Quantification of microsized fluorescent particles phagocytosis to a better knowledge of toxicity mechanisms

Methods: Fluorescent particles of variable and well-characterised sizes and surface coatings were incubated with MA (RAW 264.7 cell line). Analyses were performed using confocal microscopy and FCM. The biological toxicity of the particles was evaluated [lactate dehydrogenase (LDH) release, tumor necrosis factor (TNF)-alpha, and reactive oxygen species (ROS) production]. Results and conclusion: Confocal imaging allowed visualization of entirely engulfed beads. The amount of phagocytic cells was greater for carboxylate 2-mu m beads (49 +/- 11%) than for amine 1-mu m beads (18 +/- 5%). Similarly, side scatter geometric means, reflecting cellular complexity, were 446 +/- 7 and 139 +/- 12, respectively. These results confirm that the phagocytosis level highly depends on the size and surface chemical groups of the particles. Only TNF-alpha and global ROS production varied significantly after 24-h incubation. There was no effect on LDH and H2O2 production.