PURIFICATION AND CHARACTERIZATION OF A NOVEL SOLUBLE RECEPTOR FOR INTERLEUKIN-1

Affinity chromatography and reverse-phase high-performance liquid chromatography was used to purify a soluble interleukin 1-beta (IL-l-beta) specific binding protein from the supernatant of a human B cell line, Raji. The purified protein specifically bound I-125 IL-1-beta forming a 60-kD complex in nonreducing conditions and a 70-kD complex in reducing conditions. Binding was found to be displaceable by mature human and murine IL-1-beta and human 31-kD IL-1-beta propeptide, but not displaceable by human and murine IL-1-alpha or human IL-1 receptor (IL-1R) antagonist. Ligand blotting revealed a 47-kD molecule that specifically bound IL-1-beta. Measurement of binding affinity of the cell surface Raji IL-1R (K(d) = 2.2 nm) and the Raji soluble (s)IL-1R (K(d) = 2.7 nm) demonstrated a similar affinity for I-125 IL-1-beta. Purified sIL-1R inhibited binding of IL-1-beta to cell lines with both type 1 (80 kD) and type II (65 kD) IL-1Rs, but did not interfere with IL-l-alpha binding. This natural sIL-1R may function as an important regulatory molecule of IL-1-beta in vivo.