Type I interferons (IFNs) are important enhancers of immune responses which are downregulated in human cancers, including skin cancer. Solar ultraviolet (UV) B radiation is a proven environmental carcinogen, and its exposure contributes to the high prevalence of skin cancer. The carcinogenic effects of UV light can be attributed to the formation of cyclobutane pyrimidine dimers (CPD) and errors in the repair and replication of DNA. Treatment with a single dose of UVB (100 mJ/cm²) upregulated IFNα and IFNβ in the skin of C57BL/6 mice. IFNα and IFNβ were predominantly produced by CD11b+ cells. In mice lacking the type I IFN receptor 1 (IFNAR1), the repair of CPD following cutaneous exposure to a single dose of UVB (100 mJ/cm²) was decreased. UVB induced the expression of the DNA repair gene xeroderma pigmentosum A (XPA) in wild-type (WT) mice. In contrast, such treatment in IFNAR1 (IFNAR1-/-) mice downregulated XPA. A local UVB regimen consisting of UVB radiation (150 mJ/cm²) for 4 days followed by sensitization with hapten 2,4, dinitrofluorobenzene (DNFB) resulted in significant suppression of immune responses in both WT and IFNAR1-/- mice. However, there were significantly higher CD4+CD25+Foxp3+ regulatory T-cells in the draining lymph nodes of IFNAR1-/- mice in comparison to WT mice. Overall, our studies reveal a previously unknown action of type I IFNs in the repair of photodamage and the prevention of UVB-induced immune suppression.

Ultraviolet (UV) irradiation of the skin is related to the development of skin cancer. UVB also causes DNA damage in the form of cyclobutane pyrimidine dimers (CPDs), which can result in stable mutations. Toll-like receptor 4 (TLR4), a component of innate immunity, plays a key role in cancer. Previous studies from our laboratory have observed that TLR4 deficiency resulted in the repair of UVB-induced DNA damage, inhibition of UVB-induced immune suppression, and carcinogenesis. In this study, we determined the efficacy of TLR4 antagonist TAK-242 in regulation of UVB-induced DNA damage, inflammation, and tumor development. Our results indicate that TAK-242 treatment increased the expression of xeroderma pigmentosum group A (XPA) mRNA, resulting in the repair of UVB-induced CPDs in skin of SKH-1 mice. Treatment with TAK-242 also inhibited the activation of NLR family pyrin domain containing 3 (NLRP3) in UVB-exposed skin of SKH-1 mice. Cutaneous carcinogenesis was significantly reduced in mice treated with TAK-242 in comparison to vehicle-treated mice. The proinflammatory cytokines IL-1β, IL-6, and TNF-α were also found to be significantly greater in vehicle-treated mice than TAK-242-treated mice. Finally, treatment with TAK-242 augmented anti-tumor immune responses in mice. Our data provide further evidence that activation of the TLR4 pathway promotes the development of UV-induced non-melanoma skin cancer mediated at least in part on its negative effects on DNA damage. Moreover, treatment with the TLR4 inhibitor TAK-242 may be effective for prevention of skin cancer.

Background/Objective: Ultraviolet (UV) B radiation leads to DNA damage by generating cyclobutane pyrimidine dimers (CPDs). UVB-induced CPDs can also result in immune suppression, which is a major risk factor for non-melanoma skin cancer (NMSC). UVB-induced CPDs are repaired by nucleotide repair mechanisms (NER) mediated by xeroderma pigmentosum complementation group A (XPA). The purpose of this study was to investigate the use of TH as a chemopreventive agent against the development of skin cancer. Method: SKH-1 hairless mice were exposed were fed with TH (0.1% v/v) for two weeks and exposed to a single dose of UVB (180 mJ/cm²). Dorsal skin was harvested 24 h post-UVB exposure for evaluation of DNA damage and repair. Lymph nodes were also harvested to prepare single cell suspension for flow cytometric evaluation. For carcinogenesis experiments, SKH-1 hairless mice were given TH (0.1% v/v) ad libitum and exposed to UVB (180 mJ/cm²) thrice a week for 30 weeks. Results: Feeding SKH-1 hairless mice with TH (0.1% v/v) for two weeks prior to a single dose of UVB (180 mJ/cm²) led to a significant increase in XPA in skin and DNA repair cytokines IL-12 and IL-23 in draining lymph nodes. Furthermore, when subjected to the photocarcinogenesis protocol; mice fed with TH developed significantly fewer tumors in comparison to mice fed on drinking water. Conclusions: Our data demonstrate that TH has a protective effect against UVB-induced DNA damage, immune suppression, and skin cancer. Future studies will further investigate the potential of TH as a preventive treatment for NMSC.

IFN-λ is a type III interferon (IFN) with pleiotropic functions in modulating immune responses. To address its function in autoimmune neuroinflammation, we evaluated the development and progression of experimental autoimmune encephalitis (EAE) in IFNLR1 KO (Ifnlr1^−/−) and C57Bl/6 (WT) mice following immunization with MOG_35–55 peptide. The results show that Ifnlr1^−/− mice developed significantly more severe EAE than WT littermates with a similar day of onset, suggesting the potential of IFN-λ in reducing disease severity. We next interrogated whether IFN-λ differentially modulates EAE induced by encephalitogenic Th1 cells or Th17 cells. Encephalitogenic Th1 or Th17 generated from WT donors were transferred into WT or Ifnlr1^−/− recipient mice. Whereas encephalitogenic Th1 cells induced more severe EAE in Ifnlr1^−/− than WT recipients, the disease severity induced by encephalitogenic Th17 cells was similar. Additionally, in vitro experiments showed that Ifnlr1^−/− macrophages promoted the expansion of myelin peptide-reactive Th17 cells but not Th1 cells. Early in the disease, the spinal cords of EAE mice displayed a significantly greater proportion of Ly6C^-Ly6G⁺ cells with CXCR2⁺CD62L^lo phenotype, indicating activated neutrophils. These findings suggest that IFN-λ signaling restrains activation and migration of neutrophils to the CNS, potentially attenuating neutrophil-mediated disease progression in autoimmune neuroinflammation. Recombinant IFN-λ can be used as a potential therapeutic target for treatment of patients with multiple sclerosis as it has fewer side effects due to the restricted expression of its receptor.

Ultraviolet B (UVB) radiation triggers DNA damage and immune suppression, establishing conditions favorable for skin carcinogenesis. Previous studies have shown that a downstream adaptor for Toll-like receptors (TLRs), myeloid differentiation primary response 88 (MyD88), plays a role in UVB-induced DNA damage and immunosuppression. However, specific mechanisms for the effects on dendritic cells and T cells remain poorly understood. The objective of this study is to determine the role of MyD88 and TIR-domain-containing adaptor inducing interferon-β (TRIF), another key TLR downstream adaptor, in UVB-induced suppression of dendritic cell activity and T cell function. MyD88−/−, Trif−/−, and wild-type (WT) mice were evaluated for UVB-induced effects on dendritic cell, T cells, and contact hypersensitivity responses in skin. MyD88−/− mice exhibited significant resistance to UVB-induced immune suppression, compared to Trif−/− mice and wild-type controls. The MyD88 deficiency significantly reduced UVB-induced Treg cells that were CD4⁺CD25⁺Foxp3⁺ and produced interleukin (IL)-10. Moreover, it significantly inhibited the UVB-induced suppression of IL-12/IL-23 producing CD11c⁺ dendritic cells. Further experiments confirmed that MyD88 conditional knockout (MyD88fl/flXCD11c.Cre) mice were protected against UVB-induced immune suppression. Dendritic cells from MyD88 genomic or conditional knockout mice were resistant to UVB-induced reduction of major histocompatibility complex (MHC) class II antigens. These findings show that MyD88 plays a key role in UVB-induced immune suppression. The deficiency in the MyD88 gene inhibits UVB-induced suppression of CD11c+ dendritic cell (DC) activity and reduces UVB-induced development of Treg cells. Our studies demonstrate a new mechanism for MyD88-mediated regulation of UVB-induced immune suppression.

Background: Although ultraviolet B (UVB) radiation-induced immunosuppression is considered a key risk factor for skin cancer, individual susceptibility varies, and its mechanisms remain not fully understood. Objective: The current study collected skin biopsies from healthy volunteers before and after UVB radiation and linked UVB-induced effects in the skin to immunosuppression in the same individuals. Methods: A total of 62 healthy volunteers were recruited and randomly assigned to three groups: negative, positive, and UVB-exposed. Diphenylcyclopropenone was applied topically to induce contact hypersensitivity (CHS) responses. Skin punch biopsies were collected before and after UVB for analysis. Results: UVB exposure significantly suppressed CHS compared to the positive control. However, among 26 individuals, 7 (27%) were resistant (UVB-R), while the rest were susceptible (UVB-S) to UVB-induced immunosuppression. RNA-seq analysis of skin biopsies showed that UVB induced a higher level of immunosuppressive inflammation in UVB-S than in UVB-R individuals. Further analysis showed that UVB significantly activated the damage-associated molecular patterns only in UVB-S, but not in UVB-R individuals. Conclusion: Given the role of DAMP pathways in the development of inflammation, the results reveal a previously unrecognized mechanism: UVB-induced activation of DAMP pathways is linked to UVB-induced immunosuppressive inflammation in skin and susceptibility to immunosuppression in humans.