De-aluminated zeolite Y as a tool to study endocytosis, a delivery system revealing differences between human peripheral dendritic cells

We report the use of nanometre-sized zeolite particles as a novel approach to follow the endosomal acidification and proteolysis inside a viable cell. The method was verified by using human peripheral monocytes, a well known endocytosing cell population. Zeolite particles were subsequently used to investigate the endocytosing mechanisms of human peripheral dendritic cells (DC). Probes detecting pH neutral and acidic endosomes were adsorbed to de-aluminated zeolite Y, and used to detect endocytosis in immature human peripheral blood DC. Both the myeloid (mDC) and the plasmacytoid (pDC) dendritic cell subsets had an endocytosing capacity comparable with peripheral blood monocytes. However, the majority of both subsets of DC retained their endosomes at a neutral pH during the first hours after endocytosis and only a small number of the mDC showed any formation of acidic endosomes. Proteolytic degradation of endocytosed proteins was detected using self-quenched DQ-ovalbumin adsorbed to zeolite particles. Interestingly, a clear difference in proteolytic degradation of endocytosed ovalbumin was observed between the two subsets of DC. The mDC showed an efficient degradation of ovalbumin, while the pDC population displayed no or only minor proteolytic degradation. In conclusion, zeolite particles provide a useful tool to study the endocytosing mechanisms, and an efficient carrier of bio-molecules into the endosomal pathways of viable cells.