UVB-induced Immunosuppression Research Articles

Lipoteichoic Acid from Lacticaseibacillus rhamnosus GG Modulates Dendritic Cells and T Cells in the Gut

Lipoteichoic acid (LTA) from Gram-positive bacteria exerts different immune effects depending on the bacterial source from which it is isolated. Lacticaseibacillus rhamnosus GG LTA (LGG-LTA) oral administration reduces UVB-induced immunosuppression and skin tumor development in mice. In the present work, we evaluate the immunomodulatory effect exerted by LGG-LTA in dendritic cells (DC) and T cells, both in vitro and in the gut-associated lymphoid tissue (GALT). During cell culture, LTA-stimulated BMDC increased CD86 and MHC-II expression and secreted low levels of pro and anti-inflammatory cytokines. Moreover, LTA-treated BMDC increased T cell priming capacity, promoting the secretion of IL-17A. On the other hand, in orally LTA-treated mice, a decrease in mature DC (lamina propria and Peyer’s patches) was observed. Concomitantly, an increase in IL-12p35 and IFN-γ transcription was presented (lamina propria and Peyer’s Patches). Finally, an increase in the number of CD103+ DC was observed in Peyer’s patches. Together, our data demonstrate that LGG-LTA activates DC and T cells. Moreover, we show that a Th1-biased immune response is triggered in vivo after oral LTA administration. These effects justify the oral LTA activity previously observed.

Keratinocytes Counteract UVB-Induced Immunosuppression in Mice through HIF-1a Signaling

The transcription factor HIF-1a regulates cellular metabolism under hypoxia but also immune responses and UVB-induced skin reactions. In keratinocytes (KCs), HIF-1a is an environmental sensor orchestrating the adaptation to environmental changes. In this study, we investigated the role of HIF-1a in KCs for skin reactions to acute and chronic UVB exposure in mice. The function of HIF-1a in KCs under UVB exposure was analyzed in KC-specific HIF-1a conditional knockout (cKO) mice. cKO mice were hypersensitive to acute high-dose UVB irradiation compared with wild-type mice, displaying increased cell death and delayed barrier repair. After chronic low-dose UVB treatment, cKO mice also had stronger epidermal damage but reduced infiltration of dermal macrophages and T helper cells compared with wild-type mice. Irradiated cKO mice revealed accumulation of regulatory lymphocytes in dorsal skin-draining lymph nodes compared with wild-type and unirradiated mice. This was reflected by an augmented IL-10 release of lymph node cells and a weaker contact hypersensitivity reaction to DNFB in UVB-exposed cKO mice than in wild-type and unirradiated controls. In summary, we found that KC-specific HIF-1a expression is crucial for adaptation to UVB exposure and inhibits the development of UVB-induced immunosuppression in mice. Therefore, HIF-1a signaling in KCs could ameliorate photoaging-related skin disorders.

Keratinocyte-derived microvesicle particles mediate ultraviolet B radiation-induced systemic immunosuppression.

A complete carcinogen, ultraviolet B (UVB) radiation (290-320 nm), is the major cause of skin cancer. UVB-induced systemic immunosuppression that contributes to photocarcinogenesis is due to the glycerophosphocholine-derived lipid mediator platelet-activating factor (PAF). A major question in photobiology is how UVB radiation, which only absorbs appreciably in the epidermal layers of skin, can generate systemic effects. UVB exposure and PAF receptor (PAFR) activation in keratinocytes induce the release of large numbers of microvesicle particles (MVPs; extracellular vesicles ranging from 100 to 1000 nm in size). MVPs released from skin keratinocytes in vitro in response to UVB (UVB-MVPs) are dependent on the keratinocyte PAFR. Here, we used both pharmacologic and genetic approaches in cells and mice to show that both the PAFR and enzyme acid sphingomyelinase (aSMase) were necessary for UVB-MVP generation. Our discovery that the calcium-sensing receptor is a keratinocyte-selective MVP marker allowed us to determine that UVB-MVPs leaving the keratinocyte can be found systemically in mice and humans following UVB exposure. Moreover, we found that UVB-MVPs contained bioactive contents including PAFR agonists that allowed them to serve as effectors for UVB downstream effects, in particular UVB-mediated systemic immunosuppression.

527 Keratinocyte-Specific Function of Hypoxia-Inducible Factor-1alpha (HIF1a) in UVB-Induced Immunosuppression

527 Keratinocyte-Specific Function of Hypoxia-Inducible Factor-1alpha (HIF1a) in UVB-Induced Immunosuppression

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

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

Protective Effect of Bixin Isolated from Bixa orellana L. Seeds on UVB-Induced Inflammation and Immunosuppression of the Skin

Background: DNA damage caused by excessive ultraviolet B (UVB) radiation on the skin triggers the response to inflammatory and immunosuppression. The bixin from Bixa orellana L. has been proven to be able to inhibit cyclo-oxygenase.
 Objective: to verify whether the bixin lotion has the effect to offer protection against inflammation and immunosuppression due to acute UVB irradiation in shaved BALB /c mice.
 Methods: Protection against inflammation and immunosuppression, respectively were studied in 4 groups of mice. Each group was treated respectively with topical application of base lotion as a control; bixin lotion doses of 0.5 mg; 2.5 mg and 125 mg, for 10 days prior to and during the UVB irradiation. The Inflammation was induced by UVB irradiation, 360 mJ/cm2 once a day for 3 consecutive days, whereas the immunosuppression was induced by UVB irradiation, 360 mJ/cm2 once a day for 5 consecutive days. The inflammatory response was measured as an increase in middorsal skinfold thickness at the peak response. The immune response was measured as the contact hypersensitivity (CHS) response to oxasolon sensitization.
 Results: The results indicated that in concentration range used, bixin lotion significantly decreased the middorsal skinfold thickness at 72 hours after UVB radiation (p <0.05) compared to the control, but there was no significant difference between couples of the dose of bixin. Bixin lotion was also capable to restore the suppression of CHS from 34.22% in the control group to 11.4%; 0.5% and 0% at doses of 0.5; 2.5 and 125 mg respectively (p <0.05).
 Conclusion: Bixin lotion has the potential to reduce the inflammatory edema reaction and the suppression of CHS of mice induced by UVB radiation.
 Bangladesh Journal of Medical Science Vol.18(1) 2019 p.107-111

Retraction: (-)-Epigallocatechin-3-Gallate Prevents Photocarcinogenesis in Mice through Interleukin-12-Dependent DNA Repair.

We have shown previously that topical application of (-)-epigallocatechin-3-gallate (EGCG), the major polyphenol of green tea, prevents photocarcinogenesis in mice. EGCG prevents UVB-induced immunosuppression by inducing interleukin-12 (IL-12). As immunosuppression is a risk factor for photocarcinogenesis, we investigated the possibility that EGCG also prevents UVB-induced photocarcinogenesis through an IL-12-dependent DNA repair mechanism. To investigate this possibility, we determined the effects of EGCG on photocarcinogenesis in IL-12 knockout (KO) mice using the formation of cyclobutane pyrimidine dimers (CPD) as an indicator of the extent of UVB-induced DNA damage. Topical application of EGCG (1 mg/cm(2) skin) prevented photocarcinogenesis in wild-type (C3H/HeN) mice in terms of tumor incidence and tumor multiplicity but did not prevent photocarcinogenesis in IL-12 KO mice. UVB-induced DNA damage, as determined by the formation of CPDs and the number of sunburn cells, was resolved more rapidly in the skin of wild-type mice treated with EGCG than untreated control mice. In contrast, the extent of UVB-induced DNA damage and the numbers of sunburn cells were not significantly different in the EGCG-treated IL-12 KO mice and untreated control mice. In addition, treatment of XPA-proficient human fibroblast cells with EGCG promoted repair of UVB-induced CPDs in a dose-dependent manner but not in an XPA-deficient cells, indicating that the nucleotide excision repair mechanism is involved in EGCG-mediated DNA repair. Taken together, these results indicate for the first time that EGCG can prevent photocarcinogenesis through an EGCG-induced IL-12-dependent DNA repair mechanism.

Preventive effects of Eucommia ulmoides leaf extract and its components on UVB-induced immunosuppression in mice

Ultraviolet (UV) irradiation is a well known photo-immunosuppressant. To determine the effect of Eucommia ulmoides leaf extract (ELE) components (chlorogenic acid, geniposidic acid, and asperuloside) on UVB induced immunosuppression, we examined mice that were contact hypersensitized. Systemic immunosuppression was induced in the C57BL/6j mice that were sensitized with 0.5% oxazolone through the skin by a single exposure to UVB. Consecutive oral administration of ELE, chlorogenic acid, or geniposidic acid significantly reduced UVB-induced suppression of the contact hypersensitivity (CHS) response. The treatment with chlorogenic acid or geniposidic acid decreased the serum interleukin-10 levels in the sensitized mice after UVB irradiation. Additionally, the level of plasma reactive oxygen species and the expression of skin mast cells decreased in the chlorogenic acid-treated mice. Contrarily, the expression of regulatory T cell in the skin decreased in the geniposidic acid-treated mice. These results suggest that chlorogenic and geniposidic acids prevent the photo-immunosuppression of the CHS response.

Regulatory B cells induced by ultraviolet B through toll-like receptor 4 signalling contribute to the suppression of contact hypersensitivity responses in mice.

Ultraviolet (UV) B irradiation is known to suppress contact hypersensitivity (CHS) responses in mouse models by suppressing immune responses. However, the cellular mechanisms responsible for UVB-induced systemic suppression remain unclear. Regulatory B cells have been reported to play an inhibitory role during CHS. It is presently unknown whether regulatory B cells contribute to the effect of UVB phototherapy. To investigate the inductive effect of UVB on regulatory B cells and the underlying mechanisms by using a CHS mouse model. CHS was induced with oxazolone, and evaluated by histopathology, flow cytometry, and quantitative real-time polymerase chain reaction. We found that UVB irradiation induced regulatory B cell expansion and ameliorated CHS. UVB-induced regulatory B cells contribute to systemic immunosuppression by inhibiting the proliferation of T cells. Moreover, we determined that toll-like receptor (TLR) 4, the expression of which was upregulated in B cells after UVB exposure, played an essential role in the induction of regulatory B cells. Our data identified regulatory B cells as regulators of UVB-induced immunosuppression in CHS, and suggest the importance of the UVB-TLR4 axis in the generation of regulatory B cells.

Epidermal PPARγ influences subcutaneous tumor growth and acts through TNF-α to regulate contact hypersensitivity and the acute photoresponse.

It is known that ultraviolet B (UVB) induces PPARγ ligand formation while loss of murine epidermal PPARγ (Pparg-/-epi) promotes UVB-induced apoptosis, inflammation, and carcinogenesis. PPARγ is known to suppress tumor necrosis factor-α (TNF-α) production. TNF-α is also known to promote UVB-induced inflammation, apoptosis, and immunosuppression. We show that Pparg-/-epi mice exhibit increased baseline TNF-α expression. Neutralizing Abs to TNF-α block the increased photo-inflammation and photo-toxicity that is observed in Pparg-/-epi mouse skin. Interestingly, the increase in UVB-induced apoptosis in Pparg-/-epi mice is not accompanied by a change in cyclobutane pyrimidine dimer clearance or in mutation burden. This suggests that loss of epidermal PPARγ does not result in a significant alteration in DNA repair capacity. However, loss of epidermal PPARγ results in marked immunosuppression using a contact hypersensitivity (CHS) model. This impaired CHS response was significantly alleviated using neutralizing TNF-α antibodies or loss of germline Tnf. In addition, the PPARγ agonist rosiglitazone reversed UVB-induced systemic immunosuppression (UV-IS) as well as UV-induced growth of B16F10 melanoma tumor cells in syngeneic mice. Finally, increased B16F10 tumor growth was observed when injected subcutaneously into Pparg-/-epi mice. Thus, we provide novel evidence that epidermal PPARγ is important for cutaneous immune function and the acute photoresponse.

Abstract 2221: Honokiol stimulates immune reactivity in UV-irradiated skin through DNA demethylation-dependent functional activation of dendritic cells in mice

Abstract Solar ultraviolet radiation (UVR), and in particular UVB spectrum (290-320 nm), are considered as a complete carcinogen for cutaneous malignancies. The over-exposure of UVR suppresses the development of allergic contact hypersensitivity (CHS) response in both laboratory animals as well as in humans. CHS response is considered to be a prototypic T-cell mediated immune response. UVR-induced suppression of immune sensitivity has been implicated in skin cancer risk. Therefore, the treatment options which can inhibit UVB-induced suppression of immune sensitivity may be useful in the management of skin cancers, including both melanoma and non-melanoma. Previously, we have shown that topical treatment of honokiol inhibits UVB induced immune suppression, which was associated with the reduction in UVB-induced inflammatory mediators in the mouse skin. Here, we have further determined the underlying mechanism of action of honokiol on UVR-induced immunosuppression including its effect on epigenetic regulators and their relationship with immune sensitivity in mouse skin. Topical treatment of C3H/HeN mice with honokiol (0.5 and 1.0 mg/cm2 skin area) in hydrophilic-cream based topical formulation significantly inhibits UVB-induced suppression of CHS response (P<0.01-0.005), which was associated with reduced levels of DNA methylation as well as Dnmt activity in the mouse skin compared with non-honokiol-treated and UVB-exposed control mice. To characterize the cell population responsible for the honokiol mediated inhibition of UVB-induced immunosuppression, we used an adoptive transfer approach. DNA-methylated (most of cells) dendritic cells (DCs), isolated from the draining lymph nodes of donor mice that had been UVB-exposed and sensitized to 2,4,-dinitrofluorobenzene (DNFB) with and without honokiol (0.5 and 1.0 mg/cm2 skin area) treatment, were transferred into naïve recipient mice. The CHS response of the recipient mice to DNFB was then measured. Honokiol treatment of UVB-exposed donor mice relieved this suppression of the CHS response in naïve mice, while the recipient mice, obtained DNA-methylated DCs from UVB-exposed donor mice that were not treated with honokiol, showed significant suppression in the CHS response. The restoration of CHS response in mice receiving DCs from honokiol treated, UV-exposed donor mice was also associated with enhanced secretion of Th1-type cytokines compared with the Th1-type cytokines from the DCs obtained from non-honokiol-treated and UVB-exposed donor mice. These data suggest that honokiol mediated inhibition of UVB induced suppression of CHS response is associated with functional activation of dendritic cells and that is dependent on DNA demethylation in DCs. Note: This abstract was not presented at the meeting. Citation Format: Santosh K. Katiyar, Tripti Singh, Harish C. Pal, Ram Prasad. Honokiol stimulates immune reactivity in UV-irradiated skin through DNA demethylation-dependent functional activation of dendritic cells in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2221. doi:10.1158/1538-7445.AM2017-2221

Honokiol inhibits ultraviolet radiation-induced immunosuppression through inhibition of ultraviolet-induced inflammation and DNA hypermethylation in mouse skin

Ultraviolet (UV) radiation exposure induces immunosuppression, which contributes to the development of cutaneous malignancies. We investigated the effects of honokiol, a phytochemical found in plants of the genus Magnolia, on UVB-induced immunosuppression using contact hypersensitivity (CHS) as a model in C3H/HeN mice. Topical application of honokiol (0.5 and 1.0 mg/cm2 skin area) had a significant preventive effect on UVB-induced suppression of the CHS response. The inflammatory mediators, COX-2 and PGE2, played a key role in this effect, as indicated by honokiol inhibition of cyclooxygenase-2 (COX-2) expression and PGE2 production in the UVB-exposed skin. Honokiol application also inhibited UVB-induced DNA hypermethylation and its elevation of the levels of TET enzyme, which is responsible for DNA demethylation in UVB-exposed skin. This was consistent with the restoration of the CHS response in mice treated with the DNA demethylating agent, 5-aza-2′-deoxycytidine, after UVB exposure. There was no significant difference in the levels of inhibition of UVB-induced immunosuppression amongst mice that were treated topically with available anti-cancer drugs (imiquimod and 5-fluorouracil). This study is the first to show that honokiol has the ability to inhibit UVB-induced immunosuppression in preclinical model and, thus, has potential for use as a chemopreventive strategy for UVB radiation-induced malignancies.

The alternative complement component factor B regulates UV-induced oedema, systemic suppression of contact and delayed hypersensitivity, and mast cell infiltration into the skin.

Ultraviolet (UV) wavelengths in sunlight are the prime cause of skin cancer in humans with both the UVA and UVB wavebands making a contribution to photocarcinogenesis. UV has many different biological effects on the skin that contribute to carcinogenesis, including suppression of adaptive immunity, sunburn and altering the migration of mast cells into and away from irradiated skin. Many molecular mechanisms have been identified as contributing to skin responses to UV. Recently, using gene set enrichment analysis of microarray data, we identified the alternative complement pathway with a central role for factor B (fB) in UVA-induced immunosuppression. In the current study we used mice genetically deficient in fB (fB-/- mice) to study the functional role of the alternative complement pathway in skin responses to UV. We found that fB is required for not only UVA but also UVB-induced immunosuppression and solar-simulated UV induction of the oedemal component of sunburn. Factor B-/- mice had a larger number of resident skin mast cells than control mice, but unlike the controls did not respond to UV by increasing mast cell infiltration into the skin. This study provides evidence for a function role for fB in skin responses to UV radiation. Factor B regulates UVA and UVB induced immunosuppression, UV induced oedema and mast cell infiltration into the skin. The alternative complement pathway is therefore an important regulator of skin responses to UV.

Interleukin-17 mediated inflammatory responses are required for ultraviolet radiation-induced immune suppression.

Ultraviolet radiation (UVR) induces immunosuppression and is a major factor for development of skin cancer. Numerous efforts have been made to determine mechanisms for UVR-induced immunosuppression and to develop strategies for prevention and treatment of UVR-induced cancers. In the current study, we use IL-17 receptor (IL-17R) deficient mice to examine whether IL-17 mediated responses have a role in UVB (290-320)-induced immunosuppression of contact hypersensitivity responses. Results demonstrate that IL-17 mediated responses are required for UVB-induced immunosuppression of contact hypersensitivity responses. The systemic immune suppression and development of regulatory T cells are inhibited in UVB-treated IL-17R deficient mice compared to wild-type animals. The deficiency in IL-17R inhibits the infiltration and development of a tolerogenic myeloid cell population in UVB-treated skin, which expresses CD11b and Gr-1 and produces reactive oxygen species. We speculate that the development of the tolerogenic myeloid cells is dependent on IL-17-induced chemokines and inflammatory mediators in UVB-treated skin. The inhibition of the tolerogenic myeloid cells may be attributed to the suppression of regulatory T cells in UVR-treated IL-17R(-/-) mice. The findings may be exploited to new strategies for prevention and treatment of UVR-induced skin diseases and cancers.

Abstract 1239: Dietary grape seed proanthocyanidins inhibit UV-induced immune suppression by targeting the development of regulatory T cells in mice

Abstract Immunosuppressive effects of solar ultraviolet (UV) radiation have been implicated in the risk of non-melanoma and melanoma skin cancers in humans. Previously, we have shown that dietary grape seed proanthocyanidins (GSPs) inhibit photocarcinogenesis in mice and inhibit UV-induced suppression of allergic contact hypersensitivity (CHS) response, a prototypic T-cell-mediated immune response. Studies have shown that UV-induced T regulatory (Treg) cells or suppressor T cells have a role in immune suppression and UV-induced skin carcinogenesis is indicated by the demonstration that depletion of UV-induced T-suppressor cells can inhibit UV-induced carcinogenesis. In our continued efforts to investigate the molecular targets responsible for the prevention of immunosuppression in UV exposed mice by GSPs, we have investigated whether GSPs inhibit UV-induced immunosuppression by inhibiting the development or activity of UV-induced Treg cells in mice. To understand the mechanism, C3H/HeN mice were exposed to UV (150 mJ/cm2) radiation on 4 consecutive days with and without treatment of mice with dietary GSPs, mice were sensitized with 2,4-dinitrofluorobenzene (DNFB) 48 h after the last UV exposure, and then sacrificed 5 days after DNFB sensitization. The flow cytometry analysis of lymph node cells indicated that the numbers of Treg cells were reduced in the mice which were given GSPs in diet compared to non-GSPs-treated UV-exposed mice. We then analyzed effects of dietary GSPs (0.5%, w/w) on secretion of cytokines by Treg cells that were isolated from lymph nodes and spleens of mice that were exposed to UVB (150 mJ/cm2). Our ELISA data showed that in comparison to Treg cells isolated from control mice (GSPs-untreated), Treg cells isolated from mice that received GSPs in diet secreted a significantly higher level of IFNγ, while significantly lower levels of interleukin (IL)-10 and TGF-β, which are immunosuppressive in nature. Finally, we used an adoptive transfer approach, wherein draining lymph nodes were harvested from mice that were exposed to UVB on 4 consecutive days with and without GSPs supplementation in diet and sensitized by DNFB onto the UVB-exposed skin. Treg cells were positively selected using magnetic beads and MACS system and transferred into naïve mice that were subsequently challenged by application of DNFB on the ear skin. Naïve recipients that received Treg cells from GSPs-treated, UVB-irradiated donors exhibited CHS response, whereas no significant CHS was observed in mice which were injected Treg cells from UVB alone-exposed mice compared to control group. These data suggest that dietary GSPs inhibit UVB-induced immunosuppression by suppressing the development as well as the functional activation of Treg cells in UV-exposed mice. Citation Format: Santosh K. Katiyar, Tripti Singh, Mudit Vaid. Dietary grape seed proanthocyanidins inhibit UV-induced immune suppression by targeting the development of regulatory T cells in mice. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1239. doi:10.1158/1538-7445.AM2014-1239

Chafuroside B, an Oolong Tea Polyphenol, Ameliorates UVB-Induced DNA Damage and Generation of Photo-immunosuppression Related Mediators in Human Keratinocytes

Chafuroside B was recently isolated as a new polyphenolic constituent of oolong tea leaves. However, the effects of chafuroside B on skin function have not been examined. In this study, we investigated the protective effects of chafuroside B against UVB-induced DNA damage, apoptosis and generation of photo-immunosuppression related mediators in cultured normal human epidermal keratinocytes (NHEK). Chafuroside B at 1 µM attenuated both UVB-induced apoptosis, evaluated in terms of caspase-3/7 activity, and UVB-induced DNA damage, evaluated in terms of formation of cyclobutane pyrimidine dimers (CPD), in NHEK exposed to UVB (20 mJ/cm2). In addition, chafuroside B at 0.3 or 1 µM suppressed the UVB-induced production of interleukin (IL)-10, tumor necrosis factor (TNF)-α, and prostaglandin E2 (PGE2), as determined by ELISA, and conversely enhanced IL-12 mRNA expression and production, as measured by RT-PCR and ELISA. Further, chafuroside B at 1 µM also suppressed UVB-induced expression of receptor activator of nuclear factor κB ligand (RANKL) mRNA. These results indicate that chafuroside B promotes repair of UVB-induced DNA damage and ameliorates the generation of IL-10, TNF-α, PGE2, and RANKL, all of which are UVB-induced immunosuppression related mediators. These effects of chafuroside B may be mediated at least in part through induction of IL-12 synthesis in human keratinocytes. Because chafuroside B might have practical value as a photoprotective agent, a further study of the in vivo effects of chafuroside B seems warranted.

Prostaglandin E2 Promotes UV Radiation-Induced Immune Suppression through DNA Hypermethylation

Exposure of mice to UV radiation results in suppression of the contact hypersensitivity (CHS) response. Here, we report that the UV-induced suppression of CHS is associated with increases in the levels of cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2), and PGE2 receptors in the exposed skin. UV radiation.induced suppression of CHS was inhibited by topical treatment of the skin with celecoxib or indomethacin (inhibitors of COX-2) or AH6809 (an EP2 antagonist). Moreover, mice deficient in COX-2 were found to be resistant to UV-induced suppression of CHS. The exposure of wild-typemice to UVB radiation resulted in DNA hypermethylation, increased DNA methyltransferase (Dnmt) activity, and elevated levels of Dnmt1, Dnmt3a, and Dnmt3b proteins in the skin, and these responses were downregulated on topical treatment of the site of exposure after irradiation with indomethacin or EP2 antagonist. Topical treatment of UVB-exposed COX-2.deficient mice with PGE2 enhanced the UVB-induced suppression of CHS as well as global DNA methylation and elevated the levels of Dnmt activity and Dnmt proteins in the skin. Intraperitoneal injection of 5-aza-2′-deoxycytidine (5-Aza-dc), a DNA demethylating agent, restored the CHS response to 2,4-dinitrofluorobenzene in UVB-exposed skin and this was associated with the reduction in global DNA methylation and Dnmt activity and reduced levels of Dnmt proteins. Furthermore, treatment with 5-Aza-dc reversed the effect of PGE2 on UV-induced suppression of CHS in COX-2.deficient mice. These findings reveal a previously unrecognized role for PGE2 in the promotion of UVB-induced immunosuppression and indicate that it is mediated through PGE2 regulation of DNA methylation.

Abstract 1082: Silymarin, a phytochemical from milk thistle, inhibits UVB-induced immune suppression through DNA repair-dependent activation of dendritic cells and stimulation of effector T cells .

Abstract Ultraviolet (UV) radiation-induced immunosuppression has been implicated in the risk of skin cancers, including melanoma and non-melanoma. Topical treatment of mouse skin with silymarin, a bioactive phytochemical from milk thistle (Silybum marianum L. Gaertn.), inhibits UVB radiation-induced skin tumor development and immunosuppression in mice. To identify the molecular mechanisms underlying its effect on immune system, we used an adoptive transfer approach in which dendritic cells (DCs) from the draining lymph nodes of donor mice that had been UVB-exposed and sensitized to 2,4,-dinitrofluorobenzene (DNFB) were transferred into naïve recipient mice. The contact hypersensitivity (CHS) response of the recipient mice to DNFB was then measured. When DCs were obtained from UVB-exposed donor mice that were not treated with silymarin, the CHS response was suppressed confirming the role of DCs in the UVB-induced immunosuppression. CHS response is considered as a prototypic T-cell mediated immune response. Silymarin treatment of UVB-exposed donor mice relieved this suppression of the CHS response in the recipients. Silymarin treatment was associated with rapid repair of UVB-induced cyclobutane pyrimidine dimers (CPDs) in DCs and silymarin treatment did not prevent UV-induced immunosuppression in xeroderma pigmentosum complementation Group A (XPA)-deficient mice which are unable to repair UV-induced DNA damage. The CHS response in mice receiving DCs from silymarin-treated UV-exposed donor mice also was associated with enhanced secretion of Th1-type cytokines and stimulation of T cells. Adoptive transfer of T cells revealed that transfer of either CD8+ or CD4+ cells from silymarin-treated, UVB-exposed donors resulted in enhancement of the CHS response. Cell culture study showed enhanced secretion of IL-2 and IFNγ by CD8+ T cells, and reduced secretion of Th2 cytokines by CD4+ cells, obtained from silymarin-treated UVB-exposed mice. These data suggest that DNA repair-dependent functional activation of DCs, a reduction in CD4+ regulatory T-cell activity, and stimulation of CD8+ effector T cells contribute to silymarin-mediated inhibition of UVB-induced immunosuppression in mice. This property of silymarin can be used as an alternative strategy to augment immune system and that may help to prevent or delay the risk of skin cancers in high-risk human population. Citation Format: Mudit Vaid, Ram Prasad, Tripti Singh, Craig A. Elmets, Hui Xu, Santosh K. Katiyar. Silymarin, a phytochemical from milk thistle, inhibits UVB-induced immune suppression through DNA repair-dependent activation of dendritic cells and stimulation of effector T cells . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1082. doi:10.1158/1538-7445.AM2013-1082

Bioactive Grape Proanthocyanidins Enhance Immune Reactivity in UV-Irradiated Skin through Functional Activation of Dendritic Cells in Mice

Ultraviolet (UV) radiation-induced immunosuppression has been implicated in skin carcinogenesis. Grape seed proanthocyanidins (GSPs) have anti-skin carcinogenic effects in mice and GSPs-fed mice exhibit a reduction in UV-induced suppression of allergic contact hypersensitivity (CHS), a prototypic T-cell-mediated response. Here, we report that dietary GSPs did not inhibit UVB-induced suppression of CHS in xeroderma pigmentosum complementation group A (XPA)-deficient mice, which lack nucleotide excision repair mechanisms. GSPs enhanced repair of UVB-induced DNA damage (cyclobutane pyrimidine dimers) in wild-type, but not XPA-deficient, dendritic cells (DC). Co-culture of CD4(+) T cells with DCs from UVB-irradiated wild-type mice resulted in suppression of T-cell proliferation and secretion of T-helper (TH) 1-type cytokines that was ameliorated when the DCs were obtained from GSP-fed mice, whereas DCs obtained from GSP-fed XPA-KO mice failed to restore T-cell proliferation. In adoptive transfer experiments, donor DCs were positively selected from the draining lymph nodes of UVB-exposed donor mice that were sensitized to 2,4,-dinitrofluorobenzene were transferred into naïve recipient mice and the CHS response assessed. Naïve recipients that received DCs from UVB-exposed wild-type donors that had been fed GSPs exhibited a full CHS response, whereas no significant CHS was observed in mice that received DCs from XPA-KO mice fed GSPs. These results suggest that GSPs prevent UVB-induced immunosuppression through DNA repair-dependent functional activation of dendritic cells in mice. Cancer Prev Res; 6(3); 242-52. ©2013 AACR.

Silymarin inhibits ultraviolet radiation-induced immune suppression through DNA repair-dependent activation of dendritic cells and stimulation of effector T cells

Silymarin inhibits UVB-induced immunosuppression in mouse skin. To identify the molecular mechanisms underlying this effect, we used an adoptive transfer approach in which dendritic cells (DCs) from the draining lymph nodes of donor mice that had been UVB-exposed and sensitized to 2,4,-dinitrofluorobenzene (DNFB) were transferred into naïve recipient mice. The contact hypersensitivity (CHS) response of the recipient mice to DNFB was then measured. When DCs were obtained from UVB-exposed donor mice that were not treated with silymarin, the CHS response was suppressed confirming the role of DCs in the UVB-induced immunosuppression. Silymarin treatment of UVB-exposed donor mice relieved this suppression of the CHS response in the recipients. Silymarin treatment was associated with rapid repair of UVB-induced cyclobutane pyrimidine dimers (CPDs) in DCs and silymarin treatment did not prevent UV-induced immunosuppression in XPA-deficient mice which are unable to repair UV-induced DNA damage. The CHS response in mice receiving DCs from silymarin-treated UV-exposed donor mice also was associated with enhanced secretion of Th1-type cytokines and stimulation of T cells. Adoptive transfer of T cells revealed that transfer of either CD8+ or CD4+ cells from silymarin-treated, UVB-exposed donors resulted in enhancement of the CHS response. Cell culture study showed enhanced secretion of IL-2 and IFNγ by CD8+ T cells, and reduced secretion of Th2 cytokines by CD4+ T cells, obtained from silymarin-treated UVB-exposed mice. These data suggest that DNA repair-dependent functional activation of DCs, a reduction in CD4+ regulatory T-cell activity, and stimulation of CD8+ effector T cells contribute to silymarin-mediated inhibition of UVB-induced immunosuppression.