Interleukin-1 alpha (IL-1a, lymphocyte activating factor (LAF), hematopoietin-1, endogeneous pyrogen, mononuclear cell factor) is a pleiotropic pro-inflammatory cytokine produced in a variety of cells, including monocytes, macrophages and epithelial cells. It is involved in inflammatory and immune responses and regulation of hematopoiesis. It may therefore be of clinical use following massive immunosuppression and chemotherapy. Recombinant human IL-1a is a single non-glycosylated polypetide chain of 159 amino acids with a MW of 18 kDa. Sequence conservation of the mature protein among various species is 60% -70%, human IL-1 has been found to be biologically active on murine cell lines.