Mice deficient in PSMB8 show a reduction in MHC class I surface expression in lymphocytes44, and PSMB8 null mice fail to up-regulate pro-inflammatory chemokines and cytokines including interleukin (IL)-1β after experimentally induced colitis, leading to reduced infiltration of the colon by neutrophils and reduced expansion of T helper cells45. Here, IL1B is linked to colitis.