An imbalance of the immune system caused by pollutants has been suggested to play a role in the incidence of infectious diseases in marine mammals. The influence of metals on marine mammal health has not been adequately investigated and is still in the focus of interest. Immunotoxic pollutants, e.g., metals, may results in two main types of effects: immunosuppression or dysregulation of the immune response leading to hypersensitivity and autoimmunity. The existence of hypersensitivities in marine mammals has not been previously reported, but the chronical intake of contaminated fish suggests that these animals, as top predators, might develop such immunopathies.
These investigations on harbor seals include metal-specific effects on lymphocytes and the metal content in blood. The study includes free-living harbor seals, animals in captivity and pups during their rehabilitation time in the seal station. Metal hypersensitivities were determined with a lymphocyte transformation assay according to the MELISA® (memory lymphocyte immunostimulation assay) modification. Additionally, the concentrations of metals in blood were analyzed with mass- or fluorescence-spectrometry as a reflection of recent exposure to metals and hence the actual body burden.
The results revealed metal hypersensitivities in 7 of 11 free-living seals, in 3 of 5 seals in captivity and in 2 of 15 pups. The sensitizing metals were Mo, Ni, Ti, Cr, Al, Pb, Be and Sn. High levels of metal concentrations in blood of free-living seals developing metal-specific hypersensitivity support the suggestion of immunological dysfunction in seals feeding on fish from polluted coastal waters.
This study demonstrates the immunological impact of metals in seals. Hypersensitivity reactions, which have an increasing importance in the industrialized world and which can participate in the etiology of serious systemic diseases, seem to be important in the marine ecosystem as well.