Macrophages and dendritic cells can be targeted by mannosylated nanoparticles because immune cells, including alveolar and peritoneal macrophages, monocyte-derived dendritic cells, and Kupffer cells, constitutively express high levels of the mannose receptor (MR). Hashida and colleagues took the lead in the development of mannosylated liposomes to target macrophages and dendritic cells for delivery (in animal models) of the anti-inflammatory agent dexamethasone palmitate and the CpG DNA complex. 34, 35 The study showed that intratracheally administered mannosylated liposomes, with various ratios of mannosylated cholesterol derivatives, were preferentially taken up by alveolar macrophages. Inhibition studies showed that mediation occurred via mannose receptor endocytosis. Mannosylation significantly improved liposome internalization by macrophages. 36 Our histological analyses showed that the uptake of DM-was higher than that of D-USPIO in the atherosclerotic wall of rabbits, resulting in a greater reduction of signal from the aortic wall in MRI scans. As the amount of intracellular iron was higher in macrophage cells treated with DM-rather than D-USPIO, we posit that macrophages contained in atherosclerotic plaques are more sensitive to DM-than to D-USPIO, making it possible to acquire plaque images at lower doses of contrast agent. We also found that the distribution of DM-USPIO in the liver and lung tended to be higher than that of D-USPIO, suggesting that receptor-mediated endocytosis had a strong role in the internalization of DM-USPIO by macrophages. As mannose receptors are expressed in the liver and lung, [34] [35] [36] it is not surprising that the distribution of DM-USPIO was higher than that of D-USPIO in these organs. We cannot rule out the possibility that increased distribution in these organs results in a reduction in the amount of circulating USPIO particles, and a consequent reduction in their presence in the aortic wall. However, based on our current findings, we suggest that the affinity of DM-USPIO particles for the aortic wall affects their uptake positively, and that the effect of reduced circulation of DM-USPIO due to its distribution in the liver and lungs is not strong. This is because the circulation lifetime of USPIOs is sufficiently prolonged, in accordance with particle size. On the other hand, the amount of iron per unit weight was not different irrespective of the type of USPIO used. We attributed this to technical difficulties with our preliminary arrangements for making NMR measurements. For our NMR measurements, the uniformity of the samples was the most important issue because we used minute quantities of sample for measurement. Nevertheless, it was very difficult to obtain vessel homogenates because the vessels contained abundant fibers. Consequently, insufficient preparation of uniform homogenate samples may have impacted our NMR measurements and caused inconsistency between NMR measurements and other examinations, such as imaging and histological analysis.