerhans cell density and the formation of cis-UCA in the epidermis. This correlation was not detected between the reduction in the MSLR response following UV irradiation in vivo and cis-UCA formation.

Accessory cell ability of Langerhans cells for superantigen is resistant to ultraviolet-B light

We examined the effects of ultraviolet-B (UVB) irradiation on the accessory cell ability of Langerhans cells (LC) to induce a T-cell response to a superantigen, staphylococcal enterotoxin B (SEB). The ability of LC-enriched epidermal cells (LC-EC) to evoke a T-cell response to SEB was retained at the doses of UVB (up to 40 mJ/cm2) that profoundly affected the antigen-presenting function of LC-EC for a hapten, trinitrophenyl (TNP), and a protein antigen, conalbumin. Thus, the LC accessory function for superantigens is more resistant to UVB irradiation than that for ordinary antigens. This UVB resistance is presumably due to no requirement of antigen processing for superantigens as chemically fixed or chloroquine-treated LC-EC still retained their ability to induce T-cell responses to SEB. Higher doses of UVB (more than 60 mJ/cm2) reduced the accessory cell ability of LC-EC for SEB up to 50% of control. The addition of monoclonal antibodies against adhesion molecules between LC and T cells to the culture resulted in a substantial suppression of the T-cell response to SEB induced by nonirradiated LC-EC, while the UVB-irradiated LC-EC-induced T-cell response was not significantly blocked with these monoclonal antibodies. This suggested that the reduction of LC ability for superantigen by high doses of UVB is at least partly due to the impairment of adhesion molecules on LC by UVB irradiation.

Interleukin 1 alpha but not transforming growth factor beta inhibits tumor antigen presentation by epidermal antigen-presenting cells

Cutaneous I-A+ Langerhans cells are the principal antigen-presenting cells within the epidermis, capable of both initiating and eliciting CD4-dependent immune reactions. We recently demonstrated that epidermal Langerhans cells can present tumor-associated antigens and thus may be important in cutaneous tumor immunity. Despite the ability of Langerhans cells to present tumor antigens, they generally fail to induce protective tumor immunity against growing tumors in situ. We therefore investigated whether locally produced cytokines may be able to down-regulate the presentation of tumor-associated antigens and alloantigen by epidermal antigen-presenting cells in primed as well as in unprimed systems in vivo and in vitro. Naive syngeneic mice could be successfully immunized against the spindle cell tumor S1509a by injecting them with granulocyte-macrophage colony-stimulating factor-exposed and tumor-associated antigen-pulsed epidermal cells three times at weekly intervals. Co-incubation of epidermal cells in granulocyte-macrophage colony-stimulating factor and interleukin-1 alpha inhibited tumor-antigen presentation by epidermal antigen-presenting cells in this system and also inhibited alloantigen presentation in the primary mixed epidermal cell-lymphocyte reaction. Tumor necrosis factor-alpha appeared to be a significant mediator of the inhibitory effect of interleukin-1 alpha on the ability of epidermal antigen-presenting cells to induce protective tumor immunity, because addition of anti-tumor necrosis factor-alpha antibody abrogated the observed effect of interleukin-1 alpha. However, the effects of interleukin-1 alpha and tumor necrosis factor-alpha differed with regard to presentation of tumor-associated antigens by epidermal antigen-presenting cells in a primed system. Whereas incubation of epidermal cells in interleukin-1 alpha before or after tumor antigen pulse inhibited their ability to elicit a delayed-type hypersensitivity response against S1509a tumor-associated antigens in tumor-immune mice, culture in tumor necrosis factor-alpha significantly enhanced delayed-type hypersensitivity. Again, these in vivo data corresponded well to similar results obtained in vitro using the secondary mixed epidermal cell-lymphocyte reaction. Incubation of epidermal cells in transforming growth factor-beta, which has been shown to down-regulate T-cell-mediated immune responses in other systems, did not suppress tumor immunity in our assays. Thus, interleukin-1 alpha may be an important regulator of Langerhans cell antigen-presenting function, having effects that are partially mediated via interleukin-1 alpha-induced up-regulation of tumor necrosis factor-alpha secretion within the skin.

Regulation of Langerhans cell function by nerves containing calcitonin gene-related peptide

Several observations suggest interactions between the immune and nervous systems. Psoriasis and atopic dermatitis may worsen with anxiety and have been associated with anomalous neuropeptide regulation. Neurotransmitters affect lymphocyte function and lymphoid organs are innervated. Calcitonin gene-related peptide (CGRP) is a neuropeptide and vasodilator that modulates some macrophage functions, including antigen presentation in vitro. CGRP is associated with Langerhans cells (LC) in oesophageal mucosa, particularly during inflammation, is present in epidermal nerves and is associated with Merkel cells. We examined the ability of CGRP to modulate LC antigen-presenting function and asked if CGRP-containing nerves impinge on LC. We report here that CGRP-containing nerve fibres are intimately associated with LC in human epidermis and CGRP is found at the surface of some LC. In three functional assays CGRP inhibited LC antigen presentation. These findings indicate that CGRP may have immunomodulatory effects in vivo and suggest a locus of interaction between the nervous system and immunological function.

Langerhans cells: structure, function and role in oral pathological conditions

Langerhans cells (LCs) are dendritic bone marrow derived cells situated suprabasally in most stratified squamous epithelia, such as the epidermis and the epithelium of oral mucosa, including the gingiva. Langerhans cells are thought to act as antigen-presenting cells (APC) during induction of immune responses. The exact role of Langerhans cells in the oral mucosa is not fully understood although several investigations suggest that these cells are involved in reactions to antigen challenge under both normal and pathological situations. In this paper the structure, phenotypic markers and derivation of Langerhans cells are reviewed. In view of recent findings, the immunological characteristics and the implications of Langerhans cells in pathologic oral reactions are discussed.

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.

Differential sensitivity of freshly isolated and cultured murine Langerhans cells to ultraviolet B radiation and chemical fixation

Previous studies have demonstrated that low doses of ultraviolet B (UVB) radiation (100 J/m2) abrogate the accessory function of freshly isolated murine epidermal Langerhans cells (fLC) and cause a parallel decrease in the ability of LC to express increased amounts of ICAM-1 (CD54) in vitro. We have subsequently observed that the accessory cell function of cultured LC (cLC), as assessed by their ability to support anti-CD3 monoclonal antibody (mAb)-induced T cell mitogenesis, was not inhibited by levels of UVB exposure (100 J/m2) that completely inhibited the function of fLC, although exposure of cLC to UVB radiation (100 J/m2) resulted in a decrease in the level of ICAM-1 expression on most cLC and a concomitant decrease in cLC survival during a subsequent 24-h incubation. Time course studies revealed that T cells stimulated with anti-CD3 mAb in the presence of cLC became committed to proliferate 4-8 h after culture initiation, while 24-30 h of co-culture was required for irreversible T cell activation when fLC were utilized as accessory cells. In addition, paraformaldehyde (PFA)-fixed (non-viable) cLC supported anti-CD3 mAb-induced T cell proliferation, whereas PFA-fixed fLC were ineffective. We propose that cLC are functionally resistant to low doses of UVB radiation and chemical fixation because cLC express sufficient levels of the adhesion or co-stimulatory molecules [including ICAM-1 and Mac-1 (CD11b/CD18)] required to induce T cell activation. Conversely, fLC are sensitive to the effects of UVB radiation and chemical fixation because these physicochemical agents prevent acquisition of critically important surface molecules in culture.

Adhesion molecules CD11a, CD18, and ICAM-1 on human epidermal Langerhans cells serve a functional role in the activation of alloreactive T cells

Binding of antigen-presenting cells (APC) to T cells via adhesion molecules is thought to deliver accessory signals that are required for efficient T-cell activation. To determine whether Langerhans cells (LC) express relevant adhesion molecules on their surfaces, we employed two-color immunofluorescence. Human epidermal cells (EC), Ficoll-enriched for LC (greater than 10%), were incubated with monoclonal antibodies (MoAb) specific for the adhesion molecules CD11a (LFA-1 alpha), CD18 (LFA-1 beta), or ICAM-1; staining was evaluated by fluorescence microscopy. After 12 h of culture only HLA-DR+ cells (LC) expressed CD11a, CD18, and ICAM-1. As a test for the functional relevance of such adhesion molecule expression, we examined the capacity of the above MoAb to block LC stimulation of alloreactive T cells: EC were co-cultured with allogeneic peripheral blood mononuclear leukocytes (PBML) for 5 d in the presence or absence of MoAb; proliferation was measured by [3H]-thymidine uptake. MoAb against CD11a, CD18, or ICAM-1 reduced the allostimulatory capacity of LC by greater than 70%; combinations of these MoAb reduced proliferation even more (90%). We conclude that interaction of adhesion molecules on LC with ligands on T cells is required for optimal allo-antigen-dependent T-cell activation, perhaps by delivering accessory signals.

Evaluation of ATPase-positive Langerhans' cells in skin lesions of lupus erythematosus and experimentally induced inflammations

We examined the time-dependent dynamics of epidermal Langerhans' cells (LC) in human systemic lupus erythematosus (SLE), in MRL/Mp-lpr/lpr(MRL/lpr) mice, and in various experimental cutaneous inflammations, such as the Arthus reaction, dinitrochlorobenzene allergic dermatitis, and croton oil primary irritant dermatitis, in order to clarify the pathomechanisms of lupus skin lesions. The numbers of LC in untreated SLE patients with newly developed skin lesions decreased in the central lesional sites and increased significantly in the peripheral lesional sites. In MRL/lpr mice, the number of LC increased significantly in the central lesional sites during the initial stage and increased in the peripheral lesional sites and decreased in the central lesional sites 2-4 weeks after the onset of skin lesions. In contrast, with experimental cutaneous inflammations of guinea pigs, the increase in numbers of LC in the peripheral lesional sites was not significant during the time course of the reaction. These results suggest that the increased numbers of LC during the active and early stages of skin lesions in human SLE and MRL/lpr mice are closely related to the specific spontaneous development of skin lesions, unlike the dynamics of LC in experimental cutaneous inflammations.

Effect of UVB radiation on the biosynthesis of HLA-DR antigens

HLA-DR molecules on the surface of immunocompetent cells are thought to represent target structures for the immunomodulating effects of UV radiation during the induction of an immune response. We therefore investigated the effect of UVB radiation on the de novo synthesis of HLA-DR-gamma-chains in the cytoplasm and the expression of alpha- and beta-chains on the surface of the human lymphoblastoid B-cell line Raji. Raji cells were UVB irradiated before biochemical experiments were performed. Cells were then metabolically labeled or radioiodinated and detergent lysates immunoprecipitated using antibodies directed against the gamma- or the alpha- and beta-chain of the HLA-DR molecule. Over a wide dose range, UVB-irradiated Raji cells were shown to still express HLA-DR determinants on their surface and, even more importantly, to be capable of synthesizing HLA-DR-alpha, beta- and gamma-chains in a normal fashion. Despite this, the functional capacity of Raji cells was impaired in a dose-dependent manner. UV radiation thus seems to exert its immunomodulating effects primarily at a different level than the incriminated immune-response-associated antigens, which are expressed as recognition structures on the surface of immunocompetent cells.

Differential distribution of ATPase- and T6-positive cells (Langerhans cells) in the limbus and cornea of Hereford and non-Hereford cattle

Epithelial sheets from the limbus, cornea, and third eyelid of Hereford and non-Hereford cattle were examined for the presence of Langerhans cells (LC) using the membrane enzyme ATPase as a marker for LC. The aim of the study was to test the hypothesis that differences in LC density exist between the various ocular epithelia of these animals producing depressed immune surveillance in the case of Hereford cattle. The presence of LC in ocular tissues was confirmed by parallel studies which detected epithelial cells bearing T6, an antigen expressed by human LC. Studies using serial sections demonstrated that T6+ cells also reacted with an anti-human HLA-DR monoclonal antibody. The detection of T6+, DR+ and ATPase+ cells in ocular epithelium in the absence of infiltrating macrophages suggested that LC are present in these tissues. While there were no significant differences in the density of T6+ cells between non-Hereford and Hereford cattle, in the latter ATPase+ cells were significantly fewer in the lateral, medial, and upper limbus.

Stimulation of T cells by autologous mononuclear leukocytes and epidermal cells in psoriasis

Based on reports suggesting aberrant cell-mediated immunity and altered infiltration of immunocompetent cells into the skin in psoriasis, we studied the stimulation of T cells by autologous non-T mononuclear leukocytes (autologous mixed lymphocyte reaction, AMLR) and by epidermal cells isolated from lesional and clinically uninvolved skin in psoriasis (autologous mixed epidermal cell lymphocyte reaction, AMECLR). Age- and sex-matched individuals served as controls. We found that the AMLR in psoriasis (n = 11) was similar to that in healthy controls (n = 16); furthermore, cell proliferation was alike in the presence of either 5% AB-serum or autologous serum. By contrast, while the AMECLR in healthy controls (n = 9) resembled that in psoriatics employing epidermal cells from univolved skin, epidermal cells from lesional sites (n = 10) induced a significantly higher proliferation of autologous T cells in the AMECLR (P less than 0.01). We conclude that the in vitro stimulation of T cells by non-T mononuclear leukocytes is normal in psoriasis and is not regulated by autologous serum. Lesional psoriatic epidermal cells, however, are more active in stimulating autologous T cell proliferation than cells from univolved psoriatic or normal epidermis.

Antigen-presenting OKM5+ melanophages appear in human epidermis after ultraviolet radiation

Ultraviolet radiation of murine skin in vivo or epidermal cells (EC) in vitro dramatically inhibits the antigen-presenting capacity of EC in vitro and results in the inhibition of immune responses to antigen challenge. In humans, UV exposure in vivo markedly inhibits alloantigen presentation by EC in the EC-lymphocyte reaction (ELR) when EC are harvested immediately after the administration of 4 times the minimal erythema dose (4 MED), whereas EC harvested 72 h after 4 MED (UV-EC) exhibit enhanced allostimulatory capacity in the ELR. This enhanced ELR reactivity is due to the appearance, in the epidermis, of bone marrow-derived OKT6- DR+ cells which are distinct from Langerhans cells (LC) in their lack of surface OKT6 and in their ultrastructural morphology. This report focuses on the phenotype and function of T6- Dr+ UV-EC and on their relationship to known human antigen presenting cell (APC) subsets. Approximately 60% of T6- Dr+ UV-EC bore the monocyte marker defined by monoclonal antibody OKM5, but lacked determinants recognized by OKM1, Leu M1, Leu M3, Leu M4, Leu M5, and Mac1. All T6- Dr+ UV-EC bore the class II MHC antigen HLA-DQ (DC/DS), which is associated with a specialized subset of antigen-presenting monocytes capable of stimulation in the autologous mixed leukocyte reaction (AMLR). Panning of OKM5+ UV-EC resulted in a population of cells which was markedly enriched in melanophages and which exhibited potent alloantigen-presenting capacity in the ELR. Since OKM5+ T6- Dr+ UV-EC were similar to the specialized APC minor subset of OKM1- OKM5+ blood monocytes both in phenotype and in apparent phagocytic function, we examined other APC functions of UV-EC to assess the extent of this analogy. Relative to control EC (containing only LC as APC), UV-EC (containing functionally inactivated LC but many T6- Dr+ APC) induced significantly greater degrees of T-cell proliferation in the presence of either tetanus toxoid antigen or the mitogen concanavalin A. UV-EC, as well as panning-purified OKM5+ UV-EC, were also able to induce autologous T-cell proliferation in the absence of added antigen (autologous ELR), in contrast to control EC which were poor stimulators of an autologous ELR. Thus, although human EC 72 h after UV exposure are numerically and functionally depleted of LC, at least 2 additional subsets of T6- Dr+ APC appear in the epidermis.(ABSTRACT TRUNCATED AT 400 WORDS)

The ultrastructure of human gingival Langerhans cells in health and disease

There was a statistically significant shift towards increased proportions of type I Langerhans cells (containing many Langerhans-cell granules) and reduced proportions of both type II Langerhans cells (containing few granules) and indeterminate cells in diseased oral epithelium when compared to healthy oral epithelium. Langerhans cells and indeterminate cells were also seen in the sulcular epithelium of healthy and diseased specimens but never in junctional or pocket-lining epithelium.

Advances in the immunobiology of the skin. Implications for cutaneous malignancies

Recent advances in cutaneous immunobiology have led to the realization that skin is an important and unique immunologic organ. Studies on the immunobiology of skin cancers induced by ultraviolet radiation indicate that immune mechanisms can play a crucial role in the development of cutaneous tumors. This paper summarizes the evidence linking skin and the immune system and discusses current hypotheses concerning the mechanisms by which UV radiation interferes with cutaneous immunity. The significance of these findings for cutaneous carcinogenesis is discussed.

Effect of X-irradiation on epidermal immune function: decreased density and alloantigen-presenting capacity of Ia+ Langerhans cells and impaired production of epidermal cell-derived thymocyte activating factor (ETAF)

The mechanisms involved in the modulation of cutaneous immune responses by UV radiation have been extensively investigated; by contrast, few studies have addressed the effects of x-irradiation on epidermal immune function. We therefore investigated the effect of x-irradiation of mice on: (a) the density of epidermal Ia+ Langerhans cells (LC) in immunofluorescence studies, (b) epidermal cell (EC) allostimulatory capacity in the allogeneic EC-lymphocyte reaction (ELR), and (c) production of epidermal cell-derived thymocyte activating factor (ETAF). C3H/He and BALB/c mice were irradiated with 900, 1,800, 2,700, or 3,600 rad from a 137Cs source, and sacrificed 10 h or 3 days later. X-irradiation of mice 10 h previously only slightly decreased the density of epidermal Ia+ LC and did not affect the capacity of their EC to stimulate allogeneic responder lymphocytes in the ELR. X-irradiation of mice 3 days previously, however, resulted in a dose-dependent decrease in the density of Ia+ LC. This decrease was accompanied by a substantial reduction in EC allostimulatory capacity in the ELR at all doses of x-irradiation. ETAF production by cultured EC from mice x-irradiated 3 days previously was also found to be diminished at all doses of x-irradiation. Trypan blue exclusion studies demonstrated that the observed decreases in EC allostimulatory capacity and ETAF production were not the result of a generalized lethal effect of x-irradiation on EC. The reduction in EC allostimulatory capacity following in vivo x-irradiation could not be reversed by addition of exogenous ETAF or interleukin-1 in the ELR. Taken together, these results indicate that x-irradiation decreases the density of Ia+ LC, impairs LC alloantigen-presenting function, and reduces ETAF production. Thus cutaneous x-irradiation may affect inflammatory and neoplastic processes not only by its antimitotic activity, but also by a direct effect on EC which subserve immunologic functions.

A comparison of murine epidermal Langerhans cells with spleen dendritic cells

To establish if epidermal Langerhans cells (LC) are related to spleen dendritic cells, we have considered the morphology, phenotype, and function of the 2 cell types in culture. Cultured LC could be partially enriched (up to 50%) on the basis of 2 simple physical properties: nonadherence to plastic, and low buoyant density in dense albumin columns. The morphology of cultured LC and spleen dendritic cells were similar. In particular both cell types had many cell processes and/or veils, and cultured LC lost their distinguishing Birbeck granules. Freshly isolated LC exhibited nonspecific esterase and ATPase, as well as the F4/80 (alpha-macrophage) and 2.4G2 (alpha-Fc receptor) antigens. However all these traits were lost in culture, while Ia and Mac-1 antigens persisted. As a result, the cytochemical and antigenic phenotype of LC became similar to spleen dendritic cells. The one exception was that LC lacked the 33D1 dendritic cell antigen. The function of LC at first differed from spleen dendritic cells in that fresh LC were weak stimulators of T cell proliferation in the mixed leukocyte reaction and in sodium periodate-induced mitogenesis. However, stimulatory activity per cell increased at least 30 fold in culture so that by 2-3 days, LC were 3-10 times more potent than dendritic cells. Maturation of LC function was radioresistant and was accompanied by a small increase in cell surface Ia antigens. Although LC have been likened both to lymphoid dendritic cells and to macrophages, our data suggest a different conclusion. LC seem to be dendritic cell precursors and are immunologically immature. Possibly, lymphoid dendritic cells are in general derived from substantial pools of precursors in nonlymphoid tissues, such as epidermal LC.

Murine epidermal Langerhans cells mature into potent immunostimulatory dendritic cells in vitro

Murine epidermal Langerhans cells (LC) have been studied in tissue culture and compared to spleen dendritic cells (DC). LC comprised 3% of the starting cell suspensions and were distinguished from keratinocytes by cytology and reactivity with anti-Ia and anti-Mac-1 monoclonal antibodies. The LC were nonadherent, had a low buoyant density, did not proliferate, and could be enriched to 10-50% purity. LC continued to exhibit Ia and Mac-1 antigens for 4 d in culture. However, LC rapidly lost Birbeck granules, Fc receptors, F4/80 antigen, and cytochemical reactivity for nonspecific esterase and membrane ATPase. As a result, the ultrastructure and phenotype of cultured LC became remarkably similar to lymphoid DC. Stimulatory capacity for T cell proliferative responses (oxidative mitogenesis and the mixed leukocyte reaction) was monitored daily. Initially, stimulatory capacity was very weak, even though LC expressed substantial levels of Ia antigens. After 2-3 d in culture, LC had become 3-10 times more potent than spleen DC. 30 LC could induce significant responses in cultures of 3 X 10(5) responding T cells. Removal of Ia+ LC at the start of culture ablated the development of stimulatory activity, but exposure to 1,500 rad of ionizing irradiation did not. Mixing experiments showed that contaminating Ia- epidermal cells did not alter the function of Ia+ stimulators. Therefore, LC seem to be immunologically immature, but acquire many of the features of spleen DC during culture. We suggest that functioning lymphoid DC may, in general, be derived from less mature precursors located in nonlymphoid tissues.

Alteration in murine epidermal Langerhans cell population by various UV irradiations: quantitative and morphologic studies on the effects of various wavelengths of monochromatic radiation on Ia-bearing cells

The present study was undertaken in order to clarify the exact mode of the Langerhans cell (LC) depleting process caused by UV irradiation. Following irradiation with a single dose of various wavelengths of monochromatic UV radiation (UVR), we studied the number of Ia-positive cells in mouse epidermal sheets quantitatively, particularly with regard to dose-response relationship, action spectrum, and time course change. In addition, we studied morphologic alterations of these cells using electron- and immunoelectron microscopy (EM and IEM). We obtained the following results after a single dose of UVB radiation (200 mJ/cm2 of 300 nm) or PUVA (1% of 8-methoxypsoralen (8-MOP) 20 microliter and 1 J/cm2 of 360 nm): (1) EM and IEM showed that while some LCs simply lost their Ia marker without any structural alterations, the majority of the LCs disappeared due to actual cell damage. (2) During an "injury phase," the initial 48 h, and a "recovery phase," lasting from 4-14 days after irradiation, enlargement of the size of remaining Ia-positive LCs occurred. The degree of enlargement was closely related to the degree of reduction in number, suggesting a process compensating for the loss of the LC population. (3) It was found that the recovery rate of LCs after irradiation damage was slower than that of keratinocytes, indicating different cell kinetics between these distinct cell populations in the epidermis, i.e., restoration of LCs after irradiation seems to be achieved at least partially through a repopulation process originating in the bone marrow. Studies with irradiation of various monochromatic wavebands, with or without topical 8-MOP, showed that the action spectrum for Ia-positive cell depletion activity lay within the spectrum shorter than 300 nm for UVR alone, and between 320-380 nm for 8-MOP plus UVR. Since the action spectra were similar to those for keratinocyte damage, i.e., sunburn cell formation, induction of unscheduled DNA synthesis, and to those for UVR-induced erythema, we conclude that common mechanisms underlie these types of tissue damage.

Influence of ultraviolet radiation treatment on the survival of heterotopic skin grafts in the mouse

Isolated mouse tail skin was UV-irradiated in vitro at a dose of 40 mJ/cm2 from both sides to remove the Ia immunogenicity. Immediately after irradiation the skin was transplanted onto the flank of allogeneic mice. When there was a total H-2 difference between donor and recipient, the UV-irradiated skin did not show a prolonged survival compared to control grafts. In the case of an I-region difference only, i.e., B10.AQR grafts onto B10.T (6R) recipients, a significant prolongation of the survival time was observed, whereas 50% of the UV-treated grafts were not rejected at all.

Suppression of antibody responses to topically applied antigens by ultraviolet light irradiation. Induction of phototolerance

C3Hf/HeN or BALB/c mice, exposed to acute ultraviolet (UV) irradiation and skin-sensitized through the irradiated skin site with soluble protein antigens, exhibit humoral tolerance to subsequent systemic challenge with antigen. We have termed this phenomenon "phototolerance" (PT). With the doses of UV radiation used, PT induction is restricted to the irradiated skin site and is observed only if sensitization is performed via the cutaneous route. PT is antigen specific and operates at the afferent level of the immune response. While single PT induction regimens result in transient humoral suppression, multiple inductions before each systemic challenge can maintain the response at low levels. The capacity to induce PT to a variety of soluble protein antigens may have potentially important clinical applications.

Induction of hapten-specific lymphoid cell proliferation by liposome-carrying molecules from haptenated epidermal cells in contact sensitivity

Liposomes containing the extract of trinitrophenylated (TNP) epidermal cells stimulated lymph node cells from TNCB-sensitized mice effectively. Optimal stimulation was achieved by the liposome containing 0.06 microgram of the extract of TNP epidermal cells/microgram of phospholipid at a concentration of 20 micrograms phospholipid/ml. The response was hapten-specific and macrophage-dependent. UV irradiation of the epidermal cells abolished their ability to stimulate the lymph node cells. Furthermore, the liposomes containing the extract of TNP epidermal cells treated with anti-Ia and complement failed to stimulate the lymph node cells. The liposomes recovered their reactivity when nonhaptenated Ia antigen-rich epidermal extract was added. Taken together, it is likely that haptenated molecules and Ia antigen on the liposome stimulated T-lymphocytes in the presence of macrophages.

Immunological unresponsiveness induced by ultraviolet radiation

Immunological unresponsiveness can be initiated by exposure of mice to UV radiation, followed by the introduction of certain antigens. These antigens include epicutaneously applied chemicals that induce contact hypersensitivity (CHS), and antigens that occur on skin cancers induced by UV radiation. Mice exposed repeatedly to high doses of UV radiation during UV carcinogenesis develop immunological unresponsiveness to UV radiation-induced skin cancers, which are highly antigenic. This unresponsiveness is associated with the appearance of suppressor T lymphocytes that are specific for tumors induced by UV radiation, even though these tumors express individually specific transplantation rejection antigens. Thus, the occurrence of suppressor cells with specificity for a set of non-cross-reacting tumors suggests that a common, UV-associated regulatory antigen or determinant may be present on UV-induced skin cancers. Suppression of CHS in mice by UV radiation can be induced by two different procedures. One involves applying the sensitizer directly on skin exposed to low doses of UV-B radiation and is thought to result from a direct effect of UV radiation on cutaneous Langerhans cells. The second involves application of the sensitizer to the unirradiated skin of mice or guinea pigs exposed several days earlier to a higher dose of UV-B radiation. The mechanism of the latter phenomenon is not well understood, but there is evidence that it results from an alteration of antigen presentation by splenic macrophages. Both forms of suppression are associated with the appearance of antigen-specific suppressor lymphocytes in the animals' spleens, which prevent the induction of CHS upon transfer to a normal recipient. Either or both of these pathways could be responsible for the formation of the suppressor cells involved in UV carcinogenesis. Recent studies suggest that UV radiation may also affect immunological responsiveness in humans as well as in animals. However, the extent of such alterations and the mechanisms by which they occur are still unknown.

Human Langerhans cells in epidermal cell culture, in vitro skin explants and skin grafts onto "nude" mice

In order to find a model system which best preserves human Langerhans cells (LC) outside of the human body, three possibilities were examined: epidermal cell culture, skin explants, and skin grafts onto "nude" mice. Using OKT-6 and anti-HLA-DR monoclonal antibodies, we quantified LC in epidermal sheets or epidermal cell cultures. All observations were carried out over a period of 4 weeks. We found that under epidermal cell culture conditions, LC rapidly disappeared, to the extent that after 10 days only rare HLA-DR-positive cells could be observed. In contrast, in the presence of intact dermis (explants and grafts), 60%-80% of the original number of LC, morphologically unchanged, dendritic and OKT-6 and HLA-DR-positive, were seen. These findings suggest that human LC are either a long-lived cell population or else can proliferate locally. The systems studied may be a useful tool for future investigation of LC function.

In vitro effect of UV radiation on immune function and membrane markers of human Langerhans cells

Human Langerhans cells (LC) are located in the epidermal tissue which is naturally accessible to UV irradiation. They may be the first immunocompetent cells exposed to its effect. In the present study, the epidermal tissue was dissociated with trypsin, and epidermal cell (EC) suspensions, which contain keratinocytes, melanocytes, and LC were irradiated with UVB (10 or 20 mJ/cm2). After irradiation LC retained their surface determinants: T-6 and HLA-Dr. In addition, their number did not decrease during 3 days of culture following UVB exposure as compared with nonirradiated EC cultured in parallel. On the contrary, UV irradiation of EC resulted in decreased lymphocyte-stimulating ability in a mixed skin cell-lymphocyte culture reaction (MSLR). EC used directly after irradiation in MSLR induced about half the lymphocyte response compared to nonirradiated EC. After 24-h culture, the irradiated EC did not produce any lymphocyte response, whereas the 48-h cultures showed a slight lymphocyte stimulation. At 72 h the cultures from irradiated and nonirradiated EC showed similar responses in MSLR. The doses of UV radiation which decreased MSLR responses did not affect EC viability and did not significantly reduce their DNA content. It is suggested that under the experimental conditions used in this study the defect induced by UV irradiation was essentially functional and was the result of the transient inhibition of the antigen processing function of LC rather than of an alteration in membrane antigen expression (T-6 and HLA-Dr).

Prolongation of the survival of skin grafts in mice by PUVA treatment

The combined application of psoralen and UVA radiation to skin grafts induced a prolongation of the survival time of the grafts in mice. This was observed using the H-Y barrier, an allogeneic barrier without H-2 disparities, and a strong H-2 incompatible barrier. The effect is probably due to a reduction of antigen-presenting cells, or to other, unknown mechanisms.

The effect of aging and chronic sun exposure on human Langerhans cell populations

ATPase histochemistry was used to examine Langerhans cell (LC) populations in the skin of young persons with no evidence of solar damage and older adults with chronic actinically damaged skin. The number of LC was significantly decreased in the older age group. Significantly fewer LC were observed in exposed vs covered skin in the older individuals; no such disparity was noted in the younger subjects. Morphologic alterations in ATPase-positive cells were noted in some specimens, most of which were taken from the exposed skin of elderly persons. The results suggest an independent, although possibly additive, quantitative and qualitative influence of aging and chronic sun exposure on the LC population. Decreased numbers of LC in the sun-damaged skin of elderly individuals may play a critical permissive role in the development of cutaneous carcinoma.

Prolongation of skin graft survival in mice by in vitro PUVA treatment and failure of induction of specific immunological memory by PUVA-treated grafts

Treatment of murine skin grafts in vitro with 8-methoxypsoralen and longwave ultraviolet radiation prolonged their subsequent survival on allogeneic recipients, but not in cases where the recipients had been presensitized by a former skin graft of the same donor strain. In contrast to normal skin, grafts pretreated with 8-methoxypsoralen and longwave ultraviolet radiation were not able to induce an immunological memory as revealed by a second transplantation of normal skin. The results show that primary and secondary skin graft rejection can be affected by the combined action of psoralen and ultraviolet radiation.

Effect of indomethacin on alteration of ATPase-positive Langerhans cell density and cutaneous sunburn reaction induced by ultraviolet-B radiation

We have investigated the effect of ultraviolet-B (UVB) irradiation on the density of epidermal ATPase-positive Langerhans cells, and the modulation of this effect by indomethacin (IND). Depilated backs of albino guinea pigs were exposed to varying doses of UVB (10-550 mJ/cm2). Skin biopsies were taken serially. There was an UVB dose-dependent decrease in the density of dendritic epidermal Langerhans cells, as identified by their membrane ATPase activity. This was accompanied by thinning and shortening, or disappearance of dendritic processes. Such changes were followed by a gradual recovery of the cell density to preirradiation level by day 21. Despite the high doses of UVB given, the maximal decrease in the density of ATPase-positive cells was only 58%. Topical application of IND, a prostaglandin-synthetase inhibitor, after irradiation resulted in a decrease of the erythema; however, the decrease in the density of ATPase-positive cells was still observed. In contrast, guinea pigs that received IND topically prior to irradiation showed a decrease erythemal response, but failed to show any decrease in the density of ATPase-positive cells. Administration of IND orally for 3 days prior to UVB exposure did not prevent the decrease in the cell density. The protective effect of topical IND, applied prior to irradiation, may be explained by its in vitro absorbance at both the UVB and UVA ranges. Topical application of IND 20 min prior to exposure to UVB in 2 human subjects resulted in an increase in the minimal erythema dose, giving a sun protection factor of 1.6, which is comparable to that produced by an equimolar concentration of para-aminobenzoic acid solution. The sun-protective property of IND, together with its activity as a prostaglandin synthetase inhibitor, indicate that it potentially could be a useful sunscreen agent. Its clinical safety and efficacy, however, remain to be determined.