Purification and characterization of a 26‐kDa competitive inhibitor of interleukin 1

The urine of patients with fever above 39 °C contains an inhibitor of interleukin 1. Herein we describe the purification of the interleukin 1 inhibitor by ion‐exchange chromatography, hydrophobic chromatography, gel filtration and negative immunosorption. The purified protein has a molecular weight of 26000; its size is reduced to 24000 upon treatment with endoglycosidase F. The IL 1 inhibitor is a competitive inhibitor and acts by binding to the IL 1 receptor. The inhibitor recognizes the murine and human IL 1 receptor with similar affinity. The purified IL 1 inhibitor has a specific activity of 3 × 107 to 4.5 × 107 units/mg as tested on the human astrocytoma (U‐373) cell proliferation bioassay and murine EL4.6.1 cell IL 1 receptor‐binding assay.