Endogenous interleukin-18 modulates immune escape of murine melanoma cellsby regulating the expression of Fas ligand and reactive oxygen intermediates

It has been known that melanoma cells can suppress the immune system by the Fas ligand. The present study investigated whether interleukin (IL)-18, wh ich can enhance Fas ligand expression, is produced by B16F10 melanoma cells and is involved in immune escape of tumor cells. Immunohistology. reverse transcription-PCR, intracellular fluorescence-activated cell-sorting analys is, and immunoblotting demonstrated that melanoma cells express IL-18. C57B L/6 splenocytes cultured with culture supernatants of B16F10 melanoma cells enhanced IFN-gamma production, which was blocked by anti-IL-18 antibody, i ndicating that IL-18 in the culture supernatants is functional. In addition to IL-18, the IL-18 receptor was also detected in B16F10 melanoma cells, s uggesting a role of this cytokine in regulating the functions of B16F10 mel anoma cells. The functional effect of IL-18 on B16F10 melanoma cells was sh own by reduction of Fas ligand expression in cells treated with anti-IL-18 antibody or transfected with IL-18 antisense cDNA, In addition, the same tr eatments decreased intracellular reactive oxygen intermediate levels in B16 F10 melanoma cells, indicating that IL-18 regulates reactive oxygen interme diate production, which is involved in Fas ligand expression. Furthermore, transfection of IL-18 antisense cDNA into melanoma cells increased the susc eptibility of tumor cells to natural killer cells in vitro. When IL-18 anti sense transfectants were implanted into syngeneic mice, severe reduction of tumor cell growth was observed with concomitant infiltrated natural killer cells in the tumor area. Taken together, these results demonstrate that IL -18 has a critical role as a survival factor for B16F10 melanoma cells.