Intracellular labeling of T-cells with superparamagnetic contrast agents.

Isolated rat T-cells have been labeled intracellularly, using endocytosis uptake of two superparamagnetic contrast agents, AquaMag100 and BMS180549, which are both iron-oxide particles coated with dextran. No deterioration of cell proliferation response to mitogen stimulation was observed after labeling with either superparamagnetic contrast agent. AquaMag100 particles show aggregation and co-precipitation in culture media for T-cells. BMS180549 particles not only produce no observable aggregation or co-precipitation, but also have a higher efficiency for labeling T-cells than AquaMag100. The efficiency of cell labeling was determined by measuring the decrease in the spin-spin relaxation time of the water proton in cell samples containing 1 x 10(7) labeled T-cells/milliliter of 2% w/w gelatin. After optimization of the labeling procedures, a shortening of the spin-spin relaxation time by a factor of approximately 7 to 10 has been demonstrated. Under the present experimental conditions, the up-regulation of low density lipoprotein receptor does not increase the labeling efficiency by endocytosis. Our results suggest that intracellular labeling of specific cell types can be achieved with good efficiency and the labeled cells can be detected by magnetic resonance imaging in rat testicles in vivo.