Ps. Ross et al., SUPPRESSION OF NATURAL-KILLER-CELL ACTIVITY IN HARBOR SEALS (PHOCA-VITULINA) FED BALTIC SEA HERRING, Aquatic toxicology, 34(1), 1996, pp. 71-84
Mass mortalities among marine mammal populations in recent years have
raised questions about a possible contributory role of contaminants ac
cumulated through the marine food chain. While viruses were shown to b
e the primary cause of the outbreaks, an immunotoxic action by organoc
hlorine chemicals in affected animals could not be ruled out. We carri
ed out a 2 1/2-year immunotoxicological experiment in which two groups
of 11 harbour seals each were fed herring from either the relatively
contaminated Baltic Sea or the relatively uncontaminated Atlantic Ocea
n. Seals in the Baltic Sea group accumulated 3-4 times higher levels o
f Ah-receptor-mediated 2,3,7,8-TCDD Toxic Equivalents in blubber than
did their Atlantic counterparts following 2 years on the respective di
ets. Blood was sampled a total of 17 times during the course of the ex
periment for immunological evaluation, during which time the natural c
ytotoxic activity of peripheral blood mononuclear cells isolated from
seals fed Baltic Sea herring declined to a level approximately 25% low
er than that observed in seals fed Atlantic herring (P < 0.01). Natura
l killer (NK) cell activity has not been previously described for a ma
rine mammal species. We characterized the natural cytotoxic activity o
f harbour seal peripheral blood mononuclear cells (PBMC), and found th
is to be interleukin-2 (IL-2) responsive, sensitive to antibody anti-a
sialo GM1, and it was higher against a virus-infected target cell, lik
e NK cells described for other mammals. As NK cells are leukocytes whi
ch play an important role in the first line of defence against viruses
, the observed impairment of NK cell activity in the seals feeding on
the Baltic Sea herring suggests that exposure to contaminants may have
an adverse effect on the defence against virus infections in seals in
habiting polluted waters in Europe. This may therefore have affected t
he severity of the infections, the survival rates and the spread of in
fections during recent epizootics.