Channel catfish TCRβ and IGH receptor repertoires - Public clonotypes complement a highly diverse repertoire

The sequence diversity encompassed in the repertoires of T and B cell receptors is fundamental to their roles in adaptive immunity. The sequence diversity in the expressed complementarity determining region three of both the TCRβ and IGH receptors of the channel catfish, Ictalurus punctatus, was compared by high-throughput sequencing of two cDNA libraries constructed using samples isolated from eleven fish over 28 months. Samples were collected both before and after infection with the parasitic protozoan Ichthyophthirius multifiliis, or vaccination with a protective I. multifiliis antigen. Samples were taken from blood and fin before and at 8 and 15 months after treatment, and from blood, skin, spleen and head kidney at 28 months after treatment. The libraries were not sequenced to saturation. In both the TCRβ and IGH repertoires, approximately 70 % of clonotypes were detected only once. Two TCRβ and eight IGH public clonotypes were widely distributed over the entire 28 months. The cDNA sequence of each public clonotype was identical in all fish, suggesting that the rearranged VDJ gene coding for it is in the germline. Rearranged IGH VDJ genes from three IGH V gene families were shown to be in the germline. Seven sterile TCRβ sequences, which contained a spliced JC gene sequence but lacked V and D gene sequences, comprised most copies of TCRβ cDNAs. The TCRβ and IGH repertoires are composed of a traditional repertoire of highly diverse, primarily unique clonotypes, and a second repertoire with a few constant, public clonotypes.