A soluble factor produced by MONOCYTES; MACROPHAGES, and other cells which activates T-lymphocytes and potentiates their response to mitogens or antigens. Interleukin-1 is a general term refers to either of the two distinct proteins$, INTERLEUKIN-$1ALPHA and $INTERLEUKIN-$1BETA. The biological effects of IL-1 include the ability to replace macrophage requirements for T-cell activation.