cDNA cloning of biologically active chicken interleukin-18

By searching a chicken EST database, we identified a cDNA clone that appear ed to contain the entire open reading frame (ORF) of chicken interleukin-18 (ChIL-18). The encoded protein consists of 198 amino acids and exhibits ap proximately 30% sequence identity to IL-18 of humans and various others mam mals. Sequence comparisons reveals a putative caspase-1 cleavage site at as partic acid 29 of the primary translation product, indicating that mature C hIL-18 might consist of 169 amino acids. Bacterially expressed ChIL-18 in w hich the N-terminal 29 amino acids of the putative precursor molecule were replaced by a histidine tag induced the synthesis of interferon-gamma (IFN- gamma) in cultured primary chicken spleen cells, indicating that the recomb inant protein is biologically active.