Interleukin-1 receptor antagonist in inflammatory exudate cells of rabbits. Production, purification and determination of primary structure

A rabbit interleukin-1 (IL-1) inhibitor in inflammatory peritoneal exudate cells was purified to apparent homogeneity. This inhibitor was extracted from exudate cells of the 24-hr stage of casein-induced peritoneal inflammation and purified using isoelectrofocusing (IEF), gel filtration, followed in this order by high-performance liquid chromatography (HPLC) steps with hydroxylapatite and anionic ion exchanger. The purified factor showed a single band on silver-stained SDS-PAGE. This molecule of MW 19,000 and pI 5.5 inhibited the binding of both IL-1 alpha and beta to receptors on a thymoma cell line, EL-4 and a B-cell line, 70Z/3. We determined its primary structure by a combination of peptide chemistry and molecular cloning. The inhibitor was synthesized as a precursor composed of 177 amino acids and was processed to a mature molecule of 143 amino acids. The N-terminal amino acid of the mature inhibitor was N-acetyl-methionine residue. The deduced amino acid sequence of the inhibitor showed a 77% homology to the human IL-1 receptor antagonist (IL-1Ra) and essentially the same mode of action as seen with human IL-1Ra. We consider that this inhibitor is a rabbit counterpart of human IL-1Ra, although there are differences with respect to the molecular structure; the N-terminus of the mature rabbit IL-1Ra at a position of nine amino acids downstream from that of human IL-1Ra.