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. I investigated 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) I examined the relative usage levels of specific VH gene families between fish at different locations. to further investigate the “pathogen fingerprint” of given spawning sites, I also performed 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). Analysis of VH family usage suggests that differences exist between certain spawning locations not only for selected individual VH families, but also for multiple VH families analyzed simultaneously. Likewise, pathogen loads and infection rates are found to differ frequently between many spawning sites, while probability of infection is shown to be dependent on location for each pathogen analyzed. Analysis of VH usage and pathogen loads suggests several correlations that exist between specific usage patterns and lower pathogenic loads. Greater understanding of spawning fish immune functioning can potentially suggest a method of natural immunization against common fish pathogens and thus protect both farmed and wild populations. These differences in VH usage patterns and pathogen infection rates between spawning sites provide strong evidence in support of the Immunological Imprinting Hypothesis