The IL-1 family of cytokines encompasses eleven proteins that each share a similar β-barrel structure and bind to Ig-like receptors. Several of the well characterized members of the IL-1-like cytokines play key roles in the development and regulation of inflammation. IL-1α (IL-1F1), IL-1β (IL-1F2), and IL-18 (IL-1F4) are well-known inflammatory cytokines active in the initiation of the inflammatory reaction and in driving Th1 and Th17 inflammatory responses.
In contrast, IL-1 receptor antagonist (IL-1ra; IL-1F3) and IL-36 receptor antagonist (IL-36ra; IL-1F5) reduce inflammation by blocking the binding of the agonist receptor ligands. IL-33 (IL-1F11) is thought to function as an ‘alarmin’ released following cell necrosis to alert the immune system to tissue damage or stress. The biological properties of IL-37 (IL-1F7) are mainly those of down-regulating inflammation.