ALTERED EXPRESSION OF INTERLEUKIN-6 AND INTERLEUKIN-10 AS A RESULT OFPHOTODYNAMIC THERAPY IN-VIVO

Photodynamic therapy (PDT), which can effectively destroy malignant ti ssue, also induces a complex immune response that potentiates antitumo r immunity but also inhibits skin contact hypersensitivity (CHS) and p rolongs skin graft survival, The underlying mechanisms responsible for these effects are poorly understood but are likely to involve mediati on by cytokines. We demonstrate in a BALB/c mouse model that PDT deliv ered to normal and tumor tissue in vivo causes marked changes in the e xpression of cytokines interleukin (IL)-6 and IL-10 but not tumor necr osis factor alpha. IL-6 mRNA and protein are strongly enhanced in the PDT-treated EMT6 tumor, PDT also increased IL-6 mRNA in exposed spleen and skin, These data suggest that the general inflammatory response t o PDT may be mediated at least in part by IL-6, In addition, IL-6 may modulate the local antitumor immune response. In contrast, IL-10 mRNA in the tumor decreases following PDT, Most importantly, IL-10 is marke dly induced in the skin of mice exposed to a PDT regime that strongly inhibits the CHS response, and the kinetics of IL-10 induction coincid e with the known kinetics of CHS inhibition, We propose that the enhan ced IL-10 expression plays a role in the observed suppression of cell- mediated responses seen following PDT.