Intrinsically magnetic susceptibility in human blood and its potential impact on cell separation: Non-classical and intermediate monocytes have the strongest magnetic behavior in fresh human blood.

The presence of iron in circulating monocytes is well known as they play an essential role in iron recycling. It has been demonstrated that the iron content of blood cells can be measured through their magnetic behavior; however, the magnetic properties of different monocyte subtypes remain unknown. In this study we report, for the first time, the magnetic behavior of classical, intermediate and non-classical monocytes, which may be related to their iron storage capacity. The magnetic properties of monocytes were compared with those of other blood cells, such as lymphocytes and red blood cells in the oxyhemoglobin and methemoglobin states, and a cancer cell type. For this analysis, we used an instrument referred to as a Cell Tracking Velocimetry (CTV), which quantitatively characterizes the magnetic behavior of biological entities. Our results revealed that significant fractions of the intermediate and non-classical monocytes (up to 59% and 65% depending on the sample, respectively) have paramagnetic properties, suggesting their higher iron storage capacities. Moreover, our findings have implications for the immunomagnetic separation industry; we propose that negative magnetic isolation techniques for recovering monocytes from blood should be used with caution, as it is possible to lose magnetic monocytes when using this technique.

Quantification of the Mean and Distribution of Hemoglobin Content in Normal Human Blood Using Cell Tracking Velocimetry.

The current clinical method for detecting anemia focuses on measuring the concentration of hemoglobin (Hb) in blood. However, recent developments in particle tracking algorithms and the understanding of the relationship between Hb and magnetism has enabled the quantitative measurement of the Hb content in a single red blood cell, RBC, based on magnetophoretic mobility. To further explore this relationship, 22 human blood samples obtained from 17 healthy volunteers were analyzed by the cell tracking velocimetry system, and the calculated Hb concentration from these measurements was compared to the values measured by UV-visible spectrophotometry, the standard method for measuring Hb in clinical laboratories. The results show close correlations between the mean of the spectrophotometric and magnetophoretic methods; however, single cell analysis with the magnetophoretic mobility method allows further elucidation of the distribution of Hb concentration within RBCs from a donor sample to be determined. Histograms of these magnetophoretic mobility distributions indicate that the fraction of RBCs that are below the bulk Hb concentration that defines anemia varies not only from donor to donor but also in the same donor over time. Consistent with a variable fraction below the anemic Hb concentration, the distribution around the mean has a large range. Previous studies have indicated that RBCs lose Hb during ex vivo storage; however, it is not known if this variability in the distribution of Hb content is a function of the age of the RBCs in a donor, suggesting a variable rate in RBC production between donors, or variability in available iron at the time of RBC formation. We suggest our cell tracking velocimetry system can reveal more information regarding this matter.