Suppression of immunological memory in juvenile chinook salmon ( Oncorhynchus tshawytscha) from an urban estuary

Abstract

In this present study, juvenile chinook salmon were collected from a contaminated urban estuary, the Duwamish Waterway, as well as from a non-urban estuary, the Nisqually River estuary, to determine if exposure to toxic chemicals affects immunocompetency. Juvenile chinook salmon were also sampled from the two hatcheries that release salmon into these estuaries. The ability of anterior kidney (AK) and splenic (SP) leucocytes from primed and unprimed juvenile salmon from the Duwamish Waterway, Nisqually River estuary, and their respective hatcheries to produce a primary and secondary in vitro plaque-forming cell (PFC) response to the hapten, trinitrophenyl (TNP) was examined. Trinitrophenyl-keyhole limpet haemocyanin (TNP-KLH) was added in vitro to AK leucocytes or as TNP-lipopolysaccharide (TNP-LPS) to both AK and SP leucocytes. The primary AK and SP plaque-forming cell response to TNP in salmon from the estuaries or hatcheries was not significantly different. Primed AK leucocytes from salmon collected from the hatcheries and the non-urban estuary were able to produce a heightened secondary response to TNP-KLH; in contrast, primed AK leucocytes from salmon collected from the urban estuary were unable to produce a secondary PFC response to TNP-KLH. Anterior kidney leucocytes from salmon collected from all four areas were able to produce a heightened secondary PFC response to TNP-LPS. However, the AKs plaque-forming cell response generated in primed chinook salmon collected from the urban estuary to TNP-LPS was significantly lower than that produced in salmon from the hatchery. This suppressed PFC response in primed AK cells to TNP-LPS was not observed in primed AK leucocytes from salmon collected from the non-urban estuary and its hatchery. These results suggest that the cells involved in generating immunological memory to TNP-KLH and TNP-LPS were affected in salmon exposed to contaminants in the urban estuary, with cells which generate memory to TNP-KLH being more affected. The PFC responses of primed SP leucocytes from salmon collected from the Duwamish Waterway and Nisqually River estuaries, stimulated in vitro with TNP-LPS were not significantly different. The consequence of suppressed immunological memory in disease resistance of juvenile salmon is currently unknown.