In vitro phagocytosis assay of nano- and microparticles by chemiluminescence. I. Effect of analytical parameters, particle size and particle concentration

Chemiluminescence (CL) was used to study the uptake of differently sized model drug carriers (polystyrene latex particles) by human granulocytes. The polystyrene particles were incubated with the granulocytes on microtitre plates and the CL monitored for a period of 3 hours. The sensitivity of the chemiluminescence (CL) assay could be increased by optimization of the luminol concentration, cell number and particle number (mass) per well. The intensity (uptake)/time profiles were characterized by the intensity Imax (uptake velocity) and the area under the curve (AUC, total uptake of particles). The reproducibility within one cell isolation was good. To compare CL measurements from different isolations internal standards were included to compensate for biological variations in the granulocyte function. The total uptake of particles increased with increasing particle size and at low to medium particle concentrations. It levelled or even decreased at high particle concentrations reducing the sensitivity of the assay. The AUC correlated with the total mass of phagocytosed particles and could therefore be used to compare the uptake of nano- and microparticles differing in size.