Optimum conditions for efficient phagocytosis of rifampicin-loaded PLGA microspheres by alveolar macrophages

We examined the phagocytic activities of alveolar macrophages (NR8383 cells) toward poly(lactic-co-glycolic) acid (PLGA) microspheres (MS) loaded with the anti-tuberculosis agent rifampicin (RFP), the sizes of which were between 1 μm and 10 μm. We found that 1) the phagocytosis was dependent greatly on the particle size and the number of particles added; 2) macrophages phagocytosed considerably the PLGA microspheres loaded with RFP, the diameter of which was between 1 μm and 6 μm, but took up few 10-μm particles; 3) the population of the macrophages that phagocytosed 1-μm or 3-μm particles was larger than that of those phagocytosed 6- or 10-μm particles; 4) a considerable population of macrophages were not able to phagocytose even the 1- and 3-μm particles; 5) the most efficient deliveries of RFP into each macrophage cell and a large population of macrophages were achieved by the phagocytosis of 3-μm particles; and 6) phagocytosis did not affect macrophage viability in 4 h after the start of phagocytosis.