Evaluation des niveaux de mercure dans le sang et mise au point d'un protocole d'exposition in vitro visant à comprendre l'effet du méthyl-mercure sur l'expression de cytokines chez le phoque commun (Phoca vitulina)

The objective of this work is to lay the bases of an in vitro experimental exposure model aiming to understand the immunotoxicological effect of methylmercury of harbour seal (Phoca vitulina) T lymphocytes by analysis of their expression of cytokines messenger RNA (mRNA). Cytokines are important mediators of the immune system and their disruption lead to dysfunction of immune responses.

This pilot study is comprised of an analytical section consisting in the determination of whole blood mercury concentrations of alive and beached harbour seals from the North Sea, and an experimental section including in vitro lymphocyte cultures.

The harbour seal blood sampling is a relatively easy and non-invasive method that enables lymphocyte isolation and controlled methylmercury in vitro exposure. The blood of marine mammal constitutes an interesting window as marine mammals, located in the highest levels of the trophic chain, accumulate high levels of trace metals in their tissues. They are thus good bioindicators of marine pollution.

Optimal culture conditions and the most appropriate techniques were determined.
T lymphocytes were exposed in vitro to two methylmercury concentrations comprised in the measured concentration range, and exposure effects were studied by analysis of the cytokine mRNA production.

Results show an immunodepression at 0.2 and 1 µM in presence of mitogenic phytohemagglutinin (PHA) which specifically stimulates T lymphocytes.
The interleukin-2 (IL-2) and transforming growth factor-β (TGF-β) mRNA quantities displayed a decrease, and interleukin-4 (IL-4) mRNA was in weak quantities in all culture conditions (with or without methylmercury). That could mean that methylmercury affects the cell-mediated immunity, but repetition of the experience with a larger sampling is needed to confirm those results.