A cDNA microarray analysis to identify genes involved in the acute-phase response pathway of the olive flounder after infection with Edwardsiella tarda

The acute-phase response (APR) is an important systemic reaction that occurs within hours of an inflammatory signal caused by physical bodily injury or microbial infection. To investigate the APR of the olive flounder (Paralichthys olivaceus) following infection with a pathogen, we established an expressed sequence tag (EST)-based cDNA microarray chip composed of 13,061 PCR-amplified cDNAs encoding unique genes selected from an olive flounder EST analysis. Microarray analyses showed that the set of genes involved in the APR was strongly up-regulated in the liver of the olive flounder after infection with Edwardsiella tarda. Among the up-regulated genes, catechol-O-methyltransferase domain-containing protein 1, six-transmembrane prostate protein, haptoglobin precursor, and toll-like receptor 5 soluble form were particularly strongly up-regulated. Interestingly, the toll-like receptor 5 soluble form, which has not yet been detected in mammals, was up-regulated as much as 250-fold upon E. tarda infection. These results suggest that the APR mechanism of fish may be regulated differently from that of mammals. The data described here contribute toward our collective understanding of APR, especially in fish.