The haemocytes of the marine bivalve Mytilus galloprovincialis as a model for studying the impact of NP on innate immunity

In this PhD thesis, the effects and interactions of nanoparticles-NPs with the marine mussel Mytilus galloprovincialis were investigated through several exposure pathways, implying the use of distinct methods, in vitro and in vivo. In a first part, in vitro model served to determine the functional immune responses upon short term exposure of Mytilus hemocytes using microscopy and spectrophotometric methods. In this line, several NPs were tested in suspensions in ASW-artificial seawater and hemolymph serum-HS and showed a general activation of the immune response of Mytilus hemocytes and hemolymph components (Chapter 1 and 2). The results obtained contribute to understand the mechanisms of actions of NPs due to their nature, size and coating and also underline the importance to consider the exposure medium in the characterization and exposure experiment. Complementary experiments were carried on the change in morphology after interactions with NPs, attesting for peculiar activation of the hemocytes according to the NPs types. In a second part, the effects of NPs were also investigated at different scale of the organism (from cell to tissues) using in vivo experiments, in which mussels were exposed for several days to selected NPs, before determining immune parameters and related parameters. Mussels exposed in vivo to nanoceria-nCeO2 (Chapter 3), showed specific immunomodulatory and antioxidant effects at different levels of biological organization in the absence of Cerium tissue accumulation. In addition, the microbiota present in hemolymph of mussels has shown to be affected upon nanotitanium dioxide-nTiO2 exposure (Chapter 4). The results attested for complex interactions between immune cells, the hemocytes, activated in presence of nTiO2, and created an unfriendly medium in hemolymph, that likely lead to affect the most sensible commensal bacterial communities present. Finally, newly design experiments were performed to investigate innate immune memory/training in Mytilus (Chapter 5). Growing proofs have shown that even relying on innate response, molluscs could present a certain type of memory and recall a response upon a second encounter, also called innate immune memory. Results showed that mussels can mount a more effective response upon re-exposure to a stimulus, PS-NH2 in the present case, to avoid to trigger further stress/damages repeatedly.