Interleukin 1 beta (IL-1b) and Interleukin 1 alpha (IL-1a) have very similar biological activities on many different cell types although they are derived from different genes and share only ~20% aa sequence homology. IL-1b is synthesized as pro-IL-1b in cells and is cleaved to produce active IL-1b by Interleukin-1b converting enzyme (ICE), a cytoplasmic cysteine protease which is also known as caspase-1.