IL-1RAcP is the common co-receptor. Several members of the IL-1 family of cytokines, including IL-1 (IL-1F1 and IL-1F2), IL-1F6, IL-1F8, IL-1F9, and IL-33 (IL-1F11), bind to their specific cell surface receptors, including IL-1RI, IL-1Rrp2, and T1/ST2, but use IL-1RAcP as a common co-receptor. All of these cytokines stimulate common intracellular signalling events. IL-1RAcP is ubiquitously expressed, whereas the other IL-1 receptors are more selectively expressed in different cell types. Two receptor antagonists, IL-1Ra and IL-1F5, inhibit the biologic activities of the ligands IL-1 and IL-1F6, IL-1F8, and IL-1F9, respectively. In addition, soluble IL-1RAcP inhibits the effect of IL-1 and IL-33 when present in combination with their specific soluble receptors, including IL-1RII and sST2. ERK 1/2, extracellular-regulated kinase 1/2; IL, interleukin; IRAK, interleukin-1 receptor-associated kinase; JNK, c-jun N-terminal kinase; MAPK, mitogen-activated protein kinase; MyD88, myeloid differentiation 88; NF-κB, nuclear factor-kappa-B; TRAF6, tumour necrosis factor receptor-associated factor 6.