Role of lipid rafts in innate immunity and phagocytosis of polystyrene latex microspheres

Understanding of the association of phagocytosis of polymers with signaling of innate immunity of macrophages is the major purpose of this study. Polymer conjugates have been utilized for clinical therapy of cancer and infections, such as Mycobacterium tuberculosis, as effective vectors of drug-delivery systems. They are incorporated through phagocytosis into macrophages and activate innate immunity signaling, which plays a crucial role in its therapeutic and side effects. Macrophage phagocytosis of polystyrene latex microspheres was examined and assayed by treatment of macrophages with the cholesterol depletor methyl-β-cyclodextrin (MβCD) or the sphingolipid depletor n-octyl-β-d-glucopyranoside (OGP). Expressions of various mRNAs during phagocytosis were quantified by real-time PCR. Phagocytosis of polystyrene latex microspheres by various macrophages, such as murine monocyte-derived macrophage J774, rat alveolar macrophage NR8383, and murine Kupffer cell KC13-2, was suppressed by treatment with MβCD or OGP in a concentration-dependent manner. The expression of mRNAs of TNFα, IL-1β, IL-6 and CXCL10 genes induced by lipopolysaccharide (LPS) was not suppressed by treatment with MβCD in J774 cells. Moreover, genes that were induced by LPS were up-regulated even in the absence of LPS by the phagocytosis of polymer conjugates, but such up-regulations were not suppressed by the treatment with MβCD. It was shown that lipid rafts play a significant role in incorporation of polymer conjugates through phagocytosis of macrophages, but their association with signal transduction in innate immunity is very limited.