Channel catfish CD8α and CD8β co-receptors: Characterization, expression and polymorphism

In this study we report the identification and characterization of channel catfish, Ictalurus punctatus CD8α and CD8β genes. Both genes encode predicted proteins containing a leader, a immunoglobulin superfamily V domain, a stalk/hinge region, a transmembrane region and a positively charged cytoplasmic tail (CYT) containing the conserved teleost C-X-H motif. Catfish CD8α and CD8β are encoded as single copy genes and as in other vertebrates exhibit a conserved head to tail synteny; the CD8β gene is found 14.1 kb upstream of the CD8α gene. Both CD8α and CD8β transcripts showed a low degree of polymorphism. Finally, as determined by q-PCR both CD8α and CD8β are expressed in various catfish lymphoid tissues with the highest expression observed in thymus from 2 month old catfish-fry. In the future these results will provide the basis for evaluating the role of CD8+ CTL and other CD8-bearing cells in response to immunization or infection in the catfish.