Macrophage-produced interleukin that induces the production of interleukin-2 by T cells that have been stimulated by antigen or mitogen; at least two types exist, designated and IL-1 or a similar protein is also produced by epithelial cells and stimulates fibroblast proliferation and release of proteolytic enzymes (e.g., collagenase) and prostaglandins in inflammatory processes. IL-1 also appears to be identical to endogenous pyrogen. Formerly called lymphocyte-activating factor (LAF)