Abstract
Rainbow trout are an important aquaculture species in the United States and throughout the world. Infection and death due to environmental pathogens, often magnified by dense living conditions, provide an immunological question of how to address these threats before exposure. Currently, not enough is known about the rainbow trout immune system to effectively harness the power of their unique immune response to protect them from pathogens. In order to more effectively address the immunological issues that arise in aquaculture, we need to learn more about the adaptive immune system of teleost fishes: the repertoire of cells available in a fish to fight those pathogens and how the immune system manages antigenic challenges that are presented in the environment. This study categorizes the immune repertoire of several rainbow trout in order to present a broader understanding of the antibody diversity present in these fish. Antibody diversity is directly reflective of a fish’s capability to mount an immune response to pathogens. High-throughput sequencing of IgVH genes from the lymphoid tissues of rainbow trout was performed using Illumina MiSeq, and sequences were analyzed using the IMGT/HighV-QUEST pipeline to categorize sequences by IgVH family. Findings support previous protein studies, showing membrane IgM and IgD coexpression as well as unique expression of secreted IgD, and are consistent with current knowledge of Ig use in trout. The molecular work is unprecedented in showing expression in membrane forms of antibody and in categorizing major differences in secreted forms of antibody. The expression of secreted antibody has major implications as to how the active immune response works in teleost fish and suggests a much more important role of IgD in the immune response than previously thought. Further, this study paves the way for future investigations into the rainbow trout immune system, specifically how these fish respond to environmental antigenic challenge.