Changes in immune functions in bottlenose dolphins in the northern Gulf of Mexico associated with the Deepwater Horizon oil spill

Following the Deepwater Horizon (DWH) oil spill, the Natural Resource Damage Assessment conducted comprehensive health assessments on common bottlenose dolphins Tursiops truncatus in Barataria Bay (BB), Louisiana, in 2011, 2013 and 2014, as well as in Mississippi Sound (MS) in 2013, to assess potential health effects from exposure to oil compared to Sarasota Bay (SB), Florida dolphins not exposed to DWH oil. Immune functions demonstrated a consistent increase in T (BB 2011) and B (BB 2011 and 2013) lymphocyte proliferation compared to SB. Cytokine concentrations varied considerably in wild dolphin populations, and no significant differences were found; however, interesting trends were observed. The Th1 cytokines IL-2, IL-12, and IFN gamma, and the Th2 cytokines IL-5, IL-10, and IL-13, were 2- to 50-fold lower, and IL-4 was 3-fold higher, in BB 2011 compared to SB. Overall, the changes observed were compatible with those documented in other species following exposure to oil or PAHs and were most pronounced in BB 2011, at the place and time most affected by oil. The changes in T cell functions, and the trend towards a cytokine balance tilted towards a Th2, rather than a Th1 response, are compatible with intra-cellular bacterial infections such as Brucella, which has been identified as one of the potential contributory factors to perinatal dolphin mortalities, and changes in B cell functions are compatible with an increase in extra-cellular bacterial infections and primary bacterial pneumonia.