Interleukin-18/interferon-γ-inducing factor, a novel cytokine, up- regulates ICAM-1 (CD54) expression in KG-1 cells

Intercellular adhesion molecule-1 (ICAM-1, CD54) is a membrane glycoprotein and a member of the immunoglobulin superfamily. It plays a central role in cell to cell-mediated immune responses and is a ligand for leukocyte function-associated antigen-1 (LFA-1). We report here that a newly discovered cytokine, interferon-γ-inducing factor (IGIF) [H. Okamura et al. (1995) Nature 378, 88] recently proposed to be designated as IL-18, selectively up-regulates ICAM-1 expression in KG-1 cells, a human myelomonocytic cell line, in which IL-18 also enhances interferon-γ production. IL-18 induced heterotypic aggregation between KG-1 and Peer T cells, which was blocked by anti-ICAM-1 and/or LFA-1 antibodies. Anti- interferon-γ antibody did not block the IL-18-induced up-regulation of ICAM- 1 on KG-1 cells. These results thus show that IGIF/IL-18, enhances ICAM-1 expression in KG-1 cells in an interferon-γ-independent pathway, up- regulates ICAM-1 functions, and that IL-18 might play a potential role in immunoregulation by mediating immune cell infiltration into the tissues.