Analysis of a catfish gene resembling interleukin-8: cDNA cloning, gene structure, and expression after infection with Edwardsiella ictaluri

Chemokines are important mediators for innate immunity involved in recruitment, activation and adhesion of a variety of leukocyte types to inflammatory foci. While almost all chemokines have been identified from mammals, only a handful of fish chemokines have been identified. Here we report molecular cloning, sequence analysis, and expression of a channel catfish gene resembling interleukin-8 (IL-8). The gene has two alternatively spliced transcripts encoding 114 and 111 amino acids, respectively. The gene has four exons and three introns, typical of the CXC chemokine gene organization. In spite of the structural conservation through evolution, the piscine IL-8 genes showed a much greater sequence divergence than their counterparts among mammals. RT-PCR indicated that both spliced forms were expressed. Expression of the IL-8 like gene was up-regulated 3-5-fold in channel catfish and blue catfish after infection with pathogenic bacteria Edwardsiella ictaluri.