Recombinant human IL-18 produced in yeast is a polypeptide chain containing 157 amino acids, with 4 Cys, but no disulfide bond.

Interleukin-18 (IL-18), also known as IL-1F4, is a proinflammatory cytokine that belongs to the IL-1 superfamily and is produced by macrophages and other cells. It is expressed as a 24 kDa precursor by endothelial and epithelial cells, keratinocytes, gamma δ T cells, and phagocytes. Mature human IL-18 shares approximately 63% amino acid sequence identity with mouse and rat IL-18. IL-18 activation is induced by infection or tissue damage and leads to disease pathology in chronic inflammation. In the presence of IL-12 or IL-15, IL-18 enhances anti-viral Th1 immune responses by inducing IFN-gamma production and the cytolytic activity of CD8+ T cells and NK cells. IL-18 induces the antigen-independent production of IL-17 by gamma δ T cells and CD4+ T cells. IL-18 also promotes myeloid dendritic cell maturation and triggers neutrophil respiratory burst. In the absence of IL-12 or IL-15, IL-18 promotes production of the Th2 cytokines IL-4 and IL-13 by CD4+ T cells and basophils. IL-18 induces the antigen-independent production of IL-17 by gamma δ T cells and CD4+ T cells. IL-18 also promotes myeloid dendritic cell maturation and triggers neutrophil respiratory burst. In cancer, IL-18 has shown a variety of activities, including enhancing anti-tumor immunity, inhibiting or promoting angiogenesis, and promoting tumor cell metastasis.