Phagocytic uptake of polystyrene microspheres by alveolar macrophages: effects of the size and surface properties of the microspheres

Polystyrene microspheres with diameters of 0.2, 0.5, 1.0, 6.0 and 10 gm were added to alveolar macrophages, and their uptake was determined as the amount of superoxide generated from macrophages by the usage of chemiluminescence assay with luminol. The amount of superoxide generated was apparently higher with polystyrene microspheres with a diameter of 1 mum than those with diameters smaller than 1 mum (i.e. 0.2 or 0.5 mum) and with larger than 1 pun (6 or 10 pun). The effects of the functional groups located on the microsphere surfaces upon the uptake by alveolar macrophages were studied with polystyrene microspheres of 1 mum diameter having the primary amine, sulfate, hydroxyl, or carboxyl groups on their surfaces. We found that the macrophages most effectively trapped polystyrene microspheres with primary amine groups, those with carboxyl groups to a slightly lesser extent, and other microspheres much less amounts. The surface properties of these microspheres were determined by measuring their electrophoretic mobility in phosphate buffer solution (pH 7.4) with various ionic strengths. By the analysis of data with Ohshima's electrokinetic theory for soft particles, the surface charge density and the electrophoretic softness of the microsphere surfaces were determined. All the microsphere surfaces were found to be negatively charged, and those with primary amine groups and carboxyl groups were softer than other microspheres. From these findings, it is suggested that microspheres having soft surfaces are easily accessible to alveolar macrophages, and effectively trapped by macrophages. (C) 2002 Elsevier Science B.V. All rights reserved.