Intracellular accumulation, dissolution, and distribution of AIEgen-coated silver nanoparticles in hemocyte subpopulations of oysters

Bivalve hemocytes act as the first line of defense against foreign particles and are composed of several subpopulations with different immune functions. In order to elucidate the processes of cellular internalization and transformation of AgNPs in bivalve hemocyte subpopulations, we employed two aggregated-induced emission (AIE) fluorogens AgNPs and Ag⁺ to study the intracellular behavior of AgNPs in oyster hemocyte subpopulations composed of agranulocytes, semigranulocytes, and granulocytes. Our study demonstrated that the accumulation ability of AIE-AgNPs differed by 4.2-fold, with an order of agranulocytes < semigranulocytes < granulocytes, whereas the dissolution ability differed by 2.4-fold, with an order of agranulocytes > semigranulocytes > granulocytes. Internalized AgNPs caused lysosomal alkalization, which then resulted in the inhibition of AgNP dissolution. Dissolution rate of AIE-AgNPs was 22.5% in the total oyster hemocytes combined, and the dissolved Ag⁺ was mainly located in lysosomes (71.8%) of granulocytes. During accumulation, 32% of AgNPs were distributed in lysosomes of granulocytes, but increased to 76.7% during the depuration period. Small AgNPs could rapidly enter and dissolve in lysosomes, while large aggregates of AgNPs were first phagocytosed to form phagosomes in the cytoplasm, then fused with lysosomes as time passed. Our results provided important information to understand the intracellular behavior of AgNPs in marine organisms.