Interleukin 18 enhances Fas ligand expression and induces apoptosis in Fas-expressing human myelomonocytic KG-1 cells.

Interleukin-18 (IL-18) induces apoptosis in human myelomonocytic KG-1 cells as determined by agarose gel electrophoresis, and flow cytometry after propidium iodide (PI) staining. Apoptosis was detected 20 hours from the start of culture at concentrations of 100 ng/ml of the cytokine. Although IL-18 induces the production of large amounts of interferon gamma (IFN-y) by KG-I cells, conditioned media could not induce apoptosis of fresh cells. The protein expressions of p53 and Fas ligand by KG-1 cells, which constitutively express the Fas antigen (CD95), were found to increase after exposure to IL-18 for 20 hours. Both Fas ligand and its receptor were found to be functional by in vitro assays on Fas-expressing target cells and an agonist anti-Fas antibody, respectively. In conclusion, IL-18 enhances the expression of Fas ligand by Fas-expressing KG-1 cells and induces apoptosis in the cells through a mechanism probably involving the Fas pathway.