Cloning of cDNA for canine interleukin-18 and canine interleukin-1beta converting enzyme and expression of canine interleukin-18.

Cloning of canine interleukin-18 (IL-18) and canine interleukin-1beta converting enzyme (ICE) cDNA was carried out by using murine IL-18 cDNA and human ICE cDNA, respectively, as probes. Sequence homology to known sequences of human, mouse, or rat genes was noted at nucleotide and amino acid levels. Canine IL-18 mRNA was expressed in various canine organs, whereas canine ICE mRNA was expressed in only a few, particularly in the brain and testis. Cloned canine IL-18 cDNA was expressed in Escherichia coli. The resulting protein promoted induction of canine interferon-y (IFN-y) from stimulated canine lymphocytes. Canine IL-18 and canine IL-12 produced canine IFN-gamma synergistically. Canine IL-18 suppressed the growth of tumor cells transplanted in SCID mice. Cloned canine IL-18 should prove useful as an anticancer agent.