A homologue of interleukin 18 has been identified from rainbow trout,Oncorhynchus mykiss. The trout IL-18gene spans kb and consists of six exons and five introns, sharing the same gene organization with its human coun-terpart. The putative translated protein is 199 amino acids in length with no predicted signal peptide. Analysis of the multiple sequence alignment reveals a conserved ICE cut site, resulting in a mature peptide of 162 amino acids. The trout IL-18 shares 41–45% similarity with known IL-18 molecules and contains an IL-1 family signature motif
