Receptor-mediated endocytosis of particles by peripheral dendritic cells.

Human peripheral dendritic cells (DCs) are antigen-presenting cells with the ability to internalize antigen and present antigen-derived peptides to T cells. Human DCs express several receptors on the surface for endocytosis and other recognition receptors that bind to microbes or microbial products, which are internalized and processed. Here, we report the use of nanometer-size zeolite particles as a tool to study receptor-mediated endocytosis by the two subsets of immature DCs, myeloid (mDC) and plasmacytoid (pDC) dendritic cells. A major difference in receptor-mediated endocytosis was observed between the two populations of peripheral DCs. The pDC population demonstrated an almost complete lack of receptor-mediated endocytosis of zeolite particles, whereas the mDC population demonstrated a clear receptor-mediated endocytosis. Fc receptors are expressed by both peripheral DC populations and lipoteichoic acid (LTA) and lipopolysaccharide (LPS) are known ligands of the Toll-like receptor (TLR)-2 and TLR4, respectively, both TLRs expressed by human mDCs. An efficient receptor-mediated endocytosis of immunoglobulin G-, LTA-, and LPS-coated zeolite particles was observed by the mDC population and their endocytosing capacity depended strongly on the density of the ligand adsorbed onto the zeolite particles. In conclusion, an efficient receptor-mediated endocytosis was observed from the mDC population, whereas the pDCs demonstrated an almost complete lack of receptor-mediated endocytosis and nanometer-size dealuminated zeolite particles were a useful tool for studying receptor-mediated endocytosis in human peripheral DCs.