Abstract
The clearance of colloidal particles from the blood circulation occurs mainly in the liver, spleen and bone marrow by phagocytes lining blood sinuses in these organs of the reticuloendothelial system (RES). The relative distribution of the injected particles in these organs depends on various factors such as the size, surface properties of the injected particles and also the type of serum proteins adsorbed onto the surface of particles. Proteins that adsorb onto the surface of a particle promoting their phagocytosis are termed opsonins. On the other hand, it has been suggested that certain classes of liposomes and pathogenic microorganisms can attract suppressive substances termed dysopsonins from plasma or serum, thereby minimizing the interaction with phagocytes. From these points of view, it is very important to identify the serum opsonins or dysopsonins and to elucidate the uptake mechanisms of the particulate carrier used for the handling of the in vivo disposition of the drug loaded. We believe that understanding of these regulatory mechanisms may provide an opportunity to target or avoid particulate drug carriers into a specific organ of RES.
