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.