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exposures and immunotoxic effects is complicated by logistic, technical, and ethical
considerations.
To our knowledge, only one study has addressed the question of the immunotoxicity of
environmental pollutants in a semicontrolled
in vivo
exposure. In that study, two groups
of 11 captive harbor seals
Phoca vitulina
were fed herrings (
Clupea harengus
) from either the
relatively uncontaminated Atlantic Ocean or from the contaminated Baltic Sea over the
course of 2.5 years. The concentrations of persistent organic pollutants in the Baltic Sea
herrings were 4-10 times higher than in the Atlantic Ocean herrings. Within 1 year, results
of
in vitro
tests of immune function using peripheral blood mononuclear cells isolated
from whole blood of the harbor seals revealed significantly lower T-cell function and NK
cell response in the seals fed with Baltic Sea herrings. The specific immune response of the
seals fed Baltic herrings was also affected, showing lower
in vitro
proliferative response
to antigens after immunization, and lower
in vivo
delayed-type hypersensitivity and anti-
body responses to ovalbumin (Vos et al. 2003). These effects indicated a general alteration
of the immune response.
Considering the logistic as well as technical and ethical constraints associated with that
semicontrolled
in vivo
s t u dy,
in vitro
exposures represent an alternative and complemen-
tary approach. Moreover, they enable discrimination between direct and indirect effects
on immune cells, and investigation of the mechanisms of toxicity at cellular and molecu-
lar levels. Most of the immune functions characterized in marine mammals have been
demonstrated to be sensitive to
in vitro
exposures at environmentally relevant doses of the
major environmental contaminants measured in marine mammal tissues. These include
trace metals (De Guise et al. 1996b; Pillet et al. 2000; Camara Pellisso et al. 2008; Das et al.
2008; Kakuschke et al. 2008; Dufresne et al. 2010), OCs, and butyltins (De Guise et al. 1998b;
Nakata et al. 2002; Frouin et al. 2008), as well as PBDEs (Frouin et al. 2010b). The use of a
harbor seal cell line also proved to be useful in addressing the mechanism of toxicity in
marine mammal cells (Frouin et al. 2010a). Additional studies are therefore desirable to
better characterize this cell line in order to better comprehend the relevance of this tool.
Few studies have addressed the question of immunotoxic effects in the field not only
because of the logistic and technical constraints but also considering the difficulty of
dealing with confounding factors such as age, gender, physiological status, or historical
exposure.
The proliferative response of peripheral blood lymphocytes to mitogens has been dem-
onstrated to be impacted by exposure to OCs in different marine mammal populations.
The responses to PHA, ConA, and PWM were significantly lower in the more contami-
nated Baltic gray seal
Halichoerus grypus
pups as compared to the less contaminated pups
from the Atlantic (Sormo et al. 2009). Negative correlations between lymphocyte response
to mitogens with increasing PCB and other OC plasma levels were also reported in free-
ranging bottlenose dolphins (
Tursiops truncatus
) and polar bears (
Ursus maritimus
) (Lahvis
et al. 1995; Lie et al. 2005). Interestingly, although the responses were negatively corre-
lated to the more persistent dioxin-like compounds in the more contaminated pups from
the Baltic Sea, a positive correlation with the non-dioxin, AhR-independent PCBs was
observed in the pups from the Atlantic (Sormo
et al. 2009). A similar positive correlation
between PCB mitogen-induced lymphocyte proliferation was also shown in free-ranging
harbor seal pups from southern British Columbia (Levin et al. 2005). Bernhoft et al. (2000)
reported a negative correlation between IgG and the sum of PCB levels in the plasma of
polar bears as well as levels of PCB congeners 99, 194, and 206 and HCB. These studies
reflect the impact of PTSs on both cellular and humoral immune responses of marine
mammals.
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