A chicken homolog of mammalian interleukin‐1β : cDNA cloning and purification of active recombinant protein

Upon induction with lipopolysaccharide (LPS) the chicken macrophage cell line HD-11 secretes an activity that stimulates the synthesis of a CXC chemokine in the chicken fibroblast cell line CEC-32. We used a cDNA expression cloning strategy in COS cells to characterize this activity. The isolated cDNA clone codes for a polypeptide of 267 amino acids which lacks a hydrophobic N-terminal domain that could serve as secretory signal. Sequence homology and structural features indicate that this protein is the chicken homolog of mammalian interleukin-1β (ChIL-1β). Northern blot analysis showed that ChIL-1β RNA is quickly induced in blood monocyte-derived macrophages reaching maximal levels within one hour after onset of LPS treatment. To test for biological activity of putative mature ChIL-1β, a cDNA fragment comprising amino acids 106 to 267 of the open reading frame was expressed in Escherichia coli so that the resulting polypeptide carried a histidine tag at its N-terminus for easy purification by nickel chelate affinity chromatography. Purified His-ChIL-1β potently induced CXC chemokine RNA synthesis in CEC-32 cells. When injected intravenously into adult chickens, it quickly induced a transient increase in serum corticosterone levels.