Intracellular human IL-1: a precursor for the secreted monokine.

An intracellular monocyte derived protein possessing interleukin 1 (IL-1) activity has been compared with the secreted from of IL-1. Our results indicated that this intracellular IL-1 had an apparent size greater than that of extracellular IL-1. Data are presented to show that a rabbit heterotypic antiserum prepared against epitopes on the secreted form of human IL-1 blocked the biologic activity of intracellular IL-1 in a dose dependent manner. Intracellular IL-1 had a mass of 30-40 kDa as determined by gel filtration using sephacryl-200 gel.