Mechanism of systemic immune suppression by UV irradiation in vivo. II. The UV effects on number and morphology of epidermal Langerhans cells and the UV-induced suppression of contact hypersensitivity have different wavelength dependencies

We previously reported that broad band UV radiation or narrow bands of UV (Hbw 3 nm) of wavelengths 250 to 320 nm cause a systemic suppression of contact hypersensitivity (CHS) in mice, observed when the contact sensitizer is applied to a nonirradiated site. To determine if this effect is associated with UV-induced alterations in epidermal Langerhans cell (LC) numbers and morphology, we performed the following study. LC were identified by ATPase staining of EDTA-separated epidermal sheets. Electron microscope studies confirmed that this method was a satisfactory indicator of the presence of LC; we found no evidence for LC which did not stain for ATPase in either irradiated or unirradiated epidermis. Mice were irradiated on the back with narrow band UV of peak wavelength 270, 290, or 320 nm. The irradiated skin was excised 24 hr later and was stained as described. The number of LC with ATPase staining dendrites and the number of nondendritic LC were enumerated. We found that UV radiation of 270 or 290 nm caused 1) an alteration in LC morphology (loss of dendrites) and 2) a decrease in the total number of epidermal LC. Both effects occurred in a dose-dependent fashion. Previously, these same wavelengths of narrow band UV, but at higher doses, had been shown to cause systemic suppression of CHS. In this study, the doses of 270 or 290 nm UV that resulted in the decreased LC numbers and alterations in LC morphology described above were insufficient to cause systemic suppression of CHS. The converse was found if the irradiating waveband of UV had a peak at 320 nm. A dose of 320 nm UV that caused 50% systemic suppression of CHS had no effect on either the number or the morphology of LC at the site of irradiation. In addition, the number and morphology of LC were unaffected in the ventral epidermis (site of contact sensitization) of mice that had been previously irradiated on the back with a systemically suppressive dose of UV. We conclude: (a) UV-induced alterations in the number and morphology of LC at the site of irradiation are not necessary for the generation of systemic suppression of CHS by UV radiation; this indicates that the initial UV-absorbing event triggering systemic suppression is neither a loss of, nor morphologic alterations to, LC at the irradiation site. (b) A systemic effect of UV radiation on the number and morphology of LC at the unirradiated site of contact sensitization does not occur, and thus is not responsible for the UV-induced systemic suppression of CHS by UV radiation.     

Studies on the role of antigen-presenting cells in the systemic suppression of contact hypersensitivity by UVB radiation

Exposure of mice to UVB radiation produces a highly selective, systemic immunosuppression associated with the appearance of suppressor T lymphocytes. Suppression of delayed hypersensitivity to hapten-coupled syngeneic cells has been shown to result from an altered distribution of antigen-presenting cells. The purpose of this study was to determine whether an alteration in the activity of antigen-presenting cells could account for the systemic suppression of contact hypersensitivity (CHS) by UVB radiation. Fluorescein isothiocyanate (FITC) was used for contact sensitization because it uses different antigen-presenting cells than does oxazolone to induce CHS. Our previous studies demonstrated that CHS to oxazolone was suppressed by UVB irradiation. In these studies, we show that exposure of mice to UVB radiation before epicutaneous application of FITC onto unirradiated skin markedly decreased the CHS response to FITC painted on unexposed ears. Cyclophosphamide-sensitive suppressor T cells were detectable in the spleens of mice exhibiting decreased CHS. The antigen-presenting activity of cells in lymph nodes draining the site of epicutaneous sensitization (DLN cells) was assessed by injecting them into the hind footpads of syngeneic recipients and measuring the CHS response to FITC 6 days later. Viable DLN cells from UVB-irradiated, FITC-sensitized mice were equal to those from unirradiated, FITC-sensitized mice in their ability to induce CHS in normal recipients. No sensitization resulted when killed DLN cells were used for immunization, indicating that sensitization was not caused by reprocessing of antigen by host cells. We conclude that impairment of the CHS reaction in UVB-irradiated mice does not appear to be blocked at an initial step of antigen uptake, processing, or presentation, but must be impaired at some other step in the immunologic pathway.     

Adaptation to the UV-induced suppression of phagocytic activity in murine peritoneal macrophages following chronic exposure to solar simulated radiation.

Exposure of certain strains of mice to ultraviolet radiation (UVR) is known to suppress both local and systemic immune responses, including a reduction in the phagocytic activity of peritoneal macrophages. However, in many instances, the immunological effects have been observed following a single or a limited number of doses of UVR from sources containing a higher proportion of UVB than that emitted by the sun. The first aim of the present study was to establish whether a single exposure of C3H/HeN mice to solar simulated radiation (SSR) suppressed the ability of the peritoneal macrophages to phagocytose opsonised sheep red blood cells. The mice were irradiated with SSR from Cleo Natural lamps and a single dose of 31.9 J cm(-2) was found to be the minimal dose for significant suppression of macrophage phagocytic activity. Such a dose did not modulate the surface expression of I-A(k), CD11b, CD86 or FcgammaRII/III (CD32/16) on the macrophages. The second aim was to assess whether repeated SSR exposures with a dose below the minimal immunosuppressive dose affected macrophage activity and, if so, to test for photoadaptation by repeated exposures followed by a single, normally immunosuppressive dose of SSR, and then assaying the macrophage activity. Groups of mice were irradiated on each of 2, 10 and 30 days with 14.9 J cm(-2) SSR, followed in some instances by a single additional exposure of 31.9 J cm(-2) on the same day as the last irradiation. The phagocytic activity of the peritoneal macrophages was tested 24 h later. It was reduced by 32%, 18% and 4% respectively after 2, 10 and 30 repeated exposures to SSR, and by 39%, 21% and 7% respectively after 2, 10 and 30 repeated exposures plus the additional higher dose at the end. Thus, although the macrophage activity was initially suppressed by the SSR, photoadaptation of this immune parameter occurred following repeated exposures.     

Inhibition of UVR‐Induced Tanning and Immunosuppression by Topical Applications of Vitamins C and E to the Skin of Hairless (hr/hr) Mice 1

Exposure of C3HBYB/Wq hairless (hr/hr) mice to ultra‐violet radiation (UVR) for 15 days induced intense tanning of their dorsal skin. Small, dark freckles appeared first, gradually enlarging and coalescing as treatment progressed yielding a uniform tan. Histologically, the gross changes in skin color were matched initially by the appearance of scattered epidermal melanocytes that subsequently proliferated to form discrete, progressively expanding and abutting populations resulting in a uniform melanocyte network throughout the basal layer of the interfollicular epidermis. In contrast, when applied topically before each daily exposure to UVR, a cream or lotion vehicle containing both vitamins C and E (Vits C/E) inhibited UVR‐induced erythema and tanning. Application of Vits C/E, both before and after irradiation, was no more effective in providing photoprotection than pre‐treatment only. At the tissue level, UVR‐induced proliferation and melanogenesis of melanocytes were reduced compared with irradiated controls. The density of individual melanocyte populations was reduced, as was the number of melanocyte populations achieving merger (confluence) with others. Confluence grades and cell counts, estimating the maximum density of melanocyte populations in UVR–Vits C/E‐treated mice, were approximately two thirds those of UVR–vehicle‐treated controls. However, tanning was only one fifth that of UVR–vehicle‐treated controls, suggesting that melanogenesis was also inhibited. In addition to its inhibitory actions on irradiated melanocytes, Vits C/E also inhibited UVR‐induced suppression of contact hypersensitivity (CHS) in haired (Hr/hr) and hr/hr mice of the C3HBYB/Wq strain. The common denominators for most, if not all, of the influences of topically‐applied Vits C/E in muting the responses of the melanocyte and immune systems to UVR may stem from the vitamins’ combined ability to suppress UVR‐stimulated inflammation and its associated cascade of mediators.     

Inhibition of UVR-induced tanning and immunosuppression by topical applications of vitamins C and E to the skin of hairless (hr/hr) mice

Exposure of C3HBYB/Wq hairless (hr/hr) mice to ultra-violet radiation (UVR) for 15 days induced intense tanning of their dorsal skin. Small, dark freckles appeared first, gradually enlarging and coalescing as treatment progressed yielding a uniform tan. Histologically, the gross changes in skin color were matched initially by the appearance of scattered epidermal melanocytes that subsequently proliferated to form discrete, progressively expanding and abutting populations resulting in a uniform melanocyte network throughout the basal layer of the interfollicular epidermis. In contrast, when applied topically before each daily exposure to UVR, a cream or lotion vehicle containing both vitamins C and E (Vits C/E) inhibited UVR-induced erythema and tanning. Application of Vits C/E, both before and after irradiation, was no more effective in providing photoprotection than pre-treatment only. At the tissue level, UVR-induced proliferation and melanogenesis of melanocytes were reduced compared with irradiated controls. The density of individual melanocyte populations was reduced, as was the number of melanocyte populations achieving merger (confluence) with others. Confluence grades and cell counts, estimating the maximum density of melanocyte populations in UVR-Vits C/E-treated mice, were approximately two thirds those of UVR-vehicle-treated controls. However, tanning was only one fifth that of UVR-vehicle-treated controls, suggesting that melanogenesis was also inhibited. In addition to its inhibitory actions on irradiated melanocytes, Vits C/E also inhibited UVR-induced suppression of contact hypersensitivity (CHS) in haired (Hr/hr) and hr/hr mice of the C3HBYB/Wq strain. The common denominators for most, if not all, of the influences of topically-applied Vits C/E in muting the responses of the melanocyte and immune systems to UVR may stem from the vitamins' combined ability to suppress UVR-stimulated inflammation and its associated cascade of mediators.     

Effect of a single exposure to ultraviolet radiation on Mycobacterium bovis bacillus Calmette-Guerin infection in mice

BALB/c and C3H mice were exposed on the dorsal skin to 45 kJ/m2 of UVB radiation from FS-40 sunlamps 3 days before infection with 1 x 10(6) live units of Mycobacterium bovis bacillus Calmette-Guérin (BCG) (Tice strain) in the footpad. At regular intervals, groups of mice were tested for a delayed type hypersensitivity (DTH) response to the purified protein derivative (PPD) of tubercle bacilli, and the course of infection was monitored by measuring the size of the infected footpad, enlargement of the draining lymph node, and the number of bacteria in the spleen and lymph node. In both strains the DTH response to PPD was significantly delayed in UV-treated mice compared to unirradiated mice, when tested 21 and 42 days after BCG infection. By day 50, no significant difference was detected in the DTH response between irradiated and unirradiated mice. UV treatment reduced the size of the lymph node draining the site of BCG infection in both strains of mice and the size of the infected footpad in C3H mice but not in BALB/c mice. In both strains of mice the total number of bacteria in the spleen and the draining lymph node increased after UV irradiation. When irradiated 3, 5, 18, or 21 days after BCG infection, BALB/c mice also showed a significant decrease in their DTH response to PPD, indicating that the UV-induced suppression of BCG occurs both at the induction and the elicitation stages of the immune response. Thus, mice exposed to a single dose of UV radiation either before or after BCG infection showed an impaired DTH response to mycobacteria, which was accompanied by an increase in the multiplication of bacteria in the tissues, even though the organisms were introduced at an unirradiated site. These studies demonstrate that a systemic effect of UV irradiation can interfere with the development and expression of immunity to pathogenic bacteria in mice.     

Low doses of very low-dose-rate low-LET radiation suppress radiation-induced neoplastic transformation in vitro and induce an adaptive response

The purpose of this study was to determine whether adaptation against neoplastic transformation could be induced by exposure to very low-dose-rate low-LET radiation. HeLa x skin fibroblast human hybrid cells were irradiated with approximately 30 kVp photons from an array of (125)I seeds. The initial dose rate was 4 mGy/day. Cell samples were taken at four intervals at various times over a period of 88 days and assayed for neoplastic transformation and the presence of reactive oxygen species (ROS). The dose rate at the end of this treatment period was 1.4 mGy/day. Transformation frequencies and ROS levels were compared to those of parallel unirradiated controls. At the end of 3 months and an accumulated dose of 216 mGy, cells treated with very low-dose-rate radiation were exposed to a high-dose-rate 3-Gy challenge dose of (137)Cs gamma rays, and the effects compared with the effect of 3 Gy on a parallel culture of previously unirradiated cells. Cells exposed to very low-dose-rate radiation exhibited a trend toward a reduction in neoplastic transformation frequency compared to the unirradiated controls. This reduction seemed to diminish with time, indicating that the dose rate, rather than accumulated dose, may be the more important factor in eliciting an adaptive response. This pattern was in general paralleled by a reduction of ROS present in the irradiated cultures compared to controls. The very low-dose-rate-treated cells were less sensitive to the high challenge dose than unirradiated controls, suggesting the induction of an adaptive response. Since there was a suggestion of a dose-rate threshold for induction suppression, a second experiment was run with a fresh batch of cells at an initial dose rate of 1 mGy/day. These cells were allowed to accumulate 40 mGy over 46 days (average dose rate=0.87 mGy/day), and there was no evidence for suppression of transformation frequency compared to parallel unirradiated controls. It is concluded that doses of less than 100 mGy delivered at very low dose rates in the range 1 to 4 mGy/day can induce an adaptive response against neoplastic transformation in vitro. When the dose rate drops below approximately 1 mGy/day, this suppression is apparently lost, suggesting a possible dose-rate-dependent threshold for this process.     

Infiltration by inflammatory cells required for solar-simulated ultraviolet radiation enhancement of skin tumor growth

In this study we compared the effects of subinflammatory and inflammatory doses of solar-simulated ultraviolet (UV) radiation on enhancement of skin tumor growth, sensitization to haptens and cellular changes within the epidermis of C3H/HeN mice. Tumors transplanted into mice 3 days after exposure to inflammatory, but not subinflammatory, doses of UV radiation had a higher growth rate than those tumors inoculated into unirradiated control mice. Both doses of UV radiation suppressed the induction of contact hypersensitivity and induced tolerance when hapten was painted onto the skin 3 days after irradiation. Skin exposed to the higher, but not the lower, dose of UV radiation contained significantly increased numbers of CD11b+, CD45+ MHC class II- and CD45+ MHC class II(hi) inflammatory cells 3 days post-irradiation. The immunosuppression correlated with a reduction in Langerhans cells and dendritic epidermal T cells. Collectively, this suggests that suppression to contact sensitizers is due to the UV radiation effects on Langerhans cells and dendritic epidermal T cells. While these effects may also suppress the induction of anti-tumor immunity, at higher doses of UV radiation inflammatory cells may enhance tumor growth by a non-immunological mechanism.     

Cyclobutane pyrimidine dimer formation is a molecular trigger for solar-simulated ultraviolet radiation-induced suppression of memory immunity in humans.

We tested the hypothesis that DNA is a target for solar-simulated ultraviolet radiation (ssUVR)-induced suppression of the reactivation of memory immunity in humans. T4N5 liposomes contain the DNA repair enzyme T4 endonuclease V. This cleaves DNA at the site of ultraviolet radiation (UVR)-induced cyclobutane pyrimidine dimers (CPD), initiating DNA repair. It has previously been used to show that CPDs are a key molecular trigger for UVR-induced immunosuppression in mice. To determine whether CPD formation is involved in UVR immunosuppression in humans, nickel-allergic volunteers were irradiated with a range of doses of ssUVR. T4N5 or empty liposomes were then applied after irradiation. Nickel-induced recall immunity was assessed by reflectance spectrometry. T4N5 liposomes inhibited immunosuppression and prevented ssUVR from reducing the number of epidermal dendritic cells. T4N5 liposomes also reduced macrophage infiltration into irradiated epidermis. These studies show that enhanced removal of CPDs from human skin protects from immunosuppression, hence demonstrating that these photolesions are an important molecular event in ssUVR-induced immunosuppression in humans. CPDs also triggered loss of dendritic cells and infiltration by macrophages. It is possible that these changes to antigen presenting cells contribute to ssUVR induced suppression of recall immunity to nickel in humans.     

The role of suppressor factors in the regulation of immune responses by ultraviolet radiation-induced suppressor T lymphocytes. II. Activity of suppressor cell culture sonicates

The purpose of this study was to determine whether multiple types of suppressor factors play a role in the regulation of immune responses by ultraviolet radiation-induced suppressor T lymphocytes (UV Ts). The UV Ts were induced by applying contact allergens to the ventral, unirradiated skin of mice exposed 5 days earlier to UVB radiation. Previous studies indicated that supernatants from cultures containing UV Ts, normal lymphocytes, and hapten-modified cells suppressed contact hypersensitivity (CHS) in vivo and cytotoxic T lymphocyte (CTL) generation in vitro in a hapten-specific manner. In this report, cell-free lysates from sonically disrupted UV Ts were examined for their ability to suppress these responses. When lysates were injected into normal animals at the time of sensitization, they inhibited CHS in a hapten-nonspecific manner. In addition, the lysates suppressed not only the induction but also the elicitation of CHS, and they suppressed the generation of CTL. Lysates prepared from spleen cells obtained from non-UV-irradiated mice or UV-irradiated, unsensitized mice failed to inhibit either response. Moreover, in contrast to the lysates, the hapten-specific UV Ts culture supernatants inhibited the induction but not the elicitation of CHS. These results suggest that both hapten-specific and nonspecific inhibitory factors may participate in the regulation of immune responses by UV Ts.     

Repair of Irradiated Transforming Deoxyribonucleic Acid in Wild Type and a Radiation-Sensitive Mutant of Micrococcus radiodurans

The survival of biological activity in irradiated transforming deoxyribonucleic acid (DNA) has been assayed in the wild type and a radiation-sensitive mutant of Micrococcus radiodurans. The frequency of transformation with unirradiated DNA was lower in the mutant to about the same extent as the mutant's increased sensitivity to radiation. However, in both the wild type and the mutant, the irradiated DNA that was incorporated into the bacterial genome was repaired to the same extent as determined by the loss of transforming activity with increasing radiation dose. This applied to DNA irradiated either with ionizing or ultraviolet (UV) radiation. The rate of inactivation of biological activity after UV radiation was the same in any of the DNA preparations tested. For ionizing radiation, the rate of inactivation varied up to 40-fold, depending on the DNA preparation used, but for any one preparation was the same whether assayed in the wild type or the radiation-sensitive mutant. When recipient bacteria were irradiated with ionizing or UV radiation immediately before transformation, the frequency of transformation with unirradiated DNA fell, rapidly and exponentially in the case of the sensitive mutant but in a more complicated fashion in the wild type. The repair of DNA irradiated with ionizing radiation was approximately the same whether assayed in unirradiated or irradiated hosts. Thus, irradiation of the host reduced the integration of DNA but not its repair.     

The role of suppressor factors in the regulation of immune responses by ultraviolet radiation-induced suppressor T lymphocytes. I. Activity of suppressor cell culture supernatants

The purpose of this study was to determine whether soluble suppressor factors are involved in the regulation of immune responses by ultraviolet radiation-induced suppressor T lymphocytes (UV Ts). The UV Ts were induced by applying contact allergens to the ventral, unirradiated skin of mice that had been exposed 5 days earlier to UVB radiation. Supernatants from cultures that contained a mixture of UV Ts, normal responder lymphocytes, and hapten-modified stimulator cells were injected iv into normal recipients at the time of sensitization; they inhibited the induction of contact hypersensitivity (CHS) in vivo in an hapten-specific manner. The supernatants similarly suppressed the generation of specific cytotoxic T lymphocytes (CTL) in vitro. Moreover, supernatants from cultures that contained either UV Ts alone or UV Ts in combination with either the responder or the stimulator cells failed to suppress the CHS and CTL responses. These results suggest that hapten-specific inhibitory factors may participate in the regulation of immune responses by suppressor cells generated by epicutaneous sensitization of UV-irradiated mice.     

Melatonin and protection from whole-body irradiation: survival studies in mice

The radioprotective ability of melatonin was investigated in mice exposed to an acute whole-body gamma radiation dose of 815 cGy (estimated LD50/30 dose). The animals were observed for mortality over a period of 30 days following irradiation. The results indicated 100% survival for unirradiated and untreated control mice, and for mice treated with melatonin or solvent alone. Forty-five percent of mice exposed to 815 cGy radiation alone, and 50% of mice pretreated with solvent and irradiated with 815 cGy were alive at the end of 30 days. Irradiated mice which were pretreated with 125 mg/kg melatonin exhibited a slight increase in their survival (60%) (p=0.3421). In contrast, 85% of irradiated mice which were pretreated with 250 mg/kg melatonin were alive at the end of 30 days (p=0.0080). These results indicate that melatonin (at a dose as high as 250 mg/kg) is non-toxic, and that high doses of melatonin are effective in protecting mice from lethal effects of acute whole-body irradiation.     

Ultraviolet radiation-induced erythema in human skin

We have evaluated UVR-induced erythema in previously unexposed buttock skin of volunteers of skin types I, II, III, and IV. Studies were done with solar-simulated radiation (SSR), UVB, and UVAI and we determined the just perceptible minimal erythema dose (MED) and, in some cases, quantified erythema with a reflectance device. The results show that there is a trend for increased SSR MED with skin type, with the MED of skin type IV being approximately twice that of skin type I, a smaller difference than one might have expected. However, there is a very considerable overlap of MED between skin types which shows that MED is a very poor indictor of skin type. Quantitative dose-response and time course studies with SSR and UVAI showed broadly similar responses when comparable MED-based exposures were given. We used our data to test the new concept of the standard erythema dose (SED) with two different erythema action spectra, and confirmed that the SED approach works with the different UVR sources that we studied.     

Premature senescence in human melanocytes after exposure to solar UVR: An exosome and UV‐miRNA connection

Ultraviolet radiation (UVR) can play two roles: induce cellular senescence and convert skin melanocytes into melanoma. To assess whether this conversion might rely on melanocytes having to first acquire a senescent phenotype, we studied the effects of physiological doses of UVR (UVA + UVB) on quiescent melanocytes in vitro. Repeated doses of UVR induced these melanocytes into a senescent‐like state. Additionally, these cells secrete exosomes with specific miRNAs that differ in quantity from those of the un‐irradiated melanocytes. Many of the exosomal miRNAs that were differentially enriched regulated genes comprising a “senescence core signature” and encoding factors of the senescence‐messaging secretome (SASP), while a subset of the differentially reduced miRNAs targeted DNA repair genes that have been experimentally shown to be repressed in senescent melanocytes. Thus, the selection of specific miRNAs by exosomes and their release from melanocytes after exposure to UVR have activities in inducing these cells into premature senescence.     

Alteration of the immune response to Mycobacterium bovis BCG in mice exposed chronically to low doses of UV radiation

BALB/c mice were exposed on shaved dorsal skin to 1 minimal erythemal dose (MED) of UVB radiation (2.25 kJ/m2) from a bank of six FS-40 sunlamps three times per week. The total number of irradiations ranged from 1 to 27. At regular intervals, groups of mice were injected in the left hind foot pad with 1 x 10(6) live mycobacteria (Mycobacterium bovis BCG) 3 days after the last UVB exposure. The mice were tested 21 and 42 days after infection for a delayed type hypersensitivity (DTH) response to the purified protein derivative (PPD) of tubercle bacilli by injecting PPD into the right hind foot pad and measuring the foot pad swelling 24 hr later. The course of infection was followed by assessing the number of bacterial colony forming units in the lymph node draining the site of BCG infection and the spleen. Mice exposed from 1 to 15 times to 1 MED of UV radiation showed a significant suppression in their DTH response to PPD compared with the unirradiated mice. At the same time, the number of bacterial colony-forming units in the lymph node and spleen of the UV-irradiated mice was greater than in control mice. With continued exposure to UVB, however, the DTH response recovered to a normal level, and there was no longer an increase in the number of viable bacteria in the lymphoid organs. These results indicate that early in the course of chronic UV irradiation, mice were impaired in their ability to mount a DTH response to BCG and to clear these bacteria from their lymphoid organs; later the mice recovered from these effects of UV, with continued treatment. A dose-response study using single doses of UV radiation indicated that a dose of 2.7 kJ/m2 suppressed the DTH response by 50%. Thus, exposure of mice to a single or multiple low doses of UV radiation prior to infection can interfere with systemic immunity to mycobacteria.     

Ultraviolet enhanced reactivation of a human virus: effect of delayed infection

The ability of UV-irradiated herpes simplex virus to form plaques was examined in monolayers of CV-1 monkey kidney cells preexposed to UV radiation at different intervals before virus assay. From analysis of UV reactivation (Weigle reactivation) curves it was found that as the interval between cell UV irradiation (0-20 J/m2) and initiation of the virus assay was increased over a period of five days, (1) the capacity of the cells to support unirradiated virus plaque formation, which was decreased immediately following UV exposure to the monolayers, increased and returned to approximately normal levels within five days, and (2) at five days an exponential increase was observed in the relative plaque formation of irradiated virus as a function of UV fluence to the monolayers. For high UV fluence (20 J/m2) to the cells, the relative plaque formation by the UV-irradiated virus at five days was about 10-fold higher than that obtained from assay on unirradiated cells. This enhancement in plaque formation is interpreted as a delayed expression of Weigle reactivation. The amount of enhancement resulting from this delayed reactivation was several fold greater than that produced by the Weigle reactivation which occurred when irradiated herpes virus was assayed immediately following cell irradiation.     

Cell surface and cytokine phenotypes of skin immunocompetent cells involved in ultraviolet-induced immunosuppression

Immunocellular migrations out of and into the skin and modulations of functional cell surface molecules on antigen-presenting cells (APCs), as well as their immunoregulatory cytokine production, are important factors involved in the mechanism of UV-induced immunosuppression and tolerance. Of particular interest here are the effects of low-dose UVB exposures that can suppress the ability of a contact sensitizer to induce contact hypersensitivity (CHS) through the site (local immunosuppression) without inducing suppression of CHS induced through skin distant to the UV exposure. Such UV-irradiated skin has many changes with respect to composition of immunocompetent cells and cytokine production. After UV exposure, Langerhans cells/dendritic cells migrate from the skin to draining lymph nodes (DLNs) as they do from contact sensitizer-applied normal skin. On the other hand, UV causes monocytic/macrophagic cells to infiltrate into the dermis and then into the epidermis; these can also be shown to be induced by contact sesitizers to migrate to DLNs. Alterations in cell surface and immunoregulatory cytokine phenotypes of the cutaneous APCs in both the skin and DLNs are critical for CHS suppression and tolerance induction. Here we describe the phenotypic changes of immunocompetent cells in UV-irradiated skin in regard to CHS suppression and tolerance and methodologies to approach this area.     

Topical tocopherol acetate reduces post-UVB, sunburn-associated erythema, edema, and skin sensitivity in hairless mice.

Exposure of the skin of the back of skh-1 hairless mice to UVB (310 nm peak) irradiation at doses of 0.115-0.23 J/cm2 results after 24-48 h in an erythema which can be quantified using an erythema meter, providing a useful model of sunburn. Application of pure d-alpha-tocopherol acetate, a thick oil, to the skin immediately following the exposure to UVB significantly reduces the increase in erythema index, by 40-55%. At the lower dose (0.115 J/cm2), skin thickness (associated with edematous swelling of the sunburned skin) was measured by a novel non-invasive technique not previously reported for this purpose--magnetic resonance imaging (MRI). In two experiments the UVB-induced increase in skin thickness was significantly reduced at 24 hr by 29 and 54%, and at 48 hr by 26 and 61%. After 8 days the untreated irradiated mouse skin still showed a significant increase in thickness (24%) compared to the untreated unirradiated control, while the treated irradiated control was not significantly thicker than the unexposed control. Skin sensitivity was tested using a modification of the technique of esthesiometry, by observing rapid avoidance responses of the mouse to a pressure of 0.96 g/cm2 exerted by applying to the skin the tip of a nylon esthesiometer fiber extended to 60 mm in length. The untreated irradiated mice were more sensitive (p less than 0.07, Wilcoxon test) than the treated irradiated mice, and also significantly different from the untreated unirradiated control mice (p less than 0.04, Wilcoxon test), but the treated irradiated mice were not significantly differently sensitive when compared to the unirradiated controls (p less than 0.32). Taken together these data indicate that the erythema, edema, and skin sensitivity commonly associated with UVB-induced sunburn are significantly reduced by topical application of tocopherol acetate even after the exposure has occurred. This observation suggests that treatment of sunburn may be possible even after the irradiation has stopped, by a derivative of d-alpha-tocopherol which is stable to autooxidation.