Mouse IL-1 beta Carrier-Free Recombinant Protein, eBioscience?. Interleukin-1 beta (IL-1 beta) is a proinflammatory cytokine expressed by monocytes, macrophages, and dendritic cells. IL-1 beta is synthesized in response to inflammatory stimuli as a 31 kDa inactive pro-form that accumulates in the cytosol. Cleavage of pro-IL-1 beta into the active 17 kDa protein requires the activation of inflammasomes, which are multi-protein complexes that respond to pathogens, stress conditions, and other danger signals. Inflammasome activation triggers the processing of the caspase-1 precursor into its active form, which in turn cleaves pro-IL-1 beta. IL-1 beta lacks a signal sequence peptide for classical ER/Golgi pathway and is secreted alongside