Diminished innate, but not adaptive, immune responses in migrating adult Chinook salmon, Oncorhynchus tshawytscha (VET1P.1127)

Abstract

Abstract In wild systems, animals have to balance the energy required to mount an immune response with other requirements necessary to survive and procreate. An extreme example is migrating adult Pacific salmon species, which cease feeding at the start of their migration from salt water to fresh water. During the migration, salmon must swim against strong currents, compete for mates, evade predation, and contend with freshwater pathogens. We quantified the immune response in migrating adult Chinook salmon, Oncorhynchus tshawytscha, at different times and locations during the run using several different measures. We measured the levels of immunoglobulin heavy chain mu and heavy chain tau mRNA transcript in the anterior kidney and found that levels of both secreted and membrane bound forms of the heavy chain did not diminish during migration, and importantly, that they remained unchanged even after spawning. We also measured the innate anti-bacterial ability of plasma isolated from fish to prevent the growth of a lab strain of E. coli. Contrary to the humoral immune response, the innate anti-bacterial components of plasma diminished at later time points in the run leading up to spawning. Diminished immune response was not due to IL-10 secretion, as transcripts for this cytokine were similar at all time points that were examined. These data suggest that in the face of limited energy resources, innate immune responses diminish while adaptive responses remain unchanged.