Effect of opsonins on the uptake of magnetic starch microspheres by rat Kupffer cells

The influence of various sera and proteins on the uptake of a superparamagnetic colloid (magnetic starch microspheres (MSM); particle size, 200 nm; crystal size, 10 nm) by the isolated and perfused rat liver has been studied. It is demonstrated that the capture of MSM is slightly reduced by the addition of rat blood to the protein-free perfusion medium but highly reduced by newborn calf serum (NCS). The SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) analysis of proteins adsorbed on the nanoparticles incubated in NCS reveals major coating by albumin and IgG. The addition of bovine IgG to the perfusion fluid reduces the rate of MSM uptake in the same extent that NCS, whereas fetal calf serum that contains only traces of IgG weakly alters the MSM clearance. Finally, complemented and decomplemented NCS exhibit the same influence on the MSM hepatic extraction. It is concluded that although lectins are largely involved in the uptake of MSM administered in the absence of proteins, opsonins receptors are implicated when the perfusion medium contains relevant blood components.