Interleukin-1 beta (IL-1β) is a proinflammatory cytokine expressed by monocytes, macrophages, and dendritic cells. It is synthesized in response to inflammatory stimuli as a 31 kDa inactive pro-form that accumulates in the cytosol. Cleavage of pro-IL-1β into the active 17 kDa protein requires the activation of inflammasomes. Inflammasome activation triggers the processing of the caspase-1 precursor into its active form, which in turn cleaves pro-IL-1β. Although IL-1β is most often secreted in its active form, secretion of the uncleaved protein may be detectable under some biological conditions.
IL-1β signals through two receptors, IL-1RI and IL-1RII. These cytokines play important roles in innate host defense by triggering the production of other proinflammatory cytokines in target cells and initiating acute-phase responses. Their activity can be moderated by IL-1 Receptor Antagonist (IL-1RA), a protein produced by many cell types that blocks receptor binding through competitive inhibition. Elevated levels of IL-1β have been associated with many chronic inflammatory conditions, giving IL-RA or IL-1β neutralizing antibodies potential therapeutical value.