Cloning, sequencing, and characterization of dog interleukin-18

Interleukin-18, originally termed interferon-gamma inducing factor, is a recently described cytokine which is intimately involved in the generation of the immune response. The human and mouse sequences have been reported and studies have demonstrated the potent biological functions of this protein including the induction of interferon-gamma and the enhancement of NK cytotoxicity. This paper describes the cloning, sequencing, and characterization of the dog homologue of this gene. The coding sequence for dog IL-18 was obtained using reverse transcription-polymerase chain reaction from mRNA harvested from PMA-stimulated alveolar macrophages. Sequence analysis of the dog gene has demonstrated an open reading frame of 582 base pairs coding for a 193 amino acid precursor protein. The dog coding sequence shares 84% and 74% similarity to the human and mouse equivalents, respectively, at the nucleotide level. Based upon sequence analysis, we propose that this new gene is the dog equivalent of human IL-18.