LAUSR

Aim of the study was to evaluate USPIO labeling in different macrophage populations using a clinical 3.0T MR unit with optical and electron microscopy as the gold standard. Human monocytic cell line THP‐1 cells were differentiated into macrophages. Afterwards, M0 macrophages were incubated with IL‐4 and IL‐13 in order to obtain M2 polarized macrophages or with IFN‐gamma and LPS for classical macrophage activation (M1). These groups were incubated with USPIO‐MR contrast agent (P904) for 36 hr; M0, M0 + P904, M1 +  P904, and M2 + P904 were analyzed in gel phantoms with a 3.0T MR scanner. m‐RNA of M1 and M2 markers confirmed the polarization of THP‐1‐derived macrophages. M2 + P904 showed a much higher T1 signal (p <  0.0001), a significantly lower (p < 0.0001) T2* signal, and significantly higher R* (p < 0.0001) compared to the other populations. Hystological analysis confirmed higher iron content in the M2‐polarized population compared to both M1‐polarized (p = 0.04) and M0‐P904 (p = 0.003). Ultrastructure analysis demonstrated ubiquitous localization of P904 within the cellular compartments. Our results demonstrate that a selective USPIO‐labeling of different macrophage populations can be detected in vitro using the 3.0T clinical scanner.