Interleukin 18 binding protein (IL-18 BP) is a glycoprotein that contains a single IgG domain (C2-type). In humans, alternative splicing of the mRNA results in at least four different isoforms being generated; the most-expressed form in humans is IL-18 BPa (Dinarello et al.; Kim et al.). IL-18 BPa inhibits pro-inflammatory cytokine IL-18 by preventing it from binding to its receptor, thereby inhibiting IL-18-induced IFN-gamma production; the binding of IL-18 BPa to IL-18 is primarily due to the Ig domain (Carrascal et al.; Dinarello et al.). IL-18 is associated with an increase in cell adhesion molecules, chemokine production, stimulating vascular endothelial cells, metastatic tumor cell invasion, autoimmune diseases, emphysema, metabolic syndromes, Crohn’s disease, psoriasis, and has also been implicated in a role in heart disease (Dinarello et al.). Some studies have also shown that blocking of IL-18 activity can reduce metastasis in mouse models of melanoma (Carrascal et al.).