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Abstract
Fish represent the most numerous group of vertebrate species and are the earliest vertebrates to utilize both innate and adaptive immune responses. Fish lack bone marrow, lymph nodes, and large germinal centers that are found in mammals. Based on our recent discoveries on immune repertoires in channel catfish, we postulate that this fish has evolved an evolutionary adaptation to defend against foreign pathogens that has not previously been described; namely, rearranged VDJ genes coding for T and B cell receptors that are integrated into the germline DNA. The expression of these germline rearranged VDJ genes, which are derived from translocon V, D, and J genes, potentially provides a rapid and protective immune response to pathogens commonly found in their environment.