A Subpopulation of Monocytes in Normal Human Blood Has Significant Magnetic Susceptibility: Quantification and Potential Implications

Abstract

The presence of iron in circulating monocytes is well known as they play essential roles in iron recycling. Also, the storage of this metal as well as its incorrect uptake and/or release are important data to diagnose different pathologies. It has been demonstrated that iron storage in human blood cells can be measured through their magnetic behavior with high accuracy; however, the magnetic characteristics of monocytes have not been reported so far to the best of our knowledge. Therefore, in this work, we report, for the first time, the physical and magnetic properties of human monocytes, along with plasma platelets, oxyhemoglobin red blood cells (oxyHb‐RBCs), and methemoglobin red blood cells (metHb‐RBCs). The different cell populations were separated by Ficoll‐density gradient centrifugation, followed by a flow sorting step to isolate monocytes from peripheral blood mononuclear cells. The different fractions were analyzed by Coulter Counter (for determining the size distribution and concentration) and the sorted monocytes were qualitatively analyzed on ImageStream, a state‐of‐the‐art imaging cytometer. The analysis of the Coulter Counter and ImageStream data suggests that although there exists contamination in the monocyte fraction, the integrity of the sorted monocytes appears to be intact and the concentration was high enough to precisely measure their magnetic velocity by Cell Tracking Velocimetry. Surprisingly, monocytes reported the highest magnetic mobility from the four fractions under analysis, with an average magnetic velocity 7.8 times higher than MetHb‐RBCs, which is the only type of cells with positive magnetic velocities. This value is equivalent to a susceptibility 2.5 times higher than the value reported by fresh MetHb‐RBCs. It should be noted that this is the first study that reports that a subpopulation of human monocytes is much more magnetic than MetHb‐RBCs, opening the door to the possible isolation of human monocytes by label‐free magnetic techniques. Further, it is suggested that these magnetic monocytes could “contaminate” positively selected, immunomagnetically labeled blood cells (i.e., during a process using magnetically conjugated antibodies targeting cells, such as CD34 positive cells). Conversely, these magnetic monocytes could be inadvertently removed from a desired blood population when one is using a negative magnetic isolation technique to target cells for removal. © 2019 International Society for Advancement of Cytometry

In Flow Cytometry, Image Is Everything

“…Dey et al report the use of IFC to accurately differentiate between active and viable but not‐culturable forms of Psedomonas aeruginosa (a Gram‐negative bacterium abundant in the environment and water systems). Kim et al present their investigation of the physical and magnetic properties of monocytes in human blood together with plasma platelets, oxyhemoglobin red blood cells, and methemoglobin red blood cells by using IFC. Lelliott et al describe their development of an automated analysis method to rapidly evaluate cells that form neutrophil extracellular traps or precursors to neutrophil extracellular traps and differentiate them from cells that undergo other forms of cell death.…”

“…Dey et al (15) report the use of IFC to accurately differentiate between active and viable but not-culturable forms of Psedomonas aeruginosa (a Gram-negative bacterium abundant in the environment and water systems). Kim et al (16) present their investigation of the physical and magnetic properties of monocytes in human blood together with plasma platelets, oxyhemoglobin red blood cells, and methemoglobin red blood cells by using IFC. Lelliott 2) first introduced and experimentally demonstrated imaging in flow.…”

Isolation of Monocytes From Bovine Blood for Purposes of Culture of Dendritic Cells

“…The method utilizes the various densities of the individual types of white blood cells. The acquired cells were stained using the Pappenheim staining method (Doubek, 2003). A microscope slide was smeared with a suspension of the cells that had been stained using May-Grϋnwald solution for 3 minutes.…”

“…The purity of monocytes was tested by marking the cells with the CD11c surface molecule, followed by analysis in a BriCyte E6 flow cytometer (Mindray, China). The acquired cells were stained using the Pappenheim method (Doubek, 2003), as in the previous experiment. The cells were also observed under a light microscope, as in the previous experiment.…”

“…The number of monocytes in normal bovine blood was low due to a low representation of these cells in the blood. Their percentage representation in differential count in cattle is 3-5% (Doubek, 2003). After magnetic separation of cells, enriched fractions of marked cells were acquired.…”