Impact of exposure time, particle size and uptake pathway on silver nanoparticle effects on circulating immune cells in mytilus galloprovincialis.

Nanomaterials have increasingly emerged as potential pollutants to aquatic organisms. Nanomaterials are known to be taken up by hemocytes of marine invertebrates including Mytilus galloprovincialis. Indeed, assessments of hemocyte-related parameters are a valuable tool in the determination of potentials for nanoparticle (NP) toxicity. The present study assessed the effects from two size types of silver nanoparticles (AgNP: <50 nm and <100 nm) on the frequency of hemocytes subpopulations as immunomodulation biomarkers exposed in a mollusk host. Studies were performed using exposures prior to and after inhibition of potential NP uptake pathways (i.e. clathrin- and caveolae-mediated endocytosis) and over different durations of exposure (3, 6 and 12 h). Differential hemocyte counts (DHC) revealed significant variations in frequency of different immune cells in mussels exposed for 3 hr to either AgNP size. However, as exposure duration progressed cell levels were subsequently differentially altered depending on particle size (i.e. no significant effects after 3 h with larger AgNP). AgNP effects were also delayed/varied after blockade of either clathrin- or caveolae-mediated endocytosis. The results also noted significant negative correlations between changes in levels hyalinocytes and acidophils or in levels basophils and acidophils as a result of AgNP exposure. From these results, we concluded AgNP effects on mussels were size and duration of exposure dependent. This study highlighted how not only was NP size important, but that differing internalization mechanisms could be key factors impacting on the potential for NP in the environment to induce immunomodulation in a model/test sentinel host like M. galloprovincialis.