Interleukin-1 (IL-1) family

The Interleukin 1 (IL-1) family is a group of 11 cytokines, which plays a central role in the regulation of immune and inflammatory responses to infections or sterile insults. All of the members of IL-1 family, except of IL-1Ra, are first synthesized as a precursor protein, which means it is synthesized as a long form of protein which has to be proteolytically cleaved to a shorter, active molecule, which is generally called mature protein. IL-1 family precursors do not have a clear signalpeptide for processing and secretion and none of them are found in the Golgi, they belong to so-called leaderless secretory protein group. The similar feature of IL-1α and IL-33 is that their precursor forms can bind to their respective receptor and can activate signal transduction. But this is not a common feature for all IL-1 family members, since IL-1β and IL-18 precursor forms do not bind their receptors and require proteolytic cleavage by either intracellularcaspase-1 or extracellular neutrophilic proteases.