The goal of this project remains to elucidate the complex mechanisms which constitute the tissue response to photodynamic therapy (PDT). We have made the novel observation that PDT alters the expression of IL-6 and IL-10 message and protein in treated tissues in vivo; thus we focus this renewal application on the mechanisms and consequences of these effects. The overall hypothesis are that PDT, via its oxidative stress mechanisms, affects the transcriptional regulation of certain cytokines in vitro and in vivo, that these effects differ for different photosensitizers, depending on intracellular localizations, and that these changes in cytokine expression affect host immune function at both the local and systemic level. In Specific Aim 1 we will determine:(a) Whether PDT induced alterations in cytokine gene expression depend on photosensitizer type and localization. We expect to find photosensitizer (localization)- dependent differences in the cytokine response similar to those described for the PDT response of certain early response genes. (b) Whether PDT affects IL-10 gene regulation directly and what molecular mechanisms are involved. Based on our in vivo findings of IL-10 upregulation we expect to find IL-10 gene regulation to be directly affected by PDT in at least some of the cell types proposed for study. Since very little is known about IL- 10 gene regulation, this study will contribute to an overall understanding of IL-10 gene control as well as to specific understanding of the effects of PDT. In Specific Aim II we will determine whether the observed changes in cytokine expression influence the local or systemic host immune response, in particular the PDT-induced anti-tumor response and the PDT- suppressed contact hypersensitivity (CHS) response. We will determine (a) which cell types (especially in tumor and skin) secrete the cytokines of interest following PDT in vivo; (b) the effect of PDT on immune cell function at the tissue level, including antigen presentation and cytotoxic and cytolytic immunogenicity; (d) and whether changes in cytokine expression, especially IL-6 and IL-10, are involved in changes in immune cell function. Since both IL-6 and IL-10 are important in anti-tumor and CHS responses, it is expected that PDT induced changes in these cytokines will affect the immune response in vivo. In Specific Aim III we will determine whether the PDT induced changes in cytokine expression and changes in inflammatory and immune cell infiltrates observed preclinically also occur in patients. These studies have the long term goal of improving the overall understanding of the effect of PDT on the immune system.