Real‐time high‐resolution magnetic resonance tracking of macrophage subpopulations in a murine inflammation model: a pilot study with a commercially available cryogenic probe

Abstract

Macrophages present different polarization states exhibiting distinct functions in response to environmental stimuli. However, the dynamic of their migration to sites of inflammation is not fully elucidated. Here we propose a real-time in vivo cell tracking approach, using high-resolution (HR)-MRI obtained with a commercially available cryogenic probe (Cryoprobe™), to monitor trafficking of differently polarized macrophages after systemic injection into mice. Murine bone marrow-derived mononuclear cells were differentiated ex vivo into nonpolarized M0, pro-inflammatory M1 and immunomodulator M2 macrophage subsets and labeled with citrate-coated anionic iron oxide nanoparticles (AMNP). These cells were subsequently intravenously injected to mice bearing calf muscle inflammation. Whole body migration dynamics of macrophage subsets was monitored by MRI at 4.7 T with a volume transmission/reception radiofrequency coil and macrophage infiltration to the inflamed paw was monitored with the cryogenic probe, allowing 3D spatial resolution of 50 µm with a scan time of only 10 min. Capture of AMNP was rapid and efficient regardless of macrophage polarization, with the highest uptake in M2 macrophages. Flow cytometry confirmed that macrophages preserved their polarization hallmarks after labeling. Migration kinetics of labeled cells differed from that of free AMNP. A preferential homing of M2-polarized macrophages to inflammation sites was observed. Our in vivo HR-MRI protocol highlights the extent of macrophage infiltration to the inflammation site. Coupled to whole body imaging, HR-MRI provides quantitative information on the time course of migration of ex vivo-polarized intravenously injected macrophages.

Preferential Macrophage Recruitment and Polarization in LPS-Induced Animal Model for COPD: Noninvasive Tracking Using MRI

“…In addition, quantification of iNOS and arginase1 activity, as markers of M1 and M2 macrophages respectively, demonstrated successful polarization of bone-marrow derived macrophages and confirm that their magnetic labeling with the used SPIO nanoparticles do not modify their polarization profile. Similar findings were observed in our previous study [17] using flow cytometry analysis where no variation in the expression of surface membrane receptor was detected following iron oxide labeling.…”

“…Bone marrow (BM) derived M1 and M2 macrophages (BMDM) were obtained as previously reported [17]. Briefly, BM cells from tibiae and femora of donor mice were incubated for 7 days at 37°C in complete IMDM medium supplemented with 10 ng/ml of macrophage clone stimulating factor (R&D systems, Abingdon, UK) to obtain adherent nonpolarized-M0 macrophages.…”

MR imaging and targeting of a specific alveolar macrophage subpopulation in LPS-induced COPD animal model using antibody-conjugated magnetic nanoparticles

“…15 In addition, we have shown in another study that the ex vivo labeling of macrophage subpopulations with iron oxide nanoparticles did not affect their polarization and proliferation. 16 It was proposed that coupling of iron oxide nanoparticles with a specific antibody targeted to a particular subpopulation of macrophages could offer a promising strategy for an early and better diagnosis of different inflammatory diseases using noninvasive MRI.…”

Cell labeling with magnetic nanoparticles: Opportunity for magnetic cell imaging and cell manipulation

“…One of the new coils, such as the cryogenic probe, allows sub-milimetric resolution and gives the means to perform cellular MRI in vivo . The advantage of the cryogenic probe to improve the signal-to-noise (SNR) ratio and concomitantly improve the image resolution, has been demonstrated throughout the last decade in several studies [30,31]. …”

“…Single cell detection has been proven using high field MRI [33] or the clinical 1.5 T scanner equipped with a low noise superconducting coil [35]. As an example, Figure 10 shows high-resolution MR scans of agarose gels containing different numbers of individualized magnetically labeled cells, obtained at 4.7 T with a scanner provided with a cryogenic probe [31]. At low density, each signal void can be associated to one single cell.…”