Interleukins (IL) are immunomodulatory proteins that elicit a wide array of responses in cells and tissues. Interleukin 37 (IL-37, IL-1 F7) is a member of the IL-1 family. There are five isoforms of IL-37 (a-e) of which transcript IL-37b is known to be functional (Sharma et al. 2008). This isoform is represented in UniProt as the canonical form of IL-37 and in Reactome as the full length, unprocessed form of IL-37. Like several other IL-1 family members, IL-37 is synthesized as a precursor that requires processing (primarily by caspase 1) to attain full receptor agonist or antagonist function. (Kumar et al. 2002). IL-18 binding protein (IL-18BP) binds IL-18 with high affinity inhibiting its activity (Kim et al. 2000). Both full length and processed IL-37 bind the third extracellular domain (D3) of IL-18BP. The binding of IL-18BP to IL-37 makes it unavailable for neutralization of IL-18 activity (Bufler et al. 2002). These events ultimately lead to suppression of cytokine production in several types of immune cells resulting in reduced inflammation.