The IL-1 system includes two agonists (IL-1alpha and IL-1beta), converting enzymes, antagonists, two receptors (IL-1 R I and IL-1 R II) and the IL-1 receptor accessory protein. The IL-1 R II is part of the antagonistic IL-1 mechanism. It is also known as decoy receptor and is a non signaling molecule which functions by capturing IL-1 and preventing it from interacting with the signalling IL-1 R I. The decoy IL-1 R II can after binding to IL-1 also recruit the IL-1 receptor accessory protein and thus inhibit by coreceptor competition. Further a soluble form of IL-1 R II exists which is shed, a process in which matrix metalloproteases have been found to play a role, by various cells including monocytes, polymorphonuclear cells, B cells and fibroblasts.