Canine interleukin-5: Molecular characterization of the gene and expression of biologically active recombinant protein

Interleukin-5 (IL-5), which is produced primarily by type 2 T helper lympho cytes (Th2), is an eosinophil differentiation and activation factor. Increa sed numbers of eosinophils in peripherial blood or tissues (eosinophilia) a re observed in asthmatic human patients, in animals with helminth infection s, and in dogs with allergic diseases. Antagonism of IL-5 activity is being explored as a potential treatment of a number of disease conditions associ ated with eosinophils in animal models. In order to study the expression an d function of this cytokine in the dog, we have isolated and characterized the canine IL-5 gene, The canine IL-5 polypeptide deduced from the cDNA is composed of 134 amino acids that share varying degrees of homology with IL- 5 isolated from several mammals. The genomic structure of the canine IL-5 g ene consists of four exons and three introns in the coding region, similar to that of the previously characterized human and mouse IL-5 genes, Recombi nant canine IL-5 protein, expressed in Pichia pastoris, is biologically act ive in a cell proliferation assay. Canine IL-5 gene sequences and the biolo gically active protein described in this study will be useful reagents for future studies of this cytokine in physiologic processes and in pathologic conditions of the dog.