Cloning, heterologous expression and characterization of murine interleukin 1 receptor antagonist protein

A cDNA coding for the human interleukin 1 receptor antagonist protein (IL 1Ra) was used to clone the corresponding murine cDNA. The nucleotide sequence of the open reading frame coding for the processed form of mIL 1Ra predicted a 152‐residue protein that was 77% identical to human IL 1Ra. The cellular and tissue distribution of murine IL 1Ra (mIL 1Ra) transcripts showed high levels in macrophages and skin while lower levels were detected in tissues that contain significant numbers of resident macrophages. The portion of the mIL 1Ra cDNA that codes for the mature form of the protein was placed under the control of a Trp promoter and expressed in E. coli at a level of 37% of total cell protein. The expressed protein was secreted into the periplasm and was purified to homogeneity in a single step by cation‐exchange chromatography. Recombinant mIL 1Ra competitively inhibited 125I‐labeled IL 1α binding to murine type I IL 1R present on EL4 6.1 cells (Ki value of 0.21 nM) and antagonized IL 1‐stimulated co‐mitogenesis in murine thymocytes (0.7 x 106‐1.1 x 106 units/mg).