Passing the Parcels: Intercellular Nanoplastics Transfer in Mussels Perna viridis with Activated Immunomodulation

Nanoplastics (NPs) are generally considered to have a defined intracellular fate, being difficult to excrete or transport due to their stability. This study provides the first evidence of NPs intercellular transfer in the hemocytes of green mussels (Perna viridis), which subsequently activated the immunomodulation process. NPs were predominantly internalized by granulocytes, with a portion being translocated and deposited in lysosomes, whereas those retained in endosomes were subsequently transferred to new hemocytes (mainly granulocytes). The transfer direction was driven by the intracellular NP concentration gradients. Transfer kinetics was size-dependent, with smaller-sized NPs exhibiting greater potential but a lower rate, primarily due to their specific extracellular vesicle-mediated transfer pathway. Tunneling nanotubes provided the most efficient pathway for the intercellular transfer of NPs, as their continuous membrane structure allowed direct substance exchange. Crucially, NP redistribution was accompanied by a gradient-driven transfer of mitochondria to injured hemocytes. This process alleviated stress on the overburdened hemocytes and regulated reactive oxygen species production, subsequently enhancing phagocytic activity and promoting immune responses. These findings underscore that NPs exhibit far more active behavior in the immune system than previously understood and provide new insights into how immune cells maintain the health of marine organisms in the face of NP challenges.