Figure 2.

Association of citrate-coated superparamagnetic iron oxide nanoparticles (SPION^Citrate) to human primary T lymphocytes. (a) Changes in cellular granularity due to superparamagnetic iron oxide nanoparticle (SPION) uptake or adhesion were determined by measuring the side scatter (SSc) in flow cytometry after incubation of T cells with SPION^Citrate. Since cell death processes alter cellular morphology as well, we gated on viable DiIC₁(5)⁺ (1,1′-dimethyl-3,3,3′,3′-tetramethylindodicarbocyanine iodide, DiI) cells with intact mitochondrial membrane potential. (b) T cells were incubated for 0, 24 and 48 h with SPION^Citrate (25–100 µg Fe/mL) and the membrane impermeable fluorescent dye Lucifer Yellow (LY). If SPIONs are taken up, LY gets co-ingested and serves therefore as indicator for intracellular SPION uptake. Since LY leaks from disrupted membranes, we gated on viable DiI⁺ cells with intact mitochondrial membrane potential. (c) Quantification of cellular iron content was performed by atomic emission spectroscopy after incubation of T cells with SPION^Citrate (75 and 100 µg Fe/mL) for 24 h. The experiments were performed with three different donors. Shown are the mean values with standard deviations of one representative donor. Data of other donors can be found in Supplementary Figure S3. Significance between treatment groups and control at the respective time is indicated by asterisks: * p < 0.05, ** p < 0.005. Abbreviations: DiI: DiIC₁(5) (1,1′-dimethyl-3,3,3′,3′-tetramethylindodicarbocyanine iodide), LY: Lucifer Yellow, SPION: superparamagnetic iron oxide nanoparticle, SPION^Citrate: citrate-coated superparamagnetic iron oxide nanoparticles, SSc: side scatter.