Recent cetacean and pinniped die-offs have lead to the speculation that
environmental contaminants, such as organochlorines, are immunomodulatory, making the animals more
susceptible to viral infections, such as morbilliviruses. In this study, the blubber of 18
recently weaned harbor seal (Phoca vitulina) pups were analyzed for organochlorines and the
relationships between peripheral blood mitogen-induced lymphocyte proliferation and contaminant
concentrations were determined. PCB congener 153 was the single contaminant measured at the
highest concentration in harbor seal blubber and PCBs contributed more to the total TEQ than PCDD
and PCDF. A significant positive correlation was seen between lymphocyte proliferation and the
di-ortho PCB congeners 138, 153 and 180 for the T-cell mitogen, PHA, and the B-cell mitogen, LPS.
The best regression models for PHA and LPS, both of which included PCB 153 and 2,3,7,8-TCDD,
explained 55% and 72% of the variation in mitogen-induced proliferation, respectively. Principal
component analysis suggests that PCB congeners, more than PCDD and PCDF, account for most of the
variation in organochlorine blubber concentrations. Results suggest that body burdens of
organochlorine contaminants affect lymphocyte proliferation, a modulation of the immune system
which may result in increased susceptibility to infections.
We would like to thank the staff and volunteers at the Institute of Ocean
Sciences, Canada, and the Washington Department of Fish and Wildlife for the collection of harbor
seal blood samples. We would like to specifically thank Steve Jeffries, Lizzy Mos, Marta Assuncoa,
and Kelsey Miller. This research was supported, in part, by the Environmental Sciences Strategic
Research Fund (Fisheries and Oceans Canada). Animal care was provided by Joan Sicree (Marine
Mammal Center, Sausalito, CA), under the supervision of Dr. Dave Huff (Vancouver Aquarium), Dr.
Malcolm McAdie, and Dr. Dick Clegg.