Vesicle size influences the trafficking, processing, and presentation of antigens in lipid vesicles.

Although it is accepted that particulate Ags are more immunogenic than soluble Ags in vivo, it is unclear whether this effect can be explained solely through enhanced uptake by APCs. In this study we demonstrate that vesicle size modulated the efficiency of Ag presentation by murine macrophages and that this effect was accompanied by a profound change in trafficking of Ag. Ag prepared in large particles (560 nm) was delivered into early endosome-like, immature phagosomes, whereas smaller vesicles (155 nm) and soluble Ags localized rapidly to late endosomes/lysosomes. However, peptide/class II complexes could be detected in both compartments. Phagosomes formed on uptake of large vesicles recruit Ag-processing apparatus while retaining the characteristics of early endosomes. In contrast, smaller vesicles bypassed this compartment, appeared to go more rapidly to lysosomal compartments, and exhibited reduced Ag-presenting efficiency. We conclude that the ability of phagocytosed, particulate Ag to target early phagosomes results in more efficient Ag presentation.