Interleukin-1.

IL-1 is a polypeptide product of various cells that mediates several components of the acute-phase response to infection and injury. Its most dramatic biological property is its ability to induce arachidonate metabolites in a variety of cells including PGE in the brain, fibroblasts, synovial cells, and chondrocytes; in addition, IL-1 induces lipoxygenase products in lymphocytes and other cells. IL-1 has been cloned. There are two forms. The predominant form of IL-1 from human monocytes has a pI of 7 (also called beta) and is initially synthesized as a precursor molecule (31 kD). A minor form (less than 100-fold) also exists (pI 5, also called alpha). IL-1 seems unique among the lymphokines and monokines in that there is no signal peptide sequence for cleavage. Depending on the stimulus, intracellular levels of precursor IL-1 can be high, whereas some cell activators result in large amounts of processed IL-1. Precursor IL-1 is cleaved into a 17.5-kD peptide, which is the predominant extracellular form. IL-1 induces prostaglandins and lymphocyte activation as well as many different biological activities. These include fever, PGE production, protease release from synovial cells and chondrocytes, bone resorption, acute-phase protein synthesis, and other effects. Although there are few studies showing an IL-1 effect on the gastrointestinal tract, the multiple biological properties of IL-1 suggest that IL-1 plays a role in inflammatory bowel disease as well as in mediating some of the gastrointestinal changes observed in systemic acute-phase responses.