Sequence analysis and expression of a CXC chemokine in resistant and susceptible catfish after infection of Edwardsiella ictaluri

Chemokines represent a superfamily of chemotactic cytokines involved in recruitment, activation and adhesion of a variety of leukocyte types to inflammatory foci. We cloned and sequenced the cDNA of a CXC chemokine that is most similar to CXCL10 from channel catfish and blue catfish. Sequence analysis of PCR amplicons from a single F1 hybrid catfish indicated that channel catfish and blue catfish may have a multigene family for the CXC chemokine. The catfish CXC chemokine was expressed in a wide range of tissues including head kidney, spleen, liver, gill, skin, stomach, and intestine, but not in the muscle. Fish challenged with intracellular bacterium Edwardsiella ictaluri, the causative agent of enteric septicemia of catfish (ESC), showed dramatically elevated levels of the CXC chemokine expression, as quantified with real time RT-PCR. Differential expression profiles were observed between resistant and susceptible channel catfish strains and blue catfish. Blue catfish were characterized by only modest induction in comparison to the drastic elevation of the CXC chemokine in channel catfish.