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.