Dependence of the phagocytic uptake of polystyrene microspheres by differentiated HL60 upon the size and surface properties of the microspheres

Abstract

In order to determine whether the microsphere size affects the phagocytic uptake of microspheres in vitro, polystyrene microspheres with diameters of 0.2, 0.5, 1.0, 6.0 and 10 μm were added to a HL-60 differentiated macrophage-like cell culture system. The extent of the uptake was determined by the amount of superoxide generated from activated macrophages by the usage of a chemiluminescence (CL) assay with luminol. The release amount of superoxide was higher when polystyrene microspheres with diameters between 0.5 and 6 μm (i.e. 0.5, 1, and 6 μm were added to the macrophages than that when those with a diameter 0.2 or 10 μm were added. Especially, polystyrene microspheres with an average diameter of 1 μm were most effectively recognized as foreign materials by the macrophages. The effects of the functional groups on the microsphere surfaces upon the uptake by macrophages were studied using polystyrene microspheres with an average diameter of 1 μm, having primary amine, sulfate, hydroxyl, or carboxyl groups on their surfaces. Polystyrene microspheres having primary amine groups on their surfaces were more effectively engulfed by the macrophages than polystyrene microspheres having other functional groups. Also, polystyrene microspheres coated with human IgG was more easily recognized as foreign materials than intact polystyrene microspheres.