Photoimmunology: the mechanisms involved in immune modulation by UV radiation

Differential sensitivity of lymphocyte subpopulations to non-thermal atmospheric-pressure plasma

Non-thermal atmospheric-pressure plasmas can possibly be used for several applications in particular in medicine. Plasma treatment can be applied to living tissues and cells, e.g., to induce apoptosis and growth arrest in tumour cells or to improve wound healing. However, detailed investigations of plasma-cell interactions are strongly needed. It is not yet clear whether plasmas will be useful in stimulating immune cells to change their behaviour or function. Therefore, this study focused on the influence of non-thermal atmospheric pressure plasma on cell surface molecules of rat spleen mononuclear cells (MNC) as first important step to gain insight into plasma-immune cells interactions. Rat spleen MNC were treated with plasma by surface dielectric barrier discharge (DBD) at atmospheric pressure in air or argon. Lymphocyte subpopulations and expression of L-selectin, ICAM-1 and LFA-1α expression on T-cells were analysed by flow cytometry 1-48 h after plasma treatment. Plasma changed the ratio of T- and B-cells in favour of B-cells. Of the T-cells the helper T-cells were reduced while cytotoxic T-cells were less affected. L-selectin expressing T-cells were significantly reduced already 1h after plasma treatment and that of ICAM-1(+) and LFA-1α(+)T-cells only after 4h. These effects were time dependent and less dramatic when using DBD/argon plasma. In conclusion, different lymphocyte subpopulations show different sensitivity to plasma. Adhesion molecules as L-selectin, ICAM-1 and LFA-1α are down regulated by plasma. Whether these results can be used to modify lymphocyte homing or to activate MNC for different applications remains to be clarified.

Pilot study of the effect of ultraviolet light on pain and mood in fibromyalgia syndrome

BACKGROUND

There is a lack of effective systemic or adequate symptomatic treatment for pain associated with fibromyalgia syndrome (FMS). Anecdotes suggest ultraviolet (UV) light may be of some benefit.

PURPOSE

The purpose of the present study was to determine if UV is effective in ameliorating chronic pain in persons with FMS.

METHODS

Nineteen subjects with FMS were enrolled in a controlled trial of UV and non-UV (control) tanning beds for 2 weeks, followed by randomization to receive UV or non-UV (control) exposure for 6 additional weeks. A follow-up interview was conducted 4 weeks after the last treatment. Pain was assessed with an 11-point numerical pain rating (Likert scale), a visual analogue pain scale (VAS), and the McGill Pain Questionnaire. Mood variables were also assessed.

RESULTS

During the initial 2 weeks when subjects received both UV and non-UV (control) exposures, the 11-point Likert scale pain score decreased 0.44 points after exposure to UV from pre-exposure levels (S.E. = .095). Additionally, UV exposure resulted in greater positive affect, well-being, relaxation, and reduced pain levels when compared to non-UV (control) exposure (Odds Ratio [OR] = 2.80, p = 0.0059). Following the randomized treatment period, there was slight improvement in pain as measured by the McGill Pain Questionnaire in the UV group compared to the non-UV (control) group (12.2 versus 14.1; p = 0.049); the other pain scales yielded nonsignificant results. Assessment 4 weeks after the last treatment showed no significant differences in scores in the adjusted means for outcomes.

CONCLUSIONS

Results from this pilot study suggest that tanning beds may have some potential in reducing pain in persons with FMS.

Photoprotective effect of sesamol on UVB-radiation induced oxidative stress in human blood lymphocytes in vitro

Normal lymphocytes are highly sensitive to the damaging effect of radiation and undergo cell death. In the present study, the photoprotective effect of sesamol, a constituent of sesame oil, has been examined in the UVB-(280-320nm) irradiated human blood lymphocytes. Lymphocytes pretreated with increasing concentrations of sesamol (1, 5 and 10μg/ml) for 30min, were irradiated and lipid peroxidation and antioxidant defense were examined. UVB-irradiated lymphocytes exhibited increased levels of lipid peroxidation and disturbances in antioxidant defense. Sesamol pretreatment resulted in significant reduction in lipid peroxidation marker, thiobarbituric acid reactive substances (TBARS). Further, antioxidants like reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) increased, in a dose-dependent manner, in sesamol pretreated and UVB-irradiated lymphocytes. The maximum dose of sesamol (10μg/ml) normalized the UVB induced lipid peroxidation, indicating the photoprotective effect of sesamol in irradiated lymphocytes.

Immunomodulatory activity of betulinic acid by producing pro-inflammatory cytokines and activation of macrophages

Betulinic acid (BA), a pentacyclic triterpene isolated from Lycopus lucidus, has been reported to be a selective inducer of apoptosis in various human cancer and shown anti-inflammatory and immunomodulatory properties. We postulated that BA modulates the immunomodulatory properties at least two groups of protein mediators of inflammation, interleukin-1beta (IL-1beta) and the tumor necrosis factor-alpha (TNF-alpha) on the basis of the critical role of the monocytes and tissue macrophages in inflammatory and immune responses. TNF-alpha and IL-1beta were produced by BA in a dose dependent manner at concentration of 0.625 and 10 microg/mL. The production of NO associated with iNOS was inhibited when treated with LPS at the concentration of 2.5 to 20 microg/mL of BA whereas COX-2 expression was decreased at 2.5 to 20 microg/mL. These modulations of inflammatory mediators were examined in LPS-stimulated RAW 264.7 cells and peritoneal macrophages. The morphology of macrophage was also examined and enhanced surface CD 40 molecule was expressed when treated BA at 0.625 to approximately 5 microg/mL with or without LPS. Furthermore, BA (20 microg/mL) enhanced apoptosis by producing DNA ladder in the RAW 264.7 cells. Our results indicated that BA induced activation of macrophage and pro-inflammatory cytokines. This may provide a molecular basis for the ability of BA to mediate macrophage, suppress inflammation, and modulate the immune response.

Photoprotection by antioxidants against UVB-radiation-induced damage in pig skin organ culture

Topically applied antioxidants constitute an important group of protective agents against skin damage induced by ultraviolet radiation. The current study was performed to investigate whether a recently developed ex vivo pig skin model was suitable for short-term studies of the mechanism(s) of UVB-radiation-induced skin damage; the protective effect of topical application of alpha-tocopherol, l-ascorbic acid, alpha-lipoic acid, glutathione ethylester and N-acetylcysteine was tested. Increasing doses of the antioxidants were applied topically on ex vivo pig skin explants and allowed to penetrate for 60 min. Epidermal antioxidant bioavailability was measured before and 60 min after exposure to an ultraviolet B (UVB) radiation of 7.5 kJ/m2. Cell viability (trypan blue dye exclusion) and apoptosis were measured 48 h later in isolated keratinocytes. UVB-radiation-induced epidermal lipid peroxidation was determined immediately after exposure of the skin to a UVB dose of 28 kJ/m2. All antioxidants tested became bioavailable in pig skin epidermis, and none of them were depleted after UVB-radiation exposure. Increasing doses of the antioxidants tested decreased UVB-radiation-induced cell death and apoptosis. The highest doses of antioxidants prevented UVB-radiation-induced lipid peroxidation; alpha-lipoic acid only tended to decrease lipid peroxidation. In conclusion, a single topical dose of the above antioxidants on ex vivo pig skin can reduce UVB-radiation-induced oxidative stress and lipid peroxidation and thereby reduce apoptotic stimuli and cell death. Furthermore, the ex vivo pig skin model was a useful tool for testing compounds for their antioxidant activity.

Time and Dose-related Ultraviolet B Damage in Viable Pig Skin Explants Held in a Newly Developed Organ Culture System¶

For facilitating photochemical and toxicological studies an ex vivo skin model was developed in our laboratory using skin from domestic pigs. The model comprised the use of a complete skin piece, including the dermis and stratum corneum, of bigger areas to make future topical applications easier. Fully differentiated skin explants (5 x 50 mm, thickness 5 mm) were irradiated with ultraviolet B (UVB; 1-10 kJ/m2; 6 W/m2). Directly thereafter they were brought in culture (Dulbeccos modified Eagles medium containing hydrocortisone; air/liquid interface) for a maximum of 144 h. In nonirradiated skin explants, signs of tissue degeneration were observed after 48 h in culture (hematoxylin and eosin, light microscope). However, keratinocytes, isolated enzymatically (thermolysin and trypsin) at different time intervals in culture from nonirradiated skin explants showed negligible loss in viability (trypan blue exclusion) and increased apoptosis (terminal deoxynucleotidyl transferase-mediated deoxy uridine triphosphatase nick end labeling assay) for up to 72 h. Explants irradiated with a single dose of UVB showed a clear and reproducible dose- and time-dependent tissue degeneration, loss in keratinocyte viability and increase in apoptosis compared with nonirradiated explants at the same time interval. In conclusion, the presently designed ex vivo pig skin model can be a useful and cheap tool for future investigations of short-term UV-induced effects in combination with phototoxic and photoprotective compounds.

Calcitonin gene-related peptide and nitric oxide are involved in ultraviolet radiation-induced immunosuppression

Contact hypersensitivity responsiveness to dinitrofluorobenzene is depressed in mice that are sensitized through skin sites exposed to ultraviolet (UV) radiation. Local impairment of contact hypersensitivity by UV has been associated with a reduction in antigen-presenting cell activity within UV-irradiated skin sites marked by a decrease in the density of Ia-positive epidermal Langerhans cells. Our recent studies have demonstrated that neurogenic mediators (e.g. calcitonin gene-related peptide (CGRP) and nitric oxide (NO) contribute to cutaneous inflammation following exposure of rats to high-dose UV radiation. Since CGRP and NO inhibit antigen presentation by dendritic cells in vitro, we have investigated the possible involvement of CGRP and NO in local immunosuppression in UV-irradiated rodents. Hindpaw skin of Sprague-Dawley rats and back skin of UV-susceptible C57BL/6 mice was exposed to acute UV radiation (2.0 J/cm2 and 0.5 J/cm2, respectively). Alterations in cutaneous CGRP content were analyzed by a specific radioimmunoassay (RIA). In separate experiments, the CGRP receptor antagonist CGRP-(8-37) (10-5 M) and the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (2 X 10-5 M) were topically applied to UV-exposed skin before induction of contact hypersensitivity with dinitrofluorobenzene. Finally, we examined the effects of UV irradiation and epicutaneous application of CGRP on Ia-positive Langerhans cells by immunohistochemical analysis of epidermal sheets. It was found that UV exposure lead to a decrease in skin CGRP levels starting already 2 h after irradiation and reaching a minimum (less than 40% of non-irradiated control skin) at 6-12 h. Contact hypersensitivity reactions were significantly suppressed by UV radiation in rat skin (by 51%) and murine skin (by 80%). Topical administration of both CGRP-(8-37) and L-NAME before sensitization restored the capacity to respond to haptens applied to UV-exposed skin. Both UV exposure and topical CGRP reduced the density of Ia-positive epidermal cells. Our data indicate that CGRP may be released from sensory neurons following cutaneous UV irradiation and that CGRP and NO contribute of UV-induced local immunosuppression. Moreover, topical administration of CGRP or its antagonist may be able to modulate epidermal Langerhans cell activity in vivo.

Doses of Ultraviolet Radiation that Modulate Accessory Cell Activity and ICAM-1 Expression Are Ultimately Cytotoxic for Murine Epidermal Langerhans Cells

Mechanisms that underlie immunomodulatory properties of ultraviolet (UV) radiation remain incompletely characterized. Recently, we have studied effects of UV on the functional activity of epidermal Langerhans cells (LC) and have attempted to relate inhibitory effects of UV on LC function to modulatory effects of UV on adhesion molecule expression by LC. Exposure of LC in vitro to amounts of UVB, UVC, or psoralen+UVA (PUVA) radiation that inhibited LC function also prevented increased expression of intercellular adhesion molecule-1 by LC in vitro. Subsequent studies revealed that amounts of UV radiation that inhibited LC function and modulated ICAM-1 expression also decreased LC survival in vitro, although UV-induced LC cytotoxicity did not become apparent until 48-72 h after UV exposure. Our results are consistent with those of previous studies that suggested that low doses of UV radiation were cytotoxic for LC in situ. The potential cytotoxicity of UV radiation for LC should be considered when studies of effects of UV radiation on immune responses in skin are interpreted.

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)

Immunosuppression by ultraviolet B radiation: initiation by urocanic acid

Irradiation with UV-B, a component of natural sunlight, initiates systemic immunosuppression of delayed-type hypersensitivity responses. This may be a fundamental regulatory mechanism, controlling the interaction between mammals and potentially deleterious environmental UV radiation. Here, Frances Noonan and Edward De Fabo assess the evidence that suppression is initiated by the photoisomerization of trans-urocanic acid (UCA) in the stratum corneum, discuss the significance of this mechanism for skin cancer outgrowth and propose applications for UCA in transplantation.

Proliferative responses of lymphocytes to mitogens in the gray, short-tailed opossum, Monodelphis domestica

A South American opossum (Monodelphis domestica) is a model animal for studies on the health effects of exposure to ultraviolet radiation (UVR). As part of a broad evaluation of immune function in this animal, we have tested in vitro mitogenic responses using whole blood cultures. Lymphocytes proliferated in the presence of phytohemagglutinin (PHA), concanavalin A (Con A), and pokeweed mitogen (PWM), but were unresponsive to bacterial lipopolysaccharide (LPS).

Dietary histidine increases mouse skin urocanic acid levels and enhances UVB-induced immune suppression of contact hypersensitivity

Urocanic Acid (UCA) exists in mammalian skin primarily as the trans isomer and is photoisomerized to cis UCA upon UVB absorption. Our previous studies indicated that the photoisomerization of UCA is the initiating event in UBV-induced suppression of cell-mediated immunity (tUCA----cUCA----immune suppression). The purpose of this study was to verify the role of UCA in UV-induced immune suppression of contact hypersensitivity (CHS) in BALB/c mice. Since UCA is a metabolite of the amino acid L-histidine, we reasoned that increased dietary levels of histidine should raise skin tUCA levels. If skin tUCA is the UVB photoreceptor for immune suppression, this increase should enhance UV-induced suppression of CHS. HPLC analysis of skin from BALB/c mice given a histidine-rich diet (10%) showed that the total amount of UCA is significantly higher in these animals than in mice fed a normal diet. Further, levels of suppression of CHS of 3% and 49% in control fed mice, induced by 4.8 and 7.2 kJ/m2 UVB were significantly increased to 21% and 71% respectively in histidine-fed animals at these same UVB doses. These findings provide additional support for the UCA model for immune suppression, and provide the first evidence that UV-induced immune suppression can be enhanced by a dietary component, L-histidine.

Ultraviolet-B dose-response curves for local and systemic immunosuppression are identical

Irradiation of mice with UVB suppresses contact hypersensitivity either "locally", i.e. when sensitizer is applied to the UV irradiated site, or "systemically", i.e. when sensitizer is applied to a site distal to the site of irradiation. It has been suggested that local suppression requires lower doses of UV than does systemic suppression, and that different mechanisms are therefore responsible. We undertook a detailed analysis of the dose-response and kinetics of UV-induced local and systemic suppression of contact hypersensitivity to trinitrochlorobenzene in two strains of mice, C57BL/6 and BALB/c. We found that the UV dose-responses for systemic and local suppression were identical within the same strain. Comparison, however, of UV dose-responses between strains indicated that C57BL/6 mice required 6.4 times less UV than did BALB/c mice to generate an equivalent amount of suppression. In both strains, local suppression was initiated if sensitizer was applied immediately, or 1 or 3 days after completion of a single dose of UV. In contrast, systemic suppression was initiated only if sensitizer was applied 3 days after UV irradiation. Thus local suppression was generated in the absence of significant systemic suppression (but not vice versa), and this was dependent on time of application of sensitizer after UV irradiation, not on the dose of UV administered. Filtration of the UV source with Mylar indicated that UVB was responsible for initiating both local and systemic suppression. In summary, these results indicate that (1) genetically determined differences in susceptibility to UV suppression exist, (2) the time courses of generation of local and systemic suppression are identical, and therefore use of the terms "low dose" and "high dose" to refer respectively to local and systemic suppression by UV irradiation are incorrect. We conclude that a common mechanism initiates UV-induced local and systemic suppression of contact hypersensitivity by the immediate formation, at the site of UV irradiation, of an immunosuppressive signal which takes between 1 and 3 days to act systemically.

UVB radiation and human monocyte accessory function: differential effects on pre-mitotic events in T-cell activation

Purified T lymphocytes fail to proliferate in response to antigenic and mitogenic stimuli when cultured in the presence of accessory cells that have been exposed in vitro to sublethal doses of UVB radiation. Because proliferation represents a final stage in the T-cell activation process, the present study was conducted to determine whether T cells were able to progress through any of the pre-mitotic stages when UVB-irradiated monocytes were used as model accessory cells. In these experiments, monoclonal anti-CD3 antibodies were employed as the mitogenic stimulus. Culture of T cells with UVB-irradiated monocytes did allow the T cells to undergo an increase in intracellular free calcium, which is one of the first steps in the activation sequence. The T cells expressed interleukin-2 receptors, although at a reduced level. However, T cells failed to produce interleukin-2 above background levels when they were placed in culture with monocytes exposed to UVB doses as low as 50 J/m2. Incubation of T cells with UVB-irradiated monocytes did not affect the subsequent capacity of T cells to proliferate, since they developed a normal proliferative response in secondary culture when restimulated with anti-CD3 antibodies and unirradiated monocytes. These studies indicate that T lymphocytes become partially activated when cultured with UVB-irradiated monocytes and mitogenic anti-CD3 monoclonal antibodies. In addition, they suggest that interleukin-2 production is the T-cell activation step most sensitive to inhibition when UVB-irradiated monocytes are employed as accessory cells.