UVB-induced suppression of the mixed epidermal cell lymphocyte reaction is critically dependent on irradiance

The impact of irradiance on UVB-induced cutaneous immunosuppression: Implications on administering most efficient phototherapy

BACKGROUND

Ultraviolet B (UVB) is commonly used for treating dermatologic conditions. Recently, high irradiance UVB (HIUVB) has been suggested to be more effective for treating skin conditions as compared to its low irradiance (LI) counterpart. The biological impact of UVB radiation emitted at different irradiance on cutaneous immunity remains obscure.

OBJECTIVE

This study aimed to explore the impacts of UVB radiation administered at equivalent fluence (mJ/cm²) but different irradiance (mW/cm²) on cutaneous immune response.

METHODS

Cultured bone marrow derived dendritic cell (BMDC) were treated with equivalent fluence of UVB radiation with HIUVB or LIUVB. The phenotypic and functional alterations of BMDCs were documented. Animal models were used to validate the in vitro results in vivo and explore the mechanisms involved.

RESULTS

After equivalent fluence of UVB radiation, the HIUVB treated BMDC showed significantly lower MHCII and CD86 expressions, reduced capacity to stimulate T cell proliferation, and enhanced activation of aryl hydrocarbon receptor (AhR)-activated genes as compared to control while their LIUVB treated counterpart showed no significant change. Using animal model, the HIUVB induced significantly higher immune suppressive effect in mice as compared to their LIUVB counterpart after equivalent fluence of UVB treatment. The superior immune suppressive effect of HIUVB over LIUVB radiation was not observed when similar experiments were performed using AhR-deficient mice.

CONCLUSION

We propose irradiance played an important role modulating UVB-induced cutaneous immune suppression. Future works on UVB phototherapy, both clinical and research, should incorporate this important parameter into consideration.

Irradiance, but not fluence, plays a crucial role in UVB-induced immature pigment cell development: new insights for efficient UVB phototherapy

Light exposure modulates development of living organisms. In the field of medicine, light has frequently been used for regenerative purposes. Excimer light (308 nm) has demonstrated superior efficacy in treating vitiligo, a condition requiring development of melanoblasts and a model for studying nerve cell regeneration, as compared to narrow-band ultraviolet B (NBUVB; 311 nm). Using mouse-derived melanoblast cells to examine the pro-differentiation effects of these two light sources, we demonstrated that at equivalent fluence, excimer light induces melanoblast differentiation, while NBUVB failed to so. Mechanistically, activation of aryl hydrocarbon receptor pathway and nuclear translocation of epidermal growth factor receptor are involved in pro-differentiation effects of excimer light. Reduction in irradiance by filter abrogated the effects of excimer light in melanoblasts, even when equivalent fluence was delivered by the same light source. As ultraviolet B (UVB) irradiation is closely associated pigment cell development, future therapy employing UVB for pigmentation purposes should incorporate irradiance as a crucial specification.

Efficacy of Different UV-emitting Light Sources in the Induction of T-cell Apoptosis¶

Ultraviolet B (UV-B) radiation is a modality widely used for the treatment of different skin diseases. One of the major mechanisms of UV-B immunosuppression in this treatment modality is thought to be an apoptosis-inducing effect on T cells infiltrating the skin. We examined the T-cell apoptosis-induction capacities of four different UV light sources, with and without UV filters. The xenon chloride (XeCl) laser proved to be the strongest apoptosis inducer. The use of a phtalic acid filter eliminated UV radiation almost completely below 300 nm, which resulted in a severe decrease in the apoptosis-inducing capacity of different UV-B sources. Using the results of the measurements with polychromatic UV light sources, the wavelength dependence of UV-B light for the induction of T-cell apoptosis was also determined. The regression line of the action spectrum demonstrated a continuous decrease from 290 to 311 nm. The apoptosis-inducing capacity of the XeCl laser was almost four times higher than the calculated value according to the action spectrum, which might be attributed to the high irradiance of the laser as compared with nonlaser light sources.

Effects of UVB irradiance on conidia and germinants of the entomopathogenic Hyphomycete Metarhizium anisopliae: a study of reciprocity and recovery

We tested the effects of irradiances of 920 and 1200 mW m-2 (weighted irradiance) on the conidia and germinants of the entomopathogenic Hyphomycete Metarhizium anisopliae. The conidia were exposed to the two irradiances for 1, 2, 4, 6, 7 or 8 h. Increased exposure decreased relative percent culturability. The inactivation provoked by the irradiance of 1200 mW m-2 was higher than for the 920 mW m-2, with a reduction in the 50% lethal time (LT50) from 6 h 40 min to 4 h 26 min. Reciprocity was not observed when conidia in water suspension and germinants in different stages of the germinative process were exposed to a 17.3 kJ m-2 total dose at both irradiance levels. Although nonreciprocity was observed in all situations, its magnitude varied as a function of metabolic state and/or cell-cycle phase in which the conidia were at the exposure time. The least difference between the effects of the two irradiance levels was observed when nongerminating conidia in suspension were exposed, and the greatest was observed when conidia were exposed during an advanced germination phase. Doses of 6.6 and 17.3 kJ m-2 supplied through the two irradiance levels delayed the germination of the surviving conidia. At both doses, delay was greater during exposure to the higher irradiance. Nonreciprocity was higher for the 17.3 kJ m-2 dose. Nonreciprocity magnitude, in addition to depending on the conidial physiological state, also depended on dose. The results demonstrate the importance of evaluating the impact of the increase in irradiance during the different stages of the fungal life cycle, especially during the stages which are more sensitive to UV, and not simply in dormant conidia.

The UV waveband dependencies in mice differ for the suppression of contact hypersensitivity, delayed-type hypersensitivity and cis-urocanic acid formation

Solar radiation contains ultraviolet B (280-315 nm) and ultraviolet A (ultraviolet AII, 315-340 nm; ultraviolet AI, 340-400 nm) wavebands. Ultraviolet B is known to suppress certain aspects of cell mediated immunity. Using three ultraviolet lamps (the broad-band ultraviolet B TL-12, the narrow-band ultraviolet B TL-01 and an ultraviolet AI source), we investigated the dose and waveband dependencies for the suppression of contact hypersensitivity to oxazolone and delayed-type hypersensitivity to herpes simplex virus, plus the formation of cis-urocanic acid in C3H/HeN mice. A single exposure of 1500 J/m2 TL-12 or 10,000 J/m2 TL-01 or 500,000 J/m2 ultraviolet AI corresponded to 1 minimum erythema dose in this mouse strain. The percentage of cis-urocanic acid of the total urocanic acid rose from a background level of 1.7% to 40% with 1000 J/m2 TL-12 or 10,000 J/m2 TL-01, but only 17% cis-urocanic acid was obtained with 500,000 J/m2 ultraviolet AI. The contact hypersensitivity response was significantly suppressed after a minimum dose of 5000 J/m2 TL-12 or 50,000 J/m2 TL-01 or 500,000 J/m2 ultraviolet AI. The delayed-type hypersensitivity response was suppressed by a minimum dose of 100 J/m2 TL-12 or 10,000 J/m2 TL-01 or 1000 J/m2 ultraviolet AI. So, whereas a low dose of ultraviolet AI reduced the delayed-type hypersensitivity response, a 500-fold higher dose was required to suppress contact hypersensitivity. There was no correlation between the suppression of these responses and the concentration of cis-urocanic acid in the skin. Thus different mediators may modulate the various immune responses affected by ultraviolet exposure, depending on the wavelength of the radiation.

Efficacy of micronized titanium dioxide-containing compounds in protection against UVB-induced immunosuppression in humans in vivo

Micronized pigment-containing sunscreens may provide a good alternative to chemical sunscreens in protection against ultraviolet (UV) B-induced immunosuppression. The metal particles in these products are likely to remain on the skin surface where they can offer broadband protection for both the UVA and UVB regions. We have tested the protective capacity of three titanium dioxide (TiO2)-containing compounds in humans in vivo. The effect on sunburn cell formation has been investigated using transmission electron microscopy, while the mixed epidermal cell lymphocyte reaction (MECLR) has been used as a model for immunosuppression. Furthermore, the influence of titanium on the integrity of the stratum corneum barrier (intercellular lipids and desmosomes) has been examined using freeze fracture electron microscopy. We find that all three compounds protect against sunburn cell formation. The immunoprotection studies show that one of the three compounds does not prevent UVB-induced changes of the MECLR responses. Application of this compound without subsequent UVB irradiation also induces a significant decrease of the MECLR responses. Moreover, the same compound affects the intercellular lipid layers, and desmosomes cannot be detected. The deleterious effect of this compound is probably caused by an incomplete hydrolysis during the TiO2 synthesis. Our findings indicate that micronized pigment-containing compounds can offer good protection against short-term UVB-induced immunomodulation in humans in vivo. However, accurate screening of the synthesis of these compounds is a prerequisite for their safe use as sunscreening agents in human subjects.

Differential effects of sunscreens on UVB-induced immunomodulation in humans

Ultraviolet radiation has been shown to suppress the (skin) immune system both in animal species and in humans. Whether sunscreens can prevent immunosuppression is a matter of debate. This study investigated the protective capacity of a commercial sunscreen lotion in humans. Part of the right arm of healthy volunteers was exposed to erythemagenic ultraviolet B doses of 160 mJ per cm2 for four consecutive days. Before irradiation, sunscreen was applied either directly onto the skin or onto a piece of quartz fixed to the skin (to avoid penetration of the sunscreen in the epidermis where it cannot block the photoisomerization of trans-urocanic acid in cis-urocanic acid in the stratum corneum). The control group was irradiated without prior application of sunscreen. Four h after the last irradiation, epidermal sheets were obtained by the suction-blister method from both arms and epidermal cells were used as stimulator cells in the mixed epidermal cell lymphocyte reaction. Responses directed to epidermal cells derived from irradiated skin were expressed as percentages of responses directed to epidermal cells derived from the nonirradiated left arm. The mixed epidermal cell lymphocyte reaction responses in the control group were found to be significantly increased (205%). This enhancement of the mixed epidermal cell lymphocyte reaction responses was associated with an influx of CD36+DR+ macrophages in the irradiated skin. Application of the sunscreen, either onto a piece of quartz or directly onto the skin, prevented the increase of the mixed epidermal cell lymphocyte reaction responses and the influx of CD36+DR+ cells. In an earlier study, volunteers were exposed three times weekly to suberythemagenic doses of ultraviolet B over 4 wk, resulting in mixed epidermal cell lymphocyte reaction responses that were decreased to 20%. The same sunscreen was not able to prevent this suppression. These contradicting results indicate that the protective effect of sunscreens with respect to ultraviolet-induced immunomodulation is critically dependent on the choice of ultraviolet treatment.

Differential suppression of the human mixed epidermal cell lymphocyte reaction (MECLR) and mixed lymphocyte reaction (MLR) by cis-urocanic acid

Cis-urocanic acid (UCA), formed in the stratum corneum by UV irradiation of trans-UCA has been proposed as a mediator of UV-induced immunosuppression in the skin. In this study, we examined the in vitro effect of cis-UCA (6-100 micrograms/mL) on the human mixed lymphocyte reaction (MLR) and the mixed epidermal cell lymphocyte reaction (MECLR). Addition of cis-UCA (purified or in a mixture with trans-UCA) did not affect the MLR but was able to induce a 20% suppression of the MECLR responses. Because this effect of cis-UCA on the MECLR was not as strong as could be expected from previous in vivo results, we designed a set of experiments in order to enhance the in vitro immunosuppressive capacity of cis-UCA. Firstly, we preincubated epidermal cells with UCA (50 micrograms/mL). for 3 or 6 days before culture in the MECLR because in vivo repeated UV exposure can lead to a photostationary state, where cis-UCA may be present for several weeks. This pretreatment with cis-UCA resulted in a maximal decrease of the MECLR response of 27%, whereas trans-UCA had no effect. Secondly, we investigated whether UVB irradiation of epidermal cells could make cells more sensitive to cis-UCA. However, addition of trans- or cis-UCA did not potentiate the reduced alloactivating capacity of UVB-irradiated cells. Finally, we examined the possibility of a synergistic effect of cis-UCA with histamine. Addition of histamine suppressed the MLR and MECLR responses, but neither cis- nor trans-UCA were able to modulate this decrease. We conclude that cis-UCA can partly downregulate the human MECLR but not the MLR. The mechanism involved in this differential downregulation is not known. In this respect it is striking that cis-UCA dose not potentiate the UVB- or histamine-induced suppression of the MECLR.

UVB-induced decreased resistance to Trichinella spiralis in the rat is related to impaired cellular immunity

Our laboratory has demonstrated in preliminary experiments that UVB exposure using the Kromayer lamp can induce increased numbers of Trichinella spiralis larvae in carcasses of infected Wistar rats, without affecting specific antibody titers to this parasite. In this study, orally T. spiralis-infected Wistar rats were exposed to suberythemal doses of UVB radiation using FS40 lamps during different time periods before or after infection. A significant increase in the number of T. spiralis larvae was found in the carcasses of rats that were UVB irradiated daily for 7 consecutive days in the second week after infection. Additionally, increased numbers of larvae were also detected histologically in the tongue of rats that were exposed the first and the second week after infection. Lymphocyte stimulation assays using mesenteral lymph node cells indicated that UVB exposure also impaired the specific lymphocyte response to T. spiralis. Moreover, DTH responses to T. spiralis were severely impaired in rats that were UVB irradiated daily for 7 consecutive days in the second week after infection. Thus, these data combined with the data of the Kromayer study indicate that exposure of rats to FS40 irradiation following oral infection with T. spiralis leads to increased numbers of larvae in systemic sites and impaired T-cell immunity to the parasite.