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 effects of Origanum hypericifolium essential oil application and ultraviolet B irradiation on mouse skin: An ultrastructural study

Exposure to UV radiation can cause histopathological and ultrastructural changes in the skin. Origanum hypericifolium, an endemic Turkish plant,essential oil is mainly composed of monoterpenes. The effects of undiluted O. hypericifolium oil on the ultrastructural characteristics of the UVB-irradiated dorsal skin of mice were investigated using transmission electron microscopy. The BALB/c mice were shaved of dorsal hair and randomly housed into 4 groups: 1: control; 2: UVB-irradiated; 3: oil applied; and 4: oil applied and UVB-irradiated. The oil was applied topically to the dorsal skins of the mice on alternate days for 1week prior to UVB exposure. The skins were irradiated for a total dose of 3.5J/cm(2). The sections were stained with hematoxylin and eosin, semithin sections were stained with toluidine blue and ultrathin sections were contrasted with uranyl acetate/lead citrate. There were histopathological changes such as parakeratosis and squamous hyperplasia in the epidermal cell layers (Groups 3 and 4). There were also ultrastructural changes including lacunae formations throughout the stratum corneum layer (Groups 2, 3, and 4), enlargement of intercellular spaces (Groups 2 and 3), reduced desmosomes, narrow and elongated interdigitations, shortened, relatively indistinct and electron dense intermediate keratin filament bundles (Group 3). There were various sizes of cytoplasmic and perinucleolar vacuoles (Groups 3 and 4) and apoptotic bodies phagocytized by keratinocytes (Group 4). I conclude that undiluted oil has side-effects and the potential to inflict injury to the skin. The oil does not ameliorate the negative effects of UVB on epidermal skin cells.

Bovine papillomavirus DNA can be detected in keratinocytes of equine sarcoid tumors

Bovine papillomavirus (BPV)-1 and -2 is linked to equine sarcoids, a commonly observed skin tumor in horses that is of considerable veterinary importance. Previous studies using in situ hybridization have detected BPV DNA only in fibroblasts and not in keratinocytes of sarcoids. In contrast, normal equine skin latently infected with BPV shows a dysplastic epithelium without dermal changes, similar to lesions induced by other papillomavirus types infecting the epithelium. The first goal of our study was to describe the epidermal and dermal characteristics of several stages in sarcoid development. Next, we explored whether BPV can infect epidermal cells in the horse using real-time PCR on laser-micro-dissected keratinocytes and fibroblasts. We found that latently infected normal skin samples and a subset of early stage sarcoids show dysplastic, koilocyte-like epithelial changes. BPV DNA was detected in keratinocytes in 40% of the samples with these particular epithelial properties, whereas advanced sarcoids only had BPV DNA in the fibroblasts. These data may indicate a novel and intriguing pathway of BPV infection in the horse composed of a first step of keratinocyte infection, followed by migration of viral material towards the dermis resulting in infection of sub-epidermal fibroblasts and their fully transformed phenotype. Additionally, an example of co-existence of a dermal BPV-1 and an epidermal BPV-2 infection in the same lesion is shown, indicating that horses can harbor infection with more than one BPV type at the same time.

Epidermal Langerhans cells are not required for UV-induced immunosuppression

UV light can be highly beneficial in the treatment of skin disorders such as psoriasis. It is thought to cause immunosuppression by depleting or altering the function of epidermal Langerhans cells (LC). Our previous studies identified a novel langerin(+) dendritic cell in the dermis, distinct from LC in phenotype, circulation, and function. In this study, we determined the role of LC and dermal langerin(+) cells in UV suppression. UV light suppressed the CD8 T cell response to both contact hypersensitivity and epicutaneous protein immunization, and resulted in a dramatically altered phenotype of LC. UV light did not alter early CD8 T cell activation in the lymph nodes, but rather reduced CD8 T cell expansion at later time points. We found that dermal langerin(+) cells, but not LC, were essential for the CD8 T cell response. Furthermore, in the selective absence of LC, UV light still caused suppression of both CD8 T cell expansion and contact hypersensitivity.

A critical role for the proapoptotic protein bid in ultraviolet-induced immune suppression and cutaneous apoptosis

Apoptosis plays an important role in eliminating UV-damaged keratinocytes, but its role in UV-induced immune suppression is not clear. Langerhans cells (LCs) may function as inducers of immune suppression. We have shown that LCs derived from mice deficient in the proapoptotic Bid (BH3-interacting death domain protein) gene (Bid KO) resist apoptosis and induce amplified immune responses. In this report, we examined responses in Bid KO mice to UVB exposure. Acute UV exposure led Bid KO mice to develop fewer apoptotic cells and retain a greater fraction of LCs in the epidermal layer of skin in comparison to wild-type mice. Bid KO mice were also markedly resistant to local and systemic UV tolerance induction to hapten sensitization and contact hypersensitivity responses. Elicitation responses and inflammation at skin sensitization sites in UV-treated Bid KO mice were equal to or greater than nonsuppressed control responses. In Bid KO mice, LCs accumulated in lymph nodes to greater numbers, demonstrated longer lifespans, and contained fewer DNA-damaged cells. These studies provide evidence that Bid activation is a critical upstream mediator in UV-induced keratinocyte and LC apoptosis and that its absence abrogates UV-induced immune tolerance.

DNA damage, apoptosis and langerhans cells--Activators of UV-induced immune tolerance

Solar UVR is highly mutagenic but is only partially absorbed by the outer stratum corneum of the epidermis. UVR can penetrate into the deeper layers of the epidermis, depending on melanin content, where it induces DNA damage and apoptosis in epidermal cells, including those in the germinative basal layer. The cellular decision to initiate either cellular repair or undergo apoptosis has evolved to balance the acute need to maintain skin barrier function with the long-term risk of retaining precancerous cells. Langerhans cells (LCs) are positioned suprabasally, where they may sense UV damage directly, or indirectly through recognition of apoptotic vesicles and soluble mediators derived from surrounding keratinocytes. Apoptotic vesicles will contain UV-induced altered proteins that may be presented to the immune system as foreign. The observation that UVR induces immune tolerance to skin-associated antigens suggests that this photodamage response has evolved to preserve the skin barrier by protecting it from autoimmune attack. LC involvement in this process is not clear and controversial. We will highlight some basic concepts of photobiology and review recent advances pertaining to UV-induced DNA damage, apoptosis regulation, novel immunomodulatory mechanisms and the role of LCs in generating antigen-specific regulatory T cells.

Decrease in Langerhans Cells and Increase in Lymph Node Dendritic Cells Following Chronic Exposure of Mice to Suberythemal Doses of Solar Simulated Radiation

Exposure of certain strains of mice to ultraviolet radiation (UVR) causes suppression of some innate and adaptive immune responses. One such consequence of acute UVB exposure is a reduction in the number of Langerhans cells (LC) in the epidermis and an increase in dendritic cells (DC) in lymph nodes draining the irradiated skin sites. Exposure to chronic UVB irradiation also has effects on the immune system, but it is unknown what effects are caused by repeated doses of solar simulated radiation (SSR). Consequently, the main aims of the present study were to determine whether repeated exposure to low doses of SSR would lead to similar changes in these cell populations and whether chronic doses of SSR activate a protective photoadaptation mechanism. Groups of C3H/HeN mice were irradiated daily with 3.7 J/cm(2) SSR from Cleo Natural lamps for 2, 10, 20, 30 or 60 days. Further groups of mice received an additional dose of 7.4 J/cm(2) SSR on days 2, 10, 30 or 60 to test for photoadaptation. The numbers of LC in the epidermis and DC in the lymph nodes draining irradiated skin sites were counted 24 h after the final irradiation. With the exception of mice irradiated for only 2 days, LC were significantly reduced throughout the chronic irradiation protocol, and no recovery occurred. DC numbers were significantly increased in the draining lymph nodes of mice irradiated for 20 days and 60 days.

Alterations in human epidermal Langerhans cells by ultraviolet radiation: quantitative and morphological study

BACKGROUND

Ultraviolet (UV) exposure of human skin induces local and systemic immune suppression. This phenomenon has been well documented when UVB radiation (290-320 nm) is used. The mechanism is thought to involve Langerhans cells (LCs), the epidermal dendritic cells that play a crucial role in antigen presentation. A variety of studies have clearly demonstrated that UVB radiation decreases LC density and alters their morphology and immunological function, but little is known about the effects of the entire UV spectrum (ultraviolet solar simulated radiation, UV-SSR or UVB + UVA) or UVA (320-400 nm) radiation alone.

OBJECTIVES

The purpose of this study was to analyse and compare the effects of a single exposure of human volunteers to UV-SSR, total UVA or UVA1 (340-400 nm) in the human epidermal LC density and morphology.

METHODS

Immunohistochemistry on epidermal sheets with various antibodies and transmission electron microscopy (TEM) were used.

RESULTS

Immunostaining for class II antigen revealed that a single UV-SSR exposure, corresponding to twice the minimal erythemal dose (MED), induced a significant reduction in LC density with only slight morphological alterations of remaining cells. After a single UVA exposure, LC density showed a dose-dependent reduction with a significant effect at 60 J cm(-2) (well above the MED). Moreover, the reduction of LC dendricity was also dose-dependent and significant for doses exceeding 30 J cm(-2). UVA1 radiation was as effective as total UVA for the later endpoint. As demonstrated by TEM, the location of Birbeck granules containing epidermal cells was modified in UVA-exposed areas. They were located in the spinous rather than in the suprabasal layer. In addition, the morphology of these cells was altered. We observed a rounding up of the cell body with a reduction of dendricity. Alterations of mitochondrial membrane and ridges were also seen.

CONCLUSIONS

A single exposure of human skin in vivo to UV-SSR, UVA or UVA1 radiation results in different alterations of density and/or morphology of LCs. All these alterations may impair the antigen-presenting function of LCs leading to an alteration of immune response.

UV doses of American children and adolescents

The ultraviolet (UV) doses of American young adults were never measured, but are needed for assessing UV-related health risks. These doses were calculated using a novel approach. The National Human Activity Pattern Survey recorded the daily minute-by-minute activities of about 2000 young adults (0-19 years) over the course of 2 years to assess their exposure to environmental pollutants. From that survey, only the outdoor daylight data of northern and southern girls and boys were extracted and stratified by season and age to find the time American children (0-5 and 6-12 years) and adolescents (13-19 years) spend outside. They spend about 10% of the day outdoors, but only get about 30% of the available terrestrial UV radiation (on a horizontal plane). American children have about the same percent personal ambients as adults (3.1%), 2.8% for girls and 3.4% for boys. Adolescents have the lowest personal ambients (2.6%), 2.1% for girls and 3.1% for boys. To get their UV doses, their percent ambients are multiplied by the total available terrestrial UV. Excluding vacation, the erythemally weighted UV doses for American children are 25 kJ/m2/year, 23 for girls and 28 for boys. Adolescents get the lowest UV exposure of any group, 21 kJ/m2/year, 18 for girls and 24 for boys. Young adult northern girls get 18 kJ/m2/year and boys get 21 kJ/m2/year, whereas southern girls get 24 kJ/m2/year and boys get 31 kJ/m2/year. The youngest children (0-5 years) get slightly higher summer doses. Thus, we can now assess the UV-related health risks for American children and adolescents.

Ultraviolet light induced injury: immunological and inflammatory effects

This article reviews many of the complex events that occur after cutaneous ultraviolet (UV) exposure. The inflammatory changes of acute exposure of the skin include erythema (sunburn), the production of inflammatory mediators, alteration of vascular responses and an inflammatory cell infiltrate. Damage to proteins and DNA accumulates within skin cells and characteristic morphological changes occur in keratinocytes and other skin cells. When a cell becomes damaged irreparably by UV exposure, cell death follows via apoptotic mechanisms. Alterations in cutaneous and systemic immunity occur as a result of the UV-induced inflammation and damage, including changes in the production of cytokines by keratinocytes and other skin-associated cells, alteration of adhesion molecule expression and the loss of APC function within the skin. These changes lead to the generation of suppressor T cells, the induction of antigen-specific immunosuppression and a lowering of cell-mediated immunity. These events impair the immune system's capacity to reject highly antigenic skin cancers. This review gives an overview of the acute inflammatory and immunological events associated with cutaneous UV exposure, which are important to consider before dealing with the complex interactions that occur with chronic UV exposure, leading to photocarcinogenesis.

Migration of Langerhans cells and gammadelta dendritic cells from UV-B-irradiated sheep skin

Depletion of dendritic cells from UV-B-irradiated sheep skin was investigated by monitoring migration of these cells towards regional lymph nodes. By creating and cannulating pseudoafferent lymphatic vessels draining a defined region of skin, migrating cells were collected and enumerated throughout the response to UV-B irradiation. In the present study, the effects of exposing sheep flank skin to UV-B radiation clearly demonstrated a dose-dependent increase in the migration of Langerhans cells (LC) from the UV-B-exposed area to the draining lymph node. The range of UV-B doses assessed in this study included 2.7 kJ/m2, a suberythemal dose; 8 kJ/m2, 1 minimal erythemal dose (MED); 20.1 kJ/m2; 40.2 kJ/m2; and 80.4 kJ/m2, 10 MED. The LC were the cells most sensitive to UV-B treatment, with exposure to 8 kJ/m2 or greater reproducibly causing a significant increase in migration. Migration of gammadelta+ dendritic cells (gammadelta+ DC) from irradiated skin was also triggered by exposure to UV-B radiation, but dose dependency was not evident within the range of UV-B doses examined. This, in conjunction with the lack of any consistent correlation between either the timing or magnitude of migration peaks of these two cell types, suggests that different mechanisms govern the egress of LC and gammadelta+ DC from the skin. It is concluded that the depression of normal immune function in the skin after exposure to erythemal doses of UV-B radiation is associated with changes in the migration patterns of epidermal dendritic cells to local lymph nodes.

Differential effects of UVA1 and UVB radiation on Langerhans cell migration in mice

The UVB (280-315 nm)- and UVA1 (340-400 nm)-induced migration of Langerhans cells (LC) from the epidermis and accumulation of dendritic cells (DC) in the lymph nodes draining the exposed skin site of C3H/HeN mice have been investigated. One minimum erythemal dose (MED) of UVB (1.5 kJ/m2) and of UVA1 (500 kJ/m2) were chosen, which have been shown previously to suppress delayed hypersensitivity (DTH). UVB irradiation resulted in a reduction in epidermal LC numbers, local to the site of the exposure, which was most apparent 12 h after exposure, but, in contrast, UVA1 had no significant effect even at 72 h after exposure. UVA1 did not exert any protection against the UVB-mediated depletion in LC numbers. The reduction in local LC following UVB exposure was prevented by systemic (intraperitoneal) treatment of mice with neutralising antibodies to either tumor necrosis factor (TNF)-alpha or interleukin (IL)-beta 2 h prior to the irradiation. It has been reported previously that UVB exposure caused an increase in the number of dendritic cells (DC) in the lymph nodes draining the irradiated skin site. In the present study we have shown that UVA1 had a similar effect. Pretreatment of the mice with neutralising antibodies to IL-1beta (by intraperitoneal injection) substantially inhibited DC accumulation induced by both UV regimens. However, anti-TNF-alpha antibodies affected only the UVB-induced increase, and did not alter the elevation in DC numbers observed following UVA1 exposure. These results indicate that UVB causes the migration of LC from the epidermis and an accumulation of DC in the draining lymph nodes by a mechanism that requires both TNF-alpha and IL-1beta. In contrast, UVAI does not cause LC migration from the epidermis and the accumulation of DC in the draining lymph nodes observed following UVA1 exposure requires IL-1beta, but not TNF-alpha. It is likely therefore that UVA1 acts through a different mechanism from UVB and may target a cutaneous antigen presenting cell other than LC, such as the dermal DC.

Differential Modulation of Human Epidermal Langerhans Cell Maturation by Ultraviolet B Radiation

UVB irradiation of the skin causes immunosuppression and Ag-specific tolerance in which Langerhans cells (LC) are involved. We tested the effect of UVB on LC that had migrated out of cultured epidermal sheets derived from the skin that was irradiated ex vivo (200, 400, 800, or 1600 J/m2). Two separate subpopulations of LC were distinguished: large-sized LC with high HLA-DR expression, and HLA-DR-low, small LC. UVB stimulated the maturation of the former LC subset as demonstrated by enhanced up-regulation of CD80, CD86, CD54, CD40, and CD83 and reduced CD1a expression in comparison with unirradiated controls. In contrast, the latter LC exhibited little or no up-regulation of these molecules except for high CD1a expression and high binding of annexin V, indicating that they were apoptotic, although their CD95 expression was relatively low. Stimulation of enriched LC with CD40 ligand-transfected cells and IFN-γ revealed that the release of IL-1β, IL-6, IL-8, and TNF-α was enhanced by UVB. In comparison with HLA-DR-low LC, HLA-DR-high LC were the principal IL-8 producers as demonstrated by intracellular cytokine staining, and they retained more accessory function. There was no detectable secretion of IL-12 p70, and IL-18 production was neither affected by any stimulus nor by UVB. These results suggest a dual action of UVB on LC when irradiated in situ: 1) immunosuppression by preventing maturation and inducing apoptotic cell death in part of LC, and 2) immunopotentiation by enhancing the up-regulation of costimulatory molecules and the production of proinflammatory cytokines in another part.

Comparative immunotoxicology of ultraviolet B exposure I. Effects of in vitro and in situ ultraviolet B exposure on the functional activity and morphology of Langerhans cells in the skin of different species

Ultraviolet (UV) B-induced morphological and functional changes in the skin of mice, rats and humans were investigated. Changes in the morphological structure of Langerhans cells (LC), the major antigen-presenting cells in the skin, using confocal laser scanning microscopy, were found in mouse and rat skin after in situ exposure to high doses of UVB radiation (FS40) (3-9 kJ/m2). Similar UVB doses failed to induce alterations in the morphological structure of human LC. Alterations in the function of epidermal cells (especially LC) were studied, using the mixed skin lymphocyte response (MSLR). In vitro UVB exposure of epidermal cells (EC), derived from the skin of the different species, revealed that low doses of UVB radiation impaired the stimulatory capacity of these cells dose-dependently; mouse epidermal cells were most UVB-susceptible, while human cells were least UVB susceptible. For suppression of the stimulatory capacity of EC after in situ UVB exposure of skin tissue, higher doses of UVB radiation than the in vitro UVB exposure were needed in all species tested. Also in this in situ set-up mouse epidermal cells were most UVB-susceptible, and human epidermal cells were least UVB-susceptible. The magnitude of differences in susceptibility for UVB-induced changes in the stimulatory capacity of EC after in situ and after in vitro exposure experiments was similar. Firstly, it may be concluded that UVB impairs the functional activity of LC at a lower dose than that which alters the morphology of these cells. Secondly, it is clear that epidermal cells, especially LC, from the skin of rodents are more susceptible to UVB than epidermal cells derived from human skin. It is important to account for these differences in susceptibility when data on the effects of UVB radiation on the immune system in rodents are extrapolated to humans.

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.

Modulation of HLA-DR and CD1a expression on human cornea with low-dose UVB irradiation

PURPOSE

To evaluate the effects of low-dose UVB irradiation of HLA and CD1a expression and the toxic effects of UVB on human corneas.

METHODS

24 pairs of human corneas from 24 donors were studied. One cornea from each pair was randomly irradiated with UVB (100 mJ/cm2) after enucleation. All corneas were then organ-cultured for 2, 7, 14 or 21 days. Endothelium was studied after enucleation and organ culture. Following preservation, corneas were evaluated by means of light microscopy, morphometry and TEM. HLA and CD1a staining was performed using an immuno-alkaline-phosphatase technique.

RESULTS

Endothelial cell loss during organ culture averaged 9.1% in the UVB group and 9.2% in the control group (NS). The number of rosette and reformation figures (p = 0.004) and the coefficient of variation (p = 0.014) were higher in the control group. Epithelial sloughing was more accentuated in the UVB group. We observed the same moderate ultrastructural injuries in both groups. In the epithelium, the average number of HLA-DR+ cells per field was 0.12 in the UVB group and 0.42 in the control group (p = 0.035). In the stroma, these figures were respectively 1.04 and 1.34 (p = 0.026). In the epithelium, the average number of CD1a + cells was respectively 0. 025 and 0.078 (p = 0.019). In the preservation mediums, the average percentage of CD1a + cells was 0.07% in the UVB group and 0.27% in the control group (p = 0.014).

CONCLUSIONS

Low-dose UVB (100 mJ/cm2) decreases HLA-DR and CD1a expression of organ-cultured human corneas and induces moderate corneal injuries. Low-dose UVB might be useful for preventing allograft rejection.

Cells with UV-specific DNA damage are present in murine lymph nodes after in vivo UV irradiation

Ultraviolet radiation is absorbed in the skin, especially in the epidermis. After ultraviolet irradiation the number of major histocompatibility complex class II+, adenosine triphosphatase+ Langerhans cells and Thy-1+ dendritic epidermal cells in the epidermis decreases. Whether this decrease is due to migration of these cells or to loss of membrane markers is not clear. To address this question we have used the monoclonal antibody H3 directed against cyclobutyl thymine dimers-a form of DNA damage that is specifically induced by ultraviolet radiation-to investigate whether H3+ cells are present in the draining lymph nodes of the skin after ultraviolet irradiation of hairless, inbred mice (HRA/Skh). After a single dose of ultraviolet radiation (Westinghouse FS40, 1.5 kJ/m2), H3+ cells were present in the paracortex of the draining lymph nodes. No positive cells were found in the blood of irradiated mice. These results suggest that the H3+ cells in the lymph nodes originate from the skin. The number of H3+ cells in the draining lymph nodes increased the first 24 h after irradiation and then stabilized. Immunohistochemical double staining revealed that all H3+ cells were major histocompatibility complex II+, and that only a fraction of the cells were NLDC-145 positive. No V gamma 3 T-cell receptor bearing cells could be found in the lymph nodes after UV irradiation of the skin.

Morphological and quantitative analyses of normal epidermal Langerhans cells using confocal scanning laser microscopy

Confocal scanning laser microscopy (CSLM), when used in conjunction with computerized image processing systems, provides a powerful tool for morphological and quantitative analyses of biological tissues. In this study, normal human epidermal sheets were stained by an indirect immunofluorescence method using anti-CD1a monoclonal antibody. Positively stained epidermal Langerhans cells (LCs) were visualized using the Bio-Rad MRC-600 Confocal Imaging System. Images obtained from the confocal microscope were volumetrically rendered and quantitatively analysed using ANALYZE (Version 4.0) running on a Sun SPARC 2 Workstation. Normal epidermal LCs were shown to be large disc-like structures with five to nine long dendritic processes per cell, orientated with their flat surfaces parallel to the skin surface. LCs form a monolayer network of cells distributed evenly throughout the suprabasal layers of the epidermis, with no direct physical contact between dendritic processes. Mean LC density was estimated to be 582 per mm2 (95% confidence intervals, CI = 233-940), and mean cell volume was 612 microns3 (95% CI = 257-1020). LCs in sun-exposed sites were significantly lower in mean cell density, but larger in mean cell volume, than in covered sites. Mean surface area projected by LCs was estimated to be 26.8% (95% CI = 18.9-34.2), and this value did not show significant regional or individual variation. Our data support the notion that epidermal LCs are organized in such a way as to maximize their surface area for efficient trapping of antigens, and a reduction in LC density per unit area in sun-exposed sites is compensated for by an increase in the mean cell volume.

Effect of storage and ultraviolet B irradiation on CD14-bearing antigen-presenting cells (monocytes) in platelet concentrates

BACKGROUND

Ultraviolet B (UVB) irradiation of platelet concentrate (PCs) reduces platelet alloimmunization, but the mechanism of the effect is unclear. Evidence suggests that UVB may downregulate the expression of surface adhesion molecules on passenger antigen-presenting cells in PCs.

STUDY DESIGN AND METHODS

The effect of blood bank storage, platelet preparation from whole blood, and UVB irradiation on the quantitative expression of intercellular adhesion molecule-1 (ICAM-1, or CD54), HLA-DR, CD45, and CD11c on CD14-positive antigen-presenting cells (monocytes) was studied by using two-color flow cytometry.

RESULTS

Blood bank storage for 4 days resulted in upregulation of ICAM-1 and HLA-DR and downregulation of CD14 but left the expression of CD11c and CD45 unchanged. Preparation of PCs from fresh whole blood was associated with a rapid increase in CD11c without upregulation of ICAM-1 and HLA-DR. UVB irradiation before storage inhibited the upregulation of ICAM-1 and HLA-DR, resulted in accelerated downregulation of CD14, and was associated with increased loss of monocytes. Agitation of the PC bag during irradiation was of critical importance, since omission of agitation resulted in largely uninhibited upregulation of ICAM-1 but was still associated with significantly higher cell loss than that seen in unirradiated controls.

CONCLUSION

UVB exposure nonspecifically affects monocytes in PCs, resulting in downregulation of surface molecules that are important for antigen presentation, as well as in significant cell loss.

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.

Immunopathological study on equine insect hypersensitivity ("kasen") in Japan

Equine "kasen" is a chronic dermatitis that occurs especially during the summer months. In the present study, skin lesions of kasen that were collected by biopsy from May to October were classified histopathologically into three stages: initial (Group I, 30 cases), developing (Group II, 48 cases) and regressing (Group III, 13 cases). The characteristic lesions were hyperkeratosis, an increase in the number of T-lymphocytes and Langerhans cells (positive for class II MHC) at the epidermo-dermal junction, oedema of the dermis and perivascular infiltration of eosinophils and mast cells. Ultrastructurally, numerous Birbeck granules were observed in the cytoplasm of Langerhans cells. These lesions were striking in Group II and less so in Group III. Kasen is therefore considered to be similar to Queensland itch and sweet itch as described in Australia and Britain, respectively. The histological features were characteristic of a type I and type IV allergic dermatitis.

Neutrophils, differentiated macrophages, and monocyte/macrophage antigen presenting cells infiltrate murine epidermis after UV injury

We asked whether, as in humans, a population of antigen-presenting macrophages infiltrates the epidermis of ultraviolet (UV)-exposed BALB/c mice. Using three-color flow cytometry on cell suspensions plus in situ immunofluorescence microscopy, the phenotype of normal Langerhans cells was class II major histocompatibility complex (MHC+), CD11b+, NLDC-145+, BM8+ CD45+ and homogeneous. By contrast, in epidermal cells harvested 3 d following UV (UV-EC), there were two subsets of class II MHC+ cells: 1) class II MHChi CD11b+, and 2) class II MHClo CD11b-. Neither expressed the Langerhans cell markers BM8 and NLDC-145. In addition, there were two major populations of class II MHC- CD11b+ cells; half of these expressed the GR-1 neutrophil marker. Langerhans and dendritic epidermal T cells were markedly reduced after UV injury. By electron microscopy, immunomagnetic bead-purified CD11b+ cells in UV-EC were comprised of neutrophils, differentiated macrophages, and mononuclear cells with prominent lysosomes, but no Birbeck granules; the class II MHC+ subset resembled a monocytic cell in between differentiated macrophages and indeterminate dendritic cells. Functionally, immediately following in vivo UV exposure, the allogeneic antigen-presenting cell capacity of UV-EC was reduced to 21 +/- 6% of control epidermal cells (C-EC); by 3 d, antigen-presenting cell activity of UV-EC had recovered to 59 +/- 11% of C-EC, although at this time NLDC-145+ Langerhans cells had reached their lowest number. The recovered antigen-presenting cell activity was critically dependent upon the class II MHChiCD11b+ cells. Sensitization of BALB/c mice through skin that contained these antigen-presenting cells (3 d after UV) resulted in tolerance to dinitrofluorobenzene. By contrast, sensitization through UV-exposed skin immediately after the exposure resulted in unresponsiveness without tolerance, demonstrating temporal association of tolerance with leukocytic infiltration. In summary, murine epidermis responds to an acute UV injury in vivo with an initial abrogation of antigen-presenting activity followed by epidermal infiltration with neutrophils, differentiated macrophages, and monocytic antigen-presenting cells that are distinct from Langerhans cells with regard to expression of Langerhans cell markers and ultrastructure.

Effects of Ultraviolet Radiation on Murine Epidermal Langerhans Cells: Doses of Ultraviolet Radiation that Modulate ICAM-1 (CD54) Expression and Inhibit Langerhans Cell Function Cause Delayed Cytotoxicity In Vitro

Low doses (100 J/m2) of ultraviolet B (UVB) radiation from sunlamp fluorescent FS20 tubes inhibit the ability of freshly isolated murine epidermal Langerhans cells (LC) to support anti-CD3 MoAb-induced T-cell mitogenesis and selectively inhibit the upregulation of ICAM-1 expression by LC without causing appreciable cytotoxicity in short-term (less than or equal to 24 h) incubations (J Immunol 146:3347-3355, 1991). In the present study, epidermal cells (EC) were exposed to UVB radiation or were sham-irradiated and cultured for 24, 48, or 72 h when LC were recovered, enumerated, and assayed for simultaneous expression of I-A antigens and ICAM-1 by flow cytometry. UVB-irradiated LC that had been cultured for 24 h exhibited levels of I-A antigens comparable to those on unirradiated LC but expressed substantially less ICAM-1. After 48 and 72 h, cultured UVB-irradiated LC expressed somewhat lower levels of I-A antigens and markedly less ICAM-1 than unirradiated controls. Although similar numbers of LC were recovered from cultures initiated with UVB-irradiated and unirradiated epidermal cells after 24 h, far fewer identifiable LC were recovered from cultures seeded with irradiated cells at 48 and 72 h (approximately 50 and approximately 10% of control, respectively). The effect of UVB radiation on the survival of LC in vitro was not reversible with exogenous TNF alpha (125 U/ml) alone or granulocyte/macrophage colony-stimulating factor (5 ng/ml) and IL-1 (50 U/ml) in combination, although these cytokines had modest effects on the expression of I-A antigens and ICAM-1 by cultured UVB-irradiated LC. Results of survival studies performed with enriched LC preparations demonstrated that UVB radiation was clearly cytotoxic for LC and did not merely downregulate surface expression of I-A antigens or alter LC buoyant density. Exposure of LC to radiation from blacklight fluorescent (UVA) tubes (0.25 J/cm2) in the presence of 8-methoxypsoralen (1 micrograms/ml; PUVA) or monochromatic UVC radiation (20 J/m2) also inhibited LC accessory cell function. Results of survival studies performed with EC that had been exposed to PUVA or UVC radiation before culture were similar to those of studies performed with UVB-irradiated cells, although PUVA- and UVC-induced LC cytotoxicity was much more pronounced 48 h after culture initiation than UVB-induced cytotoxicity. UVA radiation alone augmented LC recovery at 24 and 48 h, but did not influence I-A antigen or ICAM-1 expression.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Langerhans' cells in equine cutaneous papillomas and normal skin

Langerhans' cells (LC) were investigated immunohistochemically and electron microscopically in normal equine epidermis and 133 equine cutaneous papillomas experimentally induced in five 2-year-old Thoroughbred horses. Class II major histocompatibility complex antigen-positive dendritic LC were found in the normal epidermis and ultrastructurally had the characteristic Birbeck's granules. In the developing phase of the papillomas, LC were significantly decreased in number and size, indicative of a hypofunctional state. In the regressing phase of the papillomas, LC were markedly increased in number, especially at the epidermis-dermis junction. LC with long dendrites were rich in cytoplasm with well-developed cytoplasmic organelles, including Golgi apparatus, lysosomes, Birbeck's granules, and multivesicular bodies. These LC were hyperfunctional. An infiltration of many T lymphocytes was also observed at the epidermis-dermis junction.

Langerhans cell depletion in gliotoxin-treated murine epidermis

Langerhans cells (LC) are dendritic antigen presenting cells of bone marrow origin which reside in the suprabasal layer of the epidermis. They express high concentrations of Class II MHC glycoproteins on their plasma membrane and transport cutaneous antigen to local lymph nodes for presentation to helper T cells. They are thus essential for the induction of cutaneous immunity. Gliotoxin is a member of the epipolythiodioxopiperazine (ETP) group of fungal metabolites, derived from the human pathogen Aspergillus fumigatus. It has been shown to have immunomodulating properties in vivo and in vitro, and has been proposed as a potential immunosuppressant for transplantation therapy. Epicutaneous application of gliotoxin reduced the numbers of epidermal LC by 30-35 per cent with an associated morphological change from highly dendritic to a more rounded form. Electron microscopic studies showed selective damage to LC at very low (nM) concentrations of gliotoxin, with no obvious effect on adjacent keratinocytes. LC numbers remained depleted for 13 weeks after initial treatment, suggesting that systemic suppression or prolonged retention of gliotoxin within the skin may play a role in its mechanism of action.

Immunomodulation of vascular endothelium. 1. Ultrastructural changes following ultraviolet B irradiation of peripheral veins

Immunologic function of endothelial cells is especially important in consideration of vein allografting for arterial reconstruction and in organ allotransplantation. Ultraviolet B radiation (UVB) has previously been shown to modulate graft immunogenicity, and to alter cell surface receptor function. In this study, superficial epigastric veins were UVB irradiated with 10, 24, 40, 80, and 150 mJ/cm2 while control veins were not irradiated; all specimens were examined for endothelial ultrastructural changes. Veins were perfuse-fixed at 1, 3, 7, 14, and 28 days after irradiation, and were evaluated by transmission electron microscopy and scanning electron microscopy. Control veins had a normal appearing endothelial lining, composed of elongated, attenuated endothelial cells. Veins irradiated with more than 24 mJ/cm2 displayed injured endothelial cells characterized by altered microvilli, defects in the cell surface, and a change in cell shape. The degree of cell damage correlated closely with increasing UVB dose. At doses of 80 mJ/cm2 or greater there was moderate to severe endothelial cell separation from the underlying basement membrane and an increase in cellular lysosomes. The effects of UVB were maximal at 3 days with virtual recovery in resurfacing of all specimens with endothelium 28 days after irradiation. These data suggest that UVB has a dose-dependent effect on venous endothelium that is morphologically reversible with time. Cell membrane changes seen following exposure to UVB may contribute to altered cell surface receptor function.

Effect of psoralens and ultraviolet radiation on murine dendritic epidermal cells

Monofunctional psoralens produce less phototoxicity than bifunctional psoralens after ultraviolet A (UVA) irradiation. We investigated the effect of repetitive treatments with angelicin (isopsoralen), a monofunctional psoralen, plus UVA radiation (IPUVA) on the number and morphology of dendritic epidermal cells (dEC). This effect was compared with that of 8-methoxypsoralen plus UVA radiation (PUVA), UVA alone, and UVB radiation. C3H/HeN mice were treated topically with the drugs three times/wk for 4 consecutive wk; followed each time by 1 or 2.5 J/cm2 of UVA radiation. Other groups of mice were treated with the drugs alone, UVA alone, or 0.81 J/cm2 of UVB. Epidermal sheets were stained for ATPase, Ia, and Thy-1 markers. Mice treated with PUVA and UVB exhibited severe phototoxicity, whereas no overt phototoxicity was observed in mice treated with IPUVA, UVA alone, or the drugs alone. Early during the PUVA and UVA treatments the ATPase marker was lost from dEC, followed by loss of the Ia marker; the Ia marker was lost before the ATPase marker from dEC in animals treated with IPUVA. At the end of the treatment, however, nearly total depletion of ATPase+, Ia+, and Thy-1+ dEC was observed in mice treated with PUVA and IPUVA. UVB radiation caused rapid depletion of Thy-1+ dEC as well as ATPase+ and Ia+ cells. During treatments with IPUVA, PUVA, UVA, and UVB, the Langerhans cells became rounded and lost their dendrites. These changes were quantitated by image analysis. We conclude that alterations of cutaneous immune cells can occur in the absence of overt phototoxicity, and that monofunctional and bifunctional psoralens plus low dose of UVA radiation may have different effects on dEC markers.

Differential effects of benzo[a]pyrene and dimethylbenz[a]-anthracene on Langerhans cell distribution and contact sensitization in murine epidermis

The exposure of murine skin to potent chemical carcinogens induced distinctive effects on the distribution of epidermal Langerhans cells (LC). Our previous finding that weekly applications of 7,12-dimethylbenz[a]anthracene deplete the numbers of adenosine triphosphatase (ATPase)-positive LC was extended to show that LC are also depleted on Ia and beta-glucuronidase staining. In contrast, application of the tobacco-derived carcinogen, benzo[a]pyrene (BP), caused a significant increase in Ia-positive LC density within 2 weeks and elevated levels were maintained for up to 6 months with continuous treatment. The tobacco-derived cocarcinogenic agent, catechol, also enhanced the numbers of epidermal LC. The LC in carcinogen treated epidermis were morphologically abnormal; after BP and catechol treatment LC appeared smaller with shorter dendrites, whereas in DMBA treated epidermis LC were enlarged with elongated dendrites. Application of the contact sensitizing agent, dinitrofluorobenzene, to skin treated with BP induced hyporesponsiveness rather than contact sensitivity upon subsequent antigen challenge. Hence, the function of the large number of morphologically altered LC in BP treated skin was impaired. We conclude that carcinogen-induced alterations of LC are associated with impaired immunocompetence, although different carcinogens probably operate via different mechanisms to induce such phenomena.

Dose response and time course for induction of T6- DR+ human epidermal antigen-presenting cells by in vivo ultraviolet A, B, and C irradiation

In vivo ultraviolet (UV) exposure of human skin abrogates the antigen-presenting function of T6+ DR+ Langerhans cells and induces the appearance of antigen-presenting T6- DR+ epidermal melanophages. UV-exposed epidermal cells containing T6- DR+ epidermal antigen-presenting cells, in contrast to unexposed epidermal cells containing T6+ DR+ Langerhans cells, potently activate autoreactive regulatory T cells in the absence of exogenous antigens. Autoreactive T cells may be important for regulation of other immune responses such as those which occur in photosensitive lupus erythematosus and in immune surveillance of UV-induced skin cancers. It is therefore imperative to determine the factors that govern their appearance in the skin. It was found that UVB and UVC, but not UVA, induced a dose-dependent appearance of T6- DR+ epidermal melanophages. The optimal time of appearance was 2 or 3 days after UVB and UVC exposure. In contrast, UVA was a poor inducer of T6- DR+ cells at all doses and all time points tested. Although UVA was a poor inducer of T6- DR+ epidermal cells, UVA radiation resulted in depletion of T6+ DR+ Langerhans cells from the epidermis, as did UVB and UVC radiation. This differential effect of UV wave bands on the immunocompetent cells in human skin may be related to the greater potential of UVB exposure to induce skin cancers and to exacerbate systemic lupus erythematosus.

Effects of low or high doses of short wavelength ultraviolet light (UVB) on Langerhans cells and skin allograft survival

Since Langerhans cells (LC) are normally the only cells within the epidermis to express the class II major histocompatibility complex (MHC) transplantation antigens, depletion of LC could be expected to prolong skin allograft survival by reducing the antigenic disparity between host and recipient. To assess this hypothesis, donor C57BL mouse shaved dorsal trunk or tail skin was exposed to high (200 mJ/cm2) or low (40 mJ/cm2) doses of short wavelength ultraviolet light (UVB) before grafting on to the thorax of BALB/c mouse recipients of the same sex. These strains have different major and minor transplantation antigens. The effects of UVB treatments on LC were determined by electronmicroscopy. Skin grafted 1-14 days following a single high dose of UVB irradiation was ultrastructurally depleted of LC and survived significantly longer than unirradiated skin before being rejected. After a 21-day interval between exposure and grafting when LC were again present in the epidermis there was no significant difference between treated and control graft survival. Exposure to low dose UVB irradiation only significantly increased graft survival for skin transplanted 1-3 days after irradiation; skin grafted 4 days following irradiation survived for a similar period to unirradiated control skin grafts. Electronmicroscopy showed that the low UVB dose did not deplete LC from the epidermis. We conclude that after low dose UVB treatment the class II MHC antigens on the LC plasma membrane were lost temporarily, thus prolonging graft survival, but when the plasma membrane antigens were re-expressed graft survival returned to normal.(ABSTRACT TRUNCATED AT 250 WORDS)

UVB and UVC, but not UVA, potently induce the appearance of T6- DR+ antigen-presenting cells in human epidermis

Non-Langerhans cell, antigen-presenting T6- DR+ epidermal cells (EC) appear 3 days following broad band ultraviolet radiation exposure of human skin and are responsible for the increased antigen presentation capacity of EC seen 3 days after UV exposure. To determine the UV wavelengths that induce T6- DR+ EC, volar forearm skin of 10 human volunteers was irradiated in vivo with 4 minimal erythema doses (MED) each of pure UVA (mean 482 J cm-2), UVB (mean 0.390 J cm-2), and UVC (mean 0.397 J cm-2). The purity of the light sources was as follows: UVB, 98% of the emission was in the UVB range; UVC, 97% of the irradiance was in the UVC range; UVA, 100% of the energy had wavelengths longer than 340 nm. Three days after UV irradiation with 4 MED of each wavelength band, suction blister-derived EC suspensions were prepared from the UV-exposed and unirradiated sites. Percentages of T6+ DR+ Langerhans cells (LC) and T6- DR+ EC were quantitated. Relative to control EC, which contained 2.4 +/- 0.3% T6+ DR+ LC, the mean percentage (+/- SEM) of T6+ DR+ LC contained within UV-exposed EC was significantly decreased as follows: UVB, 0.5 +/- 0.2%; UVC, 0.9 +/- 0.1%; UVA, 0.5 +/- 0.2% (n = 10). T6- DR+ EC, absent in control EC, were induced both by UVB, 5.2 +/- 1.7% and UVC; 1.5 +/- 0.4%. Despite the use of more than 1200 times greater doses in J cm-2 of UVA than UVB and UVC, UVA was a poor inducer of T6- DR+ EC (0.5 +/- 0.2%) and in about half of these individuals, T6- DR+ EC were undetectable. The UV wavelengths for induction of T6- DR+ EC lies predominantly within the UVB band, but also to a lesser extent within the UVC band. These wavelengths appear to be analogous to both the wavelengths for generation of increased host susceptibility to UV-induced murine tumors and to the wavelengths for UV-induced systemic suppression of contact hypersensitivity. However, our data indicate that UV wavelengths for decreasing the number of T6+ DR+ LC in humans differs from the wavelengths for induction of systemic suppression of contact hypersensitivity in mice. Taken together, these data suggest that the appearance of T6- DR+ EC, but not the disappearance of T6+ DR+ LC, following UV exposure may be related to the induction of such antigen-specific suppressor T cells.

Epidermal Langerhans cells undergo mitosis during the early recovery phase after ultraviolet-B irradiation

We studied the recovery phase of immune response-associated (Ia)-positive or ATPase-positive epidermal Langerhans cells (ELCs) after ultraviolet B (UVB)-induced depletion by using mouse ear epidermal sheets. An area 3 mm in diameter was irradiated with 300 nm UVB light (40 mJ/cm2). A time sequence study was carried out to 56 days. During this period the Ia-positive ELC population increased stepwise, i.e., first a rapid increase between day 7 and day 14, which we called the early recovery phase, and next a gradual increase between day 42 and day 56, which we called the late recovery phase. During the early recovery phase, we found polymorphous ELCs in the irradiated area which were giant or normal in size, dendritic or round in shape, and single or paired in distribution. Electron microscopy revealed some of round and some of paired ATPase-positive ELCs to be in metaphase or telophase of mitotic division. Within the entire observation period of our study, there was no evidence suggesting migration of ELCs from hair follicles or from the nonirradiated epidermis. These findings indicated that mitosis of ELCs contribute to their repopulation during the early recovery phase.

The effects of ultraviolet irradiation of the skin on herpes simplex virus infection: alteration in immune function mediated by epidermal cells and in the course of infection

Previously, we demonstrated that Ia+ epidermal cells (EC) have herpes simplex virus (HSV) antigen-presenting capacity in vitro and play an important role in resistance to HSV infection in vivo. In the present study, we investigated the effects of in vivo ultraviolet (UV) irradiation of the skin on the HSV-immunity function of EC both in vitro and in vivo and on the pathogenesis of HSV infection. Immune T cells cultured with EC and HSV antigen showed a proliferative response in vitro. Exposure of the skin to UV light 1 to 3 days before preparation of EC resulted in dose-dependent impairment of this proliferation. This UV-induced impairment of the accessory cell function of EC was accompanied by a parallel reduction of the number of Ia+ EC. We also transferred these EC-stimulated T cells to intracutaneously infected nude mice. Immune T cells stimulated with EC obtained from irradiated mice did not effectively clear HSV and allowed development of zosteriform skin lesions. In contrast normal-EC-stimulated immune T cells completely prevented the formation of a zosteriform rash. In addition, mice irradiated with UV on shaved midflank skin 2 days before intracutaneous inoculation of HSV showed increased severity of infection and a higher incidence of latency compared with control mice. These studies indicate that in vivo UV irradiation of the skin abrogates the immune function of EC both in vitro and in vivo, and affects HSV pathogenesis. The implication of our results for the better understanding of the effect of UV on acute and recurrent HSV infections is discussed.

Quantitative studies of the fate of epidermal Langerhans cells after X-irradiation of guinea-pig and mouse footpad skin

Langerhans cell numbers, morphology and distribution were observed in cross sections of footpad epidermis at intervals from 1 to 28 days after exposure of the hind feet of CBA/H mice or albino guinea-pigs to a single absorbed dose of 20 Gy (2000 rad) of X-rays. In mice, the number of Langerhans cells reactive with anti-macrophage F4/80 monoclonal antibody steadily declined by approximately 85% within 10 days after irradiation, consistent with previous studies, in which Langerhans cells were identified in epidermal sheets by ATPase activity or presence of Birbeck granules. Remaining Langerhans cells were exceptionally dendritic. Very few Birbeck granule-containing cells were found in murine popliteal lymph nodes before or after irradiation but damaged cells were present in superficial strata of irradiated epidermis. The morphology and number of epidermal F4/80-positive cells approached normal by 15 days after irradiation. In guinea-pigs, gradual suprabasal movement and loss of rounded, ATPase-positive Langerhans cells from the epidermis were detectable from 5 to 20 days after irradiation but the magnitude of the cell loss and redistribution was partially obscured by the simultaneous appearance of clusters of replacement Langerhans cells in the basal layer and by keratinocyte hyperplasia.