Allergen-induced contact hypersensitivity (CHS) is a T cell-mediated delayed-type immune response which has been considered to be primarily mediated by CD8+ T cytotoxic type I (Tc1) cells. IFN-γ, the prototype Tc1 (Th1) cytokine, has been implicated as the primary inflammatory cytokine for CHS. In this study, we demonstrate that neutralization of IL-17 rather than IFN-γ suppresses the elicitation of CHS. The suppression does not result from inhibition of the proliferation of allergen-activated T cells. Allergen sensitization induces the development of distinct CD8+ T cell subpopulations that produce IFN-γ or IL-17. Although CD8+ IL-17-producing cells are stimulated by IL-23, they are inhibited by IL-12, a prototypical stimulator of IFN-γ-producing Tc1 cells. This indicates that CD8+ IL-17-producing cells are distinct from Tc1 cells and are important in effector functions at the elicitation of CHS. These studies provide insights into a novel mechanism for CHS.

Hapten induced contact hypersensitivity (CHS) in the skin is a delayed type cellular immune response which can be mediated by CD8+ T cells that produce IFN-γ or IL-17. However, mechanisms for these cytokines in the elicitation of CHS remain to be fully elucidated. Here we show that adoptive transfer of CHS with hapten primed wild type CD8+ T cells is reduced in IFN-γR−/− or IL-17R−/− mice compared to wild type controls. The infiltration of granulocytes and macrophages in the hapten challenged skin of IL-17R−/− recipients is significantly reduced whereas it is less affected in IFN-γR−/− recipients although CD8+ T cell infiltration is inhibited in both recipients. In contrast, the activity of reactive oxidative species is significantly inhibited in IFN-γR−/− but is less affected in IL-17R−/− recipients. Further analysis reveals that the expression of chemokines and cytokines is differentially regulated in the hapten challenged skin of IFN-γR−/− or IL-17R−/− recipients compared to wild type controls. Interestingly, injection of recombinant IL-17 in the skin induces inflammation with a high level of leukocyte infiltration whereas injection of IFN-γ induces inflammation with a high level of reactive oxidative species. Moreover, neutralization of IL-17 in IFN-γR−/− or IFN-γ in IL-17R−/− mice further suppresses the adoptive transfer of CHS by hapten primed wild type CD8+ T cells. The study demonstrates that IFN-γ and IL-17 mediate the elicitation of CHS by different mechanisms and that both cytokines are required for optimal responses. This outcome improves understanding of pathogenesis and provides new insights into therapeutic strategies for CHS.

Slits are a group of secreted glycoproteins that play a role in the regulation of cell migration. Previous studies suggested that Slit2 might be a tumor-suppressor gene. However, it remained to be determined whether Slit2 suppressed tumor growth and metastasis in animal models. We showed that Slit2 expression was decreased or abolished in human esophageal squamous cell carcinomas (SCCs) compared to normal tissues by in situ hybridization. Stable transfection of human SCC A431 and fibrosarcoma HT1080 cells with Slit2 gene suppressed tumor growth in athymic nude mice. Apoptosis in Slit2-transfected tumors was increased, whereas proliferating cells were decreased, suggesting a mechanism for Slit2-mediated tumor suppression. This was supported by further analysis indicating that antiapoptotic molecules Bcl-2 and Bcl-xl and cell cycle molecules Cdk6 and Cyclin D1 were down-regulated in Slit2-transfected tumors. Furthermore, wound healing and Matrigel invasion assays showed that the transfection with Slit2 inhibited tumor cell migration and invasion. Slit2-transfected tumors showed a high level of keratin 8/18 and a low level of N-cadherin expression compared to empty vector-transfected tumors. More importantly, Slit2 transfection suppressed the metastasis of HT1080 tumor cells in lungs after intravenous inoculation. Collectively, our study has demonstrated that Slit2 inhibits tumor growth and metastasis of fibrosarcoma and SCC and that its effect on cell cycle and apoptosis signal pathways is an important mechanism for Slit2-mediated tumor suppression.

Apoptosis plays an important role in eliminating UV-damaged keratinocytes, but its role in UV-induced immune suppression is not clear. Langerhans cells (LCs) may function as inducers of immune suppression. We have shown that LCs derived from mice deficient in the proapoptotic Bid (BH3-interacting death domain protein) gene (Bid KO) resist apoptosis and induce amplified immune responses. In this report, we examined responses in Bid KO mice to UVB exposure. Acute UV exposure led Bid KO mice to develop fewer apoptotic cells and retain a greater fraction of LCs in the epidermal layer of skin in comparison to wild-type mice. Bid KO mice were also markedly resistant to local and systemic UV tolerance induction to hapten sensitization and contact hypersensitivity responses. Elicitation responses and inflammation at skin sensitization sites in UV-treated Bid KO mice were equal to or greater than nonsuppressed control responses. In Bid KO mice, LCs accumulated in lymph nodes to greater numbers, demonstrated longer lifespans, and contained fewer DNA-damaged cells. These studies provide evidence that Bid activation is a critical upstream mediator in UV-induced keratinocyte and LC apoptosis and that its absence abrogates UV-induced immune tolerance.

Prevention of tumors induced by environmental carcinogens has not been achieved. Skin tumors produced by polyaromatic hydrocarbons, such as 7,12-dimethylbenzanthracene (DMBA) often harbor an H-ras point mutation, suggesting that it is a poor target for early immune surveillance. The application of pyrosequencing and allele-specific PCR techniques established that mutations in the genome and expression of the Mut H-ras gene could be detected as early as one day after DMBA application. Further, DMBA sensitization raised Mut H-ras epitope-specific CTLs capable of eliminating Mut H-ras+ pre-neoplastic skin cells, demonstrating that immunosurveillance is normally induced but may be ineffective due to insufficient effector pool size and/or immune suppression. To test whether selective pre-expansion of CD8 T cells with specificity for the single Mut H-ras epitope was sufficient for tumor prevention, MHC class I-epitope-focused lentivector-infected dendritic cell (DC)- and DNA-based vaccines were designed to bias toward CTL rather than Treg induction. Mut H-ras but not wild-type H-ras epitope-focused vaccination generated specific CTL and inhibited DMBA-induced tumor initiation, growth and progression in preventative and therapeutic settings. Transferred Mut H-ras-specific effectors induced rapid tumor regression, overcoming established tumor suppression in tumor bearing mice. These studies support further evaluation of oncogenic mutations for their potential to act as early tumor-specific, immunogenic epitopes to expand relavent immunesurviellance effectors in order to block tumor formation, rather than treating established tumors.