Differences in Sockeye Salmon Antibody Composition: Testing the Immunological Imprinting Hypothesis

Anadromous fish such as sockeye salmon return to their natal streams to spawn, during which they undergo significant physiological changes including the release of cortisol, a known immunosuppressive hormone. Our lab has proposed the Immunological Imprinting Hypothesis, which suggests that juvenile anadromous fish respond to pathogens specific to their natal site by producing protective long lived plasma cells (LLPCs) that constitutively produce antibodies against those pathogens. These LLPCs are believed to be highly cortisol resistant. Thus, fish returning to their natal streams have immunological protection from pathogens found at that specific location. We are investigating the Immunological Imprinting Hypothesis through analysis of antibody composition and usage. Since 2009 samples of Sockeye Salmon spleen and anterior kidney have been harvested from two separate salmon runs in Alaska. Using quantitative PCR (qPCR) we are examining the relative usage levels of specific VH gene families between fish at different locations. To further investigate the “pathogen fingerprint” of given spawning sites, we are also performing qPCR analysis in order to compare the pathogen loads of multiple pathogens from different sites, including Bacterial Kidney Disease (Renibacterium salmoninarum), Bacterial Coldwater Disease (Flavobacterium psychrophilum), and Infectious Hematopoietic Necrosis Virus (IHNV). As we gather more data, we will test whether specific antibody compositions are associated with specific spawning sites, as well as with pathogen infection patterns. Greater understanding of spawning fish immune functioning could potentially suggest a method of natural immunization against common fish pathogens and thus protect both farmed and wild populations.